Inlets and Diffusers Questions and Answers

Answer: C

Correct answer: Only three

The first three are right. The fourth has the lip wrong: a rounded lip serves the static and low-speed case, where air must turn sharply into the intake without separating. At supersonic speed a sharp lip is wanted, since a blunt one would generate a detached bow shock and a great deal of drag.

Answer: D

Correct answer: Only three

The first three are right and the fourth contradicts the first. Statically the engine draws air from all around, so the streamtube far upstream is much wider than the intake and contracts into it. In cruise the reverse holds: the free stream is faster than the intake requires, so the streamtube is narrower and diffuses on the way in.

Answer: A

The other three are exactly what an intake exists to do. An inlet adds no energy at all: it converts kinetic energy already present into static pressure, and the best it can manage is to lose as little total pressure as possible doing so.

Answer: B

The other three arise only where shocks exist. Lip separation at static conditions is a subsonic and take-off problem, and it is why supersonic intakes with sharp lips often carry auxiliary blow-in doors for the ground case.

Answer: C

Correct answer: Fitting a boundary layer diverter

A diverter raises recovery, by keeping the low-energy fuselage boundary layer out of the intake. The other three all reduce it: a stronger terminal shock destroys more total pressure, ingested boundary layer air arrives with less to begin with, and separation in the diffuser wastes what remains.

Answer: D

Correct answer: A uniform reduction in total pressure

Distortion is non-uniformity, so a reduction that is the same everywhere is not distortion at all - it is a loss of recovery, which is a different quantity measured differently. Circumferential and radial variation and swirl are all genuine forms of distortion, and each affects the compressor in its own way.

Answer: A

The other three are genuine reasons variable geometry earns its place. It adds weight, complexity and a maintenance burden rather than saving any, which is why it appears only where a fixed intake cannot cover the envelope.

Answer: B

Throttling reduces the engine's demand while the capture area stays fixed, pushing the intake far below its matched condition. The shock then oscillates in and out of the duct, producing pressure fluctuations that can damage both structure and engine.

Answer: C

Boundary layer air is low in total pressure and highly non-uniform, so it degrades both the average and the distribution at the compressor face. A diverter costs drag and weight, and this is exactly the penalty it exists to avoid.

Answer: D

Loss across a normal shock rises steeply with upstream Mach number, so a single shock wastes far too much at 2.2. Turning the flow through several weak oblique shocks first lets the terminal normal shock be weak, which is where the recovery is regained.