Corner separation dynamics in a high-speed compressor cascade based on detached-eddy simulation

2020 ◽  
Vol 99 ◽  
pp. 105730
Author(s):  
Ruiyu Li ◽  
Limin Gao ◽  
Chi Ma ◽  
Shiyan Lin ◽  
Lei Zhao
Keyword(s):  
High Speed ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Corner Separation ◽  
Eddy Simulation

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.

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.

scholarly journals Numerical Investigation on the Influence of the Streamlined Structures of the High-Speed Train’s Nose on Aerodynamic Performances

2021 ◽  
Vol 11 (2) ◽  
pp. 784
Author(s):  
Zhenxu Sun ◽  
Shuanbao Yao ◽  
Lianyi Wei ◽  
Yongfang Yao ◽  
Guowei Yang
Keyword(s):  
Drag Reduction ◽  
Pressure Distribution ◽  
Flow Separation ◽  
High Speed ◽  
Leeward Side ◽  
Detached Eddy Simulation ◽  
Side Force ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Asymmetrical Design

The structural design of the streamlined shape is the basis for high-speed train aerodynamic design. With use of the delayed detached-eddy simulation (DDES) method, the influence of four different structural types of the streamlined shape on aerodynamic performance and flow mechanism was investigated. These four designs were chosen elaborately, including a double-arch ellipsoid shape, a single-arch ellipsoid shape, a spindle shape with a front cowcatcher and a double-arch wide-flat shape. Two different running scenes, trains running in the open air or in crosswind conditions, were considered. Results reveal that when dealing with drag reduction of the whole train running in the open air, it needs to take into account how air resistance is distributed on both noses and then deal with them both rather than adjust only the head or the tail. An asymmetrical design is feasible with the head being a single-arch ellipsoid and the tail being a spindle with a front cowcatcher to achieve the minimum drag reduction. The single-arch ellipsoid design on both noses could aid in moderating the transverse amplitude of the side force on the tail resulting from the asymmetrical vortex structures in the flow field behind the tail. When crosswind is considered, the pressure distribution on the train surface becomes more disturbed, resulting in the increase of the side force and lift. The current study reveals that the double-arch wide-flat streamlined design helps to alleviate the side force and lift on both noses. The magnitude of side force on the head is 10 times as large as that on the tail while the lift on the head is slightly above that on the tail. Change of positions where flow separation takes place on the streamlined part is the main cause that leads to the opposite behaviors of pressure distribution on the head and on the tail. Under the influence of the ambient wind, flow separation occurs about distinct positions on the train surface and intricate vortices are generated at the leeward side, which add to the aerodynamic loads on the train in crosswind conditions. These results could help gain insight on choosing a most suitable streamlined shape under specific running conditions and acquiring a universal optimum nose shape as well.

A numerical study of snow accumulation on the bogies of high-speed trains based on coupling improved delayed detached eddy simulation and discrete phase model

2018 ◽  
Vol 233 (7) ◽  
pp. 715-730 ◽  
Author(s):  
Mingyang Liu ◽  
Jiabin Wang ◽  
Huifen Zhu ◽  
Sinisa Krajnovic ◽  
Guangjun Gao
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Snow Accumulation ◽  
Phase Model ◽  
Detached Eddy Simulation ◽  
Discrete Phase Model ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flow Mechanisms ◽  
Discrete Phase

A numerical simulation method based on the improved delayed detached eddy simulation coupled with a discrete phase model is used to study the influence of the snow on the performance of bogies of a high-speed train running in snowy weather. The snow particle trajectories, mass of snow packing on the bogie, and thickness of snow accumulation have been analyzed to investigate the flow mechanisms of snow accumulation on different parts of the bogies. The results show that the snow accumulation on the first bogie of the head vehicle is almost the same as that of the second bogie, but the total accumulated snow on the top side of the second bogie is more than 74% higher than that of the first bogie. Among all the components of the bogies, the motors were found to be strongly influenced by the snow accumulation. The underlying flow mechanisms responsible for the snow accumulations are discussed.

