Exact answer known1D · pressurizedCandidate

Friction loss in a pipe

Does the model lose the right amount of pressure to friction?

Test A1P-001
Darcy (1845)
Version 1.0.0

Right answer: Exact solution · Darcy (1845)
Results: 2 models · closest 0.6 % off · see them ↓
Must: get the head loss within 1 %

Sketch, not to scale.

The model file

The suite writes this EPANET 2 input file from the test's inputs. Each engine's own copy, as it ran, is in Run it yourself under its result below.

Download A1P-001.inp 1 KB Open it on the map →

On the map: click any element to see its line in the file and every engine's result there over time.

Exact hydraulic grade line
EPA EPANET 2.2 nodal heads

Colebrook–White gives f = 0.01821 and a total loss of 3.094 m. EPANET uses the Swamee–Jain approximation, which is expected to sit about 0.6 % high here.

What happens

Water flows at 1 m/s through a 1 km, 300 mm pipe. Friction takes about 3.1 m of head, an amount fixed exactly by the Colebrook–White formula.

Why it matters

Every pipe in a water network loses head this way. Get the friction law wrong and pressures at customers' taps are wrong.

A good model must

get the head loss within 1 %
keep heads along the pipe within 5 cm

How models did

In rank order: by each model's percent difference from the right answer, the largest over the test's accuracy checks (lower is better; results within 10 % of each other share a rank). Mass error, timing and NSE are shown beside it, not folded in. Each model runs the same inputs. Compare them in the results viewer →

Rank	Model	Difference	Largest difference in	Run time
1=	EPANET 2.2 US EPA	0.6 %	Head loss	2.2 s
1=	Hydra water distribution	0.65 %	Head loss	1.0 s

EPANET 2.2

EPA EPANET 2.2, the standard water-network solver

#1= 0.6 % off

Run time, finest grid: 2.2 s · AMD EPYC 9V74 80-Core Processor, 2 cores, 15.6 GB, Linux 6.17.0-1022-azure (GitHub Actions (github-hosted, ubuntu24))

Settings: epanet (WNTR 1.5.0, libepanet22)

Head loss

• 0.6 % off

Heads along the pipe

• 1.1 cm off

0.36 % of the exact 3.09 m head loss along the pipe

Scored with method 3.0 · Score card: EPA EPANET 2.2

Run it yourself

EPA EPANET 2.2 · runs on Linux · produced by scripts/run_network_cases.py in track-a.yml.

git clone https://github.com/scott-jeffers/benchmark1d2d && cd benchmark1d2d
git checkout 71dc10fc07a9
python -m pip install -e ".[dev,engines]"
python scripts/run_network_cases.py

The model files the suite wrote for this run (.zip, 0.62 KB): the exact inputs the solver read (one folder per grid, where the test has several), with their SHA-256.

The script writes the EPANET input file from the test's inputs; the model files below are that file.

The test itself (inputs, exact answer, checks): A1P-001.zip. Check the score card with benchmark1d2d verify-card: its signature by the suite's public development key shows the card has not changed since it was written, not who wrote it.

Hydra

Hydra 17 (NEER AI, Rust): its water-distribution engine on the EPANET data model, run through its CLI with default settings

#1= 0.65 % off

Run time, finest grid: 1.0 s · AMD EPYC 9V74 80-Core Processor, 2 cores, 15.6 GB, Linux 6.17.0-1022-azure (GitHub Actions (github-hosted, ubuntu24))

Settings: hydra CLI 4.1.1 (wds engine, EPANET-format binary output)

Head loss

• 0.65 % off

Heads along the pipe

• 1.2 cm off

0.39 % of the exact 3.09 m head loss along the pipe

Scored with method 3.0 · Score card: Hydra 17.0.0 water distribution

Run it yourself

Hydra 17.0.0 water distribution · version 17.0.0/4.1.1 · runs on Linux · produced by scripts/run_network_cases.py in track-a.yml.

git clone https://github.com/scott-jeffers/benchmark1d2d && cd benchmark1d2d
git checkout 71dc10fc07a9
python -m pip install -e ".[dev,engines]"
HYDRA=$(python scripts/fetch_hydra.py .hydra)  # the pinned Hydra 17 CLI
python scripts/run_network_cases.py --hydra-exe "$HYDRA"

The model files for this run will be published with its next run.

