Investigation of Vortical Structures and Turbulence Characteristics in Corner Separation in a Linear Compressor Cascade Using DDES

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Yangwei Liu ◽  
Hao Yan ◽  
Lipeng Lu ◽  
Qiushi Li
Keyword(s):  
Wall Region ◽  
Detached Eddy Simulation ◽  
Reynolds Stresses ◽  
Compressor Cascade ◽  
Turbulence Characteristics ◽  
Vortical Structures ◽  
Corner Separation ◽  
Corner Region ◽  
Passage Vortex ◽  
Corner Vortex

Three-dimensional (3D) corner separation in a linear highly loaded compressor cascade is studied by using delayed detached-eddy simulation (DDES) method. This paper studies the flow mechanism of corner separation, including vortical structures and turbulence characteristics. The vortical structures are analyzed and the distributions of Reynolds stresses and turbulent anisotropy are also discussed in detail. The results show that there exist different kinds of vortical structures, such as horseshoe vortex, passage vortex, wake shedding vortex, and “corner vortex.” Before the corner separation forms, the passage vortex becomes the main secondary vortex and obviously enhances the corner separation. At approximate 35% chord position, the corner vortex begins to form, enlarges rapidly, and dominates the secondary flow in the cascade. The corner vortex is a compound vortex with its vortex core composed of multiple vortices. Streamwise normal Reynolds stress contributes greatest to the turbulence fluctuation in the corner region. The turbulence develops from two-dimensional (2D) turbulence in the near-wall region to one-component type turbulence in the corner region. The turbulence tends to be more anisotropic when the flow is close to the endwall within the corner separation region.

An Experimental Study of Streamwise Vortices in a Compressor Cascade

1988 ◽  
Author(s):  
Chen Fang ◽  
Chen Mao-Zhang ◽  
Jiang Hao-Kang
Keyword(s):  
Experimental Study ◽  
Vortex Pair ◽  
Secondary Vortex ◽  
Streamwise Vortices ◽  
Reynolds Stresses ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Mean Velocity ◽  
Passage Vortex ◽  
Corner Vortex

An experimental study on the production and development of streamwise vortices in a compressor cascade is reported. At four locations inside and one location outside the blade passage, the mean velocity components, three turbulent intensities and three Reynolds stresses were measured with a “x” hot wire probe. The results obtained describe the flow structure in the corner between the end-wall and blade suction surface in detail. Besides a passage vortex within the passage, there exist a shed corner vortex pair and a secondary vortex pair in the corner. The characteristics of two vortex pairs were different from that of the passage vortex. The mechanism causing the shed corner vortex pair and secondary vortex pair and the effect of these vortices on the cascade losses are discussed.

Numerical Study of the Effect of Secondary Vortex on Three-Dimensional Corner Separation in a Compressor Cascade

2016 ◽  
Vol 33 (1) ◽  
Author(s):  
Yangwei Liu ◽  
Hao Yan ◽  
Lipeng Lu
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Horseshoe Vortex ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Complex Flow ◽  
Suction Surface ◽  
Corner Separation ◽  
Delayed Detached Eddy Simulation ◽  
Passage Vortex

AbstractThe complex flow structures in a linear compressor cascade have been investigated under different incidences using both the Reynolds-averaged Navier–Stokes (RANS) and delayed detached eddy simulation (DDES) methods. The current study analyzes the development of horseshoe vortex and passage vortex in a compressor cascade based on DDES results and explores the effect of the passage vortex on corner separation using the RANS method. Results show that the effect of horseshoe vortex on three-dimensional corner separation is weak, whereas the effect of passage vortex is dominant. A large vortex breaks into many small vortices in the corner separation region, thereby resulting in strong turbulence fluctuation. The passage vortex transports the low-energetic flow near the endwall to the blade suction surface and enlarges corner separation in the cascade. Hence, total pressure loss increases in the cascade.

