Main Shock Wave Research Articles

Direct numerical simulation of turbulence amplification in a strong shock-wave/turbulent boundary layer interaction

In this study, the turbulence amplification mechanism within the strong shock-wave/turbulent boundary layer interaction is investigated using direct numerical simulation (DNS) over a 24° compression ramp with Mach 2.9 flow. A new in-house solver based on the compact finite difference scheme is introduced, and its accuracy is validated by comparing the flow statistics with existing DNS and experimental data. Within the DNS findings, two distinct turbulence kinetic energy (TKE) hotspots are identified. In contrast to previous studies, this study sheds light on shocklets, characterized by mid-frequency features, as a key factor contributing to the second TKE amplification, which occurs near the reattachment point. Streamline coordinate analysis reveals that shear effects dominate TKE production over the flow deceleration effect in the shock-wave/turbulent boundary layer interaction. The shear effect induced by the rolling up of the boundary layer initiates the first TKE amplification near the wall region in proximity to the separation point, followed by flow deceleration due to the main shock wave contributing to TKE generation. The initial detachment of the shear layer enhances the shear contribution. While TKE decreases above the separation bubble due to the positive mean velocity gradient, TKE amplifies again due to the flow deceleration caused by the secondary shock wave. In addition, the intermittently spawning shocklets above the bulge structures enhance the shear effect on the TKE production. Moreover, the generated TKE subsequently transfers to the local pressure minimum line, created by the bulges effect, thereby establishing a spatially converged maximum TKE line.

Amplification of turbulent kinetic energy and temperature fluctuation in a hypersonic turbulent boundary layer over a compression ramp

In this paper, direct numerical simulations in a Mach 6.0 hypersonic turbulent boundary layer over a 30 ° compression ramp are performed. The influence of shock wave/boundary layer interactions on the amplification of turbulent kinetic energy (TKE) and temperature fluctuation (TF) is explored, to provide an insight into the physical mechanism. In the initial part of the interaction region before the detachment of the shear layer, the amplification of the TKE and TF is found, via a frequency spectrum analysis, to be closely related to the low-frequency unsteadiness of the shock wave. Once the free shear layer is established, the shear component of the TKE production defined in the shear layer coordinate appears to act as the main contributor for the TKE amplification, owing to the mixing layer turbulence and the resultant Kelvin–Helmholtz instability. This is consistent with the result from the spectrum analysis that the TKE and TF amplification and their streamwise evolution are dominated by the spectral energy in the median-frequency range, arising from the mixing layer turbulence. As the flow moves downstream along the shock wave, the high-frequency spectral energy content of TF shows a decreasing trend, while the low-frequency spectral energy tends to increase gradually, implying that the shock wave low-frequency unsteadiness exists not only in the initial stage of the interaction region but also around the main shock wave. Under the combined influence of the shock wave intensity and interaction intensity, the median-frequency content appears to weaken first and then tends to increase before decreasing again. The variation amplitude appears to be small and generally dominates the distribution of the TF intensity.

Experimental investigation of shock response to an insensitive explosive under double-shock wave

A new integrated velocimetry system that includes terahertz-wave-based Doppler velocimetry (TDV) and a multiplied electromagnetic particle velocity gauge (EMV) is demonstrated by measuring the particle velocity history and the corresponding shock-to-detonation transition (SDT) distance in double-shock experiments of insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-2. This system overcomes the defects in resolution, testing distance, particle velocity measurement history, and shock-wave capture when TDV or EMV are used separately in double-shock experiments. The effectiveness of the integrated velocimetry system is verified via double-shock experiments, and the deviation of shock wave displacement is less than 6%. Furthermore, the desensitization effects of TATB-2 are determined by comparing the initiation behavior for the double-shock and sustained-pulse experiments. Results indicate that the longer the time of the unreactive preshock wave, the stronger the desensitization effects. Further, the reactive main shock wave in the double-shock experiment can weaken the desensitization effects of the double-shock wave.

