# outlet b.c

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 June 19, 2003, 17:32 outlet b.c #1 Tamer Guest   Posts: n/a To impliment outlet boundary conditions which of the following equations is true: d2 phi/d x2 =0 or d phi/d x =0 And how to discretize d2 phi/ d x2 =0 in finite volume formulation

 June 19, 2003, 19:17 Re: outlet b.c #2 Tamer Guest   Posts: n/a Ok I found out the answer. Setting the first derivatives of the variables u,v, and T or phi equal to zero at the exit plane is appropriate if the transverse velocity (v for example)is negligible at the boundary, which is not necessarily true for unsteady wakes exiting channels for example. Setting the second derivatives equal to zero at the exit is found to be more accurate but does not result n an unconditionally stable procedure and is not accurate as the wave boundary condition which reads: d phi/d t + c d pgi/ d x=0 The wave speed c is the mean channel inlet velocity Uo in case or horizontal channel or the average exit velocity in general.

 June 20, 2003, 13:28 Re: outlet b.c #3 Ravi Guest   Posts: n/a Hi Look at the AIAA paper - 84-1552, "Three Dimensional Unsteady Euler Equations Solution Using Flux Vector Splitting" by D.L. Whitfield and J.M. Janus. They have derived characteristic variable boundary conditions for inflows and outflows and impermeable wall. It is simple and straightforward. Ravi.

 June 25, 2003, 01:56 More explanation #4 STN Guest   Posts: n/a Dear Tamer, Could you please explain more detail about How to descretise the wave boundary condition on FVM? STN

 July 3, 2003, 21:54 Re: outlet b.c #5 Tamer Guest   Posts: n/a How can I get such an old conference? D. L. Whitfield and J. M. Janus, "Three dimensional unsteady euler equations solutions using flux vector splitting," 17th Fluid Dynamics, Plasma Dynamics, and Lasers Conf., AIAA paper no. 84--1552, June 25--27, 1984.

 July 18, 2003, 02:48 Re: outlet b.c #6 JG Guest   Posts: n/a Obviously, using zero second derivatives BC's is wrong. So is the wave boundary condition.

 July 18, 2003, 18:51 Re: outlet b.c #7 Tamer Guest   Posts: n/a Why boundary conditions of second dervative not accurate?

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