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Physics calculator

Sudden Expansion Calculator

Compute Borda–Carnot sudden-expansion loss h = (v1 − v2)² / (2g). Runs locally. Not minor-loss K as an input, not Darcy, not an orifice, and not Q=Av.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary Engine tested · Source checked · 17/17 tests · Production surface contract 3/3 · v1.0.0
Input interpretation
Enter values to calculate.
Result
—
Model
Borda–Carnot sudden-expansion head from v1 and v2. Invert v2 or A2. Optional Δp from ρ.
Scope
Borda–Carnot sudden expansion: h = (v1 − v2)² / (2g); K = (1 − v2/v1)² is reported, not an input
Verification
Engine tested · 17/17 tests · Production surface contract 3/3 · Source checked · v1.0.0
Named expert review
Optional · Not performed
Sources
Sources
Evidence
2 golden · 10 boundary · 5 property · Production surface contract 3/3 · Artifact integrity PASS
Production
Embedded snapshot: STALE · Last attested schema matched 1.0.0 snapshot / local build · Semantic contract ✓ · Last attestation PASS · current evidence changed · re-attestation required · Public/cache ✓ · Origin ✓ · Live production status PASS (0 stale; 163 CURRENT) @ 2026-09-17T13:12:27.589Z
Semantic contract
PASS

Formulas

Core equations used by this calculator.

Head lossh = (v1 − v2)² / (2g)
Loss coefficientK = (1 − v2/v1)²
Pressure dropΔp = ρ (v1 − v2)² / 2
Downstream areaA2 = A1 / (1 − √(2 g h) / v1)
iSI. g defaults to 9.80665 m/s². Expansion needs v1 > v2. This page is not minor-loss K given, not Darcy f, not an orifice, and not Q=Av.

How to use

1

Enter v₁

Upstream mean speed in m/s. URL field is v1_m_s.

2

Enter v₂

Downstream mean speed in m/s, smaller than v₁. Invert on the v₂ tab. URL field is v2_m_s.

3

Read h

h = (v1 − v2)² / (2g). Optional ρ reports Δp. Invert A₂ from A₁, v₁, and h on the A₂ tab.

Example calculations

Common configurations with formula and result.

ϟ

v1=2 m/s, v2=1 m/s

Area doubles; K=0.25

h = (2 − 1)² / (2 g)
h≈0.05099 m · Δp=500 Pa at ρ=1000
ϟ

Invert v₂

h≈0.05099 m, v1=2 m/s

v2 = v1 − √(2 g h)
v2 = 1 m/s

Sudden Expansion calculator specification

Version 1.0.0 · Engine tested

Calculation status

Review policy · Evidence

Definition
Borda–Carnot sudden expansion: h = (v1 − v2)² / (2g). Reported K = (1 − v2/v1)² is not an input. Not a catalog fitting K.
What it calculates
Borda–Carnot sudden-expansion head from v1 and v2. Invert v2 or A2. Optional Δp from ρ.
Inputs
  • mode?
  • v1
  • v2|h
  • A1?
  • rho?
  • g?
Outputs
  • h
  • v1
  • v2
  • K
  • g
  • rho
  • dP
  • A1?
  • A2?
  • mode
  • model
Formula
h = (v1 − v2)² / (2g)
Assumptions
  • Borda–Carnot sudden expansion: h = (v1 − v2)² / (2g); K = (1 − v2/v1)² is reported, not an input
  • Default g=9.80665 m/s²; default ρ=1000 kg/m³ for Δp = ρ (v1−v2)² / 2; incompressible; A2 > A1
  • Not minor-loss K given, not Darcy f, not orifice C_d, not Q=Av, not sudden contraction
Units
  • SI; v in m/s; h in m; A in m²; ρ in kg/m³; Δp in Pa; K dimensionless
Boundary conditions
  • missing v1, v2, h, or A1 when required → MISSING_REQUIRED_INPUT
  • v1 ≤ 0, h ≤ 0, or A1 ≤ 0 → VALUE_MUST_BE_POSITIVE
  • v2 ≥ v1 → VALUE_OUT_OF_RANGE
  • K, f/Re, Q, C_d → MIXED_INPUT_ENCODING
  • minor, darcy, or orifice as mode → INVALID_MODE
Example
v1=2 v2=1 → h=1/(2g) K=0.25
Validation cases

3 published on this page · 17/17 tests · Production surface contract 3/3 · View evidence

  • v1=2 v2=1 → h=1/(2g) K=0.25
  • mode=pressure v1=2 v2=1 → dP=500
  • v1=2 v2=1 K=0.25 → MIXED_INPUT_ENCODING
Sources
  • ISO 80000-4 — Mechanics — Length, speed, pressure
    Supports: h is a head; v is a speed; Δp is a pressure
  • Borda–Carnot equation — Sudden enlargement
    Supports: h=(v1−v2)²/(2g) for incompressible sudden expansion; K=(1−A1/A2)²
Calculation version
1.0.0

Background

Interpretation and common distinctions.

Compute Borda–Carnot sudden-expansion loss from the two mean speeds.

Supported and not supported

Supported — h from v1, v2 · invert v2 · invert A2 · API physics.fluid.sudden_expansion

Not supported — catalog minor-loss K, Darcy f, orifice C_d, Q=Av, sudden contraction

Agent / API notes

Capability id: physics.fluid.sudden_expansion · tool id: sudden-expansion · pin 1.0.0.

{ "v1": 2, "v2": 1 }

Modes: head (default), pressure, velocity, area. Errors: MISSING_REQUIRED_INPUT, INVALID_NUMBER, VALUE_MUST_BE_POSITIVE, VALUE_OUT_OF_RANGE, MIXED_INPUT_ENCODING, INVALID_MODE.

Calculator URL stays /calc/physics/sudden-expansion. There is no /calc/fluid.

Other calculators in this family: Minor loss, Darcy–Weisbach, Flow rate, Orifice discharge .

K Minor loss › hf Darcy–Weisbach › Q Flow rate › Q Orifice discharge ›
}

Frequently asked questions

Key distinctions behind the calculation.

Is this minor-loss K?

No. Catalog fitting K is /calc/physics/minor-loss. Sending K is MIXED_INPUT_ENCODING. This page reports K=(1−v2/v1)².

Is this Darcy–Weisbach?

No. Pipe friction from a given f is /calc/physics/darcy-weisbach. Sending f, L, D, or Re is MIXED_INPUT_ENCODING.

Is this Q = A·v?

No. Volumetric flow is /calc/physics/flow-rate. Sending Q is MIXED_INPUT_ENCODING. Continuity is used only to invert A₂.

Is this sudden contraction?

No. Expansion needs v1 > v2. Contraction uses a vena-contracta coefficient and is not this page.

Where does this run?

Locally in the browser by default. REST and MCP call the same fluid-engine suddenExpansion wrapper.