{
  "evidence": "ACTUAL_URANS_COLD_FREE_AIR_CFD_NOT_EXPERIMENT",
  "cases": [
    {
      "case": "p1-L4-URANS",
      "variant": "P1",
      "maximum_Courant": 0.5,
      "time_window_s": [
        0.2,
        0.6
      ],
      "mean_full_body_drag_N": 0.717843413559677,
      "temporal_drag_std_N": 0.0009195039146806909,
      "two_window_relative_drift": 0.0001474642618875227,
      "completed_to_0p6s": true,
      "force_multiplier": 2,
      "metadata": {
        "name": "p1-L4-U10-p2test",
        "mode": "p1",
        "surface_refinement": 4,
        "speed_ms": 10,
        "Re_length": 320000.0,
        "half_domain": true,
        "force_multiplier": 2,
        "rho_kgm3": 1.2,
        "reference_frontal_area_m2": 0.027,
        "reference_area_note": "Envelope width*height, not measured projected frontal area; use force and CdA for comparison.",
        "solver": "OpenFOAM v2412 pimpleFoam URANS kOmegaSST",
        "inlet_turbulence_intensity": 0.01,
        "turbulent_length_scale_m": 0.01,
        "ground": "No ground boundary: preliminary free-air mechanism test",
        "wheel_rotation": false,
        "heating_W": 0,
        "generator_load": 0,
        "scope": "Unvalidated numerical mechanism test. Not a high-end-car performance comparison.",
        "variant": "p1",
        "comparison": "P1/P2 shape revision under matched free-air cold-flow conditions",
        "revision": "P1 reference",
        "numerical_change": "All matched cases use p relaxation 0.18, U 0.35, k/omega 0.4; tighter inner linear solves and residual stopping.",
        "material_model": "Smooth rigid impermeable walls for all variants. Premium materials do not receive an assumed drag advantage.",
        "required_gates": "Standard mesh quality, force stability, actual residuals, mass balance and cross-mesh comparison; failed gates remain visible.",
        "source_steady_case": "p1-L4-U10-p2test",
        "initial_state": "Steady iteration 1000; not an independently converged equilibrium",
        "target_end_time_s": 0.6,
        "transient_scope": "Physical-time follow-up, same free-air/fixed-wheel mesh. No ground or thermal/rotating-blade model. Existing extended mesh concerns remain.",
        "time_step_policy": "Adaptive Co <=0.5, max dt 0.0005s, backward time integration; physical-time force averaging required."
      }
    },
    {
      "case": "p2-flow-L4-URANS",
      "variant": "P2",
      "maximum_Courant": 0.5,
      "time_window_s": [
        0.2,
        0.6
      ],
      "mean_full_body_drag_N": 0.5999215032077053,
      "temporal_drag_std_N": 0.006453514783614531,
      "two_window_relative_drift": 0.0024964250267663496,
      "completed_to_0p6s": true,
      "force_multiplier": 2,
      "metadata": {
        "name": "p2-flow-L4-U10-p2test",
        "mode": "p2-flow",
        "surface_refinement": 4,
        "speed_ms": 10,
        "Re_length": 320000.0,
        "half_domain": true,
        "force_multiplier": 2,
        "rho_kgm3": 1.2,
        "reference_frontal_area_m2": 0.027,
        "reference_area_note": "Envelope width*height, not measured projected frontal area; use force and CdA for comparison.",
        "solver": "OpenFOAM v2412 pimpleFoam URANS kOmegaSST",
        "inlet_turbulence_intensity": 0.01,
        "turbulent_length_scale_m": 0.01,
        "ground": "No ground boundary: preliminary free-air mechanism test",
        "wheel_rotation": false,
        "heating_W": 0,
        "generator_load": 0,
        "scope": "Unvalidated numerical mechanism test. Not a high-end-car performance comparison.",
        "variant": "p2-flow",
        "comparison": "P1/P2 shape revision under matched free-air cold-flow conditions",
        "revision": "P2",
        "numerical_change": "All matched cases use p relaxation 0.18, U 0.35, k/omega 0.4; tighter inner linear solves and residual stopping.",
        "material_model": "Smooth rigid impermeable walls for all variants. Premium materials do not receive an assumed drag advantage.",
        "required_gates": "Standard mesh quality, force stability, actual residuals, mass balance and cross-mesh comparison; failed gates remain visible.",
        "source_steady_case": "p2-flow-L4-U10-p2test",
        "initial_state": "Steady iteration 1000; not an independently converged equilibrium",
        "target_end_time_s": 0.6,
        "transient_scope": "Physical-time follow-up, same free-air/fixed-wheel mesh. No ground or thermal/rotating-blade model. Existing extended mesh concerns remain.",
        "time_step_policy": "Adaptive Co <=0.5, max dt 0.0005s, backward time integration; physical-time force averaging required."
