Add per-scenario channels.json sidecars and document field/channel order in README

README.md

@@ -131,6 +131,7 @@ Dataset version: **`2.0.0`** (see `version.json` at repo root; released 2026-01-
 ```
 {repo_root}/
   cylinder/
+    channels.json                     # Field / channel schema for this scenario
     in_dist_test_params_real.json
     out_dist_test_params_real.json
     remain_params_real.json
@@ -220,6 +221,7 @@ print(f"Output shape: {output_tensor.shape}") # (200, H, W, 2) = 20 × 10
   - `t` (bytes): float32 array `(T_full,)` — time stamps
   - `shape_t` (int): **complete trajectory length** (e.g., 3990, 2173)
   - `shape_h`, `shape_w` (int): spatial dimensions
+- **Field names** for each scenario are also documented machine-readably in [`{scenario}/channels.json`](#repository-layout) (with shapes and short physical descriptions).
 
 > **Note on spatial grids:** `x` and `y` are identical across all time frames, so they are stored once as `(H, W)` instead of `(T, H, W)`. For methods that require per-frame coordinate grids (e.g., PINNs), broadcast at runtime: `x_grid = np.broadcast_to(x[np.newaxis, :, :], (T, H, W))`. This is a zero-copy view with no memory overhead.
 
@@ -235,6 +237,7 @@ print(f"Output shape: {output_tensor.shape}") # (200, H, W, 2) = 20 × 10
   - `t` (bytes): float32 array `(T_full,)` — time stamps
   - `shape_t` (int): **complete trajectory length** (e.g., 2001)
   - `shape_h`, `shape_w` (int): spatial dimensions
+- **Channel order** of the 15 fields packed in `numerical` (along the last axis) is listed in [`combustion/channels.json`](combustion/channels.json) under `numerical.numerical_axis_names` (`index → name` + physical description). Authoritative units and definitions live in the [combustion dataset page](https://realpdebench.github.io/datasets/combustion/).
 
 ### Index files (JSON)
 

combustion/channels.json

@@ -0,0 +1,32 @@
+{
+  "scenario": "combustion",
+  "real": {
+    "fields": [
+      {"key": "observed", "shape": "(T, H, W)", "description": "OH* chemiluminescence (CL) intensity recorded by high-speed imaging of the swirl-stabilized NH3/CH4/air flame."}
+    ]
+  },
+  "numerical": {
+    "fields": [
+      {"key": "observed", "shape": "(T, H, W)", "description": "Surrogate intensity field corresponding to the measured OH* signal, produced by a U-Net mapping from simulated fields to the observable modality."},
+      {"key": "numerical", "shape": "(T, H, W, 15)", "description": "Fifteen simulated thermodynamic and species fields from Large Eddy Simulation (STAR-CCM+ with the Eddy Dissipation Concept; 38 species, 184 reactions). The 15 channels are packed along the last axis in the order given by `numerical_axis_names`."}
+    ],
+    "numerical_axis_names": [
+      {"index": 0,  "name": "Absolute_Pressure",            "description": "Absolute pressure field."},
+      {"index": 1,  "name": "Chemistry_Heat_Release_Rate",  "description": "Volumetric heat release rate from chemical reactions."},
+      {"index": 2,  "name": "Mole_Fraction_of_CH4",         "description": "Mole fraction of methane (CH4)."},
+      {"index": 3,  "name": "Mole_Fraction_of_CO",          "description": "Mole fraction of carbon monoxide (CO)."},
+      {"index": 4,  "name": "Mole_Fraction_of_CO2",         "description": "Mole fraction of carbon dioxide (CO2)."},
+      {"index": 5,  "name": "Mole_Fraction_of_H2O",         "description": "Mole fraction of water vapour (H2O)."},
+      {"index": 6,  "name": "Mole_Fraction_of_NH2",         "description": "Mole fraction of the amino radical (NH2)."},
+      {"index": 7,  "name": "Mole_Fraction_of_NH3",         "description": "Mole fraction of ammonia (NH3)."},
+      {"index": 8,  "name": "Mole_Fraction_of_OH",          "description": "Mole fraction of the hydroxyl radical (OH); proxy for the measured OH* chemiluminescence signal."},
+      {"index": 9,  "name": "Pressure",                     "description": "Gauge pressure field."},
+      {"index": 10, "name": "Temperature",                  "description": "Static temperature field."},
+      {"index": 11, "name": "Velocity[i]",                  "description": "x-component of the velocity vector."},
+      {"index": 12, "name": "Velocity[j]",                  "description": "y-component of the velocity vector."},
+      {"index": 13, "name": "Velocity[k]",                  "description": "z-component of the velocity vector."},
+      {"index": 14, "name": "Velocity_Magnitude",           "description": "Magnitude of the velocity vector."}
+    ]
+  },
+  "note": "Authoritative physical definitions and units are documented at https://realpdebench.github.io/datasets/combustion/."
