Experimental investigation of the transition process and boundary layer separation on a hypersonic cone-cylinder-flare geometry
Clément Caillaud 2, Mathieu Lugrin ∗,1, Sébastien Esquieu 2
1DAAA, ONERA, Paris Saclay University, F-92190 Meudon – France
2CEA-CESTA, 15 Avenue des Sablières, Le Barp, France
Experiments are conducted in the ONERA R2Ch (see figure 1) hypersonic wind tunnel to study the transitional process and boundary layer separation on the well documented CCF12 configuration (see figure 2). Experimental runs will focus on Mach 6 and 7 conditions for a broad range of Reynolds numbers (from fully laminar to fully turbulent)
The current CCF geometry consists in a 5◦ sharp or blunt cone, followed by a cylindrical section which terminates to a flare with an angle of θf = 12◦ (CCF12).
The geometry can be divided into two primary regions: the cone section, which provides a canonical convectively unstable boundary layer that supports first and second mode waves, and the cylinder-flare section, which includes a separation bubble generated by the adverse pressure gradient caused by the shock-wave at the cylinder-flare junction.
In this second region, the separation bubble has been found to be globally unstable for flare angles θf ≥ 8◦ and Reynolds numbers above Re = 11.5 × 106. At this critical Reynolds number, convectively unstable modes such as first-mode and second mode waves can also exist along the recirculation bubble and/or the reattachment point.
For cases where either the convective, the global instabilities or a combination of both, lead to transition, the non-linear terms will induce a strong modification of the bubble.
The aim of the experimental campaign is to study the aforementioned physical mechanisms, the presented results will include :
- Exploitation of high-frequency wall pressure fluctuation measurements (PCB and Kulites)
- Exploitation of high-frequency Schlieren imaging