Control of Corner Separation to Enhance Stability in a Linear Compressor Cascade by Boundary Layer Suction

The loss-generating mechanism of a linear compressor cascade at the corner stall condition was numerically studied in this paper. The hybrid RANS/LES method was used to perform the high-fidelity simulations. By comparing the results captured by SSTDES, DDES, SAS models with the experimental data, the SSTDES model is proven to be more accurate in capturing the detailed flow structure of the corner stall than the other two models. Taking the turbulence dissipation term of SSTDES model into account, the volumetric entropy generation rate and a new dimensionless local loss coefficient are proposed and used to analyze the loss-generating mechanism in this work. It was found that the main flow loss generated in this cascade could be sorted as the wake flow loss, the profile loss, the secondary flow loss and the endwall loss according to their amounts. The corner separation significantly affects the secondary flow loss, wake flow loss and profile loss in the cascade passage. The mixing between the separated boundary layer flow and the main flow, the shear between a tornado vortex and the main flow are the main sources of the secondary flow loss. The wake flow loss is the largest loss source of the cascade, accounting for 41.8% of the total loss. There are two peaks of the wake flow loss along the spanwise direction near the corner stall region. This phenomenon is related to the appearance of large velocity gradient flows when the main flows and the corner separation flows mix together. The profile loss takes up 40.06 % of the total loss. The profile loss intensity in the corner region is lower than the mid blade span due to the interaction of the boundary layer on the suction side with the corner separation.

Download Full-text

Numerical Investigation of Intermittent Corner Separation in a Linear Compressor Cascade

Volume 2A: Turbomachinery ◽

10.1115/gt2016-57311 ◽

2016 ◽

Cited By ~ 1

Author(s):

Wei Ma ◽

Feng Gao ◽

Xavier Ottavy ◽

Lipeng Lu ◽

A. J. Wang

Keyword(s):

Flow Field ◽

Large Scale ◽

Leading Edge ◽

Suction Side ◽

Detached Eddy Simulation ◽

Compressor Cascade ◽

Linear Compressor ◽

Corner Separation ◽

Eddy Simulation ◽

Linear Compressor Cascade

Recently bimodal phenomenon in corner separation has been found by Ma et al. (Experiments in Fluids, 2013, doi:10.1007/s00348-013-1546-y). Through detailed and accurate experimental results of the velocity flow field in a linear compressor cascade, they discovered two aperiodic modes exist in the corner separation of the compressor cascade. This phenomenon reflects the flow in corner separation is high intermittent, and large-scale coherent structures corresponding to two modes exist in the flow field of corner separation. However the generation mechanism of the bimodal phenomenon in corner separation is still unclear and thus needs to be studied further. In order to obtain instantaneous flow field with different unsteadiness and thus to analyse the mechanisms of bimodal phenomenon in corner separation, in this paper detached-eddy simulation (DES) is used to simulate the flow field in the linear compressor cascade where bimodal phenomenon has been found in previous experiment. DES in this paper successfully captures the bimodal phenomenon in the linear compressor cascade found in experiment, including the locations of bimodal points and the development of bimodal points along a line that normal to the blade suction side. We infer that the bimodal phenomenon in the corner separation is induced by the strong interaction between the following two facts. The first is the unsteady upstream flow nearby the leading edge whose angle and magnitude fluctuate simultaneously and significantly. The second is the high unsteady separation in the corner region.

Download Full-text

Control of Corner Separation in a Linear Highly Loaded Compressor Cascade by Boundary Layer Suction

Fluid-Structure-Sound Interactions and Control - Lecture Notes in Mechanical Engineering ◽

10.1007/978-3-662-48868-3_49 ◽

2015 ◽

pp. 307-311

Author(s):

Yangwei Liu ◽

Jinjing Sun ◽

Lipeng Lu

Keyword(s):

Boundary Layer ◽

Compressor Cascade ◽

Corner Separation ◽

Boundary Layer Suction ◽

Highly Loaded

Download Full-text

Unsteady Pressure Investigations of Corner Separated Flow in a Linear Compressor Cascade

Volume 2C: Turbomachinery ◽

10.1115/gt2015-42073 ◽

2015 ◽

Cited By ~ 5

Author(s):

Gherardo Zambonini ◽

Xavier Ottavy

Keyword(s):

Transfer Functions ◽

Leading Edge ◽

Positive Pressure ◽

Compressor Cascade ◽

Suction Surface ◽

Linear Compressor ◽

Corner Separation ◽

Unsteady Pressure ◽

Linear Compressor Cascade ◽

End Wall

The aim of this work is to present detailed unsteady pressure measurements of three-dimensional flow field in a NACA 65 linear compressor cascade. Chord-based Reynolds number of 382000 and incidence angle of 4 degrees were chosen as target configuration of the rig, which clearly presents the corner separation phenomenon at the juncture of the blade suction side and the end-wall. Concerning the experiments, a characterization of the mean and fluctuating component of wall static pressure on the surface of a specially developed blade is achieved at first. This fluctuating component is investigated utilizing nineteen high sensitivity condenser microphones plugged into blade cavities which have been carefully calibrated. Transfer functions obtained by calibration are exploited to reconstruct the time-dependent pressure signal and finally statistics, conditional ensemble averages, coherence and spectra analyses of fluctuations are presented in order to investigate the unsteady characteristics of the corner separation. High values of root mean square are individuated near the leading edge and in the separation region on the suction surface of the blade. Skewness and kurtosis show an intermittent behavior of the separation onset, which moves upstream and downstream on the suction surface. This intermittency of the separation line is probably linked with the existence of a bimodal behavior of the size of the corner separation. The analyses of coherence and conditional ensemble average between the signals at the leading edge and at the onset of the separation suggest a critical influence of angle and velocity of the incoming end-wall boundary layer on the positive pressure signatures of the shear layer, which characterize the inception of the separation.

Download Full-text

Location Effect of Boundary Layer Suction on Compressor Hub-Corner Separation

Volume 2A: Turbomachinery ◽

10.1115/gt2014-25043 ◽

2014 ◽

Cited By ~ 3

Author(s):

Ping-Ping Chen ◽

Wei-Yang Qiao ◽

Karsten Liesner ◽

Robert Meyer

Keyword(s):

Boundary Layer ◽

Pressure Loss ◽

Total Pressure ◽

Three Dimensional ◽

Base Flow ◽

Total Pressure Loss ◽

Compressor Cascade ◽

Suction Surface ◽

Corner Separation ◽

Boundary Layer Suction

The large secondary flow area in the compressor hub-corner region usually leads to three-dimensional separation in the passage with large amounts of total pressure loss. In this paper numerical simulations of a linear high-speed compressor cascade, consisting of five NACA 65-K48 stator profiles, were performed to analyze the flow mechanism of hub-corner separation for the base flow. Experimental validation is used to verify the numerical results. Active control of the hub-corner separation was investigated by using boundary layer suction. The influence of the selected locations of the endwall suction slot was investigated in an effort to quantify the gains of the compressor cascade performance. The results show that the optimal chordwise location should contain the development section of the three-dimensional corner separation downstream of the 3D corner separation onset. The best pitchwise location should be close enough to the vanes’ suction surface. Therefore the optimal endwall suction location is the MTE slot, the one from 50% to 75% chord at the hub, close to the blade suction surface. By use of the MTE slot with 1% suction flow ratio, the total-pressure loss is substantially decreased by about 15.2% in the CFD calculations and 9.7% in the measurement at the design operating condition.

Download Full-text