DIRECT NUMERICAL SIMULATION OF AIR-COOLED AND AIR-HEATED CHANNELS

We develop a theoretical framework for predicting friction and heat transfer coefficients in variable-properties forced-air convection, as typical of turbine blade cooling. To do this, we borrow concepts from high-speed wall turbulence, also featuring large temperature and density variations. Using the mean momentum balance and mean thermal balance equations we develop integral transformations that account for the effect of the variable fluid properties, and apply the inverse transformations to calculate the friction and heat transfer coefficients. The proposed theory is validated using a direct numerical simulation dataset spanning both heating and cooling conditions, and the predicted friction and heat transfer coefficients match DNS data with 1-2% accuracy.