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UNIT 9 THEORY AND PRACTICE

I Explaining tests and experiments

1 In pairs, discuss the following tests and experiments and their main advantages and
disadvantages.
1 computer models and simulations
2 reduced-scale testing
3 full-scale testing
2a In pairs, suggest how the following development tools could be used for
aerodynamic testing.
11 Computational Fluid Dynamics (CFD)
• field testing
12 a wind tunnel equipped with a rolling road

b ► 9.1 An international team of researchers are collaborating on the design of an
experimental energy-efficient vehicle. They are discussing the tools available for developing
the vehicle’s aerodynamic design. Read the conversation and answer the following
questions.
6 What options are available for wind tunnel testing in terms of scale?
7 Why are rolling roads useful in wind tunnels when testing vehicles?
8 What issue will determine whether or not a rolling road is necessary?
9 What point is made about the reliability of CFD and wind tunnel data?
10 What problem is mentioned with regard to outdoor testing?

Tony: With the aerodynamics there are three development tools available to us. The first is CFD
software - Computational Fluid Dynamics. With that, the tests would obviously be virtual, based
on a computer model. The second option is to go into a wind tunnel, with a scale model, or a
full-size mock-up. In either case, we'd probably need to use a tunnel with a rolling road.
Lisa: Would that be necessary?
Tony: Well, the thing is, the wheels generate a lot of turbulence when they're spinning. So to
simulate that, you need a rolling road.
Lisa: Yes, I know, but if we go for a bodywork design where the wheels are mostly enclosed,
which is likely, would that be an issue?
Tony: Possibly not. It depends how fully enclosed they are.
Lisa: OK. I'm just raising the question.
Tony: Sure, it's something we can look at. The third option, then, is field testing, actually
running the prototype outside on a runway, or somewhere. So we can use these tools in isolation
or as a combination. The question is, how can we gather as much data as possible with the
limited budget we have?
Guy: Well, we need to bear in mind that the problem with aero is that it's not just about data
gathering. You also have to validate the data.
CFD and wind tunnels are not a hundred percent reliable. The acid test only comes when you try
out a full-scale prototype in real conditions. We need to make sure that everything is tried-and-
tested outside, with a full-scale trial run.
Lisa: Yeah, but let's not forget we're designing a car that does a hundred kilometres an hour, it's
not a supersonic aircraft! The aero’s not going to be that critical.
Tony: Plus, with changeable weather, it's not easy to do back-to-back testing out in the field.
Guy: No, of course not. I'm just saying we need to be careful...

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