Numerical Study on Unsteadiness of Tip Clearance Flow Induced by Downstream Stator Row in Axial Compressor

2010 ◽  
Author(s):  
Yoojun Hwang ◽  
Shin-Hyoung Kang ◽  
Sungryoung Lee
Keyword(s):  
Flow Rate ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Performance Data ◽  
Tip Clearance ◽  
Inlet Guide Vane ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Rotating Instability

Numerical calculations were done to investigate unsteady flows through the tip clearance in an axial compressor. The first stage of a low speed research axial compressor with an inlet guide vane was examined after it had been confirmed that the numerically calculated performance data was in good agreement with the experimentally measured performance data. Special attention was paid to the flow during the operation of the compressor when the flow rate was low to study the flow behavior near stall. The estimated performance and the flow pattern of the compressor were found to be related to the unsteadiness of the tip leakage flow altered by the potential effect from the downstream stator row blades. It was shown that the unsteady flow calculations are necessary to predict the performance of an axial compressor, in particular, for low flow rates. On the other hand, rotating instability vortices developed due to unsteady tip leakage flow as the flow rate decreased. It was found that the flow structures corresponding to the rotating instability were merging as the flow rate decreased and the speed of the rotating instability varied with the operating conditions. Consequently, this leads to a non-synchronous vibration frequency.

Some effects of non-axisymmetric tip clearance layout on axial compressor aerodynamics

2021 ◽  
pp. 095765092110470
Author(s):  
Haohao Zhang ◽  
Haowan Zhuang ◽  
Jinfang Teng ◽  
Mingmin Zhu ◽  
Xiaoqing Qiang
Keyword(s):  
Transient Flow ◽  
Axial Compressor ◽  
Flow Fields ◽  
Tip Clearance ◽  
Inlet Guide Vane ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Overall Performance

A steady and unsteady numerical research is carried out to explore some effects of a specific non-axisymmetric tip clearance layout on the overall performance and stability of an axial compressor stage. For a 4-stage low-speed research compressor (LSRC) in Shanghai Jiao Tong University (SJTU), one-eighth annulus of the inlet guide vane and the first stage rotor was modeled for this study. After the validation for the uniform tip clearance case, a specific non-axisymmetric tip clearance layout is chosen from several random cases generated by the Gaussian Probabilistic Density Function method. Unsteady time-averaged results at the near stall condition show that the chosen non-axisymmetric layout can improve the isentropic efficiency by 1.3% and extend the stall margin by 4%. Detailed analyses on flow fields are carried out to interpret the performance improvement. Due to the circumferential layout of clearance sizes, the inlet mass flow and incidence are redistributed in both the radial and circumferential directions. It leads to blade loading and tip leakage flow varying with the tip clearance size. The quantification of blockage manifests that the blockage arising from the tip leakage flow is significantly alleviated in the non-axisymmetric layout, which leads to improvements in overall performance and stall margin. Transient flow fields at the rotor tip are also analyzed at the near stall condition. For the non-axisymmetric layout, low-momentum regions originating from larger clearance sizes oscillate and develop downstream in one blade passage period.

A Proposal for Passive Wall Treatment Applied in High Performance Axial Flow Compressors

2020 ◽  
Author(s):  
Rubén Bruno Díaz ◽  
Jesuino Takachi Tomita ◽  
Cleverson Bringhenti ◽  
Francisco Carlos Elizio de Paula ◽  
Luiz Henrique Lindquist Whitacker
Keyword(s):  
Stokes Equations ◽  
Axial Compressor ◽  
Axial Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Smooth Wall ◽  
Tip Leakage Flow ◽  
Viscous Effects ◽  
Stall Margin ◽  
Tip Leakage

