Hi, I'm running a fluent simulation for flow over an airfoil at low Reynolds number. The flow is incompressible but i seem to get Cp readings more than 1. This is not possible according to bernoulli's theory of incompressible flow. What could be the problem?

This is always a good check to see if you have things working properly. You don't say how low your Re-number is, but I've seen this happen if you set turbulence inflow values that are too high, also if you don't have fine enough resolution at the leading edge. There is also a general CFD trend for the Cp to be slightly too high, but if it's more than 1.02 it's something you have to fix.

I have met the same problem. When I used the artificial compressibility method to compute the viscous incompressible flow past a cylinder at ReD=40 to 200, the computed stagnation Cp is always greater than 1.0, say 1.07. Sometimes I saw other papers had similar excessive total pressure. I have not figure out why. Is it caused caused by viscosity effect? can any body explain further? The total pressure is more higher than free-stream total pressure when I computed airfoil.