Two-dimensional direct numerical simulations are used to study the impact of deep gaps on laminar–turbulent transition in compressible boundary-layer flow. For these, the gap depth-to-width ratio is always larger than five. They are located on a flat plate without pressure gradient. A steady base flow is used with a Mach number of 0.6, free-stream temperature of 288 K, and free-stream pressure of 1 bar. Subsequently, Tollmien–Schlichting waves are introduced by suction and blowing at the wall, and their growth over the gap is evaluated by N factors. The influence of the gap on laminar–turbulent transition is quantified by the difference ΔN compared with the N factor obtained for a flat plate without gap. A periodic influence of the gap depth on ΔN is observed. In the direct numerical simulations, acoustic waves enter the gap and form a standing wave due to reflections, similar as occurring in organ pipes. The feedback of the standing wave on the boundary-layer flow above is essential for the observed ΔN variations. In a second case, the influence of a specific gap placed in front of a forward-facing step is studied as well. Here, a reduction of the N factor and hence a delay of transition, relative to the flow with step alone, are reached due to the presence of the gap.
Impact of Deep Gaps on Laminar–Turbulent Transition in Compressible Boundary-Layer Flow
AIAA journal ; 54 , 1
2016
Article (Journal)
English
Compressible laminar boundary-layer flow
NTRS | 1978
|Laminar-turbulent transition in boundary layer
Engineering Index Backfile | 1951
|Three-dimensional compressible laminar boundary-layer flow
TIBKAT | 1951
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