Temperature measurements in convective heat transfer flows using dual-broadband, pure-rotational coherent anti-Stokes Raman spectroscopy (CARS)

This paper describes the use of dual-broadband, pure-rotational coherent anti-Strokes Raman spectroscopy (CARS) as a non-intrusive temperature diagnostic for convective-heat-transfer flows. The characteristics of the dual-broadband, pure-rotational CARS technique are discussed, and the technique is compared to other temperature measurement methods. Dual-broadband, pure-rotational CARS was used to measure mean temperature profiles in a low-Reynolds-number, turbulent boundary layer. The results are presented in wall units and compared to the thermal law of the wall for zero-pressure-gradient boundary layers. Temperature data were acquired as close as 50 μm (±25 μm) to the wall, with a spatial resolution of 50 μm normal to the heat transfer surface, and a 2σ precision limit of ±4 K. The spatial resolution of this experimental method provides detailed information in complex thermal boundary layers and allows for an estimation of the convective heat flux to within an estimated uncertainty of -5% to +25%. Single-laser-shot temperature data were acquired in a gas cell, and the potential for measurement of rms temperature fluctuations is discussed in terms of the resulting probability density functions.