pressure loss factor

Junta_20361

Hi experts,

when we define the outflow boundary condition, there is a term called "pressure loss factor".

Normally, we don't define this value and let it as 0.

But what is the purpose of this? when should we use it and how to calculate the value?

Thanks!

acupro

This is from the Command Reference Manual:

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Pressure loss for inflow, outflow, and far_field types may be modeled through the pressure_loss_factor parameter. The following term is added to the pressure element boundary condition, if one exists:(2)

 

0.5*sgn(u• n)*k*ρ*(u• n)^2

 

where k is given by pressure_loss_factor; ρ is the density; u is the velocity; n is the outward-pointing normal to the surface; and sgn(u• n) is -1 for inflow boundaries and +1 for outflow boundaries. If pressure_multiplier_function is given, it is applied to the pressure variable before this term is added. The pressure loss factor may be scaled with pressure_loss_factor_multiplier_function.

 

########

 

Sometimes you can use this to 'add' some pressure to account for some other behavior downstream of the outlet.  Another usage would be to modify the flow rate at the particular outlet for a case with multiple outlets.  There's not much detail on what values to use for k...

 

In my experience, it's not really used that much in practice.

Junta_20361

acupro_21778 said:

This is from the Command Reference Manual:

########

Pressure loss for inflow, outflow, and far_field types may be modeled through the pressure_loss_factor parameter. The following term is added to the pressure element boundary condition, if one exists:(2)

 

0.5*sgn(u• n)*k*ρ*(u• n)^2

 

where k is given by pressure_loss_factor; ρ is the density; u is the velocity; n is the outward-pointing normal to the surface; and sgn(u• n) is -1 for inflow boundaries and +1 for outflow boundaries. If pressure_multiplier_function is given, it is applied to the pressure variable before this term is added. The pressure loss factor may be scaled with pressure_loss_factor_multiplier_function.

 

########

 

Sometimes you can use this to 'add' some pressure to account for some other behavior downstream of the outlet.  Another usage would be to modify the flow rate at the particular outlet for a case with multiple outlets.  There's not much detail on what values to use for k...

 

In my experience, it's not really used that much in practice.

hi acupro,

thanks for your information

acupro

Junta_20361 said:

hi acupro,

thanks for your information

You could also think about this as an additional 'resistance' to the exiting flow.  It can also help to damp out or reduce any vortices that are exiting the domain, or possibly reduce the tendency to have reverse flow (flow entering from the outlet).