Observations of turbulent spots on a water table

Turbulent spots on a water table were studied. The Reynolds number, based on the surface speed and the water depth, at which spots can first be generated, is found to be in the range 950 to 1050. The influence of the Reynolds number and the slope of the water table on the propagation speeds of the front and the rear of the spot and on the half angle of spread was determined. A photographic technique was used to register structures within the spot. Comparisons with the theory of direct resonant growth of vertical vorticity show that the theory accounts fairly well for the spreading angle of the spot whereas the propagation speeds of the front and the rear are larger than the observed values.