Deflector shape impact on aero-acoustic noise generation and propagation

The vibroacoustic loading generated during the launch of space vehicles can cause the failure of electronic and mechanical components. Therefore, the prediction and mitigation of these vibroacoustic levels are crucial to improve the reliability of launchers and payload comfort. Because a properly designed flame deflector has the power to significantly reduce the acoustic pressure level, the aeroacoustics characteristics of diverse types of flame deflectors must be understood. Three different deflector geometries have been analysed: a wedge-type deflector, which is currently used on the VEGA rocket launch pad, a 30-degree inclined deflector, since new studies highlight its noise reduction capacity, and a flat deflector, since the impact on a flat plate is the simplest case of reflection. The sound generation and propagation in the launch platform full domain for each case were studied using dedicated computational fluid dynamics in BSC MareNostrum. To assess noise generation, the main shock waves were identified, and the evolution of the generated sound pressure was assessed. Moreover, the sound pressure levels at the fairing surface have been studied. Further research is focused right now on the use of an efficient solver running on graphics processing units that is capable of computing large-scale turbulence.

Finite-Wing and Sweep Effects on Transonic Buffet Behavior

This study experimentally investigates the effects of the sweep angle and finite wing on transonic buffet, studying two-dimensional (2-D) and three-dimensional wing configurations. Background-oriented schlieren and stereographic particle image velocimetry (PIV) have been used as measurement techniques, performing experiments on an OAT15A airfoil (clamped to both the side windows of the wind tunnel), an unswept wing, and two swept wings with sweep angles of 15 and 30 deg, respectively. The three wings are also based on the OAT15A airfoil and are clamped at the wind tunnel only at their root (free wingtip). All wings have been tested at a constant normal Mach number () with respect to the leading edge. The results show that the buffet oscillations are much stronger for the airfoil than for the three finite-span wings. A large difference in the buffet behavior can be noticed between the airfoil and the unswept wing, as is also seen in oil flow visualizations. This difference is particularly evident in correspondence of the more outboard spanwise locations, suggesting that for the unswept wing, an important role could be played by finite-wing effects: notably, the tip vortex. A spectral analysis has shown that for the swept wings, the classical 2-D buffet peak (occurring at for the present conditions) is substantially attenuated, whereas additional contributions in the range of 450–850 Hz appear. The PIV results showed, for the 30 deg sweep angle wing, a periodical occurrence of a secondary supersonic area downstream of the main shock wave structure, which is absent for the other wing models. The stereographic PIV configuration allowed the reconstruction of the spanwise-oriented velocity component, obtaining, in proximity of the trailing-edge, values of the spanwise velocity component () which are in agreement with the spanwise convection of buffet cells observed in the literature in this region.

URANS Analysis of a Launch Vehicle Aero-Acoustic Environment

Predicting and mitigating acoustic levels become critical because of the harsh acoustic environment during space vehicle lift-off. This paper aimed to study the aero-acoustic environment during a rocket lift-off. The sound propagation within a launch event was studied using dedicated computational fluid dynamics (CFD). The resolution of all the phenomena that occur is unfeasible. We discuss the turbulence simplification and propose a feasible simulation through an unsteady Reynolds-averaged Navier–Stokes (URANS) model. The results were validated with experimental data showing a good correlation near the fairing surface and an improvable accuracy in the far field. To assess noise generation, the main shock waves were identified, and the evolution of the generated sound pressure was assessed. Moreover, vertical directivity was revealed by data analysis of the pressure field surrounding the fairing.

Керування вектором тяги ракетного двигуна вдувом продуктів детонації в надзвукову частину сопла

For solving non-traditional problems of rocket flight control, in particular, for the conditions of impact of a nuclear explosion, non-traditional approaches to the organization of the thrust vector control of a rocket engine are required. Various schemes of gas-dynamic thrust vector control systems that counteract impact actions on the rocket were studied. It was found that the dynamic characteristics of traditional gas-dynamic thrust vector control systems do not allow one to solve the problem of counteracting impact actions on the rocket. Appropriate dynamic characteristics can provide a perturbation of the supersonic flow by injecting into the nozzle the detonation products with the main shock wave propagating in the supersonic flow. This way to perturb the supersonic flow in a rocket engine nozzle is investigated in this paper. In order to identify the principles of producing control forces and provide a perturbation of the supersonic flow by injecting into the nozzle the detonation products with the main shock wave propagating in the supersonic flow, a computer simulation of the nozzle flow was performed. The nozzle of the 11D25 engine developed by Yuzhnoye State Design Office and used in the third stage of the Cyclone-3 launch vehicle was taken as a basis. The thrust vector control scheme relies on the use of the main fuel component detonation. The evolution of the detonation wave in the supersonic flow of the combustion chamber nozzle was simulated numerically. According to the nature of the perturbation propagation in the nozzle, the lateral force from the perturbation has an alternating character with the perturbation stabilization in sign and magnitude when approaching the critical nozzle section. The value of the relative lateral force is sufficient for counteracting large disturbing moments of short duration. Thus, the force factors that can be used to control the rocket engine thrust vector are identified. Further research should focus on finding the optimal location of the detonation product injection in order to prevent mutual compensation of force factors.

