Hello, I am simulating a 2D circular cylinder at low Re=10 without turbulent model now. Surprisingly, I found the drag coefficient is very larger about Cd=3. Who can give me some explanation? What is the theory result for Cd at this Re? Thanks.

Theory, don't know, experiments and computations show that it is about 3. See for example White or Schlichting for the plot CD vs Re

-- Jarmo

the drag force for blunt body is mainly due to pressure drag, where the seperation of boundary layer start very soon ,so the dference in pressure force on the the both sides is very large causing high drag coeff., as Re increases the seperation point go forward hence the wake region be narrow and Cd decreases. if you need more explaination send to omrkhairy75@yahoo.com regards, khairy-Egypt