An experimental investigation is conducted to evaluate the performance and the stalling process of a fan subjected to inlet swirls,as well as the effectiveness of an Impedance Boundary-Controlled(IBC)Casing Treatment(...An experimental investigation is conducted to evaluate the performance and the stalling process of a fan subjected to inlet swirls,as well as the effectiveness of an Impedance Boundary-Controlled(IBC)Casing Treatment(CT)on the stall margin recovery.An operating cycle is proposed based on the hysteresis effect of harmonic flap oscillation of airfoils and parallel compressor theory to explain the pressure characteristic of the fan under twin swirl inlets.Twin swirls are observed to reduce the stall margin of the fan,and the circumferential location where the spike is detected turns to the intersection area of the twin swirl.The IBC CT is proven to extend the stall margin of the fan for 12.7%–22.3%when subjected to inlet swirls with an efficiency loss of around 1%.The IBC CT helps to reduce the size of the operating cycle of the fan by redistributing the blade loading and adding the system damping to dissipate the perturbation energy.展开更多
Casing treatment is a widely employed technique to increase the stall margins of turbomachineries.In the last several decades,many researches on casing treatment have been carded out.However,the mechanism of its expan...Casing treatment is a widely employed technique to increase the stall margins of turbomachineries.In the last several decades,many researches on casing treatment have been carded out.However,the mechanism of its expanding stall margins is still not very clear.Till now,most casing teatment schemes are designed for axial compressors,while the investigations on casing treatments in centrifugal compressors are rarely reported.Moreover,current investigation methods mainly focus on experiments,and perfect theoretic al analysis is not yet feasible.In order to study the effectiveness and further the mechanism of casing treatments in centrifugal compressors,in this paper,a computationally based investigation of the impact of the self-recireulating casing treatment on the performance of a radial compressor is carried out.The results indicate that,by casing bleed and injection,the casing treatment with inclined blades in the cavity expands the stall margin most.At low mass flows,the reversed flow through the cavity with inclined blades develops the counter swirl flow in front of the impeller inlet,which is considered to benefit increasing the pressure rise from the injection port to the bleed port and thereby augment the recirculating flow.At 120%design speed,the stall margin is larger than that at the design speed.However,the cost of extending the stall margin is the reduction of isentropic efficiency.A mended casing treatment by shifting the bleed port upstream is also studied.It is demonstrated that,relative to the original casing treatment,this mend can improve the efficiency evidently notwithstanding a little narrowing of the flow range.展开更多
A three-dimensional compressible flow stability model is presented in this paper, which focuses on stall inception of multi-stage axial flow compressors with a finite large radius annular duct configuration for the fi...A three-dimensional compressible flow stability model is presented in this paper, which focuses on stall inception of multi-stage axial flow compressors with a finite large radius annular duct configuration for the first time. It is shown that under some assumptions, the stability equation can be obtained yielding from a group of homogeneous equations. The stability can be judged by the non-dimensional imaginary part of the resultant complex frequency eigenvalue. Further more, based on the analysis of the unsteady phenomenon caused by casing treatment, the function of casing treatment has been modeled by a wall impedance condition which is included in the stability model through the eigenvalues and the corresponding eigenfunctions of the system. Finally, some experimental investigation and two numerical evaluation cases are conducted to validate this model and emphasis is placed on numerically studying the sensitivity of the setup of different boundary conditions on the stall inception of axial flow fan/compressors. A novel casing treatment which consists of a backchamber and a perforated plate is suggested, and it is noted that the open area ratio of the casing treatment is less than 10%, and is far smaller than conventional casing treatment with open area ratio of over 50%, which could result in stall margin improvement without obvious efficiency loss of fan/compressors.展开更多
The present work is about the stall margin enhancement ability of a kind of stall precursor-suppressed（SPS） casing treatment when fan/compressor suffers from a radial total pressure inlet distortion.Experimental res...The present work is about the stall margin enhancement ability of a kind of stall precursor-suppressed（SPS） casing treatment when fan/compressor suffers from a radial total pressure inlet distortion.Experimental researches are conducted on a low-speed compressor with and without SPS casing treatment under radial distorted inlet flow of different levels as well as uniform inlet flow.The distorted flow fields of different levels are generated by annular distortion flow generators of different heights.The characteristic curves under these conditions are measured and analyzed.The results show that the radial inlet distortion could cause a stall margin loss from 2%to30%under different distorted levels.The SPS casing treatment could remedy this stall margin loss under small distortion level and only partly make up the stall margin loss caused by distortion in large level without leading to perceptible additional efficiency loss and obvious change of characteristic curves.The pre-stall behavior of the compressor is investigated to reveal the mechanism of this stall margin improvement ability of the SPS casing treatment.The results do show that this casing treatment delays the occurrence of rotating stall by weakening the pressure perturbations and suppressing the nonlinear amplification of the stall precursor waves in the compression system.展开更多
The influence of Axial-Slot Casing Treatment(ASCT)on the performance and stability enhancement mechanisms of ASCT were experimentally and numerically investigated in a highspeed mixed-flow compressor under three diffe...The influence of Axial-Slot Casing Treatment(ASCT)on the performance and stability enhancement mechanisms of ASCT were experimentally and numerically investigated in a highspeed mixed-flow compressor under three different tip clearances.Unsteady simulations showed the compressor stalled through end-wall stall route,i.e.the spike stall inception originating from rotor tip region,which was validated by dynamical measurements.When the ASCT was applied,greater than 20%of Stall Margin Improvement(SMI)could be achieved for the compressor under each tip clearance size.The streamwise velocity contours and flow structures in the tip region and axial slots were deeply analyzed to explore how the so called‘‘suction and injection effects"generated by the ASCT manipulate tip clearance flow and enhance the stability of compressor under different tip clearances.It was found that the dominant stability enhancement mechanisms of ASCT varies with tip clearance size for the mixed-flow compressor.(A)For the small tip clearance,the dominant mechanism of stability enhancement is the blockage reduction generated in the blade passage by the suction effect of ASCT.(B)For the large tip clearance,the injection effect of the ASCT is the dominant mechanism of stability enhancement with ASCT,which plays the leading role in delaying the spillage of incoming/tip leakage flow interface at the rotor Leading Edge(LE)plane.展开更多
