Learning Forum

[Matheus1.moreira]

Hello everyone,

I am running a steady state MRF simulation in ANSYS Fluent of an axial flow pump at constant angular speed, but the results are consistently non physical: the pump behaves like a turbine. In all cases, the inlet pressure ends up higher than the outlet pressure (negative pressure rise), even though I am confident the impeller rotation axis and direction are correct.

What I observe

The solution converges (residuals drop and mass imbalance is small), but:

• inlet pressure is higher than outlet pressure

• the pressure field suggests energy extraction rather than addition

• this happens systematically regardless of boundary condition choice

Boundary conditions tried

I tested multiple inlet and outlet boundary condition pairs:

• Pressure inlet and mass flow outlet

• Mass flow inlet and pressure outlet

• Total pressure inlet and static pressure outlet

• Static pressure inlet and static pressure outlet with different values

None of these configurations produces a physically reasonable positive pressure rise.

I can provide screenshots and values if needed:

• mesh near rotor stator interface and y plus

• pressure and velocity contours and streamlines

• residuals and mass imbalance

• angular speed, target flow rate and expected pressure rise

Thank you for any help or direction.

[Petros]

Hi, what value do you set at the outlet pressure bondary condition? Is the pump pushing fluid against gravity? Also how did you set a static pressure at the inlet?

A meridional picture of the mesh would help.