schema_version: 1 name: nasa-backstep-driver-seegmiller intent: >- Model the air volume (flow passage) of the Driver-Seegmiller backward-facing-step channel for the parallel-roof (0 degree divergence) case described in the attached NASA validation page, as ONE solid suitable for CFD meshing. Use the documented ratios and the step height H = 0.5 in = 12.7 mm: step height to tunnel exit (downstream) height 1:9, step height to tunnel width 1:12, so the upstream channel height is the downstream height minus H. Cover exactly the documented computational domain x/H = -105 to +50. Frame: +x streamwise with x = 0 at the step face (upstream is negative x), +y spanwise across the tunnel width with y = 0 at one side wall, +z vertical with z = 0 at the downstream floor (the upstream floor therefore sits at z = H). Expose H, the width, the two channel heights, the roof angle, and the upstream/downstream domain lengths as named parameters, and name the flow-boundary faces (inlet, outlet, roof, upstream floor, step face, downstream floor, side walls) in the contract so the mesher can find them. The measured reattachment location is a downstream validation target, not a geometry input; do not tune anything to it. units: length: mm angle: deg material: air density_kg_m3: null process: CFD flow domain (no manufacturing) release_status: reconstruction frame: origin: >- [0, 0, 0] is the lower corner of the step face where the downstream floor, the step plane, and the y = 0 side wall meet. The step plane is x = 0. axes: x: +x follows the flow downstream; upstream is negative x and the step is at x = 0. y: +y spans the full tunnel width from the side wall at y = 0 to y = channelWidth. z: +z is vertically upward from the downstream floor at z = 0 toward the roof. datums: - name: downstreamFloorDatum description: z = 0 is the downstream floor, from x = 0 to downstreamLength. - name: stepDatum description: x = 0 is the vertical step face, from z = 0 to stepHeight, across the full width. - name: spanDatum description: y = 0 is one side wall; the other is at y = channelWidth. Do not center the span on y = 0. - name: upstreamFloorDatum description: z = stepHeight is the upstream floor, from x = -upstreamLength to 0. - name: roofDatum description: The parallel roof is the single plane z = downstreamHeight = stepHeight + upstreamHeight at the nominal configuration. - name: domainEndDatums description: Inlet x = -upstreamLength = -105*stepHeight; outlet x = downstreamLength = 50*stepHeight at the nominal configuration. envelope: min: [-1333.5, 0, 0] max: [635, 152.4, 114.3] tolerance: 0.05 parameters: - name: stepHeight value: 12.7 unit: mm provenance: stated source: 'sources/nasa-backstep-study01.md, Grid: "H is 0.5 inches." User also states H = 12.7 mm; exact conversion is 25.4 mm/in.' tolerance: 0.01 description: H, the vertical floor drop at x = 0; upstream floor elevation above the downstream floor. - name: channelWidth value: 152.4 unit: mm provenance: derived source: 'sources/nasa-backstep-study01.md, Introduction: "step height to tunnel width ratio of 1:12".' formula: 12 * stepHeight tolerance: 0.01 description: Full span from y = 0 to the second side wall; no symmetry reduction. The edit test overrides this nominal formula alone. edit_test: delta: 12.7 expect: volume_delta: 2642414.07 direction: increase tolerance_rel: 0.002 bbox_delta: [0, 12.7, 0] - name: downstreamHeight value: 114.3 unit: mm provenance: derived source: 'sources/nasa-backstep-study01.md, Introduction: "step height to tunnel exit height ratio of 1:9".' formula: 9 * stepHeight tolerance: 0.01 description: Downstream passage height from z = 0 to the parallel roof; also the nominal roof elevation. - name: upstreamHeight value: 101.6 unit: mm provenance: derived source: User intent and sources/nasa-backstep-study01.md, Introduction, zero-divergence backward-facing-step configuration. formula: downstreamHeight - stepHeight tolerance: 0.01 description: Upstream passage height measured upward from the floor at z = stepHeight to the common roof. - name: roofAngle value: 0 unit: deg provenance: stated source: 'sources/nasa-backstep-study01.md, Introduction: "zero degree divergence of the top wall"; user selects the parallel-roof case.' tolerance: 0.001 description: Roof divergence angle in the streamwise vertical plane. This contract prescribes the horizontal 0 degree configuration only. - name: upstreamLength value: 1333.5 unit: mm provenance: derived source: 'sources/nasa-backstep-study01.md, Grid: "the region from x/H = -105 to +50".' formula: 105 * stepHeight tolerance: 0.01 description: Positive distance from the inlet to the step; inlet coordinate is -upstreamLength. The edit test overrides this nominal formula