This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are rela...This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are related to the flow angle and mainstream parameters;then by adopting the classic flow topology of behind-blade wakes,the effect of operating conditions is included in the plot and a model for flow angle is thus developed.The advantage of the model is that it can achieve off-design flow angle estimations with design flow characteristics and it is compatible with CFD-based throughflow methods.This model is then implemented into a standard CFD-based throughflow solver from the previous research to estimate off-design characteristics of blade rows with proper input-output strategies.Furthermore,the effect of loss upon flow angle is also modeled as corrections to the proposed model.The model is validated on a compressor stage and the results show promising accuracy for off-design flow angle estimations.展开更多
Abstract Heat transfer and vacuum in condenser are influenced by the aerodynamic performance of steam tur- bine exhaust hood. The current research on exhaust hood is mainly focused on analyzing flow loss and optimal d...Abstract Heat transfer and vacuum in condenser are influenced by the aerodynamic performance of steam tur- bine exhaust hood. The current research on exhaust hood is mainly focused on analyzing flow loss and optimal design of its structure without consideration of the wet steam condensing flow and the exhaust hood coupled with the front and rear parts. To better understand the aerodynamic performance influenced by the tilt angle of flow guide inside a diffuser, taking a 600 MW steam turbine as an example, a numerical simulator CFX is adopted to solve compressible three-dimensional （3D） Reynolds time-aver- aged N-S equations and standard k-e turbulence model. And the exhaust hood flow field influenced by different tilt angles of flow guide is investigated with consideration of the wet steam condensing flow and the exhaust hood coupled with the last stage blades and the condenser throat. The result shows that the total pressure loss coefficient and the static pressure recovery coefficient of exhaust hood change regularly and monotonously with the gradual increase of tilt angle of flow guide. When the tilt angle of flow guide is within the range of 30~ to 40~, the static pressure recovery coefficient is in the range of 15.27% to 17.03% and the total pressure loss coefficient drops to approximately 51%, the aerodynamic performance of exhaust hood is significantly improved. And the effectiveenthalpy drop in steam turbine increases by 0.228% to 0.274%. It is feasible to obtain a reasonable title angle of flow guide by the method of coupling the last stage and the condenser throat to exhaust hood in combination of the wet steam model, which provides a practical guidance to flow guide transformation and optimal design in exhaust hood.展开更多
As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively high...As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively higher hydraulic loss, which is rarely reported. In order to investigate the influence of blade thickness on the transient flow characteristics of a centrifugal slurry pump with a semi-open impeller, transient numerical simulations were carried out on six impellers, of which the meridional blade thickness from the leading edge to trailing edge varied from 5-10 mm, 5-15 mm, 5-20 mm, 10-10 mm, 10-15 mm, and 10-20 mm, respectively. Then, two of the six impellers, namely cases 4 and 6, were manufactured and experimentally tested for hydraulic performance to verify the simulation results. Results of these tests agreed reasonably well with those of the numerical simulation. The results demonstrate that when blade thickness increases, pressure fluctuations at the outlet of the impeller become severe. Moreover, the standard deviation of the relative velocity in the middle portion of the suction sides of the blades decreases and that at the outlet of the impeller increases. Thus, the amplitude of the impeller head pulsation for each case increases. Meanwhile, the distribution of the time-averaged relative flow angle becomes less uniform and decreases at the outlet of the impeller. Hence, as the impeUer blade thickness increases, the pump head drops rapidly and the maximum efficiency point is offset to a lower flow rate condition. As the thickness of blade trailing edge increases by 10 mm, the head of the pump drops by approximately 5 m, which is approximately 10 % of the original pump head. Futhermore, it is for the first time that the time-averaged relative flow angle is being considered for the analysis of transient flow in centrifugal pump. The presented work could be a useful guideline in engineering practice when designing a centrifugal slurry pump with thick impeller blades.展开更多
The atomizer with micro cone apertures has advantages of ultra-fine atomized droplets, low power consumption and low temperature rise. The current research of this kind of atomizer mainly focuses on the performance an...The atomizer with micro cone apertures has advantages of ultra-fine atomized droplets, low power consumption and low temperature rise. The current research of this kind of atomizer mainly focuses on the performance and its application while there is less research of the principle of the atomization. Under the analysis of the dispenser and its micro-tapered aperture＇s deformation, the volume changes during the deformation and vibration of the micro-tapered aperture on the dispenser are calculated by coordinate transformation. Based on the characters of the flow resistance in a cone aperture, it is found that the dynamic cone angle results from periodical changes of the volume of the micro-tapered aperture of the atomizer and this change drives one-way flows. Besides, an experimental atomization platform is established to measure the atomization rates with different resonance frequencies of the cone aperture atomizer. The atomization performances of cone aperture and straight aperture atomizers are also measured. The experimental results show the existence of the pumping effect of the dynamic tapered angle. This effect is usually observed in industries that require low dispersion and micro- and nanoscale grain sizes, such as during production of high-pressure nozzles and inhalation therapy. Strategies to minimize the pumping effect of the dynamic cone angle or improve future designs are important concerns. This research proposes that dynamic micro-tapered angle is an important cause of atomization of the atomizer with micro cone apertures.展开更多
