Position Of Shock Wave Research Articles

Structure improvements and numerical simulation of supersonic separators

Abstract In the separation process of the conventional supersonic separator, the shockwave easily occurs in the nozzle expanding section before the cyclone, the low temperature section is short and the cooling effect is not satisfied, and the swirling flow occurs in subsonic conditions with poor efficiency. Based on this, structure improvement of the supersonic separator was carried out by reducing the nozzle expand angle and extending the length of expanding section, which helps to improve the refrigeration performance and separation efficiency of the separator. The flow characteristics of natural gas in the improved supersonic separator were obtained by three-dimensional numerical simulation. The results show that the shockwave occurs in the back of the cyclone and the improved supersonic separator can achieve a wider range of deep cooling. The shockwave moves back with the increase of the pressure loss ratio, when the pressure loss ratio increases to 70%, the position of shockwave moves back to the diffuser. The numerical results show that when the inlet pressure is 600 kPa and the pressure loss ratio is 47.5%, the improved supersonic separator has a good cooling and separation performance.

Temporal shock wave analysis produced by copper exploding wires in air at atmospheric pressure

In this work, experimental results concerning the temporal evolution of the shock wave radii generated by an exploding copper wire of fixed length are presented. The variables of the experience were the diameter dimension—from 50 to 500 μm—and the initial capacitor voltage—from 5 to 25 kV. The diagnostic device was a streak shadow image system synchronized with the experiment. The result is a parametric collection of data showing the shock wave position across the time depicting the different stages of the experience.

Prediction of shockwave location in supersonic nozzle separation using self-organizing map classification and artificial neural network modeling

Abstract One of the novel technologies for natural gas dehydration and natural gas dew-point conditioning is supersonic separation, which has remarkable features, including compact and maintenance-free design. Due to its complex design and the difficulty of experimental analysis, researchers tend to conduct numerical modeling for behavior investigation of the nozzle focusing on shockwave which is the main phenomena inside the nozzle. The present NN-model outperforms a selection of data and proposes an efficient NN-based algorithm for shockwave position estimation as the key nozzle geometry parameter. Data for the shockwave location was collected from a wide range of results from the literature and then a neural network based self-organizing map was adapted to the dataset. This created a classified dataset and the use of unreal weight and repeated experimental results from different research were avoided. A neural network was employed for modeling the shockwave location through the nozzle using a better quality dataset. Additionally, the one-dimensional inviscid theory was utilized in the recursive approach for comparison to the main proposed model. Simulation results presented in this research reveal the effectiveness of the proposed neural network technique for supersonic nozzle modeling and make it possible to determine the shockwave location from the nozzle pressure boundary conditions. The results showed that the supersonic nozzle separation have capability to be used in both low-pressure applications and high pressure ones. The dimensionless length for shockwave location is predicted in the range of 0.82–0.92 for the former and 0.72 to 0.95 for the later, depending on pressure recovery ratio.

Thermal effect on body temperature distribution of the critical flow Venturi nozzle

Abstract The expansion of the gas through a critical flow Venturi nozzle (CFVN) leads to a 50 °C temperature drop of the gas at the nozzle throat. The body of CFVN is also cooled, which produces several effects on the flow characteristics called thermal effects. Thus, there is an urgent necessary to investigate the dynamic temperature distribution of CFVN body. Firstly, experiments were conducted by a multipoint temperature acquisition system. The dynamic temperatures of 12 sampling points for each stainless steel CFVN were obtained. It is found that the dynamic response time of CFVN body temperature can be hundreds to thousands of seconds. The maximum body temperature drop of 16.5 °C was observed. Then some isotherm maps of CFVN body were obtained by the Kriging interpolation method. Finally, CFD simulations were carried out to explain the experimental results because the flow field of axisymmetric nozzle is difficult to be observed. The results revealed the position of shock wave is the main influence on body temperature distribution of CFVN. All the results can be used to further analyze the thermal effect of CFVN.

