Nodal boundary condition

Prabin Pradhananga_22497

Hi experts,

 

Could you please explain the significance of nodal boundary condition on a single node only? I have grabbed the following picture from acusolve validation manual.

https://help.altair.com/hwcfdsolvers/acusolve/topics/acusolve/turbulent_flow_through_a_pipe.htm

When I checked the model, I could see that there's fixed pressure only at a single node 8908. How does this work? 

acupro

The concept of the 'FixedPressureNode' typically applies to cases where there are no other pressure boundary conditions - and is used to set a base pressure.  For a case with an inlet and outlet - the outlet is typically set as outflow BC with a specified pressure.  That sets all other pressures in the solution relative to that pressure at the outflow boundary.  In internal flows (no inlet/outlet) there is no pressure boundary condition, so the resultant pressures can 'vary' with no relation to previous time steps / iterations.  One would still get the same pressure difference, but the values could vary.  That single node with a fixed pressure helps ground the pressure to a given level.  One would normally want to set that in a location where there is not much action in the flow.  This is not so important in a steady-state case, but can be quite important in a transient as all the time steps should be related.