Louvered Gate

[MAHLY361]

I’m attempting to model a gate with a discharge coefficient of 0.64 and a free area of 50%. The gate’s dimensions are 4 meters by 4 meters, and it’s quite thin. My strategy involves using the HVAC system with a vent that represents the total area and duct area of 2 meters by 2 meters to symbolise the free area. Additionally, since I anticipate flow in both directions, I’m including the forward and reverse losses by converting K = 1/cd^2.
I’m comparing the pressure upstream and downstream (1 meter away from the gate) to calculate the pressure drop through a rectangular orifice using hand calculations.
However, I’m not getting the correct answers. Is my approach correct, or are the values I used incorrect?

[drjfloyd]

You need to use the pressures at the face of the gate. There is a NODE PRESSURE output.

[MAHLY361]

Shouldn’t the values be measured upstream and downstream and not at the nodes. As the flow converges at the nodes. Secondly, are the parameters assumed correct for the calculations and approach.

[drjfloyd]

The pressures used in the HVAC model are computed at the face of the VENTs.

You have the correct formula for coverting Cd to K and your approach is good in terms of the duct size and applying losses.

[MAHLY361]

Thanks for your support. I am trying to compare this to the screen drag approach where a free area is specified albeit, there is no coefficient of discharge to specify in the screen drag. In the screen drag validation example the pressure drop was compared upstream further from the restriction. Hence, in my calculations I am comparing the pressure upstream and downstream of the duct, compared to hand calculations of rectangular orrifice pressure drop. When I compare this, I am not getting the same value.

[mcgratta]

We need a very simple example case in order to help further.

[drjfloyd]

The screen drag case is a closed channel with no slip walls. There is no pressure drop axially before and after the screen. We measure pressure upstream and downstream by a short distance in that case since the flow field is noisy at the particle plane.

HVAC uses the pressure at the wall vent. If you want to check the HVAC solution you need to check it at the wall vent and not away from the wall. As stated earlier there is a NODE PRESSURE output. Use that.