Showing papers on "Shock tube published in 2002"

Study of the High-Temperature Autoignition of n-Alkane/O/Ar Mixtures

Abstract: Ignition time measurements of propane, n-butane, n-heptane, and n-decane have been studied behind reflected shock waves over the temperature range of 1300-1700 K and pressure range of 1-6 atm. The test mixture compositionvaried from approximately 2-20% O 2 , and the equivalence ratio ranged from 0.5 to 2.0. To determine more precisely the fuel mole fraction of the test mixture, a new technique has been employed in which a 3.39-μm HeNe laser and multiple-pass setup is utilized to measure the fuel in situ by absorption. Ignition delay times were measured at the shock tube endwall by a CH emission diagnostic (431 nm) that viewed the shock-heated mixture through a window in the endwall. This enabled the ignition time at the unperturbed endwall conditions to be determined accurately, thereby avoiding problems inherent in measuring ignition times from the shock tube sidewall. A parametric study of the experimental data reveals marked similarity of the ignition delay time characteristics among these four n-alkanes, and a unique correlation is presented in which the stoichiometric ignition time data for all four n-alkanes has been correlated into a single expression with an R 2 value of 0.992: Τ=9.4×10 - 1 2 P - 0 . 5 5 X O 2 - 0 . 6 3 C - 0 . 5 0 exp(46,550/RT) where the ignition time is in seconds, pressure in atmospheres, the activation energy in calories per mole, X O 2 is the mole fraction of oxygen in the test mixture, and C is the number of carbons atoms in the n-alkane. Comparisons to past ignition time studies and detailed kinetic mechanisms further validate the correlations presented here.

PLIF flow visualization and measurements of the Richtmyer-Meshkov instability of an air/SF6 interface

Abstract: Investigations of the Richtmyer–Meshkov instability carried out in shock tubes have traditionally used membranes to separate the two gases. The use of membranes, in addition to introducing other experimental difficulties, impedes the use of advanced visualization techniques such as planar laser-induced fluorescence (PLIF). Jones & Jacobs (1997) recently developed a new technique by which a perturbed, membrane-free gas–gas interface can be created in a shock tube. The gases enter the shock tube from opposite ends and exit through two small slots on opposite sides of the test section, forming a stagnation point flow at the interface location. A gentle rocking motion of the shock tube then provides the initial perturbation in the form of a standing wave. The original investigation using this technique utilized dense fog seeding for visualization, which allowed large-scale effects to be observed, but was incapable of resolving smaller-scale features. PLIF visualization is used in the present study to investigate the instability generated by two incident shock strengths ( M s = 1.11 and 1.21), yielding very clear digital images of the flow. Early-time growth rate measurements obtained from these experiments are found to be in excellent agreement with incompressible linear stability theory (appropriately adjusted for a diffuse interface). Very good agreement is also found between the late-time amplitude measurements and the nonlinear models of Zhang & Sohn (1997) and Sadot et al . (1998). Comparison of images from the M s = 1.11 and 1.21 sequences reveals a significant increase in the amount of turbulent mixing in the higher-Mach-number experiments, suggesting that a mixing transition has occurred.

Advanced Hypersonic Test Facilities

Abstract: Hypersonic Ground Test Requirements Principles of Hypersonic Test Facility Development NASA's HYPULSE Facility at GASL The LENS I and II Hypervelocity Tunnels and Application to Hypersonic Vehicle Testing Under Fully Duplicated Flight Conditions The U-12 Large Shock Tube Detonation-Driven Shock Tubes and Tunnels Aerothermodynamics Research in the DLR High Enthalpy Shock Tunnel HEG Characteristics of the HIEST and its Applicability for Hypersonic Aerothermodynamic and Scramjet Research Piston Gasdynamic Units with Multicascade Compression Arc-Heated Facilities The SCIROCCO 70-MW Plasma Wind Tunnel Aerodynamic and Propulsion Test Unit Arc-Heated Facilities (LBK) as a Tool to Study Aerothermodynamic Problems of Reentry Vehicles The NASA Langley Research Center 8-ft High Temperature Tunnel NASA Glenn Research Center's Hypersonic Tunnel Facility The ONERA F4 High-Enthalpy Wind Tunnel The AEDC Hypervelocity Wind Tunnel 9 A Hypersonic Ground-Test Facility Using Magnetic Levitation and Electromagnetic Propulsion Recent Increases in Hypersonic Test Capabilities at the Holloman High Speed Test Track and Design of a Magnetically Levitated Test Track Capability Increased Launching Capabilities at AEDC's Range/Track G A New Mach 8-15 True Temperature Test Facility Concept to Meet the U.S. Shortfall in Hypersonic Test Capability New-Generation Hypersonic Adiabatic Compression Facilities with Pressure Multipliers

