Shock Tube Channel Research Articles

TimeScale Analysis, Numerical Simulation and Validation of Flame Acceleration, and DDT in Hydrogen–Air Mixtures

ABSTRACT Flame Acceleration (FA) and Deflagration to Detonation Transition (DDT) are known risks in scenarios involving accidental release and combustion of hydrogen in nuclear reactors. In the present work, chemical timescale and Borghi diagram analysis of hydrogen combustion have been presented. Based on these, a map of the flame propagation in the GraVent shock tube channel has been constructed; and it has been established that the propagation corresponds to the flamelet regime. Subsequently, CFD framework applicable to the flamelet regime such as the geometric approach with turbulent flame closure has been utilized to study deflagrations, FA and DDT. Such methods allow for the computation of pressure transients and flame propagation characteristics with a relatively coarse grid, thereby enabling a balance between computational time and accuracy. Moreover, specific sub-models based on Lewis number and tuned to lean combustion at high pressures have been implemented to further improve the accuracy of the numerical results. All numerical work has been carried out using the open-source numerical platform OpenFOAM. Several numerical simulations with uniform and transversely stratified initial distribution have been carried out and validated with experimental data. In the stratified case, an asymmetric flame front has been observed and is identified to be a key parameter leading to strong FA. Detailed analysis shows that several pressure pulses and shock complexes are formed upstream of the flame. The ensuing shock–flame interaction augments the flame speed ultimately resulting in DDT. Comparative simulations with uniform distribution also show strong FA but DDT does not take place.

A Pulsed Volume Discharge Localized in a Vortex Zone behind a Wedge in a Supersonic Flow

The development of a pulsed volume discharge with pre-ionization in a non-uniform supersonic air flow near the wedge in the shock tube channel and the gas-dynamic flow that occur after the discharge has been experimentally studied. Plasma configurations that occur near the bottom of the wedge were investigated for the discharge initiated at various stages of an unsteady flow. The self-localization conditions of a volume discharge in the vortex zone behind the wedge are analyzed at the incident shock wave Mach numbers of 2.6–3.5 (at the flow Mach numbers up to 1.50 and a density up to0.15 kg/m3).

Visualization of the shock wave diffraction on the wedge in a rectangular channel

The evolution of a shock wave interaction with a boundary layer on the surface of a shock tube channel after its reflection from a thin wedge is investigated. Visualization of the incident plane shock wave, the bow detached shock wave and flow behind the wedge in 48x24 mm channel was performed using the shadow method based on high-speed recording. The zone of boundary layer separation that occurs when the plane attached bow shock intersects with the channel wall is visualized on the basis of the pulse discharge glow recording. The flow evolution at incident shock wave Mach number of 2.3÷3.8 for the time interval up to 5 ms after the diffraction is investigated. The obtained data is compared with the corresponding CFD results: a numerical simulation based on the Euler equations of a nonstationary two-dimensional flow was performed under experimental conditions.

The Characteristics of a Nanosecond Surface Sliding Discharge in a Supersonic Airflow Flowing around a Thin Wedge

The characteristics of a distributed sliding surface discharge with a duration of ∼300 ns (plasma sheet) in a non-uniform supersonic airflow with a vortex zone behind a thin wedge have been studied in a shock tube channel. The spatial distribution of the discharge radiation, the spectra of the discharge radiation, and the discharge current are analyzed in the flows behind plane shock waves with Mach numbers 2.4–3.5 (the Mach numbers of flows are 1.16–1.47 and the density is 0.02–0.20 kg/m3). It is shown that in an airflow with a vortex zone, the surface discharge develops as a 1–3-mm-wide channel located in the region of low density behind the wedge. The calculated electron concentration in the discharge channel is an order of magnitude higher than the electron concentration when a discharge is initiated in a homogeneous medium.

Analysis of Plasmadynamic Nanosecond-Range Processes in the Formation of Shock Waves from Pulsed Discharges

We have studied the dynamics of the plasma glow of pulsed discharges (sliding surface discharge and combined volume discharge with plasma electrodes) in the nanosecond range (100–12 000 ns) in stationary air and in the flow behind the front of a plane shock wave with Mach numbers 1.7–5.0 in the shock tube channel. The temporal characteristics of the flow, the radiation spectra, and the discharge currents in air are compared in the pressure range 5–150 Torr, a pulsed voltage of 20–30 kV, and a current of about 1 kA. It is shown that the time of current under various conditions does not exceed 400 ns, and the duration of the glow can reach a few microseconds. It is shown that as a result of energy supply near the planar shock wave front, the decay of discontinuities occurs with the formation of shock waves and contact surfaces. The positions of the plasma glow regions are compared with the positions of discontinuity surfaces of numerically calculated gasdynamic parameters in the flow.

