Supersonic or subsonic BC?

kepler · September 24, 2009, 06:23

In my case a turbine rotor flow is to be solved. In the absolute reference frame the inlet boundary is subsonic, while in the relative reference frame the inlet boundary is subsonic because of revolution. My question is how to specify the BC, supersonic or subsonic?

ogloth · September 24, 2009, 11:34

If the Mach-number normal (and relative) to the inflow boundary is supersonic, take a supersonic inflow; otherwise use subsonic inflow. The same applies for the outflow boundary. In your case it probably is subsonic, assuming that the inflow boundary lies in the rotational plane.

kepler · September 24, 2009, 23:23

Following your advice, because the inflow boundary plane is parallel with the rotational plane, the rotation velocity doesn't have any influence for BC specification?

ogloth · September 25, 2009, 04:47

Correct -- what matters is the velocity normal to your boundary.

kepler · September 25, 2009, 05:24

Oliver Gloth, thank you very much.

September 24, 2009, 06:23	Supersonic or subsonic BC?	#1
kepler New Member chung yang Join Date: Mar 2009 Location: Beijing Posts: 6 Rep Power: 17	In my case a turbine rotor flow is to be solved. In the absolute reference frame the inlet boundary is subsonic, while in the relative reference frame the inlet boundary is subsonic because of revolution. My question is how to specify the BC, supersonic or subsonic?

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September 24, 2009, 11:34		#2
ogloth Senior Member Oliver Gloth Join Date: Mar 2009 Location: Todtnau, Germany Posts: 121 Rep Power: 17	If the Mach-number normal (and relative) to the inflow boundary is supersonic, take a supersonic inflow; otherwise use subsonic inflow. The same applies for the outflow boundary. In your case it probably is subsonic, assuming that the inflow boundary lies in the rotational plane.

September 24, 2009, 23:23		#3
kepler New Member chung yang Join Date: Mar 2009 Location: Beijing Posts: 6 Rep Power: 17	Following your advice, because the inflow boundary plane is parallel with the rotational plane, the rotation velocity doesn't have any influence for BC specification?

September 25, 2009, 04:47		#4
ogloth Senior Member Oliver Gloth Join Date: Mar 2009 Location: Todtnau, Germany Posts: 121 Rep Power: 17	Correct -- what matters is the velocity normal to your boundary.

September 25, 2009, 05:24		#5
kepler New Member chung yang Join Date: Mar 2009 Location: Beijing Posts: 6 Rep Power: 17	Oliver Gloth, thank you very much.