Showing papers on "Shock tube published in 1968"
TL;DR: In this article, a high speed liquid-solid impact based on particle velocity was studied, where the authors measured the shock wave velocity and pressure in high-speed liquid solid impact.
Abstract: Shock wave velocity and pressure in high speed liquid-solid impact based on particle velocity
91 citations
TL;DR: In this article, the authors measured the variation of density behind incident shock waves in carbon dioxide using a Mach-Zehnder interferometer at shock speeds of up to Mach 9 (2500°K) and showed that vibrational relaxation occurs to a state in which all vibrational modes are excited to their equilibrium values with neither the symmetric stretching nor the asymmetric stretching modes having significantly longer relaxation times than the bending mode.
Abstract: Measurements of the variation of density behind incident shock waves in carbon dioxide have been made using a Mach–Zehnder interferometer at shock speeds of up to Mach 9 (2500°K). The results show that vibrational relaxation occurs to a state in which all the vibrational modes are excited to their equilibrium values with neither the symmetric stretching nor the asymmetric stretching modes having significantly longer relaxation times than the bending mode. It has been found that the density does not change exactly exponentially with distance behind a shock front as has been assumed in the past. It has been shown that it is this assumption which led to the idea that the rate of vibrational relaxation depends not only on temperature, but also on the departure of the system from equilibrium. The present results can be accounted for if the relaxation time is a function of temperature alone. Relaxation times have been calculated taking account of the changes in the translational temperature which occur during the relaxation process. The results cover the temperature range 330°–1600°K.
36 citations
TL;DR: In this paper, an investigation of the nature of cold gas has been made by an infra-red absorption technique, and the time of arrival of driver gas at the end plate is measured from the absorption records and calculations based on a modification of the shock bifurcation model agree substantially with these experimental results.
Abstract: Following the first interaction between the reflected shock from the end wall and the advancing contact surface in a shock tube, cold gas has been observed at the end plate at a time much earlier than that predicted on the basis of simple shock tube theory. Investigation of the nature of this cold gas has been made by an infra-red absorption technique. The driver gas hydrogen is "tagged" with a small quantity of infrared active gas, and shocks are driven with this gas mixture into an infrared inactive test gas. The time of arrival of driver gas at the end plate is measured from the absorption records and calculations based on a modification of the shock bifurcation model agree substantially with these experimental results. Use is also made of an infrared absorption/emission technique to determine the temperature of the infrared source.
34 citations
TL;DR: In this paper, measurements of the electronic transition moment for the Swan A 3 Π g - X 3 - u bands have been made in emission behind incident shock waves in CO 2 -Argon gas mixtures.
Abstract: Measurements of the electronic transition moment for the C 2 (Swan) A 3 Π g - X 3 Π u bands have been made in emission behind incident shock waves in CO 2 -Argon gas mixtures. The value obtained at the (0, 0) head for the square of the dimensionless transition moment is 3·5 6 ±0·5 0 , corresponding to an absorption electronic ƒ-number of 0·035±0·005. The electronic transition moment' variation with internuclear separation is also discussed.
33 citations
TL;DR: In this article, the rate of damping of perturbations on a plane shock wave reflected from a perturbed flat wall was measured in a shock tube and compared with a modified form of a linearized theory due to Zaidel (1960).
Abstract: The rate of damping of perturbations on a shock wave reflected from a perturbed flat wall was measured in a shock tube. Incident shock wave Mach numbers of 1·45 and 1·09 in air together with sinusoidal and Gaussian wall perturbations were employed. These measurements were compared with a modified form of a linearized theory due to Zaidel (1960). The linearization was performed about the basic solution of a plane shock wave reflected normally from a flat wall.The rate of decay and the frequency and phase of oscillations agreed very well with the theoretical predictions; the amplitudes of the oscillations were some-what larger than predicted. The reflected shock shape was initially in good agreement with theory, but higher frequency perturbations on the reflected shock front caused deviations from the predicted shape after the shock front had travelled about one wall-wavelength away from the wall.The generally satisfactory agreement between theory and experiment supports the use of linearized analysis in predicting shock wave stability.
33 citations
TL;DR: In this article, the authors used optical interferometry to measure the density profile through the relaxation zone and infrared emission of CO added in small quantities to serve as an indicator of the degree of vibrational excitation of N2.
Abstract: Vibrational excitation in gas mixtures can occur both by translation‐to‐vibration (T–V) energy conversion in simple collisions and by the exchange of vibrational energy (V–V) between components. Nitrogen–oxygen mixtures containing 5%, 10%, 21%, 33%, and 50% O2 have been studied in a shock tube using both optical interferometry to measure the density profile through the relaxation zone and infrared emission of CO added in small quantities to serve as an indicator of the degree of vibrational excitation of N2. The density increase has been resolved into the sum of short and long time‐constant exponentials. The former is approximately that expected from excitation of the O2 component. The longer time constant of the increasing density is approximately that observed for the infrared emission of CO and is thus indentified with the N2 excitation. This latter is found to be more rapid than can be accounted for by a T–V process and therefore vibrational exchange with excited O2 must contribute signficantly. Data ...
