Outflow boundary condition
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Patrick Fischer
Sep 29, 2025, 4:02:37 AM (2 days ago) Sep 29
to basilisk-fr
Dear community,
In the example provided at
http://basilisk.fr/src/examples/karman.c
the outlet boundary condition of the channel is of Neumann type. It is well known, however, that such a condition is not sufficient to fully evacuate the flow and its structures from the computational domain.
Is there already, within Basilisk, an implementation of a “traction-type” outflow boundary condition, as described in the works of Bruneau and Fabrie?
Ch.-H. Bruneau and P. Fabrie, 1994, Effective downstream boundary conditions for incompressible Navier–Stokes equations, Int. J. Numer. Methods Fluids, 19, pp. 693–705.
Ch.-H. Bruneau and P. Fabrie, 1996, New efficient boundary conditions for incompressible Navier–Stokes equations: a well-posedness result, M2AN, 30.
I raise this question because in my high Reynolds number simulations, one observes at the downstream end of the channel a blow-up of values resulting from accumulation after a certain integration time.
Thank you in advance for your assistance.
In the example provided at
http://basilisk.fr/src/examples/karman.c
the outlet boundary condition of the channel is of Neumann type. It is well known, however, that such a condition is not sufficient to fully evacuate the flow and its structures from the computational domain.
Is there already, within Basilisk, an implementation of a “traction-type” outflow boundary condition, as described in the works of Bruneau and Fabrie?
Ch.-H. Bruneau and P. Fabrie, 1994, Effective downstream boundary conditions for incompressible Navier–Stokes equations, Int. J. Numer. Methods Fluids, 19, pp. 693–705.
Ch.-H. Bruneau and P. Fabrie, 1996, New efficient boundary conditions for incompressible Navier–Stokes equations: a well-posedness result, M2AN, 30.
I raise this question because in my high Reynolds number simulations, one observes at the downstream end of the channel a blow-up of values resulting from accumulation after a certain integration time.
Thank you in advance for your assistance.
j.a.v...@gmail.com
Sep 30, 2025, 6:00:15 AM (yesterday) Sep 30
to basilisk-fr
Hallo Patrick,
An alternative would be to add a sponge layer near the "exit" to help with graceful outflow using simple boundary conditions. Enforcing a coarse mesh near the boundary can also help.
See (the code) in this example:
Antoon
Op maandag 29 september 2025 om 10:02:37 UTC+2 schreef Patrick Fischer:
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