Abstract This article deals with application of grooved type casing treatment for suppression of spike stall in an isolated axial compressor rotor blade row. The continuous grooved casing treatment covering the whole ...Abstract This article deals with application of grooved type casing treatment for suppression of spike stall in an isolated axial compressor rotor blade row. The continuous grooved casing treatment covering the whole compressor circumference is of 1.8 mm in depth and located between 90% and 108% chord of the blade tip as measured from leading edge. The method of investigation is based on time-accurate three-dimensional full annulus numerical simulations for cases with and without casing treatment. Discretization of the Navier Stokes equations has been carried out based on an upwind second-order scheme and k-a-SST （Shear Stress Transport） turbulence modeling has been used for estimation of eddy viscosity. Time-dependent flow structure results for the smooth casing reveal that there are two criteria for spike stall inception known as leading edge spillage and trailing edge backftow, which occur at specific mass flow rates in near-stall conditions. In this case, two dominant stall cells of different sizes could be observed. The larger one is caused by the spike stall covering roughly two blade passages in the circumferential direction and about 25% span in the radial direction. Spike stall disturbances are accompanied by lower frequencies and higher amplitudes of the pressure signals. Casing treatment causes flow blockages to reduce due to allevi- ation of backflow regions, which in turn reduces the total pressure loss and increases the axial veloc- ity in the blade tip gap region, as well as tip leakage flow fluctuation at higher frequencies and lower amplitudes. Eventually, it can be concluded that the casing treatment of the stepped tip gap type could increase the stall margin of the compressor. This fact is basically due to retarding the movement of the interface region between incoming and tip leakage flows towards the rotor leading edge Diane and suttressing the reversed flow around the blade trailing edee.展开更多
Generally, casing treatment（CT） is a passivity method to enhance the stall margin of fan/compressor. A novel casing treatment based on the small disturbance theory and vortex and wave interaction suggestion is a met...Generally, casing treatment（CT） is a passivity method to enhance the stall margin of fan/compressor. A novel casing treatment based on the small disturbance theory and vortex and wave interaction suggestion is a method combining passive control and active control, which has been proved effective at enhancing the stall margin of fan/compressor in experiment. In order to investigate the mechanism of this kind of casing treatment, an experimental investigation of a stall precursor-suppressed（SPS） casing treatment with air suction or blowing air is conducted in the present paper. The SPS casing treatment is designed to suppressing stall precursors to realize stall margin enhancement in turbomachinery. The experimental results show that the casing treatment with blowing air of small quantity can improve the stall margin by about 8% with about 1% efficiency loss. By contrast, the SPS casing treatment with micro-bias flow does not improve the stall margin much more than that without bias flow, even worse. Meanwhile, the present investigation has also attempted to reveal the mechanism of stall margin improvement with the casing treatment.It is found that the stall margin improvements vary with the modification of the unsteady shedding flow and the unsteady wall boundary impedance. The experimental results agree fairly well with the theoretical prediction using a flow stability model of rotating stall.展开更多
On the base of an assumed steady inlet circumferential total pressure distortion, three-dimensional time-dependent numerical simulations are conducted on an axial flow subsonic compressor rotor. The performances and f...On the base of an assumed steady inlet circumferential total pressure distortion, three-dimensional time-dependent numerical simulations are conducted on an axial flow subsonic compressor rotor. The performances and flow fields of a compressor rotor, either casing treated or untreated, are investigated in detail either with or without inlet pressure distortion. Results show that the circumferential groove casing treatment can expand the operating range of the compressor rotor either with or without inlet pressure distortion at the expense of a drop in peak isentropic efficiency. The casing treatment is capable of weakening or even removing the tip leakage vortex effectively either with or without inlet distortion. In clean inlet circumstances, the enhancement and forward movement of tip leakage vortex cause the untreated compressor rotor to stall. By contrast, with circumferential groove casing, the serious flow separation on the suction surface leads to aerodynamic stalling eventually. In the presence of inlet pressure distortion, the blade loading changes from passage to passage as the distorted inflow sector is traversed. Similar to the clean inlet circumstances, with a smooth wall casing, the enhancement and forward movement of tip leakage vortex are still the main factors which lead to the compressor rotor stalling eventually. When the rotor works trader near stall conditions, the blockage resulting from the tip leakage vortex in all the passages is very serious. Especially in several passages, flow-spillage is observed. Compared to the clean inlet circumstances, circumferential groove casing treatment can also eliminate the low energy zone in the outer end wall region effectively.展开更多
In this paper,a kind of Wire Mesh Casing Treatment(WMCT)is proposed to improve the stable operating range of the compressor.In contrast to the traditional circumferential groove,as for WMCT,a layer of wire mesh is lai...In this paper,a kind of Wire Mesh Casing Treatment(WMCT)is proposed to improve the stable operating range of the compressor.In contrast to the traditional circumferential groove,as for WMCT,a layer of wire mesh is laid on the surface of the circumferential groove.Parametric studies were conducted on the low-speed axial flow compressor,including the groove width,axial location,and mesh count.The optimum axial location for WMCT is related to its groove width.A higher wire mesh count results in a smaller compressor stall margin improvement.Steady simulations were carried out to study the effect of WMCT on the flow structure of the compressor.The wire mesh in the WMCT has a certain flow resistance,which restricts the flow into and out of the groove.Due to the WMCT,the flow parameter in the tip region of the rotor is less sensitive to changes in the operating conditions of the compressor.The WMCT causes the rotor tip blade loading to shift backward,inhibiting the formation of spill forward of the leakage flow,and thus improving the stability of the compressor.The flow resistance on the groove surface is a new degree-of-freedom for the casing treatment designer.展开更多
Using an inviscid model with inlet total pressure gradient and a J. D. Denton scheme, this paper for the first time numerically solves the 3D flow field of compressor casing treatment, and also explores some boundary ...Using an inviscid model with inlet total pressure gradient and a J. D. Denton scheme, this paper for the first time numerically solves the 3D flow field of compressor casing treatment, and also explores some boundary singularities and numerical stability. Agreement is attained in qualitative explanations of some, casing treatment test results and its mechanism.展开更多