alone. edit_test: delta: 12.7 expect: volume_delta: 196644.768 direction: increase tolerance_rel: 0.002 bbox_delta: [12.7, 0, 0] - name: downstreamLength value: 635 unit: mm provenance: derived source: 'sources/nasa-backstep-study01.md, Grid: "the region from x/H = -105 to +50".' formula: 50 * stepHeight tolerance: 0.01 description: Positive distance from the step to the outlet. The edit test overrides this nominal formula alone; reattachment does not set this length. edit_test: delta: 12.7 expect: volume_delta: 221225.364 direction: increase tolerance_rel: 0.002 bbox_delta: [12.7, 0, 0] features: - id: flowDomain kind: extrude count: 1 description: >- One connected, watertight air solid: the six-edge stepped x-z outline extruded across channelWidth. The nominal outline is (-upstreamLength, stepHeight), (0, stepHeight), (0, 0), (downstreamLength, 0), (downstreamLength, downstreamHeight), (-upstreamLength, downstreamHeight). The opening at x = 0 above stepHeight is interior air, with no partition face. parameters: [stepHeight, channelWidth, downstreamHeight, upstreamHeight, roofAngle, upstreamLength, downstreamLength] verify: - method: bbox note: Finished solid bounds must match the contract envelope in the specified frame. - method: section section: spanMid - method: count section: spanMid count: 1 note: One outer loop in the stepped longitudinal section; acceptance.solid_count independently requires one 3D body. - method: solid points: [[-12.7, 76.2, 63.5], [12.7, 76.2, 63.5]] note: Fluid exists on both sides of x = 0 above the upstream floor. Solid means air-domain interior here. - id: upstreamPassage kind: channel count: 1 description: Rectangular upstream air passage from x = -upstreamLength to 0, z = stepHeight to the roof, across the full width. parameters: [upstreamLength, channelWidth, upstreamHeight, stepHeight, downstreamHeight] verify: - method: section section: upstreamMid - method: solid points: [[-666.75, 76.2, 63.5]] - method: void points: [[-666.75, 76.2, 6.35]] note: The region below the upstream floor is outside the air solid, even though it lies inside the overall bounding box. - method: face face: inlet - method: face face: upstreamFloor - id: backwardStep kind: profile count: 1 description: One sharp vertical floor drop at x = 0 with height stepHeight and width channelWidth; the step-face outward normal from the air is -x. parameters: [stepHeight, channelWidth] verify: - method: face face: stepFace - method: void points: [[-6.35, 76.2, 6.35]] - method: solid points: [[6.35, 76.2, 6.35]] - method: section section: belowStep - method: count section: belowStep count: 1 note: A horizontal section below stepHeight contains only the downstream rectangle, with one outer loop and no hole. - id: downstreamPassage kind: channel count: 1 description: Rectangular downstream air passage from x = 0 to downstreamLength, z = 0 to downstreamHeight, across the full width. parameters: [downstreamLength, channelWidth, downstreamHeight] verify: - method: section section: downstreamMid - method: solid points: [[317.5, 76.2, 57.15]] - method: face face: outlet - method: face face: downstreamFloor - id: parallelRoof kind: wall count: 1 description: One continuous planar fluid boundary at z = downstreamHeight across both reaches, with zero streamwise divergence and outward normal +z. parameters: [roofAngle, downstreamHeight, upstreamHeight, stepHeight, channelWidth, upstreamLength, downstreamLength] verify: - method: face face: roof - method: section section: aboveStep - id: sideWalls kind: wall count: 2 description: Two full stepped-profile fluid boundaries at y = 0 and y = channelWidth; wall material and wall thickness are outside the modeled air volume. parameters: [channelWidth, upstreamLength, downstreamLength, stepHeight, upstreamHeight, downstreamHeight] verify: - method: face face: sideWallY0 - method: face face: sideWallYMax - method: void points: [[-666.75, -12.7, 63.5], [317.5, 165.1, 57.15]] note: Both probes are outside the full-width flow passage. interfaces: - name: flowBoundaryNames description: Preserve the eight meshing face names inlet, outlet, roof, upstreamFloor, stepFace, downstreamFloor, sideWallY0, and sideWallYMax, with outward normals from the air solid. must_not_change: true - name: meshableFluidRegion description: Preserve one watertight fluid solid with no internal partitions, internal holes, solid tunnel-wall bodies, fillets, or artificial reattachment features. must_not_change: true - name: fixedStepFrame description: Preserve the step at x = 0, downstream floor at z = 0, and span datum at y = 0 during the declared width and length edits. must_not_change: true acceptance: bbox_tolerance: 0.05 volume: expected: 31708968.84 