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Old   June 20, 2008, 03:24
Default YPlus Values and SST Model
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I've had a lot of difficulties modelling an experimental setup with a fan and have posted questions to this group before. After developing quite a complex numerical model I am now getting results which are not too bad, when compared with the experimental values, but I have a couple of questions which I hope someone who has fan modelling experience may be able to help me with.

I am using the SST turbulence model as it is very important for my modelling to be able to see where separation occurs on the blades. I have been using Y+ values of 1 and 2 to calculate the first prism height of the boundary layer, which I understand is neceesary for SST, along with having at least 10 nodes within the boundary layer.

To see just where the automatic wall function is being employed I have made contours of yplus on the blades and I can't get these below 2 unless I use a y+ of 0.5, which means I'm predominantly using the auto wall function in the modelling. The residuals never go much below 10E-3, but I am monitoring the torque and this flattens off quite well, which I am taking to be a converged solution.

I have also experimented with different time steps (currently I'm using 1/rotational speed), but this makes little difference to the convergence. I am getting quite big residuals for momentum in certain parts of the domain, when I alter the domain size.

I am a bit lost as to how to proceed, since I seem to be dealing with quite a few variables.

My question is to anyone who has used SST for fan modelling and wants to get a good picture of the flow over the blades, what type of convergence do you get and what yplus are you using.

Thanks in advance for any suggestions.

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Old   June 22, 2008, 18:47
Default Re: YPlus Values and SST Model
Glenn Horrocks
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What is the blade Reynolds number? Are using the turbulence transition model? Do the blades have a gross separation or are they near the design operating point and are largely attached flows?

Glenn Horrocks
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