CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   Heat Transfer Coefficient in Compressible Flow 3D turbine cascade (http://www.cfd-online.com/Forums/cfx/85976-heat-transfer-coefficient-compressible-flow-3d-turbine-cascade.html)

 Karkoura March 10, 2011 16:35

Heat Transfer Coefficient in Compressible Flow 3D turbine cascade

Hi,

I am using CFX to model a 3D turbine cascade. My ultimate objective is to compute the heat transfer coefficient distribution at the blade surface.

The flow is subsonic compressible so I am using "Total Energy" and "Air Ideal Gas" for the working fluid.

CFD Post outputs data for two particular variables. The "wall heat flux (q) " and the "wall heat transfer coefficient (h) ". From the CFX manual, I understand that these two are related by:
h = q / (T_wall - T_adjacentwall)
These values are very high and not in agreement with experimental data.

I tried to compute the wall heat flux myself by using the following:

q = -k * (Twall - Tadjacent wall) / y

where
k is the thermal diffusivity
Twall is the wall temperature (which I had specified as a boundary condition)
Tadjacent wall is the temperature of the first node away from the wall.
and
y is the distance of the first node away from the wall to the wall itself (this value I defined when I was creating the O-grid mesh around the airfoil in ICEM CFD)

Still I see that the variable are underpredicted compared to experimental data and the trend of heat transfer distribution with streamwise direction on the blade surface is not smooth and fluctuating.

I would appreciate any comments and knowledge you can share about computing the heat transfer coefficient in compressible flow.