CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

What are Roe States?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 7, 1999, 18:32
Default What are Roe States?
  #1
Joan Mir
Guest
 
Posts: n/a
Hello everyone:

I'm trying to do a boundary condition modification on my Beam & Warming Euler implicit scheme. I'm being told to use a form of characteristic boundary conditions based on a flux difference formulation due to Barth, in the form:

Qb = 0.5*(Qinf +Qe) - 0.5*(sgn(A)*(Qinf-Qe))

with sgn(A)= Xsgn(lambda(A))X**(-1) evaluated at a Roe state between node point i and i+1. Do you happen to know what a Roe state is?

Wishing you luck, Joan
  Reply With Quote

Old   June 9, 1999, 09:38
Default Re: What are Roe States?
  #2
Patrick Godon
Guest
 
Posts: n/a
Hi there,

I have been using boundary conditions on characteristics for quite a while but I never heard of a Roe state. It seems that your equation is a vector equation for the primitive variables, and inf and e apparently denotes the value of the variables outside and inside the computational domain respectively (i.e. exact values imposed from outside and computed values from inside). I am not familiar with the notation you use (sgn, etc..X, I guess lambda is related to the eigen values of the matrix A or so?).

What are your equations exactly? I guess momenta and density (if compressible), do you have an energy equation? what is the equation of state if any? I might try to help with explicitly writting down the characteristic equations for the flow in standard forms.

In practice for most of the problems a linearization of the equations has to be carried out in order to simplify the set of equations and solve for the eigenvector (characteristics) and egeinvalues (propagation velocities of the characteristics). The linearization has to be carried out 'around' (for example) the steady state solution of the flow or an approximation to it (for example a good guess of the solution, or an unperturbed state of the flow). This is what Roe state might refer to, but I am not sure, untill I have not seen the flow equations and the way the characteristics are found.

If this does not help, let me know more about the equations and the flow and then the characteristics can be found.

Cheers, Patrick.
  Reply With Quote

Old   June 9, 1999, 16:11
Default Some References
  #3
Patrick Godon
Guest
 
Posts: n/a
See also the two review articles:

Givoli, 1991, J. of Comput. PHys., 94, p.1.

Turkel, 1983, Comput. Fluids, 11, p.121

and if you can find it:

Roe, 1986, ICASE report 86-75, NASA Langley, Hampton, VA.

PG.
  Reply With Quote

Old   June 13, 1999, 22:41
Default Re: What are Roe States?
  #4
Ming
Guest
 
Posts: n/a
Hi,

Roe state is a special average state at the interface between node point i and i+1. Roe state for primitive variables U including velocity u, v and total enthalpy H, can be evaluated according to the following formula:

U_Roe = ( U_i * SQRT(rho_i) + U_i+1 * SQRT(rho_i+1) )/( SQRT(rho_i) + SQRT(rho_i+1) )

where rho is density. The Roe state for density is obtained by

rho_Roe = SQRT( rho_i * rho_i+1 )

you can also have a look of Roe's original paper on Roe average(state) at J. Computational Phy. Vol. 43, 1981.
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Convergence on unstable steady states ekor FLUENT 0 August 24, 2010 05:50
ROE Riemann Solver and MUSCL ares Main CFD Forum 10 May 7, 2010 04:47
Roe implement about preconditioning ricklee Main CFD Forum 7 July 7, 2006 06:14
roe solver with entropy fix mehdi Main CFD Forum 1 February 26, 2006 06:36
Roe States (average) in curvilinear coordinates? Bernard Parent Main CFD Forum 3 February 29, 2000 12:02


All times are GMT -4. The time now is 01:47.