Rayleigh–Taylor instability of viscoelastic drops at high Weber numbers

Abstract: Movies of the breakup of viscous and viscoelastic drops in the high-speed airstream behind a shock wave in a shock tube have been reported by Joseph, Belanger & Beavers. They performed a Rayleigh-Taylor stability analysis for the initial breakup of a drop of Newtonian liquid and found that the most unstable Rayleigh-Taylor wave fits nearly perfectly with waves measured on enhanced images of drops from the movies, but the effects of viscosity cannot be neglected. Here we construct a Rayleigh-Taylor stability analysis for an Oldroyd-B fluid using measured data for acceleration, density, viscosity and relaxation time λ 1 . The most unstable wave is a sensitive function of the retardation time λ 2 which fits experiments when λ 2 /λ 1 = O(10 -3 ). The growth rates for the most unstable wave are much larger than for the comparable viscous drop, which agrees with the surprising fact that the breakup times for viscoelastic drops are shorter. We construct an approximate analysis of Rayleigh-Taylor instability based on viscoelastic potential flow which gives rise to nearly the same dispersion relation as the unapproximated analysis

Oxidation of small alkenes at high temperature

Abstract: If the mechanism of formation of alkenes, the main primary products of the combustion of alkanes above 1000 K, is now well understood, their ways of degradation have been much less studied. Following a previous modeling of the oxidation of propene in a static and a jet-stirred reactors by using an automatically generated mechanism, the present paper shows new validations of the same mechanism for ignition delays in a shock tube. It also describes the extension of the rules used for the automatic generation to the case of 1-butene. The predictions of the mechanism produced for the oxidation of 1-butene are compared successfully with two sets of experimental results: the first obtained in a jet-stirred reactor between 900 and 1200 K; the second being new measurements of ignitions delays behind reflected shock waves for temperatures from 1200 up to 1670 K, pressures from 6.6 to 8.9 atm, equivalence ratios from 0.5 to 2, and with argon as bath gas. Flux and sensitivity analyses show that the role of termination reactions involving the very abundant allylic radicals is less important for 1-butene than for propene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 666–677, 2002

Some recent finite volume schemes to compute Euler equations using real gas EOS

Abstract: This paper deals with the resolution by finite volume methods of Euler equations in one space dimension, with real gas state laws (namely, perfect gas EOS, Tammann EOS and Van Der Waals EOS). All tests are of unsteady shock tube type, in order to examine a wide class of solutions, involving Sod shock tube, stationary shock wave, simple contact discontinuity, occurrence of vacuum by double rarefaction wave, propagation of a one-rarefaction wave over ‘vacuum’, … Most of the methods computed herein are approximate Godunov solvers: VFRoe, VFFC, VFRoe ncv (τ, u, p) and PVRS. The energy relaxation method with VFRoe ncv (τ, u, p) and Rusanov scheme have been investigated too. Qualitative results are presented or commented for all test cases and numerical rates of convergence on some test cases have been measured for first- and second-order (Runge–Kutta 2 with MUSCL reconstruction) approximations. Note that rates are measured on solutions involving discontinuities, in order to estimate the loss of accuracy due to these discontinuities. Copyright © 2002 John Wiley & Sons, Ltd.

Combined cycle pulse detonation turbine engine

Abstract: A turbofan engine includes a pulse detonation system to create a temperature rise and a pressure rise within the engine to generate thrust from the engine. The system includes a pulse detonation augmentor including a shock tube sub-system. The shock tube sub-system includes a plurality of shock tubes which mix air and fuel introduced to the pulse detonation augmentor and detonate the mixture. The detonation creates hot combustion gases which are directed from the engine to produce thrust for the engine. Alternatively, the system includes a pulse detonation augmentation system that replaces a core engine of a turbo-fan engine.

