The simultaneous measurement of time-resolved surface heat flux and freestream turbulence at a stagnation point

Abstract

Two rapid-response thin-film heat flux gage systems have been used to measure time-resolved unsteady heat transfer signals. The Heat Flux Microsensor is a passive gage which measures the temperature difference across a thin thermal resistance. The second sensor, an actively powered gage operated by a constant temperature anemometer, measures heat flux by measuring dissipated power. These gages have frequency performance windows of 50 kHz and 250 Hz, respectively.

Each gage was calibrated for both steady and unsteady response. They were then placed at a flow stagnation point. A velocity probe is positioned outside the boundary layer adjacent to the gage. Simultaneous monitoring of these signals allowed the time-resolved documentation of the effects of local freestream turbulence on boundary layer heat transfer.

The resulting time traces indicate a direct correlation between the turbulent velocity fluctuations and heat flux variation. The effects of apparent single-frequency turbulent components are isolated on both the velocity and heat flux signals. These signals are analyzed to determine their relative amplitude and phase characteristics. The results are compared to similar relationships characterized in regularly pulsating laminar flow regimes.