ISSN Online: 2377-424X
ISBN CD: 1-56700-226-9
ISBN Online: 1-56700-225-0
International Heat Transfer Conference 13
DYNAMICS OF CONVECTIVE HEAT TRANSFER IN A BOUNDARY LAYER SUBMITTED TO FREESTREAM TURBULENCE
Abstrakt
We have developed a technique adapted for measuring the convective heat flux averaged in space but local in time, over a flat surface. With a laminar incoming flow, we calibrate our sensor with a standard law for the stationnary Nusselt number in a turbulent boundary layer, and obtain the measure of the Nusselt number with an uncertainty of 1 unit. With a turbulent free jet incoming flow, we perform dynamic measurements of the convective heat transfer signal with a low pass cutoff frequency of 1 kHz. Space averaged heat flux spectra scales like time frequency to the -5/3 power, suggesting that all scales in the incoming turbulent flow are involved in the transfer process, and not only the biggest ones. We also measure cross-correlations between fluid velocity outside the boundary layer and heat flux signals. The maxima for the correlation coefficient does not coincide with a zero time delay, but there exists a lag between the incoming turbulent velocity fluctuations and their cooling effect on the wall. The value of this lag corresponds to a boundary layer characteristic time, formed with friction velocity and boundary layer thickness.