Supersonic jet and shock interactions

Abstract: Supersonic fluid flow and the interaction of strong shock waves to produce jets of material are ubiquitous features of inertial confinement fusion (ICF), astrophysics, and other fields of high energy-density science. The availability of large laser systems provides an opportunity to investigate such hydrodynamic systems in the laboratory, and to test their modeling by radiation hydrocodes. We describe experiments to investigate the propagation of a structured shock front within a radiation-driven target assembly, the formation of a supersonic jet of material, and the subsequent interaction of this jet with an ambient medium in which a second, ablatively driven shock wave is propagating. The density distribution within the jet, the Kelvin–Helmholz roll-up at the tip of the jet, and the jet’s interaction with the counterpropagating shock are investigated by x-ray backlighting. The experiments were designed and modeled using radiation hydrocodes developed by Los Alamos National Laboratory, AWE, and Lawrence Livermore National Laboratory. The same hydrocodes are being used to model a large number of other ICF and high energy-density physics experiments. Excellent agreement between the different simulations and the experimental data is obtained, but only when the full geometry of the experiment, including both laser-heated hohlraum targets (driving the jet and counter-propagating shock), is included. The experiments were carried out at the University of Rochester’s Omega laser [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)].

Digital compensation of pressure sensors in the time domain

Abstract: This contribution presents an innovative technique to determine the transfer function of pneumatic and fast-response pressure probes. The dynamic response is determined experimentally with pressure step-tests. In the case of conventional instrumentation fast-opening valves or balloon explosions are used. For the fast-response pressure sensors, shock tube tests are performed. The response of the probe is fitted in the time domain with the response of an m-order linear system. This numerical system is then used to correct the lag and dynamic error of the measurement chain.

Observation of supersonic shock wave mitigation by a plasma aero-spike

Abstract: A wind-tunnel model in the shape of a 30° half-angle truncated-cone is designed to generate a strong bow shock behind a weak conical (oblique) shock wave attached to the tip of a protruding central-electrode, in a non-ionized supersonic flow. Plasma is generated between two shocks by an on-board discharge. Its effect on shock waves is explored. The results show that the plasma spike has drastically modified the original complicated shock structure to a simple structure having only a single conical shock attached to the tip of the model, similar to the one generated by a perfect cone.

High pressure, high temperature shock tube studies of ethane pyrolysis and oxidation

Abstract: A unique high-pressure single pulse shock tube has been used to obtain the first experimental data for ethane oxidation and pyrolysis at very high pressures and temperatures. Experiments were performed at two nominal reaction pressures of 340 bar and 613 bar in the temperature range 1050 K to 1450 K. The major stable species were identified and their concentrations determined using gas chromatography. Several minor species, with up to four carbon atoms and including oxygenates, were also observed in the oxidation studies. Three models based on literature mechanisms for hydrocarbon oxidation were used to simulate the experimental data. All of the models simulate the pyrolysis data well although only one of the models was capable of accurately describing the oxidation data.

Guided wave modes in porous cylinders: experimental results.

Abstract: In this paper guided wave modes in porous media are investigated. A water-saturated porous cylinder is mounted in the test section of a shock tube. Between the porous sample and the wall of the shock tube a water-filled annulus exists. For very small annulus width, bulk waves are generated and one-dimensional modeling is sufficient. Otherwise two-dimensional effects become important and multiple guided wave modes occur. Using a newly developed traversable positioning system in the shock tube, the frequency-dependent phase velocities and damping coefficients in the 1–120 kHz frequency range were measured. Prony’s method was used for data processing. Agreement was found between the experimental data and the two-dimensional modeling of the shock tube which was based on Biot’s theory.

Radiative Interaction Between Driver and Driven Gases in an Arc-Driven Shock Tube

Abstract: An electric-arc driven shock tube was operated with hydrogen as the driven gas and either hydrogen or helium as the driver gas. Electron density was measured behind the primary shock wave spectroscopically from the width of the Beta line of hydrogen. The measured electron density values were many times greater than the values calculated by the Rankine - Hugoniot relations. By accounting for the radiative transfer from the driver gas to the driven gas, the measured electron density values were numerically recreated.

Forward-Running Detonation Drivers for High-Enthalpy Shock Tunnels

Abstract: To improve the quality of driving flows generated with detonation-driven shock tunnels operated in the forward-running mode, various detonation drivers with specially designed sections were examined. Four configurations of the specially designed section, three with different converging angles and one with a cavity ring, were simulated by solving the Euler equations implemented with a pseudo kinetic reaction model. From the first three cases, it is observed that the reflection of detonation fronts at the converging wall results in an upstream-traveling shock wave that can increase the flow pressure that has decreased due to expansion waves, which leads to improvement of the driving flow. The configuration with a cavity ring is found to be more promising because the upstream-traveling shock wave appears stronger and the detonation front is less overdriven. Although pressure fluctuations due to shock wave focusing and shock wave reflection are observable in these detonation-drivers, they attenuate very rapidly to an acceptable level as the detonation wave propagates downstream. Based on the numerical observations, a new detonation-driven shock tunnel with a cavity ring is designed and installed for experimental investigation. Experimental results confirm the conclusion drawn from numerical simulations. The generated driving flow in this shock tunnel could maintain uniformity for as long as 4 ms. Feasibility of the proposed detonation driver for high-enthalpy shock tunnels is well demonstrated.

