Parametric study of tip injection was implemented experimentally on a subsonic axial flow compressor to understand the underlying flow mechanisms of stability improvement of the compressor with discrete tip injection....Parametric study of tip injection was implemented experimentally on a subsonic axial flow compressor to understand the underlying flow mechanisms of stability improvement of the compressor with discrete tip injection.Injector throat height varied from 2 to 6 times the height of rotor tip clearance,and circumferential coverage percentage ranged from 8.3% to 25% of the annulus.Static pressure fluctuations over the rotor tip were measured with fast-response pressure transducers.Whole-passage time-accurate simulations were also carried out to help us understand the flow details.The combinations of tip injection with traditional casing treatments were experimentally studied to generate an engineering-acceptable method of compressor stall control.The results indicate that the maximum stability improvement is achieved when injectors are choked despite their different sizes.The effect of circumferential coverage percentage on compressor stability depends on the value of injector throat height for un-choked injectors,and vice versa.Tip blockage in the blade passage is greatly reduced by the choked injectors,which is the primary reason for stability enhancement.The accomplishment of blockage diminishment is maintained in the circumferential direction with the unsteady effect of tip injection,which manifests as a hysteresis between the recovery of tip blockage and the recovery of tip leakage vortex.The unsteady effect is primarily responsible for the effectiveness of tip injection with a partial circumferential coverage.Tip injection cannot enhance the stability of the rotor with axial slots significantly,but it can improve the stability of the rotor with circumferential grooves further.The combined structure of tip injection with circumferential grooves is an alternative for engineering application.展开更多
A series of experiments and numerical simulations are carried out in a high-speed axial compressor to systematically investigate the influence and underlying flow mechanisms of micro tip injection on enhancing compres...A series of experiments and numerical simulations are carried out in a high-speed axial compressor to systematically investigate the influence and underlying flow mechanisms of micro tip injection on enhancing compressor stability.Different geometric structures of micro tip injection have been investigated,including the axial positions of injector port,injected mass flow rate and injector diameter.First,seven designed micro tip injection structures and one solid wall casing are tested in the compressor test rig to elucidate the influence of different micro tip injection parameters on the compressor stability.Then,numerical simulations are conducted to analyze the underlying flow mechanisms of micro tip injection with different design parameters on enhancing the compressor stability.The experimental and numerical investigation reveal that when the injection port is located upstream of the low-speed region,the compressor stability is significantly enhanced.The tip injection with larger injected mass flow can obtain higher stall margin improvement.Smaller injector diameter produces higher injection momentum and velocity,contributing to greater improvement on the compressor stability.展开更多
A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolated axial compressor rotor is presented, intending to better understand the flow mechanism behind stall...A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolated axial compressor rotor is presented, intending to better understand the flow mechanism behind stall control measures that act on tip clearance flow. Under the influence of injection the unsteadiness of self-induced tip clearance flow could be weakened. Also the radial migration of tip clearance vortex is confined to a smaller radial extent near the rotor tip and the trajectory of tip clearance flow is pushed more downstream. So the injection is beneficial to improve compressor stability and increase static pressure rise near rotor tip region. The results of injection with different injected mass flow rates show that for the special type of injector adopted in the paper the effect of injection on tip clearance flow may be different according to the relative strength between these two streams of flow. For a fixed injected mass flow rate, reducing the injector area to increase injection velocity can improve the effect of injection on tip clearance flow and thus the compressor stability. A comparison of calculations between single blade passage and multiple blade passages validates the utility of single passage computations to investigate the tip clearance flow for the case without injection and its interaction with injected flow for the case with tip injection.展开更多