Computation of Supersonic Branching Flow with Aerosol Particle Separation

Supersonic branching flows are commonly found in industrial processes like the supersonic aerosol particle separation process and the supersonic inlet of combined aeroengines. In this research, we carry out a numerical study on the supersonic branching flow to reveal its features and its effects on aerosol particle separation. It is found that there are four flow regimes and a critical state in the supersonic branching flow in terms of the shock wave positions, which are determined by the backpressures of the two outlets. The gas flow rate ratio and the particle separation ratio are closely related to the flow regimes. There is a steady working zone where the gas flow rate ratio and the particle separation ratio maintain as constant as the two backpressures vary. In swirling flows, there is a drift of the critical state. In the range of particle sizes studied here, the particle motion is not sensitive to the variations of the particle size in the absence of swirl, but it is not the case for swirling flows. Finally, some features of the steady working zone are discussed. This work is a preliminary research into supersonic branching flow and provides a foundation for the design of relevant devices.

The exact Riemann solutions to the generalized Chaplygin gas equations with friction

Abstract The exact solutions to the Riemann problem for the one-dimensional generalized Chaplygin gas equations with a Coulomb-like friction term are constructed explicitly. The delta shock wave arises in the Riemann solutions provided that the initial data satisfy some certain conditions, although the system is strictly hyperbolic and the two characteristic fields are genuinely nonlinear. The position, strength and propagation speed of delta shock wave are obtained from the generalized Rankine–Hugoniot conditions. It is shown that the Coulomb-like friction term make waves (including rarefaction, shock and delta shock) bend into parabolic shapes for the Riemann solutions.

New Approaches to the Modeling and Calculation of Supercritical Expansion and Micro- and Nanoparticle Formation

Mathematical modeling of the rapid expansion of supercritical solution (nitrogen, nitrogen–water, propane–methanol–phenanthrene) and formation of particles was performed. A 2D model of expanded supercritical fluid jet and unique calculation algorithms were developed and applied for the calculations. The calculations allowed determination of jet boundaries, shape, and position of normal and barrel shock waves, condensation front, and particles size distribution. Parameter sensitivity analysis of the model helped to identify which parameters are of key importance for the production of particles with the required size and properties.

Numerical study of passive cavity control on high-pressure ratio single expansion ramp nozzle under over-expansion condition

Single expansion ramp nozzle (SERN) is widely used in the propulsion system of hypersonic vehicle; it has good effect on weight loss, and also can reduce the nozzle base drag and friction loss effectively. But under the condition of transonic region, the flow is severely over-expanded in the SERN, and the corresponding performance of SERN is sharply declined. In order to improve the SERN performance under over-expansion condition, the passive flow control technique application of passive cavity on SERN is investigated numerically by solving Reynolds average Navier–Stokes equations, and with standard two-equation k-ɛ turbulent models adopted. The influences of major geometric parameters of passive cavity on the flow field and performance of passive cavity SERN are deeply explored. Results show passive cavity structure has active influence on the performance of SERN under the over-expansion condition. The shock position moves upstream and separation region increases in the passive cavity SERN. The number of the shock train in the passive cavity SERN decreases. And the second peak of the pressure distribution is obviously higher than that it has for the baseline SERN. The performance of passive cavity SERN is related to the size of separation zone and its starting position, which is determined by the position of the first hole in the passive cavity. Percent of porosity has a dominant influence on the flow field of passive cavity SERN. The position of the first hole in the passive cavity changes with the variation of percent of porosity, and the corresponding starting position of the flow blowing out from the passive cavity is different, resulting in the different position and intensity of the anterior oblique compression shock wave. The axial thrust coefficient of passive cavity SERN decreases with the increase in percent of porosity accordingly. The flow structures of passive cavity SERN change little with variety of aperture and cavity depth when percent of porosity remains constant, the axial thrust coefficient of passive cavity SERN are almost tantamount at this case. Compared to the effect of percent of porosity, the influence of aperture and cavity depth on flow field are much smaller. The influence of aperture and cavity depth on the performance of the passive cavity SERN can be ignored in the design.

