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
In the present paper the attention is focused on correlation between fan noise and velocity fluctuations of tip leakage vortex around rotor blade of a low pressure axial flow fan at the maximum pressure operating poin...In the present paper the attention is focused on correlation between fan noise and velocity fluctuations of tip leakage vortex around rotor blade of a low pressure axial flow fan at the maximum pressure operating point. We measured time fluctuating velocity near the rotor tip around the rotor blades by using a hot-wire sensor from a relative flame of refer- ence fixed to the rotor blades. As the results, it is clear that the velocity fluctuation due to tip leakage vortex has weak periodicity and the hump portion appeared in its spectrum. If the flow rate was lower than the design condition, the tip leakage flow became to attach to the following blade and the sound pressure level at frequency of velocity fluctuation of this flow was increased. The correlation measurements between the velocity fluctuation of tip leakage flow and the aerodynamic noise were made using a rotating hot-wire sensor near the rotor tip in the rotating frame. The correlation between the velocity fluctuation due to tip leakage flow and acoustic pressure were increased due to generation of weak acoustic resonance at the maximum pressure operating point.展开更多
The cascade model was tested using transient liquid crystal temperature measurement technology.The effects of main flow Reynolds number,blowing ratio and tip clearance height on the convective heat transfer coefficien...The cascade model was tested using transient liquid crystal temperature measurement technology.The effects of main flow Reynolds number,blowing ratio and tip clearance height on the convective heat transfer coefficient of the turbine outer ring were studied.Two feature lines were marked on the turbine outer ring corresponding to the position of the blade.The conclusions are as follows:The tip clearance leakage flow has a great influence on the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the blowing ratio are kept constant,gradually increasing the main flow Reynolds number will result in an increase in the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the main flow Reynolds number are kept constant and the blowing ratio is gradually increased,the convective heat transfer coefficient of the turbine outer ring is almost constant.The heat transfer coefficient of the turbine outer ring surface is little affected by the blowing ratio;The clearance height has great influence on the heat transfer characteristics of the turbine outer ring.Under the typical working condition in this paper,when the tip clearance height ratio is 1.6%,the convective heat transfer coefficient of the outer surface of the turbine is the highest.展开更多
In the steady operation condition, the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rot...In the steady operation condition, the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rotors, including the radial rotor, the forward-skewed rotor and the back- ward-skewed rotor. The three-dimensional viscous flow fields of the fans are computed. In the experiments, the two-dimensional plane particle image velocimetry (PIV) system is used to measure the flow fields in the tip region of three different pitchwise positions of each fan. The results show that the computational results agree well with the experimental data in the flow field of the tip region of each fan. The tip leakage vortex core segments based on method of the eigenmode analysis can display clearly some characteristics of the tip leakage vortex, such as the origination position of tip leak- age vortex, the development of vortex strength, and so on. Compared with the radial rotor, the other two skewed rotors can increase the stability of the tip leakage vortex and the increment in the forward-skewed rotor is more than that in the backward-skewed one. Among the tip leakage vortices of the three rotors, the velocity of the vortex in the forward-skewed rotor is th6 highest in the circumferential direction and the lowest in the axial direction.展开更多
In previous studies,a theoretical model was developed after Acoustic Resonance(AR)was experimentally detected in a four-stage compressor,and AR inception was proposed to be triggered by an unknown sound source,which i...In previous studies,a theoretical model was developed after Acoustic Resonance(AR)was experimentally detected in a four-stage compressor,and AR inception was proposed to be triggered by an unknown sound source,which is a pressure perturbation of a specific frequency with a suitable circumferential propagation speed.The present paper,which is not dedicated to the simulation of acoustic field,aims to identify the specific sound source generated by the unsteady tip leakage flow using the unsteady Computational Fluid Mechanics(CFD)approach.After a comprehensive analysis of an Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation,a pressure