This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based...This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing treatment configuration reveal an important modification of the vortex topology at the rotor tip clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is proposed.展开更多
Casing treatment is one possible way of regaining axial compressor operating range. However, most of casing treatments extend the operating range with the cost of efficiency penalty. A new form of multiple cylindrical...Casing treatment is one possible way of regaining axial compressor operating range. However, most of casing treatments extend the operating range with the cost of efficiency penalty. A new form of multiple cylindrical holes casing treatment(MHCT) with pre-swirl blowing for the NASA Rotor-37 has been designed based on profound understanding of the stall inception. Unsteady numerical simulations have been performed for Rotor-37 with and without MHCT. Parametric studies of the total extraction holes area and their axial locations show that the compressor performance deteriorates as the area ratio increases but the stall margin is extended and there is an optimum extraction holes axial location for stall margin extending. The better configuration of MHCT could extend the stall margin by 6.2% with only 0.23% peak efficiency reduction. Detailed analysis of the physical mechanism behind the stall margin improvement shows that the casing treatment could eliminate the passage blockage by suppressing breakup of tip leakage vortex and decrease the blade load in tip region, which both contribute to improve stall margin of transonic axial compressors.展开更多
High-pressure ratio and wide operating range are highly required for a turbocharger in diesel engines. A recirculation flow type casing treatment is effective for flow range enhancement of centrifugal compressors. Two...High-pressure ratio and wide operating range are highly required for a turbocharger in diesel engines. A recirculation flow type casing treatment is effective for flow range enhancement of centrifugal compressors. Two ring grooves on a suction pipe and a shroud casing wall are connected by means of an annular passage and stable recirculation flow is formed at small flow rates from the downstream groove toward the upstream groove through the annular bypass. The shape of baseline recirculation flow type casing is modified and optimized by using a multi-point optimization code with a metamodel assisted evolutionary algorithm embedding a commercial CFD code CFX from ANSYS. The numerical optimization results give the optimized design of casing with improving adiabatic efficiency in wide operating flow rate range. Sensitivity analysis of design parameters as a function of efficiency has been performed. R is found that the optimized casing design provides optimized recirculation flow rate, in which an increment of entropy rise is minimized at grooves and passages of the rotating impeller.展开更多
As demonstrated by former work,the holed casing treatment can be used to expand the stall margin of a centrifugal compressor with unshrouded impeller.In addition,the choked margin can also be expanded as experimental ...As demonstrated by former work,the holed casing treatment can be used to expand the stall margin of a centrifugal compressor with unshrouded impeller.In addition,the choked margin can also be expanded as experimental results indicated.Moreover,the compressor performance,especially the efficiency,on the whole working range is improved.As shown by experiments,the stall margin and choked margin of the compressor are extended,and the maximum efficiency improvement is 14%at the large flowrate of 1.386.Numerical simulations were carried out to analyze the flow in the impeller and in the holes in the case of large flowrate.The results indicate that in large flowrate conditions,there is a low-pressure region on the throat part of the impeller passage,leading to the bypass flows appearing in the holes,which means the flow area at the inlet of the impeller is increased.The bypass flow can also contribute to the decrease of the Mach number at the throat part near the shroud end-wall which implies that the choked margin is expanded.Besides,as the bypass flow would inhibit the development of the vertexes in the tip clearance and suppress the flow recirculation in the shroud end-wall region,both the pressure ratio and efficiency of the compressor are improved,which agrees well with the experiments.展开更多
The hybrid slot-groove(S-G)casing treatment(CT),which combines the advantages of slot and groove in consideration of stall margin enhancing and efficiency penalty,was experimentally investigated under circumferential ...The hybrid slot-groove(S-G)casing treatment(CT),which combines the advantages of slot and groove in consideration of stall margin enhancing and efficiency penalty,was experimentally investigated under circumferential distorted inflows.Previous experiments showed that the hybrid S-G CT can extend the stability by 19.79%with uniform inflow condition.To further estimate its stability enhancement ability with distorted inflow,three types of circumferential total pressure distortion inflow that the distorted intensities(DC(60))are equal to 0.90%,4.12%,and 24.75%,are selected to conduct a serial of experiments.Results demonstrated that the stability of the compressor were deteriorated by 7.87%,9.19%and 39.08%respectively under three distorted inflows.It was founded that,under the above-mentioned distorted inflows,the hybrid S-G CT was able to extend the stability by 18.48%,17.81%,and 13.80%,respectively,which proved the strong anti-distortion ability of the hybrid S-G CT.By using the dynamic pressure sensors fixed on the casing wall,the unsteady measurements demonstrated that the stall precursor with uniform and circumferential distorted inflows are always spiky-wave;thus the hybrid S-G CT can play an excellent stability enhancement capability.The analytical results with power spectral density proved that,when at the same flow point,the perturbation,with frequency being around the rotating stall frequency band,was distinctly suppressed by hybrid S-G CT,thus delaying the rotating stall.The stall precursor detected in the casing wall depicted that unlike the short length-scale of stall precursor(5–6 blade passage)under smooth casing;the hybrid S-G CT can create a stall precursor with long length-scale.Under the distortion intensities from 0 to 4.12%,the length scale of the stall precursors occupies approximately 10–12 blade passages.As the distortion intensity further increases to 24.75%,the length scale of stall precursor increases to occupy 16–17 blade passages.This phenomenon can guide the stall warning studies with compressors using CT in the future.展开更多
Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor.However,its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until no...Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor.However,its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until now.To conquer this issue,unsteady full-annulus simulations were conducted to investigate the stall mechanism of a mixed-flow compressor with and without axial slot casing treatment(ASCT).The circumferential propagating speed of spike inception resolved by the numerical approach is 87.1%of the shaft speed,which is identical to the test data.The numerical results confirmed that the mixed-flow compressor fell into rotating stall via spike-type with and without ASCT.The flow structure of the spike inception was investigated at 50%design rotational speed.Instantaneous static pressure traces extracted upstream of the leading edge had shown a classic spiky wave.Furthermore,it was found that with and without ASCT,the mixed-flow compressor stalled through spike with the characteristic of tip leakage spillage at leading edge and tip leakage backflow from trailing edge,which is different from a fraction of the centrifugal compressor.The resultant phenomenon provides conoborating evidence for that unlike in axial-flow compressor,the addition of ASCT does not change the stall characteristics of the mixed-flow compressor.The flow structure that induced spike inception with ASCT is similar to the case with smooth casing.In the throttling process,tip leakage flow vortex had been involved in the formation of tornado vortices,with one end at the suction side,and the other end at the casing-side.The low-pressure region relevant to the downward spike is caused by leading-edge separation vortex or tornado vortex.The high-pressure region relevant to the upward spike is induced by blockage from the passage vortex.These results not only can provide guidance for the design of casing treatment in mixed-flow compressor,but also can pave the way for the stall waring in the highly-loaded compressors of next-generation aeroengines.展开更多
