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.

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.

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.

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

2020 ◽  
Vol 142 (2) ◽  
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.

Visualizations of Flow Structures in the Rotor Passage of an Axial Compressor at the Onset of Stall

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
David Tan ◽  
Joseph Katz
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Incidence Angle ◽  
Axial Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Stereoscopic Particle Image Velocimetry ◽  
High Speed Imaging ◽  
Vortical Structures ◽  
Flow Phenomena

Experiments preformed in the JHU refractive index matched facility examine flow phenomena developing in the rotor passage of an axial compressor at the onset of stall. High-speed imaging of cavitation performed at low pressures qualitatively visualizes vortical structures. Stereoscopic particle image velocimetry (SPIV) measurements provide detailed snapshots and ensemble statistics of the flow in a series of meridional planes. At prestall condition, the tip leakage vortex (TLV) breaks up into widely distributed intermittent vortical structures shortly after rollup. The most prominent instability involves periodic formation of large-scale backflow vortices (BFVs) that extend diagonally upstream, from the suction side (SS) of one blade at midchord to the pressure side (PS) near the leading edge of the next blade. The 3D vorticity distributions obtained from data recorded in closely spaced planes show that the BFVs originate form at the transition between the high circumferential velocity region below the TLV center and the main passage flow radially inward from it. When the BFVs penetrate to the next passage across the tip gap or by circumventing the leading edge, they trigger a similar phenomenon there, sustaining the process. Further reduction in flow rate into the stall range increases the number and size of the backflow vortices, and they regularly propagate upstream of the leading edge of the next blade, where they increase the incidence angle in the tip corner. As this process proliferates circumferentially, the BFVs rotate with the blades, indicating that there is very little through flow across the tip region.

Evaluation of Compressor Blading With Blade End Slots and Full-Span Slots in a Highly Loaded Compressor Cascade

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Yumeng Tang ◽  
Yangwei Liu ◽  
Lipeng Lu
Keyword(s):  
Incidence Angle ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Main Flow ◽  
The Self ◽  
Flow Structures ◽  
Compressor Cascade ◽  
Corner Separation ◽  
High Incidence ◽  
Highly Loaded

Abstract Blade end slots were proposed to control corner separation in a highly loaded compressor cascade in our previous studies. This study focuses on the evaluation of compressor blading with blade end slots and full-span slots. First, the two-dimensional configuration performance is evaluated both for the datum and slotted profiles. The slotted configuration could effectively suppress separation, especially under positive incidence conditions when the separation is large. Thus, two three-dimensional blading with full-span slots and blade end slots (20% span height from the endwall) are compared. Results show that blading with full-span slots could effectively reduce the loss and enlarge pressure rise under relative high incidence angles, while blading with blade end slots could effectively reduce the loss and enlarge pressure rise above an incidence angle of −4 deg. Blading with slots alters the flow structures and reorganizes the flow in the blade end regions. The self-adaptive jets from the slots reenergize the low-momentum flow downstream and restrain its migration toward the mid-span, so that the corner separation is reduced and the performance is enhanced. The loss for the end slotted blade is lower than that of the full-span slotted blade under incidence angles within 4 deg. This is because the additional mixing loss of the jet and the main flow are caused by the full-span slots at the mid-span regions where the flow remains attached for the blade end slots.

Experimental and Numerical Investigation on the Aerodynamic Performance of a Compressor Cascade Using Blended Blade and End Wall

2017 ◽  
Author(s):  
Jiabin Li ◽  
Lucheng Ji ◽  
Weilin Yi
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Turbulence Model ◽  
Numerical Study ◽  
Incidence Angle ◽  
Good Effect ◽  
Compressor Cascade ◽  
Corner Separation ◽  
Sst Turbulence Model ◽  
End Wall

