Question

a) The figure 3a below shows a commercial vehicle and a car. Sketch the flow pattern that you would expect to find for each vehicle where the fluid has ideal

and real properties. Also for each case, provide a brief explanation of the flow pattern you have presented and the impact on the approach that is needed to analyse the flow. Include in your discussion any likely pressure variations that occur over the vehicle body. (You may wish to copy the image into your answer document). b) Figure 3b shows the upper part of the vehicle windscreen covered in a film of water. If the vehicle is stationary and starting from first principles, estimate the volume flow down the screen per unit of screen width. Explain and justify any assumptions that you make. If the vehicle is moving, how will this affect the flow down the screen and will it modify the analysis and if so, what assumption needs to be changed and why. c) Aspects of the flow for the vehicle shapes shown in Figure 3a can be analysed using a boundary layer approach. Explain where this may be applied for the car. Given a speed of 96 km/hr estimate the extent to which laminar and turbulent flows contribute and for the commercial vehicle (truck), estimate the wake dimension. The vehicle is 10 m long by 2.8 m wide by 3.5 m high. Also estimate the power required to drive the truck along a level road. d) Detailed design is undertaken using a computational approach. For one of the vehicles,set out the process that you would adopt for doing this and how you would prescribe velocity and/or velocity gradients to model a stationary and moving vehicle.

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