Existence Of Shock Waves Research Articles

Detekcija udara i poboljšanje dizajna za pneumatski kontrolni ventil

The existence of shockwaves in pneumatic valves can greatly affect their efficiency and cause damage to important parts. This study focuses on the examination of a cost-effective pneumatic directional control valve with the aim of augmenting its output mass flow rate. Emphasis is placed on scrutinizing and modifying the critical flow area to facilitate increased flow rates under specific upstream pressures while eliminating the formation of shockwaves. To achieve these objectives, numerical simulations are harnessed to accurately capture the onset of shockwave formation and elucidate the associated conditions, allowing optimizing valve's capacity without introducing the risk of shockwave occurrence. The modified valve design demonstrated the capability to eliminate shockwave formation within the valve while concurrently increasing the mass flow rate by up to 70% within the same range of inlet pressures. This novel approach holds substantial promise for enhancing system response and represents a significant contribution to the field of pneumatic control valve design.

Measurement of the Thin Liquid Film at the Wet-Gas Outlet of the Supersonic Separator by FPC Conductance Sensor

Gas-liquid two-phase flow widely exists in the natural gas transportation industry. Accurate measurement of the liquid film is conducive to enhancing the efficiency and economy of supersonic separators. Therefore, a flexible printed circuit (FPC) liquid film conductance sensor based on array arrangement is designed. Firstly, the geometric parameters of sensors are optimized by the finite element method. The modules of electrical signal excitation and collection system based on FPGA are designed. A liquid film calibration device is built to calibrate the FPC sensor, the liquid film thickness is fitted through calibration experiments, and the fitting curve error is within ±5.0 %. Secondly, to analyze the liquid film thickness and velocity at the wet-gas outlet section of the supersonic separator, serval experiments are carried out in different working conditions, and the signals of liquid film thickness are processed by time and frequency domain analysis. The results reveal that the liquid film thickness has a bimodal characteristic, where the thickness of the thin base layer is about 70 μm, and fluctuating layer thickness is related to working conditions. The normalized energy ratio and fluctuation characteristics significantly changed under different frequency bands. At the same time, the existence of shock waves seriously influences the generation of liquid film, resulting in a decrease in the liquid film thickness seriously. Last, the cross-correlation algorithm is used to analyze the liquid film velocity. The different signal transmitter and receiver electrode orders can realize the velocity measurement in different directions. The experimental results show that the liquid film velocity at the outlet of the supersonic separator maintains at 54.8 mm/s ~ 339.0 mm/s when the back pressure ranges from 0.350-0.717, the maximum <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RMSE</i> of flow direction velocity is 4.51 mm/s and the maximum <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RMSE</i> of circumferential direction velocity is 3.38 mm/s.

The Finite Element Numerical Study of Transonic Flow of Moist Air with Nonequilibrium Condensation

The finite element numerical simulation of the transonic flow with condensation is studied in this paper. The transformed weak form is numerically discretized by using the classical Galerkin finite element spatial discretization scheme and the backward Euler difference time discretization scheme. Because the coupled Euler equations are convection equations, the results obtained by the classical Galerkin method often have nonphysical numerical oscillations, so the stabilization method is introduced. Another important feature of compressible Euler equation is the existence of shock wave. Because the thickness of shock wave is small and difficult to capture, the shock wave can be better captured by adding artificial viscosity term. Here, the streamline upwind/Petrov–Galerkin (SUPG) finite element method with good stability and the isotropic diffusion method with shock capture ability are used to solve the problem of transonic flow with condensation. In the simulation of steady problems, in order to improve the calculation accuracy of the existing area of the shock wave, the adaptive mesh refinement technology is added, which refines the mesh in the region of the shock wave to improve the resolution of the shock wave. Numerical experiments verify the feasibility and stabilization of the numerical method. Finally, the simulation of transonic flow around NACA-0012 and parallel-jet nozzle A1 has obtained the better numerical results.