This paper presents the experimental results to understand the performance of moderately loaded high speed single stage transonic axial flow compressor subjected to various configurations of axial extensions of bend s...This paper presents the experimental results to understand the performance of moderately loaded high speed single stage transonic axial flow compressor subjected to various configurations of axial extensions of bend skewed casing treatment with moderate porosity.The bend skewed casing treatment of 33%porosity was coupled with rectangular plenum chamber of depth equal to the slots depth.The five axial extensions of 20%,40%,60%,80%and 100%were used for the experimental evaluations of compressor performance.The main objective was to identify the optimum extension of the casing treatment with reference to rotor leading edge which results in maximum stall margin improvements with minimum loss in the stage efficiency.At each axial extension the compressor performance is distinctive.The improvement in the stall margin was very significant at some axial extensions with 4%–5%penalty in the stage efficiency.The compressors stage shows recovery in terms of efficiency at lower axial extensions of 20%and 40%with increase in the peak stage efficiency.Measurements of flow parameters showed the typical behaviors at near stall flow conditions.Hot wire sensor was placed at the rotor upstream in the tip region to capture the oscillations in the inlet axial and tangential velocities at stall conditions.In the absence of casing treatment the compressor exhibit abrupt stall with very high oscillations in the inlet axial and tangential velocity of the flow.The extents of oscillations reduce with bend skewed casing treatment.Few measurements were also performed in the plenum chamber and salient results are presented in this paper.展开更多
The effects of blade bowing on the performance of a high pressure-ratio turbocharger centrifugal compressor were studied by experiments and numerical simulation.The results showed that the negative bowing was capable ...The effects of blade bowing on the performance of a high pressure-ratio turbocharger centrifugal compressor were studied by experiments and numerical simulation.The results showed that the negative bowing was capable of increasing the choke mass rate and the efficiency but decreased the surge mass flow rate,while the positive bowing had the opposite effects.When coupling with the self-recirculation casing treatment,the surge mass flow rate of the compressor with negative bowing blade was almost identical with that of the prototype,while the choke mass flow rate was still larger,and the total effect contributed to an increase of the stable flow range by 5.85%at design speed.Besides,the flow mechanism of the coupling effects of blade bowing and self-recirculation casing treatment was discussed.展开更多
The paper investigates the effect of a single circumferential groove casing treatment(CGCT) on a transonic compressor rotor numerically.In particular,the effect of the groove at different axial locations on the flow f...The paper investigates the effect of a single circumferential groove casing treatment(CGCT) on a transonic compressor rotor numerically.In particular,the effect of the groove at different axial locations on the flow field is studied in detail and stall margin improvement is also discussed.The present results show that the groove close to the leading edge plays a crucial role in stabilizing the near stall flow structures and,hence,improves the stall margin.The groove at the mid-chord-section of the blade can help exchange and transfer momentums between different directions,and suppress the flow unsteadiness,leading to increased efficiency in rotor performance and extended operation range.The groove located near the blade trailing edge has limited effects on stall margin improvement and may cause additional penalty in efficiency.Through comparison with the recent work on CGCT,some common flow physics can be observed.展开更多
This paper will first carry out experimental investigations on a test compressor which is a large-scale,two-stage and low-speed axial one to evaluate the participation of a novel casing treatment(stall precursor-suppr...This paper will first carry out experimental investigations on a test compressor which is a large-scale,two-stage and low-speed axial one to evaluate the participation of a novel casing treatment(stall precursor-suppressed casing treatment,SPS CT).The compressor performance for its pressure rise characteristics and efficiency are tested and illustrated.Besides,the time-averaged steady and the time-resolved unsteady measurement in this paper finally lead to some further analyses about the stall evolution of this compressor tending to uncover the process of the stall evolution and the mechanism of the SPS CT.The overall performance results indicate that the SPS CT can extend the compressor stall margin by 3%e11%with very limited efficiency loss.And the mechanism for such casing treatment has also been revealed as stall-precursor suppression by observing the evolution of the inception waves.In addition,modeling work have been conducted subject to the effects of SPS CT on the test two-stage axial compressor.The compressor stability model is able to investigate the effects of different geometrical parameters on the compressor stability and then make an optimal design for the SPS CT when it is applied on the test compressor.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52306035 and 52325602)the Science Center for Gas Turbine Project,China(Nos.P2022-A-II-002-001 and P2022-C-II-003-001)+1 种基金the National Science and Technology Major Project,China(Nos.Y2022-II-0002-0005 and Y2022-II-0003-0006)the Key Laboratory of Pre-Research Management Centre,China(No.6142702200101)。
文摘An experimental investigation is conducted to evaluate the performance and the stalling process of a fan subjected to inlet swirls,as well as the effectiveness of an Impedance Boundary-Controlled(IBC)Casing Treatment(CT)on the stall margin recovery.An operating cycle is proposed based on the hysteresis effect of harmonic flap oscillation of airfoils and parallel compressor theory to explain the pressure characteristic of the fan under twin swirl inlets.Twin swirls are observed to reduce the stall margin of the fan,and the circumferential location where the spike is detected turns to the intersection area of the twin swirl.The IBC CT is proven to extend the stall margin of the fan for 12.7%–22.3%when subjected to inlet swirls with an efficiency loss of around 1%.The IBC CT helps to reduce the size of the operating cycle of the fan by redistributing the blade loading and adding the system damping to dissipate the perturbation energy.