A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine.Three perforated-rib layouts are considered,wherein a perforated rib is installed at(A)the Suc...A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine.Three perforated-rib layouts are considered,wherein a perforated rib is installed at(A)the Suction-Side squealer(SS-rib),(B)the Pressure-Side squealer(PS-rib),and(C)the additional squealer along the blade Camber Line(CL-rib).A numerical method is used to show how the novel rib layouts affect the aerodynamic performance of the tip leakage flow.Results show that the coolant jets issuing from the perforated-rib injection holes penetrate deeper into the tip clearance than those in the baseline squealer-tip case,and how the perforated-rib coolant injection affects the tip leakage flow depends strongly on the rib layout.The PS-rib and CL-rib layouts appear promising for controlling the tip leakage flow,playing a significant role in reducing the total pressure loss and improving the turbine blade’s isentropic efficiency.In particular,under an injection mass flow ratio of 1%and a tip clearance of 1%blade span,the PS-rib layout reduces the leakage mass flow rate by 27%and increases the isentropic efficiency by 1.25%compared with those in the baseline squealer-tip case.Meanwhile,the advantages of the PS-rib layout in tip leakage control are confirmed under small and large tip clearances.展开更多
The mechanism of compressor stall margin enhancement using the tip air injection is explored.The transonic compressor,NASARotor 37,is taken as the object to study the tip clearance flow under active control of tip air...The mechanism of compressor stall margin enhancement using the tip air injection is explored.The transonic compressor,NASARotor 37,is taken as the object to study the tip clearance flow under active control of tip air injection by numerical simulations.The effects of injection parameters(injection total temperature,injection position,injection angle,injection mass flow,injection port size,injection type and etc)on the stall margin extension are emphatically analyzed.Results show that the enhancement of tip leakage vortex enlarges the low-energy region induced by the shock wave in the row channel when the working condition is moving to stall point.In addition,the enhancement of radial vortex increases its entrainment ability,which tends to expand separation zone.Once the tip injection imposed,the decrease of the leakage vortex intensity widens the stall margin,while the total pressure loss increases to some extent due to the mixing of the tip micro jet with the mainstream.It is found that injection parameters should be restricted to a moderate region so as to achieve a good stall margin extension without an excessive increase in the pressure loss.展开更多
This paper presents a numerical investigation of an active tip-clearance control method based on cooling injectionfrom the blade tip surface. It aims to study the influences of air injection on controlling tip clearan...This paper presents a numerical investigation of an active tip-clearance control method based on cooling injectionfrom the blade tip surface. It aims to study the influences of air injection on controlling tip clearance flow, withemphasis on the effects of the injection location on secondary flow and the potential thermal benefits from thecooling jet. The results show that injection location plays an important role in the redistribution of secondary flowwithin the cascade passage. Injection located much closer to the pressure-side comer performs better in reducingtip clearance massflow and its associated losses. However, it also intensifies tip passage vortex, due to less restraintderiving from the reduced tip clearance vortex. Lower plenum total pressure is required to inject equivalentamount of cooling air, but the heat transfer condition on the blade tip surface is a bit worse than that with injectionfrom the reattachment region. Thus the optimum location of air injection should be at the tip separation vortex region.展开更多
The adaptive feedback control of stability with circumferential inlet distortion has been experimentally investigated in a low-speed,axial compressor.The flat-baffles with different span heights are used to simulate d...The adaptive feedback control of stability with circumferential inlet distortion has been experimentally investigated in a low-speed,axial compressor.The flat-baffles with different span heights are used to simulate different distorted inflow cases.Compared with auto-correlation and root-mean-square analysis,cross-correlation analysis used to predict early stall warning does not depend on the distortion position.Hence,the cross-correlation coefficient was used to monitor the stable status of the compressor and provide the feedback signal in the active control strategy when suffering from different distortions.Based on the stall margin improvement of tip air injection obtained under different distorted inflow cases and the sensitivity analysis of cross-correlation coefficients to injected momentum ratios,tip air injection was adopted as the actuator for adaptive feedback control.The digital signal processing controller was designed and applied to achieve adaptive feedback control in distorted inflow conditions.The results show that the adaptive feedback control of air injection nearly achieves the same stall margin improvement as steady air injection under different distortion intensities with a reduced injection mass flow.Thus,the proposed adaptive feedback control method is ideal for the engine operation with circumferential distorted inflow,which frequently occurs in flight.展开更多
The present paper introduces a new concept for passive turbine tip-leakage control. The basic idea of the method is the connection of the blade leading edge and the blade tip by an internal channel. Due to the differe...The present paper introduces a new concept for passive turbine tip-leakage control. The basic idea of the method is the connection of the blade leading edge and the blade tip by an internal channel. Due to the difference between the stagnation pressure at the leading edge and the low pressure at the blade tip, a small amount of the working fluid is extracted from the blade passage. At the blade tip, a jet is injected roughly perpendicular to the tip gap flow driven by the blade pressure difference. It is proposed that the jet blocks at least a part of the tip gap flow. Since the tip-leakage losses are proportional to the tip gap mass flow rate, the tip injection results in a reduction of the associated losses. After the introduction of the concept, an analytical model is presented which describes the reduction of the tip gap discharge coefficient due to the tip injection. Furthermore, the analytical model is supported by the results of a preliminary CFD analysis. Finally, the potential of the efficiency improvement by the passive blade tip injection method is reported.展开更多
