Numerical Investigation of Aerodynamic Braking for a Ground Vehicle

Original Contribution


The purpose of this article is to observe the effect of an air brake on the aerodynamics of a ground vehicle and also to study the influence of change in the parameters like the velocity of the vehicle, the angle of inclination, height, and position of the air brake on the aerodynamics of the vehicle body. The test subject used is an Ahmed body which is a generic 3D car body as it retains all the aerodynamic characteristics of a ground vehicle. Numerical investigation has been carried out by RNG k-ε turbulence model. Results are presented in terms of streamlines and drag coefficient to understand the influence of pertinent parameters on flow physics. It is found that with the use of an air brake, though the drag coefficient remains more or less constant with velocity, it increases with the increase in height and angle of inclination of the air brake. But the effect of position of air brake on the coefficient of drag is surprising since for certain heights of the air brake the drag coefficient is maximum at the foremost point and as the air brake moves towards the rear it is first observed to decrease and then increase. It is also observed that with the increase in height of the air brake the drag coefficient monotonically decreases as the position of the air brake is moved towards the rear. Taguchi method has been employed with L16 orthogonal array to obtain the optimal configuration for the air brake. For each of the selected parameters, four different levels have been chosen to obtain the maximum drag coefficient value. The study could provide an invaluable database for the optimal design of an airbrake for a ground vehicle.


Aerodynamics Computational fluid dynamics Aerodynamic brake Ahmed body Ground vehicle Optimization Taguchi method 



Anti-lock braking system


Boundary layer


Re-normalization group


Adj MS

Adjusted mean squares

Adj SS

Adjusted sums of squares


Drag coefficient

C, C, Cµ, σε, σk

RNG k-ε model parameters


Total degrees of freedom




Gravity, 9.81 m/s2


Height of the air brake, cm


Turbulent kinetic energy per unit mass, m2/s2


Length of the car, m


Pressure, N/m2


p value


Reynolds number

Seq SS

Sequential sums of squares


Mean strain rate tensor


Velocity, m/s


Velocity of the vehicle, m/s


Length of the air brake from the defined origin, cm

Greek letters


Density, kg/m3


Viscosity, N-s/m2


Dissipation rate of turbulent kinetic energy per unit mass, m2/s2


Angle of Inclination of the air brake, degree


Constants in RNG k-ε model


Ratio of turbulence to mean shear time scale


RNG k-ε model parameter




i, j, k

Spatial coordinates





The author is thankful NIT Warangal for assistance in performing simulations.


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Copyright information

© The Institution of Engineers (India) 2017

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringNational Institute of Technology WarangalWarangalIndia

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