Material mixing in shock-induced pseudotachylites, Vredefort impact structure, South Africa

Impact-generated pseudotachylites (PTs) have been extensively studied in the Vredefort Impact Structure, South Africa, and have been shown to correspond chemically and isotopically to their host rocks. Such melts are frequently described as forming strictly in situ with lithic clasts derived from the immediate wall rocks. Mixed compositions are rare, where PTs are observed directly along a lithological contact. In this study, we document the presence of vast numbers of granitic clasts within dolerite-hosted PT veins within the Vredefort impact structure. The groundmasses of dolerite-hosted PT veins have two distinct geochemical compositions: (1) mafic, and (2) intermediate. The two compositional melt phases have a sharp contact, indicating immiscibility and/or mingling. Shocked zircon and monazite within the granite clasts enclosed in a dolerite-hosted PT vein indicate shock deformation prior to clast transport into the dolerite. In monazite, we report a new shock microtwin geometry 180°/[104].The mechanisms by which granitic clasts were emplaced in the dolerite-hosted veins are complex. Previous experimental work has suggested that varying shock velocity in different lithologies may be responsible for material mixing. In addition, the thermal pulse accompanying the shock wave would have caused quartz in the granite to transform into volumetrically larger high-temperature polymorphs, significantly increasing the granite volume compared to the adjacent dolerite. Together with fluctuation of stresses (post-impact reverberations) after the passage of the main shock wave, this volume adjustment initiated brittle fracturing of the dolerite. A negative pressure gradient was generated within the dolerite that allowed granitic material to be injected into the dolerite-hosted melt veins.

Dynamical structure of the pulsating atmosphere of RR Lyrae

Context. RRab stars are large amplitude pulsating stars in which the pulsation wave is a progressive wave. Consequently, strong shocks, stratification effects, and phase lag may exist between the variations associated with line profiles formed in different parts of the atmosphere, including the shock wake. The pulsation is associated with a large extension of the expanding atmosphere, and strong infalling motions are expected. Aims. The objective of this study is to provide a general overview of the dynamical structure of the atmosphere occurring over a typical pulsation cycle. Methods. We report new high-resolution observations with high time resolution of Hα and sodium lines in the brightest RR Lyrae star of the sky: RR Lyr (HD 182989). A detailed analysis of line profile variations over the whole pulsation cycle is performed to understand the dynamical structure of the atmosphere. Results. The main shock wave appears when it exits from the photosphere at φ ≃ 0.89, i.e., when the main Hα emission is observed. Whereas the acceleration phase of the shock is not observed, a significant deceleration of the shock front velocity is clearly present. The radiative stage of the shock wave is short: 4% of the pulsation period (0.892 < φ < 0.929). A Mach number M > 10 is required to get such a radiative shock. The sodium layer reaches its maximum expansion well before that of Hα (Δφ = 0.135). Thus, a rarefaction wave is induced between the Hα and sodium layers. A strong atmospheric compression occurring around φ = 0.36, which produces the third Hα emission, takes place in the highest part of the atmosphere. The region located lower in the atmosphere where the sodium line is formed is not involved. The amplification of gas turbulence seems mainly due to strong shock waves propagating in the atmosphere rather than to the global compression of the atmosphere caused by the pulsation. It has not yet been clearly established whether the microturbulence velocity increases or decreases with height in the atmosphere. Furthermore, it seems very probable that an interstellar component is visible within the sodium profile.

