The tip-leakage vortex(TLV)cavitation is a challenging issue for a variety of axial hydraulic turbines and pumps from both technical and scientific viewpoints.The flow characteristics of the TLV cavitation were widely...The tip-leakage vortex(TLV)cavitation is a challenging issue for a variety of axial hydraulic turbines and pumps from both technical and scientific viewpoints.The flow characteristics of the TLV cavitation were widely studied in the past decades,but the knowledge about the tip-leakage cavitating flow is still limited.The present paper reviews the progresses in the researches of the TLV cavitation,including the numerical methods for the TLV cavitation,the flow characteristics of the TLV,the influences of the TLV cavitation on the local flow field and the control strategies of the TLV cavitation.It is indicated that the non-condensable gas may play an important role in the development of the TLV cavitation,and this fact should be considered during a careful simulation of the TLV cavitation.It is also suggested that the development of the TLV cavitation will significantly influence the distributions of the vorticity and the turbulence kinetic energy.Due to the complexity of the TLV cavitation,it is still an open question how to suppress the TLV cavitation in a simple but effective way.Finally,based on these understandings,some advanced topics for the future work are suggested to further promote the study of the TLV cavitation,for a deeper knowledge about the TLV cavitation.展开更多
In the present paper, the Vortex Identified Zwart-Gerber-Belamri（VIZGB） cavitation model coupled with the SST-CC turbulence model is used to investigate the unsteady tip-leakage cavitating flow induced by a NACA0009...In the present paper, the Vortex Identified Zwart-Gerber-Belamri（VIZGB） cavitation model coupled with the SST-CC turbulence model is used to investigate the unsteady tip-leakage cavitating flow induced by a NACA0009 hydrofoil. A qualitative comparison between the numerical and experimental results is made. In order to quantitatively evaluate the reliability of the numerical data, the verification and validation（V＆V） procedures are used in the present paper. Errors of numerical results are estimated with seven error estimators based on the Richardson extrapolation method. It is shown that though a strict validation cannot be achieved, a reasonable prediction of the gross characteristics of the tip-leakage cavitating flow can be obtained. Based on the numerical results, the influence of the cavitation on the tip-leakage vortex（TLV） is discussed, which indicates that the cavitation accelerates the fusion of the TLV and the tip-separation vortex（TSV）. Moreover, the trajectory of the TLV, when the cavitation occurs, is close to the side wall.展开更多
Tip leakage flow(TLF)trajectory in a pump with gas entrainment is investigated via visualization experiments and numerical simulations.Starting position of tip leakage vortex(TLV)is determined accurately by numerical ...Tip leakage flow(TLF)trajectory in a pump with gas entrainment is investigated via visualization experiments and numerical simulations.Starting position of tip leakage vortex(TLV)is determined accurately by numerical simulation.Under high liquid flow rate(Q_(l))and high inlet gas volume fraction(IGVF)conditions,TLF flows from suction surface to pressure surface near the leading edge of blade,and the direction of TLF gradually changes along the chord which flows from pressure surface to suction surface near the tailing edge.The angle between TLF and blade mean camberline increases progressively as either Q_(l)or IGVF decreases,and starting position of TLV moves towards leading edge direction.As Q_(l)or IGVF decreases,value of vorticity increases and high vorticity region moves towards leading edge.The entropy production rate at blade tip clearance is high,and entropy diffuses from pressure surface to suction surface due to jet flow in blade tip clearance.The greater the amount of accumulated gas there is,the greater the amount of entropy in the area.In addition,when gas is entrained in pump,there are many low frequency fluctuations generated in blade tip clearance.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 tip clearance induces the tip leakage vortex(TLV),which has a great impact on the pressure fluctuation characteristics of the multiphase pump.To investigate the effect of the tip clearance on the pressure fluctuat...The tip clearance induces the tip leakage vortex(TLV),which has a great impact on the pressure fluctuation characteristics of the multiphase pump.To investigate the effect of the tip clearance on the pressure fluctuations,based on the Reynolds time-averaged Navier-Stokes equation and the shear stress transfer(SST)k-ωturbulence model,the three-dimensional turbulent flow in the pump is numerically simulated for different tip clearances in the water and gas-liquid two-phase cases by using the ANSYS CFX software and the results are verified with experimental data.It is shown the greater pressure fluctuation intensity corresponds with the TLV both in the water and gas-liquid two-phase cases.In the meantime,the location of the maximum pressure fluctuation intensity is related to the tip clearance size.In addition,for different tip clearances,the pressure fluctuation intensity with the rotor and stator interaction(RSI)is relatively larger.The difference is that when R_(tc)=1.5 mm,the pressure fluctuation intensity near the impeller middle point is also relatively larger.On the whole,the pressure fluctuation intensity in the gas-liquid two-phase case is larger than that in the water case.Furthermore,the gas causes the frequency of the high-amplitude pressure fluctuation in the impeller and the diffuser to be shifted from 7 f_(n)(f_(n) denotes impeller rotational frequency)and 3 f_(n) to the low-frequency region,respectively.The pressure fluctuations at the blade-passing frequency(BPF)and the multiple BPFs gradually disappear.Meanwhile,the amplitude at the dominant frequency in the gas-liquid two-phase case is at least one order of magnitude smaller than that in the water case,and the peak-to-peak value of the pressure fluctuation is also much smaller.展开更多
基金the National Natural Science Foundation of China(Grant Nos.51822903,1772239)the China Postdoctoral Science Foundation(Grant No.2020M682471).
