# Particle Tracking - Expression for Coefficient of Restitution

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 February 2, 2024, 05:58 Particle Tracking - Expression for Coefficient of Restitution #1 New Member   Join Date: Jun 2022 Posts: 2 Rep Power: 0 Hello together, I'm doing a particle tracking in a turbo machinery and I'm mostly interested in the particle behavior at the blades. I'm assuming, that the particles bounce of the walls, so I set a value for the perpendicular and parallel coefficient of restitution. In experiments at my university we saw, that it is to easy to assume a constant value for the coefficients of restitution. So my idea is to create an expression, which depends on the particle velocity directly before the impact and the wall impact angle of the particle. -> Perpendicular CoR = f(Particle.Velocity, Wall Impact Angle) -> Parallel CoR = f(Particle.Velocity, Wall Impact Angle) I already tried to implement the expressions, but there were some problems. The particle velocity is a non-scalar variable, which is not allowed to put in the coefficient of restitution. I also tried to create my own velocity variable ( -> Particle.Vel = sqrt(Particle.Velocity u^2 + Particle.Velocity v^2 + Particle.Velocity w^2) ) but there is another error message, that this is a field valued variable and the coefficient of restitution only allows single valued parameters. Do you know how to fix that problem? Another problem is, that I don't find a variable for the wall impact angle, that I can call in the expression. Do you know, if there is a variable I can call? I already read in other threads, that this should be possible, but I never saw an solution that worked. Thank you very much for your help!

 February 2, 2024, 18:21 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,727 Rep Power: 143 I don't think you can do this in CEL. I think you will need to do it with user fortran. Have a look in the documentation for the user fortran routines for particle tracking. Opaque and PatLe like this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 Tags particle tracking