[sidharath]

I am trying to calculate the mass flow across a cavity section in CFX-CFD-Post.

1. In Function Calculator tab, I used "massFLow" function to calculate the mass flow through the desired location/surface.

2. I calculated massFlowave density, massFlowave normal velocity and Area of the surface. Mass flow is then computed from the density, area and velocity.

The mass flow results in step 1. and step 2 are very different and I think the step 1 result is realistic.

Can anyone help me in diagnosing what exactly i am doing wrong in step 2.

Numerical model details:

I am modelling a centrifugal compressor using RANS in Ansys-CFX. I am modelling a near surge unsteady operating point as steady state and I acknowledge its consequences. It shouldn't bear any connection with the mass flow ambiguity I am facing I reckon.

I've attached the image of surface I am using to calculate the mass flow.

Any pointers would be great.
Thank you

[Opaque]

Keep in mind the following:

Average of a*b*c is not equal to the Average of a * Average of b * Average of c unless the three variables a, b and c are constants in the "space of the average", say "area average", "time average", "massflow average", etc..

[sidharath]

I'll keep this in mind and I did the similar calculation at another region of stable flow and area weighted average values of rho and velocity yields the mass flow that is comparable to directly computed massFlow values.