Shock-free compressible vortex rings impinging on a stationary surface: Effects of surface angle variation

An experimental study has been conducted on the impingement of compressible vortex rings on stationary, inclined, smooth surfaces. Four surface angle inclinations were evaluated: 90° (perpendicular to the flow longitudinal axis), 75°, 60°, and 45°. The flow was assumed axisymmetric for the 90° benchmark case. A single pressure ratio of ∼4 was used, corresponding to an experimental incident shock wave Mach number of ∼1.31, generating a shock-free compressible vortex ring.Results showed two main flow processes: the interaction of the reflected shock wave with the approaching vortical structure, and the impingement of the vortex ring on the surface. At surface inclination angles other than 90°, these processes are asymmetrical and the shape of the reflected shock is modified by the approaching vortex ring. The lower outer section of the reflected shock wave is initially diffracted by the lower core of the vortex ring, its central section is then captured by the central section of the torus, and ultimately the upper outer section is diffracted by the upper core. The vortex ring subsequently impinges on the surface with the lower core impacting first, undergoing an asymmetrical stretching and deformation.Flow field studies showed an initial decrease in velocity magnitude and vorticity field as the flow transitioned from a symmetrical to an asymmetrical impingement, possibly due to the uneven formation of the boundary layer. The velocity magnitude and vorticity field of the upper core subsequently increase again, as a result of the upwards deflection of the flow. Oppositely, the lower core is seen to dissipate.Surface pressure measurements confirmed the asymmetry in the flow development. As the surface angle is varied, the pressure at the central measurement location is seen to decrease as the position of the stagnation point is altered. An interesting feature within the surface measurements is a strong lateral acceleration due to the formation of vortex lines which roll around the main vortex core.

► The interaction of the reflected shock wave generates an asymmetrical toroidal shock wave.
► The dissipation process of the core impinging first is increased with an increase in surface angle.
► There exists a variation in the velocity magnitude between the two vortex rings’ cores.
► Circular vortex lines which asymmetrically wrap around the impinging vortex ring.