The unstable flow phenomena in compressors, such as stall and surge, are closely related to the e ciency and the operating region. It is indispensable to capture the unstable flow structure in compressors and understa...The unstable flow phenomena in compressors, such as stall and surge, are closely related to the e ciency and the operating region. It is indispensable to capture the unstable flow structure in compressors and understand the mechanism of flow instability at low flow rates. Cooperated with the manufacturer, an industrial centrifugal compressor with a vaneless di user is tested by its performance test rig and our multi-phase dynamic measurement system. Many dynamic pressure transducers are circumferentially mounted on the casing surface at seven radial locations, spanning the impeller region and the di user inlet region. The pressure fields from the design condition to surge are measured in details. Based on the multi-phase dynamic signals, the original location of stall occurring can be determined. Meanwhile, the information of the unstable flow structure is obtained, such as the circumferential mode and the propagating speed of stall cells. To get more details of the vortex structure, an unsteady simulation of this tested compressor is carried out. The computational result is well matched with the experimental result and further illustrates how the unstable flow structure in the impeller region gradually a ects the stability of the total machine at low flow rates. The dynamic mode decomposition(DMD) method is applied to get the specific flow pattern corresponding to the stall frequency. Both experimental and computational analysis show that the flow structure at a particular radial location in the impeller region has a great impact on the stall and surge. Some di erences between the computational and experimental result are also discussed. Through these two main analytical methods, an insight into the unstable flow structure in an industrial compressor is gained. The result also plays a crucial role in the guidance of the compressor stabilization techniques.展开更多
The interference of two circular cylinders has been researched for many years. In this study, the research work was concentrated on two cylinders in some special staggered arrangement. The velocity signal was measure...The interference of two circular cylinders has been researched for many years. In this study, the research work was concentrated on two cylinders in some special staggered arrangement. The velocity signal was measured with a hot wire anemometer and recorded with a TEAC portable data recorder. The relationship between spectrum and time was established by making 200 spectrum analysis in se- quence. The gap flow is unstable when two cylinders are arranged in L/D=2, T/D=1. Mainly, it can be looked as flow past a single blunt body and the Strouhal number is 0.15, The second peak arises in the power spectrum when the gap flow appears at irregular time interval. Sometimes it may be higher than the first one. The Strouhal num- ber corresponding to the second peak is 0.33. But at most of the time it is lower than the first one and even disap- peared. This is meaningful for exploring the mechanisms of interference induced oscillations in flow past two cylin- ders.展开更多
A study is made of the distribution of the diagnostic quantity vector E and the teleconnection structure of 30-50 (quasi-40) day oscillation, together with the dependence on the conversion of barotropic unstable energ...A study is made of the distribution of the diagnostic quantity vector E and the teleconnection structure of 30-50 (quasi-40) day oscillation, together with the dependence on the conversion of barotropic unstable energy of mean flow in terms of ECWMF daily 500 hPa grid data in winter, indicating that the energy transportation is closely associated with the westerly jet position, with zonal (meridional) propagation in the strong (weak) wind region, that considerable conversion of barotropic energy occurs at the jet exit region where low-frequency oscillation gains energy from the mean flow, leading to maximum kinetic energy for the oscillation observed there, which is marked by evident barotropy in striking contrast to the baroclinicity at low latitudes and that the teleconnection core is related to the center of action in the atmosphere and bound up with the pattern of the west wind.展开更多
The complex tip flow instability and its induced non-synchronous vibration have become significant challenges,especially as aerodynamic loading continues to increase.This study investigates the effects of tip clearanc...The complex tip flow instability and its induced non-synchronous vibration have become significant challenges,especially as aerodynamic loading continues to increase.This study investigates the effects of tip clearance on non-synchronous propagating flow disturbances of compressor rotors under high aerodynamic loading conditions by conducting full-annulus unsteady numerical simulations with three typi-cal tip clearance values for a 1-1/2 stage transonic compressor.The non-synchronous aerodynamic excitation frequency,circumferential mode characteristics,and annular unstable flow structures are analyzed under near stall conditions.The results show that the total pressure ratio and normalized mass flow parameters first increase and then decrease as the tip clearance increases from 0.5%C(where C represents the tip chord length)to 2%C under high aerodynamic loading conditions,instead of constantly decreasing.For the 0.5%C tip clearance case,the traveling large-scale tornado-like separation vortices cause a low non-synchronous aerodynamic excitation frequency and severe pressure fluctuations.The periodic shedding and reattachment processes of the rotor blades separated by 2–3 pitches result in 19 dominant mode orders in the circumferential direction.As the tip clearance increases from 1%C to 2%C,the difference of tip flow structures in each blade passage is significantly weakened,and the dominant mode order of the disturbance is equal to the rotor blade-passing number.The pressure fluctuation is mainly caused by cross-channel tip leakage flow,and the aerodynamic excitation frequency exhibits evident broadband hump charac-teristics,which has been reported as a rotating instability phenomenon.展开更多
