scholarly journals Aerodynamic Study of an Ahmed Body with the Help of CFD Simulation

2020 ◽  
Author(s):  
Indrashis Saha ◽  
Tathagatha Mukherjee ◽  
Ankit Saha ◽  
Richa Pandey
Keyword(s):  
Cfd Simulation ◽  
Fuel Efficiency ◽  
Turbulence Models ◽  
Numerical Data ◽  
Primary Objective ◽  
The Body ◽  
Stream Velocity ◽  
Noise Emission ◽  
Slant Angle ◽  
Ahmed Body

Automotive aerodynamics comprises of the study of aerodynamics of road vehicles. Its main goals are reducing drag, minimizing noise emission, improving fuel economy, preventing undesired lift forces and minimizing other causes of aerodynamic instability at high speeds. The Ahmed body has the form of a highly simplified car, consisting of a blunt nose with rounded edges fixed onto a box-like middle section and a rear end that has an upper slanted surface, the angle of which can be varied. It retains vital features of real vehicles in order to study the flow fields around it and the related turbulence models which characterizes the actual flow at elevated Reynolds number. In the present study, the aerodynamic behavior of this body is investigated numerically by the aid of commercial CFD tool: Ansys Fluent. The results of the simulation are validated with available experimental data and results of the simulations from other literatures. The numerical data were obtained for a fixed free stream velocity of 25 m/s at the inlet. The simulations were performed at a fixed slant angle of 25 degree and zero yaw angle. The present study focuses on how local refinement of mesh inside the concerned body and the outside, helps affect the results and for which grid dependency test is the primary objective of this paper. The present study also helps demonstrate how the drag of the body behaves, which is mainly the effect of pressure drag force generated at the rear portion of the body. The study also focuses on important properties like the velocity magnitude at different locations for different meshing cases, and to capture the flow pattern in the front or near the wake region. The study can be further helpful to future researchers in determining resistance, fuel efficiency etc. helping designers to optimize in specialized areas for better efficiency.

Numerical Simulation of Flow Around a Simplified Car Body

2003 ◽  
Author(s):  
Emmanuel Guilmineau
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Boundary Conditions ◽  
Turbulence Models ◽  
Test Case ◽  
Slant Angle ◽  
Acceptable Limit ◽  
Numerical Errors ◽  
Car Body ◽  
Ahmed Body

Simulations have been carried out for the generic car body (Ahmed body) for 25° and 35° slant angle. At a previous Workshop [1, 2], the results of different groups showed significant variations, even when the same turbulence models were used. This indicates that either the grids used in the investigation are too coarse to reduce the numerical errors below an acceptable limit, or that other factors, like boundary conditions, model implementation had a significant effect on the simulations. In any case, the results of the simulations were inconclusive, leading to a revaluation of this test case. In this study, we investigate numerically the flow around the Ahmed body for 25° and 35° slant angle. Results are compared with experimental data of Becker et al. [3].

scholarly journals The nature of the vortical structures in the near wake of the Ahmed body

2017 ◽  
Vol 231 (9) ◽  
pp. 1239-1244 ◽  
Author(s):  
James Venning ◽  
David Lo Jacono ◽  
David Burton ◽  
Mark C Thompson ◽  
John Sheridan
Keyword(s):  
Water Channel ◽  
Field Measurements ◽  
The Body ◽  
Wake Flow ◽  
Generic Model ◽  
Toroidal Vortex ◽  
Near Wake ◽  
Slant Angle ◽  
Vortical Structures ◽  
Ahmed Body

This study presents the results from high-spatial-resolution water-channel velocity-field measurements behind an Ahmed body with 25° rear slant angle. The Ahmed body represents a simplified generic model of a hatchback automobile that has been widely used to study near-wake flow dynamics. The results help clarify the unresolved question of whether the time-mean near-wake flow structure is topologically equivalent to a toroidal vortex or better described by a pair of horizontally aligned horseshoe vortices, with their legs pointing downstream. The velocimetry data presented allows the tracking of the vortical structures throughout the near wake through a set of orthogonal planes, as well as the measurement of their circulation. The spanwise vortices that form as the flow separates from the top and bottom rear edges are shown to tilt downstream at the sides of the body, while no evidence is found of a time-mean attached toroidal vortex, at least for the Reynolds number (based on the square root of the frontal area) of [Formula: see text] under consideration.

