Computational Fluid Dynamics Multiple Choice Questions on “CFD Advantages and Disadvantages”.
1. Computational investigation is _____________ experimental investigation.
a) Faster than
b) At the same speed of
c) Slower than
d) Cannot be compared
Answer: a
Clarification: Computational investigation can be carried out at a higher speed when compared to experiments especially when the models are simple and suitable for computation.
2. What is the disadvantage in predicting a complex problem with a very limited objective in CFD?
a) Time-consuming
b) Impossible to solve
c) Slower
d) Expensive
Answer: d
Clarification: For difficult problems with complex geometry, strong non-linearity, etc., if the objective is very limited, then use of CFD will become costlier than experimenting. For such cases, experimental results are suitable.
3. What is the advantage of numerical methods over analytical method?
a) Speed
b) Cost
c) Flexibility
d) Time
Answer: c
Clarification: Analytical methods of solving a problem is not applicable for many of the cases. Only a tiny part of the range of practical problems can be solved using analytical methods. Numerical methods can be used to solve a very wide range of practical problems.
4. Why ideal conditions should be simulated in CFD?
a) Experimental analysis is impossible for ideal conditions
b) Experimental set-up will have imperfections
c) Experimental set-up will lead to wrong solutions
d) Experimental analysis can be done for ideal cases
Answer: b
Clarification: Some research purposes will need non-practical processes to be analysed. Setting up experimental analysis for such cases involves a lot of steps and that may not yield proper results as the set-up cannot be perfect.
5. CFD can give ____________ results than experiments.
a) Detailed
b) Accurate
c) Reliable
d) Approximate
Answer: a
Clarification: Flow properties at only particular points can be obtained in experiments. CFD can provide information about multiple flow properties at many points in a single analysis.
6. For optimization of designs, CFD is ___________
a) Slow and expensive
b) Cost-effective but slow
c) Fast but expensive
d) Cost-effective and fast
Answer: d
Clarification: For design optimization, multiple tests should be done on different cases and many trials should be done. CFD is faster and cost-effective than experiments in this case.
7. An optimal prediction is ______________
a) Computational only
b) A combination of Computational and Experimental
c) Analytical only
d) Experimental only
Answer: b
Clarification: Experimental results are difficult to obtain in all the places, especially, in the locations of mounting. If we solely rely upon CFD, problem may arise out of wrong modelling. So, it is always better to use CFD models to get detailed results and using experiments to validate them.
8. Consider the following case. A teacher wants to show the effects of severe turbulence over an aircraft to the students. What is the best way to simulate it?
a) Wind tunnel with analytical backup
b) Wind tunnel with CFD backup
c) Flow visualization in wind tunnel
d) Turbulence modelling and animation using CFD tools
Answer: c
Clarification: As the intention is to just show the flow, CFD is not preferable. Solving turbulence model in CFD with animation needs complex solutions. So, in this case, choosing wind tunnel and visualizing the flow is the best way.
9. ____________ of a mathematical model is a limitation to CFD.
a) Reliability
b) Accuracy
c) Solvability
d) Validity
Answer: d
Clarification: Validity of a mathematical model is the relevancy of the model with the problem taken. If the mathematical model does not comply with the problem being solved, the entire prediction may go wrong.
10. I have to model a simple rectangular wing for my experimental aircraft testing a new technology on it. I have to choose an airfoil among the ten options given for my wing which would give the best aerodynamic performance. Suggest the best method to test and fix one airfoil.
a) CFD analysis
b) Literature
c) Wind tunnel models
d) Calculations
Answer: a
Clarification: This is an optimization case. CFD can be used to do trial and error analysis on the best fitting wing.