Detached-Eddy Simulation of Ground Effect on the Wake of a High-Speed Train

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Chao Xia ◽  
Xizhuang Shan ◽  
Zhigang Yang
Keyword(s):  
Vortex Shedding ◽  
High Speed ◽  
Vortex Pair ◽  
Ground Effect ◽  
Longitudinal Vortex ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Side Force ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

The influence of ground effect on the wake of a high-speed train (HST) is investigated by an improved delayed detached-eddy simulation. Aerodynamic forces, the time-averaged and instantaneous flow structure of the wake are explored for both the stationary ground and the moving ground. It shows that the lift force of the trailing car is overestimated, and the fluctuation of the lift and side force is much greater under the stationary ground, especially for the side force. The coexistence of multiscale vortex structures can be observed in the wake along with vortex stretching and pairing. Furthermore, the out-of-phase vortex shedding and oscillation of the longitudinal vortex pair in the wake are identified for both ground configurations. However, the dominant Strouhal number of the vortex shedding for the stationary and moving ground is 0.196 and 0.111, respectively, due to the different vorticity accumulation beneath the train. A conceptual model is proposed to interpret the mechanism of the interaction between the longitudinal vortex pair and the ground. Under the stationary ground, the vortex pair embedded in a turbulent boundary layer causes more rapid diffusion of the vorticity, leading to more intensive oscillation of the longitudinal vortex pair.

scholarly journals Large-eddy simulation of 3-D corner separation in a linear compressor cascade

2015 ◽  
Vol 27 (8) ◽  
pp. 085105 ◽  
Author(s):  
Feng Gao ◽  
Wei Ma ◽  
Gherardo Zambonini ◽  
Jérôme Boudet ◽  
Xavier Ottavy ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Linear Compressor Cascade

Simulation of Dynamic Stall on an Elastic Rotor in High-Speed Turn Flight

2020 ◽  
Vol 65 (2) ◽  
pp. 1-12
Author(s):  
Johannes Letzgus ◽  
Manuel Keßler ◽  
Ewald Krämer
Keyword(s):  
High Speed ◽  
Separated Flow ◽  
Flight Test ◽  
Dynamic Stall ◽  
Minor Role ◽  
Detached Eddy Simulation ◽  
Rotor Aerodynamics ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
A Minor

A highly loaded, high-speed turn flight of Airbus Helicopters' Bluecopter demonstrator helicopter is simulated to investigate dynamic stall using a loose computational fluid dynamics/structural dynamics (CFD/CSD) coupling of the flow solver FLOWer and the rotorcraft comprehensive code CAMRAD II. The rotor aerodynamics is computed using a high-fidelity delayed detached-eddy simulation (DDES). A three-degree-of-freedom trim of an isolated rotor is performed, yielding main-rotor control angles that agree well with the flight-test measurements. The flow field in this flight condition is found to be highly unsteady and complex, featuring massively separated flow, blade–vortex interaction, multiple dynamic-stall events, and shock-induced separation. The computed pitch-link loads are compared to flight-test measurements. This shows that all CFD/CSD cases underpredict the amplitudes of the flight test and yield phase shifts. However, overall trends agree reasonably. Also, varying the computational setup reveals that the shear stress transport–DDES turbulence model performs better than Spalart–Allmaras–DDES, that the consideration of the rotor hub and fuselage improves the agreement with flight-test data, and that the elastic twist plays only a minor role in the dynamic-stall events.

