Heat-transfer effects in compressible turbulent boundary layers with and without pressure gradients

Beschreibung

This thesis investigates two aspects of heat transfer in compressible turbulent boundary layers: (1) the influence of wall heat transfer on thermal turbulence across Mach numbers, and (2) the combined effects of pressure gradients and heat transfer, using direct numerical simulations. The first part introduces a regime diagram categorizing zero pressure-gradient boundary layers by Mach number and wall temperature effects. By combining flow velocity and enthalpy differences into a single parameter, the study unifies most Mach and heat-transfer influences into a predictive framework. This enables consistent interpretation of thermal behavior across varying conditions. Cooling regimes - weak, moderate, or strong - are classified based on the wall-normal location of the temperature peak, which reflects the balance between viscous heating and wall cooling. The Reynolds-number dependence of this peak position provides further insight into earlier DNS findings, separating heat-transfer effects from compressibility-driven ones. The second part examines supersonic boundary layers under adverse pressure gradients with decreasing Mach number and various wall thermal conditions - heated, adiabatic, weakly cooled, and moderately cooled. These simulations validate earlier self-similar analyses, quantify engineering metrics such as the Stanton number, and extend the theory for pressure-gradient boundary layers. Emphasis is placed on the outer layer and wake region, where pressure gradients have the strongest impact. Deviations in models like the velocity-temperature relation are found to be similar to zero pressure-gradient cases, suggesting they are not primarily caused by the pressure gradient.

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Tobias Gibis

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