Showing papers on "Shock tube published in 2020"

Measurement of “Shock Wave Parameters” in a Novel Table-Top Shock Tube Using Microphones

Abstract: A new manually operated pressure driven shock tube is proposed and demonstrated. Shock wave-associated parameters like velocity, Mach number, pressure, and temperature are computed using acoustic method. Experiment involves manually loading train of pressure pulses into a driver tube using a bicycle pump. The high pressure buildup in driver tube ruptures the diaphragm at critical pressure and generates a propagating shock wave in the driven section coupled with sensor section in which a couple of microphones are separated by a fixed distance. The propagating shock wave acoustical profile is recorded and its arrival time lag is measured using sound recording software. In a conventional method, piezo-electric pressure sensors are utilized to measure both pressure and time lag of shock wave between the sensors. In the proposed method, microphones are utilized to measure time lag of shock wave with sampling frequency of 768 KHz using computer supporting audio software. Utilizing time data, the said shock wave parameters are evaluated and reported. The performance of the proposed shock tube is compared with manually operated piston-driven Reddy tube.

Shock wave-induced switchable magnetic phase transition behaviour of ZnFe2O4 ferrite nanoparticles

Abstract: The present work is designed to investigate the impact of shock waves on Zinc Ferrite nanoparticles (ZnFe2O4) NPs. The test material was prepared by precipitation method and shock wave recovery experiment is done by tabletop pressure driven shock tube. The shock wave induced changes in structural, morphological and magnetic properties are noticed by various analytical techniques such as powder X-ray Diffractometer (PXRD), fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) and the obtained PXRD results shows no significant structural changes. Switchable paramagnetic to superparamagnetic behaviour is observed during the shock wave loaded conditions. The mechanism of shock wave induced magnetic phase transition is discussed.

Convergent Richtmyer–Meshkov instability of light gas layer with perturbed outer surface

Abstract: The Richtmyer–Meshkov instability of a helium layer surrounded by air is studied in a semi-annular convergent shock tube by high-speed schlieren photography. The gas layer is generated by an improved soap film technique such that its boundary shapes and thickness are precisely controlled. It is observed that the inner interface of the shocked light gas layer remains nearly undisturbed during the experimental time, even after the reshock, which is distinct from its counterpart in the heavy gas layer. This can be ascribed to the faster decay of the perturbation amplitude of the transmitted shock in the helium layer and Rayleigh–Taylor stabilization on the inner surface (light/heavy) during flow deceleration. The outer interface first experiences ‘accelerated’ phase inversion owing to geometric convergence, and later suffers a continuous deformation. Compared with a sole heavy/light interface, the wave influence (interface coupling) inhibits (promotes) growth of instability of the outer interface.

On using converging shock waves for pressure amplification in shock tubes

Abstract: While conventional shock tubes have a distinct advantage in dynamic calibration methods due to their inherent capability to generate pressure pulses of desired amplitude and fast rise time, they ar ...

A numerical study of particle jetting in a dense particle bed driven by an air-blast

Abstract: In this work, the particle jetting behavior in a blast-driven dense particle bed is studied at early times. Four-way coupled Euler–Lagrange simulations are performed using a high-order discontinuous Galerkin spectral element solver coupled with a high-order Lagrangian particle solver, wherein the inter-particle collisions are resolved using a discrete element method collision model. Following the experiments of Rodriguez et al. [“Formation of particle jetting in a cylindrical shock tube,” Shock Waves 23(6), 619–634 (2013)] and the simulations of Osnes et al. [“Numerical simulation of particle jet formation induced by shock wave acceleration in a Hele-Shaw cell,” Shock Waves 28(3), 451–461 (2018)], the simulations are performed in a quasi-two-dimensional cylindrical geometry (Hele-Shaw cell). Parametric studies are carried out to assess the impact of the coefficient of restitution and the strength of the incident shock on the particle jetting behavior. The deposition of vorticity through a multiphase (gas–particle) analog of Richtmyer–Meshkov instability is observed to play a crucial role in channeling the particles into well-defined jets at the outer edge of the particle bed. This is confirmed by the presence of vortex pairs around the outer jets. Furthermore, the effect of the relaxation of the relative velocity between the two phases on the vorticity generation is explored by analyzing the correlation between the radial velocity of particles and the radial velocity of the gas at the particle location.

