Fundamentals of Aerodynamics Questions and Answers

Answer: D

Correct answer: Weight

A body force acts throughout the volume of the fluid without contact, and gravity is the only one of consequence in ordinary aerodynamics. Pressure, shear stress and skin friction all act on surfaces, and they are what integrate to give the aerodynamic force on a body.

Answer: A

Over the whole ordinary envelope of pressure and temperature, air obeys the perfect gas law closely enough for engineering purposes. Only at very high temperatures, where dissociation begins, does the assumption break down.

Answer: B

Temperature falls with height, and the speed of sound follows temperature, so the same true airspeed represents a larger fraction of it. This is why long climbs are flown at constant indicated airspeed and then at constant Mach number.

Answer: C

Correct answer: Rho one A one V one equals rho two A two V two

Mass flow is conserved along a stream tube, so \( \rho A V \) is constant. In incompressible flow the density cancels and \( AV \) alone is constant, which is why a narrowing duct speeds the flow up; in compressible flow the density term is what makes a converging-diverging nozzle behave as it does.

Answer: D

Correct answer: The flow accelerates through the reduced area

Continuity forces the velocity up through the throat, and Bernoulli’s equation then requires the static pressure to fall by the amount the dynamic pressure has risen. The total pressure is unchanged - nothing has been added or removed, only exchanged between the static and dynamic terms.

Answer: A

Steadiness, absence of viscosity and constant density are all required; whether the flow is laminar or turbulent is not part of the derivation, though in practice turbulence implies viscous losses that violate the inviscid assumption.

Answer: B

In incompressible flow the total pressure is what a tube facing directly into the stream reads, and it stays constant along a streamline in the absence of losses. Any fall in total pressure between two points indicates loss, whether viscous or through a shock.

Answer: C

Correct answer: The relevant similarity parameters are matched

Model results transfer when the dimensionless groups that govern the physics are the same: Reynolds number where viscous effects matter, Mach number where compressibility does. Matching absolute speed or size is neither necessary nor sufficient - it is the ratios that determine the flow pattern.

Answer: D

Correct answer: Reynolds number cannot usually be matched at model scale

A model a tenth of full size would need ten times the speed at the same conditions to match the Reynolds number, which is generally impossible without pressurising or cooling the tunnel. The model is therefore tested at a lower Reynolds number, and its boundary layer behaves differently - particularly at transition and separation, which is where the discrepancies show.

Answer: A

Coefficients are dimensionless and therefore transfer between scales when the similarity parameters match, which is exactly why they are defined. The dimensional quantities of force, area and weight all differ with size.