In the process of performance prediction of waterjet system,the flow loss of inlet duct is usually reckoned by the rule of thumb. But its value is often overestimated to some extent,resulting in error of prediction ac...In the process of performance prediction of waterjet system,the flow loss of inlet duct is usually reckoned by the rule of thumb. But its value is often overestimated to some extent,resulting in error of prediction accuracy. This paper introduces a new method to determine the flow loss by means of computational fluid dynamic (CFD). Firstly,the fluid field around waterjet system is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations using commercial CFD code Fluent. Then an additional User-Defined Scalar (UDS) equation is embedded into Fluent to get the virtual dividing surface between the internal flow ingested into the inlet duct and the external flow beneath the hull,which is named as streamtube. By virtual of the streamtube the flow loss can be calculated according to the difference of total pressure between the duct outlet and the capture area ahead of the intake. The results from CFD calculation show that the flow loss coeflcient of a typical flush-type inlet duct is varying from 0.05 to 0.12 at different operation conditions,being obviously less than the value of 0.2-0.3 from empirical rules. With the results of this paper the prediction accuracy on propulsive performance of the waterjet system can be improved further.展开更多
In order to reduce the losses caused by tip-leakage flow, axisymmetric contouring is applied to the casing of a two-stage unshrouded high pressure turbine（HPT） of aero-engine in this paper. This investigation focuse...In order to reduce the losses caused by tip-leakage flow, axisymmetric contouring is applied to the casing of a two-stage unshrouded high pressure turbine（HPT） of aero-engine in this paper. This investigation focuses on the effects of contoured axisymmetric-casing on the blade tipleakage flow. While the size of tip clearance remains the same as the original design, the rotor casing and the blade tip are obtained with the same contoured arc shape. Numerical calculation results show that a promotion of 0.14% to the overall efficiency is achieved. Detailed analysis indicates that it reduces the entropy generation rate caused by the complex vortex structure in the rotor tip region, especially in the tip-leakage vortex. The low velocity region in the leading edge（LE） part of the tip gap is enlarged and the pressure side/tip junction separation bubble extends much further away from the leading edge in the clearance. So the blocking effect of pressure side/tip junction separation bubble on clearance flow prevents more flow on the tip pressure side from leaking to the suction side, which results in weaker leakage vortex and less associated losses.展开更多
The exhaust volute is a device that can change the exhaust direction of the ship’s gas turbine to reduce the flow loss of the high-temperature and high-speed turbine exhaust gas in the box-type exhaust volute,thereby...The exhaust volute is a device that can change the exhaust direction of the ship’s gas turbine to reduce the flow loss of the high-temperature and high-speed turbine exhaust gas in the box-type exhaust volute,thereby improving its power output performance.This paper first investigates the internal flow field characteristics of the exhaust volute via numerical simulation and reveals the main source of the internal resistance loss of the volute.On the premise of not affecting the installation size of the volute and matching it with other components in the cabin,the design scheme of volute bottom shunt and volute chamfer are then optimized in accordance with the flow characteristics inside the volute.Numerical simulation results show that the partial flow structure at the bottom of the volute can effectively improve the low-velocity region and the vortex flow at the bottom of the volute,and the chamfered angle scheme can control the regular expansion and compression of the airflow.When the volute adopts the appropriate chamfer angle and the bottom split-flow structure,the total pressure loss can be reduced by 19.6%,and the static pressure recovery coefficient can be increased by 42.05%.展开更多
On the basis of the analysis about present water resource situation in China,the disadvantage of the for- mula of flow loss and water using coefficient on anti-seep channel which have been applying in channel de- sign...On the basis of the analysis about present water resource situation in China,the disadvantage of the for- mula of flow loss and water using coefficient on anti-seep channel which have been applying in channel de- sign and water saving irrigation administration will be indicated in the paper. The characteristics of that the loss of conveying water is changeable with the now changing have been take into account in the new formula. The formula is validated by the example of middle permeable channel (A=1.90,m=0.40). The calculate re- sult is more precision. Also some formula has been given,they can be referred to the worker of the irrigation administration.展开更多
