Effect of a blade end slot on supersonic compressor cascade hub-corner separation

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

LES Investigation of Boussinesq Constitutive Relation Validity in a Corner Separation Flow

Volume 2C: Turbomachinery ◽

10.1115/gt2018-75792 ◽

2018 ◽

Author(s):

Jean-François Monier ◽

Nicolas Poujol ◽

Mathieu Laurent ◽

Feng Gao ◽

Jérôme Boudet ◽

...

Keyword(s):

Strain Rate ◽

Stress Tensor ◽

Reynolds Stress ◽

Constitutive Relation ◽

Strain Rate Tensor ◽

Separation Flow ◽

Compressor Cascade ◽

Corner Separation ◽

Reynolds Stress Tensor ◽

Mean Strain

The present study aims at analysing the Boussinesq constitutive relation validity in a corner separation flow of a compressor cascade. The Boussinesq constitutive relation is commonly used in Reynolds-averaged Navier-Stokes (RANS) simulations for turbomachinery design. It assumes an alignment between the Reynolds stress tensor and the zero-trace mean strain-rate tensor. An indicator that measures the alignment between these tensors is used to test the validity of this assumption in a high fidelity large-eddy simulation. Eddy-viscosities are also computed using the LES database and compared. A large-eddy simulation (LES) of a LMFA-NACA65 compressor cascade, in which a corner separation is present, is considered as reference. With LES, both the Reynolds stress tensor and the mean strain-rate tensor are known, which allows the construction of the indicator and the eddy-viscosities. Two constitutive relations are evaluated. The first one is the Boussinesq constitutive relation, while the second one is the quadratic constitutive relation (QCR), expected to render more anisotropy, thus to present a better alignment between the tensors. The Boussinesq constitutive relation is rarely valid, but the QCR tends to improve the alignment. The improvement is mainly present at the inlet, upstream of the corner separation. At the outlet, the correction is milder. The eddy-viscosity built with the LES results are of the same order of magnitude as those built as the ratio of the turbulent kinetic energy k and the turbulence specific dissipation rate ω. They also show that the main impact of the QCR is to rotate the mean strain-rate tensor in order to realign it with the Reynolds stress tensor, without dilating it.

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

Modification of Shear Stress Transport Turbulence Model Using Helicity for Predicting Corner Separation Flow in a Linear Compressor Cascade

Journal of Turbomachinery ◽

10.1115/1.4045658 ◽

2020 ◽

Vol 142 (2) ◽

Cited By ~ 1

Author(s):

Yangwei Liu ◽

Yumeng Tang ◽

Ashley D. Scillitoe ◽

Paul G. Tucker

Keyword(s):

Shear Stress ◽

Turbulence Model ◽

Incidence Angle ◽

Computational Cost ◽

Separation Flow ◽

Compressor Cascade ◽

Production Term ◽

Corner Separation ◽

Shear Stress Transport ◽

Sst Model

Abstract Three-dimensional corner separation significantly affects compressor performance, but turbulence models struggle to predict it accurately. This paper assesses the capability of the original shear stress transport (SST) turbulence model to predict the corner separation in a linear highly loaded prescribed velocity distribution (PVD) compressor cascade. Modifications for streamline curvature, Menter’s production limiter, and the Kato-Launder production term are examined. Comparisons with experimental data show that the original SST model and the SST model with different modifications can predict the corner flow well at an incidence angle of −7 deg, where the corner separation is small. However, all the models overpredict the extent of the flow separation when the corner separation is larger, at an incidence angle of 0 deg. The SST model is then modified using the helicity to take account of the energy backscatter, which previous studies have shown to be important in the corner separation regions of compressors. A Reynolds stress model (RSM) is also used for comparison. By comparing the numerical results with experiments and RSM results, it can be concluded that sensitizing the SST model to helicity can greatly improve the predictive accuracy for simulating the corner separation flow. The accuracy is quite competitive with the RSM, whereas in terms of computational cost and robustness it is superior to the RSM.

Download Full-text

Investigation of Leading Edge Tubercles with Different Wavelengths in an Annular Compressor Cascade

International Journal of Turbo and Jet Engines ◽

10.1515/tjj-2017-0064 ◽

2018 ◽

Vol 0 (0) ◽

Cited By ~ 1

Author(s):

Tan Zheng ◽

Xiaoqing Qiang ◽

Jinfang Teng ◽

Jinzhang Feng

Keyword(s):

Leading Edge ◽

Humpback Whales ◽

Wave Number ◽

Loss Reduction ◽

Streamwise Vortices ◽

Compressor Cascade ◽

Corner Separation ◽

Stall Angle ◽

Geometry Parameter ◽

And Behavior

Abstract Humpback whales possess bumpy tubercles on the leading edge of their flippers. Due to these leading edge tubercles, whales are able to produce high degree of maneuverability. Inspired by the flippers, this paper applies sinusoidal-like tubercles to the leading edge of blades in an annular compressor cascade, and presents a numerical investigation to explore the effects of tubercles with the aim of controlling the corner separation and reducing losses. Steady 3D RANS simulations are performed to investigate the aerodynamic performance and behavior of the corner separation in compressor cascades with and without leading edge tubercles. A crucial geometry parameter of the tubercles, wavelength, is varied to obtain different configurations. Results show that a smaller wavelength (more wave number) corresponds to a larger loss reduction and the maximum loss reduction reaches to 46.0%. Also, it is found that leading edge tubercles result in a stall delay and the maximum stall angle improvement reaches to 28.1%. Flow visualizations show that leading edge tubercles could induce the formation of counter-rotating streamwise vortices. The interaction between the streamwise vortices and corner separation is thought to be the primary flow mechanism generated by leading edge tubercles in an annular compressor cascade.

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