Abstract Numerical simulations were carried out with the purpose of investigating the effect of applying circumferential grooves at axial compressor casing passive wall treatment to enhance the stall margin and change the tip leakage flow. The tip leakage flow is pointed out as one of the main contributors to stall inception in axial compressors. Hence, it is of major importance to treat appropriately the flow in this region. Circumferential grooves have shown a good performance in enhancing the stall margin in previous researches by changing the flow path in the tip clearance region. In this work, a passive wall treatment with four circumferential grooves was applied in the transonic axial compressor NASA Rotor 37. Its effect on the axial compressor performance and the flow in the tip clearance region was analyzed and set against the results attained for the smooth wall case. A 2.63% increase in the operational range of the axial compressor running at 100%N, was achieved, when compared with the original smooth wall casing configuration. The grooves installed at compressor casing, causes an increase in the flow entropy generation due to the high viscous effects in this gap region, between the rotor tip surface and casing with grooves. These viscous effects cause a drop in the turbomachine efficiency. For the grooves configurations used in this work, an efficiency drop of 0.7% was observed, compared with the original smooth wall. All the simulations were performed based on 3D turbulent flow calculations using Reynolds Averaged Navier-Stokes equations, and the flow eddy viscosity was determined using the two-equation SST turbulence model. The details of the grooves geometrical dimensions and its implementation are described in the paper.

Stall Inception and Development Process Due to Tip Leakage Flow in Axial Compressor Rotor Blades Row

2014 ◽  
Vol 30 (3) ◽  
pp. 307-313 ◽  
Author(s):  
R. Taghavi-Zenou ◽  
S. Abbasi ◽  
S. Eslami
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Leading Edge ◽  
Rotor Blades ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Compressor Rotor

ABSTRACTThis paper deals with tip leakage flow structure in subsonic axial compressor rotor blades row under different operating conditions. Analyses are based on flow simulation utilizing computational fluid dynamic technique. Three different circumstances at near stall condition are considered in this respect. Tip leakage flow frequency spectrum was studied through surveying instantaneous static pressure signals imposed on blades surfaces. Results at the highest flow rate, close to the stall condition, showed that the tip vortex flow fluctuates with a frequency close to the blade passing frequency. In addition, pressure signals remained unchanged with time. Moreover, equal pressure fluctuations at different passages guaranteed no peripheral disturbances. Tip leakage flow frequency decreased with reduction of the mass flow rate and its structure was changing with time. Spillage of the tip leakage flow from the blade leading edge occurred without any backflow in the trailing edge region. Consequently, various flow structures were observed within every passage between two adjacent blades. Further decrease in the mass flow rate provided conditions where the spilled flow ahead of the blade leading edge together with trailing edge backflow caused spike stall to occur. This latter phenomenon was accompanied by lower frequencies and higher amplitudes of the pressure signals. Further revolution of the rotor blade row caused the spike stall to eventuate to larger stall cells, which may be led to fully developed rotating stall.

Characteristics of the Tip Leakage Vortex in a Low-Speed Axial Compressor With Different Rotor Tip Gaps

2012 ◽  
Author(s):  
Zhibo Zhang ◽  
Xianjun Yu ◽  
Baojie Liu
Keyword(s):  
Axial Compressor ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Tip Clearance ◽  
Test Facility ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

The detailed evolutionary processes of the tip leakage flow/vortex inside the rotor passage are still not very clear for the difficulties of investigating of them by both experimental and numerical methods. In this paper, the flow fields near the rotor tip region inside the blade passage with two tip gaps, 0.5% and 1.5% blade height respectively, were measured by using stereoscopic particle image velocimetry (SPIV) in a large-scale low speed axial compressor test facility. The measurements are conducted at four different operating conditions, including the design, middle, maximum static pressure rise and near stall conditions. In order to analyze the variations of the characteristics of the tip leakage vortex (TLV), the trajectory, concentration, size, streamwise velocity, and the blockage parameters are extracted from the ensemble-averaged results and compared at different compressor operating conditions and tip gaps. The results show that the formation of the TLV is delayed with large tip clearance, however, its trajectory moves much faster in an approximately linear way from the blade suction side to pressure side. In the tested compressor, the size of the tip gap has little effects on the scale of the TLV in the spanwise direction, on the contrary, its effects on the pitch-wise direction is very prominent. Breakdown of the TLV were both found at the near-stall condition with different tip gaps. The location of the initiation of the TLV breakdown moves downstream from the 60% chord to 70% chord as the tip gap increases. After the TLV breakdown occurs, the flow blockage near the rotor tip region increases abruptly. The peak value of the blockage effects caused by the TLV breakdown is doubled with the tip gap size increasing from 0.5% to 1.5% blade span.