Based on flow loss, a new automatic pipe-routing algorithm is proposed for electromechanical product in 3D space, which consists of pre-processing and optimization search. Utilizing chaos theory, a chaos grid preproce...Based on flow loss, a new automatic pipe-routing algorithm is proposed for electromechanical product in 3D space, which consists of pre-processing and optimization search. Utilizing chaos theory, a chaos grid preprocessing model （CGPM） is established to efficiently pick up the solution space and reduce the search range in the pre-processing, which simplifies the optimization search. A modified particle swarm optimization （PSO） algorithm is presented to seek for an approximate optimal trajectory in the solution space in the optimization search based on standard PSO algorithm and migration characters of people. The comparison of experiments and analysis results shows that the modified PSO algorithm is capable of preventing prematurity effectively and searching for the optimal trajectory more efficiently. Theoretical analysis proves that the modified PSO algorithm converges at global optimum. The examples show that the automatic pipe-routing algorithm based on flow loss is effective and practical for eleetromechanieal product.展开更多
Boundary layer ingesting(BLI)fans are required to operate under distorted inflow conditions,which significantly reduces their efficiency[1,2].Accurately predicting fan losses is crucial for designing high-performance,...Boundary layer ingesting(BLI)fans are required to operate under distorted inflow conditions,which significantly reduces their efficiency[1,2].Accurately predicting fan losses is crucial for designing high-performance,distortion-tolerant fans.展开更多
This paper summarizes the results of the authors' 4 year experimental studies on the secondary flow losses in turbine cascades. Cascade wind tunnel experiments were carried out concerning the influence of aspect r...This paper summarizes the results of the authors' 4 year experimental studies on the secondary flow losses in turbine cascades. Cascade wind tunnel experiments were carried out concerning the influence of aspect ratios, incidence, turning angles and outer endwall divergent angles in order to unveil the evolution mechanism of secondary flow losses in turbine cascades without end clearance. Some methods for controlling the secondary flows are investigated including the blade leaning, blade cambering, endwall convergence and leading edge extension at two ends of the blade.展开更多
With the advantages of high efficiency and compact structure,supercritical carbon dioxide(sC02)Brayton cycles have bright prospects for development in energy conversion field.As one of the core components of the power...With the advantages of high efficiency and compact structure,supercritical carbon dioxide(sC02)Brayton cycles have bright prospects for development in energy conversion field.As one of the core components of the power cycle,the centrifugal compressor tends to operate near the critical point(304.13 K,7.3773 MPa).Normally,the compressor efficiency increases as the inlet temperature decreases.When the inlet temperature is close to the critical point,the density increases sharply as the temperature decreases,which results in quickly decreasing of volume flow rate and efficiency reducing.The flow loss mechanism of the sCO_(2) compressor operating at low flow rate is studied in this paper.Computational fluid dynamics(CFD) simulations for sCO_(2)compressor were carried out at various inlet temperatures and various mass flow rates.When the sCO_(2)compressor operates at low volume flow rate,the flow loss is generated mainly on the suction side near the trailing edge of the blade.The flow loss is related to the counterclockwise vortexes generated on the suction side of the main blade.The vortexes are caused by the flow separation in the downstream region of the impeller passage,which is different from air compressors operating at low flow rates.The reason for this flow separation is that the effect of Coriolis force is especially severe for the sCO_(2) fluid,compared to the viscous force and inertial force.At lower flow rates,with the stronger effect of Coriolis force,the direction of relative flow velocity deviates from the direction of radius,resulting in its lower radial component.The lower radial relative flow velocity leads to severe flow separation on the suction side near the trailing edge of the main blade.展开更多
The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the c...The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the cascade performance under real engine operating conditions.The Reynolds number has been varied in the range 100000<Re<300000,where lower and upper limits are typical of cruise and take-off/landing conditions,respectively.The effects induced by the incoming wakes at the reduced frequency f+=0.62 on both profile and secondary flow losses have been investigated.Total pressure,velocity and secondary kinetic energy distributions at the downstream tangential plane have been measured by means of a miniaturized 5-hole probe.These quantities provide information on both blade wake and secondary flow structures(passage and horse-shoe vortices).The analysis of the results allows the evaluation of the aerodynamic performance of the HL front-loaded blade in terms of both profile and secondary losses.展开更多