Shock wave interaction with a thermal layer produced by a plasma sheet actuator

This paper explores the phenomena associated with pulsed discharge energy deposition in the near-surface gas layer in front of a shock wave from the flow control perspective. The energy is deposited in 200 ns by a high-current distributed sliding discharge of a ‘plasma sheet’ type. The discharge, covering an area of mm2, is mounted on the top or bottom wall of a shock tube channel. In order to analyse the time scales of the pulsed discharge effect on an unsteady supersonic flow, we consider the propagation of a planar shock wave along the discharge surface area 50–500 μs after the discharge pulse. The processes in the discharge chamber are visualized experimentally using the shadowgraph method and modelled numerically using 2D/3D CFD simulations. The interaction between the planar shock wave and the discharge-induced thermal layer results in the formation of a lambda-shock configuration and the generation of vorticity in the flow behind the shock front. We determine the amount and spatial distribution of the electric energy rapidly transforming into heat by comparing the calculated flow patterns and the experimental shadow images. It is shown that the uniformity of the discharge energy distribution strongly affects the resulting flow dynamics. Regions of turbulent mixing in the near-surface gas are detected when the discharge energy is deposited non-uniformly along the plasma sheet. They account for the increase in the cooling rate of the discharge-induced thermal layer and significantly influence its interaction with an incident shock wave.

Protecting shield influence on pressure decrease at shock wave interaction with the wall

Pressure decrease is investigated at reflection, from the end of the shock tube channel, of the shock wave passing through its sand layer. The influence of the layer location on the pressure pulse extension and on the decrease of the maximal pressure amplitude behind the shock wave is studied.

A compact laboratory device for accelerating thin strikers

We describe a method for accelerating a thin (~1 mm thick) striker with a diameter of 35 mm in a shock tube channel up to velocities above to ~275 m/s under the pressure of detonation products of acetylene–oxygen fuel mixture. Impact of this striker on a ~1-cm-thick water layer generates a nonstationary decaying shock wave (Taylor wave) with amplitude of ~0.2 GPa on escape from the free surface.

Pressure dynamics in a supersonic flow during initiation of pulse surface sliding discharges

The supersonic air flow at Mach numbers of 1.1–1.6 in a shock tube is experimentally investigated during initiation of nanosecond pulse surface sliding discharges. The shadow images of the flow field after discharge initiation, which characterize the dynamics of shock waves propagating from the discharge area, are obtained. Periodic pressure pulsations on the shock tube channel wall are recorded. The pressure dynamics is shown to correspond to both the motion of shock waves from the discharge area and a supersonic flow of the discharge-excited gas near the channel wall. The pressure increase on the shock tube channel wall was 6–18%, as compared to the pressure in an unperturbed flow.

Mathematical simulation of the ejection of a gas suspension from a shock-tube channel under the action of a compressed gas

Results are presented of a numerical calculation of an unsteady two-dimensional axisymmetric wave flow of an inert monodispersed gas suspension from the channel of a shock tube into the surrounding gaseous space under the action of a gas compressed in a high-pressure chamber. The acceleration of dispersed particles inside the tube and in the submerged space behind the diffracting air shock-wave front is analyzed. The effect of the formation of a vortex dispersed ring during dispersion of a particle cloud is discussed. The influence of the governing parameters of the ejected gas suspension layer and the driving gas on the distance of dispersion of a dispersed particle cloud is investigated.

The 1986 hypervelocity impact symposium: October 21–24, 1986 municipal auditorium host hotel: St. Anthony inter-continental hotel San Antonio, Texas

A critical appraisal is made of the design, research, development, and operation of the novel UTIAS implosion-driven hypervelocity launchers and shock tubes. Explosively driven (PbN6-leadazide, PETN-pentaerythritetetranitrate) implosions in detonating stoichiometric hydrogen-oxygen mixtures have been successfully developed as drivers for hypervelocity launchers and shock tubes in a safe and reusable facility. Intense loadings at very high calculated pressures (almost megabar range), densities (g/cm3) and temperatures (thousands °K), at the implosion centre, cause severe problems with projectile integrity. Misalignment of the focal point can occur and add to the difficulty in using small calibre (6–8 mm dia.) projectiles. In addition, the extreme driving conditions cause barrel expansion, erosion, and possible gas leakage from the base to the head of the projectile which cut the predicted muzzle velocities to half or a third of the lossless calculated values. However, in the case of a shock-tube operation these difficulties are minimized or eliminated and the possibilities of approaching Jovian re-entry velocities are encouraging. In a recent run using about 100 g of explosive PETN and 400 psi 2H2 + O2 a shock Mach number Ms ≈ 60 was obtained in air at an initial pressure of 1 torr in a 1.0-in.-dia. shock-tube channel. In addition, the use of focused, explosive-driven implosion waves may have many other physical and technological applications.

