[EngineeringStudent]

Hello all,
I am trying to simulate the flow behaviour in a mixing tank, while I can get a solution, it is not what I expected. So, my impellors tip speed is 4.9 m/s (I am confident I have done this calculation correctly and also confident the radians/s I put into the frame motion was right). However when looking at my max velocity plot i have a considerable region above the impeller with a velocity magnitude greater than this (6.7m/s) . So my question is, am I wrong for thinking the tip speed should be the maximum velocity achievable?


Sorry I could not figure out how to add pictures

I'm not sure if this is useful but it is a 75mm Diameter (height = 10mm) 4 blade pitched blade turbine, rotating at 1250 rpm (130.9rad/s). I have all surfaces set as stationary no slip, (except symmetry condition for surface), am using k - omega sst, and have a maximum y+ only slightly above 1.

[EngineeringStudent]

Capture.jpg

model.PNG
resid.jpg

[Guvennergiz]

Did you check the mesh dependency?

[EngineeringStudent]

Hello,
thankyou for your reply, after mesh independence I did see abit of improvement in my results! However it turns out this is normal by the looks of it, After looking at many papers I found one that has the same sort of maximum velocity position that exceeds the impeller tip speed. I suppose the low pressure zone behind the blade acts like the top of an aerofoil and speeds up the fluid or something.

Just incase in 5 years time someone is wondering the paper I was referring to :
https://www.sciencedirect.com/scienc...96890412002531

Thanks again mate,
Have a good one!