Pseudo Shock Research Articles

Material Point Method Simulation of the Equation of State of Polymer-Bonded Explosive under Impact Loading at Mesoscale

Mesoscale simulation using the material point method (MPM) was conducted to study the pressure–volume (PV) variations of Octahydro-1,3,5,7-Tetranitro-1,2,3,5-Tetrazocine (HMX)/Estane polymer-bonded explosive (PBX) under impact loading. The PV isotherms and Hugoniot data were calculated for the different porosities and binder volume fractions. The PV isotherms were used to determine the parameters for the Birch– Murnaghan equation of state (EOS) for the PBX. From the EOS, the isothermal bulk modulus (K0) and its pressure derivative (K′0) were calculated. Additionally, the pseudo particle velocity and pseudo shock velocity variations were used to obtain the bulk wave speed c and dimensionless coefficient s for the Mie–Grüneisen EOS. The simulations provide an alternative approach for determining an EOS that is consistent with experimental observations.

Numerical investigation on the flow structures of the multi-strut mixing enhancement ejector

A new type of multiple jets ejector called the multi-strut mixing-enhancement ejector (MSE) has been developed in previous studies. The excellent suction and supercharging abilities of this ejector have been demonstrated through a series of cold flow tests. However, the current knowledge on MSE is limited. Numerical investigations on MSE have not been conducted in previous studies. Therefore, the present study aims to conduct a series of numerical investigation on the MSE to analyse the transform regularities of the flow structures at various secondary flow conditions and explore the evolution processes of multiple 2D jet interactions in a confined space. Results show that the flow structures of the MSE are extremely complicated and different from the traditional single jet supersonic ejector. When the secondary flow is zero, the collisions of multiple supersonic primary flows generate multiple abreast oblique shocks, and the intersections and reflections of these oblique shock waves form a shock diamond matrix in the mixer and convergent section. In addition, a novel head-shape pseudo shock is observed in the secondary throat due to the coupling interactions of multiple oblique and adverse pressure gradients, which contain three parallel X-type shocks and an extremely intricate ‘butterfly-type’ shock behind. Under various secondary flow mass rate conditions, the secondary flows limit the expansions of the primary flows in the supersonic diffuser, thereby decreasing the number and intensity of oblique shocks in the mixer and convergent section, followed by the changes in the head shape of the pseudo shock in the secondary throat. Besides, the evolution processes of multiple 2D jets interactions demonstrate a complicated 3D effect. The wave loss, friction loss and mixing loss are the main factors that affect the evolution processes of multiple jets in the mixer and convergent section. The waves cause the jets to expand and compress along the flow direction, the friction loss results in vertical separation at the interface between the primary jets and the walls, and the mixing of flows causes the horizontal recess of the primary jets. These factors also have different effects on the jet’s evolution under various secondary flow conditions. The shock and friction losses are the main factors that affect the jet’s evolution when ER is small (ER ≤ 0.037). However, with the increase in ER, the effect of both losses weakens, and mixing loss becomes the dominant factor.

Large eddy simulation of pseudo shock structure in a convergent–long divergent duct

In this paper, the Pseudo shock structure in a convergent–long divergent duct is investigated using large eddy simulation on the basis of Smagorinsky–Lilly,​ Wall-Adapting Local Eddy-Viscosity and Algebraic Wall-Modeled LES subgrid models. The first objective of the study is to apply different subgrid models to predict the structure of Lambda form shocks system, while the ultimate aim is to obtain further control of the shock behavior. To achieve these goals, the dynamic grid adaption and hybrid initialization techniques are applied under the 3D investigation to reduce numerical errors and computational costs. The results are compared to the existing experimental data and it is found that the WMLES subgrid model results in more accurate predictions when compared to the other subgrid models. Subsequently, the influences of the divergent section length with the constant ratio of the outlet to throat area and, the effects of discontinuity of the wall temperature on the flow physics are investigated. The results indicate that the structure of compressible flow in the duct is affected by varying these parameters. This is then further discussed to provide a deeper physical understanding of the mechanism of Pseudo shock motion.