perturbation of non-integer multiple of rotor frequency is found at the blade tip.Since the essence of the tip leakage flow is a jet flow driven by the pressure difference between two sides of blade,a simplified tip leakage flow model is adopted using Large Eddy Simulation(LES)in order to simulate the jet flow through a tip clearance.It is found that the convection velocity of shedding vortices fits the expected propagation speed of the sound source,the frequency is also close to one of the dominating frequencies in the URANS simulation,and the resultant combination frequency coincides with the experimentally measured AR frequency.Since such a simplified model successfully captures the key physical mechanisms,it is concluded that this paper provides a piece of unambiguous evidence on the role of unsteady tip leakage vortex in triggering the AR inception of the multistage compressor.展开更多
Tip leakage flow(TLF)in compressors,which can cause flow blockage in blade passage and induce efficiency loss,is also a potential threat to the unsteady flow stability of modern aeroengines.This paper provides an over...Tip leakage flow(TLF)in compressors,which can cause flow blockage in blade passage and induce efficiency loss,is also a potential threat to the unsteady flow stability of modern aeroengines.This paper provides an overview of the significance of tip leakage flow research,and introduces relevant previous studies.After calculating by different methods,large eddy simulation(LES)is demonstrated again as a suitable compromise between accuracy and computational cost for the unsteady flow study.Two types of simplified tip leakage flow models using LES are adopted with a focus on the unsteady characteristics of shedding vortices in a cavity plane.This paper applies these models to study the unsteady tip leakage flow which triggers the onset of acoustic resonance in a multistage axial compressor.Compared with the detected acoustic resonance frequency of 5.22 rotational frequency(RF)in the previous experiment,the computed combination frequency in the 2-D model is equal to 5.232RF,and the simplified 3-D unsteady tip leakage flow model results in a combination frequency of 5.316RF.Therefore,based on the small relative error between model results and experimental results,the simplified numerical models are validated to be sufficiently accurate,and theoretically provide a useful basis for the subsequent research of unsteady tip leakage flow in turbomachinery.展开更多
The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged Navier-Stokes equations.The micro-axial fan,which is widely used in cooling systems ...The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged Navier-Stokes equations.The micro-axial fan,which is widely used in cooling systems of electronic devices,has a tip clearance of 6%of the axial chord length of the blade.At the design rotation speed,four cases near the peak efficiency point(PEP)with self-induced unsteadiness and four steady cases which have much weaker pressure fluctuations are investigated.Using the"interface"separating the incoming main flow and the TLF defined by Duet al.[1],an explanation based on the propagation of the low energy spot and its multi-passing through the high gradient zone of the relative total pressure,is proposed to clarify the originating mechanism of the unsteadiness.At the operating points near the PEP,the main flow is weaker than the TLF and the interface moves upstream.The low energy spot which propagates along in the close behind of the interface has opportunity to circulate in the circumferential direction and passes through the sensitive interfaces several times,a slight perturbation therefore may be magnified significantly and develops into the self-induced unsteadiness.The explanation is demonstrated by numerical results.展开更多
The complex flow characteristics in the tip region of a tandem cascade with tip clearance have been calculated and analyzed using Delayed Detached Eddy Simulation(DDES).The coherent mechanism of the vortex structures ...The complex flow characteristics in the tip region of a tandem cascade with tip clearance have been calculated and analyzed using Delayed Detached Eddy Simulation(DDES).The coherent mechanism of the vortex structures near the blade tip was discussed,and the unsteady behaviors and features in the tip flow field were analyzed.Additionally,the interaction between the tip leakage flow and the gap jet was revealed.The results show that,compared to the datum cascade,the blade tip load of the rear blade increases while that of the front blade decreases.Unsteady fluctuations of the tandem cascade are mainly caused by the interaction between the tip leakage flow and gap jet,and by the mixing of the vortex structures,but there is no essential change in the spectrum feature of the tip leakage flow.Finally,a detailed analysis of the development of vortices in the tip region is conducted by the topological structures of the flow field.Combined with the three-dimensional vortex structures,the schematic diagram of the vortex system of the datum single-row cascade and tandem cascade is summarized.展开更多