tolerance_rel: 0.002 provenance: derived note: >- At roofAngle = 0, V = channelWidth * (upstreamLength * upstreamHeight + downstreamLength * downstreamHeight). Equivalently, V = channelWidth * ((upstreamLength + downstreamLength) * downstreamHeight - upstreamLength * stepHeight), using the nominal height relationship. Units mm3. surface_area: expected: 1050965.64 tolerance_rel: 0.002 provenance: derived note: >- Let A = upstreamLength * upstreamHeight + downstreamLength * downstreamHeight. At roofAngle = 0, S = 2*A + channelWidth * (2*(upstreamLength + downstreamLength) + upstreamHeight + downstreamHeight + stepHeight). This is the sum of all eight external boundary-face areas, including inlet and outlet caps; the shared opening at x = 0 is not a boundary. Units mm2. center_of_mass: expected: [-323.406976744186, 76.2, 61.2848837209302] tolerance: 0.05 provenance: derived note: >- Uniform-volume centroid, independent of air density. Let Au = upstreamLength * upstreamHeight, Ad = downstreamLength * downstreamHeight, A = Au + Ad. Cx = (Au*(-upstreamLength/2) + Ad*(downstreamLength/2))/A; Cy = channelWidth/2; Cz = (Au*(stepHeight + upstreamHeight/2) + Ad*(downstreamHeight/2))/A. Formulas assume the specified zero-divergence nominal geometry. Units mm. solid_count: 1 sections: - id: upstreamMid plane: x at: -666.75 expect: area: 15483.84 area_tolerance_rel: 0.002 loops: 1 holes: 0 islands_min: 1 description: x = -upstreamLength/2; area = channelWidth*upstreamHeight, spanning z = stepHeight to downstreamHeight and y = 0 to channelWidth. - id: downstreamMid plane: x at: 317.5 expect: area: 17419.32 area_tolerance_rel: 0.002 loops: 1 holes: 0 islands_min: 1 description: x = downstreamLength/2; area = channelWidth*downstreamHeight, spanning z = 0 to downstreamHeight and the full width. - id: spanMid plane: y at: 76.2 expect: area: 208064.1 area_tolerance_rel: 0.002 loops: 1 holes: 0 islands_min: 1 description: y = channelWidth/2; area = upstreamLength*upstreamHeight + downstreamLength*downstreamHeight. One six-edge stepped outline, with no internal boundary at x = 0 above the step. - id: belowStep plane: z at: 6.35 expect: area: 96774 area_tolerance_rel: 0.002 loops: 1 holes: 0 islands_min: 1 description: z = stepHeight/2; area = downstreamLength*channelWidth. Only x = 0 to downstreamLength contains air at this elevation. - id: aboveStep plane: z at: 63.5 expect: area: 299999.4 area_tolerance_rel: 0.002 loops: 1 holes: 0 islands_min: 1 description: z = stepHeight + upstreamHeight/2; area = (upstreamLength + downstreamLength)*channelWidth. Both reaches form one uninterrupted rectangle. faces: - name: inlet plane: x at: -1333.5 normal: "-" area: 15483.84 area_tolerance_rel: 0.002 tolerance: 0.05 center: [76.2, 63.5] mode: one - name: outlet plane: x at: 635 normal: "+" area: 17419.32 area_tolerance_rel: 0.002 tolerance: 0.05 center: [76.2, 57.15] mode: one - name: roof plane: z at: 114.3 normal: "+" area: 299999.4 area_tolerance_rel: 0.002 tolerance: 0.05 center: [-349.25, 76.2] mode: one - name: upstreamFloor plane: z at: 12.7 normal: "-" area: 203225.4 area_tolerance_rel: 0.002 tolerance: 0.05 center: [-666.75, 76.2] mode: one - name: stepFace plane: x at: 0 normal: "-" area: 1935.48 area_tolerance_rel: 0.002 tolerance: 0.05 center: [76.2, 6.35] mode: one - name: downstreamFloor plane: z at: 0 normal: "-" area: 96774 area_tolerance_rel: 0.002 tolerance: 0.05 center: [317.5, 76.2] mode: one - name: sideWallY0 plane: y at: 0 normal: "-" area: 208064.1 area_tolerance_rel: 0.002 tolerance: 0.05 center: [-323.406976744186, 61.2848837209302] mode: one - name: sideWallYMax plane: y at: 152.4 normal: "+" area: 208064.1 area_tolerance_rel: 0.002 tolerance: 0.05 center: [-323.406976744186, 61.2848837209302] mode: one blockout: volume_min: 31645550.90232 volume_max: 31772386.77768 export_volume_tolerance_rel: 0.002 references: - path: sources/nasa-backstep-study01.md kind: text role: authoritative sha256: 2aca80462b8cd0fd2554c59a156e6a1149921d26b51fbe763e393f3a065e05b2 units: in (step height); dimensionless (ratios and x/H); deg (roof); ft (described grid coordinates); m/s (validation velocity) revision: NASA page created 1998-12-11, last updated 2021-02-10; supplied offline text reproduction with figures omitted. note: >- NASA Glenn WIND Backstep Study #1, https://www.grc.nasa.gov/WWW/wind/valid/backstep/backstep01/backstep01.html. Geometry evidence comes from Introduction and Grid. Boundary Conditions describe numerical treatment, not additional physical holes or wall thickness. Comparisons of the Results supplies validation data only; no reattachment quantity is a geometry parameter. No images, grid coordinate files, CAD, or mesh references were supplied. open_questions: []