[Nektar-users] Adding Body force for the Channel flow

Dear all, I am now trying to compute the channel flow using the Compressible Flow Solver. I have found the body force with derivatives non-trivial to add. Once the flow in a channel has reached a fully developed state, inertial forces in the channel, which are related to the mean favourable streamwise pressure gradient (pressure drop in a duct), are balanced with the wall friction forces. In this case, the body force f would be in the following form f=-tw/h, where tw is the wall friction containing velocity derivatives, h is the channel scale. Can anybody tell me how to perform this flow in Nektar? Thank you very much! Best Jian Yu