This paper focuses on the simulation analysis of stripe formation and dynamic features of intersecting pedestrian flows.The intersecting flows consist of two streams of pedestrians and each pedestrian stream has a des...This paper focuses on the simulation analysis of stripe formation and dynamic features of intersecting pedestrian flows.The intersecting flows consist of two streams of pedestrians and each pedestrian stream has a desired walking direction.The model adopted in the simulations is the social force model, which can reproduce the self-organization phenomena successfully. Three scenarios of different cross angles are established. The simulations confirm the empirical observations that there is a stripe formation when two streams of pedestrians intersect and the direction of the stripes is perpendicular to the sum of the directional vectors of the two streams. It can be concluded from the numerical simulation results that smaller cross angle results in higher mean speed and lower level of speed fluctuation. Moreover, the detailed pictures of pedestrians＇ moving behavior at intersections are given as well.展开更多
The influence of fiber orientation,flow yaw angle and length-to-thickness ratio on flutter characteristics of angle-ply laminated plates in supersonic flow is studied by finite element approach.The structural model is...The influence of fiber orientation,flow yaw angle and length-to-thickness ratio on flutter characteristics of angle-ply laminated plates in supersonic flow is studied by finite element approach.The structural model is established using the Reissner-Mindlin theory in which the transverse shear deformation is considered.The aerodynamic pressure is evaluated by the quasi-steady first-order piston theory.The equations of motion are formulated based on the principle of virtual work.With the harmonic motion assumption,the flutter boundary is determined by solving a series of complex eigenvalue problems.Numerical study shows that （1） The flutter dynamic pressure and the coalescence of flutter modes depend on fiber orientation,flow yaw angle and length-to-thickness ratio;（2） The laminated plate with all fibers aligned with the flow direction gives the highest flutter dynamic pressure,but a slight yawing of the flow from the fiber orientation results in a sharp decrease of the flutter dynamic pressure;（3） The angle-ply laminated plate with fiber orientation angle equal to flow yaw angle gives high flutter dynamic pressure,but not the maximum flutter dynamic pressure;（4） With the decrease of length-to-thickness ratio,an adverse effect due to mode transition on the flutter dynamic pressure is found.展开更多
A three-dimensional Navier-Stokes solver is used to investigate the separation and superposition of the influences from upstream and downstream rotors in an axial-radial combined compressor for unsteady design applica...A three-dimensional Navier-Stokes solver is used to investigate the separation and superposition of the influences from upstream and downstream rotors in an axial-radial combined compressor for unsteady design applications. The data from rotor/stator and stator/rotor configurations show that the unsteady flow response in axial stator passage is caused only by one rotor. The results from the rotor/stator/rotor configuration revealed the superimposed characteristic of influences from upstream and downstream the rotor. The impact of the superimposed characteristic was studied by analyzing the virtual relative flow angle at the stator exit. The results show that the axial velocity in the passage of axial stator can be influenced by wake from upstream axial rotor and potential field of downstream radial rotor. While they are coupled to have an effect on the unsteady flow in axial statot passage, the excitation or suppression phenomena appear and lead to different levels of deterministic fluctuation kinetic energy. Their locations are determined by the frequencies of the involved influences. In addition, the variability of superimposed characteristic （ excitation and suppression） at the stator exit modulates the inlet flow angle for downstream rotor.展开更多
The wing rock motion is frequently suffered by a wing-body configuration with low swept wing at high angle of attack. It is found from our experimental study that the tip perturbation and wing longitudinal locations a...The wing rock motion is frequently suffered by a wing-body configuration with low swept wing at high angle of attack. It is found from our experimental study that the tip perturbation and wing longitudinal locations affect significantly the wing rock motion of a wing-body. The natural tip perturbation would make the wing rock motion of a nondeterministic nature and an artificial mini-tip perturbation would make the wing rock motion deterministic. The artificial tip perturbation would, as its circumferential location is varied, generate three different types of motion patterns： （1） limit cycle oscillation, （2） irregular oscillation, （3） equilibrium state with tiny oscillation. The amplitude of rolling oscillation corresponding to the limit cycle oscillatory motion pattern is decreased with the wing location shifting downstream along the body axis.展开更多