The flow loss of a helical channel Magnetohydrodynamic （MHD） thruster without MHD effect was numerically studied with 3-D simulations, and a flow loss coefficient （ was defined to quantify the flow loss and its inf...The flow loss of a helical channel Magnetohydrodynamic （MHD） thruster without MHD effect was numerically studied with 3-D simulations, and a flow loss coefficient （ was defined to quantify the flow loss and its influencing factors were studied. The results show that （ decreases in a first-order exponential manner with the pitch of a helical wall and the Reynolds number, and it declines slowly when t / T 〉 0.2 and Re 〉 10^5, a flow guide makes the flow more smooth and uniform, especially in the flow guide and helical wall sub-regions and thus reduces the flow loss greatly, by about 30% with the averaged value of （ from 0.0385 to 0.027, a rectifier weakens the helical flow and strengthens the axial one in the rectifier and outlet sub-regions, thus reduces the rotational kinetic pressure with the averaged value of ξ declining about 4% from 0.0385 to 0.037, and ξ decreases with a rectifier＇s axial length when Re 〉 10^5 .展开更多
In Brayton cycle energy storage systems powered by supercritical carbon dioxide(sCO_(2)),compressors are among themost critical components.Understanding their internal flowloss characteristics is,therefore,essential f...In Brayton cycle energy storage systems powered by supercritical carbon dioxide(sCO_(2)),compressors are among themost critical components.Understanding their internal flowloss characteristics is,therefore,essential for enhancing the performance of such systems.This study examines the main sCO_(2) compressor from Sandia Laboratory,utilizing entropy production theory to elucidate the sources and distribution of energy losses both across the entire machine and within its key flow components.The findings reveal that turbulent viscous dissipation is the predominant contributor to total entropy production.Interestingly,while the relative importance of the entropy produced by various sources as the mass flow rate rises remains essentially unchanged,the total entropy production exhibits a nonmonotonic trend,first decreasing and then increasing with the mass flow rate.High entropy production in the impeller is primarily concentrated in the clearance region and along the rear cover of the impeller tip.In the diffuser,it is most pronounced on the front and rear plates and within the central flow path.Meanwhile,in the volute,the highest entropy production occurs around the diffuser outlet and along the outer region of the volute’s centerline.展开更多
The flow field in junction is complicated due to the ripple property of oil flow velocity and different frequencies of two pumps in aircraft. In this study, the flow fields of T-junction and Y-junction were analyzed u...The flow field in junction is complicated due to the ripple property of oil flow velocity and different frequencies of two pumps in aircraft. In this study, the flow fields of T-junction and Y-junction were analyzed using shear stress transport （SST） model in ANSYS/CFX software. The simulation results identified the variation rule of velocity peak in T-junction with different frequencies and phase-differences, meanwhile, the eddy and velocity shock existed in the corner of the T-junction, and the limit working state was obtained. Although the eddy disappeared in Y-junction, the velocity shock and pressure loss were still too big. To address these faults, an arc-junction was designed. Based on the flow fields of arc-junction, the eddy in the junction corner disappeared and the maximum of velocity peak declined compared to T-and Y-junction. Additionally, 8 series of arc-junction with different radiuses were tested to get the variation rule of velocity peak. Through the computation of the pressure loss of three junctions, the arc-junction had a lowest loss value, and its pressure loss reached the minimum value when the curvature radius is 35.42 mm, meanwhile, the velocity shock has decreased in a low phase.展开更多
For a transonic axial-flow compressor, the numerical simulations, verified against experimental data, were used to study the inherent correlation between the evolutionary process of the vortex structures and the flow ...For a transonic axial-flow compressor, the numerical simulations, verified against experimental data, were used to study the inherent correlation between the evolutionary process of the vortex structures and the flow loss in a compressor stator passage during the throttling process. The flow loss was divided accurately and quantitatively, based on the evolutionary process of the vortex structures. According to the position of the singular points of the vortex structures, the influence of the evolution of the vortex structures on the generation and development of the flow loss was analyzed on a microscale scale. Thereafter, this paper provided the vortex dynamic mechanism of the flow loss, which was important to enrich the theoretical system of the flow field in the compressor. The results show that: the flow loss at the top of the stator tip is caused by the low-energy fluid clusters, which are transported and accumulated by the vortices from the endwall; the transport effect of the pressure separation vortex at the upper half-height only migrates the position of the flow losses, but there is new flow loss generated by its shear action to the endwall. The dominant flow loss during the throttling process concentrates upon the closed separation bubble around the middle of the suction side of the stator.展开更多