scholarly journals Study of the Effect of Vertical Airfoil Endplates on Diffusers in Vehicle Aerodynamics

Designs ◽  
2021 ◽  
Vol 5 (3) ◽  
pp. 45
Author(s):  
Laura Porcar ◽  
Willem Toet ◽  
Pedro Javier Gamez-Montero
Keyword(s):  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Simulation Software ◽  
The Body ◽  
Ride Height ◽  
Diffuser Flow ◽  
Vehicle Aerodynamics ◽  
High Level ◽  
Ahmed Body

Diffusers and the floor ahead of them create the majority of the downforce a vehicle creates. Outside motorsports, the diffuser is relatively unused, although its interaction with the ground is a consistent field of study owing to the aerodynamic benefits. The diffuser flow behavior is governed by three fluid-mechanical mechanisms: ground interaction, underbody upsweep, and diffuser upsweep. In addition, four different flow regimes appear when varying ride height, the vortices of which have great importance on downforce generation. The present study focuses on the diffuser’s fluid-dynamic characteristics undertaken within an academic framework with the objective of finding and understanding a high level of performance in these elements. Once the functioning of diffusers has been analyzed and understood, a new configuration is proposed: rear vertical airfoil endplates. The aim of the paper is to study the effect in performance of vertical airfoil endplates on diffusers in vehicle aerodynamics in a simplified geometry. The candidate to this geometry is the inversed Ahmed body, a geometry that is used as a model that simulates the flow behavior of car diffusers. Three different diffuser configurations are performed, namely 0° diffuser, 25° diffuser, and in the third case vertically installed rear vertical airfoil endplates are added to the 25° diffuser Ahmed body to change the flow field. These analyses are carried out by using open-source CFD simulation software OpenFOAM. An inlet velocity of 20 m/s is considered, as this is a typical velocity when cornering in motorsport. It is concluded that the 25° diffuser configuration generated more downforce than the 0° diffuser, which makes sense as the aim of adding a diffuser is to increase the amount of downforce produced. In addition, and as a result of the newly proposed configuration, the 25° diffuser Ahmed body with the vertical airfoil endplates emerges in a substantial increase of downforce thanks to the low-pressure zone generated at the back of the body.

Numerical Simulation of Unsteady Flow around Ahmed Body with Active Flow Control

2013 ◽  
Vol 275-277 ◽  
pp. 402-408
Author(s):  
Bing Xin Wang ◽  
Zhu Hui ◽  
Zhi Gang Yang
Keyword(s):  
Flow Control ◽  
Recirculation Zone ◽  
Active Flow Control ◽  
The Body ◽  
Slant Angle ◽  
Control Approach ◽  
Pressure Drag ◽  
Active Flow ◽  
Velocity Pressure ◽  
Ahmed Body

The numerical investigations presented in this paper deal with active flow control approach at the rear end of the Ahmed body model with the slant angle of 25°.Results of the velocity, pressure and vorticity field demonstrate the main reasons that cause the pressure drag. The influence of the spanwise and streamwise vortices rolling up from the slant and the edges on the recirculation zone behind the body is examined. A control slot is set on the separated line at the conjunction of the roof and the slant. Two different actuation concepts by blowing and suction steady jets through the slot lead to a drug increase of 5.61% and a drug reduction of 13.20% with the efficiency of 12.53% respectively.

External aerodynamic investigation over Ahmed body for optimal topology selection between upper and under bodywork using ANN approach

2021 ◽  
Author(s):  
Virendra Talele ◽  
Nitish Karambali ◽  
Akshay Savekar ◽  
Sarthak Khatod ◽  
Sachin Pawar
Keyword(s):  
Drag Coefficient ◽  
Carbon Dioxide Emissions ◽  
Correlation Study ◽  
Primary Objective ◽  
Optimal Topology ◽  
Ann Model ◽  
Slant Angle ◽  
Post Process ◽  
Artificial Neural Network Ann ◽  
Ahmed Body

Aerodynamic improvements primarily result in decreased fuel usage and carbon dioxide emissions into the atmosphere. Numerous governments support ongoing aerodynamics development initiatives as a means of addressing the energy problem and reducing air pollution, Ahmed body investigation helps research to investigate versatile approaches and flexibility of design. This study is carried over a generic design of Ahmed body model. We attempted a passive arrangement system to reduce drag coefficient with a correlation of cases such as in primary objective varying parameter of slant angle from 20∘ to 30∘ proposed to monitor the behavior of drag coefficient. Once we finalized the optimum slant angle, which gives a lower drag coefficient, the next proposed configuration is to vary passive arrangement between lower and upper blend length to see the deflection of the boundary layer in correlation with the drag coefficient. The final topology is selected, which gives the lowest drag coefficient. The post-process correlation study was proposed by using an artificial neural network (ANN) scheme. The ANN model is developed between an achieved set of data from CFD investigation, ANN model indicates a strong correlation between the varying percentage of blend angle and increment percentage of the drag coefficient.

