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

1. Which among these is used to specify a particular problem which we consider for solving in CFD?

a) Boundary conditions

b) Governing equations

c) Governing laws

d) Solution method

View Answer

Explanation: Boundary conditions can define a particular problem. When the same governing equations are used to solve different problems, boundary conditions are the one which makes the problem unique.

2. What are the two major types of boundary conditions?

a) Wall and symmetry

b) Inlet and outlet

c) Dirichlet and Neumann

d) Initial and physical

View Answer

Explanation: Dirichlet and Neumann boundary conditions are the two boundary conditions. They are used to define the conditions in the physical boundary of a problem.

3. Which of these best define the Dirichlet boundary conditions for the property Φ at a point ‘b’ in a boundary?

a) \(\frac{\partial^3 \Phi}{\partial^3 x}\)

b) \(\frac{\partial^2 \Phi}{\partial^2 x}\)

c) \(\frac{\partial\Phi}{\partial x}\)

d) Φ_{b}

View Answer

Explanation: Dirichlet boundary conditions are where the values of the properties are directly given. So, among the options given, Φ

_{b}represents the Dirichlet boundary condition.

4. The boundary condition represented in the following diagram is ___________

a) Dirichlet

b) Periodic

c) Neumann

d) Axisymmetric

View Answer

Explanation: In the diagram, the heat flux value is given. This kind of boundary condition where the flux of a property is given is called the Neumann boundary condition.

5. The Neumann and Dirichlet boundary conditions are _________ and _________ in mathematical terms.

a) value specified, flux specified

b) flux specified, value specified

c) flux specified, gradient specified

d) value specified, time specified

View Answer

Explanation: In mathematical terms, Neumann Boundary conditions are called flux specified and Dirichlet boundary conditions are called value specified boundary conditions. These names are based on their characteristics.

6. In Dirichlet boundary conditions, the flux values _________

a) can be calculated

b) are unknowns

c) are known

d) are 0

View Answer

Explanation: In Dirichlet boundary conditions, the value of the flow property will be given. By using this, the flux values can be created. They are not unknowns.

7. Initial conditions are used for __________ problems.

a) time-dependent problems

b) boundary value problems

c) control volume problems

d) finite difference problems

View Answer

Explanation: For time-dependent problems, initial conditions are used to specify the conditions at t=0. This will be helpful to find the solutions at the time points.

8. Which among these is a combination of value specified and flux specified boundary conditions?

a) Dirichlet

b) Mixed

c) Neumann

d) Symmetry

View Answer

Explanation: Type 3 boundary conditions are the mixed boundary conditions. Mixed boundary condition combines Neumann and Dirichlet boundary conditions.

9. Which of these is not a combination of Neumann and Dirichlet Boundary conditions?

a) Cauchy boundary conditions

b) Wall boundary conditions

c) Mixed boundary conditions

d) Robin boundary conditions

View Answer

Explanation: Wall boundary conditions are the boundary conditions specified at walls. The other types (Cauchy, mixed and Robin boundary conditions) are different combinations of Dirichlet and Neumann Boundary conditions.

10. Which is not a type of boundary conditions in CFD?

a) Cyclic boundary conditions

b) Symmetry boundary conditions

c) Wall boundary conditions

d) Nodal boundary conditions

View Answer

Explanation: Boundary conditions are not defined at nodes and nodal boundary conditions do not exist. There are many types of boundary conditions in CFD. Some of them are

- Wall boundary conditions
- Symmetry boundary conditions
- Inlet boundary conditions
- Outlet boundary conditions
- Constant pressure boundary conditions
- Periodic or cyclic boundary conditions

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