An investigation of Mach number effects on the interaction of a shock wave with a cylindrical bubble, is presented. We have conducted simulations with the Euler equations for various incident shock Mach numbers (MS) in the range of 1.22 ≤ MS ≤ 6, using high-resolution Godunov-type methods and an implicit solver. Our results are found in a very good agreement with previous investigations and further reveal additional gasdynamic features with increasing the Mach number. At higher Mach numbers larger deformations of the bubble occur and a secondary-reflected shock wave arises upstream of the bubble. Negative vorticity forms at all Mach numbers, but the "c-shaped" vortical structure appeared at MS = 1.22 gives its place to a circular-shaped structure at higher Mach numbers. The computations reveal that the (instantaneous) displacements of the upstream, downstream and jet interfaces are not significantly affected by the incident Mach number for values (approximately) greater than MS = 2.5. With increasing the incident Mach number, the speed of the jet (arising from the centre of the bubble during the interaction) also increases.
A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are discretized by the second order upwind differencing scheme, decoupling with the SIMPLE (semi-implicit method for pressure linked equations) algorithm and are solved using a finite volume approach. The fluid flow and heat transfer characteristics are presented for the Reynolds numbers based on the channel hydraulic diameter ranging from 10 4 to 4 × 10 4. The effects of rib shape and orientation on heat transfer and pressure drop in the channel are investigated for six different rib configurations. Rib arrays of 45˚ inclined and 45˚ V-shaped are mounted in inline and staggered arrangements on the lower and upper walls of the channel. In addition, the performance of these ribs is also compared with the 90˚ transverse ribs.
The study of non-stationary flows featuring shock waves is motivated by the need to understand the physics of shock wave phenomena, as well as by the variety of applications in which shock waves appear spanning from engineering to astrophysics. In the case of shock (blast) wave propagation in an enclosure the interest stems from explosion dynamics which arises from the very sudden release of chemical, nuclear, electrical or mechanical energy in a limited space.Even though past studies have investigated instabilities occurring when two fluids of different densities are impulsively accelerated into each other by a shock wave, known as Richtmyer-Meshkov (or impulsive Rayleigh-Taylor) instability (6,18) , the investigation of flow instabilities arising from the interaction of blast waves with a solid structure has received scarce attention. Flow instabilities have been experimentally detected in the case of cylindrical blast waves (7,14) . Burrows and Fryxell (1992) (5) have also shown that instabilities can occur in the mantles of nascent neutron stars implying that the standard spherically symmetric models of neutron star birth and supernova explosion may be inadequate. The above findings follow earlier analytical work (4) regarding the formation of convective ABSTRACT The paper presents an investigation of flow instabilities occurring in shock-wave propagation and interaction with the walls of an enclosure. The shock-wave propagation is studied in connection with perturbed and unperturbed cylindrical blasts, initially placed in the centre of the enclosure, as well as for three different blast intensities corresponding to Mach numbers M s = 2, 5 and 10. The instability is manifested by a symmetry-breaking of the flow even for the case of an initially perfectly-symmetric blast. It is shown that the symmetry-breaking initiates around the centre of the enclosure as a result of the interaction of the shock waves reflected from the walls, with the low-density region in the centre of the explosion. The instability leads to fast attenuation of the shock waves, especially for smaller initial blast intensities. The computations reveal that the vortical flow structures arising from the multiple shock reflections and flow instability are Mach number dependent. The existence of perturbations of large amplitude in the initial condition strengthens the instability and has significant effects on the instantaneous wall pressure distributions. The computational investigation has been performed using high-resolution Riemann solvers for the gas dynamic equations.
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