Posted: May 3rd, 2015

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ASSIGNMENT BRIEF

Introduction

Understanding of aerodynamic and road loads is very important in establishing acceleration and braking characteristics, stability as well as fuel consumption characteristics of vehicles. More and more semi-trailers have started to use cab deflectors to minimise drag and hence fuel consumption. Therefore, aerodynamic characteristics of such deflectors need to be evaluated very carefully.

Specifications:

It is expected that students will develop a computer model of a semi-trailer of their own choice(without a cab deflector)  using CAD Package of their own choice. After developing the computer model students are expected to investigate possibility of using a cab deflector to reduce drag and hence fuel consumption  using CFD package FLUENT.

1) Students are required to analyse the effect of presence of a cab deflector on drag force acting on the vehicle. The design velocity should be 55 MPH should act opposite to the direction of motion of the vehicle. Calculate drag force on all faces of the semi-trailer for both with and without cab deflector simulations.

2) Investigate the response of the vehicle if flowing air approaches the vehicle at an angle. Assuming flow velocity to be same, compute drag, lift and side forces acting on the vehicle for flow angles of 15⁰ and 30^o .

4)  Investigate the effect of length of development of flow (take two different upstream lengths 20 x height of the vehicle and 30 x height of the vehicle) on the accuracy of results obtained. This analysis needs to be carried out at 55 MPH with air flow opposite to the semitrailer motion. Only use the model with cab deflector.

5) Investigate the effect of width of flow field around the vehicle (Take two different widths, 3 times the width of the vehicle and 10 times width of the vehicle.) on the accuracy of results. This analysis needs to be carried out at 55 MPH with air flow opposite to the semitrailer motion. Only use the model with cab deflector.

6) Design, develop and execute validation programme for the simulations carried out. For example, you may use Rapid prototype machine for developing a small scale model of the vehicle. This model could be tested in the wind tunnel. The other option may be to use the data published in the literature.

7) Based on the investigations above propose an optimal shape of the cab deflector. Clearly justify your choice.