Shock wave modification via shock induced ion doping

Abstract: The present invention relates to an apparatus and method which partially ionizes a portion of the gas flow through a shock wave, employing the electrostatic forces produced by the resultant ion doped region in and behind the shock wave to reduce the intensify of the shock wave. Such a method or apparatus is detailed to be employed at the tips of a rotating compressor or turbine blade; to the flow through a gas duct in an aircraft engine inlet; at the tips of a propeller or rotorcraft blade or on the surfaces or an aircraft.

Spectral and structural properties of carbon nanoparticle forming in C3O2 and C2H2 pyrolysis behind shock waves

Abstract: The diversity of carbon particles, forming durin pyrolysis of C 3 O 2 and C 2 H 2 behind shock waves in thewide temperature range 1200–3800 K, was investigated. The process of condensed carbon particle formation was observed in situ by the multichannel registration of the time profiles of optical properties of media in the UV, visible, and near-IR ranges. Besides that, the probes of postshock materials, deposited on the walls of the shock tube, were analyzed bylow- and high-resolution transition electron microscopy (TEM) and by electron microdiffraction (MDF) measurements. The comparison of extinction properties of young growting particles with the electron microscopic analysis of solidified substance gave a notion about the peculiarities of carbon particle formation process from the diffeerent carbon-bearing gases at various temperatures. particles, forming from both substances at 1500–200 K, look similar to usual soot, and the absence of hydrogen in C 3 O 2 leads to faster formation and graphitization of particles. At the tempratures 2100–2600 K, the decrease of the paticle formation rate and the fall of final particle yield in all mixtures is observed. After C 3 O 2 pyrolysis experiments, gigantic film-like spheres with the size up to 700 nm were observed on the walls. The peculiarity of the high-temperature (2700–3200 K) process of carbon particle formation in C 3 O 2 pyrolysis is the high degree of crystallization of the final particles.

Numerical study of the lift force influence on two-phase shock tube boundary layer characteristics

Abstract: The importance of the lift force acting on the dispersed phase in the boundary layer of a laminar gas-particle dilute mixture flow generated by a shock wave is investigated numerically. The particle phase is supposed to form a continuum and is described by an Eulerian approach. The ability of the Eulerian model to simulate particle flows and the importance of the two-way coupling are proven by comparison with experimental data as well as with the numerical results from schemes based on a Lagrangian approach. The models used for the lift force are discussed through comparisons between numerical and experimental results found in the literature. Some results about the formation of a dust cloud are numerically reproduced and show the major role of the lift force. Simulations of two-dimensional two-phase shock tube flows are also performed including the lift force effects. Although the wave propagation is weakly influenced by the lift force, the force modifies substantially the dynamics of the flow near the wall.

A Shock Tube Study of Benzylamine Decomposition: Overall Rate Coefficient and Heat of Formation of the Benzyl Radical

Abstract: The decomposition rate of benzylamine (C6H5CH2NH2) and the heat of formation of the benzyl radical (C6H5CH2) were determined in shock tube experiments combined with RRKM calculations. To obtain the decomposition rate of benzylamine, the NH2 mole fraction was measured using frequency-modulation absorption spectroscopy behind reflected shock waves. The initial slope of the NH2 concentration is directly proportional to the decomposition rate and the initial concentration of benzylamine. The rate expression for the decomposition reaction for the temperature range 1225−1599 K and the pressure range 1.19−1.47 bar is k1 = (5.49 × 1014)e-33110/[T(K)] s-1 with an uncertainty of ±15%. To obtain the high-pressure-limit rate expression for benzylamine decomposition, we performed RRKM calculations using the parameters obtained from the experimental data of this study and those of the VLPP study of Golden et al.4 The resulting high-pressure-limit rate for the temperature range 1000−1600 K is k∞ = (1.07 × 1016.0)e-36470...

