Oblique shock

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

Shock-wave/boundary-layer interaction control using streamwise slots in transonic flows

Abstract: The effect of streamwise slots on the interaction of a normal shock wave with a turbulent boundary layer has been investigated experimentally at a Mach number of 1.29. The surface-pressure distribution for the controlled interaction was found to feature a distinct plateau. This was caused by a change in shock structure from a typical unseparated normal shock-wave/boundary-layer interaction to a large bifurcated lambda-type shock pattern, which led to a reduction of total pressure losses. A strong spanwise variation of boundary-layer properties was observed downstream of the slots, whereas the modified shock structure was relatively two-dimensional. Surface flow visualization confirmed that the slots introduced a region of recirculation into the boundary layer, similar to passive control with uniform surface ventilation. Surface flow visualization revealed the presence of a pair of counter-rotating vortices, confirmed by crossflow velocity measurements. Because of the reduction of total pressure losses, streamwise slots can reduce aircraft wave drag at transonic cruise while incurring only small viscous penalties. A similar control device can also be of use in supersonic intakes where total pressure losses limit engine performance

Numerical Simulations of Interaction between Stellar Wind and Interstellar Medium

Abstract: Hydrodynamic interaction between supersonic spherical wind emitted from an astronomical object and a uniform streaming flow is simulated numerically assuming the flow to be axisymmetric, adiabatic and inviscid. Examples of such a phenomenon are a comet in the solar wind, and the solar wind or a stellar wind in an interstellar medium. Three cases of the incident flow, i.e., subsonic, supersonic and hypersonic flow, are considered. Discontinuities in the flow, i.e., a bow shock, a contact surface, an inner shock, a Mach disc and a slip surface are identified. The contact surface and the slip surface are found to be Kelvin- Helmholtz unstable. Other instabilities occurring near the stagnation region and the inner shock are also found.

A mechanism for unsteady separation in over-expanded nozzle flow

Abstract: Shock wave induced separation in an over-expanded planar nozzle is studied through numerical simulation. These Large-Eddy Simulations (LES) model previous experiments which have shown unsteady motion of the shock wave in flows with similar geometries but offered little insight into the underlying mechanism. Unsteady separation in nozzle flow leads to “side loads” in the rocket engine which can adversely affect the stability of the rocket. A mechanism for the low-frequency shock motion is identified and explained using the LES data. This mechanism is analyzed for a series of over-expanded planar nozzles of various area ratios and nozzle pressure ratios. The effect of grid resolution and Reynolds number on the instability is discussed. A simple reduced order model for the unsteady shock behavior is used to further validate the proposed mechanism. This model is derived from first principles and uses data from the LES calculations to capture the effects of the turbulent boundary layer and shear layer.

Numerical simulations of shock-vortex interactions in supersonic jet screech

Abstract: Supersonic jet screech is a form of jet noise which adversely impacts both the environment and the life of aircraft structures. A basic understanding of the mechanisms which generate the screech tone and determine its amplitude is therefore important. In the present study we perform direct numerical simulations (DNS) of the interaction of an oblique shock with instability waves of a finite thickness supersonic shear layer. We thereby retain the basic elements of an isolated jet screech source. The simulations are carried out in two dimensions using a high order accurate spatial scheme with nonreflecting boundary conditions. The unsteady shock motion is resolved with the essentially non-oscillatory (ENO) discontinuity capturing scheme. The shear layer (M = 1.2, Re = 1000 based on initial vorticity thickness) is forced at the most unstable frequency such that the instability waves develop into fully formed vortices upstream of the shock. The interaction of the vortices with the shock causes streamwise oscillations in the shock near its tip. On the subsonic side of the shear layer, the acoustic wave is released as the shock tip deflects upstream through the braid region between vortices. This acoustic field is approximately cylindrical and its directivity is nearly uniform. The acoustic waveform is comprised of a sharp compression followed by a longer expansion. On the supersonic side of the shear layer, a complex wave field is observed. Cases in which the incident shock is replaced by a nearly isentropic compression wave produce qualitatively similar behavior. Acoustic pressure amplitude is found to Copyright ©1998 Ted A. Manning and Sanjiva K. Lele. Published by the American Institute of Aeronautics and Astronautics with permission. talso affiliated with the Department of Mechanical Engineering, Stanford University. scale with compression wave strength. Acoustic wave form is insensitive to compression wave amplitude and profile width for cases examined. This research is directed toward modeling the screech generation process.

Impact Angle Control of Interplanetary Shock Geoeffectiveness

Abstract: We use OpenGGCM global MHD simulations to study the nightside magnetospheric, magnetotail, and ionospheric responses to interplanetary (IP) fa st forward shocks. Three cases are presented in this study: two inclined oblique shocks, here after IOS-1 and IOS-2, where the latter has a Mach number twice stronger than the former. Both shocks have impact angles of 30$^o$ in relation to the Sun-Earth line. Lastly, we choose a frontal perpendicular shock, FPS, whose shock normal is along the Sun-Earth line, with the same Mach number as IOS-1. We find that, in the IOS-1 case, due to the north-south asymmetry, the magnetotail is deflected southward, leading to a mild compression. The geomagnetic activity observed in the nightside ionosphere is then weak. On the other hand, in the head-on case, the FPS compresses the magnetotail from both sides symmetrically. This compression triggers a substorm allowing a larger amount of stored energy in the magnetotail to be released to the nightside ionosphere, resulting in stronger geomagnetic activity. By comparing IOS-2 and FPS, we find that, despite the IOS-2 having a larger Mach number, the FPS leads to a larger geomagnetic response in the nightside ionosphere. As a result, we conclude that IP shocks with similar upstream conditions, such as magnetic field, speed, density, and Mach number, can have different geoeffectiveness, depending on their shock normal orientation.