Improved Delayed Detached Eddy Simulation (IDDES) of a 1.5 Stage Axial Compressor Non-Synchronous Vibration

2020 ◽  
Author(s):  
Purvic Patel ◽  
Yunchao Yang ◽  
Gecheng Zha
Keyword(s):  
Rotor Blade ◽  
High Speed ◽  
Stokes Equations ◽  
Axial Compressor ◽  
Suction Side ◽  
Tip Vortex ◽  
Weno Scheme ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

Abstract This paper utilizes the Improved Delayed Detached Eddy Simulation (IDDES) to investigate the non-synchronous vibration (NSV) mechanism of a 1.5 stage high-speed axial compressor. The NSV occurs at a part speed in the rig test. A low diffusion E-CUSP approximate Riemann solver with a third order Weighted Essentially Non-Oscillating (WENO) scheme for the inviscid flux and a second order central differencing scheme for the viscous flux are employed to solve the 3D time accurate Navier-Stokes equations. The fully conservative sliding boundary condition is used to preserve the wake-propagation. The aerodynamic instability in the tip region induces two alternating low pressure regions near the leading and the trailing edge on the suction side of the rotor blade. It is observed that the circumferential tip vortex motion in the rotor passage above 75 % span and its coupling forces cause NSV at the operating speed. This instability moves in the counter-rotating direction in the rotational frame. The NSV results using URANS simulation is also presented for comparison. The predicted frequency with the IDDES and URANS using rigid blades agrees well with the measured frequency in the rig test. In addition to the NSV, the IDDES solver also captures the dominant engine order frequencies. The tip flow structures show the vortex filament with one end on the suction side of the rotor blade and other side terminating on the casing or the pressure side of the rotor blade.

Adaptive Detached Eddy Simulation of End-Wall Flow in a Linear Compressor Cascade

2020 ◽  
Author(s):  
Zifei Yin
Keyword(s):  
Pressure Coefficient ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Local Flow ◽  
Linear Compressor ◽  
Eddy Simulation ◽  
Wall Flow ◽  
Linear Compressor Cascade ◽  
End Wall ◽  
Des Model

Abstract Delayed detached eddy simulations and wall-modeled eddy simulations using the adaptive DES model were performed to simulate corner separation in the Ecole Centrale de Lyon linear compressor cascade. The adaptive DES model directly uses length scale to define eddy viscosity, which makes it nature to compute the model constant CDES dynamically. The dynamic procedure adapts viscosity to local flow and grid. Delayed detached eddy simulations, with and without the dynamic procedure, were performed to demonstrate the benefit of adapting viscosity to local flow. Recycling method was adopted to generate inflow unsteady turbulent boundary layer for wall-modeled eddy simulations. The wall-modeled eddy simulation showed improvement over delayed-DES, in terms of static pressure coefficient around the blade and total pressure loss at downstream locations.

Anti-snow performance of snow shields designed for brake calipers of a high-speed train

2018 ◽  
Vol 233 (2) ◽  
pp. 121-140 ◽  
Author(s):  
Jiabin Wang ◽  
Guangjun Gao ◽  
Yan Zhang ◽  
Kan He ◽  
Jie Zhang
Keyword(s):  
High Speed ◽  
Snow Accumulation ◽  
Cold Weather ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Discrete Phase Model ◽  
Railway Line ◽  
Eddy Simulation ◽  
Flow Features ◽  
Discrete Phase

When high-speed trains run on a snowy railway line in cold weather, a large amount of snow and ice will accumulate on the brake calipers, which can lead to huge safety problems. In this paper, to solve this issue, a numerical method based on the detached eddy simulation was used to explore the flow features of a high-speed train running in cold weather. The accuracy of mesh resolution and methodology of Computational Fluid Dynamics (CFD) was validated against the wind tunnel tests. A discrete phase model was used to investigate the process of snow accumulation on the brake calipers by analysing the movement characteristics of snow particles. Based on this analysis, three kinds of anti-snow packing shields for the brake calipers were designed, and the shielding effects were compared via numerical simulations. The results show that a large amount of snow particles below the bogie directly impact the brake calipers causing massive snow packing on the bottom surfaces; some snow particles reflected from the rear equipment cabin cover return to the bogie region and accumulates on the upper surfaces. With the application of anti-snow packing shields with trapezoidal-, triangular- and cambered-shaped openings, the rates of snow accumulation on the brake calipers were reduced by 18.53, 26.68 and 38.81%, respectively. The cambered type provides the best anti-snow packing performance for the brake calipers.

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