Cascade Data Re-Use Traceability Record
Document: TRC-CRUISE-VAL-001
Date: April 8, 2026
Prepared by: J. Kim (CFD Lead)
Reviewed by: S. Thompson (Independent Reviewer)

Purpose: Document the use of COU1 cascade rig validation data as validation
evidence for COU2 (cruise) predictions, and the operating-point mismatch this
entails.

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Source Dataset: cascade_rig_temperature_data.csv (48-TC rake, aero-evidence-cou1)

Dataset Design Intent:
  - Validate CFD model at TAKE-OFF Reynolds (1.26e6) and Mach (0.94)
  - Cascade Re = 1.20e6 (4.8% below engine take-off)
  - Cascade M  = 0.92 (2.1% below engine take-off)
  - Mid-span coverage ONLY
  - Designed and instrumented at the take-off operating point

COU2 Application:
  - Apply same dataset to validate CFD at CRUISE Reynolds (0.85e6) and Mach (0.88)
  - Cascade Re is now 41% HIGHER than engine cruise (not 4.8% lower)
  - Cascade M is 4.5% above engine cruise
  - Operating regime mismatch: cascade is at fully-turbulent high-Re regime;
    cruise is at lower-Re regime where Nusselt-Re exponent differs.

Known physics differences not captured in the re-used cascade data:

  (a) Heat transfer regime: Nu ~ Re^0.8 at cascade Re (fully turbulent);
      Nu ~ Re^0.7 at cruise Re (transitional-turbulent regime for HPT airfoil).
      Heat transfer coefficient ratio is not linear in Re.

  (b) Boundary layer transition location: cruise transition occurs ~8% chord
      further aft than cascade (estimated from XFOIL en-envelope). Affects
      suction-side heat load distribution.

  (c) Radiation: cruise lower gas temperature (1450K vs 1650K) means different
      flame-to-surface radiation contribution, not dominant but non-zero.

  (d) Surface roughness effects: cruise operation includes accumulated surface
      roughness from in-service oxidation/deposits, not represented in cascade
      polished-surface testing.

Compensation Attempts:
  - None. The CFD is run at cruise BCs directly; the cascade data is used
    only to anchor the CFD-measurement error distribution established at
    take-off conditions (1.8% mean, 4.2% max).

Rationale for Re-Use:
  - No cruise-specific validation data exists for this blade geometry.
  - Budgetary and schedule constraints preclude new cascade campaign before
    the next MRL review.
  - Assumption: error distribution established at take-off bounds error at
    cruise. This assumption is NOT validated.

Board Position: See review_board_minutes_cruise_2026Q2.txt, Items 3-6.
