1. Lecture Objectives -Analyze some examples related to natural ventilation

2. 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

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

4. 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

5. Simulation period and time step 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 Set of steady state simulations (there is no link in-between previous and next time step)

6. Time step  Uniform Variable –Linear –Piecewise User defined

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

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

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

10. Grid type and resolution Tetra Structured Unstructured

11. Grid type and resolution Polyhedral mesh

12. Example Analysis of Natural Ventilation

13. Natural Ventilation: Science Park, Gelsenkirchen, Germany

16. Natural Ventilation and CFD simulation Wind driven outdoor flow Buoyancy driven indoor flow Solution approach –Model boundary condition in-between outdoor and indoor domain –Couple CFD with 1) energy simulation program (buoyancy driven flow) 2) multi-zone modeling program (inter-zonal flow)

17. External flow Wind profile

18. Buoyancy driven indoor flow Important parameters Geometry Heat sources –Intensity (defined temperature or heat flux) –Distribution –Change (for unsteady-state problem) Openings Defined –Pressure –Velocity

19. Natural Ventilation: Stack-driven flow in an atrium

20. Natural Ventilation: Wind scoop

21. Natural Ventilation: Duct and underfloor cross ventilation

22. Natural Ventilation: Chimney ventilation

23. Natural Ventilation: Solar-assisted ventilation

24. Window Design

25. Natural Ventilation: Open University Design Studio, Milton Keynes, UK