Thermal Effects of Liquid/Supercritical Carbon Dioxide Arising From Fluid Expansion in Fracturing

Summary Liquid/supercritical carbon dioxide (L/SC-CO2) fracturing is an emerging technology for shale gas development because it can effectively overcome problems related to clay swelling and water scarcity. Recent applications show that L/SC-CO2 fracturing can induce variations in temperature. Understanding of this phenomenon is rudimentary and needs to be carefully addressed to improve the understanding of CO2 thermodynamic behavior, and thus helps to optimize CO2 fracturing in the field. In this paper, we develop a numerical model to assess the impact of thermal effect on fracture initiation during CO2 fracturing. The model couples fluid flow and heat transfer in the fracture, and is verified by a peer-reviewed solution and observation in laboratory experiments. The velocity, pressure, and temperature are calculated at various time to demonstrate the thermodynamic behavior during fracture initiation. A pseudo shock wave is observed, associated with a compression wave and an expansion wave, which finally leads to an increase in temperature in the new fracture and a decrease in temperature in the initial fracture. The thermal stress is derived to investigate the difference between hydraulic fracturing and CO2 fracturing. The results show that thermal stress, resulting from CO2 fracturing initiation, is comparable to the rock strength, which will help induce microfractures, and thus promote the fracture complexity. The formation pressure after CO2 fracturing is also calculated to evaluate the pressure-buildup potential. This work highlights the importance of CO2 expansion during and after fracturing. It is one of the unique features that differs from hydraulic fracturing. For field-design recommendations, to enhance the thermal effect of CO2 fracturing, it is a good strategy to pump CO2 at high pressure and low temperature into the reservoirs with high Young's modulus, low Poisson's ratio, low permeability, and high geothermal temperature (or large depth). This paper does not address the dynamics of fracture propagation under the influence of thermal effect. Rather, it intends to demonstrate the potential of the thermal effect of CO2 fluid in assisting the fracture propagation, and the importance of incorporating the compressibility of CO2 into fracture modeling and operation design. Failing to account for this thermal effect might underestimate the fracture complexity and stimulated reservoir volume.

Performance of Circular to Non Circular Shape Scramjet Isolators

This paper details the influence of geometry variation such as shape transition of the isolator from its entry to exit on overall performance of scramjet isolators. The experiments are conducted to assess the performance of two isolator geometries of circle to pentagon and circle to hexagon. The pseudo shock length is obtained for the two cases by observing the sudden pressure rise in pressure plots taken along the wall. It is found that the shock train length is shorter for circular to pentagon duct compared with the other duct. Hence, this duct is preferable in order to prevent inlet non-start induced by the pressure rise in the combustion chamber.

CFD study on inlet unstart prediction of dual-mode scramjet

Dual-mode scramjet has become a viewpoint in the research fields of propulsion systems of aeronautics and astronautics. The key operating process of the dual-mode scramjet is from a started situation to an unstarted situation. The operating process composes of three phases. The first phase is when the pseudo shock wave is in the combustor. The second phase is when the pseudo shock wave is in the isolator. The last phase is when inlet unstart happens. In this study, two-dimensional numerical model has been made to replicate the process before inlet unstart. The location of pseudo shock wave has been determined in according to the location of the plug. As the throat area of the plug is decreasing, pseudo shock wave goes upstream. The prediction of inlet unstart has been focused in terms of the throat area ratio. The transition point of throat area ratio just before inlet unstart has been indicated. The transition points of throat area ratio in steady simulation and unsteady simulation are different. This is because the transition information needs time to spread from the plug to upstream location. The difference could be used for predicting the inlet unstart.