Shock wave bifurcation in channels with a bend

The study addresses 2D and 3D turbulent transonic flows in divergent channels with a bend, where a shock wave is formed upstream of the sonic line/surface arisen over an expansion corner of the lower wall. Solutions of the Reynolds-averaged Navier–Stokes equations are obtained with a finite-volume solver of the second-order accuracy on fine meshes. Numerical simulations reveal a considerable hysteresis in the shock wave position versus the supersonic Mach number given at the inlet. A dependence of the hysteresis on the slopes of walls and length of channel is analyzed. The bifurcation band persists when unsteady perturbations are imposed at the inlet. A physical interpretation of the shock wave instability is suggested.

The Riemann problem for the Chaplygin gas equations with a source term

The Riemann solutions for the one‐dimensional Chaplygin gas equations with a Coulomb‐like friction term are constructed explicitly. It is shown that the delta shock wave appears in the Riemann solutions in some certain situations. The generalized Rankine‐Hugoniot conditions of delta shock wave are established and the position, propagation speed and strength of delta shock wave are given, which enables us to see the influence of Coulomb‐like friction term on the Riemann solutions for the Chaplygin gas equations clearly. In addition, the relations connected with the area transportation are derived which include mass and momentum transportation.

Numerical study of shock wave interaction on transverse jets through multiport injector arrays in supersonic crossflow

Abstract In the present paper, the influence of shock wave position on sonic transverse hydrogen micro-jets in supersonic crossflow is investigated. This study focuses on mixing and shock interaction of the hydrogen jet in a Mach 4.0 crossflow with various jet conditions. Flow structure and fuel/air mixing mechanism were investigated numerically. Parametric studies were conducted on the position of the shock wave by using the Reynolds-averaged Navier–Stokes equations with Menter׳s Shear Stress Transport turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features dependent on the shock position. Results show a different flow structures than for a typical micro jet, with a location of the oblique shock on the flow of the hydrogen jet. According to the results, for oblique shock on the first jet, the mixing performance in high pressure ratio increases more than 20% in downstream. Furthermore, a significant reduction (up to 20%) occurs in the maximum concentration of the hydrogen jet at downstream when the intersection of incident shock is on the top of the last jets. Moreover, hydrogen-air mixing rate increase and the concentration of the hydrogen micro jet are uniformly distributed in the surface close to shock. Thus, an enhanced mixing zone occurs in the vicinity of the intersection of the jet and the shock wave.

Application of background-oriented schlieren (BOS) technique to a laser-induced underwater shock wave

An ultra-high-speed imaging system based on the background-oriented schlieren (BOS) technique has been built in order to capture a laser-induced underwater shock wave. This BOS technique is able to provide two-dimensional density-gradient field of fluid and requires a simple setup. The imaging system consists of an ultra-high-speed video camera, a laser stroboscope, and a patterned background. This system takes images every \(0.2\,\upmu \hbox {s}\). Furthermore, since the density change of water disturbed by the shock is exceedingly small, the system has high spatial resolution \(\sim \!\!10\,\upmu \hbox {m/pixel}\). Using this BOS system, temporal position of a shock wave is examined. The position agrees well with that measured by conventional shadowgraph, which indicates that the high-speed imaging system can successfully capture the instantaneous position of the underwater shock wave that propagates with the speed of about 1500 m/s. The local density gradient can be determined up to \(O(10^3\,\hbox {kg/m}^4)\), which is confirmed by the gradient estimated from the pressure time history measured by a hydrophone.