Probing the Effects of NOx and SOx Impurities on Oxy-Fuel Combustion in Supercritical CO2: Shock Tube Experiments and Chemical Kinetic Modeling

Abstract: The direct-fired supercritical carbon dioxide cycles are one of the most promising power generation methods in terms of their efficiency and environmental friendliness. Two important challenges in implementing these cycles are the high pressure (300 bar) and high CO2 dilution (>80%) in the combustor. The design and development of supercritical oxy-combustors for natural gas require accurate reaction kinetic models to predict the combustion outcomes. The presence of a small amount of impurities in natural gas and other feed streams to oxy-combustors makes these predictions even more complex. During oxy-combustion, trace amounts of nitrogen present in the oxidizer is converted to NOx and gets into the combustion chamber along with the recirculated CO2. Similarly, natural gas can contain a trace amount of ammonia and sulfurous impurities that get converted to NOx and SOx and get back into the combustion chamber with recirculated CO2. In this work, a reaction model is developed for predicting the effect of impurities such as NOx and SOx on supercritical methane combustion. The base mechanism used in this work is GRI Mech 3.0. H2S combustion chemistry is obtained from Bongartz et al. while NOx chemistry is from Konnov. The reaction model is then optimized for a pressure range of 30–300 bar using high-pressure shock tube data from the literature. It is then validated with data obtained from the literature for methane combustion, H2S oxidation, and NOx effects on ignition delay. The effect of impurities on CH4 combustion up to 16 atm is validated using NOx-doped methane studies obtained from the literature. In order to validate the model for high-pressure conditions, experiments are conducted at the UCF shock tube facility using natural gas identical mixtures with N2O as an impurity at ∼100 bar. Current results show that there is a significant change in ignition delay with the presence of impurities. A comparison is made with experimental data using the developed model and predictions are found to be in good agreement. The model developed was used to study the effect of impurities on CO formation from sCO2 combustors. It was found that NOx helps in reducing CO formation while the presence of H2S results in the formation of more CO. The reaction mechanism developed herein can also be used as a base mechanism to develop reduced mechanisms for use in CFD simulations.

Interaction of a planar shock wave and a water droplet embedded with a vapour cavity

Abstract: The interaction of a shock wave and a water droplet embedded with a vapour cavity is experimentally investigated in a shock tube for the first time. The vapour cavity inside the droplet is generated by decreasing the surrounding pressure to the saturation pressure, and an equilibrium between the liquid phase and the gas phase is obtained inside the droplet. Direct high-speed photography is adopted to capture the evolution of both the droplet and the vapour cavity. The formation of a transverse jet inside the droplet during the cavity-collapse stage is clearly observed. Soon afterwards, at the downstream pole of the droplet, a water jet penetrating into the surrounding air is observed during the cavity-expansion stage. The evolution of the droplet is strongly influenced by the evolution of the vapour cavity. The phase change process plays an important role in vapour cavity evolution. The effects of the relative size and eccentricity of the cavity on the movement and deformation of the droplet are presented quantitatively.

StanShock: a gas-dynamic model for shock tube simulations with non-ideal effects and chemical kinetics

Abstract: A high-order, quasi-one-dimensional, reacting, compressible flow solver is developed to simulate non-ideal effects and chemical kinetics in shock tube systems. To this end, physical models for the thermoviscous boundary-layer development, area variation, gas interfaces, and reaction chemistry are considered. The model is first verified through simulations of steady isentropic nozzle flow, multi-species Sod’s problem, laminar premixed flame, and ZND detonation test cases. Comparisons with experiments are made by examining end-wall pressure traces that are gathered from shock tube experiments designed to test the code’s capabilities. Subsequently, the solver is utilized for uncertainty quantification and design optimization of a driver insert. Both applications prove to be highly efficient, indicating the utility of the solver for the design of experiments in consideration of non-ideal gas-dynamic effects.