To reveal the cavitation forms of tip leakage vortex(TLV)of the axial flow pump and the flow mechanism of the flow field,this research adopts the partially-averaged Navier-Stokes(PANS)model to simulate the cavitation ...To reveal the cavitation forms of tip leakage vortex(TLV)of the axial flow pump and the flow mechanism of the flow field,this research adopts the partially-averaged Navier-Stokes(PANS)model to simulate the cavitation values of an axial flow pump,followed by experimental validation.The experimental result shows that compared with the shear stress transport(SST)k-ωmodel,the PANS model significantly reduces the eddy viscosity of the flow field to make the vortex structure clearer and allow the turbulence scale to be more robustly analyzed.The cavitation area within the axial flow pump mainly comprises of TLV cavitation,clearance cavitation and tip leakage flows combined effect of triangular cloud cavitation formed.The formation and development of cavitation are accompanied by the formation and evolution of vortex,and variations in vortex structure also generate and promote the development of cavitation.In addition,an in-depth analysis of the relationship between the turbulent kinetic energy(TKE)transport equation and cavitation patterns was also conducted,finding that the regions with relatively high TKE are mainly distributed around gas/liquid boundaries with serious cavitation and evident gas-liquid change.This phenomenon is mainly attributed to the combined effect of the pressure action term,stress diffusion term and TKE production term.展开更多
The steady and unsteady leakage flow and heat transfer characteristics of the rotor blade squealer tip were conducted by solving Reynolds-Averaged Navier-Stokes (RANS) equations with k-co turbulence model. The first...The steady and unsteady leakage flow and heat transfer characteristics of the rotor blade squealer tip were conducted by solving Reynolds-Averaged Navier-Stokes (RANS) equations with k-co turbulence model. The first stage of GE-E3 engine with squealer tip in the rotor was adopted to perform this work. The tip clearance was set to be 1% of the rotor blade height and the groove depth was specified as 2% of the span. The results showed that there were two vortexes in the tip gap which determined the local heat transfer characteristics. In the steady flow field, the high heat transfer coefficient existed at several positions. In the unsteady case, the flow field in the squealer tip was mainly influenced by the upstream wake and the interaction of the blades potential fields. These unsteady effects induced the periodic variation of the leakage flow and the vortexes, which resulted in the fluctuation of the heat transfer coefficient. The largest fluctuation of the heat transfer coefficient on the surface of the groove bottom exceeded 16% of the averaged value on the surface of the squealer tip.展开更多
The near casing flow fields inside the rotor passage of a 1.5 stage axial compressor with different blade-loading levels and tip gap sizes were measured by using stereoscopic particle image velocimetry(SPIV). Based on...The near casing flow fields inside the rotor passage of a 1.5 stage axial compressor with different blade-loading levels and tip gap sizes were measured by using stereoscopic particle image velocimetry(SPIV). Based on a carefully defined blockage extracting method, the variations of blockage parameter inside the blade passage were analyzed. It was found that the variation of blockage parameter appeared as a non-monotonic behavior inside the blade passage in most cases. This non-monotonic behavior became much more remarkable as the blade loading increases or mass flow rate decreases.The variations of the blockage parameter inside the blade passage had close relation to the evolutionary procedures of the tip leakage vortex(TLV). The destabilization of the TLV caused a rapid increasing of the blockage parameter. After the TLV lost the features of a concentrated streamwise vortex,the blockage parameter usually got a peak value. And then, because of the intense turbulent mixing between the TLV low momentum flow and its surrounding flows, the flow deficit inside the TLV recovered.展开更多
Aerodynamic performance of an axial flow fan is closely related to its tip clearance leakage flow. In this paper, the hot-wire anemometer is used to measure the three dimensional mean velocity near the blade tips. Mor...Aerodynamic performance of an axial flow fan is closely related to its tip clearance leakage flow. In this paper, the hot-wire anemometer is used to measure the three dimensional mean velocity near the blade tips. Moreover, the filtered N-S equations with finite volume method and RNG k-s turbulence model are adopted to carry out the steady simulation calculation of several fans that differ only in tip flange shape and number. The large eddy simulation and the FW-H noise models are adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation agree roughly with that of