This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based...This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing treatment configuration reveal an important modification of the vortex topology at the rotor tip clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is proposed.展开更多
In this paper, a computational investigation of circumferential groove casing treatment in a highly-loaded low-reaction transonic compressor rotor is conducted, in which the stage reaction is significantly reduced due...In this paper, a computational investigation of circumferential groove casing treatment in a highly-loaded low-reaction transonic compressor rotor is conducted, in which the stage reaction is significantly reduced due to a larger meridional contraction with respect to conventional transonic compressors. Steady computation at near-stall point is performed first to capture the stall inception of the rotor with smooth casing. Detailed observations, which mainly focus on the tip leakage flow behavior, obstruction and vortical structures in the tip region, determine the reason for the compressor stall. There is tip leakage vortex breakdown in the tip region. Moreover, it yields passage obstruction, and finally leads to the compressor stall. Then, attempts are made to investigate how the circumferential grooves can be applied for the compressor’s stall margin enhancement without compromising efficiency. Three configurations are obtained and analyzed by changing axial position and the number of the circumferential grooves. The results of computational parametric study indicate the optimal location of the groove is near the leading edge and the downstream grooves combine their influence on the compressor’s stabilization and performance in a cumulative manner. The optimal circumferential groove configuration produces an increase of 1% in total pressure ratio at the near-stall point and a gain of 3.7% in stall margin, without any penalty in efficiency. Furthermore, the impact the grooves will exert on the flow mechanisms between the grooves and the main flow is also considered.展开更多
Numerical investigation on the self-induced unsteadiness of tip leakage flow(TLF) for an axial low-speed compressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used...Numerical investigation on the self-induced unsteadiness of tip leakage flow(TLF) for an axial low-speed compressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used to solve the unsteady Reynolds averaged Navier-Stokes(URANS) equations. It is found that the single grooves at various axial locations could have a large impact on the self-induced unsteadiness and the stall margin improvement(SMI) of compressor. The trend of SMI with groove center location demonstrates that the groove located near the mid of blade tip chord generates the best SMI. The worst groove is located about 20% Cax after the blade leading edge. The root-mean-squre of static pressure(RMSP) contours at 99.5% span and fast Fourier transform for the static pressure traces recorded in the tip clearance region for each casing are analyzed. The results demonstrate that the single groove location not only affects the oscillating strength but also the frequency of the unsteady tip leakage flow. At the near-stall point of smooth casing, the self-induced unsteadiness of TLF is enhanced most by the best grooved casing for SMI. While, the self-induced unsteadiness disappears when the worst groove for SMI is added. The characteristic frequency of TLF is about 0.55 blade passing frequency(BPF) with smooth casing. The frequency components become complicated as the single groove moves from the leading edge to the trailing edge of the blade.展开更多
Enhancing stall margin has a great importance for the development of turbo compressors. The application of circumferential grooved casing treatment(CGCT) is a useful method of increasing the stable operating range of ...Enhancing stall margin has a great importance for the development of turbo compressors. The application of circumferential grooved casing treatment(CGCT) is a useful method of increasing the stable operating range of the compressor, and the effectiveness of this kind of casing treatment have been proved by numerous experiments. In this paper, a single circumferential casing groove is placed along the shroud side of the vaned diffuser. To clarify the effect of circumferential groove on the centrifugal compressor stability and corresponding flow mechanism, numerical investigations with different radial location, axial depth and radial width were carried out to compare the results. The computational fluid dynamics(CFD) analyses results show that the centrifugal compressor with a single circumferential groove in diffuser passage can extend stable operating range while the efficiency over the whole operating range decreases a little. Efforts were made to study blade level flow mechanisms to determine how the circumferential groove impacts the compressor's stall margin(SM) and performance. Some comparisons of the flow features with different parameter of grooved casing treatment are performed, and the results indicate that the low energy flow in the tip clearance is sucked into the groove and the area of the low energy fluid region shrinks, which helps to improve the stall margin of the centrifugal compressor. The numerical results showed that a combination of position,width and depth of circumferential groove will maximize stall margin improvement(SMI) of the centrifugal compressor.展开更多
The paper investigates the effect of a single circumferential groove casing treatment(CGCT) on a transonic compressor rotor numerically.In particular,the effect of the groove at different axial locations on the flow f...The paper investigates the effect of a single circumferential groove casing treatment(CGCT) on a transonic compressor rotor numerically.In particular,the effect of the groove at different axial locations on the flow field is studied in detail and stall margin improvement is also discussed.The present results show that the groove close to the leading edge plays a crucial role in stabilizing the near stall flow structures and,hence,improves the stall margin.The groove at the mid-chord-section of the blade can help exchange and transfer momentums between different directions,and suppress the flow unsteadiness,leading to increased efficiency in rotor performance and extended operation range.The groove located near the blade trailing edge has limited effects on stall margin improvement and may cause additional penalty in efficiency.Through comparison with the recent work on CGCT,some common flow physics can be observed.展开更多
文摘This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing treatment configuration reveal an important modification of the vortex topology at the rotor tip clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is proposed.
