ARTICLE:

• DYNAMICS OF CONVECTIVE HEAT TRANSFER IN A BOUNDARY LAYER SUBMITTED TO FREESTREAM TURBULENCE  download article

E. Sanz
Laboratoire de Mécanique des Fluides et d'Acoustique, France

C. Nicot
Laboratoire de Mécanique des Fluides et d'Acoustique, France

R. Point
Laboratoire de Mécanique des Fluides et d'Acoustique, France

F. Plaza
Laboratoire de Mécanique des Fluides et d'Acoustique, France

ABSTRACT

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.

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