1. Lecture Objectives
Meshing
Unsteady State CFD

2. Grid type and resolution
Hexa
Uniform hexa
Nonuniform hexa
Unstructured hexa
Body-fitted coordinate hexa
- Structured
Unstructured
Tetra mesh
Structured
Polyhedral mesh

3. Grid type and resolution hexa
Unstructured hexa (2-D)
Uniform
boundary-fitted, structured grid
Nonuniform (2-D)

4. Grid type and resolution Tetra
Structured
Unstructured

5. Grid type and resolution Polyhedral mesh

6. Computational resource saving by mesh type

7. Unsteady-state (Transient) CFD simulations
Computationally very expensive
Steps
Identify the problem
Many problems do not require unsteady-state sim.
Identify equations which should be unsteady-state
Define the simulation period
Define the required time steps
Adjust other simulation parameters
turbulence model, mesh, convergence criteria, number of required iterations, etc.
Require substantial investigation for each problem

8. Computationally very expensive
Change of  in volume dxdydz In Time
Discretize equation
System of equation for each time step
ap and f are function of Dt
f is function of previous value for F x =
1) Solve the system using the simple algorithm
2) Change the boundary conditions
3) Update the coefficient
4) Solve the new system of equations A F

9. Steady-state, unsteady-state or quasi-steady-state
Examples
Airflow around the airplane
Airflow in the room
Airflow around the building
Injection of pollutant in the chamber experiment
Flow in the automobile engine cylinder
DNS simulation of flow in the boundary layer

10. Simulation period and time step
Depends on the boundary condition of
considered phenomenon
Time step
Depends on the time scale
With too large time step quasi-steady-state simulation
Set of steady state simulations
(there is no link in-between previous and next time step)

11. Time step Dt
Uniform
Variable
Linear
Piecewise
User defined

12. Transient boundaries For unsteady-state airflow created by transient