# Computational Fluid Dynamics Questions and Answers – Applications

This set of Computational Fluid Dynamics Multiple Choice Questions & Answers (MCQs) focuses on “Applications”.

1. For which of the following purposes can an automobile company not use the CFD tool?
a) Study heat transfer between its parts
b) Increase aerodynamic performance
d) Increasing fuel economy

Explanation: For increasing the load capacity, the strength of the vehicle should be more. Therefore, a structural analysis would be ideal for that purpose. There will not be a need for fluid flow analysis.

2. The internal flow analysis of an automobile running based on Otto-cycle will need a ___________ analysis.
a) Transient
c) Finite difference
d) Finite element

Explanation: The piston inside an internal combustion Otto-engine moves up and down continuously which makes the flow unsteady. A flow of fluid can be called steady if its properties do not vary with time.

3. Which of these forces will have to be analysed using CFD to improve the aerodynamic performance of a vehicle?
a) Lift
b) Drag
c) Thrust
d) Weight

Explanation: The drag force is the one which pushes a body backward during its motion. Therefore, to increase the efficiency of a vehicle, there should be less drag.

4. Which of these will not be applicable for CFD in naval applications?
a) Propeller Design
c) Lift analysis
d) Stability in manoeuvring

Explanation: Hydrodynamic analysis on the propeller of a naval vehicle is done. As a vehicle will be moving through the air, wind loads should also be analysed. The stability of a vehicle when it changes its position (manoeuvring) is also analysed. But, the lift force need not be analysed.

5. CFD can be used to understand the flow behaviour of liquid metal during mould filling. This can be used to ____________
a) Change the mould according to fluid flow
b) Choose the best metal
c) Improve casting techniques
d) Change temperature

Explanation: The mould cannot be changed according to fluid flow. It should have the shape of the product needed. Choosing the metal depends upon the application and structural concern. The temperature change may affect the quality of the product. By knowing the flow pattern, casting techniques can be improved.

6. Which of these models would be the best for flow over a submarine?
a) 3-D Navier-Stokes equation for compressible flow without a turbulence model
b) 3-D Navier-Stokes equation for incompressible flow without a turbulence model
c) 3-D Navier-Stokes equation for compressible flow with a turbulence model
d) 3-D Navier-Stokes equation for incompressible flow with a turbulence model

Explanation: Incompressible flow is chosen as the flow of water will mostly be incompressible unless the flow velocity is very high. Turbulence model is chosen as the flow properties will get abrupt change due to high Reynolds number.

7. CFD applications provide information for the design of furnaces with ____ thermal efficiency and ____ emissions of pollutants.
a) Increased, reduced
b) Reduced, increased
c) Reduced, reduced
d) Increased, increased

Explanation: Thermal efficiency should be increased to get the best out of the input energy. Considering the environmental effects, the emission of pollutants should be less.

8. Which is not an internal analysis?
a) Combustion
b) Turbulence
c) Flow over compressor
d) Exhaust pipes

Explanation: Flow over the compressors actually takes place inside a gas turbine engine. But, analysing the flow over the compressor blades is an external flow analysis.

9. What would be the major difference between aerodynamic and hydrodynamic analyses?
a) Temperature
b) Reynolds Number
c) Velocity
d) Domain

Explanation: Reynolds number of the flow would be the major change as the density and viscosity of water will be higher than that of air. Therefore, while modelling a hydrodynamic flow, care should be taken.

10. This created a problem in modelling supersonic blunt nose.
a) Change of flow equations from elliptic to hyperbolic
b) High speed with high temperature
c) Supersonic Mach number
d) High temperatures

Explanation: Straight to the nose of the vehicle, the shock is normal. This results in a subsonic region and elliptic flow equations. But, downstream the shock is oblique which creates a supersonic region resulting in the elliptic equation. This was the problem in modelling supersonic blunt nose. In later years this was overcome by a better model.

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