surface roughness

sieginc. · September 14, 2012, 19:01

If I have an object like this:

It's a model of an inductor, the coils are 18 gage wire. My question is do I need to apply a roughness to this surface, or will STAR recognize the "bumps" along the geometry? I had someone tell me that STAR will consider these surfaces smooth as part of wall treatment but applying a roughness seems unnecessary if the wires are modeled individually as they are. Now, if each coil pack was just a solid cylindrical shape then I could see why a roughness would be needed but I'm not sure.

triple_r · November 2, 2012, 10:42

You are absolutely right. If the wires are modelled individually, then there is no need to apply an equivalent roughness. You will need to have a fine enough grid near the wires for the fluid to "see" the bumps though. If your mesh is not fine enough, then probably you are better off with modelling the coils as solid cylindrical objects and specifying an equivalent roughness to that surface.

September 14, 2012, 19:01	surface roughness	#1
sieginc. Member adam Join Date: Oct 2011 Posts: 52 Rep Power: 15	If I have an object like this: It's a model of an inductor, the coils are 18 gage wire. My question is do I need to apply a roughness to this surface, or will STAR recognize the "bumps" along the geometry? I had someone tell me that STAR will consider these surfaces smooth as part of wall treatment but applying a roughness seems unnecessary if the wires are modeled individually as they are. Now, if each coil pack was just a solid cylindrical shape then I could see why a roughness would be needed but I'm not sure.

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November 2, 2012, 10:42		#2
triple_r Senior Member Reza Join Date: Mar 2009 Location: Appleton, WI Posts: 116 Rep Power: 17	You are absolutely right. If the wires are modelled individually, then there is no need to apply an equivalent roughness. You will need to have a fine enough grid near the wires for the fluid to "see" the bumps though. If your mesh is not fine enough, then probably you are better off with modelling the coils as solid cylindrical objects and specifying an equivalent roughness to that surface.