tests, which proves the numerical calculation method is feasible.The effects of tip flange shapes and numbers on the blade tip vortex structure and the characteristics are analyzed. The results show that tip flange of the fan has a certain influence on the characteristics of the fan. The maximum efficiencies for the fans with tip flanges are shifted towards partial flow with respect to the design point of the dattun fan. Furthermore, the noise characteristics for the fans with tip flanges have become more deteriorated than that for the datum fan. Tip flange contributes to forming tip vortex shedding and the effect of the half-cylinder tip flange on tip vortex shedding is obvious. There is a distinct rela- tionship between the characteristics of the fan and tip vortex shedding.The research results provide the profitable reference for the internal flow mechanism of the performance optimization of small axial flow fans.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
For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition ...For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.展开更多
Blade lean has been intensively utilized in axial compressors.In this study,three families of highly loaded compressor cascades featuring different aspect ratios(AR)with different levels of blade lean were designed an...Blade lean has been intensively utilized in axial compressors.In this study,three families of highly loaded compressor cascades featuring different aspect ratios(AR)with different levels of blade lean were designed and simulated with and without tip clearance.The influences of blade lean on corner separation and tip leakage flow(TLF)were investigated.Results show that blade lean can exert spanwise pressure gradient confined to the fore part,spanwise mass flow rate re-distribution exhibiting differently at fore and rear part of blade,and stage reaction variations.AR has a significant influence on blade lean.With the increase of AR,corner separation grows significantly and requires a higher lean level to be controlled.TLF eliminates corner separation of linear cascades but also increases the loss of leaned cascades;blade lean introduces 22%higher tip leakage mass flow,but exhibits 43%(blade M)and 38%(blade E)lower tip leakage loss.The flow mechanism can be mainly accounted by the reduction of bulk flow velocity,tip leakage velocity and the velocity difference near leading edge(LE).High AR cascade induces re-distribution of TLF along blade chord and reduces leakage loss compared with low AR counterpart.展开更多
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In the present paper the attention is focused on correlation between fan noise and velocity fluctuations of tip leakage vortex around rotor blade of a low pressure axial flow fan at the maximum pressure operating point. We measured time fluctuating velocity near the rotor tip around the rotor blades by using a hot-wire sensor from a relative flame of refer- ence fixed to the rotor blades. As the results, it is clear that the velocity fluctuation due to tip leakage vortex has weak periodicity and the hump portion appeared in its spectrum. If the flow rate was lower than the design condition, the tip leakage flow became to attach to the following blade and the sound pressure level at frequency of velocity fluctuation of this flow was increased. The correlation measurements between the velocity fluctuation of tip leakage flow and the aerodynamic noise were made using a rotating hot-wire sensor near the rotor tip in the rotating frame. The correlation between the velocity fluctuation due to tip leakage flow and acoustic pressure were increased due to generation of weak acoustic resonance at the maximum pressure operating point.
文摘The cascade model was tested using transient liquid crystal temperature measurement technology.The effects of main flow Reynolds number,blowing ratio and tip clearance height on the convective heat transfer coefficient of the turbine outer ring were studied.Two feature lines were marked on the turbine outer ring corresponding to the position of the blade.The conclusions are as follows:The tip clearance leakage flow has a great influence on the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the blowing ratio are kept constant,gradually increasing the main flow Reynolds number will result in an increase in the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the main flow Reynolds number are kept constant and the blowing ratio is gradually increased,the convective heat transfer coefficient of the turbine outer ring is almost constant.The heat transfer coefficient of the turbine outer ring surface is little affected by the blowing ratio;The clearance height has great influence on the heat transfer characteristics of the turbine outer ring.Under the typical working condition in this paper,when the tip clearance height ratio is 1.6%,the convective heat transfer coefficient of the outer surface of the turbine is the highest.
基金This project is supported by National Natural Science Foundation of China (No. 50406017).
