The oblique “hydraulic jump”

I am working towards the Venturi flume partly because it is an excellent vehicle to practice using simple mathematical models in mechanical engineering and partly because of the analogy with the flow of gases through convergent-divergent nozzles. Figure 10-15 shows a photograph of the flow pattern in rapid flow in a laboratory channel with a piece shaped like an isosceles triangle with small base angles attached to one wall. At the first change in direction at the wall an undular wave is usually seen to form on the surface at an angle to the wall of the channel. In this wave the water appears to change direction to follow the oblique wall, to increase in depth, but to continue to flow with rapid flow. At the next change in direction the surface level falls smoothly, the velocity increases, and the water flows more or less parallel to the second face. Then at the third change in direction another surface wave-forms and then the flow follows the wall at the original depth. The waves are all attenuated quite quickly and die out before reaching the other wall if the channel is of reasonable width. It seems that it can be explained in terms of a sequence of a hydraulic jump followed by a hydraulic drop and then by another hydraulic jump.

These waves can be seen in the gutters of streets when there is heavy rain.

 

I am not wholly convinced that they are hydraulic jumps