Mixing augmentation mechanism induced by the pseudo shock wave in transverse gaseous injection flow fields

The mixing process between the injectant and air is very crucial for the engineering implementation of the scramjet engine, and this is due to the very short resident time of fuel in supersonic flows. In the current study, the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model have been employed to investigate the transverse injection flow field with the pseudo shock wave induced by the high back pressure, and the freestream Mach number is 3.75. At the same time, the influence of the back pressure on the flow field properties has been evaluated as well. The obtained results show that the pseudo shock wave induced by the back pressure plays an important role in the mixing enhancement between the injectant and air. When the back pressure ratio is larger than 5.0, the mixing efficiency increases with the increase of the back pressure ratio. However, when the back pressure ratio is 3.0, the near-field mixing process has been improved, and accordingly its mixing efficiency in this region is larger than the benchmark. This implies that the intense combustion downstream of the injector can enhance the mixing process between the injectant and air, and the mixing and combustion process can be enhanced mutually. When the pseudo shock wave has been pushed upstream of the wall orifice, more injectant has been brought into the separation zone upstream of the injector, and this is beneficial for the mixing process between the injectant and air.

Mean and Turbulent Velocity Field for Jet Injected into Supersonic Flow with Pseudo-Shock Wave

The mean and turbulent velocity field of a transverse jet in a supersonic flow with a pseudo shock wave by stereoscopic particle image velocimetry was measured. Both the mainstream and the injectant were unheated air. The pseudo shock wave was generated and controlled by means of a flow plug driven by a stepping motor. To study the influence of the generation anddevelopment of the pseudo shockwave,measurements are taken for four different cases of the pseudo shock wave location, including one without a pseudo shock wave. Sequences of up to 750 image pairs for each measurement plane were acquired. From these data, the mean and turbulent characteristics of the flowfield were examined, such as mean velocity and vorticity, turbulence intensities, Reynolds stresses, and turbulence kinetic energy.Themeanvelocity andvorticity indicate that the pseudo shockwave gradually lowered the flow speed of the mainstream and increased the size of the counter-rotating vortex pair. The pseudo shock wave strongly disturbed the flowfield, inducing complicated three-dimensional distortions. The pseudo shock wave disturbed theflowfields near thewalls, and the turbulence kinetic energy in this areawas kept at a high level over long streamwise distances. The streamwise fluctuation intensity was about 4 times stronger than that of the vertical and lateral components, and the streamwise velocity components fluctuated even more greatly than the cross-sectional velocity components. The transverse injection moderately affected not only turbulence around the jet, but also the turbulent characteristics caused by the pseudo shock wave. The injection not only produced turbulence around the jet, but also suppressed the velocity fluctuation caused by the pseudo shock wave.

Effect of Local Flow Parameters on Skin-Friction Coefficient in Hypersonic Airbreathing Engines

Effects of Rex, Re , Tw=Taw, and Me on the local skin-friction coefficient (Cf ) in a hypersonic airbreathing combustor with various combustion modes were examined. Measurements were performed in the hypersonic airbreathing combustor with airflowMach number and unit Reynolds numbers at the entrance of combustor of 2.5 and 1:6 10 3:5 10 m , respectively. The ranges of total temperature, total pressure of airflow and fuel equivalence ratio were varied, i.e., 1000–2000 K, 1.0–1.8 MPa, and 0–0.4, respectively, to change Rex, Re , Tw=Taw, and Me. Direct skin-friction measurements were conducted. The state of flow was also surveyed in the streamwise locationwhere skin frictionwasmeasured to attain core-flowparameters, velocity profile, andmomentum thickness. When boundary-layer transition occurred due to combustion, evaluation ofCf by the vanDriestmethod using either by Rex or by Re was not effective. When there was separation with a long oblique shock train and a pseudo shock wave system in the precombustion region due to combustion, evaluation of Cf by the method using Rex was not effective because the origin of the turbulent boundary layer was changed in the downstream combustor.