A Study of Corner Separation in a Linear Compressor Cascade Based on SBES Model

2019 ◽  
Author(s):  
Bingxiao Lu ◽  
Jinfang Teng ◽  
Mingmin Zhu ◽  
Xiaoqing Qiang ◽  
Wei Ma
Keyword(s):  
Large Scale ◽  
Incidence Angle ◽  
Separated Flow ◽  
Turbulent Fluctuation ◽  
Separation Region ◽  
Reynolds Stresses ◽  
Compressor Cascade ◽  
Vortical Structures ◽  
Corner Separation ◽  
Turbulent Characteristics

Abstract Under the condition of large incidence angle in an axial compressor, corner separation will occur in corner region. When the blade loading increases, there may even be corner stall. This three dimensional complex flow structure is high intermittent and unsteady. In order to study the flow mechanisms, a hybrid RANS/LES turbulence model (SBES) was used to simulate the corner separation in the cascade. Firstly, the evolution of vortical structures in the corner separation region were analyzed. The boundary layer and the backflow in the corner separation region encounter, forming vortices with opposite rotation and developing downstream continuously. This cause the unsteady flow in corner separation. In addition, the shedding of detached eddies at the trailing edge is another sources of unsteadiness. Secondly, based on studying the turbulent characteristics, it can be seen that there is active turbulent fluctuation in the corner separation region. The turbulence is high anisotropic because the distribution and the values of Reynolds stresses in different directions are quite different. Thirdly, the mechanism of bimodal phenomenon was explained in this paper. Bimodal means there are two peaks in the velocity probability histogram, it is found in the region between separated flow and non-separated flow. This indicates that there are two non-periodic switching flow modes. Through the analysis of this paper, we find that it is related to the development of large scale coherent vortical structures.

Numerical Investigation of Intermittent Corner Separation in a Linear Compressor Cascade

2016 ◽  
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.

scholarly journals Investigation of Vortical Structures and Turbulence Characteristics in Corner Separation in an Axial Compressor Stator Using DDES

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2123
Author(s):  
Jun Li ◽  
Jun Hu ◽  
Chenkai Zhang
Keyword(s):  
Three Dimensional ◽  
Axial Compressor ◽  
Suction Side ◽  
Turbulence Energy ◽  
Separation Flow ◽  
Mechanism Analysis ◽  
Separation Region ◽  
Detached Eddy Simulation ◽  
Vortical Structures ◽  
Corner Separation

In order to investigate the flow structure and unsteady behavior of three-dimensional corner separation, a delayed detached-eddy simulation (DDES) method based on the Spalart–Allmaras (SA) model is performed on the third-stage stator of a multistage low-speed axial compressor. The stator simulation is validated by experiments before flow mechanism analysis. The complicated flow fields in the stator are then described step by step. Firstly, the structure and development process of vortices in corner separation flow are analyzed. Secondly, the velocity histogram of the monitor points in the mainstream and corner separation regions is obtained, and the velocity distribution of the corner separation region is discussed. Finally, Reynolds stress, Lumley anisotropy, turbulence energy spectra, and helicity density are discussed to understand the turbulence behavior of the corner separation flow in the stator. The results show that the corner separation appears at even the design condition and different kinds of vortical structures appear in the stator hub corner. The unsteadiness of corner separation flow is mainly reflected in the separation on the suction side of the blade and the wake shedding. Turbulence anisotropy and energy backscatter are found to be dominant in the separation region, which is correlated to the high shear stress.

Experimental investigation on the performance of compressor cascade using blended-blade-end-wall contouring technology

2017 ◽  
Vol 232 (15) ◽  
pp. 2833-2844 ◽  
Author(s):  
Weilin Yi ◽  
Lucheng Ji
Keyword(s):  
Three Dimensional ◽  
Cross Flow ◽  
Control Flow ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Three Dimensional Flow ◽  
Turning Angle ◽  
Corner Region ◽  
Passage Vortex ◽  
End Wall

Three-dimensional flow separations commonly occur in the corner region formed by the blade suction surface and end wall in compressors. How to control or reduce these separations is a vital problem for aerodynamic designers all the time. Blended blade and end wall contouring technology has been proposed to control flow separation for several years and validated in many cases using the numerical method, but experimental data was not obtained so far. So in this paper, the baseline cascade scaling from the NACA65 airfoil with 42° turning angle is designed, tested, and analyzed firstly. Then, based on the experimental results of the baseline cascade, blended blade and end wall contouring is applied to the suction surface and hub corner region of the baseline cascade and the detailed experiment is carried out. The results show that the blended blade and end wall contouring technology can decrease the total pressure loss by 8% and 7% at 0° and +10° incidence angles separately. The improved span range mainly focuses on the 10–25% span height. The rolling change of the passage vortex influenced by the accumulation of low energy fluid driven by cross flow in the hub corner should be the main reason for the performance improvement.