文摘In the steady operation condition, the experiments and the numerical simulations are used to investigate the tip leakage flow fields in three low pressure axial flow fans with three kinds of circumferential skewed rotors, including the radial rotor, the forward-skewed rotor and the back- ward-skewed rotor. The three-dimensional viscous flow fields of the fans are computed. In the experiments, the two-dimensional plane particle image velocimetry (PIV) system is used to measure the flow fields in the tip region of three different pitchwise positions of each fan. The results show that the computational results agree well with the experimental data in the flow field of the tip region of each fan. The tip leakage vortex core segments based on method of the eigenmode analysis can display clearly some characteristics of the tip leakage vortex, such as the origination position of tip leak- age vortex, the development of vortex strength, and so on. Compared with the radial rotor, the other two skewed rotors can increase the stability of the tip leakage vortex and the increment in the forward-skewed rotor is more than that in the backward-skewed one. Among the tip leakage vortices of the three rotors, the velocity of the vortex in the forward-skewed rotor is th6 highest in the circumferential direction and the lowest in the axial direction.
基金the National Natural Science Foundation of China(Nos.51976116 and 51976125)the Natural Science Fund of Shanghai,China(No.19ZR1425900)+1 种基金the Open Research Subject of Key Laboratory(Fluid Machinery and Engineering Research Base)of Sichuan Province,China(No.szjj2019-022)Alexander von Humboldt Foundation.
文摘In previous studies,a theoretical model was developed after Acoustic Resonance(AR)was experimentally detected in a four-stage compressor,and AR inception was proposed to be triggered by an unknown sound source,which is a pressure perturbation of a specific frequency with a suitable circumferential propagation speed.The present paper,which is not dedicated to the simulation of acoustic field,aims to identify the specific sound source generated by the unsteady tip leakage flow using the unsteady Computational Fluid Mechanics(CFD)approach.After a comprehensive analysis of an Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation,a pressure perturbation of non-integer multiple of rotor frequency is found at the blade tip.Since the essence of the tip leakage flow is a jet flow driven by the pressure difference between two sides of blade,a simplified tip leakage flow model is adopted using Large Eddy Simulation(LES)in order to simulate the jet flow through a tip clearance.It is found that the convection velocity of shedding vortices fits the expected propagation speed of the sound source,the frequency is also close to one of the dominating frequencies in the URANS simulation,and the resultant combination frequency coincides with the experimentally measured AR frequency.Since such a simplified model successfully captures the key physical mechanisms,it is concluded that this paper provides a piece of unambiguous evidence on the role of unsteady tip leakage vortex in triggering the AR inception of the multistage compressor.
基金supported by the National Natural Science Foundation of China(No.51976116)National Science and Technology Major Project(No.j2019-ii-0006-0026)the Open Research Subject of Key Laboratory of Aerodynamic Noise Control(No.ANCL20230201).
文摘Tip leakage flow(TLF)in compressors,which can cause flow blockage in blade passage and induce efficiency loss,is also a potential threat to the unsteady flow stability of modern aeroengines.This paper provides an overview of the significance of tip leakage flow research,and introduces relevant previous studies.After calculating by different methods,large eddy simulation(LES)is demonstrated again as a suitable compromise between accuracy and computational cost for the unsteady flow study.Two types of simplified tip leakage flow models using LES are adopted with a focus on the unsteady characteristics of shedding vortices in a cavity plane.This paper applies these models to study the unsteady tip leakage flow which triggers the onset of acoustic resonance in a multistage axial compressor.Compared with the detected acoustic resonance frequency of 5.22 rotational frequency(RF)in the previous experiment,the computed combination frequency in the 2-D model is equal to 5.232RF,and the simplified 3-D unsteady tip leakage flow model results in a combination frequency of 5.316RF.Therefore,based on the small relative error between model results and experimental results,the simplified numerical models are validated to be sufficiently accurate,and theoretically provide a useful basis for the subsequent research of unsteady tip leakage flow in turbomachinery.