A shock-capturing scheme with a novel limiter for compressible flows solved by smoothed particle hydrodynamics

There are many compressible flows involving strong discontinuities in nature and engineering applications. Their behaviors are complicated by the existence of shock waves, rarefaction waves and contact discontinuities. To investigate these flows, a shock-capturing scheme based on smoothed particle hydrodynamics (SPH) is proposed. In this scheme, Roe’s approximate Riemann solver cooperated with a novel limiter is embedded into the SPH governing equations to capture shocks. This limiter is simple and effective to control numerical dissipations, and the use of this limiter eliminates the tunable artificial viscosity as required by the conventional SPH. Additionally, to restore the accuracy limited by heterogeneous particle distribution that is usually encountered in the simulation of strongly-compressible flows, the gradient operator in the continuity equation is corrected by a renormalization procedure. Last but not least, for initial particle distribution, unlike the equal mass particle distribution commonly used in compressible SPH simulations, the equal spacing particle distribution is adopted in this scheme, which makes it much easier to model multidimensional problems. The present scheme has been verified by a set of benchmark tests involving contact discontinuities, extreme shock waves and strong rarefaction waves, some of which are firstly simulated by the SPH method.

Possible Evidence of Hydrogen Emission in the First-overtone and Multimode RR Lyrae Variables

Abstract The nature of shock waves in nonfundamental mode RR Lyrae stars remains a mystery because of limited spectroscopic observations. We apply a pattern recognition algorithm on spectroscopic data from SDSS and LAMOST and report the first evidence of hydrogen emission in first-overtone (RRc) and multimode (RRd) RR Lyrae stars showing the “first apparition,” which is the most prominent observational characteristic of shock in RR Lyrae variables. We find 10 RRc stars in SDSS, 10 RRc stars in LAMOST, and 3 RRd stars in LAMOST that show blueshifted Balmer emissions. The emission features possibly indicate the existence of shock waves. We calculate the radial velocities of the emission lines, which are related to the physical conditions occurring in the radiative zone of shock waves. Using photometric observations from ZTF, we present a detailed light-curve analysis for the frequency components in one of our RRd stars with hydrogen emission, RRdl3, for possible modulations. With the enormous volume of upcoming spectral observations of variable stars, our study raises the possibility of connecting the unexplained Blazhko effect to shock waves in nonfundamental mode RR Lyrae stars.

Study on Aerodynamic Characteristics of Supersonic Airfoil

With the invention of the aircraft, it has become much faster and larger than the original Wright Brothers aircraft. When the speed is high enough to cross the speed of sound, air conditions will be different than that in low speed due to the existence of shock wave. In this work, we introduce several numerical ways to analyze the performance of the airfoil when the speed is higher than the speed of sound. With these numerical methods, we analyzed the performance of diamond-shaped airfoil under different angles of attack and speed. With this data, engineers can choose a better airfoil to attain a lower drag coefficient as well as lift coefficient when designing a high-speed aircraft.

On the possibility of the existence of shock waves in nonisothermic plasma

The possibility of the existence of shock waves in nonisothermic plasma with Te » Ti, in which isothermal ion sound exists, Te = const, is theoretically studied. It is shown that propagation of only a density perturbation in the form of a nonlinear solitary wave (soliton) is possible in such plasma. Electron and ion charges are separated in the density solitary wave with the formation of a double electric layer with a strong electric field. The field potential shape, amplitude, and front width of the wave are found.

A travel time reliability model of urban expressways with varying levels of service

