obtain non-uniform velocity profile

Atit Koonsrisuk

I'd like to verify something then I set my problem in the following ways:

- Air ideal gas flows in the constant diameter tube positioned axially along Y-axis. 'g' is set in the downward direction of Y-axis. The flow inlet is at one end (bottom) of the tube and flow outlet is at another end (top). - There is the 500 w/m^3 volumetric heat source fully filled in the tube (domain). - B.C.'s: inlet: INLET with p_total=0, t_static=308K; outlet: OUTLET with p_static=0; walls: WALL adiabatic and free-slip. - CFX-Mesh is generated the mesh. The 'Face Spacing Type' is 'Angular Resolution'. No mesh control, no inflation. - Heat transfer model is 'Total Energy' and Turbulence model is 'None'.

I expected to get the uniform axial velocity at the plane normal to Y-axis, but it is not. At the inlet, for example, the velocity is varied from 4.19 to 4.31 m/s and from 4.18 to 4.63 at outlet.

Do anyone have idea why I didn't get the uniform velocity profile? Thank you for your kind consideration.

Atit