Plane blast wave interaction with an elongated straight and inclined heat-generated inhomogeneity

Abstract

The unstable evolution of an elongated elliptically shaped inhomogeneity that is embedded in ambient air and aligned both normal and at an angle to an incident plane blast wave of impact Mach number 2.15 is investigated both experimentally and numerically. The elliptic inhomogeneities and the blast waves are generated using gas heating and exploding wire technique and their interaction is captured optically using shadowgraph method. While two symmetric counter-rotating vortices due to Richtmyer–Meshkov instability are observed for the straight interaction, the formation of a train of vortices similar to Kelvin–Helmholtz instability, introducing asymmetry into the flow field, are observed for an inclined interaction. During the early phase of the interaction process in the straight case, the growth of the counter-rotating vortices (based on the sequence of images obtained from the high-speed camera) and circulation (calculated with the aid of numerical data) are found to be linear in both space and time. Moreover, the normalized circulation is independent of the inhomogeneity density and the ellipse thickness, enabling the formulation of a unique linear fit equation. Conversely, the circulation for an inclined case follows a quadratic function, with each vortex in the train estimated to move with a different velocity directly related to its size at that instant. Two factors influencing the quadratic nature are identified: the reduction in strength of the transmitted shock thereby generating vortices with reduced vorticity, along with the gradual loss of vorticity of the earlier-generated vortices.

On using converging shock waves for pressure amplification in shock tubes

“…The facility is a compact, 2D blast wave generator with visual access constructed within the group recently. The details on its construction, operation and the visualization systems can be found in [24], as it is beyond the scope of this work. Figure 5 shows the shadowgraph images captured in the facility.…”

“…The basic idea of the scheme is to split the flux vector using artificial wave speeds that adjust the direction of wave propagation [27]. The numerical scheme has been tried, tested and validated on a variety of problems, with it consistently demonstrating good accuracy [22,[28][29][30][31]. The axisymmetric version of the code has been specifically utilized to study spherical implosion shocks [22] where it was validated against experimental data.…”

Hydrodynamic instabilities of two successive slow/fast interfaces induced by a weak shock

“…Schlieren images of the shock-induced two successive slow/fast interface evolutions acquired from experiments and simulations are shown in figure 7( a – f ). The magnitude of the density gradient () field in the simulations is calculated as (Quirk & Karni 1996; Sembian, Liverts & Apazidis 2018) Taking the L50-IP case as an example, the deformations of the two interfaces are discussed in detail. After the IS impacts the perturbed II, the rippled RW is reflected upstream, and the rippled TS moves towards the II (121 s).…”

Hydrodynamic instabilities of a dual-mode air–SF6 interface induced by a cylindrically convergent shock

“…The magnitude of the density-gradient field in the simulation is calculated as (Quirk & Karni 1996; Sembian, Liverts & Apazidis 2018) The numerical results are shown in the bottom half of the images in figure 3. It can be observed that both waves and interfacial morphologies in simulations qualitatively agree well with the experimental results.…”

“…The magnitude of the density-gradient field in the simulation is calculated as (Quirk & Karni 1996;Sembian, Liverts & Apazidis 2018)…”