1 Reply Latest reply on Oct 27, 2011 1:51 AM by Mark Vergot

    Modeling impeller in CFD to determine efficiency.

    Stacie Cornaire

      I'm new to solidworks flow and have been trying to learn how to set up a study to determine the polytrophic efficiency of an impeller. I haven't had much luck with creating such study. I'm looking for someone that has done this kind of analysis, any advice, suggestions or hints in using flow sim.


      My set up in solidworks is an assembly of the inlet shroud and impeller. i used the wizard with the settings of internal flow with rotation, fluid of steam, adiabatic walls and left the initial conditions as default. I created a solid part that outlined the impeller shape, disabled it in the component control and set it as the rotating region with a rpm. I then know I should set up my boundary conditions. I've used different combinations of the theoretical information for my boundary conditions since you can only use one condition on an inlet and outlet and I have more than that. If someone could tell me what is most important and to use for the boundaries I'd appreciate it. Also I'm not sure what my goals should be that I use in the study. Below is all the theoretical information I have on the design I'm trying to run.


      gas= steam

      Inlet temp= 268F

      Inlet total press.=40psia

      Outlet total press.= 80psia

      Outlet static press.= 62psia

      Outlet temp.= 455F

      volume flow=6,450 ACFM

      mass flow= 10 lb/sec

      efficiency= .79

      analysis set up.pngsolid region.png

        • Re: Modeling impeller in CFD to determine efficiency.
          Mark Vergot

          I usually run simulations including the volute, but it should be similar to set up. I use it to test a new design to create a part of a performance curve and get an idea of the power usage/ efficiency. I normally set the boundary condtions for the volute and wear plates as real wall - stator. The inlet and outlet I set to total static pressures, with the inlet as 1 atmosphere and the outlet at to a pressure to set the total dynamic head at which point of the performance I want to test.

          For goals, I set inlet and and outlet surface goals of mass flow rate for convergence, and total average pressure for non-convergence.

          For effeciency, I set another surface goal on the impeller vanes for z-component of torque (rotation about the z-axis).

          For convergence, I set the the flow criteria to between 1-5kg/s depending on the impeller and for the torque between 20-50 Nm. You need to turn off the number of iterations for convergence or the simulation will stop before it has actually converged. When the simulation converges the inlet and outlet mass flow rates should be close to equal and opposite. From experience the torque is usually fairly jumpy compared to the flows so I use more loose criteria for it.

          You'll need to fiddle around with your model and settings a lot because there are so many things that affect the simulation. I recommend starting with a large mesh setting at first and tighten it once you can get it working. Also, I've found when sometimes having troubles with convergence around BEP, to run a simulation at a lower head value.

          Once the simulation converges, you should have all the data to calculate your efficiency. ie. flow, head, rpm & torque.