The script writes the EPANET input file from the test's inputs; the model files below are that file.

Not run yet: HEC-RAS 7.0, TELEMAC-2D, ANUGA, GeoClaw, LISFLOOD-FP, TUFLOW, MIKE 21, Iber, BASEMENT, Delft3D FM

Run it and add yours →

Status of this test

Candidate. To become frozen it needs: maintainer review recorded.

Download inputs (.zip)Cite this test View on GitHub

Technical details for reviewers Checks, reference, inputs, sources

Checks and why each limit was chosen

Check	Difference measured as a percentage of	Latest	Why this check
head_loss relative_head_loss of h · in the score	already a percentage	–	Exact Colebrook–White head loss within 1 %: the accuracy Swamee & Jain (1976) give for their explicit approximation over 5e3 < Re < 1e8, so a solver using any standard explicit friction formula passes and a wrong friction law or a units error fails.
head_profile L2 of h · in the score	of the exact 3.09 m head loss along the pipe	–	Heads along the pipe within 5 cm of the linear exact profile: catches a correct total loss distributed wrongly.
convergence not applicable	–	–	Steady closed-form pipe flow: a network solver has no grid to refine, so observed order of accuracy does not apply.

Reference

Exact solution from references.darcy_weisbach.head_loss.

Promotion checklist

Only frozen tests have fixed inputs and answers. This list is computed from the manifest and the published score cards; the rules are in the method.

✓Data licence verifiedfor candidateanalytic-public
✓All inputs availablefor candidateall committed or fetched by SHA-256
✓Reference (truth) availablefor candidateanalytic generator
✓Every tolerance justifiedfor candidateeach gating criterion has a rationale
✓A published run passesfor frozen2 passing score card(s)
✓Order of accuracy shownfor frozennot applicable: Steady closed-form pipe flow: a network solver has no grid to refine, so observed order of accuracy does not apply.
✓Two independent codes passfor frozenpassing codes: EPA EPANET 2.2, Hydra 17.0.0 water distribution
✗Maintainer review recordedfor frozenno maintainer review recorded

Inputs

File	Role	Format	SHA-256	Get it
`inputs/params.json`	case_parameters	json	`60886c40a737…`	Download

About this test

Physics

Steady flow from a reservoir (head 100 m) through a horizontal pipe, $L = 1000$ m, $D = 0.3$ m, roughness $\varepsilon = 0.15$ mm, withdrawn at $V = 1$ m/s. With $\nu = 10^{-6}$ m²/s, $Re = 3.0\times10^5$ and the Colebrook–White equation, solved to machine precision, gives $f = 0.018210$. The exact head loss is

$$\Delta h = f\,\frac{L}{D}\,\frac{V^2}{2g} = 3.094\ \text{m},$$

and the hydraulic grade line falls linearly along the pipe.

What it checks

The friction law a solver uses and how it applies it. Explicit formulas (Swamee–Jain, Haaland) are within about 1 % of Colebrook–White in this range, so they pass; a fixed friction factor, the wrong viscosity or a units error fails. EPA EPANET 2.2, which uses Swamee–Jain, comes out 0.60 % high, as theory predicts (0.65 %).

Case history

1.0.0 — friction factor from Colebrook–White instead of a fixed $f = 0.02$; head-loss metric relative to the exact drop; grid convergence marked not applicable (steady closed-form flow).

Citation

Colebrook, C. F. (1939). "Turbulent flow in pipes, with particular reference to the transition region between the smooth and rough pipe laws." J. ICE, 11(4), 133–156. Swamee, P. K., and Jain, A. K. (1976). "Explicit equations for pipe-flow problems." J. Hydraul. Div., 102(5), 657–664.

Sources

Darcy, H., Weisbach, J. (1845). Classical Darcy–Weisbach pipe-friction relation (as used in EPANET hydraulics). EPA/600/R-20/133 §3.

Test A1P-001_darcy_weisbach_single_pipe · version 1.0.0 · data licence analytic-public