A simple technique for developing and visualising stratified fluid dynamics: the hot double-bucket

Laboratory experiments are an important and powerful method for investigating stratified fluid dynamics. Visualising the physics of interest, however, is challenging and often limits the effectiveness of the laboratory approach. Improved techniques and methodologies that simplify visualisation will broaden the application of laboratory experiments with stratified fluid dynamics. Here, we propose a simple variation to the “double-bucket” method, commonly used to generate stratified environments for laboratory experiments, that leads to the formation of robust, discrete, uniformly-spaced double-diffusive layers that are able to be visualised with a shadowgraph. This technique, which we refer to as the “hot double-bucket” method, provides a realtime global shadowgraph view of the movement of isopycnal surfaces throughout the stratified environment. To demonstrate the utility of the hot double-bucket method we visualise the propagation of small-amplitude internal waves and compare our observations with the theoretically derived dispersion relation. Graphic abstract: [Figure not available: see fulltext.]