The present paper deals with the flow in an entrance region of a tapered vessel.Pressure distribution formula . axial and radial distribution formulas,shear stressdistribution formula of.flow field and shear stress di...The present paper deals with the flow in an entrance region of a tapered vessel.Pressure distribution formula . axial and radial distribution formulas,shear stressdistribution formula of.flow field and shear stress distribution formula of vessel wallare derived. Relative numerical computations are made and analyzed.Discussion of the effects of tapered angle on the pressure distribution and vessel wall stress distributionare emphasized.展开更多
An effect of the swirling flow on the combustion performance is studied by the computational fluid dynamics(CFD) in a micro-gas turbine with a centrifugal compressor, dump diffuser and forward-flow combustor. The dist...An effect of the swirling flow on the combustion performance is studied by the computational fluid dynamics(CFD) in a micro-gas turbine with a centrifugal compressor, dump diffuser and forward-flow combustor. The distributions of air mass and the Temperature Pattern Factor(as: Overall Temperature Distribution Factor-OTDF) in outlet are investigated with two different swirling angles of compressed air as 0° and 15° in three combustors. The results show that the influences of swirling flow on the air distribution and OTDF cannot be neglected. Compared with no-swirling flow, the air through outer liner is more, and the air through the inner liner is less, and the pressure loss is bigger under the swirling condition in the same combustor. The Temperature Pattern Factor changes under the different swirling conditions.展开更多
Flow and physical properties were measured for three fuel powders： sawdust, brown coal and hard coal. Besides physical properties, e.g., particle size, bulk density and moisture content, flowability was investigated ...Flow and physical properties were measured for three fuel powders： sawdust, brown coal and hard coal. Besides physical properties, e.g., particle size, bulk density and moisture content, flowability was investigated using the standard shear testing technique of the Jenike shear cell. Flow functions of the three powders used for characterization of bulk flow and design of hoppers were determined, and then compared and discussed. The flow functions of the three powders are located in different regions： while brown coal and hard coal were classified respectively as easy flowing and cohesive material, sawdust was found in regions varying from cohesive to easy fowing at low consolidation stress. The measured effective angle of internal friction and angle of wall friction were 55° and 31.4° for sawdust; 36.2° and 26° for brown coal; and 43.3° and 27.8° for hard coal. Using the measured powder flow properties, Jenike＇s procedure was then followed to estimate and compare the critical hopper dimensions for mass flow of the three powders.展开更多
The methods used for flow characterization of a powder mass include the angle of repose （AOR）, Carr index （CI）, and powder flow tester （PFT）. The use of nanosilica as a flow modifier （glidant） is very common i...The methods used for flow characterization of a powder mass include the angle of repose （AOR）, Carr index （CI）, and powder flow tester （PFT）. The use of nanosilica as a flow modifier （glidant） is very common in industry. This study aims to compare the glidant effect of hydrophobic and hydrophilic silica on a poorly flowable active pharmaceutical ingredient （ibuprofen） by different flow characterization techniques. Different percentages （0.5, 1.0, and 2.0 wt%） of both types of mixed silica–ibuprofen powders were evaluated by the AOR, CI, bulk density, and PFT. The flow factor, effective angle of friction, and cohesion were determined to explain the bulk powder properties. The results show that different types of silica show different levels of flow property improvement, but the techniques do not equally discriminate the differences. Hydrophobic silica results in better improvement of the flow property than hydrophilic silica, probably because of its better surface coverage of silica on the host particles. Change of the bulk density with applied pressure was significant for the different powders. This study demonstrates that combining several characterization methods provides a better understanding of bulk powder flow properties with respect to powder–process relationships than a single flow indicator.展开更多
The high-load compressor plays an important role in further improving the performance of aero-engine.However,the complex shock waves in the cascade channel also bring more aerodynamic losses.This paper proposes a supe...The high-load compressor plays an important role in further improving the performance of aero-engine.However,the complex shock waves in the cascade channel also bring more aerodynamic losses.This paper proposes a supersonic compressor cascade modeling method based on the theory of unique inlet flow angle,and the aerodynamic design and optimization of a cascade with inlet Mach number 1.85 are studied by combining the numerical optimization method and planar cascade experiment.The results show that pressure increase can be achieved by multiple shock waves which are obtained by the reflection of the leading edge detached shock wave in the initial supersonic cascade channel at the design point,which verifies the feasibility of the design method.After optimization,the aerodynamic performance of the cascade has been improved to different degrees at the design point and off-design point.When the static pressure ratio is 3.285,the total pressure recovery coefficient reaches 86.82%at the design point,which is on the advanced level of the same type of cascade.The experimental results of planar cascade schlieren and surface pressure measurement also verify the correctness of the simulation method,which provides useful references for the subsequent compressor design.展开更多
