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# Computational Fluid Dynamics – Philosophy

1 - Question

Which among the following is a reason why we do not completely rely upon ground tests for analysing fluid dynamics?

a) Three-dimensional flows cannot be analysed

b) Facilities do not exist in all fight regimes

c) The output generated is not as accurate as theoretical analysis

d) Long run-time

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Answer: bExplanation: Ground test facilities can be used to model three-dimensional flows also and even they produce accurate results in a less run-time. But they cannot be used to test all flight regimes as they want artificial set-up for every single property of the flow.

2 - Question

Which one do you think is not possible with wind tunnels for testing trans-atmospheric vehicles?

a) Continuously changing Mach number

b) Transonic flows

c) Simultaneously modelling high Mach numbers and high temperatures

d) Hypersonic flows

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Answer: cExplanation: Continuous change in Mach numbers can be done in wind tunnels. Transonic and hypersonic wind tunnels also exist. If we try to model high speeds at high temperatures, the wind tends to reduce the temperature as we have wind flowing over the stationary model in a wind tunnel.

3 - Question

CFD is the third approach for fluid flow analysis. What are the other two approaches?

a) Theoretical and experimental

b) Physical and Mathematical

c) Numerical and experimental

d) Experimental and physical

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Answer: aExplanation: Pure theoretical and pure experimental approaches were the two approaches prior to the advent of CFD. To overcome the disadvantages in both of these approaches, Computational Fluid Dynamics was invented.

4 - Question

When were the foundations of experimental fluid dynamics laid?

a) 19th century

b) 18th century

c) 16th century

d) 17th century

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Answer: dExplanation: Experimental fluid dynamics was started in France and England in the 17th century when the relation between force and velocity is found from experiments.

5 - Question

The eighteenth and nineteenth centuries witnessed the development of theoretical fluid dynamics in ____ countries.

a) Asian

b) American

c) European

d) African

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Answer: cExplanation: Theoretical fluid dynamics was developed in European countries in the 18th and 19th centuries first theoretical derivation of drag equation is found. D ∝ ρ SV2

6 - Question

This invention of the 20th century and accurate numerical methods have revolutionized the way we analyse Fluid Dynamics.

a) High-speed digital computers

b) Personal computers

c) Submarines

d) Rocketry

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Answer: aExplanation: Invention of high-speed digital computers allowed modelling and simulating fluid flows with high accuracy as the level of computing involved in the numerical methods is very high. Without this, it would have been very difficult to solve the numerical algorithms.

7 - Question

Which of the following is not true about CFD?

a) There will be a need for theory and experiments

b) CFD is an equal partner of theoretical and experimental analyses

c) CFD will complement theoretical and experimental Fluid Dynamics

d) CFD will replace the approaches of pure theory and pure experiments

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Answer: dExplanation: The future of fluid dynamics will rest upon a proper balance of pure experiment, pure theory and computational fluid dynamics, each complementing one another in their limitations.

8 - Question

The design of this experimental NASA aircraft was aided by CFD in early days.

a) Northrop

b) HiMAT

c) Douglas

d) Rockwell

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Answer: bExplanation: HiMAT (Highly Manoeuvrable Aircraft Technology) is a NASA experimental aircraft designed to test concepts of high manoeuvrability. Wind tunnel tests showed that there will unacceptable drag. Wings of this aircraft is redesigned using CFD to overcome this problem.

9 - Question

CFD analyses Fluid Dynamics using this method.

a) Analytical

b) Physical

c) Numerical

d) Experimental

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Answer: cExplanation: As the experimental analysis of fluid flow problems are very expensive, CFD uses theoretical method to analyse them. Among the two theoretical methods stated above (Analytical and Numerical), the analytical method uses approximations which makes the theory unreliable. So, CFD uses the numerical method.

10 - Question

CFD provides results of ____________

a) Continuous time varying results at discrete locations

b) Discrete points of space and time

c) Continuous spatial results at discrete time points

d) Continuous in time and space

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Answer: bExplanation: CFD discretizes the equations and also the domain and solves the discretized equations for only the points in the discretized domain using numerical methods.