Impinging Jet. Outlet Boundary Condition

Vincent

Hello,

I am trying to simulate an impinging jet flow with a domestic finite volume code in cartesian coordinate.

First, i have done 2D simulation for laminar case; i place the outlet far away from the stagnation point and i set to zero all first derivative of velocity component respect to normal boundary direction at the outlet.

The same outlet boundary condition "works" for slot jet simulation (at least for laminar case, turbulent case need some modifications of B.C).

But now i move to an other step : trying to simulate a round impinging jet. Like the code is in cartesian coodinate, the fluid domain is a rectangular box. One problem is implementation of "good" B.C at the 4 outlet faces. Do you have some idea about which B.C using ?

I have already try : 1/ Zero for all first derivative respect to outlet normal direction; but i lost the cylindrical behavior of the flow and get a non physical solution. 2/ Zero for all second derivatives is too instable for the computation. 3/ Convectives boundary conditions (like in the article of Braza) but this type of B.C really don t like the recirculation zone at the outlet. 4/ I am now trying (a bad idea) to implement a pressure outlet b.c, but i don t like this option (because i have no idea of the distribution of pressure or gradient pressure at the outlet)

Is there somebody who found "good" outlet B.C for this type of problem ? Some ideas or comments ?

Thanks for reading all ... Vincent.