In the flow on a mobile bed in an open channel, sand ripple often appears after the sediment begins to move. Different scholars have different views on the formation of sand ripples. This paper holds that as the rippl...In the flow on a mobile bed in an open channel, sand ripple often appears after the sediment begins to move. Different scholars have different views on the formation of sand ripples. This paper holds that as the ripple in general is very small, its formation is due to the instability of the laminar flow or the evolution of the small-scale coherent structures in the sublayer adjacent to the wall of the open channel. When the shear stresses caused by the disturbing waves or the coherent structure near the bed surface boundary and the water flow itself are greater than the shields stresses, responses on the bed surface appear and the sand ripple forms. If the frequency of the shear stress caused by the disturbance is close to the natural frequency of the sand grains that produced resonance, such a phenomenon is called the 'detection property' of the sediment. It is at this point that the maximum resonance appears and the sand ripple develops rapidly.展开更多
A commercial N-S solver has been employed for simulation and investigation ofthe unsteady flow field inside the tip clearance of a turbine rotor. The main objective of thispaper is to introduce a new method of energy ...A commercial N-S solver has been employed for simulation and investigation ofthe unsteady flow field inside the tip clearance of a turbine rotor. The main objective of thispaper is to introduce a new method of energy loss calculation for the flow field in tip clearanceregion of a turbine rotor blade. This method can be easily used in all kinds of flow fields. Regionsof high viscous effects have been found to be located near the shroud rather than the blade tip. Itis shown that the time-averaged loss of energy in tip leakage flow is dissimilar for differentrotor blades. This result is a helpful hint that can be taken by blade designers to designnon-uniform rotor blades with different geometric and aerodynamic loads to minimize the energy loss.展开更多
The pressure loss of cross-flow perforated of physical modeling, simulation and data processing. muffler has been computed with the procedure Three-dimensional computational fluid dynamics （CFD） has been used to inv...The pressure loss of cross-flow perforated of physical modeling, simulation and data processing. muffler has been computed with the procedure Three-dimensional computational fluid dynamics （CFD） has been used to investigate the relations of porosities, flow velocity and diameter of the holes with the pressure loss. Accordingly, some preliminary results have been obtained that pressure loss increases with porosity descent as nearly a hyperbolic trend, rising flow velocity of the input makes the pressure loss increasing with parabola trend, diameter of holes affects little about pressure loss of the muffler. Otherwise, the holes on the perforated pipes make the air flow gently and meanly, which decreases the air impact to the wall and pipes in the muffler. A practical perforated muffler is used to illustrate the available of this method for pressure loss computation, and the comparison shows that the computation results with the method of CFD has reference value for muffler design.展开更多
Rainfall intensity and slope gradient are two of the most important factors affecting the variations of runoff nitrogen(N).However,the effects of slope gradient and rainfall intensity on N loss via surface flow and in...Rainfall intensity and slope gradient are two of the most important factors affecting the variations of runoff nitrogen(N).However,the effects of slope gradient and rainfall intensity on N loss via surface flow and interflow on weathered granite slopes are poorly understood.In this study,12 artificial rainfalls(three rainfall intensities and four slope gradients)were simulated to investigate the coupling loss characteristics of surface flow–interflow–total nitrogen(TN),nitrate nitrogen(NO_3^--N)and ammonia nitrogen(NH_4^+-N)on weathered granite slopes.The results show that slope gradient has a greater impact on the surface flow when the rainfall intensity is relatively large.The effect gradually weakens with the decrement of rainfall intensity.The interflow yield increases firstly with the prolongation of rainfall duration,then tends to be stable and finally decreases.The total surface flow percentage increases with rainfall intensity while it decreases with increasing slope gradient with a range of 10.88%-71.47%.The TN loss concentration of the surface flow continually decreases with rainfall duration while that of the interflow shows different fluctuations.However,the TN loss loads of both surface flow and interflow increase with increasing rainfall intensity and slope gradient.The NO_3^--N concentration of interflow is much higher than that of the surface flow.The NH_4^+-N concentration is always less than that of NO_3^--N with no significant difference between surface flow and interflow.The percentages of the TN,NO_3^--N,and NH_4^+-N total loss load and concentration of surface flow and interflow were analyzed.The results show that N loss via both surface flow and interflow occurs mainly in the form of NO_3^--N.Most of the N loss is caused by interflow which is the preferential path of runoff nutrient loss.These findings provide data support and underlying insights for the control of runoff and N loss on the weathered granite slopes.展开更多