The superimposed influences of the blade rows in a multistage compressor are important because different matches of upstream and downstream blades can result in significant differences in the stator wake oscillation. ...The superimposed influences of the blade rows in a multistage compressor are important because different matches of upstream and downstream blades can result in significant differences in the stator wake oscillation. Numerical investigation of the axial stator wake oscillation, which is affected upstream by the axial rotor and downstream by the radial rotor, was performed in an axial-radial combined compressor. Many configurations with different blade numbers and locations, which influence axial stator wake oscillation were investigated. When rotors have equal blade numbers, the axial stator wake oscillates periodically versus time within time T(moving blade passing 1/3 revolution). In contrast, stator wake oscillates irregularly within T when rotors have different blade numbers. A model-split subtraction method is presented in order to separate the influences of the individual blade rows on the wake oscillation of the axial stator. Analysis from the rotor-stator configuration showed that the unsteady flow angle fluctuation response is caused by the upstream rotor. For the rotor-stator-rotor configuration, the unsteady flow angle fluctuations are influenced by upand downstream blade rows. With the model-split subtraction method, the upand downstream influences on the flow angle fluctuation could be clearly separated and quantified. Low amplitudes could be observed when the influences from upand downstream moving rows were superimposed with the "positive peaknegative peak" type wave. Clocking investigations were carried out to change the relative superimposed phase of influences from the surrounding blade rows in order to modulate the amplitudes of the axial stator wake oscillation. However, the amplitudes did not reach the maximum when they were superimposed with "positive peak-positive peak" type wave due to the impact of the interaction between the two moving blade rows.展开更多
A turbocharger compressor working in commercial vehicles, especially in some passenger cars, often works together with some pipes with complicated geometry as an air intake system, due to limit of available space in i...A turbocharger compressor working in commercial vehicles, especially in some passenger cars, often works together with some pipes with complicated geometry as an air intake system, due to limit of available space in internal combustion engine compartments. These pipes may generate various distortions of physical parameters of the air at the inlet of the compressor and therefore the compressor aerodynamic performance deteriorates. Sometimes, the turbocharging engine fails to work at some operation points. This paper investigates the effects of various swirl distortions induced by different bending-torsional intake ducts on the aerodynamic performance of a turbocharger compressor by both 3D numerical simulations and experimental measurements. It was found that at the outlet of the pipes the different inlet ducts can generate different swirl distortions, twin vortices and bulk-like vortices with different rotating directions. Among them, the bulk-like vortices not only affect seriously the pressure distribution in the impeller domain, but also significantly deteriorate the compressor performance, especially at high flow rate region. And the rotating direction of the bulk-like vortices is also closely associated with the efficiency penalty. Besides the efficiency, the transient flow rate through a single impeller channel, or the asymmetric mass flow crossing the whole impeller, can be influenced by two disturbances. One is from the upstream bending-torsional ducts; other one is from the downstream volute.展开更多
In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single partic...In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy （SEM）, confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Cart index, This was confirmed by bulk measurements of the particle-particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.展开更多
The paper presents results of simulation of turbulent heat transfer and hydrodynamics over a free rotating disk using an integral method based on power-law velocity and temperature profiles and three different laws fo...The paper presents results of simulation of turbulent heat transfer and hydrodynamics over a free rotating disk using an integral method based on power-law velocity and temperature profiles and three different laws for the tangent of the flow swirl angle tan. It appeared that a quadratic correlation of tan is the most proper one for a free rotating disk. Resulting equation for the Nusselt number is in a better agreement with experimental data of different authors than known Dorfman formula.展开更多
基金funded through the National Science and Technology Major Project(2017-Ⅲ-0009-0035)National Natural Science Foundation of China(Grant No.52276031)。
文摘This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are related to the flow angle and mainstream parameters;then by adopting the classic flow topology of behind-blade wakes,the effect of operating conditions is included in the plot and a model for flow angle is thus developed.The advantage of the model is that it can achieve off-design flow angle estimations with design flow characteristics and it is compatible with CFD-based throughflow methods.This model is then implemented into a standard CFD-based throughflow solver from the previous research to estimate off-design characteristics of blade rows with proper input-output strategies.Furthermore,the effect of loss upon flow angle is also modeled as corrections to the proposed model.The model is validated on a compressor stage and the results show promising accuracy for off-design flow angle estimations.
