[hnemati]

Dears

I have a question regarding the time derivative of pressure in low-Mach number approximation of NS equations. Referring to the work " Numerical study of a channel
flow with variable properties" done by Nicoud, depending on the whether the simulation system is closed or open, the time derivative of pressure can be defined as ... (see the equation 8 of his paper) for closed system or zero for open system.
Could somebody tell me why for open system this is zero?
Thank you all

[FMDenaro]

Originally Posted by hnemati

Dears

I have a question regarding the time derivative of pressure in low-Mach number approximation of NS equations. Referring to the work " Numerical study of a channel
flow with variable properties" done by Nicoud, depending on the whether the simulation system is closed or open, the time derivative of pressure can be defined as ... (see the equation 8 of his paper) for closed system or zero for open system.
Could somebody tell me why for open system this is zero?
Thank you all

I suppose that is due to the fact that it is assumed to be the (constant) atmospheric pressure