4 Replies Latest reply on Dec 12, 2013 11:21 AM by Jared Conway

# Axial Fan Rotating Region- Pressure/Velocity Averaging at Inlet and Outlet Surfaces

I have set up a simulation of an axial fan using internal flow and a rotating region.  (This is a slightly different scenario than my previous post because of the duct shapes used in this one).  The inlet ducting makes a 90 degree angle-- I know this is an awful design, but that is the point of the simulation. I want to see how the 90 degree angle affects fan performance.  There is a non-uniform pressure and velocity distribution at the inlet surface of my rotating region extruded body.  There is a low pressure region toward the outside of the 90 degree bend and a high pressure region towards the inside of the 90 degree bend.  However, when I look at the flows through the fan, they are uniform all the way around.  The pressure profiles around each of the 8 blades are virtually identical.  It seems that the flow through the fan is unaffected by the non-uniform inlet conditions...  The only reason for this as far as I can see would be if Solidworks averages the inlet conditions across the entire surface of the rotating region inlet and then applies that to the rotating region.  Is this the case?  If so, I will need a different method of simulating this problem... Thoughts/ideas?

• ###### Re: Axial Fan Rotating Region- Pressure/Velocity Averaging at Inlet and Outlet Surfaces

There is no averaging going on. Post a picture and let us see what's up. How big is the rotating region compared to the rotor? They should be very close in outside dimensions.

• ###### Re: Axial Fan Rotating Region- Pressure/Velocity Averaging at Inlet and Outlet Surfaces

averaging at the face isn't happening but the assumptions around rotating regions might be causing you a problem. have you looked at the technical reference and solving engineering problems documents regarding how the flow simulation rotating region works? one of the assumptions that the majority of the flow is entering uniformly and axially.

• ###### Re: Axial Fan Rotating Region- Pressure/Velocity Averaging at Inlet and Outlet Surfaces

Thank you guys. I think I found my answer in the technical reference.  If I understand this correctly, the averaging of a ring means that I will get circumfrentially averaged boundary conditions to the rotating region in each ring.  I guess this means that if my goal is to see the performance effect of different pressure conditions at different circumfrential points on the inlet, the rotating region will not work because the boundary condition applied to the rotating region will be the same all the way around the rotation axis.  Conditions vary radially but not circumfrentially.  That Fig. 1.2 I think is sort of misleading.  Is the rotation axis supposed to be pointed into the page?  I hope I am interpretting this correctly.  Now what I see when I run the simulation makes sense.

• ###### Re: Axial Fan Rotating Region- Pressure/Velocity Averaging at Inlet and Outlet Surfaces

the rotation axis is right, the rotation region is basically a bunch of disks

i'm not following what you're trying to define vs circumferential and radial components. it might be helpful to describe the full scope of this application.

also, generally when you're going to try pushing the limits, i'd suggest connecting with your reseller so they can double check with the developers. even with almost 10 years experience, if you brought this project to us as a consulting project (based on what i think you're trying to do), i would check with the deveopers to make sure i'm not missing something.