基金Supported by National Natural Science Foundation of China(Grant Nos.51576036,51476192)Science and Technology Development Planning Foundation of Jilin Province of China(Grant No.20140204040SF)
文摘Abstract Heat transfer and vacuum in condenser are influenced by the aerodynamic performance of steam tur- bine exhaust hood. The current research on exhaust hood is mainly focused on analyzing flow loss and optimal design of its structure without consideration of the wet steam condensing flow and the exhaust hood coupled with the front and rear parts. To better understand the aerodynamic performance influenced by the tilt angle of flow guide inside a diffuser, taking a 600 MW steam turbine as an example, a numerical simulator CFX is adopted to solve compressible three-dimensional （3D） Reynolds time-aver- aged N-S equations and standard k-e turbulence model. And the exhaust hood flow field influenced by different tilt angles of flow guide is investigated with consideration of the wet steam condensing flow and the exhaust hood coupled with the last stage blades and the condenser throat. The result shows that the total pressure loss coefficient and the static pressure recovery coefficient of exhaust hood change regularly and monotonously with the gradual increase of tilt angle of flow guide. When the tilt angle of flow guide is within the range of 30~ to 40~, the static pressure recovery coefficient is in the range of 15.27% to 17.03% and the total pressure loss coefficient drops to approximately 51%, the aerodynamic performance of exhaust hood is significantly improved. And the effectiveenthalpy drop in steam turbine increases by 0.228% to 0.274%. It is feasible to obtain a reasonable title angle of flow guide by the method of coupling the last stage and the condenser throat to exhaust hood in combination of the wet steam model, which provides a practical guidance to flow guide transformation and optimal design in exhaust hood.
基金Supported by National Natural Science Foundation of China(Grant No.51239005)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively higher hydraulic loss, which is rarely reported. In order to investigate the influence of blade thickness on the transient flow characteristics of a centrifugal slurry pump with a semi-open impeller, transient numerical simulations were carried out on six impellers, of which the meridional blade thickness from the leading edge to trailing edge varied from 5-10 mm, 5-15 mm, 5-20 mm, 10-10 mm, 10-15 mm, and 10-20 mm, respectively. Then, two of the six impellers, namely cases 4 and 6, were manufactured and experimentally tested for hydraulic performance to verify the simulation results. Results of these tests agreed reasonably well with those of the numerical simulation. The results demonstrate that when blade thickness increases, pressure fluctuations at the outlet of the impeller become severe. Moreover, the standard deviation of the relative velocity in the middle portion of the suction sides of the blades decreases and that at the outlet of the impeller increases. Thus, the amplitude of the impeller head pulsation for each case increases. Meanwhile, the distribution of the time-averaged relative flow angle becomes less uniform and decreases at the outlet of the impeller. Hence, as the impeUer blade thickness increases, the pump head drops rapidly and the maximum efficiency point is offset to a lower flow rate condition. As the thickness of blade trailing edge increases by 10 mm, the head of the pump drops by approximately 5 m, which is approximately 10 % of the original pump head. Futhermore, it is for the first time that the time-averaged relative flow angle is being considered for the analysis of transient flow in centrifugal pump. The presented work could be a useful guideline in engineering practice when designing a centrifugal slurry pump with thick impeller blades.