Turbulent mixing of driver and driven gases in a shock tube channel

Turbulent mixing of driver and driven gases in a shock tube channel

ON A DUSTY GAS SHOCK TUBE*

AbstractAnalytical and numerical methods were used to investigate the flow induced by a shock wave in a shock tube channel containing air laden with suspended small solid particles. Exact results are given for the frozen and equilibrium shock wave properties as a function of the diaphragm‐pressure ratio and shock wave Mach numbers. The driver contained air at high pressure. A modified random choice method, together with an operator‐splitting technique, shows clearly the decay both of a discontinuous frozen shock wave and of a contact discontinuity and the formation both of a stationary shock structure and of an effective contact front of finite thickness. The effects of particle diameter, particle‐number density, and diaphragm‐pressure ratio on the transitional behavior of the flow are investigated in detail. The alteration of the flow properties owing to the presence of particles is discussed thoroughly and compared with classical shock tube flows.

On a dusty-gas shock tube

Analytical and numerical methods were used to investigate the flow in­duced by a shock wave in a shock-tube channel containing air laden with suspended small solid particles. Exact results are given for the frozen and equilibrium shock-wave properties as a function of diaphragm-pressure ratio and shock-wave Mach numbers. The driver contained air at high pressure. A modified random-choice method together with an operator-splitting technique show clearly both the decay of a discontinuous frozen shock wave and a contact discontinuity, and the formation of a stationary shock structure and an effective contact front of finite thickness. The effects of particle diameter, particle-number density and diaphragm- pressure ratio on the transitional behaviour of the flow are investigated in detail. The alteration of the flow properties owing to the presence of particles is discussed thoroughly and compared with classical shock-tube flows.

Appraisal of UTIAS implosion-driven hypervelocity launchers and shock tubes

A critical appraisal is made of the design, research, development, and operation of the novel UTIAS implosion-driven hypervelocity launchers and shock tubes. Explosively driven (PbN 6-leadazide, PETN-pentaerythritetetranitrate) implosions in detonating stoichiometric hydrogen-oxygen mixtures have been successfully developed as drivers for hypervelocity launchers and shock tubes in a safe and reusable facility. Intense loadings at very high calculated pressures (almost megabar range), densities (g/cm 3) and temperatures (thousands °K), at the implosion centre, cause severe problems with projectile integrity. Misalignment of the focal point can occur and add to the difficulty in using small calibre (6–8 mm dia.) projectiles. In addition, the extreme driving conditions cause barrel expansion, erosion, and possible gas leakage from the base to the head of the projectile which cut the predicted muzzle velocities to half or a third of the lossless calculated values. However, in the case of a shock-tube operation these difficulties are minimized or eliminated and the possibilities of approaching Jovian re-entry velocities are encouraging. In a recent run using about 100 g of explosive PETN and 400 psi 2H 2 + O 2 a shock Mach number M s ≈ 60 was obtained in air at an initial pressure of 1 torr in a 1.0-in.-dia. shock-tube channel. In addition, the use of focused, explosive-driven implosion waves may have many other physical and technological applications.

Direct shock tube measurements of oxygen-atom recombination rates

Oxygen-atom recombination rates have been measured over the temperature range 3000 to 3800 K using a method which affords direct control over the recombination process stimulated in a rapidly expanded sample of gas in a shock tube. A knife edge ‘trap’ was placed in the shock tube channel in order to provide partial reflection of incident shock waves. Density variations in the expanded gas region were measured with a quantitative interferometric chronometer by using the helium-neon laser as a light source. Simultaneous pressure measurements enable the relaxation effect to be detected from a comparison of the local change of pressure with the density variations. A strong temperature dependence for the recombination rate coefficients with the oxygen molecule as the dominant catalyst was obtained in the limits (2·0 to 0·4) × 10 15 cm 6 mole −2 sec −1 at 3000 to 3800 K respectively. The data agree well with recombination rates evaluated from dissociation rate measurements. Some gas dynamic applications of the results to quasi-stationary expanded shock tube flow analysis are discussed. Measured decay distances of the recombination relaxation in rarefaction waves generated in non-equilibrium flows around a corner are in accordance with the recombination rate data.