Shock Wave Instability in a Channel with an Expansion Corner

2D and 3D transonic flows in a channel of variable cross-section are studied numerically using a solver based on the Reynolds-averaged Navier–Stokes equations. The flow velocity is supersonic at the inlet and outlet of the channel. Between the supersonic regions, there is a local subsonic region whose upstream boundary is a shock wave, whereas the downstream boundary is a sonic surface. The sonic surface gives rise to an instability of the shock wave position in the channel. Computations reveal a hysteresis in the shock position versus the inflow Mach number. A dependence of the hysteresis on the velocity profile given at the inlet is examined.

Study of the shock wave induced by closing partial road in traffic flow

There often occurs traffic accident or road construction in real traffic, which leads to partial road closure. In this paper, we set up a traffic model for the partial road closure. According to the Nagel-Schreckenberg (NS) cellular automata update rules, the road can be separated into cells with the same length of 7.5 m. L = 4000 (corresponding to 30 km) is set to the road length in the simulations. For a larger system size, our simulations show that the results are the same with those presented in the following. In our model, vmax rtial road is closed (for convenience, we define the road length as L1), vmax 2= 2 (corresponding to 54 km/h) in the section of normal road (we define the road length as L2). In our simulations, let L1= L2 = 2000. We would like to mention that changing these parameter values does not have a qualitative influence on the simulation results. The simulation results demonstrate that three stationary phases exist, that is, low density (LD), high density (HD) and shock wave (SW). Two critical average densities are found:the critical point ρcr 1= 3/8 separates the LD phase from the SW phase, and ρcr 2= 1/2 separates the SW phase from the HD phase. We also analyze the relationship between the average flux J and average density ρ. In the LD phase J = 4/3ρ, in the HD phase J= 1 -ρ and J is 0.5 in the SW phase. We investigate the dependence of J on ρ. It is shown that with the increase of ρ, J first increases, at this stage J corresponds to the LD phase. Then J remains to be a constant 0.5 when the critical average density ρcr 1 is reached, and J corresponds to the SW phase (this time,J reaches the maximum value 0.5). One goal of traffic-management strategies is to maximize the flow. We find that the optimal choice of the average density is 3/8 ρρcr 2 is reached, J decreases with the increase of average density, which corresponds to the HD phase. We also obtain the relationship between the shock wave position and the average density by theoretical calculations, i.e. Si = i+4-8ρ, which is in agreement with simulations.

Numerical simulation of real gas flows in natural gas supersonic separation processing

Abstract The real gas effects on natural gas supersonic separation were investigated using a computational fluid dynamics approach with ideal gas and real gas models. The computed results showed that the fluid properties calculated by the ideal gas law diverged significantly from the real gas cases in the supersonic zones, while the real gas models predicted a similar result from one to the other. The deviation of the gas Mach number between the ideal and real gas models was about 13.50% at the nozzle exit, while the error in the gas density was more than 20% in the whole supersonic separators. The shock wave position calculated by the real gas model was ahead of the one calculated by the ideal gas law. The shock position moved forward with the increasing inlet pressure, while the real gas predicted value was always in front of the ideal gas value. The relative error of the gas Mach number exceeded 15% with an inlet temperature of 283 K.

Nanosecond Time-Resolved Measurements of Transient Hole Opening During Laser Micromachining of an Aluminum Film

Laser micromachining of an aluminum film on a glass substrate is investigated using a time-resolved transmission imaging technique with nanosecond resolution. Micromachining is performed using a 7 ns pulse-width Nd:YAG laser operating at the 1064 nm wavelength for fluences ranging from 2.2 to 14.5 J/cm2. A nitrogen laser-pumped dye laser with a 3 ns pulse-width and 500 nm wavelength is used as a light source for visualizing the transient hole area. The dye laser is incident on the free surface and a CCD camera behind the sample captures the transmitted light. Images are taken from the back of the sample at various time delays with respect to the beginning of the ablation process, allowing the transient hole area to be measured. For low fluences, the hole opening process is delayed long after the laser pulse and there is significant scatter in the data due to weak driving forces for hole opening. However, for fluences at and above 3.5 J/cm2, the starting time of the process converges to a limiting minimum value of 12 ns, independent of laser fluence. At these fluences, the rate of hole opening is rapid, with the major portion of the holes opened within 25 ns. The second stage of the process is slower and lasts between 100 and 200 ns. The rapid hole opening process at high fluences can be attributed to recoil pressure from explosive phase change. Measurements of the transient shock wave position using the imaging apparatus in shadowgraph mode are used to estimate the pressure behind the shock wave. Recoil pressure estimates indicate pressure values over 90 atm at the highest fluence, which decays rapidly with time due to expansion of the ablation plume. The recoil pressure for all fluences above 3.1 J/cm2 is higher than that required for recoil pressure driven flow due to the transition to explosive phase change above this fluence.