Unsteady flow structures around a high-drag Ahmed body

2015 ◽  
Vol 777 ◽  
pp. 291-326 ◽  
Author(s):  
B. F. Zhang ◽  
Y. Zhou ◽  
S. To
Keyword(s):  
Coherent Structures ◽  
Leading Edge ◽  
Side Surface ◽  
The Body ◽  
Flow Structures ◽  
Rear Window ◽  
Hairpin Vortices ◽  
Recirculation Bubble ◽  
Slant Angle ◽  
Ahmed Body

This work aims to gain a relatively thorough understanding of unsteady predominant coherent structures around an Ahmed body with a slant angle of $25^{\circ }$, corresponding to the high-drag regime. Extensive hot-wire, flow visualization and particle image velocimetry measurements were conducted in a wind tunnel at $\mathit{Re}=(0.45{-}2.4)\times 10^{5}$ around the Ahmed body. A number of distinct Strouhal numbers (St) have been found, two over the rear window, three behind the vertical base and two above the roof. The origin of every St has been identified. The two detected above the roof are ascribed to the hairpin vortices that emanate from the recirculation bubble formed near the leading edge and to the oscillation of the core of longitudinal vortices that originate from bubble pulsation, respectively. The two captured over the window originate from the hairpin vortices and the shear layers over the roof and side surface, respectively. One measured in the wake results from the structures emanating alternately from the upper and lower recirculation bubbles. The remaining two detected behind the lower edge of the base are connected to the cylindrical struts, respectively, which simulate wheels. These unsteady structures and corresponding St reconcile the widely scattered St data in the literature. The dependence on Re of these Strouhal numbers is also addressed, along with the effect of the turbulent intensity of oncoming flow on the flow structures. A conceptual model is proposed for the first time, which embraces both steady and unsteady coherent structures around the body.

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.

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 Optimal nonlinear eddy viscosity in Galerkin models of turbulent flows

2015 ◽  
Vol 766 ◽  
pp. 337-367 ◽  
Author(s):  
Bartosz Protas ◽  
Bernd R. Noack ◽  
Jan Östh
Keyword(s):  
Turbulent Flows ◽  
High Speed ◽  
Eddy Viscosity ◽  
Broad Class ◽  
Constitutive Relations ◽  
Body Height ◽  
Mixing Layer ◽  
The Body ◽  
Stream Velocity ◽  
Initial Vorticity

AbstractWe propose a variational approach to the identification of an optimal nonlinear eddy viscosity as a subscale turbulence representation for proper orthogonal decomposition (POD) models. The ansatz for the eddy viscosity is given in terms of an arbitrary function of the resolved fluctuation energy. This function is found as a minimizer of a cost functional measuring the difference between the target data coming from a resolved direct or large-eddy simulation of the flow and its reconstruction based on the POD model. The optimization is performed with a data-assimilation approach generalizing the 4D-VAR method. POD models with optimal eddy viscosities are presented for a 2D incompressible mixing layer at $\mathit{Re}=500$ (based on the initial vorticity thickness and the velocity of the high-speed stream) and a 3D Ahmed body wake at $\mathit{Re}=300\,000$ (based on the body height and the free-stream velocity). The variational optimization formulation elucidates a number of interesting physical insights concerning the eddy-viscosity ansatz used. The 20-dimensional model of the mixing-layer reveals a negative eddy-viscosity regime at low fluctuation levels which improves the transient times towards the attractor. The 100-dimensional wake model yields more accurate energy distributions as compared to the nonlinear modal eddy-viscosity benchmark proposed recently by Östh et al. (J. Fluid Mech., vol. 747, 2014, pp. 518–544). Our methodology can be applied to construct quite arbitrary closure relations and, more generally, constitutive relations optimizing statistical properties of a broad class of reduced-order models.

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