基金supported by National Natural Science Foundation of China(Grant No.50776056)National Hi-tech Research and Development Program of China(863 Program,Grant No.2006AA05Z250)
文摘Casing treatment is a widely employed technique to increase the stall margins of turbomachineries.In the last several decades,many researches on casing treatment have been carded out.However,the mechanism of its expanding stall margins is still not very clear.Till now,most casing teatment schemes are designed for axial compressors,while the investigations on casing treatments in centrifugal compressors are rarely reported.Moreover,current investigation methods mainly focus on experiments,and perfect theoretic al analysis is not yet feasible.In order to study the effectiveness and further the mechanism of casing treatments in centrifugal compressors,in this paper,a computationally based investigation of the impact of the self-recireulating casing treatment on the performance of a radial compressor is carried out.The results indicate that,by casing bleed and injection,the casing treatment with inclined blades in the cavity expands the stall margin most.At low mass flows,the reversed flow through the cavity with inclined blades develops the counter swirl flow in front of the impeller inlet,which is considered to benefit increasing the pressure rise from the injection port to the bleed port and thereby augment the recirculating flow.At 120%design speed,the stall margin is larger than that at the design speed.However,the cost of extending the stall margin is the reduction of isentropic efficiency.A mended casing treatment by shifting the bleed port upstream is also studied.It is demonstrated that,relative to the original casing treatment,this mend can improve the efficiency evidently notwithstanding a little narrowing of the flow range.
基金National Natural Science Foundation of China (50736007, 50890181)the Innovation Foundation of BUAA for PhD Graduates (300383)
文摘A three-dimensional compressible flow stability model is presented in this paper, which focuses on stall inception of multi-stage axial flow compressors with a finite large radius annular duct configuration for the first time. It is shown that under some assumptions, the stability equation can be obtained yielding from a group of homogeneous equations. The stability can be judged by the non-dimensional imaginary part of the resultant complex frequency eigenvalue. Further more, based on the analysis of the unsteady phenomenon caused by casing treatment, the function of casing treatment has been modeled by a wall impedance condition which is included in the stability model through the eigenvalues and the corresponding eigenfunctions of the system. Finally, some experimental investigation and two numerical evaluation cases are conducted to validate this model and emphasis is placed on numerically studying the sensitivity of the setup of different boundary conditions on the stall inception of axial flow fan/compressors. A novel casing treatment which consists of a backchamber and a perforated plate is suggested, and it is noted that the open area ratio of the casing treatment is less than 10%, and is far smaller than conventional casing treatment with open area ratio of over 50%, which could result in stall margin improvement without obvious efficiency loss of fan/compressors.
基金supported by National Natural Science Foundation of China(51236001 and 51576008)National Basic Research Program of China(2012CB720201)+1 种基金Aeronautical Science Foundation of China(2014ZB51018)Fundamental Research Funds for the Central Universities
文摘The present work is about the stall margin enhancement ability of a kind of stall precursor-suppressed（SPS） casing treatment when fan/compressor suffers from a radial total pressure inlet distortion.Experimental researches are conducted on a low-speed compressor with and without SPS casing treatment under radial distorted inlet flow of different levels as well as uniform inlet flow.The distorted flow fields of different levels are generated by annular distortion flow generators of different heights.The characteristic curves under these conditions are measured and analyzed.The results show that the radial inlet distortion could cause a stall margin loss from 2%to30%under different distorted levels.The SPS casing treatment could remedy this stall margin loss under small distortion level and only partly make up the stall margin loss caused by distortion in large level without leading to perceptible additional efficiency loss and obvious change of characteristic curves.The pre-stall behavior of the compressor is investigated to reveal the mechanism of this stall margin improvement ability of the SPS casing treatment.The results do show that this casing treatment delays the occurrence of rotating stall by weakening the pressure perturbations and suppressing the nonlinear amplification of the stall precursor waves in the compression system.
基金the National Science Foundation of China(Nos.51676184,51636001 and 51922098)the National Science and Technology Major Project(Nos.2017-II-00040017 and 2017-II-0005-0018)the National Key R&D Program of China(No.2018YFB0606100)。
文摘The influence of Axial-Slot Casing Treatment(ASCT)on the performance and stability enhancement mechanisms of ASCT were experimentally and numerically investigated in a highspeed mixed-flow compressor under three different tip clearances.Unsteady simulations showed the compressor stalled through end-wall stall route,i.e.the spike stall inception originating from rotor tip region,which was validated by dynamical measurements.When the ASCT was applied,greater than 20%of Stall Margin Improvement(SMI)could be achieved for the compressor under each tip clearance size.The streamwise velocity contours and flow structures in the tip region and axial slots were deeply analyzed to explore how the so called‘‘suction and injection effects"generated by the ASCT manipulate tip clearance flow and enhance the stability of compressor under different tip clearances.It was found that the dominant stability enhancement mechanisms of ASCT varies with tip clearance size for the mixed-flow compressor.(A)For the small tip clearance,the dominant mechanism of stability enhancement is the blockage reduction generated in the blade passage by the suction effect of ASCT.(B)For the large tip clearance,the injection effect of the ASCT is the dominant mechanism of stability enhancement with ASCT,which plays the leading role in delaying the spillage of incoming/tip leakage flow interface at the rotor Leading Edge(LE)plane.
