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# MCQs on Hypersonics and Computational Fluid Dynamics

Why is analyzing hypersonic bodies dependent on the use of computational fluid dynamics (CFD)?

a) Lack of experimental facility

b) Complex to analyse hypersonic body

c) Time consuming

d) Hypersonic flight regimes are hypothetical

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a

Explanation: The hypersonic bodies which fly at very high Mach numbers exist today which are tough to analyse experimentally because it is hard to replicate such high Mach numbers in a wind tunnel. The hyperonic flow has very high Reynolds number and tempertaure which is not easy to replicate. For these reasons, engineers resort to the use of computational fluid dynamics to design vehicle flying in hypersonic regime. The results are accurate enough.

Experimental work on hypersonic bodies involves testing Mach number, Reynolds number and temperature simultaneously.

a) True

b) False

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b

Explanation: When carrying out pure experiments on hypersonic bodies, the tests carry out either involves Mach number, Reynolds number or temperature attained. All the parameters cannot be tested at the same time or same testing facility. Thus the data procured is always a compilation of multiple data sources.

Which of these characteristics vary as a result of chemically reacting gas compared to the perfect gas?

a) Pitching moment coefficient

b) Temperature

c) Drag

d) Lift

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a

Explanation: Chemically reactive flow affects the pitching moment over the space shuttle in hypersonic flow. Usually, for a chemically reactive gas, the pressure on the forward part of the shuttle body is higher and it is lower in the rearward part. This leads to a positive pitching moment of the shuttle.

Which of these is not the reason to resort to CFD for solving hypersonic problems?

a) Inexpensive

b) Fast

c) Accurate

d) Complex use

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d

Explanation: Hypersonic flow makes use of computational fluid dynamics to get accurate results because it is very inexpensive, is fast and gives straighforward results. The practical engineering problems are approximated by making some assumptions to find pressure distribution, lift drag etc. The hypersonic flow usually varies from subsonic and supersonic flow because of the presence of a thick boundary layer between the surface and thin shock wave. This cannot be solved by the conventional boundary layer methods. Hence CFD plays an important role in finding the results.

Which of these approaches is not used to find the solution of the fully viscous flowfield in hypersonic flow?

a) Viscous shock-layer solutions

b) Parabolized Navier-Stokes solution

c) Full Navier-Stokes equation

d) Boundary-layer solution

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d

Explanation: In analyzing the hypersonic flow, it is assumed that the flow is viscous throughout. There are three main approaches taken which are-Viscous shock-layer solutions, parabolized Navier-Stokes solution and full Navier-Stokes equation. These three equations are much more accurate than the boundary-layer equations in order to solve the fully viscous shock layer present over the blunt body in a hypersonic flow.