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.

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.

Optimizing Jets for Active Wake Control of Ground Vehicles

2013 ◽  
Author(s):  
Domenic L. Barsotti ◽  
Sandra K. S. Boetcher
Keyword(s):  
Drag Reduction ◽  
Turbulence Model ◽  
Vortex Shedding ◽  
Flow Separation ◽  
Detached Eddy Simulation ◽  
Ground Vehicles ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Model Flow ◽  
Ahmed Body

The present study investigates the simulation of slot jets on the rear of an Ahmed body to reduce drag. Improved Delayed Detached Eddy Simulation (IDDES) turbulence model is used to model flow separation and vortex shedding on a 25° Ahmed body. Several optimizations are conducted to maximize drag reduction with a net reduction of 16%. This is accomplished by creating a fluid structure in the wake.

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.

A DDES study of the flow past a prolate spheroid using a high-order U-MUSCL scheme

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040075
Author(s):  
Yu-Chen Yang ◽  
Zhen-Ming Wang ◽  
Ning Zhao
Keyword(s):  
Flow Separation ◽  
Vortex Structure ◽  
Prolate Spheroid ◽  
High Order ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Flow Past ◽  
Delayed Detached Eddy Simulation ◽  
Flow Phenomena

Flow past a prolate spheroid, which is a representative simplified configuration for vehicles such as maneuvering ships, submarines and missiles, comprises a series of complex flow phenomena including pressure-induced flow separation, which results in unsteady forces and movements that may be detrimental to vehicles’ performance. In this paper, a Delayed Detached Eddy Simulation (DDES) method combined with a new high-order U-MUSCL scheme is proposed to more precisely and accurately capture the flow separation and vortex structure. This method is applied to simulate the aerodynamic performance of the 6:1 prolate spheroid at an AOA of [Formula: see text] with the Reynolds number of [Formula: see text]. Axial pressure distribution of five individual chord wise sections and flow field structure of the aft body are analyzed. Numerical results agree well with the experimental data. It can be concluded that DDES combined with three-order U-MUSCL scheme demonstrates reliable performance since it captures the vortex structure of aft body distinctly and predicts the separation and reattachment points of the secondary vortex precisely.

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.

scholarly journals Adaptability of Turbulence Models for Pantograph Aerodynamic Noise Simulation

2019 ◽  
Vol 2019 ◽  
pp. 1-20 ◽  
Author(s):  
Xiao-ming Tan ◽  
Peng-peng Xie ◽  
Zhi-gang Yang ◽  
Jian-yong Gao
Keyword(s):  
Shear Stress ◽  
Wind Tunnel ◽  
High Speed ◽  
Aerodynamic Noise ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Shear Stress Transport ◽  
Delayed Detached Eddy Simulation ◽  
Relative Errors ◽  
Les Model

This study was targeted at CX-PG-type Faiveley pantograph of high-speed train and cylinders and analysed the fluctuating flow field around these objects by using the large eddy simulation (LES) model, the scale adaptive simulation (SAS) model, the improved delayed detached eddy simulation with shear-stress transport-kω (IDDES sst-kω) model, the delayed detached eddy simulation with shear-stress transport-kω (DDES sst-kω) model, and the delayed detached eddy simulation with realizable-kε (DDES R-kε) model. The space distributions of velocity, vorticity, and vortex structures were compared to investigate their performances on simulating fluctuating flow fields and computing aeroacoustic sources through Fourier transformation based on the surface fluctuating pressures. Furthermore, the far-field radiated noise was calculated based on the Ffowcs Williams–Hawkings equation. Based on the computation precision of the five models, a feasible turbulent model was selected for simulating aerodynamic noise. The relative errors to the results from wind-tunnel experiments of the sound pressure level (SPL) were obtained as 0.7%, 1.6%, 7.8%, 3.8%, and 12.1%, respectively, and the peak Strouhal numbers were obtained as 2.0%, 8.5%, 5.5%, 11.5%, and 51.0% for cylinder simulation. Moreover, the relative errors of SAS, IDDES sst-kω, DDES sst-kω, and DDES R-kε models to the result from LES of SPL were respectively obtained as 2.3%, 4.5%, 5.6%, and 10.8% for pantograph. Thus, it is conclusive that none of the aforementioned models are comparable with the LES model with respect to the precision in the aeroacoustic simulation. However, SAS, IDDES sst-kω, and DDES sst-kω are practically competent with the LES model considering the numerical simulations with respect to the engineering computation precision. The numerical computation model was verified using the wind-tunnel test results.

