[layla Al- sabbagh]

Dear all,

I´m trying to simulate the hydraulic jump below ogee spillway using flow 3d. The problem is I don't know which is better to use as a downstream BC:
specified pressure (tail depth) or outflow.

[MSM1985]

I would suggest to use 'specified pressure boundary'. There can be three variation in such boundary depending on your design conditions:

1) Pressure with fluid height => if you are maintaining a tailwater downstream of jump

2) Pressure with fluid fraction=1 => if the flow is sub-critical in the downstream reach

3) Pressure with fluid fraction=1 => if the flow is super-critical in the downstream reach

[layla Al- sabbagh]

Originally Posted by MSM1985

I would suggest to use 'specified pressure boundary'. There can be three variation in such boundary depending on your design conditions:

1) Pressure with fluid height => if you are maintaining a tailwater downstream of jump

2) Pressure with fluid fraction=1 => if the flow is sub-critical in the downstream reach

3) Pressure with fluid fraction=1 => if the flow is super-critical in the downstream reach

When i use pressure with fluid height corresponding to downstream depth of jump, is this boundary behave like outlet (outflow) or the flow may be return back.

[MSM1985]

This will depend on hydraulic design of basin/jump. If Tailwater > Tailwater required, jump will moved towards chute; otherwise it will move towards downstream channel or might sweepout if tailwater < Min. tailwater required. The software just solve equations based on your input and model the exact situation.