Experimental confirmation of the von Neumann theory of shock wave reflection transition

Abstract: For many years there has been debate regarding why shock wave reflection off a solid surface has allowed regular reflection to persist beyond the incidence angles where it becomes theoretically impossible. Theory predicts that at some limiting angle the reflection point will move away from the wall and Mach reflection will occur. Previous studies have suggested that the paradox could be due to the presence of the growing viscous boundary layer immediately behind the point of reflection, and some numerical studies support this view. This paper takes the approach of establishing an experimental facility in which the theoretical assumptions regarding the surface of reflection are met, i.e. that the reflecting surface is perfectly smooth, perfectly rigid, and adiabatic. This is done by constructing a bifurcated shock tube facility in which a shock wave is split into two plane waves that are then allowed to reflect off each other at the trailing edge of wedge. The plane of symmetry between the waves then acts as the perfect reflection surface.Through a careful set of visualization experiments, and the use of multivariate analysis to take account of the uncertainty in shock Mach number, triple-point trajectory angle, and slightly different shock wave arrival times at the trailing edge, the current work shows that the transition from one type of reflection to the other does indeed occur at the theoretical value. Conventional tests of reflection off a solid wall show significantly different transition results. Furthermore, it is also shown that the thermal boundary layer plays an important role in this regard. It is thus confirmed that viscous and thermal effects are the reason for the paradox. Reasons are also suggested for the counter-intuitive behaviour of the reflected shock wave angle.

Gas Turbine Engine Durability Impacts of High Fuel-Air Ratio Combustors: Part 2 — Near Wall Reaction Effects on Film-Cooled Heat Transfer

Abstract: As commercial and military aircraft engines approach higher total temperatures and increasing overall fuel-to-air ratios, the potential for significant chemical reactions on a film-cooled surface is enhanced. Currently there is little basis for understanding the effects on aero-performance and durability due to such secondary reactions. A shock tube experiment was employed to generate short duration, high temperature (1000–2800 K) and pressure (6 atm.) flows over a film-cooled flat plate. The test plate contained two sets of 35° film cooling holes that could be supplied with different gases, one side using air and the other nitrogen. A mixture of ethylene and argon provided a fuel rich freestream that reacted with the air film resulting in near wall reactions. The relative increase in surface heat flux due to near wall reactions was investigated over a range of fuel levels, momentum blowing ratios (0.5–2.0), and Damkohler numbers (ratio of flow to chemical time scales) from near zero to 30. For high Damkohler numbers, reactions had sufficient time to occur and increased the surface heat flux by 30 percent over the inert cooling side. When these results are appropriately scaled, it is shown that in some situations of interest for gas turbine engine environments significant increases in surface heat flux can be produced due to chemical reactions in the film-cooling layer. It is also shown that the non-dimensional parameters Damkohler number (Da), blowing ratio (B), heat release potential (H* ), and scaled heat flux (Qs ) are the appropriate quantities to predict the augmentation in surface heat flux that arises due to secondary reactions.Copyright © 2002 by ASME

Shock-planar curtain interactions in two dimensions: Emergence of vortex double layers, vortex projectiles, and decaying stratified turbulence

Abstract: Vortex double layers and vortex projectiles (VPs) are the essential coherent structures which emerge in the shock excited planar-parallel “curtain” (s/f/s) simulations of a two-dimensional shock tube with the piecewise parabolic method. These opposite signed layers, formed by shock induced baroclinic deposition of vorticity, “bind” and are strongly affected by secondary reflected shocks and vortex interactions. This versatile configuration, easily obtained in the laboratory, allows us to study the formation, evolution, and reacceleration of VPs and stratified turbulence and mixing.

Turbulence in Plasma-Induced Hypersonic Drag Reduction

Abstract: With the use of a pressure-ruptured shock tube, an experimental study of the dynamics of shock waves in weakly ionized argon, krypton, xenon, and neon glow discharge plasmas has been performed. For Mach numbers in the range 1.5 ‐3, our results show that there is an increase in the velocity of a shock wave when it makes a transition from a neutral gas to a weakly ionized plasma, and the effect increases with increasing atomic weight. The observations indicate that the shock acceleration cannot be accounted for by thermal effects. However, the useof turbulence models based on reduced kinetic theory and second-order phase transitions suggests a consistent role for turbulence in plasma-induced hypersonic drag reduction.

Combined cycle pulse detonation turbine engine operating method

Abstract: A turbofan engine includes a pulse detonation system to create a temperature rise and a pressure rise within the engine to generate thrust from the engine. The system includes a pulse detonation augmentor including a shock tube sub-system. The shock tube sub-system includes a plurality of shock tubes which mix air and fuel introduced to the pulse detonation augmentor and detonate the mixture. The detonation creates hot combustion gases which are directed from the engine to produce thrust for the engine. Alternatively, the system includes a pulse detonation augmentation system that replaces a core engine of a turbo-fan engine.