Experimental Study of the Skin-Friction Topology Around the Ahmed Body in Cross-Wind Conditions

2021 ◽  
Author(s):  
Hung Tran The ◽  
Masayuki Anyoji ◽  
Takuji Nakashima ◽  
Keigo Shimizu ◽  
Anh Dinh Le
Keyword(s):  
Skin Friction ◽  
Aerodynamic Drag ◽  
Force Balance ◽  
Windward Side ◽  
Wind Condition ◽  
Grid Data ◽  
Slant Angle ◽  
Balance System ◽  
Slant Surface ◽  
Ahmed Body

Abstract In this study, skin friction around a ½-scale Ahmed body was measured experimentally at a Reynolds number of Re = 2×105. The slant angle of the Ahmed body was 25° and the yaw angles ranged from 0° to 8°. This study focused on the flow structure on the slant surface under different cross-wind conditions. A force balance system was applied to measure the aerodynamic drag of the model. The global skin-friction topology was measured by applying a luminescent oil layer with a sub-grid data processing algorithm. The method used to measure the skin friction was conducted for the first time on the Ahmed body. The results indicated that the technique is highly capable of extracting the skin-friction topology. For a yaw angle below 3°, the flow on the slant surface was not significantly affected by the cross-wind condition and the drag of the model was nearly constant. However, at yaw angles above 3°, the flow on the slant surface was highly affected by the roof longitudinal vortexes on the windward side, leading to a dramatic increase in the drag of the model. High consistency in the drag and skin-friction fields was observed. The detailed skin-friction structure at different yaw angles will be discussed in this study.

Experimental Study of Flow Control Over a Standard Road Vehicle Using Plasma Actuator

2020 ◽  
Vol 22 (4) ◽  
pp. 1047-1060
Author(s):  
S. Shadmani ◽  
S. M. Mousavi Nainiyan ◽  
R. Ghasemiasl ◽  
M. Mirzaei ◽  
S. G. Pouryoussefi
Keyword(s):  
Flow Control ◽  
Pressure Distribution ◽  
Drag Force ◽  
Separated Flow ◽  
Plasma Actuator ◽  
Road Vehicle ◽  
Slant Angle ◽  
Total Drag ◽  
Slant Surface ◽  
Ahmed Body

AbstractAhmed Body is a standard and simplified shape of a road vehicle that's rear part has an important role in flow structure and it's drag force. In this paper flow control around the Ahmed body with the rear slant angle of 25° studied by using the plasma actuator system situated in middle of the rear slant surface. Experiments conducted in a wind tunnel in two free stream velocities of U = 10m/s and U = 20m/s using steady and unsteady excitations. Pressure distribution and total drag force were measured and smoke flow visualization carried out in this study. The results showed that at U = 10m/s using plasma actuator suppress the separated flow over the rear slant slightly and be effective on pressure distribution. Also, total drag force reduces in steady and unsteady excitations for 3.65% and 2.44%, respectively. At U = 20m/s, using plasma actuator had no serious effect on the pressure distribution and total drag force.

scholarly journals Experimental Study of Flow Control Over an Ahmed Body Using Plasma Actuator

2020 ◽  
Vol 22 (1) ◽  
pp. 239-252
Author(s):  
S. Shadmani ◽  
S. M. Mousavi Nainiyan ◽  
R. Ghasemiasl ◽  
M. Mirzaei ◽  
S. G. Pouryoussefi
Keyword(s):  
Flow Control ◽  
Pressure Distribution ◽  
Drag Force ◽  
Separated Flow ◽  
Plasma Actuator ◽  
Slant Angle ◽  
Total Drag ◽  
Slant Surface ◽  
Actuator System ◽  
Ahmed Body

AbstractAhmed Body is a standard and simplified shape of a road vehicle that's rear part has an important role in flow structure and it's drag force. In this paper flow control around the Ahmed body with the rear slant angle of 25° studied by using the plasma actuator system situated in middle of the rear slant surface. Experiments conducted in a wind tunnel in two free stream velocities of U = 10 m/s and U = 20 m/s using steady and unsteady excitations. Pressure distribution and total drag force was measured and smoke flow visualization carried out in this study. The results showed that at U = 10 m/s using plasma actuator suppress the separated flow over the rear slant slightly and be effective on pressure distribution. Also total drag force reduces in steady and unsteady excitations for 3.65% and 2.44%, respectively. At U = 20 m/s, using plasma actuator had no serious effect on the pressure distribution and total drag force.

scholarly journals Turbulent Drag Reduction Characteristics of Bionic Nonsmooth Surfaces with Jets

2019 ◽  
Vol 9 (23) ◽  
pp. 5070
Author(s):  
XiaoWen Song ◽  
MingXiao Zhang
Keyword(s):  
Drag Reduction ◽  
Skin Friction ◽  
Sliding Friction ◽  
Aerodynamic Drag ◽  
Active Surface ◽  
Unit Cell ◽  
Windward Side ◽  
Turbulent Drag Reduction ◽  
Pressure Drag ◽  
Turbulent Drag