Ground effects on the hypervelocity jet flow and the stability of projectile

ABSTRACTThe significant influence of the ground on the hypervelocity jet flow as well as the stability of the projectile cannot be discarded due to the intensity and the wide influence range. The present study examines two three-dimensional simulation models, one with the ground effects included and the other without, based on FLUENT software, using the finite volume method (FVM). The simulation models couple the FVM model with a standard k-ε turbulence model and unstructured dynamic grid based on the Local Remeshing method. An intermediate ballistic model and the six-degrees-of-freedom model are also utilized. For the 300-caliber 1730 m/s countermass propelling gun, two different flow phenomena, with and without the ground effects, were examined. The simulation results indicate that the effect of the ground surface on the jet flow and the projectile emerged gradually at 1.5 ms. The hypervelocity muzzle shock wave was reflected off the ground, creating a new shock-wave phenomenon in the opposite direction. The wave system interacted with the muzzle shock wave so that the pressure in the lower half of the domain was significantly higher than that in the upper half. This phenomenon produced a complete shock-wave surface. Shock waves at the ground produced a vortex, which gradually expanded and developed. The wavefront, which was formed by the ground reflection, led to a new wavefront, producing vortices at the wavefront and propagated towards the front and rear of the main shock wave. The hypervelocity jet flow twisted and generated a more complex wave system. The distorted gas jet caused the projectile to be disturbed, and the lift and torque were influenced so that the parameters such as the angular velocity of the rotation were changed.

Influence of slit sizes on the interaction structure of supersonic turbulent air flow with a multi-component injection jet in a channel

The supersonic air flow in a flat channel with transverse injection of a turbulent hydrogen jet through a slit in the bottom wall is numerically simulated. The solution of the initial Favre-averaged Navier-Stokes equations closed by the k-ω turbulence model is performed using an algorithm built on the basis of the WENO scheme. The interaction of a shock-wave structure with boundary layers on the lower and upper walls under conditions of an internal turbulent flow is investigated, namely, the effect of the width of the jet slit is studied. It is found that, in addition to the known shock-wave structures arising from the interaction of the incident flow with the transverse jet and the interaction of the main shock wave with the boundary layers near the walls, there is an additional system of shock waves and separation of the flow on the bottom wall at some distance from the jet downwards flow. Comparison with experimental data showed satisfactory agreement. undefined undefined Звуковая функция ограничена 200 символами Настройки : История : Обратная связь : Donate Закрыть

Enhancement of refrigeration performance by energy transfer of shock wave

The objective of this paper is to enhance the refrigeration performance by energy transfer of shock wave. The matching of shock compression and expansion refrigeration is the key to research. Firstly, the efficiency of shock wave transfer energy is discussed. Then, a two dimensional numerical model of wave rotor refrigeration is established. And wave diagram is drawn by numerical calculation, which reveals the principle of refrigeration and the relationship between pressurization and refrigeration. Finally, an experimental platform was established and experiment work is carried out to obtain performance parameters. The results show that shock wave compression is close to isentropic compression. Using the shock wave, the expansion work of refrigeration can be efficiently recovered. Under the design condition, about 50% of pressure energy could be restored. There are three main shock waves in the channels. Only shock wave S1 can be exploited to enhance refrigeration and other shock waves should be avoided. There is an optimum value for the pressure of high temperature port, which observably affects the temperature drop of the novel refrigerator. Under the experimental condition, the performance curves of the refrigerator and temperature distribution in refrigerator are obtained.

Effects of liquid properties on the dynamics of under-liquid laser-induced shock process

We compared the shock processes induced when focusing a single laser pulse (1064 nm, FWHM = 13 ns) onto the surface of epoxy resin blocks immersed in glycerol, water, liquid paraffin, and silicone oils. A custom-designed time-resolved photoelasticity imaging technique was applied to observe the strength of stress wave induced inside the solid target and the propagation of shock waves in the liquid with time resolution of nanoseconds. We demonstrated that the shock impedance of the liquid caused a noticeable effect on the strength of laser-induced stress wave: Ablation in the liquid with a higher shock impedance resulted in a stronger stress. By using glycerol instead of water as the confining medium, the pulse energy required to induce a certain level of stress was reduced by about 20 %. The dynamical behaviors of the main shock wave and the reflected wave in inverted V-shape in each liquid are also discussed in details.