Shock-Tube Laser Absorption Measurements of CO and H2O during Iso-Octane Combustion

Abstract: The oxidation of iso-octane was studied in two different shock tubes by recording mole fraction time histories of CO and H2O at various equivalence ratios (0.5, 1.0, and 2.0) at around 1.5 atm, bet...

Effects of High Fuel Loading and CO2 Dilution on Oxy-Methane Ignition Inside a Shock Tube at High Pressure

Abstract: Ignition delay times were measured for methane/O2 mixtures in a high dilution environment of either CO2 or N2 using a shock tube facility. Experiments were performed between 1044 K and 1356 K at pressures near 16 ± 2 atm. Test mixtures had an equivalence ratio of 1.0 with 16.67% CH4, 33.33% O2, and 50% diluent. Ignition delay times were measured using OH* emission and pressure time-histories. Data were compared to the predictions of two literature kinetic mechanisms (ARAMCO MECH 2.0 and GRI Mech 3.0). Most experiments showed inhomogeneous (mild) ignition which was deduced from five time-of-arrival pressure © <2020> by ASME. This manuscript version is made available under the CC-BY 4.0 license http://creativecommons.org/licenses/by/4.0/ 2 transducers placed along the driven section of the shock tube. Further analysis included determination of blast wave velocities and locations away from the end wall of initial detonations. Blast velocities were 60-80% of CJ-Detonation calculations. A narrow high temperature region within the range was identified as showing homogenous (strong) ignition which showed generally good agreement with model predictions. Model comparisons with mild ignition cases should not be used to further refine kinetic mechanisms, though at these conditions, insight was gained into various ignition behavior. To the best of our knowledge, we present first shock tube data during ignition of high fuel loading CH4/O2 mixtures diluted with CO2 and N2. INTRODUCTION With the development of gas turbines moving towards a more efficient and cleaner future, use of methane (CH4) combustion is being closely examined due to the negative impacts of high carbon monoxide (CO), carbon dioxide (CO2), and nitrous oxide (NOx) emissions and issues regarding high fuel consumption. In addition, the future of space is rapidly moving towards creating spacefaring colonies and having a fuel (liquid methane) that can be easily manufactured as well as a fuel that does not require a large amount of consumption for a given power output is essential. Methane is a prime candidate rocket fuel due to its potential accessibility and manufacturability on distant worlds, such as leveraging the predominantly CO2 atmosphere of Mars in a Sabatier reaction to yield methane [1]. Additional specific impulse improvements can be realized over more traditional methods and fuels such as liquid hydrogen and kerosene (RP-1), particularly in the so-called full-flow staged combustion cycle. Typically, air and methane have been used in gas turbine engines to fuel high energy processes; however, in the presence of air, nitrous oxides © <2020> by ASME. This manuscript version is made available under the CC-BY 4.0 license http://creativecommons.org/licenses/by/4.0/ 3 and CO2 will inevitably form exhausting into the atmosphere. By combusting methane with pure oxygen (oxy-methane) in a closed-loop CO2 cycle, NOx formation and exhausted CO2 are eliminated. Instead, the CO2 product is isolated and available for sequestration, or bottling for industrial use, with remaining levels recycled back into the closed system as a combustion diluent. Running this described system at supercritical conditions can further cut costs and increase efficiency as the combined oxy-methane, with higher density supercritical CO2 diluent (sCO2), requires less pumping power for the same power output, while running with high power output comparable to conventional cycles (see refs. [2-7] for sCO2 power cycles). In a full-flow staged combustion cycle used in rocket engines, both oxidizer and fuel pre burners burn fuel lean and rich, respectively, in which all oxidizer and fuel flow through. Entering the main chamber are fuel-rich and oxygen-rich exhaust gases with products consisting of CO2 and H2O. As main combustion occurs in the presence of CO2, the chemical kinetic understanding of oxy-methane diluted with CO2 becomes important to accurately account for reactivity, especially at elevated pressures. SpaceX is in the midst of producing and testing such an engine, which is slated to operate at an astonishing chamber pressure of 300 bar – something that has never been achieved. This is the third engine ever to be developed and operational using the full-flow staged combustion cycle [8]; future endeavors and design optimizations will benefit from higher fidelity chemical kinetic mechanisms accounting for this reactivity. Although CH4 combustion is well understood across a variety of conditions and fuel loadings, the addition of CO2 adds additional complexity that has not been accounted for in chemical kinetic mechanisms, as none of the validation work has been done with CO2as a primary diluent [9]. Furthermore, the effects of high fuel loading and the associated ignition behavior