Neutral beam injection heating is one of the main auxiliary heating methods in controllable nuclear fusion research. In the EAST neutral beam injector, a water flow calorimetry （WFC） system is applied to measure the...Neutral beam injection heating is one of the main auxiliary heating methods in controllable nuclear fusion research. In the EAST neutral beam injector, a water flow calorimetry （WFC） system is applied to measure the heat load on the electrode system of the ion source and the heat loading components of the beamline. Due to the heat loss in the return water pipe, there are some measuring errors for the current WFC system. In this paper, the errors were measured experimentally and analyzed theoretically, which lay a basis for the exact calculation of beam power deposition distribution and neutralization efficiency.展开更多
文摘In the process of performance prediction of waterjet system,the flow loss of inlet duct is usually reckoned by the rule of thumb. But its value is often overestimated to some extent,resulting in error of prediction accuracy. This paper introduces a new method to determine the flow loss by means of computational fluid dynamic (CFD). Firstly,the fluid field around waterjet system is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations using commercial CFD code Fluent. Then an additional User-Defined Scalar (UDS) equation is embedded into Fluent to get the virtual dividing surface between the internal flow ingested into the inlet duct and the external flow beneath the hull,which is named as streamtube. By virtual of the streamtube the flow loss can be calculated according to the difference of total pressure between the duct outlet and the capture area ahead of the intake. The results from CFD calculation show that the flow loss coeflcient of a typical flush-type inlet duct is varying from 0.05 to 0.12 at different operation conditions,being obviously less than the value of 0.2-0.3 from empirical rules. With the results of this paper the prediction accuracy on propulsive performance of the waterjet system can be improved further.
文摘In order to reduce the losses caused by tip-leakage flow, axisymmetric contouring is applied to the casing of a two-stage unshrouded high pressure turbine（HPT） of aero-engine in this paper. This investigation focuses on the effects of contoured axisymmetric-casing on the blade tipleakage flow. While the size of tip clearance remains the same as the original design, the rotor casing and the blade tip are obtained with the same contoured arc shape. Numerical calculation results show that a promotion of 0.14% to the overall efficiency is achieved. Detailed analysis indicates that it reduces the entropy generation rate caused by the complex vortex structure in the rotor tip region, especially in the tip-leakage vortex. The low velocity region in the leading edge（LE） part of the tip gap is enlarged and the pressure side/tip junction separation bubble extends much further away from the leading edge in the clearance. So the blocking effect of pressure side/tip junction separation bubble on clearance flow prevents more flow on the tip pressure side from leaking to the suction side, which results in weaker leakage vortex and less associated losses.
基金Supported by the National Science and Technology Major Project(No.J2019-Ⅲ-0017).
文摘The exhaust volute is a device that can change the exhaust direction of the ship’s gas turbine to reduce the flow loss of the high-temperature and high-speed turbine exhaust gas in the box-type exhaust volute,thereby improving its power output performance.This paper first investigates the internal flow field characteristics of the exhaust volute via numerical simulation and reveals the main source of the internal resistance loss of the volute.On the premise of not affecting the installation size of the volute and matching it with other components in the cabin,the design scheme of volute bottom shunt and volute chamfer are then optimized in accordance with the flow characteristics inside the volute.Numerical simulation results show that the partial flow structure at the bottom of the volute can effectively improve the low-velocity region and the vortex flow at the bottom of the volute,and the chamfered angle scheme can control the regular expansion and compression of the airflow.When the volute adopts the appropriate chamfer angle and the bottom split-flow structure,the total pressure loss can be reduced by 19.6%,and the static pressure recovery coefficient can be increased by 42.05%.
文摘On the basis of the analysis about present water resource situation in China,the disadvantage of the for- mula of flow loss and water using coefficient on anti-seep channel which have been applying in channel de- sign and water saving irrigation administration will be indicated in the paper. The characteristics of that the loss of conveying water is changeable with the now changing have been take into account in the new formula. The formula is validated by the example of middle permeable channel (A=1.90,m=0.40). The calculate re- sult is more precision. Also some formula has been given,they can be referred to the worker of the irrigation administration.