실제기체 상태방정식을 적용한 열압축기 내부유동에 대한 수치해석

열압축기는 고압 증기를 이용하여 저압 증기를 중간압으로 이송하는 일종의 이젝터이다. 이젝터에 대한 기존의 수치해석 연구는 대부분 작동유체를 이상기체로 취급하고 있으나 상변화가 발생하는 경우 이상기체 거동에서 크게 벗어날 수 있다. 따라서 본 연구에서는 이상기체 상태방정식 대신 Redlich-Kwong 방정식을 적용하여 열압축기 내부 유동을 수치 해석하였고, realizable k-ε 모델과 SST k-ω 모델을 비교한 결과 SST k-ω 모델이 shock diamond 패턴과 박리 및 난류경계층을 잘 예측하는 것을 확인할 수 있었다. 또한 실제기체 상태방정식을 사용한 경우가 이상기체 상태방정식을 사용한 경우에 비해 상대적으로 디퓨저 입구 부분과 디퓨저 목부분에서 에너지 손실이 많은 것을 알 수 있었으며, 디퓨저 출구부분에서 shock train에 의한 압력상승은 상대적으로 적으나 pseudo shock에 의한 압력상승은 동일한 것으로 확인되었다.

プラズマジェットで支援された超音速燃焼場に対する 擬似衝撃波形成の影響に関する数値解析

Hydrogen combustion assisted by the oxygen plasma jet (PJ) in a Mach 1.9 supersonic internal flow was numerically investigated. Mixing and combustion behavior were compared between upstream and downstream fuel injections. For hydrogen injection downstream of the PJ, only weak combustion occurred even with a relatively high electric power input because of the rapid decrease in the ignitability of the PJ plume in the downstream. In contrast, intensive combustion easily occurred for hydrogen injection upstream of the PJ, with a relatively low electric power input, and a pseudo shock wave (PSW) was formed upstream of the fuel injector. The position of the PSW strongly affected the fuel mixing with the main airflow. The mixing and combustion of the fuel were rapidly enhanced by the formation of the leading shock wave of the PSW upstream of the fuel injector. Counter-rotating vortex pairs behind the fuel jet and PJ were enlarged by the PSW formation. The enlarged vortex structure behind the PJ was the main cause of the combustion enhancement.

Numerical schemes with high order of accuracy for the computation of shock waves

High order accurate scheme is highly desirable for flow computation with shocks. After analysis has been made for the reason of the generation of non-physical oscillations around the shock in numerical computations, a third-order, upwind biased, shock capturing scheme was proposed. Also, a new shock fitting method, called pseudo shock fitting method, was suggested, which in principle can be with any order of accuracy. Test cases for one dimensional flows show that the new method is very satisfactory.

Pseudo-Shock in Straight Duct with Porous Wall and Bypass System.

As the basic study of the passive control of the shock oscillation, steady pseudo shock in the rectangular ducts with the porous wall and the bypass system was investigated experimentally and numerically. The expriments were carried out in a blow-down supersonic wind tunnel at a free stream Mach number of 2.0. Numerical simulations were made with the 2-D compressible Navier Stokes code. In sloving the equations, 2nd-order accurate Harten-Yee's upwind TVD scheme and κ-ε turbulence model were used. It is shown that the boundary layer thickness under the first shock wave of the pseudo-shock is controlled by the passive control method without noticeable changes of the pseudo-shock strcuture. But the total pressure loss downstream of the pseudo-shock is reduced by this method. And the effects of some parameters influencing the passive control method are studied numerically.

Numerical Analysis of Passive Control of Pseudo-Shock.

Oscillation of the pseudo shock in the rectangular duct with the porous wall was investigated numerically. In the simulation, 2nd order accurate, Harten Yee's upwind TVD scheme was used for high resolution and numerical stability, and Chien's κ-e two equation model was used as the turbulence model. To simulate the effect of the blowing and suction on the porous wall, Darcy's law was used on the porous wall boundary. The boundary layer thickness under the first shock wave oscillates due to the shock oscillation, which changes the strength of the first shock wave changes, so that it suppresses the pressure fluctuation downstream of the first shock wave. The effects of some parameters of the passive control on the pseudo-shock oscillation were investigated.