with immense CO2 dilution have not been investigated in detail. Studies of oxy© <2020> by ASME. This manuscript version is made available under the CC-BY 4.0 license http://creativecommons.org/licenses/by/4.0/ 4 methane combustion with CO2 dilution have been performed in previous literature [10-17], though largely at intermediate to lower pressures [14, 18, 19] in a shock tube. For example, Hargis et al. has investigated oxy-fuel combustion within a high pressure shock tube at pressures from 1 to 10 atm and 1450 to 1900 K; it was observed that increasing the level of CO2led to increased bifurcation. Despite the presence of significant reflected-shock bifurcation in mixtures containing high levels of CO2, the resulting ignition delay times were commensurate with calculated temperature and pressure behind reflected shock waves [20]. Other studies of oxymethane mixtures include different levels of CO2 dilution, but with a final conclusion finding that as the amount of CO2 is increased, there is an insignificant, gradual increase in ignition delay time [14, 21, 22], though as Hargis et al. [20] explains, this becomes more apparent at higher pressures. In an effort to extend understanding of highly CO2dilute mixtures with high fuel loading, steps here are being made firstly at a moderate pressure with future work aimed at elevated pressures near 100 atm. In the current work, a highly CO2 diluted oxy-methane mixture was explored at pressures near 16 ± 2 atm and temperatures from 1044 – 1356 K. This mixture consisted of 16.67% CH4, 33.33% O2, and 50% CO2. The CO2 dilution was kept at a constant mole fraction of 0.5 in these experiments. The ignition delay times from these experiments were then compared to an oxymethane mixture utilizing N2 as a diluent consisting of 16.67% CH4, 33.33% O2, and 50% N2. All gathered data was also compared to predictions by kinetic mechanisms, GRI Mech 3.0 [9] and ARAMCO 2.0 [23]. To the best of our knowledge, this study presents new insights into oxymethane ignition with high levels of CO2 dilution and high fuel loading. © <2020> by ASME. This manuscript version is made available under the CC-BY 4.0 license http://creativecommons.org/licenses/by/4.0/ 5 EXPERIMENTAL METHOD All experiments were performed in the high purity, double-diaphragm shock tube facility located at the University of Central Florida in Orlando, Florida (see refs. [11, 18, 24-32]). This shock tube has an internal diameter of 14.17 cm. Both sections were separated by a polycarbonate, scored diaphragm. In some cases, a stacked, double-diaphragm arrangement was used to achieve desired experimental conditions. Before each experiment, both driver and driven sections were vacuumed down with Agilent DS102 rotary vane pumps to a rough level. The driven side was then further vacuumed down with an Agilent V301 turbomolecular pump; experiments were only proceeded with upon reaching a sufficient vacuum level on the order of 10-5 Torr or lower. Vacuum pressure was monitored with a convection and ion gauge from Kurt J. Lesker (KJL275804LL and KJLC354401YF, respectively). The velocity of the incident shock wave was measured using five time-of-arrival pressure transducers (PCB 113B26) spaced at the last 1.4 m of the driven section (Fig. 1), which were attached to four timer-counters (Agilent 53220A, 0.1 ns resolution); this calculated velocity was then extrapolated to the end wall section. With velocity known, the temperature (T5) and pressure (P5) behind the reflected shock wave were then calculated using the 1-D ideal shock relations. For all experiments, attenuation of the incident shock wave was found to be less than 2%/m. Mixtures were manometrically made using high purity gases from Praxair. Once the mixture was made, it was left to mix in a 33 L stainless steel mixing tank fitted with a magnetically-driven stirrer. One Baratron (MKS 628D) was used to measure partial pressure during mixture preparation, which has an accuracy of ±0.5%. © <2020> by ASME. This manuscript version is made available under the CC-BY 4.0 license http://creativecommons.org/licenses/by/4.0/ 6 The pressure behind the reflected shock wave was measured using sidewall mounted Kistler 603B1 and PCB 113B26 pressure transducers located approximately 2 cm from the end wall. At the same location emissions were measured with a New Focus UV photoreceiver (Model 2032) fitted with a 310 ±10 nm filter supplied by Edmund Optics (Stock #67-752) targeting the excited radical OH*. A CO2gas laser (Access Laser L4GS) was aligned through the shock tube to aid in defining time-zero, via schlieren spikes; this will be discussed further in the next section. Figure 2 shows the locations of these diagnostics. NONIDEALITIES OF THE SYSTEM Since all mixtures consisted of a diatomic (N2) or polyatomic (CO2) diluent, bifurcation was observed in all experiments. In these cases, a boundary layer forms lacking the necessary momentum (energy-deficient) to pass through the normal reflected shock wave and greatly interacts when compared to a monatomic bath gas like He or Ar. This interaction is more pronounced likely due to the increased molecular degrees of freedom. From Mark [33], it w

