# Generalized Navier Boundary Condition

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 December 3, 2013, 00:12 Generalized Navier Boundary Condition #1 New Member   Join Date: May 2012 Posts: 17 Rep Power: 7 Hello Foamers, I am trying to implement the Generalized Navier Boundary Condition beta*U_slip + mu*dU/dn + gamma*(cos(theta_d) - cos(theta_e))*n_a*delta with beta: friction coefficient mu: viscosity n_w: normal of the wall gamma: surface tension theta_d: dynamic contact angle theta_e: equilibrium contact angle n_a: normal of fluid interface (alpha) delta: contact line segment I thought the partialSlip BC would be a good starting point, but I cannot figure out how to add a constant (surface tension part) to that BC. Has anyone experience writing a mixed/robin BC for a velocity field? Thanks! Arnout

 December 4, 2013, 20:58 #2 New Member   Join Date: May 2012 Posts: 17 Rep Power: 7 Trying to understand the partialSlip BC, so I can figure out how to modify it, but having some trouble. The BC should be equal to: v dot n = 0 (a*v+(1-a)*(grad(v) dot n)) dot t = 0 with n the surface normal and t a tangential vector. grad has to be dimensionless. This can be discretized as: (a*v_w + (1-a)*(v_w - v_p)L/d) = 0 with _w the value at the wall, _p in the cell center, d the distance between the wall and the cell center, and L a unit length. Looking at the snGrad function I expect the equation: snGrad = ((1-a)/(1-a+a*d/L) * (I-n^2) dot v_p - v_p)/d However, the code reads: snGrad = ((1-a) * (I-n^2) dot v_p - v_p)/d and I cannot figure out why.

 Tags generalized navier bc, gnbc, mixed bc, robin bc

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