Thermal imaging study of temperature fields in shallow flows

Thermography has been used to investigate the scalar transport in shallow-water jet and wake flows. Warm water was injected uniformly over the depth into these flows, and the temperature variations at the water surface were captured by a thermal camera. The mixing of the warm water with the ambient fluid in shallow flows, as the result of turbulent diffusion and dispersion, was analysed. The development of the mean and fluctuating temperature along the flow was examined and compared with the past studies of scalar transport in shallow jets and wakes. The results agree well with the theoretical analyses and the previous measurements, where dye was used as the tracer. Through the detailed studies, it has been demonstrated that thermal imaging technique provides a new quantitative method for studying turbulent mixing phenomena in shallow waters. Compared with conventional scalar measurement techniques, the biggest merit of the thermal imaging method is that it involves a very simple experimental setup.

► We present a novel application of the thermal imaging technique.
► Turbulent mixing properties are revealed by measuring temperature distributions.
► Scalar distribution at surface characterises the shallow water mixing phenomenon.
► Temperature difference needs to be small to restrict the density change.
► Water flume should be insulated to reduce the heat loss.