Roe-Solver Instability at Mach=1

Dwayne · July 6, 2013, 08:34

Hey Guys,

can somebody tell me the reasons why Roes solver become instable at Mach=1? The literature says that the solver becomes a central-differences-method at Mach=1 because the right side of the Roe-flux vanishes, is this true? Isn't it only one eigenvalue of the jacobian that becomes zero?

Thanks for help!

immortality · July 7, 2013, 04:00

hi
What software you use?

Dwayne · July 7, 2013, 06:36

Quote:

Originally Posted by immortality

hi
What software you use?

I use Matlab to calculate a one-dimensional shock-tube-problem for the Euler-Equations.

immortality · July 7, 2013, 07:50

how?is there such program in Matlab or you have written it?

Dwayne · July 7, 2013, 08:06

Quote:

Originally Posted by immortality

how?is there such program in Matlab or you have written it?

I have written it.

Dwayne · July 8, 2013, 13:00

Nobody any idea?

praveen · July 9, 2013, 21:13

At sonic point one eigenvalue becomes zero. This leads to loss of dissipation in one of the eigenfields. It manifests as an entropy violating jump inside a sonic rarefaction. Look for "entropy fix" to overcome this problem.

Dwayne · July 10, 2013, 05:57

Quote:

Originally Posted by praveen

At sonic point one eigenvalue becomes zero. This leads to loss of dissipation in one of the eigenfields. It manifests as an entropy violating jump inside a sonic rarefaction. Look for "entropy fix" to overcome this problem.

Ok i understand, thank you!

July 6, 2013, 08:34	Roe-Solver Instability at Mach=1	#1
Dwayne New Member Join Date: Jul 2013 Posts: 11 Rep Power: 12	Hey Guys, can somebody tell me the reasons why Roes solver become instable at Mach=1? The literature says that the solver becomes a central-differences-method at Mach=1 because the right side of the Roe-flux vanishes, is this true? Isn't it only one eigenvalue of the jacobian that becomes zero? Thanks for help! immortality likes this.

July 7, 2013, 04:00		#2
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	hi What software you use? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

July 7, 2013, 07:50		#4
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	how?is there such program in Matlab or you have written it? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

July 9, 2013, 21:13		#7
praveen Super Moderator Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18	At sonic point one eigenvalue becomes zero. This leads to loss of dissipation in one of the eigenfields. It manifests as an entropy violating jump inside a sonic rarefaction. Look for "entropy fix" to overcome this problem. Dwayne likes this. __________________ http://cpraveen.github.io http://twitter.com/cfdlab http://github.com/cpraveen

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