High-fidelity simultaneous measurements of velocity and temperature fluctuations using a dual-wire sensor within thermal boundary layers

Abstract A customised dual-wire sensor, incorporating both a cold-wire and a hot-wire, has been developed to enable simultaneous measurement of temperature and velocity at the same wall-normal location within a thermal boundary layer. This study details the sensor’s design, its in-situ calibration technique, and addresses potential sensor drift, offering guidance for its effective utilisation. While the results obtained from this sensor confirm the similarity between the wall-normal profiles for mean temperature and velocity, profiles of the temperature variance present a less obvious plateau in the logarithmic region when compared to the streamwise velocity variance. The simultaneously acquired instantaneous signals also reveal the markedly different characteristics of the streamwise velocity and temperature fluctuations at the edge of the boundary layer, highlighting the dissimilarity between velocity and temperature (with the latter exhibiting a unique one-sided distribution).