Using Gas-Driven Shock Tubes to Produce Blast Wave Signatures

Abstract: The increased incidence of improvised explosives in military conflicts has brought about an increase in the number of traumatic brain injuries (TBIs) observed. Although physical injuries are caused by shrapnel and the immediate blast, encountering the blast wave associated with improvised explosive devices (IEDs) may be the cause of traumatic brain injuries experienced by warfighters. Assessment of the effectiveness of personal protective equipment (PPE) to mitigate TBI requires understanding the interaction between blast waves and human bodies and the ability to replicate the pressure signatures caused by blast waves. Prior research has validated compression-driven shock tube designs as a laboratory method of generating representative pressure signatures, or Friedlander-shaped blast profiles; however, shock tubes can vary depending on their design parameters and not all shock tube designs generate acceptable pressure signatures. This paper presents a comprehensive numerical study of the effects of driver gas, driver (breech) length, and membrane burst pressure of a constant-area shock tube. Discrete locations in the shock tube were probed, and the blast wave evolution in time at these points was analyzed to determine the effect of location on the pressure signature. The results of these simulations are used as a basis for suggesting guidelines for obtaining desired blast profiles.

Laser-based CO concentration and temperature measurements in high-pressure shock-tube studies of n-heptane partial oxidation

Abstract: This paper presents a laser-based absorption technique for measuring temperature and CO concentration in high-pressure shock tubes. Two fundamental vibrations of CO (v" = 0, P8, 4.73 µm and v" = 1, R21, 4.56 µm) were selected for high-temperature sensitivity with a reduced influence from pressure broadening compared to previous work. Single-pass absorption (80 mm path length) was measured with two quantum-cascade lasers. The technique was demonstrated by measuring time-resolved temperature for non-reactive mixtures at 1100–1960 K and 1.2–9.7 bar. During partial oxidation of n-heptane, temperature and CO concentrations were measured with 4 µs time resolution at 1360–1670 K and 5.8–8.2 bar. Interference from broadband CO2 absorption was quantified and subtracted. Measured data in the burnout state are in excellent agreement with predictions from kinetics mechanisms (Mehl et al. Proc Combust Inst 33:193, 2011; Zhang et al. Combust Flame 172:116, 2016) over the entire range of operating conditions, which validates the performance of the current laser-absorption technique in reactive-mixture measurements. Additionally, time-resolved temperature and CO-concentration measurements agree well with predictions based on the Mehl et al. mechanism.