基金Supported by National Natural Science Foundation of China(Grant Nos.51375227,91223201)
文摘The atomizer with micro cone apertures has advantages of ultra-fine atomized droplets, low power consumption and low temperature rise. The current research of this kind of atomizer mainly focuses on the performance and its application while there is less research of the principle of the atomization. Under the analysis of the dispenser and its micro-tapered aperture＇s deformation, the volume changes during the deformation and vibration of the micro-tapered aperture on the dispenser are calculated by coordinate transformation. Based on the characters of the flow resistance in a cone aperture, it is found that the dynamic cone angle results from periodical changes of the volume of the micro-tapered aperture of the atomizer and this change drives one-way flows. Besides, an experimental atomization platform is established to measure the atomization rates with different resonance frequencies of the cone aperture atomizer. The atomization performances of cone aperture and straight aperture atomizers are also measured. The experimental results show the existence of the pumping effect of the dynamic tapered angle. This effect is usually observed in industries that require low dispersion and micro- and nanoscale grain sizes, such as during production of high-pressure nozzles and inhalation therapy. Strategies to minimize the pumping effect of the dynamic cone angle or improve future designs are important concerns. This research proposes that dynamic micro-tapered angle is an important cause of atomization of the atomizer with micro cone apertures.
基金Project supported by the National Natural Science Foundation of China(Grant No.61233001)the Fundamental Research Funds for the Central Universities,China(Grant No.2017JBM014)
文摘This paper focuses on the simulation analysis of stripe formation and dynamic features of intersecting pedestrian flows.The intersecting flows consist of two streams of pedestrians and each pedestrian stream has a desired walking direction.The model adopted in the simulations is the social force model, which can reproduce the self-organization phenomena successfully. Three scenarios of different cross angles are established. The simulations confirm the empirical observations that there is a stripe formation when two streams of pedestrians intersect and the direction of the stripes is perpendicular to the sum of the directional vectors of the two streams. It can be concluded from the numerical simulation results that smaller cross angle results in higher mean speed and lower level of speed fluctuation. Moreover, the detailed pictures of pedestrians＇ moving behavior at intersections are given as well.
基金supported by China Postdoctoral Science Founda-tion (20090451045)
文摘The influence of fiber orientation,flow yaw angle and length-to-thickness ratio on flutter characteristics of angle-ply laminated plates in supersonic flow is studied by finite element approach.The structural model is established using the Reissner-Mindlin theory in which the transverse shear deformation is considered.The aerodynamic pressure is evaluated by the quasi-steady first-order piston theory.The equations of motion are formulated based on the principle of virtual work.With the harmonic motion assumption,the flutter boundary is determined by solving a series of complex eigenvalue problems.Numerical study shows that （1） The flutter dynamic pressure and the coalescence of flutter modes depend on fiber orientation,flow yaw angle and length-to-thickness ratio;（2） The laminated plate with all fibers aligned with the flow direction gives the highest flutter dynamic pressure,but a slight yawing of the flow from the fiber orientation results in a sharp decrease of the flutter dynamic pressure;（3） The angle-ply laminated plate with fiber orientation angle equal to flow yaw angle gives high flutter dynamic pressure,but not the maximum flutter dynamic pressure;（4） With the decrease of length-to-thickness ratio,an adverse effect due to mode transition on the flutter dynamic pressure is found.
基金Supported by Ministerial Level Advanced Research Foundation(404050301.4)the National Natural Science Foundation of China(51176013)the Chinese Specialized Research Fund for the Doctoral Program of Higher Education(20111101130002)
文摘A three-dimensional Navier-Stokes solver is used to investigate the separation and superposition of the influences from upstream and downstream rotors in an axial-radial combined compressor for unsteady design applications. The data from rotor/stator and stator/rotor configurations show that the unsteady flow response in axial stator passage is caused only by one rotor. The results from the rotor/stator/rotor configuration revealed the superimposed characteristic of influences from upstream and downstream the rotor. The impact of the superimposed characteristic was studied by analyzing the virtual relative flow angle at the stator exit. The results show that the axial velocity in the passage of axial stator can be influenced by wake from upstream axial rotor and potential field of downstream radial rotor. While they are coupled to have an effect on the unsteady flow in axial statot passage, the excitation or suppression phenomena appear and lead to different levels of deterministic fluctuation kinetic energy. Their locations are determined by the frequencies of the involved influences. In addition, the variability of superimposed characteristic （ excitation and suppression） at the stator exit modulates the inlet flow angle for downstream rotor.
