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Lecture Objectives

Lecture Objectives. Meshing Unsteady State CFD. Grid type and resolution. Hexa Uniform hexa Nonuniform hexa Unstructured hexa Body-fitted coordinate hexa - Structured Unstructured Tetra mesh Structured Unstructured Polyhedral mesh. Grid type and resolution hexa.

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Lecture Objectives

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  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 • Unstructured Polyhedral mesh

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

  4. Grid type and resolutionTetra Structured Unstructured

  5. Grid type and resolutionPolyhedral mesh

  6. Computational resource saving by mesh type

  7. 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 Unsteady-state (Transient)CFD simulations

  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 forF = 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-stateor 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 Depends on the boundary condition of considered phenomenon Time step Depends on the time scale With too large time step quasi-steady-state simulation Simulation period and time step 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 boundaries

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