Possible to define inlet velocity at normal to face?


#1

I wonder that inlet velocity can be defined at normal to face.
I’m now working for wind comfort with various wind directions. For example, N,E,W,S wind directions will be fine if I make a background box with parallel X or Y direction. My question is that if Inlet face does not parallel with X or Y directions, is there any ways to put inlet value on normal to inlet face (i.e. wind direction is 30 degree)?
In simulation part of Simscale, there are only define X-, y-, z- velocity (it seems that only inlet velocity parallel with coordinate. is there any function about define inlet velocity at normal to face?

Regards
JYC


#2

Hi @sohwind,

Do you mean that you want to define different wind directions, for example a 45 degree NS diagonal wind direction?

If so, you can do so by setting all faces of the entire bounding box that is not the top or ground as the two vectors of the direction of your wind. Another way would be to have a large enough domain encompassing your entire geometry that is circular, that way you can properly define which direction (still in both their vector components) that the wind is coming in from and it should be accurate.

Cheers.

Regards,
Barry


#3

Hi, Barry

Thanks for your quick answer. If I use a boundary layer profiles for wind speed and turbulent intensity at inlet (express function of vertical profile), do I also decompose vertical profile function into each x-y directions? I have no idea how to do that. do you have any clues to do that?

Thanks for your help.

Regards
JY


#4

Hi @sohwind,

Ah so you plan to use an ABL inlet? Thats going to be much more complex to calculate.

Yes you are able to do that. However of course its a little complicated. So you should know that every calculation is based on your velocity and the other critical factor is your ABL velocity. Do note that these two are different and you will need to read through literature or sample projects like here in order to get out the equations you need. I’ll give a brief overview here.

You have 3 primary equations, one for velocity, one for turbulent kinetic energy (TKE) and one for dissipation depending on the model used. For the last one, you generally pick between k-esp or k-omega SST. For k-esp, there is a specific equation for deducing esp for a given TKE and the TKE relates back to your velocity. For k-omega SST, your omega values relate back to the esp equation.

All these values are related directly to a specific layer at a specific height and at a specific velocity. Now with your dual component wind velocity, you effectively have to do this set of calculations twice.

I don’t think its very clear from this over simplified generalization of how to do it, you will need to read through and understand every single component of the calculation as seen in the project i referenced. Such is the pain of trying to get a proper ABL inlet. So do let me know if after some time you’ve looked through all the information and am still not sure.

Good luck.

Cheers.

Regards,
Barry


#5

Hi, Barry,

Sorry for late response. Thank you for your answer.
Let me find the best way to do that.

Regards
JYC