基金the support of the National Natural Science Foundation of China(Nos.51576162 and51236006)The Doctorate Foundation of Northwestern Polytechnical University(No.CX201422)
文摘Parametric study of tip injection was implemented experimentally on a subsonic axial flow compressor to understand the underlying flow mechanisms of stability improvement of the compressor with discrete tip injection.Injector throat height varied from 2 to 6 times the height of rotor tip clearance,and circumferential coverage percentage ranged from 8.3% to 25% of the annulus.Static pressure fluctuations over the rotor tip were measured with fast-response pressure transducers.Whole-passage time-accurate simulations were also carried out to help us understand the flow details.The combinations of tip injection with traditional casing treatments were experimentally studied to generate an engineering-acceptable method of compressor stall control.The results indicate that the maximum stability improvement is achieved when injectors are choked despite their different sizes.The effect of circumferential coverage percentage on compressor stability depends on the value of injector throat height for un-choked injectors,and vice versa.Tip blockage in the blade passage is greatly reduced by the choked injectors,which is the primary reason for stability enhancement.The accomplishment of blockage diminishment is maintained in the circumferential direction with the unsteady effect of tip injection,which manifests as a hysteresis between the recovery of tip blockage and the recovery of tip leakage vortex.The unsteady effect is primarily responsible for the effectiveness of tip injection with a partial circumferential coverage.Tip injection cannot enhance the stability of the rotor with axial slots significantly,but it can improve the stability of the rotor with circumferential grooves further.The combined structure of tip injection with circumferential grooves is an alternative for engineering application.
基金supported by National Natural Science Foundation of China(No.52076179)National Science and Technology Major Projects of China(No.J2019-I-0011).
文摘A series of experiments and numerical simulations are carried out in a high-speed axial compressor to systematically investigate the influence and underlying flow mechanisms of micro tip injection on enhancing compressor stability.Different geometric structures of micro tip injection have been investigated,including the axial positions of injector port,injected mass flow rate and injector diameter.First,seven designed micro tip injection structures and one solid wall casing are tested in the compressor test rig to elucidate the influence of different micro tip injection parameters on the compressor stability.Then,numerical simulations are conducted to analyze the underlying flow mechanisms of micro tip injection with different design parameters on enhancing the compressor stability.The experimental and numerical investigation reveal that when the injection port is located upstream of the low-speed region,the compressor stability is significantly enhanced.The tip injection with larger injected mass flow can obtain higher stall margin improvement.Smaller injector diameter produces higher injection momentum and velocity,contributing to greater improvement on the compressor stability.
基金This work was supported by National Natural Science Foundation of China with project No.50406027.This support is gratefully acknowledged.
文摘A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolated axial compressor rotor is presented, intending to better understand the flow mechanism behind stall control measures that act on tip clearance flow. Under the influence of injection the unsteadiness of self-induced tip clearance flow could be weakened. Also the radial migration of tip clearance vortex is confined to a smaller radial extent near the rotor tip and the trajectory of tip clearance flow is pushed more downstream. So the injection is beneficial to improve compressor stability and increase static pressure rise near rotor tip region. The results of injection with different injected mass flow rates show that for the special type of injector adopted in the paper the effect of injection on tip clearance flow may be different according to the relative strength between these two streams of flow. For a fixed injected mass flow rate, reducing the injector area to increase injection velocity can improve the effect of injection on tip clearance flow and thus the compressor stability. A comparison of calculations between single blade passage and multiple blade passages validates the utility of single passage computations to investigate the tip clearance flow for the case without injection and its interaction with injected flow for the case with tip injection.
基金supported by the National Science and Technology Major Project,China(No.2017-III-0001-0025)the Interdisciplinary Innovation Foundation for Graduates at Nanjing University of Aeronautics and Astronautics in China(No.KXKCXJJ202002).
