Computational Fluid Dynamics Multiple Choice Questions on “CFD Solution Procedure”.
1. Which of these will not come under the three main elements of CFD packages?
a) Pre-processor
b) Post-processor
c) Code creator
d) Solver
Answer: c
Clarification: In order to provide their users with easy access to its solver, CFD packages have sophisticated input and output interfaces. The three main elements of CFD packages are pre-processor, solver and post-processor.
2. The region of interest for analysis in CFD is called as _______________
a) Cell
b) Domain
c) Mesh
d) Grid
Answer: b
Clarification: The region of interest for solving a particular fluid flow problem is called domain. The first step in pre-processing is to define the geometry of this domain.
3. Over 50% of the time spent in the industry on a CFD project is devoted to the definition of the domain geometry and grid generation. Which one will be the reason for this?
a) More grids will give better results
b) Calculation time is directly proportional to the number of cells
c) To generate non-uniform grids
d) To generate an optimal grid which is a compromise between desired accuracy and solution cost
Answer: d
Clarification: Accuracy of a CFD solution directly depends on the number of grids. On the other hand, if there are more grids, the cost of computation will increase. To overcome this, a grid which is a compromise between both of these should be generated. So, a lot of time is spent on grid generation.
4. Which of these could be an optimal mesh?
a) Non-uniform
b) Uniform
c) Grids with increasing lengths
d) Grids with decreasing lengths
Answer: a
Clarification: A uniform grid has all the cells with the same dimensions. The flow properties may not vary uniformly in the domain. Therefore, a non-uniform grid with more cells in the areas with large variations is an optimal way of grid generation.
5. The solution of a flow problem is defined at discrete points in the domain is called as _________
a) Elements
b) Cells
c) Grids
d) Nodes
Answer: d
Clarification: Nodes are the intersection of cells in a domain. These are the points where the flow properties are defined after solving the problem. The flow is not analysed in continuous points of the domain.
6. CFD packages solve the algebraic equations of flow using ____________ method.
a) Direct
b) Iterative
c) Analytical
d) Trial and error
Answer: b
Clarification: The physical phenomena makes the algebraic equations complex and non-linear. Hence, an iterative method is used in CFD packages to solve these equations.
7. Validation of a CFD code requires information about ____________
a) Boundary conditions
b) Domain
c) Grids
d) Cells
Answer: a
Clarification: Validation is the process of checking the accuracy of a CFD analysis. This needs highly detailed information about the boundary conditions.
8. Which of these will fall into the post-processing category?
a) Definition of boundary conditions
b) Grid generation
c) Flow visualization
d) Discretization
Answer: c
Clarification: Post-processing is the final step in CFD after pre-processing and solving. This involves various methods of visualizing the flow as well as getting quantitative information.
9. The step – specification of boundary conditions – in CFD comes under ________________
a) Post-processing
b) Solving
c) Discretizing
d) Pre-processing
Answer: d
Clarification: Boundary conditions at the cells which are in touch with the domain boundaries must be specified before starting to solve a problem in CFD. So, it comes under pre-processing.
10. Which is the input part of a CFD problem?
a) Post-processing
b) Flow visualization
c) Pre-processing
d) Solving
Answer: c
Clarification: The pre-processing part of a CFD problem is the first step before starting to process the problem. This is where the inputs are specified.