Testing a model upright and then inverted is a standard technique for removing
Answer: A
Inverting the model reverses the sign of the angularity error while leaving the true aerodynamic forces unchanged, so averaging the two runs cancels it. It is a cheap and effective check, and a discrepancy between the two runs is itself a useful diagnostic.
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The principal reason computational fluid dynamics has not replaced wind-tunnel testing is
Answer: B
Attached, well-behaved flows are computed reliably, but transition, separation and unsteady turbulent behaviour still depend on models that must be calibrated and checked against experiment. The two are used together, with the tunnel anchoring the computation rather than competing with it.
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A balance reads a lift of \( 1200 \) N and a drag of \( 90 \) N. The model's lift-to-drag ratio is nearest to
Answer: C
Dividing, \( 1200/90 = 13.3 \). Because drag is the far smaller number, any systematic error in the drag channel matters much more proportionally than the same error in lift would, which is exactly why flow angularity is calibrated so carefully.
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Flow angularity of \( 0.5 \) degrees resolves what fraction of a lift of \( 1200 \) N into the drag channel?
Answer: D
The component is \( 1200 \sin 0.5^\circ = 1200 \times 0.00873 = 10.5 \) N. Against a true drag of perhaps 90 N that is a twelve per cent error from half a degree of misalignment, which shows why upright-and-inverted testing is worth the extra runs.
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Assertion (A): Wind-tunnel models are often tested both upright and inverted.
Reason (R): Inverting the model reverses the sign of the flow angularity error while leaving the true forces unchanged.
Select the correct answer from the options below.
Answer: A
Both are true and the second explains the first. Averaging the two runs cancels the angularity contribution, and a difference between them is itself a warning that something in the setup needs attention. Half a degree of misalignment can bias drag by ten per cent or more.
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Assertion (A): Computational methods have not displaced the wind tunnel.
Reason (R): Transition and separation still rest on models that require experimental calibration.
Select the correct answer from the options below.
Answer: B
Both statements are true and the second is the reason for the first. Attached flows are computed well, but the phenomena that decide maximum lift, buffet and drag creep are exactly the ones the turbulence models handle least reliably. Tunnel and computation are used together.
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Consider the following statements about force measurement in a tunnel:
1. A six-component balance resolves three forces and three moments.
2. Flow angularity biases the drag channel more seriously than the lift channel.
3. Magnetic suspension eliminates support interference.
Which of the statements given above is or are correct?
Answer: C
All three are correct. The second holds because drag is much the smaller quantity, so a given absolute error is proportionally far larger there, and the third is the reason magnetic suspension is pursued despite its cost and complexity.
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Consider the following statements about the relationship between CFD and tunnel testing:
1. Attached flows are computed reliably by modern methods.
2. Transition and separation still require experimental validation.
3. Wind tunnels are now used only for teaching.
Which of the statements given above is or are correct?
Answer: D
The first two are correct and describe how the two tools are actually used together. The third is plainly false: every transport aircraft programme still runs thousands of hours of tunnel time, precisely because the phenomena that decide performance limits are the ones CFD predicts least confidently.
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The overall purpose of the correction chain applied to raw tunnel data is to
Answer: A
Every correction, whether for blockage, buoyancy, angularity or support interference, exists to strip away the influence of the tunnel itself. What should remain is the behaviour the model would have shown in free air, which is the only thing that transfers to full scale.
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Which single factor most limits how directly wind-tunnel results transfer to full scale?
Answer: B
Almost every other difficulty can be corrected or calibrated away, but the Reynolds number gap changes the physics of the boundary layer itself, moving transition and separation. Trip strips, pressurisation and cryogenic operation are all attempts to close that one gap.
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