The authors investigate the stability of a steady ideal plane flow in an arbitrary domain in terms of the L^2 norm of the vorticity. Linear stability implies nonlinear instability provided the growth rate of the line...The authors investigate the stability of a steady ideal plane flow in an arbitrary domain in terms of the L^2 norm of the vorticity. Linear stability implies nonlinear instability provided the growth rate of the linearized system exceeds the Liapunov exponent of the flow. In contrast,a maximizer of the entropy subject to constant energy and mass is stable. This implies the stability of certain solutions of the mean field equation.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51276108)
文摘The unstable flow phenomena in compressors, such as stall and surge, are closely related to the e ciency and the operating region. It is indispensable to capture the unstable flow structure in compressors and understand the mechanism of flow instability at low flow rates. Cooperated with the manufacturer, an industrial centrifugal compressor with a vaneless di user is tested by its performance test rig and our multi-phase dynamic measurement system. Many dynamic pressure transducers are circumferentially mounted on the casing surface at seven radial locations, spanning the impeller region and the di user inlet region. The pressure fields from the design condition to surge are measured in details. Based on the multi-phase dynamic signals, the original location of stall occurring can be determined. Meanwhile, the information of the unstable flow structure is obtained, such as the circumferential mode and the propagating speed of stall cells. To get more details of the vortex structure, an unsteady simulation of this tested compressor is carried out. The computational result is well matched with the experimental result and further illustrates how the unstable flow structure in the impeller region gradually a ects the stability of the total machine at low flow rates. The dynamic mode decomposition(DMD) method is applied to get the specific flow pattern corresponding to the stall frequency. Both experimental and computational analysis show that the flow structure at a particular radial location in the impeller region has a great impact on the stall and surge. Some di erences between the computational and experimental result are also discussed. Through these two main analytical methods, an insight into the unstable flow structure in an industrial compressor is gained. The result also plays a crucial role in the guidance of the compressor stabilization techniques.
文摘The interference of two circular cylinders has been researched for many years. In this study, the research work was concentrated on two cylinders in some special staggered arrangement. The velocity signal was measured with a hot wire anemometer and recorded with a TEAC portable data recorder. The relationship between spectrum and time was established by making 200 spectrum analysis in se- quence. The gap flow is unstable when two cylinders are arranged in L/D=2, T/D=1. Mainly, it can be looked as flow past a single blunt body and the Strouhal number is 0.15, The second peak arises in the power spectrum when the gap flow appears at irregular time interval. Sometimes it may be higher than the first one. The Strouhal num- ber corresponding to the second peak is 0.33. But at most of the time it is lower than the first one and even disap- peared. This is meaningful for exploring the mechanisms of interference induced oscillations in flow past two cylin- ders.
基金This work is supported by National Natural Science Foundation of China.
文摘A study is made of the distribution of the diagnostic quantity vector E and the teleconnection structure of 30-50 (quasi-40) day oscillation, together with the dependence on the conversion of barotropic unstable energy of mean flow in terms of ECWMF daily 500 hPa grid data in winter, indicating that the energy transportation is closely associated with the westerly jet position, with zonal (meridional) propagation in the strong (weak) wind region, that considerable conversion of barotropic energy occurs at the jet exit region where low-frequency oscillation gains energy from the mean flow, leading to maximum kinetic energy for the oscillation observed there, which is marked by evident barotropy in striking contrast to the baroclinicity at low latitudes and that the teleconnection core is related to the center of action in the atmosphere and bound up with the pattern of the west wind.
基金This work is supported by the National Science and Technology Major Project(J2022-IV-0010-0024).
文摘The complex tip flow instability and its induced non-synchronous vibration have become significant challenges,especially as aerodynamic loading continues to increase.This study investigates the effects of tip clearance on non-synchronous propagating flow disturbances of compressor rotors under high aerodynamic loading conditions by conducting full-annulus unsteady numerical simulations with three typi-cal tip clearance values for a 1-1/2 stage transonic compressor.The non-synchronous aerodynamic excitation frequency,circumferential mode characteristics,and annular unstable flow structures are analyzed under near stall conditions.The results show that the total pressure ratio and normalized mass flow parameters first increase and then decrease as the tip clearance increases from 0.5%C(where C represents the tip chord length)to 2%C under high aerodynamic loading conditions,instead of constantly decreasing.For the 0.5%C tip clearance case,the traveling large-scale tornado-like separation vortices cause a low non-synchronous aerodynamic excitation frequency and severe pressure fluctuations.The periodic shedding and reattachment processes of the rotor blades separated by 2–3 pitches result in 19 dominant mode orders in the circumferential direction.As the tip clearance increases from 1%C to 2%C,the difference of tip flow structures in each blade passage is significantly weakened,and the dominant mode order of the disturbance is equal to the rotor blade-passing number.The pressure fluctuation is mainly caused by cross-channel tip leakage flow,and the aerodynamic excitation frequency exhibits evident broadband hump charac-teristics,which has been reported as a rotating instability phenomenon.
文摘The authors investigate the stability of a steady ideal plane flow in an arbitrary domain in terms of the L^2 norm of the vorticity. Linear stability implies nonlinear instability provided the growth rate of the linearized system exceeds the Liapunov exponent of the flow. In contrast,a maximizer of the entropy subject to constant energy and mass is stable. This implies the stability of certain solutions of the mean field equation.