基金support of the National Natural Science Foundation of China(NSFC),Grant No.51706052。
文摘In this paper, a computational investigation of circumferential groove casing treatment in a highly-loaded low-reaction transonic compressor rotor is conducted, in which the stage reaction is significantly reduced due to a larger meridional contraction with respect to conventional transonic compressors. Steady computation at near-stall point is performed first to capture the stall inception of the rotor with smooth casing. Detailed observations, which mainly focus on the tip leakage flow behavior, obstruction and vortical structures in the tip region, determine the reason for the compressor stall. There is tip leakage vortex breakdown in the tip region. Moreover, it yields passage obstruction, and finally leads to the compressor stall. Then, attempts are made to investigate how the circumferential grooves can be applied for the compressor’s stall margin enhancement without compromising efficiency. Three configurations are obtained and analyzed by changing axial position and the number of the circumferential grooves. The results of computational parametric study indicate the optimal location of the groove is near the leading edge and the downstream grooves combine their influence on the compressor’s stabilization and performance in a cumulative manner. The optimal circumferential groove configuration produces an increase of 1% in total pressure ratio at the near-stall point and a gain of 3.7% in stall margin, without any penalty in efficiency. Furthermore, the impact the grooves will exert on the flow mechanisms between the grooves and the main flow is also considered.
基金supported by National Natural Science Foundation of China with project No.51010007,No.51106153
文摘Numerical investigation on the self-induced unsteadiness of tip leakage flow(TLF) for an axial low-speed compressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used to solve the unsteady Reynolds averaged Navier-Stokes(URANS) equations. It is found that the single grooves at various axial locations could have a large impact on the self-induced unsteadiness and the stall margin improvement(SMI) of compressor. The trend of SMI with groove center location demonstrates that the groove located near the mid of blade tip chord generates the best SMI. The worst groove is located about 20% Cax after the blade leading edge. The root-mean-squre of static pressure(RMSP) contours at 99.5% span and fast Fourier transform for the static pressure traces recorded in the tip clearance region for each casing are analyzed. The results demonstrate that the single groove location not only affects the oscillating strength but also the frequency of the unsteady tip leakage flow. At the near-stall point of smooth casing, the self-induced unsteadiness of TLF is enhanced most by the best grooved casing for SMI. While, the self-induced unsteadiness disappears when the worst groove for SMI is added. The characteristic frequency of TLF is about 0.55 blade passing frequency(BPF) with smooth casing. The frequency components become complicated as the single groove moves from the leading edge to the trailing edge of the blade.
基金National Natural Science Foundation of China(No.51776155)
文摘Enhancing stall margin has a great importance for the development of turbo compressors. The application of circumferential grooved casing treatment(CGCT) is a useful method of increasing the stable operating range of the compressor, and the effectiveness of this kind of casing treatment have been proved by numerous experiments. In this paper, a single circumferential casing groove is placed along the shroud side of the vaned diffuser. To clarify the effect of circumferential groove on the centrifugal compressor stability and corresponding flow mechanism, numerical investigations with different radial location, axial depth and radial width were carried out to compare the results. The computational fluid dynamics(CFD) analyses results show that the centrifugal compressor with a single circumferential groove in diffuser passage can extend stable operating range while the efficiency over the whole operating range decreases a little. Efforts were made to study blade level flow mechanisms to determine how the circumferential groove impacts the compressor's stall margin(SM) and performance. Some comparisons of the flow features with different parameter of grooved casing treatment are performed, and the results indicate that the low energy flow in the tip clearance is sucked into the groove and the area of the low energy fluid region shrinks, which helps to improve the stall margin of the centrifugal compressor. The numerical results showed that a combination of position,width and depth of circumferential groove will maximize stall margin improvement(SMI) of the centrifugal compressor.
基金supported by the GE Aviation under its University Strategic Alliance(USA) programsupported by the National Natural Science Foundation of China(Grant Nos.10932005 and 11272183)
文摘The paper investigates the effect of a single circumferential groove casing treatment(CGCT) on a transonic compressor rotor numerically.In particular,the effect of the groove at different axial locations on the flow field is studied in detail and stall margin improvement is also discussed.The present results show that the groove close to the leading edge plays a crucial role in stabilizing the near stall flow structures and,hence,improves the stall margin.The groove at the mid-chord-section of the blade can help exchange and transfer momentums between different directions,and suppress the flow unsteadiness,leading to increased efficiency in rotor performance and extended operation range.The groove located near the blade trailing edge has limited effects on stall margin improvement and may cause additional penalty in efficiency.Through comparison with the recent work on CGCT,some common flow physics can be observed.
