# coupled walls vs constant wall T

 Register Blogs Members List Search Today's Posts Mark Forums Read

 August 13, 2017, 14:22 coupled walls vs constant wall T #1 New Member   Yang Join Date: Jun 2015 Posts: 25 Rep Power: 11 I set up two geometries, one with a solid wire and fluid around the wire (a) and one with only the fluid (b). (a) has wall BCs for the fluid and solid shadow, both at 2000K (temperature thermal condition). (b) has wall BC at 2000K (temperature thermal condition). Otherwise, both have the same setup. The sizes of the flowfields are slightly different but should be irrelevant for this situation. Yet, the thermal boundary layer (?) for (b) is much thicker than (a). Why is that? Is it possible to make these match? (a) temperature field (sliver at the bottom): http://imgur.com/Dy6fhto (b) temperature field: http://imgur.com/Rkbt1Qh

August 13, 2017, 18:17
#2
Senior Member

Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,712
Rep Power: 66
Quote:
 Originally Posted by yow (a) has wall BCs for the fluid and solid shadow, both at 2000K (temperature thermal condition).
This is no longer a coupled wall because you've fixed it's temperature. Hence, (a) and (b) should be exactly same because you are now comparing a constant temperature wall with a constant temperature wall.

I really can't much sense of your pictures. Where the heck is the wire?

Also, why are the top, right, & bottom boundaries at a temperature of 2000K?

 August 13, 2017, 18:30 #3 New Member   Yang Join Date: Jun 2015 Posts: 25 Rep Power: 11 Thank you for your reply LuckyTran. Only the bottom is at 2000K for both. I guess the top and right are just outlined in red; their temperature is 300K (just checked). The thermal "boundary layer" of (a) is so thin it looks the same but it's 2000K.

 August 14, 2017, 18:58 #4 New Member   Yang Join Date: Jun 2015 Posts: 25 Rep Power: 11 Found the difference; I accidentally used "scalable wall function" in my viscous model which made the thermal BL much thinner, probably b/c it was scaling my already refined wall mesh?

 Tags coupled, temperature, wall boundary conditions