基金funded by the National Natural Science Foundation of China under Grant 50876031by Shanghai Municipal Education Commission under Grant 10ZZ40
文摘The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged Navier-Stokes equations.The micro-axial fan,which is widely used in cooling systems of electronic devices,has a tip clearance of 6%of the axial chord length of the blade.At the design rotation speed,four cases near the peak efficiency point(PEP)with self-induced unsteadiness and four steady cases which have much weaker pressure fluctuations are investigated.Using the"interface"separating the incoming main flow and the TLF defined by Duet al.[1],an explanation based on the propagation of the low energy spot and its multi-passing through the high gradient zone of the relative total pressure,is proposed to clarify the originating mechanism of the unsteadiness.At the operating points near the PEP,the main flow is weaker than the TLF and the interface moves upstream.The low energy spot which propagates along in the close behind of the interface has opportunity to circulate in the circumferential direction and passes through the sensitive interfaces several times,a slight perturbation therefore may be magnified significantly and develops into the self-induced unsteadiness.The explanation is demonstrated by numerical results.
基金co-supported by the National Science and Technology Major Project,China(No.2017-Ⅱ-0001-0013)the National Natural Science Foundation of China(Nos.52106057 and 51790512)+2 种基金the Fundamental Research Funds for the Central Universities,China(No.D5000210483)the Foundation of State Level Key Laboratory of Airfoil and Cascade Aerodynamics,China(Nos.D5150210006 and D5050210015)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX2022013).
文摘The complex flow characteristics in the tip region of a tandem cascade with tip clearance have been calculated and analyzed using Delayed Detached Eddy Simulation(DDES).The coherent mechanism of the vortex structures near the blade tip was discussed,and the unsteady behaviors and features in the tip flow field were analyzed.Additionally,the interaction between the tip leakage flow and the gap jet was revealed.The results show that,compared to the datum cascade,the blade tip load of the rear blade increases while that of the front blade decreases.Unsteady fluctuations of the tandem cascade are mainly caused by the interaction between the tip leakage flow and gap jet,and by the mixing of the vortex structures,but there is no essential change in the spectrum feature of the tip leakage flow.Finally,a detailed analysis of the development of vortices in the tip region is conducted by the topological structures of the flow field.Combined with the three-dimensional vortex structures,the schematic diagram of the vortex system of the datum single-row cascade and tandem cascade is summarized.
基金supported by the National Natural Science Foundation of China(Grant No.52376035).
文摘To reveal the cavitation forms of tip leakage vortex(TLV)of the axial flow pump and the flow mechanism of the flow field,this research adopts the partially-averaged Navier-Stokes(PANS)model to simulate the cavitation values of an axial flow pump,followed by experimental validation.The experimental result shows that compared with the shear stress transport(SST)k-ωmodel,the PANS model significantly reduces the eddy viscosity of the flow field to make the vortex structure clearer and allow the turbulence scale to be more robustly analyzed.The cavitation area within the axial flow pump mainly comprises of TLV cavitation,clearance cavitation and tip leakage flows combined effect of triangular cloud cavitation formed.The formation and development of cavitation are accompanied by the formation and evolution of vortex,and variations in vortex structure also generate and promote the development of cavitation.In addition,an in-depth analysis of the relationship between the turbulent kinetic energy(TKE)transport equation and cavitation patterns was also conducted,finding that the regions with relatively high TKE are mainly distributed around gas/liquid boundaries with serious cavitation and evident gas-liquid change.This phenomenon is mainly attributed to the combined effect of the pressure action term,stress diffusion term and TKE production term.
基金supported by China National Basic Research Program (973 Program),Project No.2007 CB 210107
文摘The steady and unsteady leakage flow and heat transfer characteristics of the rotor blade squealer tip were conducted by solving Reynolds-Averaged Navier-Stokes (RANS) equations with k-co turbulence model. The first stage of GE-E3 engine with squealer tip in the rotor was adopted to perform this work. The tip clearance was set to be 1% of the rotor blade height and the groove depth was specified as 2% of the span. The results showed that there were two vortexes in the tip gap which determined the local heat transfer characteristics. In the steady flow field, the high heat transfer coefficient existed at several positions. In the unsteady case, the flow field in the squealer tip was mainly influenced by the upstream wake and the interaction of the blades potential fields. These unsteady effects induced the periodic variation of the leakage flow and the vortexes, which resulted in the fluctuation of the heat transfer coefficient. The largest fluctuation of the heat transfer coefficient on the surface of the groove bottom exceeded 16% of the averaged value on the surface of the squealer tip.