文摘Based on flow loss, a new automatic pipe-routing algorithm is proposed for electromechanical product in 3D space, which consists of pre-processing and optimization search. Utilizing chaos theory, a chaos grid preprocessing model （CGPM） is established to efficiently pick up the solution space and reduce the search range in the pre-processing, which simplifies the optimization search. A modified particle swarm optimization （PSO） algorithm is presented to seek for an approximate optimal trajectory in the solution space in the optimization search based on standard PSO algorithm and migration characters of people. The comparison of experiments and analysis results shows that the modified PSO algorithm is capable of preventing prematurity effectively and searching for the optimal trajectory more efficiently. Theoretical analysis proves that the modified PSO algorithm converges at global optimum. The examples show that the automatic pipe-routing algorithm based on flow loss is effective and practical for eleetromechanieal product.
基金supported by the National Key Research and Development Program(Grant No.2022YFF0708903)the Ningbo Key Technology Re-search and Development Program(Grant No.2023Z018)+3 种基金the National Natural Science Foundation of China(Grant No.52275043)the Youth Fund of National Natural Science Foundation of China(Grant Nos.72301015,52105046)the Young Elite Scientist Sponsorship Program by China Association for Science and Technology(Grant Nos.2022QNRC001,YESS20220292)the Liupanshan Laboratory Basic Research Program(Grant No.LPS-2024-KY-D-JC-0009)。
文摘Boundary layer ingesting(BLI)fans are required to operate under distorted inflow conditions,which significantly reduces their efficiency[1,2].Accurately predicting fan losses is crucial for designing high-performance,distortion-tolerant fans.
文摘This paper summarizes the results of the authors' 4 year experimental studies on the secondary flow losses in turbine cascades. Cascade wind tunnel experiments were carried out concerning the influence of aspect ratios, incidence, turning angles and outer endwall divergent angles in order to unveil the evolution mechanism of secondary flow losses in turbine cascades without end clearance. Some methods for controlling the secondary flows are investigated including the blade leaning, blade cambering, endwall convergence and leading edge extension at two ends of the blade.
基金supported by the National Key Research and Development Program of China (No. 2018YFB1501004)。
文摘With the advantages of high efficiency and compact structure,supercritical carbon dioxide(sC02)Brayton cycles have bright prospects for development in energy conversion field.As one of the core components of the power cycle,the centrifugal compressor tends to operate near the critical point(304.13 K,7.3773 MPa).Normally,the compressor efficiency increases as the inlet temperature decreases.When the inlet temperature is close to the critical point,the density increases sharply as the temperature decreases,which results in quickly decreasing of volume flow rate and efficiency reducing.The flow loss mechanism of the sCO_(2) compressor operating at low flow rate is studied in this paper.Computational fluid dynamics(CFD) simulations for sCO_(2)compressor were carried out at various inlet temperatures and various mass flow rates.When the sCO_(2)compressor operates at low volume flow rate,the flow loss is generated mainly on the suction side near the trailing edge of the blade.The flow loss is related to the counterclockwise vortexes generated on the suction side of the main blade.The vortexes are caused by the flow separation in the downstream region of the impeller passage,which is different from air compressors operating at low flow rates.The reason for this flow separation is that the effect of Coriolis force is especially severe for the sCO_(2) fluid,compared to the viscous force and inertial force.At lower flow rates,with the stronger effect of Coriolis force,the direction of relative flow velocity deviates from the direction of radius,resulting in its lower radial component.The lower radial relative flow velocity leads to severe flow separation on the suction side near the trailing edge of the main blade.
文摘The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the cascade performance under real engine operating conditions.The Reynolds number has been varied in the range 100000<Re<300000,where lower and upper limits are typical of cruise and take-off/landing conditions,respectively.The effects induced by the incoming wakes at the reduced frequency f+=0.62 on both profile and secondary flow losses have been investigated.Total pressure,velocity and secondary kinetic energy distributions at the downstream tangential plane have been measured by means of a miniaturized 5-hole probe.These quantities provide information on both blade wake and secondary flow structures(passage and horse-shoe vortices).The analysis of the results allows the evaluation of the aerodynamic performance of the HL front-loaded blade in terms of both profile and secondary losses.
