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Throttled API 6A Gate Valve Internal Flow: Vena Contracta Jet & Pressure Drop (CFD)
3D turbulent water flow (RANS k-ω SST, U_in = 3.5 m/s) through a partially throttled (35% open) DN80 high-pressure gate valve passage, resolving the 24.1 m/s vena contracta jet, 1.69 MPa pressure drop, and downstream recirculation vortex.
When a high-pressure oilfield gate valve operates in a partially throttled position during flowback or choke transitions, the descending gate slab restricts the bore into a crescent-shaped orifice. This 3D CFD model represents the internal fluid volume (D_fluid) of an API 6A DN80 (Ø80 mm bore) gate valve throttled to 35% open with an expanded upper bonnet chamber. Water enters at U_in = 3.5 m/s (ρ = 998.2 kg/m³). The flow accelerates sharply beneath the lower edge of the gate into a 24.06 m/s vena contracta jet (6.87× inlet velocity), inducing a static pressure drop of Δp = 1,686.9 kPa (1.69 MPa), a localized low-pressure separation pocket behind the gate (−802.2 kPa gauge), and an axial hydraulic thrust of F_X = 5,482.0 N acting on the gate and body walls.
1. Geometry & FEA Mesh
- •Single B-Rep internal fluid passage (D_fluid): Ø80 mm upstream and downstream pipe bores (L = 420 mm total, X ∈ [-180, 240] mm) connected through a central bonnet chamber throttled by a solid gate slab.
- •Unstructured 3D tetrahedral mesh: 12,469 tetrahedra and 3,419 nodes (volume discretization error 0.50%).
- •Working fluid: liquid water (ρ = 998.2 kg/m³, dynamic viscosity μ = 1.002×10⁻³ Pa·s) solved with Menter k-ω SST turbulence.
- •Directly complements the structural API 6A `gate_valve_body` solid stress case by resolving the internal hydrodynamic pressure and jet erosion zones.
2. Loads & Boundary Conditions
- •Upstream circular pipe inlet at X = −180 mm (surface number 1): uniform water velocity U_in = 3.5 m/s along +X ([1, 0, 0]).
- •Downstream circular pipe outlet at X = +240 mm (surface number 18): static gauge pressure p_out = 0 Pa.
- •All internal pipe walls, bonnet cavity surfaces, and gate slab faces (surfaces 2–17): viscous no-slip wall (u = 0).
3. Simulation Results & Findings
- ✓High-velocity vena contracta jet beneath the gate reaches |U|_max = 24.06 m/s (6.87× U_in), identifying the primary seat-ring erosion zone.
- ✓Area-averaged inlet-to-outlet static pressure drop is Δp = 1,686.9 kPa (1.69 MPa), with upstream stagnation pressure reaching +1,689.1 kPa and post-gate vortex core suction reaching −802.2 kPa.
- ✓Net axial hydrodynamic force acting on the throttled gate and internal passage walls is F_X = 5,482.0 N (5.48 kN), required for sizing the valve stem actuator.
Pipeline and valve manufacturers use WebCAE CFD to calculate flow coefficients (Cv/Kv), seat erosion velocities, cavitation margins, and stem actuator thrust forces directly from 3D CAD passages.
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