Oblique shock

About: Oblique shock is a research topic. Over the lifetime, 6551 publications have been published within this topic receiving 119823 citations.

Identification of super- and subcritical regions in shocks driven by coronal mass ejections

Abstract: In this work, we focus on the analysis of a coronal mass ejection (CME) driven shock observed by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment. We show that white-light coronagraphic images can be employed to estimate the compression ratio X = {rho}{sub d}/{rho}{sub u} all along the front of CME-driven shocks. X increases from the shock flanks (where X {approx_equal} 1.2) to the shock center (where X {approx_equal} 3.0 is maximum). From the estimated X values, we infer the Alfven Mach number for the general case of an oblique shock. It turns out that only a small region around the shock center is supercritical at earlier times, while higher up in the corona the whole shock becomes subcritical. This suggests that CME-driven shocks could be efficient particle accelerators at the initiation phases of the event, while at later times they progressively loose energy, also losing their capability to accelerate high-energy particles. This result has important implications on the localization of particle acceleration sites and in the context of predictive space weather studies.

Pressure distribution and energy flow in the focal region of two different electromagnetic shock wave sources.

Abstract: In extracorporeal shock wave lithotripsy there is still a lack of knowledge about the basic physical terms that are essential for a scientific comparison of lithotripters with different technologies. The main goal of this article is to introduce the relation between pressure distribution, acoustic energy flow and intensity. The procedure of how these data can be achieved quantitatively is described. Technical data of two different commercially available electromagnetic shock wave sources are presented. The results show that acoustic energy flow and intensity depend on the variation of the shock wave parameters and the focal area.

Shock waves and drag in the numerical calculation of isentropic transonic flow

Abstract: Properties of the shock relations for steady, irrotational, transonic flow are discussed and compared for the full and approximate governing potential in common use. Results from numerical experiments are presented to show that the use of proper finite difference schemes provide realistic solutions and do not introduce spurious shock waves. Analysis also shows that realistic drags can be computed from shock waves that occur in isentropic flow. In analogy to the Oswatitsch drag equation, which relates the drag to entropy production in shock waves, a formula is derived for isentropic flow that relates drag to the momentum gain through an isentropic shock. A more accurate formula for drag, based on entropy production, is also derived, and examples of wave drag evaluation based on these formulas are given and comparisons are made with experimental results.

Normal Shock/Boundary-Layer Interaction Control Using Aeroelastic Mesoflaps

Abstract: A normal shock/boundary-layer interaction control technique termed mesoflaps for aeroelastic recirculating transpiration has been investigated in a planar Mach 1.37 wind tunnel. In this flow-control system, an array of small flaps is mounted over a cavity; the flaps deflect aeroelastically under the pressure loads imposed by the normal shock, thereby allowing recirculation from downstream of the shock to upstream. Qualitative analysis of the mesoflap control was investigated with spark shadowgraph visualizations and oil-streak surface-flow visualizations, whereas quantitative analysis was achieved by measuring surface pressure distributions and boundary-layer velocity profiles. Nine different mesoflap arrays were investigated, in addition to the solid-wall reference case. It was found that flap thickness and, therefore, transpiration rate, had a demonstrable effect on static and total pressure recovery, in addition to boundary-layer integral properties. Although some of the arrays did not provide a performance benefit, one particular flap array was found to have significantly higher static and total pressure recoveries than the solid-wall reference case, while simultaneously demonstrating a reduction in boundary-layer momentum thickness and unchanged displacement thickness.

Behaviour of a shock train under the influence of boundary-layer suction by a normal slot

Abstract: The interaction of a shock train with a normal suction slot is presented. It was found that when the pressure in the suction slot is smaller or equal to the static pressure of the incoming supersonic flow, the pressure gradient across the primary shock is sufficient to push some part of the near wall boundary layer through the suction slot. Due to the suction stabilized primary shock foot, the back pressure of the shock train can be increased until the shock train gradually changes into a single normal shock. During the experiments, the total pressure and therewith the Reynolds number of the flow were varied. The structure and pressure recovery within the shock train is analysed by means of Schlieren images and wall pressure measurements. Because the boundary layer is most important for the formation of a shock train, it has been measured by a Pitot probe. Additionally, computational fluid dynamics is used to investigate the shock boundary-layer interaction. Based on the experimental and numerical results, a simplified flow model is derived which explains the phenomenology of the transition of a shock train into a single shock and derives distinct criteria to maintain a suction enhanced normal shock. This flow model also yields the required suction mass flow in order to obtain a single normal shock in a viscous nozzle flow. Furthermore, it allows computation of the total pressure losses across a normal shock under the influence of boundary-layer suction.