# Can circum-avg-axial give flow rate?

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 January 10, 2007, 12:20 Can circum-avg-axial give flow rate? #1 Amit Guest   Posts: n/a Sponsored Links I've been using Fluent for a while now, and I've noticed that something is very odd about the circum-avg-axial function. In simulating incompressible flow through any internal geometry, the average value of axial velocity should remain constant (with a weighting factor of the local radius). In simulating a pipe constriction, resulting in backflow, the average of axial velocity should remain also remain constant with weighting of r (integral of u dot n r dr d theta= flow rate = constant). When I run circum-avg-axial on the constriction geometry ( axial velocity times the radius) however, I do not get a constant value. The value fluctuates wildly, especially around the region of the geometry change. I have tried the circum-avg-axial of: axial-velocity axial-velocity * radial coordinate axial-velocity * radial coordinate ^ 2 I do not think any of these is giving me the equivalent to the local flow rate. Why does circum-avg-axial give this wrong output? Or what function combination should I be using to calculate the flow rate from axial velocity at a given axial distance down my pipe? It is important that I get flow rate at a specific axial distance-- such as z = 1 or 2, and not flow rate on the entire interior. Thanks in advance for your help, Amit

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