Direct Numerical Simulations of K-Type Transition in a Flat-Plate Boundary Layer with Supercritical Fluids
Pietro Carlo Boldini (TU Delft - Energy Technology)
Benjamin Bugeat (University of Leicester)
Jurriaan W.R. Peeters (TU Delft - Energy Technology)
Markus Kloker (University of Stuttgart)
Rene Pecnik (TU Delft - Energy Technology)
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Abstract
We investigate the controlled K-type breakdown of a flat-plate boundary-layer with highly non-ideal supercritical fluid. Direct numerical simulations are performed at a Mach number of M∞=0.2 for one subcritical (liquid-like regime) temperature profile and one strongly-stratified transcritical (pseudo-boiling) temperature profile with slightly heated wall. In the subcritical case, the formation of aligned Λ-vortices is delayed compared to the reference ideal-gas case of Sayadi et al. (J. Fluid Mech., vol. 724, 2013, pp. 480–509), with steady longitudinal modes dominating the late-transitional stage. When the wall temperature exceeds the pseudo-critical temperature, streak secondary instabilities lead to the simultaneous development of additional hairpin vortices and near-wall streaky structures near the legs of the primary aligned Λ-vortices. Nonetheless, transition to turbulence is not violent and is significantly delayed compared to the subcritical regime.