SIMULTANEOUS MEASUREMENTS OF TEMPERATURE AND ITS DISSIPATION USING PAIRS OF PARALLEL COLD WIRES

The link between fluctuations of a passive scalar and its dissipation is an important problem for various aspects of turbulent flow modellin g both with and without chemical reaction. This paper first reports ex perimental methods for simultaneous measurements of the three derivati ves involved in temperature dissipation using cold wire probes in a bo undary layer over a weakly heated flat plate. Particular attention is paid to the determination of the optimal length and spacing between se nsors, including a four-wire probe of fixed dimensions, for such gradi ent measurements. Corrections to be applied to account for the effect of the fixed geometry are analyzed. Results about joint statistics, in cluding conditional temperature pdfs, between the scalar and its dissi pation are then reported and compared to previous results which mainly concerned conditional dissipation rates.