文摘A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine.Three perforated-rib layouts are considered,wherein a perforated rib is installed at(A)the Suction-Side squealer(SS-rib),(B)the Pressure-Side squealer(PS-rib),and(C)the additional squealer along the blade Camber Line(CL-rib).A numerical method is used to show how the novel rib layouts affect the aerodynamic performance of the tip leakage flow.Results show that the coolant jets issuing from the perforated-rib injection holes penetrate deeper into the tip clearance than those in the baseline squealer-tip case,and how the perforated-rib coolant injection affects the tip leakage flow depends strongly on the rib layout.The PS-rib and CL-rib layouts appear promising for controlling the tip leakage flow,playing a significant role in reducing the total pressure loss and improving the turbine blade’s isentropic efficiency.In particular,under an injection mass flow ratio of 1%and a tip clearance of 1%blade span,the PS-rib layout reduces the leakage mass flow rate by 27%and increases the isentropic efficiency by 1.25%compared with those in the baseline squealer-tip case.Meanwhile,the advantages of the PS-rib layout in tip leakage control are confirmed under small and large tip clearances.
文摘The mechanism of compressor stall margin enhancement using the tip air injection is explored.The transonic compressor,NASARotor 37,is taken as the object to study the tip clearance flow under active control of tip air injection by numerical simulations.The effects of injection parameters(injection total temperature,injection position,injection angle,injection mass flow,injection port size,injection type and etc)on the stall margin extension are emphatically analyzed.Results show that the enhancement of tip leakage vortex enlarges the low-energy region induced by the shock wave in the row channel when the working condition is moving to stall point.In addition,the enhancement of radial vortex increases its entrainment ability,which tends to expand separation zone.Once the tip injection imposed,the decrease of the leakage vortex intensity widens the stall margin,while the total pressure loss increases to some extent due to the mixing of the tip micro jet with the mainstream.It is found that injection parameters should be restricted to a moderate region so as to achieve a good stall margin extension without an excessive increase in the pressure loss.
文摘This paper presents a numerical investigation of an active tip-clearance control method based on cooling injectionfrom the blade tip surface. It aims to study the influences of air injection on controlling tip clearance flow, withemphasis on the effects of the injection location on secondary flow and the potential thermal benefits from thecooling jet. The results show that injection location plays an important role in the redistribution of secondary flowwithin the cascade passage. Injection located much closer to the pressure-side comer performs better in reducingtip clearance massflow and its associated losses. However, it also intensifies tip passage vortex, due to less restraintderiving from the reduced tip clearance vortex. Lower plenum total pressure is required to inject equivalentamount of cooling air, but the heat transfer condition on the blade tip surface is a bit worse than that with injectionfrom the reattachment region. Thus the optimum location of air injection should be at the tip separation vortex region.
基金co-supported by the National Natural Science Foundation of China(No.51922098)the National Science and Technology Major Project of China(No.2017-Ⅱ-0004-0017)the Special Fund for the Member of Youth Innovation Promotion Association of CAS(No.2018173).
文摘The adaptive feedback control of stability with circumferential inlet distortion has been experimentally investigated in a low-speed,axial compressor.The flat-baffles with different span heights are used to simulate different distorted inflow cases.Compared with auto-correlation and root-mean-square analysis,cross-correlation analysis used to predict early stall warning does not depend on the distortion position.Hence,the cross-correlation coefficient was used to monitor the stable status of the compressor and provide the feedback signal in the active control strategy when suffering from different distortions.Based on the stall margin improvement of tip air injection obtained under different distorted inflow cases and the sensitivity analysis of cross-correlation coefficients to injected momentum ratios,tip air injection was adopted as the actuator for adaptive feedback control.The digital signal processing controller was designed and applied to achieve adaptive feedback control in distorted inflow conditions.The results show that the adaptive feedback control of air injection nearly achieves the same stall margin improvement as steady air injection under different distortion intensities with a reduced injection mass flow.Thus,the proposed adaptive feedback control method is ideal for the engine operation with circumferential distorted inflow,which frequently occurs in flight.
文摘The present paper introduces a new concept for passive turbine tip-leakage control. The basic idea of the method is the connection of the blade leading edge and the blade tip by an internal channel. Due to the difference between the stagnation pressure at the leading edge and the low pressure at the blade tip, a small amount of the working fluid is extracted from the blade passage. At the blade tip, a jet is injected roughly perpendicular to the tip gap flow driven by the blade pressure difference. It is proposed that the jet blocks at least a part of the tip gap flow. Since the tip-leakage losses are proportional to the tip gap mass flow rate, the tip injection results in a reduction of the associated losses. After the introduction of the concept, an analytical model is presented which describes the reduction of the tip gap discharge coefficient due to the tip injection. Furthermore, the analytical model is supported by the results of a preliminary CFD analysis. Finally, the potential of the efficiency improvement by the passive blade tip injection method is reported.
