Colour surface flow visualisation of interfering slender bodies at Mach 3

A study to understand the flow physics produced by two slender bodies in close proximity in high-speed airflow was undertaken. The interference flow field generated by the bodies is dominated by shock and expansion waves, and of particular significance is the complex interaction of the bow-shock wave emanating from the disturbance generator, striking the surface of the disturbance receiver. To gain insight into the shock wave-body interaction, the traditional surface oil flow visualisation technique was extended to include colour, which assists the eye in tracking the streak lines back to their separation and reattachment regions. In addition, the fine particle sizes of the colour pigment produced crisper and more definitive separation lines over the body, in comparison to the traditional monochrome pigments, such as lamp-black or titanium-dioxide. Subsequently, the dried surface pattern was lifted off the body using matte-acetate tape, digitised and then straightened using datum markings along the sting. This allowed the shock impingement location and shock diffraction path over the body to be established quantitatively, which was used to validate numerical simulations. The experimental and computational data showed good agreement for all configurations considered, providing complementary information about the disturbance-induced effects generated in the interference flow field, and provided detailed insight into the near-surface flow topology produced by the shock wave-slender body interaction.