Computational Fluid Dynamics Questions and Answers for Experienced people on “Boundary Conditions – Constant Pressure and Periodic”.
1. When do we use a constant pressure boundary condition?
a) When there is an impermeable boundary
b) When there is constant pressure
c) When we do not know the flow distribution but we know the pressure at the boundaries
d) When we do not know the pressure at the boundaries
Answer: c
Clarification: When the flow distribution including velocity are not properly known but the boundary pressures are known, a constant pressure boundary condition is used.
2. While applying the constant pressure boundary condition, which of these is done?
a) Pressure is set to 0
b) Pressure correction is set to 1
c) Pressure correction is set to zero
d) Pressure is set to 1
Answer: c
Clarification: When constant pressure boundary is used, pressure is set to a fixed value which is the boundary pressure value and pressure correction is set to zero.
3. Which of these pose a problem in constant pressure boundaries?
a) Velocity
b) Flow direction
c) Density
d) Heat flux direction
Answer: b
Clarification: Constant pressure boundaries are used when the velocity is unknown. The main problem in this is the flow direction. It has to be found while solving the flow properties.
4. Which of these conditions is used to find the velocity component of the boundary while using constant pressure boundary condition?
a) Conservation of angular momentum
b) Conservation of linear momentum
c) Energy conservation
d) Continuity
Answer: d
Clarification: Velocity components are obtained as part of the solution procedure. The flow directions are obtained by ensuring that continuity is satisfied at every cell.
5. Constant pressure boundary condition makes the pressure correction cell nearest to the boundaries to act as ____________
a) Source or sink of mass
b) Source or sink of heat
c) Convection cell
d) Diffusion cell
Answer: a
Clarification: While implementing constant pressure boundary conditions, the nearest pressure correction cell acts as a source or sink of mass. This happens for all pressure boundary cells.
6. The velocity components in the nodes which are not at the boundary are found using ____________
a) energy equation
b) continuity equation
c) equations of state
d) momentum equation
Answer: d
Clarification: The velocities in the non-boundary nodes are found using u and v-momentum equations. After this, the boundary side velocity component is obtained using these values.
7. Periodic or cyclic boundary conditions are a type of ____________
a) wall boundary conditions
b) constant pressure boundary conditions
c) inlet boundary conditions
d) symmetry boundary conditions
Answer: d
Clarification: Periodic or cyclic boundary conditions are repeated symmetry boundary conditions. The matching of variables in Periodic or cyclic boundary conditions is done in the same way how it is done for symmetry boundary conditions.
8. For cyclic boundary conditions, which of these should be equated?
a) The flow variables
b) Gradient of the flow variables
c) Flux of the flow variables
d) Second derivative of the flow variables