The Influence of Tip Clearance Momentum Flux on Stall Inception in a High-Speed Axial Compressor

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Joshua D. Cameron ◽  
Matthew A. Bennington ◽  
Mark H. Ross ◽  
Scott C. Morris ◽  
Juan Du ◽  
...  
Keyword(s):  
Momentum Flux ◽  
High Speed ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Axial Position ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage

Experimental and numerical studies were conducted to investigate tip-leakage flow and its relationship to stall in a transonic axial compressor. The computational fluid dynamics (CFD) results were used to identify the existence of an interface between the approach flow and the tip-leakage flow. The experiments used a surface-streaking visualization method to identify the time-averaged location of this interface as a line of zero axial shear stress at the casing. The axial position of this line, denoted xzs, moved upstream with decreasing flow coefficient in both the experiments and computations. The line was consistently located at the rotor leading edge plane at the stalling flow coefficient, regardless of inflow boundary condition. These results were successfully modeled using a control volume approach that balanced the reverse axial momentum flux of the tip-leakage flow with the momentum flux of the approach fluid. Nonuniform tip clearance measurements demonstrated that movement of the interface upstream of the rotor leading edge plane leads to the generation of short length scale rotating disturbances. Therefore, stall was interpreted as a critical point in the momentum flux balance of the approach flow and the reverse axial momentum flux of the tip-leakage flow.

Numerical Study on Unsteadiness of Tip Clearance Flow and Performance Prediction of Axial Compressor

2011 ◽  
Author(s):  
Yoojun Hwang ◽  
Shin-Hyoung Kang
Keyword(s):  
Flow Characteristic ◽  
Numerical Study ◽  
Axial Compressor ◽  
Wave Pattern ◽  
Performance Data ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Blade Passage ◽  
Rotating Speed ◽  
Rotating Instability

Numerical calculations were performed to investigate unsteady features of tip clearance leakage flow in an axial compressor. The first stage rotor of a low speed axial compressor with a large tip clearance was examined. It was confirmed that the numerically calculated performance data were in good agreement with the experimentally measured performance data. Using frequency analysis, the flow characteristic near the casing induced by tip clearance leakage flow was found to be not associated with the rotating speed of the rotor. This characteristic is called rotating instability or self-induced unsteadiness. We found that the circumferential length scale of the rotating instability of the compressor was longer than a pitch of a blade passage; therefore, a multi-blade passage was adopted to study the flow structure more precisely. The flow characteristic was described by the frequency, the circumferential length, and the phase velocity, and was changed by operating points toward stall. The behavior of the flow was characterized by circumferentially traveling waves. Hence, the mechanism governing the development of the unsteady feature was further examined in terms of the rotating wave pattern of the pressure distribution. Furthermore, the unsteady feature of the tip clearance leakage flow affected the prediction of compressor performance by altering blockage, flow turning, and loss near the casing.

Numerical Study on the Effects of Casing Treatment on Unsteadiness of Tip Leakage Flow in an Axial Compressor

2012 ◽  
Author(s):  
Yoojun Hwang ◽  
Shin-Hyoung Kang
Keyword(s):  
Numerical Study ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Operating Range ◽  
Compressor Rotor ◽  
Flow Through

A low speed axial compressor with casing treatment of axial slots was numerically investigated. Time-accurate numerical calculations were performed to simulate unsteady flow in the rotor tip region and the effects of casing treatment on the flow. Since the compressor rotor had a large tip clearance, it was found that the tip leakage flow had an inherent unsteady feature that was not associated with rotor rotation. The unsteadiness of the tip leakage flow was induced by changes in the blade loading due to the pressure distribution formed by the tip leakage flow. This characteristic is called rotating instability or self-induced unsteadiness. The frequency of the flow oscillation was found to decrease as the flow rate was reduced. On the other hand, as expected, the operating range was improved by casing treatment, as shown by calculations in good agreement with the experimentally measured data. The unsteadiness of the tip leakage flow was alleviated by the casing treatment. The interaction between the flow in the tip region and the re-circulated flow through the axial slots was observed in detail. The removal and injection of flow through the axial slots were responsible not only for the extension of the operating range but also for the alleviation of the unsteadiness. Analyses of instantaneous flow fields explained the mechanism of the interaction between the casing treatment and the unsteady oscillation of the tip leakage flow. Furthermore, the effects of changes in the amount of re-circulation and the location of the removal and injection flow on the unsteadiness of the tip leakage flow were examined.