基金supported by the National Natural Science Foundation of China (10432020, 10872019 and 10702004)
文摘The wing rock motion is frequently suffered by a wing-body configuration with low swept wing at high angle of attack. It is found from our experimental study that the tip perturbation and wing longitudinal locations affect significantly the wing rock motion of a wing-body. The natural tip perturbation would make the wing rock motion of a nondeterministic nature and an artificial mini-tip perturbation would make the wing rock motion deterministic. The artificial tip perturbation would, as its circumferential location is varied, generate three different types of motion patterns： （1） limit cycle oscillation, （2） irregular oscillation, （3） equilibrium state with tiny oscillation. The amplitude of rolling oscillation corresponding to the limit cycle oscillatory motion pattern is decreased with the wing location shifting downstream along the body axis.
文摘The present paper deals with the flow in an entrance region of a tapered vessel.Pressure distribution formula . axial and radial distribution formulas,shear stressdistribution formula of.flow field and shear stress distribution formula of vessel wallare derived. Relative numerical computations are made and analyzed.Discussion of the effects of tapered angle on the pressure distribution and vessel wall stress distributionare emphasized.
基金supported by National Natural Science Foundation of China with project No.51406202
文摘An effect of the swirling flow on the combustion performance is studied by the computational fluid dynamics(CFD) in a micro-gas turbine with a centrifugal compressor, dump diffuser and forward-flow combustor. The distributions of air mass and the Temperature Pattern Factor(as: Overall Temperature Distribution Factor-OTDF) in outlet are investigated with two different swirling angles of compressed air as 0° and 15° in three combustors. The results show that the influences of swirling flow on the air distribution and OTDF cannot be neglected. Compared with no-swirling flow, the air through outer liner is more, and the air through the inner liner is less, and the pressure loss is bigger under the swirling condition in the same combustor. The Temperature Pattern Factor changes under the different swirling conditions.
文摘Flow and physical properties were measured for three fuel powders： sawdust, brown coal and hard coal. Besides physical properties, e.g., particle size, bulk density and moisture content, flowability was investigated using the standard shear testing technique of the Jenike shear cell. Flow functions of the three powders used for characterization of bulk flow and design of hoppers were determined, and then compared and discussed. The flow functions of the three powders are located in different regions： while brown coal and hard coal were classified respectively as easy flowing and cohesive material, sawdust was found in regions varying from cohesive to easy fowing at low consolidation stress. The measured effective angle of internal friction and angle of wall friction were 55° and 31.4° for sawdust; 36.2° and 26° for brown coal; and 43.3° and 27.8° for hard coal. Using the measured powder flow properties, Jenike＇s procedure was then followed to estimate and compare the critical hopper dimensions for mass flow of the three powders.
文摘The methods used for flow characterization of a powder mass include the angle of repose （AOR）, Carr index （CI）, and powder flow tester （PFT）. The use of nanosilica as a flow modifier （glidant） is very common in industry. This study aims to compare the glidant effect of hydrophobic and hydrophilic silica on a poorly flowable active pharmaceutical ingredient （ibuprofen） by different flow characterization techniques. Different percentages （0.5, 1.0, and 2.0 wt%） of both types of mixed silica–ibuprofen powders were evaluated by the AOR, CI, bulk density, and PFT. The flow factor, effective angle of friction, and cohesion were determined to explain the bulk powder properties. The results show that different types of silica show different levels of flow property improvement, but the techniques do not equally discriminate the differences. Hydrophobic silica results in better improvement of the flow property than hydrophilic silica, probably because of its better surface coverage of silica on the host particles. Change of the bulk density with applied pressure was significant for the different powders. This study demonstrates that combining several characterization methods provides a better understanding of bulk powder flow properties with respect to powder–process relationships than a single flow indicator.
基金funded by the National Science and Technology Major Project(J2019-II-0016-0037).
