How do I add laminar flow grilles?
Let us consider an example where we would like to add two 1200mm x 600mm laminar flow grilles each having a supply flow rate of 0.125m3/sec.
The velocity used for a diffuser/supply and extract boundary can be fully determined from the volumetric flow rate, the area of the boundary and the angle which the air comes out of the boundary.
For boundaries with a 0 degree discharge angle:
flow_rate (m3/s) = velocity (m/s) * area (m2)
therefore
velocity = flow_rate/area
velocity = 0.125/(1.2*0.6) = 0.17361 m/s
For boundaries with a non zero degree discharge angle the component in the direction normal to the boundary must be the same as the 0 degree case to satisfy mass conservation (i.e. to get the correct volumetric flow rate into the computational domain).
But the velocity in the direction of discharge would be:
velocity = flow_rate/area/cos(discharge_angle)
velocity = 0.17361 / cos(discharge_angle)
If this is not giving you the velocity you would expect based on the specs of the grille then it is important to consider how the figure in the specs is derived. If this is the case please feel free to send in the grille specs and our support team will check them for you.
If it is the MicroFlo prediction for the velocity far away from the grille you are talking about, rather than the speed at the boundary, then this will depend on the mesh you use. A coarse mesh will mean the flow from the grille will diffuse too quickly (when compared to reality) and the throw will be under-predicted. Increasing the number of cells will improve the accuracy of the results.
