2025-03 - Overshooting of steep stepped channel

In a steep stepped channel, jet deflection at the crest can overshoot as a free-falling jet bypassing the steps. To illustrate this issue, a comparison was made between a steep stepped channel (65-deg) with uniform step height and a configuration with a curved first top step using OpenFOAM simulations.
In my previous simulation, I showed how a 45-deg stepped channel dissipates flow energy (see the animation here: • 2025-02 - Stepped chan... ). This setup was replicated, but with the slope increased from 45-deg to 65-deg. The results revealed an overshooting phenomenon at the top of the channel, where the jet bypassed the first few steps, resulting in an undesirable flow pattern, as shown in the animation above on the left. I had overlooked this issue before, and this animation serves as a reminder to me to avoid it in future designs.
The key parameters of the channels are as follows:
Slope: 65-deg (45-deg in the previous simulation)
Drop in height: Approx. 6 m
Discharge: 0.2 m3/s
Channel dimensions: 0.75 m (w) x 0.75 m (h)
Step dimensions: 0.15 m (l) and 0.3 m (h)
Approach channel: Flat
Downstream has a 450 mm dia cross-road pipe
The CFD results suggest that introducing a curved inlet to the steps could reduce flow overshooting, and improve the attachment of the flow to the steps.

[@ranjitdesai7852]

This is interesting!