文摘The tip-leakage vortex(TLV)cavitation is a challenging issue for a variety of axial hydraulic turbines and pumps from both technical and scientific viewpoints.The flow characteristics of the TLV cavitation were widely studied in the past decades,but the knowledge about the tip-leakage cavitating flow is still limited.The present paper reviews the progresses in the researches of the TLV cavitation,including the numerical methods for the TLV cavitation,the flow characteristics of the TLV,the influences of the TLV cavitation on the local flow field and the control strategies of the TLV cavitation.It is indicated that the non-condensable gas may play an important role in the development of the TLV cavitation,and this fact should be considered during a careful simulation of the TLV cavitation.It is also suggested that the development of the TLV cavitation will significantly influence the distributions of the vorticity and the turbulence kinetic energy.Due to the complexity of the TLV cavitation,it is still an open question how to suppress the TLV cavitation in a simple but effective way.Finally,based on these understandings,some advanced topics for the future work are suggested to further promote the study of the TLV cavitation,for a deeper knowledge about the TLV cavitation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51576143,11772239 and 91752105)the Science and Technology on Water Jet Propulsion Laboratory(Grant No.61422230101162223002)
文摘In the present paper, the Vortex Identified Zwart-Gerber-Belamri（VIZGB） cavitation model coupled with the SST-CC turbulence model is used to investigate the unsteady tip-leakage cavitating flow induced by a NACA0009 hydrofoil. A qualitative comparison between the numerical and experimental results is made. In order to quantitatively evaluate the reliability of the numerical data, the verification and validation（V＆V） procedures are used in the present paper. Errors of numerical results are estimated with seven error estimators based on the Richardson extrapolation method. It is shown that though a strict validation cannot be achieved, a reasonable prediction of the gross characteristics of the tip-leakage cavitating flow can be obtained. Based on the numerical results, the influence of the cavitation on the tip-leakage vortex（TLV） is discussed, which indicates that the cavitation accelerates the fusion of the TLV and the tip-separation vortex（TSV）. Moreover, the trajectory of the TLV, when the cavitation occurs, is close to the side wall.
基金supported by the National Natural Science Foundation of China(Grant Nos.52409119,52439006,52079108 and 52309118).
文摘Tip leakage flow(TLF)trajectory in a pump with gas entrainment is investigated via visualization experiments and numerical simulations.Starting position of tip leakage vortex(TLV)is determined accurately by numerical simulation.Under high liquid flow rate(Q_(l))and high inlet gas volume fraction(IGVF)conditions,TLF flows from suction surface to pressure surface near the leading edge of blade,and the direction of TLF gradually changes along the chord which flows from pressure surface to suction surface near the tailing edge.The angle between TLF and blade mean camberline increases progressively as either Q_(l)or IGVF decreases,and starting position of TLV moves towards leading edge direction.As Q_(l)or IGVF decreases,value of vorticity increases and high vorticity region moves towards leading edge.The entropy production rate at blade tip clearance is high,and entropy diffuses from pressure surface to suction surface due to jet flow in blade tip clearance.The greater the amount of accumulated gas there is,the greater the amount of entropy in the area.In addition,when gas is entrained in pump,there are many low frequency fluctuations generated in blade tip clearance.
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Projects supported by the National Key Research and Development Program of China(Grant No.2018YFB0905200)。
文摘The tip clearance induces the tip leakage vortex(TLV),which has a great impact on the pressure fluctuation characteristics of the multiphase pump.To investigate the effect of the tip clearance on the pressure fluctuations,based on the Reynolds time-averaged Navier-Stokes equation and the shear stress transfer(SST)k-ωturbulence model,the three-dimensional turbulent flow in the pump is numerically simulated for different tip clearances in the water and gas-liquid two-phase cases by using the ANSYS CFX software and the results are verified with experimental data.It is shown the greater pressure fluctuation intensity corresponds with the TLV both in the water and gas-liquid two-phase cases.In the meantime,the location of the maximum pressure fluctuation intensity is related to the tip clearance size.In addition,for different tip clearances,the pressure fluctuation intensity with the rotor and stator interaction(RSI)is relatively larger.The difference is that when R_(tc)=1.5 mm,the pressure fluctuation intensity near the impeller middle point is also relatively larger.On the whole,the pressure fluctuation intensity in the gas-liquid two-phase case is larger than that in the water case.Furthermore,the gas causes the frequency of the high-amplitude pressure fluctuation in the impeller and the diffuser to be shifted from 7 f_(n)(f_(n) denotes impeller rotational frequency)and 3 f_(n) to the low-frequency region,respectively.The pressure fluctuations at the blade-passing frequency(BPF)and the multiple BPFs gradually disappear.Meanwhile,the amplitude at the dominant frequency in the gas-liquid two-phase case is at least one order of magnitude smaller than that in the water case,and the peak-to-peak value of the pressure fluctuation is also much smaller.
