Interactions among baroclinically-generated vortex rings in building up an acting spike to a bow shock layer

Vortex rings with a constant circulation are repetitively generated by depositing laser pulse energies ahead of a bow shock wave over a 20-mm diameter, flat-head cylinder in Mach 1.94 flow. Each vortex ring is formed after baroclinic interaction between a laser-heated gas and the bow shock wave. With increasing the pulse repetition frequency, f0, mutual interactions among the vortex rings become stronger; alternate pitching motions at f0=10–20 kHz and “slip-through” motions at f0=30 kHz appear. Beyond that, a quasisteady-state acting spike which decreases the stagnation pressure is built up.