supercritical flow

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This student video outlines the principles and mathematics behind the hydraulic jump, a commonly occurring phenomenon that occurs when a high velocity liquid flows into a low velocity zone. In order to slow down, the liquid’s kinetic energy converts to potential energy, resulting in an increase in height. Though often seen in kitchen sinks or rivers, the principle is also commonly used in dams and other manmade structures to control erosion of surrounding features. (Video credit: T. Price, D. Alexander, A. Rodabough, and D. Jensen)

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One of the factors that complicates geophysical flows is that both the atmosphere and the ocean are stratified fluids with many stacked layers of differing densities. These variations in density can generate instabilities, trap rising or sinking fluids, and transmit waves. The animations above show flow over two ridges with dye visualization (top), velocity (middle), and contours of density (bottom). The upstream influence of the left ridge creates a smooth, focused flow that quickly becomes turbulent after the crest. The jet rebounds as a turbulent hydraulic jump before slowing again upstream of the second ridge. Like the first ridge, the second ridge also generates a hydraulic jump on the lee side. Clearly both stratification and the local topography play a big role in how air moves over and between the ridges. If prevailing winds favor these kinds of flows, it can help generate local microclimates. (Image credit and submission: K. Winters, source videos)