基金Financial support of the Aerodynamics and Compressible Turbomachinery Research Laboratory at Iran University of Science and Technology is highly appreciated
文摘Abstract This article deals with application of grooved type casing treatment for suppression of spike stall in an isolated axial compressor rotor blade row. The continuous grooved casing treatment covering the whole compressor circumference is of 1.8 mm in depth and located between 90% and 108% chord of the blade tip as measured from leading edge. The method of investigation is based on time-accurate three-dimensional full annulus numerical simulations for cases with and without casing treatment. Discretization of the Navier Stokes equations has been carried out based on an upwind second-order scheme and k-a-SST （Shear Stress Transport） turbulence modeling has been used for estimation of eddy viscosity. Time-dependent flow structure results for the smooth casing reveal that there are two criteria for spike stall inception known as leading edge spillage and trailing edge backftow, which occur at specific mass flow rates in near-stall conditions. In this case, two dominant stall cells of different sizes could be observed. The larger one is caused by the spike stall covering roughly two blade passages in the circumferential direction and about 25% span in the radial direction. Spike stall disturbances are accompanied by lower frequencies and higher amplitudes of the pressure signals. Casing treatment causes flow blockages to reduce due to allevi- ation of backflow regions, which in turn reduces the total pressure loss and increases the axial veloc- ity in the blade tip gap region, as well as tip leakage flow fluctuation at higher frequencies and lower amplitudes. Eventually, it can be concluded that the casing treatment of the stepped tip gap type could increase the stall margin of the compressor. This fact is basically due to retarding the movement of the interface region between incoming and tip leakage flows towards the rotor leading edge Diane and suttressing the reversed flow around the blade trailing edee.
基金supported by National Natural Science Foundation of China (Nos. 51236001, 51406229 and 51106154)National Basic Research Program of China (No. 2012CB720201)+1 种基金Aeronautical Science Foundation of China (No. 2014ZB51018)Fundamental Research Funds for the Central Universities
文摘Generally, casing treatment（CT） is a passivity method to enhance the stall margin of fan/compressor. A novel casing treatment based on the small disturbance theory and vortex and wave interaction suggestion is a method combining passive control and active control, which has been proved effective at enhancing the stall margin of fan/compressor in experiment. In order to investigate the mechanism of this kind of casing treatment, an experimental investigation of a stall precursor-suppressed（SPS） casing treatment with air suction or blowing air is conducted in the present paper. The SPS casing treatment is designed to suppressing stall precursors to realize stall margin enhancement in turbomachinery. The experimental results show that the casing treatment with blowing air of small quantity can improve the stall margin by about 8% with about 1% efficiency loss. By contrast, the SPS casing treatment with micro-bias flow does not improve the stall margin much more than that without bias flow, even worse. Meanwhile, the present investigation has also attempted to reveal the mechanism of stall margin improvement with the casing treatment.It is found that the stall margin improvements vary with the modification of the unsteady shedding flow and the unsteady wall boundary impedance. The experimental results agree fairly well with the theoretical prediction using a flow stability model of rotating stall.
基金National Natural Science Foundation of China (10377013)
文摘On the base of an assumed steady inlet circumferential total pressure distortion, three-dimensional time-dependent numerical simulations are conducted on an axial flow subsonic compressor rotor. The performances and flow fields of a compressor rotor, either casing treated or untreated, are investigated in detail either with or without inlet pressure distortion. Results show that the circumferential groove casing treatment can expand the operating range of the compressor rotor either with or without inlet pressure distortion at the expense of a drop in peak isentropic efficiency. The casing treatment is capable of weakening or even removing the tip leakage vortex effectively either with or without inlet distortion. In clean inlet circumstances, the enhancement and forward movement of tip leakage vortex cause the untreated compressor rotor to stall. By contrast, with circumferential groove casing, the serious flow separation on the suction surface leads to aerodynamic stalling eventually. In the presence of inlet pressure distortion, the blade loading changes from passage to passage as the distorted inflow sector is traversed. Similar to the clean inlet circumstances, with a smooth wall casing, the enhancement and forward movement of tip leakage vortex are still the main factors which lead to the compressor rotor stalling eventually. When the rotor works trader near stall conditions, the blockage resulting from the tip leakage vortex in all the passages is very serious. Especially in several passages, flow-spillage is observed. Compared to the clean inlet circumstances, circumferential groove casing treatment can also eliminate the low energy zone in the outer end wall region effectively.
基金supported by the National Natural Science Foundation of China(Nos.52325602 and U2241276)the Science Center for Gas Turbine Project,China(Nos.P2022-A-Ⅱ-002-001,P2022-C-Ⅱ-001-001 and P2022-CⅡ-003-001)+1 种基金the National Science and Technology Major Project,China(No.2017-Ⅱ-0005-0018)supported by the Key Laboratory of Pre-Research Management Centre,China(No.6142702200101)。
文摘In this paper,a kind of Wire Mesh Casing Treatment(WMCT)is proposed to improve the stable operating range of the compressor.In contrast to the traditional circumferential groove,as for WMCT,a layer of wire mesh is laid on the surface of the circumferential groove.Parametric studies were conducted on the low-speed axial flow compressor,including the groove width,axial location,and mesh count.The optimum axial location for WMCT is related to its groove width.A higher wire mesh count results in a smaller compressor stall margin improvement.Steady simulations were carried out to study the effect of WMCT on the flow structure of the compressor.The wire mesh in the WMCT has a certain flow resistance,which restricts the flow into and out of the groove.Due to the WMCT,the flow parameter in the tip region of the rotor is less sensitive to changes in the operating conditions of the compressor.The WMCT causes the rotor tip blade loading to shift backward,inhibiting the formation of spill forward of the leakage flow,and thus improving the stability of the compressor.The flow resistance on the groove surface is a new degree-of-freedom for the casing treatment designer.