文摘The flow loss of a helical channel Magnetohydrodynamic （MHD） thruster without MHD effect was numerically studied with 3-D simulations, and a flow loss coefficient （ was defined to quantify the flow loss and its influencing factors were studied. The results show that （ decreases in a first-order exponential manner with the pitch of a helical wall and the Reynolds number, and it declines slowly when t / T 〉 0.2 and Re 〉 10^5, a flow guide makes the flow more smooth and uniform, especially in the flow guide and helical wall sub-regions and thus reduces the flow loss greatly, by about 30% with the averaged value of （ from 0.0385 to 0.027, a rectifier weakens the helical flow and strengthens the axial one in the rectifier and outlet sub-regions, thus reduces the rotational kinetic pressure with the averaged value of ξ declining about 4% from 0.0385 to 0.037, and ξ decreases with a rectifier＇s axial length when Re 〉 10^5 .
基金supported by theDouble First-Class Key ProgramofGansu ProvincialDepartment of Education(grant number GCJ2022-38)Science and Technology Program of Gansu Province(grant number 22ZD6GA038)Key Research and Development Program of Gansu Province—Industrial Project(grant number 25YFGA021).
文摘In Brayton cycle energy storage systems powered by supercritical carbon dioxide(sCO_(2)),compressors are among themost critical components.Understanding their internal flowloss characteristics is,therefore,essential for enhancing the performance of such systems.This study examines the main sCO_(2) compressor from Sandia Laboratory,utilizing entropy production theory to elucidate the sources and distribution of energy losses both across the entire machine and within its key flow components.The findings reveal that turbulent viscous dissipation is the predominant contributor to total entropy production.Interestingly,while the relative importance of the entropy produced by various sources as the mass flow rate rises remains essentially unchanged,the total entropy production exhibits a nonmonotonic trend,first decreasing and then increasing with the mass flow rate.High entropy production in the impeller is primarily concentrated in the clearance region and along the rear cover of the impeller tip.In the diffuser,it is most pronounced on the front and rear plates and within the central flow path.Meanwhile,in the volute,the highest entropy production occurs around the diffuser outlet and along the outer region of the volute’s centerline.
基金supported by the National Natural Science Foundation of China(No.51175014)
文摘The flow field in junction is complicated due to the ripple property of oil flow velocity and different frequencies of two pumps in aircraft. In this study, the flow fields of T-junction and Y-junction were analyzed using shear stress transport （SST） model in ANSYS/CFX software. The simulation results identified the variation rule of velocity peak in T-junction with different frequencies and phase-differences, meanwhile, the eddy and velocity shock existed in the corner of the T-junction, and the limit working state was obtained. Although the eddy disappeared in Y-junction, the velocity shock and pressure loss were still too big. To address these faults, an arc-junction was designed. Based on the flow fields of arc-junction, the eddy in the junction corner disappeared and the maximum of velocity peak declined compared to T-and Y-junction. Additionally, 8 series of arc-junction with different radiuses were tested to get the variation rule of velocity peak. Through the computation of the pressure loss of three junctions, the arc-junction had a lowest loss value, and its pressure loss reached the minimum value when the curvature radius is 35.42 mm, meanwhile, the velocity shock has decreased in a low phase.
基金supported by a project funded by the China Postdoctoral Science Foundation(Grant No.2017M621268)the National Natural Science Foundation of China(Grant Nos.51436002,51506020,and 51706051)
文摘For a transonic axial-flow compressor, the numerical simulations, verified against experimental data, were used to study the inherent correlation between the evolutionary process of the vortex structures and the flow loss in a compressor stator passage during the throttling process. The flow loss was divided accurately and quantitatively, based on the evolutionary process of the vortex structures. According to the position of the singular points of the vortex structures, the influence of the evolution of the vortex structures on the generation and development of the flow loss was analyzed on a microscale scale. Thereafter, this paper provided the vortex dynamic mechanism of the flow loss, which was important to enrich the theoretical system of the flow field in the compressor. The results show that: the flow loss at the top of the stator tip is caused by the low-energy fluid clusters, which are transported and accumulated by the vortices from the endwall; the transport effect of the pressure separation vortex at the upper half-height only migrates the position of the flow losses, but there is new flow loss generated by its shear action to the endwall. The dominant flow loss during the throttling process concentrates upon the closed separation bubble around the middle of the suction side of the stator.