Unsteady Investigation on Tip Flow Field and Rotating Stall in Counter-Rotating Axial Compressor

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Limin Gao ◽  
Ruiyu Li ◽  
Fang Miao ◽  
Yutong Cai
Keyword(s):  
Flow Field ◽  
Second Harmonic ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Tip Leakage ◽  
Future Goals

Contra-rotating axial compressor/fan (CRAC) is a promising technology to meet the future goals aircraft industry. Massive time accurate simulations are performed to investigate rotating stall in CRAC containing two counter-rotating rotors. Particularly, the back pressure increasing with a very small step to avoid missing flow field transition from stability to instability. Due to the canceling of the stator, the instability of downstream rotor is more stronger. The present studies mostly focus on the downstream rotor. The tip leakage flow field is analyzed in detail under near stall condition, which indicates that a secondary leakage flow plays an important role in the unsteadiness of CRAC's unsteady flow field. The frequency analysis in the tip clearance of downstream rotor under multiple near stall conditions captured the transition of the second harmonic frequency which can be used as stall inception signal. Moreover, the rotating stall onset process in real CRAC is simulated on the numerical stall.

Numerical investigation of tip clearance size effect on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor

2017 ◽  
Vol 231 (3) ◽  
pp. 474-484 ◽  
Author(s):  
Xiaochen Mao ◽  
Bo Liu
Keyword(s):  
Size Effect ◽  
Axial Compressor ◽  
Size Variation ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Remarkable Effect ◽  
Tip Leakage ◽  
Dual Stage ◽  
The Impact

Based on a validation of the numerical methods with an experiment, numerical simulations are carried out to study the effect of tip clearance size on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor. The predicted results showed that the variation of the tip clearance size in rotor2 has a more significant impact on the overall performance and stall margin of the compressor. In addition, the impact of the tip clearance size effect is mainly on the rotor with the tip clearance size variation. The variation of the tip clearance size in rotor2 almost has no influence on the performance of rotor1, while the performance of rotor2 is increased about 1.37% at near-stall point when the tip clearance size of rotor1 is increased to 1.0 mm from 0.5 mm. At peak efficiency condition, the tip clearance size variation in rotor1 has remarkable influence on the tip leakage vortex intensity, onset point and trajectory in rotor1, but has little influence on those in rotor2. However, the tip clearance size variation in rotor2 has remarkable effect on those in both rotors. Different tip clearance size combination schemes can impact the stall-free characteristic in the counter-rotating axial compressor.

Numerical simulation of unsteady tip clearance flow in an isolated axial compressor rotor blades row

2011 ◽  
Vol 226 (1) ◽  
pp. 82-93 ◽  
Author(s):  
R Taghavi-Zenouz ◽  
S Eslami
Keyword(s):  
Experimental Data ◽  
Axial Compressor ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Clearance Flow

Three-dimensional unsteady numerical simulations were carried out to analyse tip clearance flow in a low-speed isolated axial compressor rotor blades row. A flow solver has been used for the current study utilizing the large eddy simulation (LES) technique. Periodic tip leakage flow and its propagation trajectories were simulated in detail. A number of pseudo pressure transducers were imposed on the pressure side of the blade for detection of unsteady surface pressures to provide a calculation of tip leakage flow frequencies. Two different sizes of tip clearance were considered for simulations and analyses. Non-dimensional frequencies of the tip leakage flow were calculated and final results were compared to those of existing numerical and experimental data. Final results demonstrated that in contrast to the Reynolds averaged Navier–Stokes (RANS) model, the LES method shows considerable dependency of frequency characteristics of the tip leakage flow to the gap size and can detect different frequency spectrums along the blade surface. All the results obtained through the current numerical approach were in close agreement with those of existing experimental data.

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