SUBJECT: AUTO 400 DATE: 13/12/12 Ground Vehicle Aerodynamics TIME: 1.5 Hr

INSTRUCTIONS TO CANDIDATES:Answer all questions.All necessary work must be shown and any assumptions must be stated clearly. Simple calculators may be used. Wherever needed:

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QUESTION 1 [30 Marks]In the Figures below, we identify the different flow regions associated with uniform flow over a cylinder:a. In the first set of Figures (Fig. 1a), identify the flow regions/characteristics that

the arrows indicate.

Fig. 1a: Basic features of the flow past a circular cylinder

θ

b. In Figure 1b, three pressure distributions are shown associated with uniform flow over a cylinder. Identify which one corresponds to inviscid flow and which ones to the flow conditions of Fig. 1a. Explain your choice.

c. Figure 1c shows the drag coefficient as a function of Reynolds number for a smooth cylinder. On the curve there are 5 points (A-E). Indicate which ones correspond to the flow conditions of Fig. 1a. Explain your choice.

Fig. 1b: Surface pressure distributions

Fig. 1c: Drag coefficient as a function of Reynolds number

QUESTION 2 [20 Marks]A 25000 kg truck coasts down a steep mountain grade without brakes, as shown in the Figure. The truck’s ultimate steady-state speed, V, is determined by a balance between weight, rolling resistance, and aerodynamic drag. Assuming that the rolling resistance for a truck on concrete is 1.2% of the weight and that the drag coefficient is 0.76, determine V.

QUESTION 3 [25Marks]The pressure distribution on the surface of an automobile is shown on the Figure below. Explain the character of the pressure distribution, and comment on the direction of the net drag force and the net lift force.

Figure: Pressure distribution on the surface of an automobile

Figure: Truck coasting down a steep mountain

QUESTION 4 [25 Marks]The Figure below shows the cross section of an air intake manifold.

a. Explain the design objective associated with the guide vanes. b. Do you think the surface finish of the manifold should be rough or polished?

Explain.