文摘The high-load compressor plays an important role in further improving the performance of aero-engine.However,the complex shock waves in the cascade channel also bring more aerodynamic losses.This paper proposes a supersonic compressor cascade modeling method based on the theory of unique inlet flow angle,and the aerodynamic design and optimization of a cascade with inlet Mach number 1.85 are studied by combining the numerical optimization method and planar cascade experiment.The results show that pressure increase can be achieved by multiple shock waves which are obtained by the reflection of the leading edge detached shock wave in the initial supersonic cascade channel at the design point,which verifies the feasibility of the design method.After optimization,the aerodynamic performance of the cascade has been improved to different degrees at the design point and off-design point.When the static pressure ratio is 3.285,the total pressure recovery coefficient reaches 86.82%at the design point,which is on the advanced level of the same type of cascade.The experimental results of planar cascade schlieren and surface pressure measurement also verify the correctness of the simulation method,which provides useful references for the subsequent compressor design.
基金Financially supported by National Natural Science Foundation of China(No.51176013)Chinese Specialized Research Fund for the Doctoral Program of Higher Education(No.20091101110014)
文摘The superimposed influences of the blade rows in a multistage compressor are important because different matches of upstream and downstream blades can result in significant differences in the stator wake oscillation. Numerical investigation of the axial stator wake oscillation, which is affected upstream by the axial rotor and downstream by the radial rotor, was performed in an axial-radial combined compressor. Many configurations with different blade numbers and locations, which influence axial stator wake oscillation were investigated. When rotors have equal blade numbers, the axial stator wake oscillates periodically versus time within time T(moving blade passing 1/3 revolution). In contrast, stator wake oscillates irregularly within T when rotors have different blade numbers. A model-split subtraction method is presented in order to separate the influences of the individual blade rows on the wake oscillation of the axial stator. Analysis from the rotor-stator configuration showed that the unsteady flow angle fluctuation response is caused by the upstream rotor. For the rotor-stator-rotor configuration, the unsteady flow angle fluctuations are influenced by upand downstream blade rows. With the model-split subtraction method, the upand downstream influences on the flow angle fluctuation could be clearly separated and quantified. Low amplitudes could be observed when the influences from upand downstream moving rows were superimposed with the "positive peaknegative peak" type wave. Clocking investigations were carried out to change the relative superimposed phase of influences from the surrounding blade rows in order to modulate the amplitudes of the axial stator wake oscillation. However, the amplitudes did not reach the maximum when they were superimposed with "positive peak-positive peak" type wave due to the impact of the interaction between the two moving blade rows.
基金sponsored by the Key Projects of Hebei Provincial Department of Education(No.ZD2016095)the Program of Science and Technology Research and Development of Handan(1621212047-2)
文摘A turbocharger compressor working in commercial vehicles, especially in some passenger cars, often works together with some pipes with complicated geometry as an air intake system, due to limit of available space in internal combustion engine compartments. These pipes may generate various distortions of physical parameters of the air at the inlet of the compressor and therefore the compressor aerodynamic performance deteriorates. Sometimes, the turbocharging engine fails to work at some operation points. This paper investigates the effects of various swirl distortions induced by different bending-torsional intake ducts on the aerodynamic performance of a turbocharger compressor by both 3D numerical simulations and experimental measurements. It was found that at the outlet of the pipes the different inlet ducts can generate different swirl distortions, twin vortices and bulk-like vortices with different rotating directions. Among them, the bulk-like vortices not only affect seriously the pressure distribution in the impeller domain, but also significantly deteriorate the compressor performance, especially at high flow rate region. And the rotating direction of the bulk-like vortices is also closely associated with the efficiency penalty. Besides the efficiency, the transient flow rate through a single impeller channel, or the asymmetric mass flow crossing the whole impeller, can be influenced by two disturbances. One is from the upstream bending-torsional ducts; other one is from the downstream volute.
基金the EU for financial support through the Framework 6 Marie Curie Action "NEWGROWTH", contract number MEST-CT-2005-020724Johnson Matthey Plc and Birmingham Science City for funding and supporting this research
文摘In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy （SEM）, confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Cart index, This was confirmed by bulk measurements of the particle-particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.
文摘The paper presents results of simulation of turbulent heat transfer and hydrodynamics over a free rotating disk using an integral method based on power-law velocity and temperature profiles and three different laws for the tangent of the flow swirl angle tan. It appeared that a quadratic correlation of tan is the most proper one for a free rotating disk. Resulting equation for the Nusselt number is in a better agreement with experimental data of different authors than known Dorfman formula.