      }
    },
    {
      "case": "p1-L4-URANS-Co025",
      "variant": "P1",
      "maximum_Courant": 0.25,
      "time_window_s": [
        0.2,
        0.6
      ],
      "mean_full_body_drag_N": 0.7184714315697108,
      "temporal_drag_std_N": 0.0035671287352903682,
      "two_window_relative_drift": 8.428677643756401e-05,
      "completed_to_0p6s": true,
      "force_multiplier": 2,
      "metadata": {
        "name": "p1-L4-U10-p2test",
        "mode": "p1",
        "surface_refinement": 4,
        "speed_ms": 10,
        "Re_length": 320000.0,
        "half_domain": true,
        "force_multiplier": 2,
        "rho_kgm3": 1.2,
        "reference_frontal_area_m2": 0.027,
        "reference_area_note": "Envelope width*height, not measured projected frontal area; use force and CdA for comparison.",
        "solver": "OpenFOAM v2412 pimpleFoam URANS kOmegaSST",
        "inlet_turbulence_intensity": 0.01,
        "turbulent_length_scale_m": 0.01,
        "ground": "No ground boundary: preliminary free-air mechanism test",
        "wheel_rotation": false,
        "heating_W": 0,
        "generator_load": 0,
        "scope": "Unvalidated numerical mechanism test. Not a high-end-car performance comparison.",
        "variant": "p1",
        "comparison": "P1/P2 shape revision under matched free-air cold-flow conditions",
        "revision": "P1 reference",
        "numerical_change": "All matched cases use p relaxation 0.18, U 0.35, k/omega 0.4; tighter inner linear solves and residual stopping.",
        "material_model": "Smooth rigid impermeable walls for all variants. Premium materials do not receive an assumed drag advantage.",
        "required_gates": "Standard mesh quality, force stability, actual residuals, mass balance and cross-mesh comparison; failed gates remain visible.",
        "source_steady_case": "p1-L4-U10-p2test",
        "initial_state": "Steady iteration 1000; not an independently converged equilibrium",
        "target_end_time_s": 0.6,
        "transient_scope": "Physical-time follow-up, same free-air/fixed-wheel mesh. No ground or thermal/rotating-blade model. Existing extended mesh concerns remain.",
        "time_step_policy": "Adaptive Co <=0.25, max dt 0.0005s, backward time integration; physical-time force averaging required."
      }
    },
    {
      "case": "p2-flow-L4-URANS-Co025",
      "variant": "P2",
      "maximum_Courant": 0.25,
      "time_window_s": [
        0.2,
        0.6
      ],
      "mean_full_body_drag_N": 0.6005160140384408,
      "temporal_drag_std_N": 0.0061172023146540055,
      "two_window_relative_drift": 0.002743401964256738,
      "completed_to_0p6s": true,
      "force_multiplier": 2,
      "metadata": {
        "name": "p2-flow-L4-U10-p2test",
        "mode": "p2-flow",
        "surface_refinement": 4,
        "speed_ms": 10,
        "Re_length": 320000.0,
        "half_domain": true,
        "force_multiplier": 2,
        "rho_kgm3": 1.2,
        "reference_frontal_area_m2": 0.027,
        "reference_area_note": "Envelope width*height, not measured projected frontal area; use force and CdA for comparison.",
        "solver": "OpenFOAM v2412 pimpleFoam URANS kOmegaSST",
        "inlet_turbulence_intensity": 0.01,
        "turbulent_length_scale_m": 0.01,
        "ground": "No ground boundary: preliminary free-air mechanism test",
        "wheel_rotation": false,
        "heating_W": 0,
        "generator_load": 0,
        "scope": "Unvalidated numerical mechanism test. Not a high-end-car performance comparison.",
        "variant": "p2-flow",
        "comparison": "P1/P2 shape revision under matched free-air cold-flow conditions",
        "revision": "P2",
        "numerical_change": "All matched cases use p relaxation 0.18, U 0.35, k/omega 0.4; tighter inner linear solves and residual stopping.",
        "material_model": "Smooth rigid impermeable walls for all variants. Premium materials do not receive an assumed drag advantage.",
        "required_gates": "Standard mesh quality, force stability, actual residuals, mass balance and cross-mesh comparison; failed gates remain visible.",
        "source_steady_case": "p2-flow-L4-U10-p2test",
        "initial_state": "Steady iteration 1000; not an independently converged equilibrium",
        "target_end_time_s": 0.6,
        "transient_scope": "Physical-time follow-up, same free-air/fixed-wheel mesh. No ground or thermal/rotating-blade model. Existing extended mesh concerns remain.",
        "time_step_policy": "Adaptive Co <=0.25, max dt 0.0005s, backward time integration; physical-time force averaging required."
      }
    }
  ],
  "matched_comparisons": [
    {
      "maximum_Courant": 0.5,
      "P1_drag_N": 0.717843413559677,
      "P2_drag_N": 0.5999215032077053,
      "conditional_drag_reduction_fraction": 0.16427246962845943
    },
    {
      "maximum_Courant": 0.25,
      "P1_drag_N": 0.7184714315697108,
      "P2_drag_N": 0.6005160140384408,
      "conditional_drag_reduction_fraction": 0.16417551533477392
    }
  ],
  "time_step_sensitivity": [
    {
      "variant": "P1",
      "mean_drag_change_when_halving_Courant_fraction": 0.0008748676914365205
    },
    {
      "variant": "P2",
      "mean_drag_change_when_halving_Courant_fraction": 0.0009909810326129698
    }
  ],
  "limits": [
    "Same retained L4 free-air meshes and fixed wheels. No moving ground, resolved rotating blades, thermal air path, road suction or installed wheel deployment.",
    "Standard mesh checks passed originally, but extended concave-cell checks failed. Wall layers and near-wall resolution remain limitations.",
    "The 0.2-0.6 s mean is a short URANS sampling window. Temporal fluctuations are numerical model fluctuations, not experimental uncertainty.",
    "The comparison concerns the original P1/P2 cold-flow shapes. New wheel pockets and the pressure tray do not inherit these drag results.",
    "A whole-body shape benefit can coexist with the cost of extracting turbine power; neither is assumed away."
  ],
  "physical_measurements": 0
}