Wind-tunnel testing of a new transport aircraft is typically used to
Answer: C
A modern programme computes far more configurations than it could ever test, then uses the tunnel to anchor those computations and to produce the data the certification authorities require. Structural strength and engine performance are established on entirely separate rigs.
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A water tunnel is sometimes used instead of a wind tunnel because
Answer: D
The same Reynolds number is reached at a far lower speed in water, so vortex formation and breakdown unfold slowly enough to be filmed and understood. Dye injection gives exceptionally clear visualisation, which is why water tunnels are favoured for studying delta-wing vortices.
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A smoke tunnel is chiefly useful for
Answer: A
Fine filaments of smoke trace the streamlines and make separation and circulation immediately visible, which is why smoke tunnels are so effective for teaching and for a first look at a shape. They are qualitative instruments and are not used for force data.
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A tunnel intended for automotive testing usually incorporates a moving ground plane because
Answer: B
On a real road the ground moves with the vehicle and carries no boundary layer relative to it. A fixed tunnel floor grows one, corrupting the underbody flow and the wheel wakes, so a rolling belt and boundary-layer suction ahead of it are used to reproduce the true condition.
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A model is tested at \( 40 \) m/s in water rather than air. Taking water as \( 1000 \) times denser and \( 55 \) times more viscous, the Reynolds number is multiplied by about
Answer: C
Reynolds number goes as density over viscosity, so the factor is \( 1000/55 = 18.2 \). The same Reynolds number is therefore reached at roughly one eighteenth of the speed, which is exactly what makes unsteady vortex behaviour observable in a water tunnel.
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Assertion (A): Water tunnels are favoured for studying delta-wing vortex behaviour.
Reason (R): The same Reynolds number is reached at a far lower speed in water than in air.
Select the correct answer from the options below.
Answer: D
Both are true and the second explains the first. Roughly eighteen times lower speed for the same Reynolds number means the flow evolves slowly enough to film and interpret, and dye injection gives a clarity that smoke in air cannot match.
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Consider the following statements about specialised tunnel facilities:
1. A water tunnel reaches a given Reynolds number at a much lower speed than air.
2. An automotive tunnel needs a moving ground plane to represent the road.
3. A smoke tunnel is the preferred facility for accurate drag measurement.
Which of the statements given above is or are correct?
Answer: A
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: water is about fifteen times more viscous than air but eight hundred times denser, so the same Reynolds number is reached at roughly a fifteenth of the speed - which is why water tunnels suit slow, detailed flow visualisation. And an automotive tunnel needs a moving ground and rotating wheels, since a stationary floor grows its own boundary layer that a road does not have. Statement 3 is wrong: a smoke tunnel is a low-speed visualisation facility with no balance and no useful accuracy for drag.
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Match each specialised facility in List I with its distinguishing purpose in List II.
List I
A. Water tunnel
B. Smoke tunnel
C. Automotive tunnel
D. Cryogenic tunnel
List II
1. Showing streamlines at low speed for teaching
2. Slow, clear observation of unsteady vortex flows
3. Full-scale Reynolds number at transonic Mach number
4. Testing over a moving ground plane
Select the correct match.
Answer: B
Each facility exists because a general-purpose tunnel cannot do that particular job well. Between them they cover clarity of observation, teaching, a correctly represented ground condition, and the Reynolds number that ordinary tunnels cannot reach.
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Which of the following is NOT a reason a moving ground plane is used in automotive testing?
Answer: C
The belt reproduces the correct boundary condition at the ground; it does nothing for the Reynolds number, which is set by speed, size and the fluid. The other three all describe why the fixed floor is wrong and what it spoils.
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Taken together, the corrections and calibrations described in this topic exist because
Answer: D
Every reading contains the influence of walls, supports, stream misalignment and the tunnel's own turbulence alongside the aerodynamics of the shape. The whole apparatus of corrections is there to separate the two, so that what is reported is the model's behaviour in free air.
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