文摘Using an inviscid model with inlet total pressure gradient and a J. D. Denton scheme, this paper for the first time numerically solves the 3D flow field of compressor casing treatment, and also explores some boundary singularities and numerical stability. Agreement is attained in qualitative explanations of some, casing treatment test results and its mechanism.
文摘This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing treatment configuration reveal an important modification of the vortex topology at the rotor tip clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is proposed.
基金Financial support from the National Natural Science Foundation of China(Project No.51176187 and 51206163)International special cooperation projects(Project No.2014DFR70080)
文摘Casing treatment is one possible way of regaining axial compressor operating range. However, most of casing treatments extend the operating range with the cost of efficiency penalty. A new form of multiple cylindrical holes casing treatment(MHCT) with pre-swirl blowing for the NASA Rotor-37 has been designed based on profound understanding of the stall inception. Unsteady numerical simulations have been performed for Rotor-37 with and without MHCT. Parametric studies of the total extraction holes area and their axial locations show that the compressor performance deteriorates as the area ratio increases but the stall margin is extended and there is an optimum extraction holes axial location for stall margin extending. The better configuration of MHCT could extend the stall margin by 6.2% with only 0.23% peak efficiency reduction. Detailed analysis of the physical mechanism behind the stall margin improvement shows that the casing treatment could eliminate the passage blockage by suppressing breakup of tip leakage vortex and decrease the blade load in tip region, which both contribute to improve stall margin of transonic axial compressors.
基金financially supported by Harada memorial foundation and Japan Science and Technology Agency
文摘High-pressure ratio and wide operating range are highly required for a turbocharger in diesel engines. A recirculation flow type casing treatment is effective for flow range enhancement of centrifugal compressors. Two ring grooves on a suction pipe and a shroud casing wall are connected by means of an annular passage and stable recirculation flow is formed at small flow rates from the downstream groove toward the upstream groove through the annular bypass. The shape of baseline recirculation flow type casing is modified and optimized by using a multi-point optimization code with a metamodel assisted evolutionary algorithm embedding a commercial CFD code CFX from ANSYS. The numerical optimization results give the optimized design of casing with improving adiabatic efficiency in wide operating flow rate range. Sensitivity analysis of design parameters as a function of efficiency has been performed. R is found that the optimized casing design provides optimized recirculation flow rate, in which an increment of entropy rise is minimized at grooves and passages of the rotating impeller.
基金supported by the National Natural Science Foundation of China(Grant No.50776056)the High Technology Research and Development Program of China("863"Program)(Grant No. 2009AA05Z201)
文摘As demonstrated by former work,the holed casing treatment can be used to expand the stall margin of a centrifugal compressor with unshrouded impeller.In addition,the choked margin can also be expanded as experimental results indicated.Moreover,the compressor performance,especially the efficiency,on the whole working range is improved.As shown by experiments,the stall margin and choked margin of the compressor are extended,and the maximum efficiency improvement is 14%at the large flowrate of 1.386.Numerical simulations were carried out to analyze the flow in the impeller and in the holes in the case of large flowrate.The results indicate that in large flowrate conditions,there is a low-pressure region on the throat part of the impeller passage,leading to the bypass flows appearing in the holes,which means the flow area at the inlet of the impeller is increased.The bypass flow can also contribute to the decrease of the Mach number at the throat part near the shroud end-wall which implies that the choked margin is expanded.Besides,as the bypass flow would inhibit the development of the vertexes in the tip clearance and suppress the flow recirculation in the shroud end-wall region,both the pressure ratio and efficiency of the compressor are improved,which agrees well with the experiments.
基金the support of the grants of National Natural Science Foundation of China(No.51922098,No.51636001 and No.51790510)the National Science and Technology Major Project(2017-Ⅱ-0005-0018,2017-Ⅱ-0004-0017)the Special Fund for the Member of Youth Innovation Promotion Association of CAS(2018173)。
文摘The hybrid slot-groove(S-G)casing treatment(CT),which combines the advantages of slot and groove in consideration of stall margin enhancing and efficiency penalty,was experimentally investigated under circumferential distorted inflows.Previous experiments showed that the hybrid S-G CT can extend the stability by 19.79%with uniform inflow condition.To further estimate its stability enhancement ability with distorted inflow,three types of circumferential total pressure distortion inflow that the distorted intensities(DC(60))are equal to 0.90%,4.12%,and 24.75%,are selected to conduct a serial of experiments.Results demonstrated that the stability of the compressor were deteriorated by 7.87%,9.19%and 39.08%respectively under three distorted inflows.It was founded that,under the above-mentioned distorted inflows,the hybrid S-G CT was able to extend the stability by 18.48%,17.81%,and 13.80%,respectively,which proved the strong anti-distortion ability of the hybrid S-G CT.By using the dynamic pressure sensors fixed on the casing wall,the unsteady measurements demonstrated that the stall precursor with uniform and circumferential distorted inflows are always spiky-wave;thus the hybrid S-G CT can play an excellent stability enhancement capability.The analytical results with power spectral density proved that,when at the same flow point,the perturbation,with frequency being around the rotating stall frequency band,was distinctly suppressed by hybrid S-G CT,thus delaying the rotating stall.The stall precursor detected in the casing wall depicted that unlike the short length-scale of stall precursor(5–6 blade passage)under smooth casing;the hybrid S-G CT can create a stall precursor with long length-scale.Under the distortion intensities from 0 to 4.12%,the length scale of the stall precursors occupies approximately 10–12 blade passages.As the distortion intensity further increases to 24.75%,the length scale of stall precursor increases to occupy 16–17 blade passages.This phenomenon can guide the stall warning studies with compressors using CT in the future.