Urban expressways usually experience several levels of service (LOS) because of the stop-and-go traffic flow caused by congestion. Moreover, multiple shock waves generate at different LOS interfaces. The dynamic of shock waves strongly influences the travel time reliability (TTR) of urban expressways. This study proposes a path TTR model that considers the dynamic of shock waves by using probability-based method to characterize the TTR of urban expressways with shock waves. Two model parameters are estimated, namely distribution of travel time (TT) per unit distance and travel distances in different LOS segments. Generalized extreme value distribution and generalized Pareto distribution are derived as distributions of TT per unit distance for six different LOS. Distribution parameters are estimated by using historical floating car data. Travel distances in different LOS segments are calculated based on shock wave theory. The range of TT along the path, which can help drivers arrange their trips, can be obtained from the TTR model. Finally, comparison is made among the proposed TTR model, generalized Pareto contrast model, which does not consider different LOS or existence of shock waves, and normal contrast model, which assumes TT per unit distance as normal distribution without considering shock wave. Results show that the proposed model achieves higher prediction accuracy and reduces the prediction range of TT. The conclusions can be further extended to TT prediction and assessment of measures to improve reliability of TT in a network.

The final 112-frame movie of the 43 GHz SiO masers around the Mira Variable TX Cam

AbstractThe proximity of the SiO masers to the star, makes them a powerful tool for studying the properties of the extended stellar atmosphere. This project is a long monitoring campaign of the 43 GHz SiO masers (v=1 J=1→0) around the Mira Variable TX Cam. The target source was observed with the Very Long Baseline Array (VLBA) from the 24th of May 1997 to the 25th of January 2002 in bi-weekly or monthly intervals, covering 3.06 stellar cycles. The time-span and frequency of observations helped us examine the long and short-term properties of the emission and study the dynamics of the gas, the existence of shock waves and their contribution to the morphology and kinematics. Maps from each epoch were concatenated into a 112-frame movie showing the evolution of the emission around TX Cam.

Acoustics of tachyon Fermi gas

We consider a Fermi gas of free tachyons as a continuous medium and find whether it satisfies the causality condition. There is no stable tachyon matter with the particle density below critical value ${n}_{T}$ and the Fermi momentum ${k}_{F}&lt;\sqrt{\frac{3}{2}}m$ that depends on the tachyon mass $m$. The pressure $P$ and energy density $E$ cannot be arbitrary small, but the situation $P&gt;E$ is not forbidden. Existence of shock waves in tachyon gas is also discussed. At low density ${n}_{T}&lt;n&lt;3.45{n}_{T}$ the tachyon matter remains stable but no shock wave survives.

Kinematics of the v=1, J=1→0 SiO masers at 43 GHz towards TX Cam - a new 73-frame movie

We present a new version of the movie of the SiO masers around the Mira variable TX Cam. It consists of 73 frames (60 observed epochs) with data covering almost two complete stellar cycles between 1997 May 24 and 2000 May 21. Observations were carried out using the Very Long Baseline Array in biweekly and later at monthly intervals. The purpose of this paper is to discuss the global properties of the emission in the extended atmosphere of the star as well as the kinematics of individual components. The existence of shock waves and their contribution to the morphology and the kinematics of the gas is also examined and compared with theoretical models. Contrary to the dominant expansion observed in the first cycle, both expansion and contraction are observed in the second cycle. The maser variability is correlated with the pulsation of the star but not with the optical intensity. Most of the individual components identified follow the behaviour of the ring, but there are exceptions with more complex three-dimensional trajectories.

QUALITATIVE ANALYSIS OF THE KHOKHLOV–ZABOLOTSKAYA–KUZNETSOV (KZK) EQUATION

The Khokhlov–Zabolotskaya–Kuznetzov (KZK) equation is considered as a model of nonlinear acoustic which describes the nonlinear propagation of a finite-amplitude focused sound beam which is essentially one-directional, in the thermo-viscous medium.1,7,8The aim of this paper is the study of the existence, uniqueness, stability, regularity, continuous dependence on the initial value and blow-up of solution of the KZK equation in Sobolev spaces Hsof periodic on x functions and with mean value zero. Existence of shock waves for the model with zero viscosity is proved using S. Alinhac's method.2Global existence in time of the beam's propagation in viscous media is established for small enough initial data. Existence result is proved by two methods: first by the fractional step method in the particular case ℝ3and s = 3 to justify the numerical results of Thierry Le Pollès25and second for the general case ℝnand s &gt; [n/2] + 1 by the approach used in Refs. 12 and 13 for the Kadomtsev–Petviashvili (KP) equation.

