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The transition criteria for the windward surface of the Shuttle Orbiter, which is composed of a large number of thermal protection tiles, must include the effect of distributed roughness arising from joints and possible tile misalignments. Theoretical flowfield parameters and heat-transfer distributions were used to analyze boundarylayer transition data. Data were obtained for Mach numbers from 8 to 12 over a range of Reynolds number based on model length from 1.8 to 17.6 x 10 6 with surface temperatures from 0.114 to 0.4357,. The transition correlations were approximately the same both for the misaligned-tile models and for the grit-roughened model. The incipient value of Re ktr was 30, the critical value was 110, and the effective value was 180. Nomenclature h = local heat-transfer coefficient /,ref = heat -transfer coefficient for the stagnation point of the reference sphere k = height of the misaligned tiles L = axial model length, 0.5734m (1.881 ft) M = Mach number Re k = Reynolds number based on conditions at the top of the misaligned tile [Eq. (1)] Re y = Reynolds number based on the flow conditions at a distance y from the wall Re e = Reynolds number based on local flow properties and the momentum thickness Re WfL = Reynolds number based on freestream flow properties and the model length T = temperature U = streamwise component of the velocity x = axial coordinate a = angle of attack <5* = displacement thickness 6 = momentum thickness jji = viscosity £ = relative transition location defined in Eq. (2) p -density Subscripts e = evaluated at the edge of the boundary layer / = evaluated at the particular run of interest [see Eq.(2)] t = evaluated at the stagnation conditions tr = evaluated at the transition location w = evaluated at the wall oo = evaluated at the freestream conditionsPresented as Paper 81-0417 at the AIAA 19th Aerospace Sciences Meeting, St. Louis, Mo., Jan. 12-15,

Numerical computations of flowfields and laminar heating rates around the Space Shuttle Orbiter windward surface, including the root of the wing leading edge, are presented to illustrate the sensitivity of these calculations to several flowfield modeling assumptions. Specifically, results obtained using the axisymmetric analogue concept to predict "three-dimensional" heating rates, in conjunction with exact three-dimensional inviscid flowfield solutions and two-dimensional boundary-layer analysis, show the sensitivity of boundary-layer edge conditions and heating rates to considerations of: 1) the inviscid flowfield "entropy layer," 2) equilibrium air vs chemically and vibrationally frozen flow, and 3) nonsimilar terms in ttie boundary-layer computations. In addition, a cursory comparison between flowfield predictions (made at critical points in the current design trajectory) obtained from these methods and current Orbiter design methods has established a benchmark for selecting and adjusting these and future design methodologies.

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