scholarly journals Computational study of active flow control drag reduction device for utility vehicle

2019 ◽  
Vol 128 ◽  
pp. 09003
Author(s):  
Jęedrzej Mosiężny ◽  
Bartosz Ziegler
Keyword(s):  
Drag Reduction ◽  
Computational Study ◽  
Active Flow Control ◽  
Separated Flow ◽  
Flow Region ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Active Flow ◽  
Base Drag

The study presents a computational study of a drag reduction device based on an active boundary layer control for a generic truck-trailer utility road vehicle. The conceptual device is in accordance with upcoming EU regulations regarding attachable aerodynamic devices for heavy utility vehicles. Design and principles of operation of the conceptual device are presented. The device is intended to increase decrease the trailer’s base drag coefficient by manipulation of the separated flow region behind the vehicle base. Results of a steady state Reynolds averaged analysis and Delayed Detached Eddy Simulation are presented to show the discrepancies of fluid flow patterns between baseline and augmented configuration as well as between mentioned CFD approaches. Results for drag reduction for baseline truck-trailer configuration and aerodynamically augmented configuration are presented.

Numerical simulation of the effects of obstacle deflectors on the aerodynamic performance of stationary high-speed trains at two yaw angles

2017 ◽  
Vol 232 (3) ◽  
pp. 913-927 ◽  
Author(s):  
Ji-qiang Niu ◽  
Dan Zhou ◽  
Xi-feng Liang
Keyword(s):  
High Speed ◽  
Simulation Method ◽  
Aerodynamic Performance ◽  
Wake Flow ◽  
Detached Eddy Simulation ◽  
Aerodynamic Forces ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
High Speed Trains ◽  
Yaw Angle

In this study, based on the shear-stress transport κ–ω turbulent model, the improved delayed detached eddy simulation method has been used to simulate the unsteady aerodynamic performance of trains with different obstacle deflectors at two yaw angles (0° and 15°). The numerical algorithm is used and some of the numerical results are verified through wind tunnel tests. By comparing and analysing the obtained results, the effects of the obstacle deflectors on the force of the trains as well as the pressure and flow structure around the trains are elucidated. The results show that the obstacle deflectors primarily affect the flow field at the bottom of the head car as well as the wake flow, and that the internal oblique-type obstacle deflector (IOOD) markedly improves the aerodynamic performance of the trains, by decreasing most of the aerodynamic forces of the train cars and minimising their fluctuations. Further, a nonzero yaw angle weakens or even changes the effect of the IOOD on the aerodynamic forces of the train cars. However, the effect of the IOOD is more on the tail car.

An improved delayed detached eddy simulation study of the bogie cavity length effects on the aerodynamic performance of a high-speed train

2020 ◽  
Vol 234 (12) ◽  
pp. 2386-2401 ◽  
Author(s):  
Jiabin Wang ◽  
Guglielmo Minelli ◽  
Yan Zhang ◽  
Jie Zhang ◽  
Sinisa Krajnović ◽  
...  
Keyword(s):  
High Speed ◽  
Cavity Length ◽  
Longitudinal Vortex ◽  
Resistance Force ◽  
Wake Region ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Near Wake ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

This paper uses an improved delayed detached eddy simulation method to investigate the unsteady flow features of the high-speed trains with various cavity lengths at Re = 1.85×106. The improved delayed detached eddy simulation results are validated against the experimental data obtained during previous wind tunnel tests. The effects of cavity length on the resistance force, flow structures beneath the high-speed train and in the wake are analyzed. The results show that a longer cavity significantly increases the streamwise velocity level near the rear plates and forms a stronger impinging flow on the rear plates, and thus contributes to a higher value of resistance. Furthermore, a longer cavity decreases the pressure coefficients around the near wake region from the top of the ballast to the tail nose in the vertical direction and thereby increases the pressure drag of the high-speed train. Additionally, a longer bogie cavity is found to increase the longitudinal vortex scales in the near wake region. All these changes on the flow field bring to 5.8% and 11.5% drag increase when the bogie cavities are elongated by 20% and 40%, respectively, of the wheelbase.

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