Dear all, I am studying 2D channel flow with spatially periodic wall modification, where a sinusoidal streamwise velocity profile is imposed at the lower wall. I first solve the problem using a fixed flow-rate constraint and compute the corresponding mean pressure gradient. I then use this pressure gradient in a separate simulation with a fixed pressure-gradient constraint to recover the flow rate. While this procedure works correctly for the baseline Poiseuille flow (no wall modification), it fails when the wall forcing is applied: the recovered flow rate does not match the prescribed one. I would appreciate any insight into possible causes of this inconsistency or guidance on how to implement this comparison correctly in Nektar++.