Abstract
Experimental and numerical studies of turbulent heat transfer near a step change in wall temperature have been conducted in connection with an error analysis of small, transient, heat flux gages. The surface temperature of such a gage typically rises above the temperature of the surrounding metal wall, which influences the heat flux to the gage. Data from such gages must be corrected for the effect of this temperature rise. The correction is typically made by superposition using an unheated starting-length correlation, a procedure that has been in practice for many years.
In the present work, experimental data from a small, isothermal calorimeter were compared with output from STAN7, a 2-D turbulent boundary layer code, and with predictions based on a textbook correlation. The experiments and the numerical predictions agree within +/−6%, but the correlation underpredicts the required correction by 15–20% over the first half-boundary layer thickness downstream of the step change. As a consequence, data from small gages cannot be properly corrected using the accepted correlation.
A new expression is proposed for Stanton number downstream of a step in wall temperature, which can be used as an accurate correction algorithm for use with small gages.