Interference of unidirectional shock waves

Subject of study. We consider interference of unidirectional shock waves or, as they are called, catching up shock waves. The scope of work is to give a classification of the shock-wave structures that arise in this type of interaction of shock waves, and the area of their existence. Intersection of unidirectional shock waves results in arising of a shock-wave structure at the intersection point, which contains the main shock wave, tangential discontinuity and one more reflected gas-dynamic discontinuity of unknown beforehand type. The problem of determining the type of reflected discontinuity is the main problem that one has to solve in the study of catching shock waves interference. Main results. The paper presents the pictures of shock-wave structures arising at the interaction of catching up shock waves. The areas with a regular and irregular unidirectional interaction of shocks are described. Characteristic shock-wave structures are of greatest interest, where reflected gas-dynamic discontinuity degenerates into discontinuous characteristics. Such structures have a number of extreme properties. We have found the areas of existence for such shock-wave structures. There are also areas in which the steady-state solution is not available. The latter has determined revival of interest for the theoretical study of the problem, because the facts of sudden shock-wave structure destruction inside the air intake of supersonic aircrafts at high Mach numbers have been discovered. Practical significance. The theory of interference for unidirectional shock waves and design procedure are usable in the design of supersonic air intakes. It is also relevant for application possibility investigation of catching up oblique shock waves to create overcompressed detonation in perspective detonation air-jet and rocket engines.

Plasma control of shock wave configuration in off-design mode of M = 2 inlet

The objective of this work was to study the steering effect of a weakly ionized plasma on a supersonic flow structure in a two-dimensional aerodynamic configuration with a three-shock compression ramp in an off-design operational mode. Experiments were performed in wind tunnel T-313 of ITAM SB RAS, with the model air inlet designed for operation at a flow of Mach number M = 2. The inlet was tested at M = 2, 2.5, and 3 and with Re = (25–36) × 106/m and an angle of attack AoA = 0°, 5°, and 8°. For the regulation of the inlet characteristics, a plasma generator with electrical power W pl = 2–10 kW was flush-mounted upstream of the compression ramp. A significant plasma effect on the shock configuration at the inlet and on the flow parameters after air compression is considered. It is shown that the main shock wave angle is controllable by means of the plasma power magnitude and, therefore, can be accurately adjusted to the cowl lip of an inlet with a fixed geometry. An additional plasma effect has been demonstrated through a notable increase in the pressure recovery coefficient in a flowpass extension behind the inlet because of an nearly isentropic pattern of flow compression with the plasma turned on. Numerical simulation brings out the details of 3D distribution of the flow structure and parameters throughout the model at thermal energy deposition in inlet near the compression surfaces. We conclude that the plasma-based technique may be a feasible method for expanding supersonic inlet operational limits.

Exploring remote earthquake triggering potential across EarthScopes' Transportable Array through frequency domain array visualization

AbstractTo better understand earthquake source processes involved in dynamically triggering remote aftershocks, we use data from the EarthScope Transportable Array (TA) that provide uniform station sampling, similar recording capabilities, large spatial coverage, and, in many cases, repeat sampling at each site. To avoid spurious detections, which are an inevitable part of automated time domain amplitude threshold detection methods, we develop a frequency domain earthquake detection algorithm that identifies coherent signal patterns through array visualization. This method is tractable for large data sets, ensures robust catalogs, and delivers higher resolution observations than what are available in current catalogs. We explore seismicity rate changes local to the TA stations following 18 global main shocks (M ≥ 7) that generate median peak dynamic stress amplitudes of 0.001–0.028 MPa across the array. From these main shocks, we find no evidence of prolific or widespread remote dynamic triggering in the continental U.S. within the main shock's wave train or following main shock stress transients within 2 days. However, limited evidence for rate increases exist in localized source regions. These results suggest that for these data, prolific, remote earthquake triggering is a rare phenomenon throughout a wide range of observable magnitudes. We further conclude that within the lower range of previously reported triggering thresholds, surface wave amplitude does not correlate well with observed cases of dynamic triggering. We propose that other characteristics of the triggering wavefield, in addition to specific conditions at the site, will drive the occurrence of triggering at these amplitudes.