충격파 경계층 상호작용에서 난류모델 및 난류점성의 효과

Two compression ramp problems and an impinging shock problem are computed to investigate influence of turbulence models and eddy viscosity on the shock-wave / boundary layer interaction. A Navier-Stokes boundary layer generation code was applied to the generation of inflow boundary conditions. Computational results are validated well with the experimental data and effects of turbulence models are investigated. It is shown that the behavior of turbulence (eddy) viscosity directly affects both the extent of the separation and shock-wave positions over the separation.

Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles

Spatially and temporally resolved temperature measurements behind an expanding blast wave are made using picosecond (ps) N2 coherent anti-Stokes Raman scattering (CARS) following laser flash heating of mixtures containing aluminum nanoparticles embedded in ammonium-nitrate oxidant. Production-front ps-CARS temperatures as high as 3600 ± 180 K—obtained for 50-nm-diameter commercially produced aluminum-nanoparticle samples—are observed. Time-resolved shadowgraph images of the evolving blast waves are also obtained to determine the shock-wave position and corresponding velocity. These results are compared with near-field blast-wave theory to extract relative rates of energy release for various particle diameters and passivating-layer compositions.

Drag reduction research in supersonic flow with opposing jet

Abstract A CFD study on drag reduction in supersonic flow with opposing jet has been conducted. Flowfield parameters, reattachment point position and surface pressure distributions are obtained and validated with experiments. From the analysis on the physical mechanism of drag reduction, it shows the phenomenon that, when the opposing jet blows, the high pressure region is located between the bow shock wave and the Mach disk, which makes the nose region much lower pressure. As the pressure ratio increases, the high pressure region is gradually pushed away from the surface. Larger the total pressure ratio is, the lower of the drag coefficient is. To study the effect of the intensity of opposing jet more reasonably, a new parameter R PA has been introduced by combining the flux and the total pressure ratio. The study shows that the same shock wave position and drag coefficient can be obtained with the same R PA with different fluxes and the total pressures, which means the new parameter could stand for the intensity of opposing jet and could be used to analyze the influence of opposing jet on flow field and aerodynamic force.

Experimental Study of Interaction between Supersonic Duct Flow and Jets and Rods Surrounded by the Porous Cavity

In this study, an experiment was performed to clarify the flow field, in which the jets or rods were normally injected into a main supersonic flow surrounded by a porous cavity, and this report figures out flow direction and stability in the cavity with thermal tuft probe. In the experiment, a porous cavity is attached to a main duct and rods or jets are inserted to the main duct on the porous cavity. To reveal this flow field, the thermal tuft probe was adopted to experimentally investigate the flow direction in the cavity. In addition to the experiment with the jets, the experiments with rods instead of jet were conducted. In the experiments, the effect of the combination of jets or rods and a porous cavity is studied by means of visualization of schlieren method, pressure distributions and the flow direction in the cavity with the thermal tuft probe. Three cases for arrangements are tested in the experiments. As the results, it is found that the flow direction in the cavity is greatly influenced by the starting shock wave position and the rod or jet. The pressure ratio at which the starting shock wave passes through the porous cavity is affected by the jets and rods. Moreover it is found that the flow in the cavity is influenced by the jet and rod even after the starting shock wave move downstream of the porous cavity.