基金funded by the National Natural Science Foundation of China,Grant No.51006007,51136003 and 50976009
文摘The near casing flow fields inside the rotor passage of a 1.5 stage axial compressor with different blade-loading levels and tip gap sizes were measured by using stereoscopic particle image velocimetry(SPIV). Based on a carefully defined blockage extracting method, the variations of blockage parameter inside the blade passage were analyzed. It was found that the variation of blockage parameter appeared as a non-monotonic behavior inside the blade passage in most cases. This non-monotonic behavior became much more remarkable as the blade loading increases or mass flow rate decreases.The variations of the blockage parameter inside the blade passage had close relation to the evolutionary procedures of the tip leakage vortex(TLV). The destabilization of the TLV caused a rapid increasing of the blockage parameter. After the TLV lost the features of a concentrated streamwise vortex,the blockage parameter usually got a peak value. And then, because of the intense turbulent mixing between the TLV low momentum flow and its surrounding flows, the flow deficit inside the TLV recovered.
基金supported by grants from the National Natural Science Foundation of China(No.51006090)the Major Special Project of Technology Office in Zhejiang Province(No.2011C11073,No.2011C16038)
文摘Aerodynamic performance of an axial flow fan is closely related to its tip clearance leakage flow. In this paper, the hot-wire anemometer is used to measure the three dimensional mean velocity near the blade tips. Moreover, the filtered N-S equations with finite volume method and RNG k-s turbulence model are adopted to carry out the steady simulation calculation of several fans that differ only in tip flange shape and number. The large eddy simulation and the FW-H noise models are adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation agree roughly with that of tests, which proves the numerical calculation method is feasible.The effects of tip flange shapes and numbers on the blade tip vortex structure and the characteristics are analyzed. The results show that tip flange of the fan has a certain influence on the characteristics of the fan. The maximum efficiencies for the fans with tip flanges are shifted towards partial flow with respect to the design point of the dattun fan. Furthermore, the noise characteristics for the fans with tip flanges have become more deteriorated than that for the datum fan. Tip flange contributes to forming tip vortex shedding and the effect of the half-cylinder tip flange on tip vortex shedding is obvious. There is a distinct rela- tionship between the characteristics of the fan and tip vortex shedding.The research results provide the profitable reference for the internal flow mechanism of the performance optimization of small axial flow fans.
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 Natural Sci-ence Foundation of China under Grant No.51106174
文摘For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.
基金supported by National Natural Science Foundation of China(No.51806174)the Natural Science Foundation of Shaanxi Province(No.2019-JQ137)+1 种基金the Fundamental Research Funds for the Central Universities(No.G2018KY0303)National Natural Science Foundation of China(No.51790512)。
文摘Blade lean has been intensively utilized in axial compressors.In this study,three families of highly loaded compressor cascades featuring different aspect ratios(AR)with different levels of blade lean were designed and simulated with and without tip clearance.The influences of blade lean on corner separation and tip leakage flow(TLF)were investigated.Results show that blade lean can exert spanwise pressure gradient confined to the fore part,spanwise mass flow rate re-distribution exhibiting differently at fore and rear part of blade,and stage reaction variations.AR has a significant influence on blade lean.With the increase of AR,corner separation grows significantly and requires a higher lean level to be controlled.TLF eliminates corner separation of linear cascades but also increases the loss of leaned cascades;blade lean introduces 22%higher tip leakage mass flow,but exhibits 43%(blade M)and 38%(blade E)lower tip leakage loss.The flow mechanism can be mainly accounted by the reduction of bulk flow velocity,tip leakage velocity and the velocity difference near leading edge(LE).High AR cascade induces re-distribution of TLF along blade chord and reduces leakage loss compared with low AR counterpart.