Lecture Objectives

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
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
4
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

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 Dt

• 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
Unstructured hexa (2-D)
Uniform
boundary-fitted, structured grid
Nonuniform (2-D)
10
Grid type and resolutionTetra
Structured
Unstructured
11
Grid type and resolutionPolyhedral mesh
12
Example Analysis of

• Natural Ventilation

13
Natural VentilationScience Park, Gelsenkirchen,
Germany
14
(No Transcript)
15
Natural VentilationScience 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 VentilationStack-driven flow in an
atrium
20
Natural VentilationWind scoop
21
Natural VentilationDuct and underfloor cross
ventilation
22
Natural VentilationChimney ventilation
23
Natural VentilationSolar-assisted ventilation
24
Window Design
25
Natural VentilationOpen University Design
Studio, Milton Keynes, UK
26
Natural VentilationOpen University Design
Studio, Milton Keynes, UK