基金The authors are grateful for the support of National Natural Science Foundation of China for the grant with Project No.51636001,No.51790510,and No.51922098the National Science and Technology Major Project(2017-11-0004-0017,2017-H-005-0018)The authors would also appreciate the kind help of Prof.Seume,and the German Research Foundation(DFG)for supporting the experiments as part of the Collaborative Research Centre 880(Sonderforschungsbereich SFB 880).
文摘Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor.However,its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until now.To conquer this issue,unsteady full-annulus simulations were conducted to investigate the stall mechanism of a mixed-flow compressor with and without axial slot casing treatment(ASCT).The circumferential propagating speed of spike inception resolved by the numerical approach is 87.1%of the shaft speed,which is identical to the test data.The numerical results confirmed that the mixed-flow compressor fell into rotating stall via spike-type with and without ASCT.The flow structure of the spike inception was investigated at 50%design rotational speed.Instantaneous static pressure traces extracted upstream of the leading edge had shown a classic spiky wave.Furthermore,it was found that with and without ASCT,the mixed-flow compressor stalled through spike with the characteristic of tip leakage spillage at leading edge and tip leakage backflow from trailing edge,which is different from a fraction of the centrifugal compressor.The resultant phenomenon provides conoborating evidence for that unlike in axial-flow compressor,the addition of ASCT does not change the stall characteristics of the mixed-flow compressor.The flow structure that induced spike inception with ASCT is similar to the case with smooth casing.In the throttling process,tip leakage flow vortex had been involved in the formation of tornado vortices,with one end at the suction side,and the other end at the casing-side.The low-pressure region relevant to the downward spike is caused by leading-edge separation vortex or tornado vortex.The high-pressure region relevant to the upward spike is induced by blockage from the passage vortex.These results not only can provide guidance for the design of casing treatment in mixed-flow compressor,but also can pave the way for the stall waring in the highly-loaded compressors of next-generation aeroengines.
基金Authors take this opportunity to thank Director,CSIRNAL,for funding the research program through elevenths five year plan and allow publishing the results.
文摘This paper presents the experimental results to understand the performance of moderately loaded high speed single stage transonic axial flow compressor subjected to various configurations of axial extensions of bend skewed casing treatment with moderate porosity.The bend skewed casing treatment of 33%porosity was coupled with rectangular plenum chamber of depth equal to the slots depth.The five axial extensions of 20%,40%,60%,80%and 100%were used for the experimental evaluations of compressor performance.The main objective was to identify the optimum extension of the casing treatment with reference to rotor leading edge which results in maximum stall margin improvements with minimum loss in the stage efficiency.At each axial extension the compressor performance is distinctive.The improvement in the stall margin was very significant at some axial extensions with 4%–5%penalty in the stage efficiency.The compressors stage shows recovery in terms of efficiency at lower axial extensions of 20%and 40%with increase in the peak stage efficiency.Measurements of flow parameters showed the typical behaviors at near stall flow conditions.Hot wire sensor was placed at the rotor upstream in the tip region to capture the oscillations in the inlet axial and tangential velocities at stall conditions.In the absence of casing treatment the compressor exhibit abrupt stall with very high oscillations in the inlet axial and tangential velocity of the flow.The extents of oscillations reduce with bend skewed casing treatment.Few measurements were also performed in the plenum chamber and salient results are presented in this paper.
基金supported by the National Natural Science Foundation of China(Grant No.51176087)
文摘The effects of blade bowing on the performance of a high pressure-ratio turbocharger centrifugal compressor were studied by experiments and numerical simulation.The results showed that the negative bowing was capable of increasing the choke mass rate and the efficiency but decreased the surge mass flow rate,while the positive bowing had the opposite effects.When coupling with the self-recirculation casing treatment,the surge mass flow rate of the compressor with negative bowing blade was almost identical with that of the prototype,while the choke mass flow rate was still larger,and the total effect contributed to an increase of the stable flow range by 5.85%at design speed.Besides,the flow mechanism of the coupling effects of blade bowing and self-recirculation casing treatment was discussed.
基金supported by the GE Aviation under its University Strategic Alliance(USA) programsupported by the National Natural Science Foundation of China(Grant Nos.10932005 and 11272183)
文摘The paper investigates the effect of a single circumferential groove casing treatment(CGCT) on a transonic compressor rotor numerically.In particular,the effect of the groove at different axial locations on the flow field is studied in detail and stall margin improvement is also discussed.The present results show that the groove close to the leading edge plays a crucial role in stabilizing the near stall flow structures and,hence,improves the stall margin.The groove at the mid-chord-section of the blade can help exchange and transfer momentums between different directions,and suppress the flow unsteadiness,leading to increased efficiency in rotor performance and extended operation range.The groove located near the blade trailing edge has limited effects on stall margin improvement and may cause additional penalty in efficiency.Through comparison with the recent work on CGCT,some common flow physics can be observed.
基金the National Natural Science Foundation of China(Nos.51906004,51822601 and 5156008)National Science and Technology Major Project(2017-II-0005-0018).
文摘This paper will first carry out experimental investigations on a test compressor which is a large-scale,two-stage and low-speed axial one to evaluate the participation of a novel casing treatment(stall precursor-suppressed casing treatment,SPS CT).The compressor performance for its pressure rise characteristics and efficiency are tested and illustrated.Besides,the time-averaged steady and the time-resolved unsteady measurement in this paper finally lead to some further analyses about the stall evolution of this compressor tending to uncover the process of the stall evolution and the mechanism of the SPS CT.The overall performance results indicate that the SPS CT can extend the compressor stall margin by 3%e11%with very limited efficiency loss.And the mechanism for such casing treatment has also been revealed as stall-precursor suppression by observing the evolution of the inception waves.In addition,modeling work have been conducted subject to the effects of SPS CT on the test two-stage axial compressor.The compressor stability model is able to investigate the effects of different geometrical parameters on the compressor stability and then make an optimal design for the SPS CT when it is applied on the test compressor.
