# Trapezoidal microchannel and slip velocity. Help needed.

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 March 28, 2014, 14:36 Trapezoidal microchannel and slip velocity. Help needed. #1 New Member   Join Date: Jul 2013 Posts: 1 Rep Power: 0 Hello guys. First of all thumbs up for a great forum. Superb job! I am trying to simulate a laminar, steady state, incompressible liquid (water) flow through a micro-channel (trapezoid cross section), with a uniform inlet-velocity (couple of mm/sec). The simulation's velocity results are then compared to actual microPIV measurements on a super-hydrophilic and a super-hydrophobic microchannel. The fluent solution, with no-slip wall boundary conditions, provides velocity profiles in accordance with the measurements on the super-hydrophilic microchannel. For the actual super-hydrophobic channel, experiments provide the slip velocity (and slip length) of the flow for the small base and the sidewall of the microchannel. Now I need a way to fix these channel-height-related slip values on the fluid domain and calculate a solution. I tried using DEFINE_PROFILE UDFs to impose wall motion velocities (but the results are nowhere near the measurements). Also I have been trying to use fixed velocities in the fluid domain with no luck so far. Some questions: 1) Is FLUENT able to handle non-uniform wall motion for wall boundaries (in reality no wall can move that way...)? e.g. Code: ```Vel(x)=a*y+b // a=a1, b=b1 for 0 <= y = 0.) && (y < 0.000041027)) { a = 0.731231; b = 0.00125; } else if (y < 0.000049232) { a = 12.181716; b = 0.00078; } else if (y < 0.000065643) { a = 100.544204; b = -0.00357; } else if (y < 0.000082053) { a = 12.796535; b = 0.00219; } else if (y < 0.000098464) { a = -38.389605; b = 0.00639; } else if (y < 0.000114875) { a = -91.403822; b = 0.01161; } else if (y < 0.000147696) { a = -22.850956; b = 0.003735; } else if (y < 0.00015196) { a = -30.435494; b = 0.004855; } else { a=0.; b=0.; } F_PROFILE(c,t,nv) = a*y + b; end_c_loop(c,t) } if (THREAD_ID(t)==idbottom) begin_c_loop(c,t) { C_CENTROID(x,c,t); F_PROFILE(c,t,nv) = 0.00125; end_c_loop(c,t) } }``` If I haven't explained appropriately my case please ask for clarifications. Any ideas, pointers and/or corrections will be much appreciated! Last edited by thapostol; March 28, 2014 at 14:41. Reason: typos

 Tags laminar incompressible, microchannel, slip velocity, udf