Shock transmission and its interactions with exhaust gases from an open detonation tube

When a detonation exits a confined tube into open air, the transmitted shock weakens rapidly as the flow expands, interacts with the ground, and couples to the hot exhaust plume. We simulate this process using two-dimensional reactive Navier–Stokes calculations with a chemical–diffusive model, resolving the internal detonation dynamics and the external field in a coupled tube–atmosphere domain with a ground surface. At the tube exit, an acoustic-impedance mismatch generates a transmitted shock and an upstream-propagating rarefaction train that reduce the driving pressure and promote separation of the shock from the expanding product jet. Outside the tube, baroclinic torque deposits vorticity along the curved shock–plume interface, followed by shear-layer roll-up as Kelvin–Helmholtz instability becomes dominant. Ground impingement produces a reflected shock that reshocks the lower flow, further distorting the transmitted wave and enhancing mixing. Centerline pressure histories exhibit a blast-like signature—an initial overpressure peak, exponential decay, and a negative phase—before relaxing to an acoustic disturbance. A parametric study shows that tube diameter and ground clearance primarily control the transmitted overpressure, whereas the reactive mixture (hydrogen–air vs ethylene–air) has only a modest influence once diffraction into the far field occurs.