[Mohamed911]

Hello everyone,

I'm working on 4 parts axial pump (Inducer, rotor, diffuser, straightener), and to minimize the calculation time, I tried to used design point to get the pump efficiency and the head pressure at different rotational speeds:

Parts:
Inducer: S1
Rotor: R1
Diffuser: S2
Straightener: S3

Pressure Head:
massFlowAve(Total Pressure in Stn Frame )@S1 Outlet - massFlowAve(Total Pressure in Stn Frame )@S3 Inlet)

Torque: (J)
torque_z()@R1 Blade

Density: (Kg/m^3)
massFlowAve(Density)@Inlet

Flow rate (m^3/s)
massFlow()@S3 Outlet / areaAve(Density)@S3 outlet

Angular velocity (rad/s)
-7000 [rev/min]

Efficency
(Flow rate * Pressure head) / (Torque * Angular velocity)

at the design point, I used 4 angular velocities (7000,10000,12000, and 15000). however, when I update them I get a constant pressure head and a constant torque at all point

If you have any ideas on how I fix it or if the equations I used are wrong.. please let me know


Thank you

[ghorrocks]

FAQ: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

In your case, as the pressure head is the same at all points, I would look at how you define pressure head and how you have defined the simulation boundary conditions.

[Mohamed911]

the boundary conditions I'm using are:
Inlet :static pressure (60 mmHg)
Outlet: Mass flow rate (0.0875 kg/m^3)
Walls: No-slip
Turbulent: k-e stard model

Ps: inelt area = outlet area

[ghorrocks]

You cannot debug this from the few inputs you attach. You have to look at the details of how you set it up and how the solver worked. You cannot do this over the forum. You need to do this yourself by looking at the details.

[Mohamed911]

the conditions I'm using are all correct, I already did all simulations using the same condition and the pressure head is variating (at the same flow rate, the pressure head increases when we increase the angular velocity)

[Opaque]

Get two output files for different design points, and compare them side by side, and try to understand any difference, or too many "coincidences"

That is one way to understand how many different calculations you really did, not how many you submitted.

[Mohamed911]

I did it. I used the same equations in every simulation manually, and I did get different pressure heads and different efficacy.

the problem is that I had to do all the simulations individually

[ghorrocks]

You will find the experienced CFX users on the this forum rarely use CFX inside workbench, but use it stand-alone. The link between CFX and workbench is not reliable sometimes and you full control of what the solver is doing. It appears you have just found this same problem.