Nowadays, the corner separation, occurring near the corner region formed by the suction surface of blade and end wall, has been an important limitation for the increasing of the aerodynamic loading in the compressor. The previous numerical studies indicate that the Blended Blade and End Wall (BBEW) technology is useful in delaying, or reducing, or even eliminating the corner separation. To further validate the concept, this paper presents combined experimental and numerical investigations on a BBEW cascade and its prototype. Firstly, the NACA65 linear compressor cascade with the turning angle 42 degrees was designed and tested in a low-speed wind tunnel. Then, the cascade with blended blade and end wall design was made and tested in the same wind tunnel. The experimental results show that the design of blended blade and end wall can improve the performance of the cascade when the incidence angle was positive or at the design point, and the total pressure loss coefficient was reduced by 7%–8%. The performance improvement mainly located from 10%–25% span heights. Secondly, based on the experimental data, the numerical study made by our internal code Turbo-CFD shows the difference of the simulation precision of the results, obtained from four different turbulence model after the mesh independence test. The four turbulence model is Spalart-Allmaras model, standard k-ε model, standard k-ω model, and shear stress transport k-ω model. For this case, the SST turbulence model has better performance compared with others. Thirdly, based on the results which were calculated with the turbulence model SST, the effect of the blended blade and end wall design was discussed. The numerical study shows that the design with the blended blade and end wall can have a good effect on the corner flow of the cascade. The strong three-dimensional corner separation, caused by the accumulation of the flow happening at the trail of the suction side was avoided, and the flow losses of the prototype cascade were reduced. Above all, the experiment shows that the design with blended blade and end wall can improve the performance of the cascade. Compared with the experiment data, the SST turbulence model shows the best results of the flow field. Based on the numerical results, the details of the flow field and the effect of the blended blade and end wall design on the corner separation are discussed and analyzed.

Effect of Freestream Velocity on the Three-Dimensional Separated Flow Region in Front of a Cylinder

1991 ◽  
Vol 113 (1) ◽  
pp. 37-44 ◽  
Author(s):  
W. A. Eckerle ◽  
J. K. Awad
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Vortex Formation ◽  
Wind Tunnel Test ◽  
Surface Flow ◽  
Cylinder Surface ◽  
Separation Region ◽  
Reynolds Stresses ◽  
Freestream Velocity ◽  
Displacement Thickness

Details of the horseshoe vortex formation around a cylinder were studied to determine the flow parameters that affect the flow separation in front of the cylinder. An experimental setup consisting of a circular cylinder vertically mounted on the floor of the wind tunnel test section was assembled. The approaching turbulent boundary layer was four centimeters thick. Pressures were measured on the cylinder surface and the tunnel floor with surface static pressure taps. Surface flow visualizations were accomplished to locate singlar points and the size of separation region on the endwall surface. Interior mean and fluctuating velocity data and Reynolds stresses in front of the cylinder were nonintrusively measured with a two-component Laser Doppler Anemometer system. Freestream stagnation at the endwall/cylinder surface occurred in all cases, but two types of separation were identified in this investigation. The flow pattern in the separation region depends on the freestream momentum and the boundary layer displacement thickness. A large-scale fully developed vortex was formed in the plane of symmetry for low approaching freestream velocities. A fully developed vortex was not present at higher approach velocities. Maximum production of turbulent kinetic energy was measured around the core of the vortex when fully formed.

Detached Eddy Simulation of Transition in Turbomachinery: Linear Compressor Cascade

2021 ◽  
pp. 1-10
Author(s):  
Zifei Yin ◽  
Paul Durbin
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Adaptive Model ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Linear Compressor Cascade

Abstract The adaptive, l2-omega delayed detached eddy simulation model was selected to simulate the flow in the V103 linear compressor cascade. The Reynolds number based on axial chord length is 138,500. Varies inflow turbulent intensities from 0% to 10% were tested to evaluate the performance of the adaptive model. The adaptive model is capable of capturing the laminar boundary layer and the large scale perturbations inside it. The instability of large scale disturbances signals the switch to a hybrid simulation of turbulent boundary layer -- the transition front is thus predicted. In the case of separation-induced transition, the adaptive model, which uses eddy simulation in separated flow, can predict the separation bubble size accurately. Generally, the adaptive, delayed detached eddy simulation model can simulate the transitional separated flow in a linear compressor cascade, with a correct response to varying turbulent intensities.

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.

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