Q: How can I extract the heat transfer coefficent from a pair of cfd models?

Hello,

I am using FLUENT to model the heat transfer from a hot gas to a cooled wall - a large vane in fact. I wish to find the heat transfer coefficient for convection to the cooled wall. The vane is cooled internally by cool air, though I do not intend to include this internal geometry.

It has been suggested to me that I might compare the results from a pair of CFD solutions; one where the cooled wall is adiabatic, and one where it is held at a cooled temperature.

This second model does allow me to find the trend in heat flux along the surface of the vane, but how do I use the results from both models to find the heat transfer coefficient? Has any one used such an approach?

The Nusselt number is a function of the Reynolds number to some power x and the Prandtle number to some power y. The x and y are obtained from experimental data. The CFD simulation will give you the velocity field around the blade, this as you know is a rotating field and takes some time before it converges so be patient and good luck. Another line of thought, but be careful as I have not tried it is to use q=k(dt/dx)=h(Delta T) and then h= k(dt/dx)/(Delta T) or you can check the published data e.g. the home study course "The Design of Gas Turbine Engines" prepared by the IGTI a division of the ASME. Also "Heat Transfer" volume 2 by Max Jakob has some good information though it is an old book.

Now you are using FLUENT, then you can assign a reasonable number of Point Monitors that will record the variable's values of the right hand side of the previous equation, the rest is just an excel sheet, And as I posted before check your values against the published values.