Incompressible and Compressible Limits of Coupled Systems of Nonlinear Schrödinger Equations

Recently, coupled systems of nonlinear Schrodinger equations have been used extensively to describe a double condensate, i.e. a binary mixture of Bose-Einstein condensates. In a double condensate, an interface and shock waves may occur due to large intraspecies and interspecies scattering lengths. To know the dynamics of an interface and assure the existence of shock waves in a double condensate, we study the incompressible and the compressible limits respectively of two coupled systems of nonlinear Schrodinger equations. The main idea of our arguments is to define a “H-functional” like a Lyapunov functional which can control the propagation of densities and linear momenta. Such an idea is different from the one using the standard Wigner transform to investigate the incompressible and the compressible limits of a single nonlinear Schrodinger equation. \(\mathfrak{V}\)

Analysis of intersonic crack growth in unidirectional fiber-reinforced composites

Recent experiments on dynamic fracture of unidirectional fiber-reinforced graphite/epoxy composite materials showed that, in Mode I, the crack tip velocity could never exceed the shear wave speed, while the crack tip velocity in Mode II not only exceeded the shear wave speed but also approached a stable velocity at which the crack grew for a substantial period of time in experiments. The experimentally obtained fringe patterns also clearly showed the existence of shear shock waves when the crack tip velocity exceeded the shear wave speed. In the present study, we have obtained the asymptotic fields near an intersonically propagating crack tip. It is shown that Mode-I intersonic crack propagation is impossible because the crack tip energy release rate supplied by the elastic asymptotic field is negative and unbounded, which is physically unacceptable since a propagating crack tip cannot radiate out energy. For Mode II, however, it is established that there exists a single crack tip velocity (higher than the shear wave speed) that gives a finite and positive crack tip energy release rate. At all other intersonic crack tip speeds the energy release rate supplied by the elastic asymptotic field is identically zero. This critical crack tip velocity agrees well with the stable crack tip velocity observed in experiments. The synthetically obtained fringe patterns based on the asymptotic field also agree with experimentally obtained fringe patterns, particularly on the existence of the shock waves.

Dynamic characteristics of gas jets from subsonic and supersonic nozzles for high pressure gas laser cutting

During laser cutting of stainless steels, titanium and aluminum alloys, a coaxial and high pressure inert gas jet is used to improve the cut edge quality. The process normally consumes a large amount of inert gas and has a poor tolerance to variation in process parameters. This is solely because the gas nozzles are mostly of the conical and convergent type in which the gas jets are subsonic. Based on two dimensional steady state gas dynamic theory, computer simulation and shadowgraphic techniques, the gas jet patterns from conical nozzles and the newly designed supersonic nozzles are analyzed. The distribution of pressure, momentum, gas density and existence of shock waves are predicted and mapped. Based on these characteristics, the effect of the gas jets upon the cut quality is explained. It is concluded that a supersonic gas jet offers the best flow characteristics for high pressure laser cutting.

Physical parameters affecting sonoluminescence: A self-consistent hydrodynamic study

We studied the dependence of thermodynamic variables in a sonoluminescing ~SL! bubble on various physical factors, which include viscosity, thermal conductivity, surface tension, the equation of state of the gas inside the bubble, as well as the compressibility of the surrounding liquid. The numerical solutions show that the existence of shock waves in the SL parameter regime is very sensitive to these factors. Furthermore, we show that even without shock waves, the reflection of continuous compressional waves at the bubble center can produce the high temperature and picosecond time scale light pulse of the SL bubble, which implies that SL may not necessarily be due to shock waves.

Shock waves in a chain of two-level atoms with exchange and dipole-dipole interactions

We use a small-amplitude multiple scale expansion to investigate the existence of shock waves in a chain of two-level atoms with both exchange and dipole-dipole interactions. We show that the exchange interaction allows the formation of the system of both bright and dark shock waves. Conversely, the dipole-dipole interaction results in the instability of the background and, as a consequence, in the prevention of the formation of shock waves. The analytical results are found to be in good qualitative agreement with a direct numerical integration of the system.