Limited Dynamic Earthquake Triggering in the Socorro Magma Body Region, Rio Grande Rift, New Mexico

Abstract Dynamic earthquake triggering, the process through which stresses transmitted through the passage of seismic waves can trigger remote faults to fail, has been shown to be fairly common throughout the globe and especially in seismically active areas of high heat flow and geothermal activity. We explore the possibility of dynamic earthquake triggering around the Socorro magma body, a feature within the Rio Grande rift in New Mexico that exhibits high heat flow and heightened seismicity. Because the area fits the environment type in which triggering preferentially occurs, we examine 319 global mainshocks with M w ≥6.0 for the possibility of increased seismicity rates following the passage of the mainshock waves. We examine local event locations and origin times relative to mainshock phase arrivals for patterns distinguishing triggering mainshocks from nontriggering mainshocks. We find a small triggering response during the time period analyzed, unlike following the 2002 Denali fault earthquake (DFE). This small response corresponds to smaller peak dynamic stresses than are found in other triggering studies ( M w >7.0), at a regional to small teleseismic distance (

Emission lines and shock waves in RR Lyrae stars

Context. Emission lines observed in radially pulsating stars are thought to be produced by atoms de-exciting after being excited by a shock wave that is traveling into and then compressing, heating, and accelerating the atmospheric gas. Aims. With the help of recent observations, we examine the origin of all the different types of emission lines of hydrogen and helium that appear during a pulsation cycle. Methods. To analyze the physical origin of emission lines, we used the different models of atmospheric dynamics of RR Lyrae stars that have been calculated so far. Results. In contrast to a recent explanation, we propose that the redshifted emission component of Hα , which occurs near the pulsation phase 0.3, is produced by the main shock. In this case, the emission is the natural consequence of the large extension of the expanding atmosphere. Therefore, this (weak) emission should only be observed in RR Lyrae stars for which the main shock will propagate far enough from the photosphere. It appears as a P-Cygni type profile. We estimate the shock front velocity during the shock propagation in the atmosphere and show that it decreases by 40% when the Hα emitting-shock passes from the photospheric level to the upper atmosphere. The Hα P-Cygni profile observed in long-period Cepheids also seems to be caused by the main shock wave. Although to date He II has only been detected in some Blazhko stars, a comprehensive survey of RR Lyrae stars is necessary to confirm this trend, so we can say that the most intense shocks will only be observed in Blazhko stars. Conclusions. The development of a model of atmospheric pulsation that takes the effects of 2D and 3D convection into account, seems to be a necessary step to fully quantify the effects of shock waves on the atmospheric dynamics of radially pulsating stars.

Computational investigation of the mitigation of an underwater explosion

The protection effects of a mitigation layer in an underwater explosion are investigated here. The explosion shock loads on a mitigated structure are computed by a Mie–Gruneisen mixture model. Validation tests show that the model is efficient for the underwater explosion problem. Then underwater explosion problems with different mitigation layers are simulated here. In these simulations, special attention is paid on the second shock wave, which is induced by the reflection of the main shock wave. From the results, it is found that the shock impedance of the mitigation layer plays an important role. It determines not only the property of second shock loads, but also the occurrence of protection effects of the mitigation layer. After that the protection effects of layer thickness and explosive–structure distance are studied here. It is found that these factors influence the main shock slightly, but have significant influence on the second shock. In addition, the compressible structure can also be protected by the mitigation layer.

Experimental investigation on starting process of supersonic single-stage air ejector

This paper deals with experimental study of flow field of starting process in two-dimensional, single-stage supersonic ejector on different air total pressure. Schlieren pictures of flow field were taken, static pressure distributions on side wall were measured. The obtained results show that, on critical pressure, the starting main shock waves in ejector oscillated back and forth between the second throat and the middle section of the mixing chamber, it causes the pressure in the second half of the mixing chamber acutely fluctuated.When the working pressure of the active flow is higher than the critical starting pressure, ejector starts normally and the inner flow-field of the mixing chamber keeps stable and the shock waves in the second throat have a certain degree of oscillation. After ejector starts, the operating pressure of the active flow may be lower than the starting pressure.