文摘In the flow on a mobile bed in an open channel, sand ripple often appears after the sediment begins to move. Different scholars have different views on the formation of sand ripples. This paper holds that as the ripple in general is very small, its formation is due to the instability of the laminar flow or the evolution of the small-scale coherent structures in the sublayer adjacent to the wall of the open channel. When the shear stresses caused by the disturbing waves or the coherent structure near the bed surface boundary and the water flow itself are greater than the shields stresses, responses on the bed surface appear and the sand ripple forms. If the frequency of the shear stress caused by the disturbance is close to the natural frequency of the sand grains that produced resonance, such a phenomenon is called the 'detection property' of the sediment. It is at this point that the maximum resonance appears and the sand ripple develops rapidly.
文摘A commercial N-S solver has been employed for simulation and investigation ofthe unsteady flow field inside the tip clearance of a turbine rotor. The main objective of thispaper is to introduce a new method of energy loss calculation for the flow field in tip clearanceregion of a turbine rotor blade. This method can be easily used in all kinds of flow fields. Regionsof high viscous effects have been found to be located near the shroud rather than the blade tip. Itis shown that the time-averaged loss of energy in tip leakage flow is dissimilar for differentrotor blades. This result is a helpful hint that can be taken by blade designers to designnon-uniform rotor blades with different geometric and aerodynamic loads to minimize the energy loss.
文摘The pressure loss of cross-flow perforated of physical modeling, simulation and data processing. muffler has been computed with the procedure Three-dimensional computational fluid dynamics （CFD） has been used to investigate the relations of porosities, flow velocity and diameter of the holes with the pressure loss. Accordingly, some preliminary results have been obtained that pressure loss increases with porosity descent as nearly a hyperbolic trend, rising flow velocity of the input makes the pressure loss increasing with parabola trend, diameter of holes affects little about pressure loss of the muffler. Otherwise, the holes on the perforated pipes make the air flow gently and meanly, which decreases the air impact to the wall and pipes in the muffler. A practical perforated muffler is used to illustrate the available of this method for pressure loss computation, and the comparison shows that the computation results with the method of CFD has reference value for muffler design.
基金supported by the National Natural Science Foundation of China (4187706541471221)
文摘Rainfall intensity and slope gradient are two of the most important factors affecting the variations of runoff nitrogen(N).However,the effects of slope gradient and rainfall intensity on N loss via surface flow and interflow on weathered granite slopes are poorly understood.In this study,12 artificial rainfalls(three rainfall intensities and four slope gradients)were simulated to investigate the coupling loss characteristics of surface flow–interflow–total nitrogen(TN),nitrate nitrogen(NO_3^--N)and ammonia nitrogen(NH_4^+-N)on weathered granite slopes.The results show that slope gradient has a greater impact on the surface flow when the rainfall intensity is relatively large.The effect gradually weakens with the decrement of rainfall intensity.The interflow yield increases firstly with the prolongation of rainfall duration,then tends to be stable and finally decreases.The total surface flow percentage increases with rainfall intensity while it decreases with increasing slope gradient with a range of 10.88%-71.47%.The TN loss concentration of the surface flow continually decreases with rainfall duration while that of the interflow shows different fluctuations.However,the TN loss loads of both surface flow and interflow increase with increasing rainfall intensity and slope gradient.The NO_3^--N concentration of interflow is much higher than that of the surface flow.The NH_4^+-N concentration is always less than that of NO_3^--N with no significant difference between surface flow and interflow.The percentages of the TN,NO_3^--N,and NH_4^+-N total loss load and concentration of surface flow and interflow were analyzed.The results show that N loss via both surface flow and interflow occurs mainly in the form of NO_3^--N.Most of the N loss is caused by interflow which is the preferential path of runoff nutrient loss.These findings provide data support and underlying insights for the control of runoff and N loss on the weathered granite slopes.
基金supported by the National Magnetic Confinement Fusion Science Program of China(No.2013GB101001)the International Science&Technology Cooperation Program of China(No.2014DFG61950)
文摘Neutral beam injection heating is one of the main auxiliary heating methods in controllable nuclear fusion research. In the EAST neutral beam injector, a water flow calorimetry （WFC） system is applied to measure the heat load on the electrode system of the ion source and the heat loading components of the beamline. Due to the heat loss in the return water pipe, there are some measuring errors for the current WFC system. In this paper, the errors were measured experimentally and analyzed theoretically, which lay a basis for the exact calculation of beam power deposition distribution and neutralization efficiency.
