The unsteady flux of heat and momentum from a flat plate

Abstract

The unsteady viscous fluid stress on a flat plate was computed numerically from a simplified unsteady momentum equation which is not restricted by a frequency parameter and compares favorably with the available (frequency restricted) calculations. The unsteady heat flux from the same plate is examined for three boundary conditions: (a) free-stream speed oscillations with a constant surface and free-stream temperature, (b) free-stream temperature oscillations with a constant surface temperature and constant free-stream speed, and (c) uniform surface temperature oscillations with a constant free-stream speed and temperature. The heat flux in response to speed oscillations has a maximum value at low frequencies and a larger bandwidth than the response to free-stream temperature oscillations. When the boundary layer is unsteady, the response of the heat flux to surface temperature oscillations is not comparable to either the response to speed oscillations or the response to free-stream temperature oscillations. The results have implications for the interpretation and calibration of constant temperature anemometer and constant temperature thermometer output signals in regions with small amplitude temperature and streamwise velocity fluctuations.