Investigation of Corner Separation in a Linear Compressor Cascade Using DDES

2015 ◽  
Author(s):  
Yangwei Liu ◽  
Hao Yan ◽  
Lipeng Lu
Keyword(s):  
Flow Field ◽  
Eddy Viscosity ◽  
Three Dimension ◽  
Separation Region ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Simple Modification ◽  
Corner Separation ◽  
Eddy Simulation

Delayed Detached Eddy Simulation (DDES) method, compared with the RANS method, can more accurately predict the complexity and unsteadiness naturally associated with the compressor flow. DDES method, which incorporates a simple modification into the initial detached eddy simulation (DES) introduces kinematic eddy viscosity into turbulence model to take both effects of grid spacing and eddy-viscosity field into considerations. An attempt is made in the present paper to apply DDES for investigating the flow field in a compressor cascade. Three-dimension (3D) corner separation, which is also referred as corner separation, have been identified as an inherent flow feature of the corner formed by the blade suction surface and endwall of axial compressors. The flow visualization and the quantification of passage blockage expose that corner separation contribute most to the total passage blockage. In order to accurately predict 3D corner separation by employing CFD and increase the performance in compressor routine design by controlling such phenomenon, this paper tries to figure out its mechanism and investigate the turbulence flow field by using DDES method. Numerical simulations are conducted under different incidences in a linear PVD compressor cascade. The results show passage vortex starting at mid-chord position in cascade develops into dominant secondary vortex and obviously enhances corner separation in the PVD cascade. DDES method, which can capture intensive vortex flow and predict complicated flow at the separation region, also illustrates the corner vortex breaks into small stripe vortices which mix with the mainstream flow at the blade trailing edge. The total pressure loss is high in the corner separation region.

Study on Optimization Design and Flow Control Mechanism of Little Blades in a Compressor Cascade

2020 ◽  
Author(s):  
Zhengtao Guo ◽  
Wuli Chu ◽  
Xiangyi Chen
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
Horseshoe Vortex ◽  
Aerodynamic Performance ◽  
Compressor Cascade ◽  
Height Range ◽  
Corner Region ◽  
Pressure Surface ◽  
Passage Vortex ◽  
End Wall

Abstract In view of the characteristics of flow separation in the compressor cascade corner region, a new flow control method for installing little blades in the front of the cascade passage was proposed, which took into account the flow control advantages of end wall fences and vortex generators. Firstly, the little blades could hinder the cross flow on the end wall and the development of the horseshoe vortex pressure surface branch. Secondly, the little blades could generate induced vortices to take away the low-energy fluid near the end wall and the corner region. Based on numerical simulations, the effects of different pitchwise positions, stagger angles and heights of the little blades on the aerodynamic performance of the cascade were studied, and the optimal little blades were obtained by NSGA-II using EBF neural network as the agent model. The results show that the little blades have the optimal pitchwise position, stagger angle and height range for improving the aerodynamic performance of the cascade. When the optimized little blades are introduced in the baseline cascade, the stable working range of the cascade is expanded, and the stall type of the cascade changes from the hub-corner stall to the overload of flow separation near the mid-span. At the near stall attack angle of the baseline, the total pressure loss coefficient is reduced by about 10.38% and the static pressure coefficient is increased by about 4.31%. Meanwhile, the loss of the lower span is decreased and the diffuser capacity of the whole span is improved. The passage secondary loss and wake loss are reduced because of the delay of corner separation. Moreover, the strength of the end wall vortex is weakened and the end wall vortex no longer develops as part of the passage vortex. The induced vortex, horseshoe vortex pressure surface branch and initial passage vortex develop into new passage vortex.

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