Oscillation of Circular Pseudo-Shock in Radial and Spiral Supersonic Flow.

Oscillation of the circular pseudo shock in the radial and spiral supersonic flow between two parallel discs was investigated both numerically and experimentally. In the simulation, 2 nd-order accurate, Harten-Yee's upwind TVD scheme was used for high resolution and numerical stability, and Baldwin-Lomax's algebraic model was used as the turbulence model. To simulate shock wave oscillation, the back pressure was fluctuated at the outlet boundary. The X-type pseudo shock, which appears at higher Mach number, is more stable than the A type one, which appears at lower Mach number. Oscillation of mode 0 is predominant when the swirl is absent, while it becomes weaker and higher modes appear with the increase in the swirl.

Relation between Structure of Pseudo-Shock Waves and Discrete Frequency Noise. Analysis by Binary Image Method.

The effect of the structure and behavior of pseudo shock wave on jet noise containing discrete frequency has been studied by digital image processing. The shock waves were visualized by Schlieren method or a high-speed camera, and the motion of the over-compression regions was studied by the digital image processing. It was clarified that the behavior of over compression regions was periodical, and these periods were closely related to the generation of discrete frequency noise.

Behavior of Supersonic Radial Flow in a Disk MHD Generator. 1st Report. Measurements and Three-Dimensional Calculations for Non-Power Generation Modes.

Structures of supersonic radial flow in a disk MHD channel have been investigated by experiments and numerical calculations. Total pressure profiles across the channel height and static pressure distributions along the radial direction on both surfaces of a disk MHD channel were measured in the absence of the MHD effect. Furthermore, three-dimensional time-dependent calculations by means of the MUSCL-type TVD scheme were carried out. Measurements and calculations have shown that the working gas flow becomes asymmetric in the height direction due to some pseudo shock waves, and a large region of flow separation exists downstream of the channel.

Numerical simulation of reactive flow on the IBM ES/3090 Vector Multiprocessor

Prohibiting knock damage in internal combustion engines presents severe restrictions for engineers. Laboratory experiments are expensive or even impossible; nevertheless, numerical attempts that employ supercomputers have been rarely undertaken. The numerical approach described in this paper combines a recent shock-capturing finite-volume scheme for the compressible Navier Stokes equations, with semi-implicit treatment of the chemical source terms. An algorithm is described and validated by experiment that is optimaliy adapted to vector and parallel computersT. he algorithm has been implemented on the IBM Enterprise System/3090™ (ES/3090™) Vecto Multiprocessor. Performance measurements are discussed. The potential of the codeis illustrated by an example: formation of pseudos hock waves due to interaction of a shock wave with turbulent boundary layer flow.

Piecewise-one-dimensional models of supersonic combustion and pseudo shock in a duct

Piecewise-one-dimensional models of supersonic combustion and pseudo shock in a duct

AMNESIC AND AVERSIVE EFFECTS OF ELECTROCONVULSIVE SHOCK.

4 groups of 5 rats were pre-trained to run to a goalbox for food reinforcement and then were given differential goalbox treatment. Groups FS-PECS received foot-shock (FS) and pseudo (P) electroconvulsive shock (ECS) in goalbox and did not differ in trials to fear acquisition from a group receiving FS and ECS in goalbox. Group FS-ECS extinguished goalbox fear faster than Group FS-PECS demonstrating amnesic properties of ECS. Group ECS received only ECS in goalbox and was slower in fear acquisition and faster in fear extinction than either Groups FS-PECS or FS-ECS. Fear acquisition by Group ECS demonstrated aversive properties of ECS. A fourth group received only PECS in goalbox and showed no fear acquisition.