# ERCOFTAC Ahmed Body 25° — case082

Validation case from the **ERCOFTAC Classic Collection — case082**, MOVA project (Models for Vehicle Aerodynamics, 1998–2001). Experiments: H. Lienhart, S. Becker, C. Stoots — LSTM Erlangen.

## Required metrics
1. **LDA mean velocity + Reynolds-stress profiles** on canonical x-z and y-z planes through slant + wake
2. **Surface pressure** Cp on the rear (slant + base)
3. **Boundary-layer hot-wire profiles** at top / side / underbody locations (transferable across slant angles)
4. **Drag/lift scalars** (CD, CL) — see `baseline_komegasst/scalars.json`

## Folder layout
```
ERCOFTAC_AhmedBody25/
├── baseline_komegasst/   k-ω SST RANS extracted at experimental locations (.csv)
│   └── scalars.json      CD, CL, body geometry, Cp range — single source of truth for scalars
├── highfidelity/         ERCOFTAC LDA + pressure + BL hot-wire (37 .dat + .csv pairs)
└── plots/                Pre-rendered comparison figures + plot_profiles.py
```

The full OpenFOAM case (mesh, fields, run scripts, VTK extraction, force-integration code) is hosted separately on the heavy CFD-asset Hugging Face dataset linked in the paper.

## Generated figures (in `plots/`)
- `Ahmed25_wake_U_contours` / `_uw_contours` / `_k_contours` — y-z plane field comparisons (4 stations × Exp/Baseline)
- `Ahmed25_wake_profile_U` / `_uw` / `_k` — symmetry-plane wake profile stagger (10 stations, x = 38..638 mm)
- `Ahmed25_slant_profile_U` / `_k` — slant-region (y=0) profile stagger (12 stations, x = -243..-3 mm)
- `Ahmed25_Cp_rear` — surface pressure on slant centerline + base centerline

## Baseline scalars (k-ω SST, t=30)
| Quantity | Value | Reference (exp / lit.) |
|---|---|---|
| CD pressure  | 0.362 | — |
| CD friction  | 0.035 | — |
| **CD total** | **0.398** | 0.285 (Ahmed 1984) ; 0.32–0.40 (k-ω SST lit.) |
| Friction share of CD | 8.9% | — |
| CL total     | 0.022 | — |
| Cp range     | -0.81 .. -0.12 | -1.57 .. -0.14 (LSTM) |
| Body wetted area | 1.326 m² | — |
| Frontal area (h·w) | 0.112 m² | — |

Friction component obtained via `simpleFoam -postProcess -func wallShearStress -time 30` then read into `compute_forces.py` via `vtkOpenFOAMReader`.

## Solver / setup
- **Solver**: `simpleFoam` (incompressible steady)
- **Turbulence model**: `kOmegaSST` (pure baseline)
- **Mesh**: snappyHexMesh-generated
- **Inflow**: U_inlet = (40, 0, 0) m/s ⇒ U_b = 40 m/s
- **Reference**: Re_h = 768 000, h = 288 mm, slant = 222 mm @ 25°
- **Coordinates**: x = 0 at body rear, y = 0 symmetry plane, z = 0 ground plane (units mm in .dat / .csv data files)
- **Converged at**: t = 30 (steady)

## Submission format
Drop CSV files in `MODEL_DIR` matching the highfidelity column conventions:
- `ahmed-25-y000-whole.csv` — symmetry plane (whole) cols: `x, y, z, U, V, W, urms, vrms, wrms, uv, uw, ...`
- `ahmed-25-{xm088, xp000, xp200, xp500}-yz.csv` — wake-development y-z planes (canonical scoring stations)
- `ahmed-25-yp{000,100,180,195}-xz.csv` / `ahmed-25-ym195-xz.csv` — slant-region x-z planes
- `ahmed-25-yp000-bl.csv` — symmetry-plane BL profile (u, w only)
- `ahmed-25-press.csv` — rear surface Cp: `x, y, z, Cp` (mm units)

Then `python plots/plot_profiles.py` overlays baseline + LDA + your model.

## Provenance
- High-fidelity: `ahby-allfiles.tar.gz` from ERCOFTAC Classic Collection case082, extracted via `tar -xzf`.
- OpenFOAM case: `OF_Baseline_Cases/AhmedBody/`. Mesh built on an HPC cluster. Tested with OpenFOAM 7.

## Citations
- Ahmed, S.R., Ramm, G., Faltin, G. (1984). *Some salient features of the time-averaged ground vehicle wake*. SAE Tech. Paper 840300. https://doi.org/10.4271/840300
- Lienhart, H., Stoots, C., Becker, S. (2000). *Flow and turbulence structures in the wake of a simplified car model (Ahmed model)*. DGLR Fach Symp. der AG STAB, Stuttgart.
- Lienhart, H., Becker, S. (2003). *Flow and Turbulence Structure in the Wake of a Simplified Car Model*. SAE Paper 2003-01-0656. https://doi.org/10.4271/2003-01-0656