Transient growth in diabatic boundary layers with fluids at supercritical pressure

Is transient growth critical for boundary-layer stability in fluids at supercritical pressure with their strong property variations across the pseudo-boiling line? This study on non-modal growth and its competition with modal growth under various heat-transfer scenarios reveals new insights into instability mechanisms in non-ideal fluids. We identify optimal growth in streamwise-modulated streaks as the fluid is heated beyond the pseudo-boiling line, with transcritical Mode II responsible. In this scenario, transition below the critical Reynolds number might prevail, mimicking the effect of an adverse pressure gradient in the ideal-gas regime.