Aiming at aerodynamic drag reduction for transportation systems, a new active surface is proposed that combines a bionic nonsmooth surface with a jet. Simulations were performed in the computational fluid dynamics software STAR-CCM+ to investigate the flow characteristics and drag reduction efficiency. The SST K-Omega model was used to enclose the equations. The simulation results showed that when the active surface simultaneously reduced the skin friction and overcame the sharp increase of pressure drag caused by a common nonsmooth surface, the total net drag decreased. The maximum drag reduction ratio reached 19.35% when the jet velocity was 11 m/s. Analyses of the turbulent kinetic energy, pressure distribution, and velocity profile variations showed that the active surface reduced the peak pressure on the windward side of the nonsmooth unit cell, thereby reducing the total pressure drag. Moreover, the recirculation formed in the unit cell transformed the fluid–wall sliding friction into fluid–fluid rolling friction like a rolling bearing, thereby reducing the skin friction. This study provides a new efficient way for turbulent drag reduction to work.

Active Flow Control of the 3D Separation on a Ahmed Body Using Steady Microjet Arrays

2010 ◽  
Author(s):  
S. Aubrun ◽  
F. Alvi ◽  
A. Leroy ◽  
A. Kourta
Keyword(s):  
Flow Control ◽  
Aerodynamic Drag ◽  
Separation Bubble ◽  
Active Flow Control ◽  
Aerodynamic Load ◽  
Flow Topology ◽  
Rear Window ◽  
Slant Angle ◽  
Control Approach ◽  
Ahmed Body

A model of a generic vehicle shape, the Ahmed body with a slant angle of 25°, is equipped with an array of blowing steady microjets 6mm downstream of the separation line between the roof and the slanted rear window. The goal of the present study is to evaluate the effectiveness of this actuation method in reducing the aerodynamic drag, by reducing or suppressing the 3D closed separation bubble located on the slanted surface. The efficiency of this control approach is quantified with the help of aerodynamic load measurements. The changes in the flow field when control is applied are examined using PIV measurements and skin friction visualizations. By activating the steady microjet array, the drag coefficient was reduced by 9 to 11%, depending on the Reynolds number. The modification of the flow topology under progressive flow control is particularly studied.

scholarly journals Investigation of wheelhouse shapes on the aerodynamic characteristics of a generic car model

2021 ◽  
Vol 13 (12) ◽  
pp. 168781402110668
Author(s):  
Haichao Zhou ◽  
Qingyun Chen ◽  
Runzhi Qin ◽  
Lingxin Zhang ◽  
Huiyun Li
Keyword(s):  
Aerodynamic Drag ◽  
Simulation Method ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Vehicle Speed ◽  
Cavity Volume ◽  
Detached Eddy Simulation ◽  
Slant Angle ◽  
Drag Coefficients ◽  
Ahmed Body

As vehicle speed increases, the aerodynamic drag reduction becomes increasingly significant. The aim of this paper is to find out the effects of the wheelhouse shapes on the aerodynamics of an Ahmed body with a 35 slant angle. In this paper, based on the detached-eddy simulation method, the effects of the three classic different wheelhouse on the aerodynamic performance and near wake of the Ahmed body are presented. The mesh resolution and methodology are validated against the published test results. The results show that the front wheelhouse has a significant impact on the aerodynamic performance of the Ahmed body, leading to different aerodynamic drag forces and flow fields. Enlarging the wheelhouse cavity volume could result in a gradual increase in aerodynamic drag coefficients, the ratio of the wheelhouse cavity volume increased by 2.9% and 9.8%, the drag coefficients increased by 2.5% and 4.5% respectively. The increase in aerodynamic drag was primarily caused by flow separation in the large cavity volume wheelhouse.

Active drag reduction of a high-drag Ahmed body based on steady blowing

2018 ◽  
Vol 856 ◽  
pp. 351-396 ◽  
Author(s):  
B. F. Zhang ◽  
K. Liu ◽  
Y. Zhou ◽  
S. To ◽  
J. Y. Tu
Keyword(s):  
Drag Reduction ◽  
The Body ◽  
Force Balance ◽  
Effective Control ◽  
Rear Window ◽  
Flow Measurements ◽  
Slant Angle ◽  
Vertical Base ◽  
Active Drag ◽  
Ahmed Body

Active drag reduction of an Ahmed body with a slant angle of $25^{\circ }$, corresponding to the high-drag regime, has been experimentally investigated at Reynolds number $Re=1.7\times 10^{5}$, based on the square root of the model cross-sectional area. Four individual actuations, produced by steady blowing, are applied separately around the edges of the rear window and vertical base, producing a drag reduction of up to 6–14 %. However, the combination of the individual actuations results in a drag reduction 29 %, higher than any previous drag reductions achieved experimentally and very close to the target (30 %) set by automotive industries. Extensive flow measurements are performed, with and without control, using force balance, pressure scanner, hot-wire, flow visualization and particle image velocimetry techniques. A marked change in the flow structure is captured in the wake of the body under control, including the flow separation bubbles, over the rear window or behind the vertical base, and the pair of C-pillar vortices at the two side edges of the rear window. The change is linked to the pressure rise on the slanted surface and the base. The mechanisms behind the effective control are proposed. The control efficiency is also estimated.