+}

controlled_cylinder/channels.json

@@ -0,0 +1,17 @@
+{
+  "scenario": "controlled_cylinder",
+  "real": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity component, measured by Particle Image Velocimetry (PIV) under active flow control."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity component, measured by Particle Image Velocimetry (PIV) under active flow control."}
+    ]
+  },
+  "numerical": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity component from CFD simulation with the same control input as the paired experiment."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity component from CFD simulation."},
+      {"key": "p", "shape": "(T, H, W)", "description": "Pressure field from CFD simulation."}
+    ]
+  },
+  "note": "Each field is stored as a separate column in the Arrow dataset. Control parameters (Reynolds number, control frequency) are encoded in the trajectory filenames and in the *_params_*.json index files. Authoritative physical definitions and units are documented at https://realpdebench.github.io/datasets/controlled_cylinder/."
+}

cylinder/channels.json

@@ -0,0 +1,17 @@
+{
+  "scenario": "cylinder",
+  "real": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity component, measured by Particle Image Velocimetry (PIV)."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity component, measured by Particle Image Velocimetry (PIV)."}
+    ]
+  },
+  "numerical": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity component from CFD simulation."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity component from CFD simulation."},
+      {"key": "p", "shape": "(T, H, W)", "description": "Pressure field from CFD simulation."}
+    ]
+  },
+  "note": "Each field is stored as a separate column in the Arrow dataset. Authoritative physical definitions and units are documented at https://realpdebench.github.io/datasets/cylinder/."
+}

foil/channels.json

@@ -0,0 +1,17 @@
+{
+  "scenario": "foil",
+  "real": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity component around the NACA0025 foil cross-section, measured by Particle Image Velocimetry (PIV)."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity component, measured by Particle Image Velocimetry (PIV)."}
+    ]
+  },
+  "numerical": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity from CFD simulation around the foil cross-section."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity from CFD simulation."},
+      {"key": "p", "shape": "(T, H, W)", "description": "Pressure field from CFD simulation."}
+    ]
+  },
+  "note": "Each field is stored as a separate column in the Arrow dataset. Geometric parameters (angle of attack, Reynolds number) are stored in the *_params_*.json index files. Authoritative physical definitions and units are documented at https://realpdebench.github.io/datasets/foil/."
+}

fsi/channels.json

@@ -0,0 +1,17 @@
+{
+  "scenario": "fsi",
+  "real": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity component around the vibrating cylinder, measured by Particle Image Velocimetry (PIV)."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity component, measured by Particle Image Velocimetry (PIV)."}
+    ]
+  },
+  "numerical": {
+    "fields": [
+      {"key": "u", "shape": "(T, H, W)", "description": "Streamwise velocity from coupled fluid-structure simulation."},
+      {"key": "v", "shape": "(T, H, W)", "description": "Transverse velocity from coupled fluid-structure simulation."},
+      {"key": "p", "shape": "(T, H, W)", "description": "Pressure field from coupled fluid-structure simulation."}
+    ]
+  },
+  "note": "Each field is stored as a separate column in the Arrow dataset. Structural parameters (mass ratio, damping ratio, Reynolds number) are stored in the *_params_*.json index files. Authoritative physical definitions and units are documented at https://realpdebench.github.io/datasets/fsi/."
+}