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Sluicegate Tutorial with FlowStudio

This walkthrough shows how to use FlowStudio’s sluice gate (rectangular channel) worksheet: upstream pool depth from specific energy, downstream gradually varied flow, and—when the case allows—hydraulic jump placement plus an empirical jump length (SI units).

Open FlowStudio → https://flow.syncster.dev

What you are solving

A bottom sluice in a wide rectangular channel passes a discharge Q. The worksheet assumes a contracted depth at the vena contracta, y2 = Cca, where a is gate opening and Cc is a contraction coefficient (often near 0.6–0.65). From specific energy matching between the upstream pool and the contracta—together with a check against uniform normal depth yn for the approach channel—the sheet finds upstream pool depth y1.

Downstream, it integrates Manning-based gradually varied flow from the gate. If the contracta is supercritical and you set a subcritical tailwater yt (or leave tailwater blank so the sheet can default to yn when that is valid), it locates a Belanger jump where the supercritical profile reaches the depth whose sequent is yt, applies an empirical jump length correlation, then continues subcritical GVF to the end of your reach.

Step 1 — Create the worksheet

Sign in if prompted, then create or open a project. Add a new worksheet and choose Sluice gate (rectangular channel). Open the sheet so you see the intro paragraph, the input grid, and the Compute gate & profile button.


Step 2 — Enter channel, gate, and reach

Enter SI values: bottom width b, Manning n, bed slope S0 (m/m), discharge Q, opening a, contraction Cc, upstream reach length Lu (plotted pool), downstream profile length L, and integration steps (RK4 Δx nominal count). For a reproducible demo you might try, for example: b = 5 m, n = 0.025, S0 = 0.0004, Q = 12 m³/s, a = 0.45 m, Cc = 0.61, Lu = 20 m, L = 200 m, steps = 48—tune to your case.

Leave Tailwater yt blank to let the sheet use normal depth yn as tailwater when that is physically consistent; or type a subcritical tailwater to force a specific jump target.

Step 3 — Compute and read the summary

Click Compute gate & profile. The Summary table lists normal depth yn, critical depth, pool depth y1, contracted depth y2, velocities, Froude numbers, specific energy at the contracta, and—if a jump is applied— jump station xj, pre-jump depth y′, tailwater used, estimated jump length Lj (Chow / Chaudhry correlation), Froude before the jump, and where subcritical GVF resumes (xs). A short note under the title explains the run (afflux, drowned jump, or extend-L messages).


Step 4 — Long-section profile and section view

The long section plots depth vs distance: negative x is the upstream pool at y1, the gate at x = 0, then downstream GVF. If a jump is modeled, you should see supercritical depth approaching xj, a short horizontal segment at tailwater depth over the estimated jump length, then subcritical profile. The cross section at the pool shows width b and depth y1.


Jump length, references, and common pitfalls

  • Jump length Lj uses the empirical form Lj = 220 y′ tanh[(Fr′ − 1)/22] for a horizontal rectangular channel, as summarized in standard references (e.g. Chow; Chaudhry) and engineering summaries such as LMNO — Hydraulic jump. It is not a CFD result; treat it as order-of-magnitude for visualization and teaching.
  • If tailwater is too high relative to the sequent depth at the gate, the sheet warns of a drowned / submerged jump and keeps a supercritical reach only—adjust yt, slope, n, or Q to match your scenario.
  • If Fr2 < 1 at the contracta, no jump splice is applied; check opening, Q, and b.
  • If the note says the jump is not in reach, increase downstream L or change tailwater / slope so the M3 profile can reach the required pre-jump depth.
  • Very small y1/a
may trigger a warning that outflow may not behave as a free sluice—results are indicative.

Wrap-up

You’ve walked through the sluice gate worksheet: energy-based pool depth, downstream GVF, optional Belanger jump with empirical length, and where to read Lj and xs in the Summary and notes. Cross-check against hydraulic texts, physical models, or project standards for design decisions.

Run the sheet live at https://flow.syncster.dev.

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