Algebraic turbulence modeling for swept shock-wave/turbulent boundary-layer interactions

New algebraic turbulence modeling is derived that is appropriate for the simulation of swept shock-wave/ turbulentboundary-layerinteractions.Inthequasiconicalseparation vortex,whichappearsin thesetypesofows, thelow-intermittencyouterpartoftheboundary layerrotatesaroundthecoreofthevortex and penetrates into the separation bubble at the reattachment region, forming a low-turbulence tongue that lies along the surface under the vortex. This physical feature was considered in the derivation of a new equation for calculation of the eddy- viscosity coef® cient in the region of the separation vortex. The Baldwin± Lomax formulation is followed, because it is easily implemented in a Navier± Stokes computation scheme. Also, an alternative eddy-viscosity coef® cient is presented that is closer to Clauser's linear relation than the original Baldwin± Lomax relations. The proposed calculation scheme is completed by a simple rule for calculation of the thickness of the boundary layer in types of ¯ ows where, because of the existence of shock waves and mixing layers, multiple maxima exist in the moment of vorticity pro® les. Application of the new turbulence modeling in supersonic sharp-® n± plateows resulted in good agreement with theexperimental evidence. Also, a preliminary application of the new relations to a crossing shock con® guration indicated that this complexow can be simulated quite well.

Physics of vortical flows

Separation in three-dimensional flows leads to the formation of vortical structures resulting from rolling up of the viscous flow sheet, initially contained in a thin boundary layer, which springs up from the surface into the outer perfect fluid flow. A clear physical understanding of this phenomenon must be based on a rational analysis of the flowfield structure using the critical-point theory. With the help of this theory, it is possible to interpret correctly the surface flow patterns that constitute the imprints of the outer flow and to give a rational and coherent description of the vortical system generated by separation. This kind of analysis is applied to separated flows forming on typical obstacles, the field of which has been thoroughly studied by means of visualizations and probings using multihole pressure probes and laser velocimetry. Thus, the skin friction line patterns of a transonic channel flow and of a multibody launcher are interpreted. Then, the vortical systems of a delta wing and an afterbody at an incidence are considered. The last two configurations are a missile fuselage-type body and an oblate ellipsoid. I. Introduction F LIGHT at high-incidenc e of combat aircraft or hypersonic vehicles during re-entry, as well as that of tactical missiles, raises practical interest on the study of three-dimensional separated flows. Applications also concern internal flows, in particular air intakes and turbomachines in which the often complex geometry of the channel and the existence of shock waves almost inevitably lead to boundary-laye r separation. In three-dimensional flows, separation entails the formation of vortical structures—frequently, but improperly, called vortices to simplify—form ed by rolling up of the viscous flow sheet, previously confined in a thin layer attached to the wall, which suddenly springs into the outer nondissipative flow. Although it has been known for a long time, this phenomenon is still incompletely understood from a physical point of view and it is delicate to model due to the flowfield complexity, all the components of which are difficult to capture properly. Many predictive methods are based on perfect fluid models, the first of which use the vortex sheet concept. Such a sheet is defined as a surface of tangential discontinuity for the velocity field. The computational method can use different schemes: doublets, vortex filaments, vortex particles, and so forth. Publications in this domain are too numerous to be cited here. A greater accuracy in flow prediction can be obtained in the solution of the complete Euler equations, which allows, in theory, automatic capture of sheet-like disconti

Entropy and causality as criteria for the existence of shock waves in low temperature heat conduction

A set of symmetric hyberbolic field equations, describing heat conduction in dielectric solids at low temperatures, is studied with respect to the propagation of temperature shock waves. The field equations have been derived from the Boltzmann-Peierls equation and include the phenomenon of second sound, a special form of wavelike energy transport occuring in some crystals in a temperature range close to absolute zero.