Commercial CFD Code Validation for Simulation of Heavy-Vehicle External Aerodynamics

2003 ◽  
Author(s):  
W. David Pointer ◽  
Tanju Sofu ◽  
David Weber
Keyword(s):  
Aerodynamic Drag ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Department Of Energy ◽  
Force Balance ◽  
Heavy Vehicles ◽  
Safety And Health ◽  
Energy Economy ◽  
Computational Fluid Dynamics Cfd ◽  
Vehicle Technologies

The issue of energy economy in transportation has grown beyond traditional concerns over environment, safety and health to include new concerns over national and international security. In collaboration with the U.S. Department of Energy Office of FreedomCAR and Vehicle Technologies’ Working Group on Aerodynamic Drag of Heavy Vehicles, Argonne National Laboratory is investigating the accuracy of aerodynamic drag predictions from commercial Computational Fluid Dynamics (CFD) Software. In this validation study, computational predictions from two commercial CFD codes, Star-CD [1] and PowerFLOW [2], will be compared with detailed velocity, pressure and force balance data from experiments completed in the 7 ft. by 10 ft. wind tunnel at NASA Ames [3, 4] using a Generic Conventional Model (GCM) that is representative of typical current-generation tractor-trailer geometries.

Aerodynamic Drag Reduction Investigation for a Simplified Road Vehicle Using Plasma Flow Control

2016 ◽  
Author(s):  
Bahram Khalighi ◽  
Joanna Ho ◽  
John Cooney ◽  
Brian Neiswander ◽  
Thomas C. Corke ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Flow Control ◽  
Plasma Flow ◽  
Aerodynamic Drag ◽  
Force Balance ◽  
Plasma Actuators ◽  
Ground Vehicles ◽  
Mean Velocity ◽  
Local Flow ◽  
Plasma Flow Control

The effect of plasma flow control on reducing aerodynamic drag for ground vehicles is investigated. The experiments were carried out for a simplified ground vehicle using single dielectric barrier discharge (SDBD) plasma actuators. The plasma actuators were designed to alter the flow structure in the wake region behind the vehicle. The Ahmed body was modified to allow eight different vehicle geometries (with backlight or slant angles of 0° and 35°). Each of these were further modified by rounding the edges with different radii. Flow visualizations such as particle streams and surface oil were used to quantify features of the local flow field. The drag on the models was measured using a force balance as well as by integrating the mean velocity profiles in the model wakes. The results indicated that flow modifications needed to be applied symmetrically (upper to lower and/or side to side). This was demonstrated with the 0° backlight angle (square-back) that had all four side-corners rounded. Plasma actuators were applied to all four of the rounded edges to enhance the ability to direct the flow into the wake. Wake measurements showed that steady actuation at a fixed actuator voltage reduced the drag by an average of 20% at the lower velocities (below 15 m/s) and by 3% at the highest velocity tested (20 m/s). Model constraints prevented increasing the plasma actuator voltage that was needed to maintain the higher drag reduction observed at the lower speeds.

Theoretical and Numerical Calculation on the Added Mass of Ahmed Body

2017 ◽  
Vol 865 ◽  
pp. 247-252
Author(s):  
Gui Tao Du
Keyword(s):  
Numerical Calculation ◽  
Theoretical Calculation ◽  
Calculation Method ◽  
Aerodynamic Drag ◽  
Added Mass ◽  
The Body ◽  
Power Performance ◽  
Car Body ◽  
The Impact ◽  
Ahmed Body

Because of the added mass, the aerodynamic drag of the automobile will increase obviously when accelerating in the still air. In this paper, it firstly gave the definition of the added mass, and presented that there was little research on the calculation of the added mass of automobile. Then through the analysis of the theoretical calculation method for the added mass, it pointed out that, for the added mass of the car-body with a complex shape, there was much difficulty in the theoretical calculation. Alternatively, a numerical calculation method for the added mass of car-body was derived. The simulation model adopted the Ahmed body and the corresponding verification experiment was completed in the Tongji Automotive Wind Tunnel center. The results indicate that the added mass is a constant which is only dependent on the body-shape. For the model investigated, the added mass is 0.0052kg that is approximately equal to the air displaced by the car-body. As the body accelerates to 4m/s2, the aerodynamic drag is increased by 1.89% because of added mass. Therefore, it needs to pay more attention to the impact that the added mass has on the dynamic performance of vehicle when proceeding the aerodynamic designs (especially for the high power performance vehicles). Meanwhile, it still makes a correction to the conventional aerodynamic drag formula. This paper also demonstrates that, with the analysis of the flow-field of car-body, the added mass essentially stems from the additionally work done by the car-body to increase the kinetic energy of external fluid as it speeds up.

A novel free floating accelerometer force balance system for shock tunnel applications

Shock Waves ◽  
2005 ◽  
pp. 407-412
Author(s):  
R. Joarder ◽  
D. R. Mahaptra ◽  
G. Jagadeesh
Keyword(s):  
Shock Tunnel ◽  
Force Balance ◽  
Balance System
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