Loss Coefficient for Opening Boundary Condition

Liliane Maciel · March 7, 2015, 18:15

Hello everybody,

I haven't realized yet if the loss coefficient (f) used by CFX is the same of the loss coefficient ( $\zeta$ ) I have seen in other references. I have the opening discharge coefficient value and I have to set the loss coefficient in CFX, but I am not sure how those coefficients are related.Here is what I found in the Ansys Help:

Quote:

You can optionally specify a Loss Coefficient which can be used to model the pressure drop across a screen or other planar resistance at the opening. The pressure drop is calculated using:

$\Delta$ p $_{loss}$ = $\frac{1}{2}$ f $\rho$ Un²

where f is a specified Loss Coefficient and Un is the normal component of velocity at the opening boundary location.

and the relation I found in some papers between discharge coefficient (Cd) and loss coefficient ( $\zeta$ ) is the following:
Cd = $\frac{1}{\sqrt{\zeta}}$

Is $\zeta$ and f the same?

ZeroState · February 18, 2018, 03:05

Hi Liliane, I got stuck in this same question that you asked here few years ago. I din't found any smoking gun, but to me the discharge coefficient is indeed related to this resistance loss coefficient parameter.

I've reached this point after studying the modelling process of entire walls made of perforated bricks. Geometric modelling has been dropped as computational costs soared. Instead we are using porous domain in order to simulate the behaviour of such walls made of cobogós. If that is (or was) you case, or should it be of anyone searching answers on the internet, it is also important to highlight that as the angle of attack (between wind diretion and building) varies, the value for the discharge coefficient will also change, and so should the resistance loss coefficient.

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February 18, 2018, 03:05		#2
ZeroState New Member Bruno Raviolo Join Date: Sep 2015 Posts: 6 Rep Power: 11	Hi Liliane, I got stuck in this same question that you asked here few years ago. I din't found any smoking gun, but to me the discharge coefficient is indeed related to this resistance loss coefficient parameter. I've reached this point after studying the modelling process of entire walls made of perforated bricks. Geometric modelling has been dropped as computational costs soared. Instead we are using porous domain in order to simulate the behaviour of such walls made of cobogós. If that is (or was) you case, or should it be of anyone searching answers on the internet, it is also important to highlight that as the angle of attack (between wind diretion and building) varies, the value for the discharge coefficient will also change, and so should the resistance loss coefficient.