Z E M C H 2 0 1 2 I n t e r n a t i o n a l C o n f e r e n c e
770
Figure 12: Unstructured mesh showing the Sawtooth
roof model and the main domain.
Figure 13: Pressure Coefficient (Cp) at
outlet opening wall surface. The Cp was
plotted along a vertical line 1.40m away
from the centre of outlet opening
.
Table 3. Convergence tests criteria for the leeward sawtooth roof
Model A1 - Pressure Coefficient (Cp) at outlet opening surface (1m
away from middle axis).
Model A1
Grid
Wind
velocity
Cp at axis S
[∆Cp]
RMS
residual
value
Course (Grid20)
1m/s
-0.305 to -0.395
-0.090
1 x 10
−4
Medium (Grid40)
1m/s
-0.294 to -0.362
-0.068
1 x 10
−4
Fine (Grid60)
1m/s
-0.282 to - 0.356
-0.074
1 x 10
−4
4.2. Boundary conditions
In this study, we analysed the normal (0°) wind direction and three wind velocities: 1m/s;
3 m/s, 5m/s and 10 m/s.
4.3. Solver settings
The simulation were performed with the software Ansys CFX (ANSYS 2010). The RNG
k
-ε turbulence model was chosen for this study because of its good performance in
predicting the surface pressure (Yang 2004); (Ramponi & Blocken 2012).
5.
Results and discussion
The comparison of the pressure coefficient Cp for each sawtooth roof models (A1, B1
and D1), are shows in figure 14. This comparison shows that model D1 got a slightly
higher pressure coefficient module than the other ones. As highlighted previously,
maximising the pressure coefficient module (-Cp) on the outlet opening surface is the
objective function. The bigger this pressure coefficient module, the greater the ventilation
rates can be.
