Unsteadiness in hypersonic leading-edge separation

Hypersonic leading-edge separation is studied toward understanding the varying shock-related unsteadiness with freestream Reynolds number ( $$1.66 \times 10^5 \le \text{Re}_D 5.85 10^5$$ ) in newly constructed hypersonic Ludwieg tunnel (HLT) at a design Mach of $$M_\infty =6.0$$ . An axisymmetric flat-face cylinder base body diameter $$D=35$$ mm fitted axial protrusions different fineness $$d/D=0.1,0.2,0.26,0.34$$ $$L/D=1.4$$ and slenderness $$L/D=0.7,1,1.4,1.9$$ $$d/D=0.2$$ ratio to induce wide range intensities. Qualitative quantitative assessments are made using schlieren imaging, planar laser Rayleigh scattering, unsteady pressure measurements. A well-known to-and-fro shock motion called pulsation flapping shock-shear layer oscillation observed as $$\text{Re}_D$$ changes. shorter protrusion length $$L/D=0.7$$ ), associated pulsation, produces loading four orders higher than cases longer lengths flapping. There exists critical $$L/D \ge 1.4$$ beyond which separated shear trips turbulence introduces fluctuations recirculation region increases. The intensity turbulent dampened by an order magnitude, provided reattachment angle shallow increasing $$d/D 0.34$$ also set geometrical parameters $$L/D=1, d/D=0.2$$ for modes (pulsation flapping) switch between themselves during successive runs, probably due upstream fluctuations. From modal analysis scattering images, first dominant that drive identified translatory flapping, sinuous large small-scale shedding.