The NASA Lewis Research Center and the University of Akron have developed and demonstrated a two-dimensional, transient, numerical finite difference model of a plug-type heat flux gauge/probe assembly incorporating temperature-dependent material properties and surface radiation. The model's predictions have been compared with experimental results, showing that it can properly predict steady-state temperatures measured along the post of the gauge and in the surrounding material in which the gauge is mounted. The model, which has aided in quantifying expected two-dimensional conduction effects, can be used for future studies involving different applications.
We found that the temperature of the outer periphery of the gauge has a strong effect on temperatures of the gauge post but a much smaller effect on the temperature gradients along the post. Radial temperature gradients were predicted in the post, particularly near the ends, but in general, they were negligible. However, in the application studied here, radial temperature gradients were predicted to be significant above the post near the gauge centerline. As a result, the heat flux predicted at the surface of the gauge was not the same as the heat flux predicted along the post. The magnitude of the difference depends on the particular application since both the level of heat flux and the temperature of the surrounding material influence the two-dimensional heat transfer effects.
Advantages of the plug-type heat flux gauge include not disrupting the aerodynamic flow and its proven ability to withstand extremely harsh conditions. The numerical predictions of the present study suggest that possible design improvements include increasing the post radius, decreasing the air gap outer radius, decreasing the thickness of the hot surface above the post, and back-filling the air gap with a thermally conducting, but electrically nonconducting, material.
This work was performed by Steve Rooke of The University of Akron and Gustave C. Fralick and Curt H. Liebert of the NASA Lewis Research Center.
Previous articleLast updated May 5, 1997
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