Wind Tunnel Testing Questions and Answers

Answer: A

Each component addresses one requirement of a good circuit: quality of the stream reaching the model, straightness of that stream, efficient recompression after the test section, and turning the flow round the circuit without loss.

Answer: B

These four are the standard corrections applied to almost every low-speed tunnel result. Confusing horizontal buoyancy with the model's weight is the classic error; it is entirely a pressure-gradient effect produced by the tunnel itself.

Answer: C

Each regime imposes its own requirement. Subsonic testing needs only a fan and a duct; transonic testing needs relief at the walls; supersonic testing needs a nozzle and an efficient diffuser; and hypersonic testing needs enthalpy that only a brief, violent process can supply.

Answer: D

The four are complementary rather than competing: two look at the surface and two at the field, and between them they give separation lines, shock positions, the velocity field and the pressure distribution without a single pressure tap being drilled.

Answer: A

Every route to a higher Reynolds number costs something, and the choice between them is what distinguishes one facility from another. The table is essentially the design decision behind every large transonic tunnel built since the 1970s.

Answer: B

A smaller model lowers the Reynolds number in proportion to its length, which is the very problem the other three options exist to solve. Note that raising the speed works but spoils the Mach number, which is why the first two are preferred.

Answer: C

Closed circuits cost considerably more, since they need a return duct, corner vanes and a larger building. Their advantages are entirely operational, which is why open-circuit tunnels still dominate teaching laboratories where capital cost governs.

Answer: D

The name is misleading: horizontal buoyancy has nothing to do with weight. It is entirely a pressure-gradient effect, produced when the tunnel's own wall boundary layers thicken and contract the effective area along the section.

Answer: A

Solid walls make transonic interference worse, and near Mach one they cause the section to choke outright. Ventilated walls let flow spill in or out and were the innovation that made routine transonic testing possible.

Answer: B

The arithmetic is right but the consequence is fatal: a flight speed of 70 m/s becomes 700 m/s in the tunnel, which is beyond Mach 2 and destroys the compressibility similarity being sought. This is precisely why pressurised and cryogenic tunnels exist.