27 citations
TL;DR: UV Fe I, Cr I and II lines gf values obtained by flash absorption spectroscopy on pressure driven shock tube were obtained by as discussed by the authors, where the flash was applied to the shock tube.
Abstract: UV Fe I, Cr I and II lines gf values obtained by flash absorption spectroscopy on pressure driven shock tube
26 citations
TL;DR: In this article, a statistical review of all the current data available on the homogeneous oxidation of ammonia indicates that the activation energy is more precisely 37·7 ± 2·6 kcal mole−1.
26 citations
25 citations
TL;DR: In this article, the vibrational relaxation of nitrous oxide has been investigated by following the density changes occurring behind incident shock waves using a Mach-Zehnder interferometer.
Abstract: The vibrational relaxation of nitrous oxide has been investigated by following the density changes occurring behind incident shock waves using a Mach–Zehnder interferometer. Measurements made up to an equilibrium temperature of 1700°K (Mach 7) show that neither the symmetric stretching mode nor the asymmetric stretching mode has a significantly longer relaxation time than the bending mode. The rate of relaxation has been measured as the gas relaxes towards equilibrium. During this process, the translational temperature of the gas falls, and it has been found that this fall in temperature will account for the observed increase of the relaxation time. Relaxation times have been measured from 320° to 850°K.
TL;DR: F values of bands of carbon monoxide fourth positive system using aerodynamic shock tube operated with self rupturing diaphragm were reported in this article, using a self-destructive self-surging diaphrasal valve.
Abstract: F values of bands of carbon monoxide fourth positive system using aerodynamic shock tube operated with self rupturing diaphragm
TL;DR: In this paper, the double diaphragm technique was used in conjunction with a free piston driver to achieve a shock Mach number of 50, which is the highest known for a single piston driver.
Abstract: DIAPHRAGM-TYPE shock tubes have been widely used in studies of gases at high temperatures1,2. Their particular virtue is that they produce a reasonably homogeneous sample of test gas, with known properties, in the region between the shock wave and the interface zone. But one disadvantage is that the speed of the shock wave produced, and hence the temperature in the gas sample, is limited by the temperature of the driver gas. Substantial efforts have been made to increase driver gas temperatures. Among these, heating by an arc discharge has produced shock Mach numbers of approximately 40 (ref. 3), while heating by free piston compression4 has yielded values of approximately 30. It has been realized for some years that shock wave heating, using the double diaphragm technique5,6, afforded a means of improving the performance of shock tubes. Model experiments are reported here which show that this principle can be used, in conjunction with a free piston driver, to achieve shock Mach numbers of 50.
01 Apr 1968
TL;DR: Relationship of shock standoff distance, at sonic and stagnation points, to body geometry of blunt bodies at zero angle of attack was explored in this article, where the body geometry was modeled as a triangle.
Abstract: Relationship of shock standoff distance, at sonic and stagnation points, to body geometry of blunt bodies at zero angle of attack
TL;DR: In this article, the authors measured the acceleration of normal ionizing shock waves produced in a coaxial electromagnetic shock tube and found that they exhibit the Chapman-Jouguet behavior, with current flow in the shock front, and no separation of shock and drive currents.
Abstract: Experiments have been conducted on normal ionizing shock waves produced in a coaxial electromagnetic shock tube. Steady shock velocities were measured as a function of initial gas pressure, drive current, and applied axial magnetic field. The speeds agreed well with theoretical values. Measurements were made of the switch‐on magnetic field, the upstream transverse electric field, and the density ratio across the front. The data all show that trans‐Alfvenic shocks (uA l f1 < us ≲ 3uA l f1) exhibit Chapman‐Jouguet behavior, with current flow in the shock front, and no separation of shock and drive currents. In contrast, super‐Alfvenic shocks (us ≳ 3uA l f1) appear to be gas dynamic in nature. Spectroscopic measurements and shock‐reflection studies demonstrated the presence of a nonluminous front and shock‐heated gas preceding the luminous drive current.
TL;DR: In this paper, the interaction of gaseous shock and detonation waves with liquid layers has been studied in a shock tube in order to elucidate the ignition mechanism in heterogeneous systems consisting of a liquid fuel film and a gas oxidizer.
TL;DR: In this article, a simulation of rocket exhaust plumes and effects on vehicles in space environment is presented, where the authors simulate a shock tube simulation of the plume and the effects on the vehicles in the environment.
Abstract: Shock tube simulation of rocket exhaust plumes and effects on vehicles in space environment
TL;DR: In this paper, a linearised solution of the unsteady one-dimensional conservation equations is obtained which describes the variations in the average flow properties external to the boundary layer, and a simple method of estimating shock tube test times is outlined, based on self similar solutions of the constant shock speed analysis.
Abstract: A theoretical and experimental investigation of the limitation on shock tube test times which is caused by the development of laminar and turbulent boundary layers behind the incident shock is presented. Two theoretical methods of predicting the test time have been developed. In the first a linearised solution of the unsteady one-dimensional conservation equations is obtained which describes the variations in the average flow properties external to the boundary layer. The boundary layer growth behind the shock is related to the actual extent of the hot flow and not, as in previous unsteady analyses, to its ideal extent. This new unsteady analysis is consequently not restricted to regions close to the diaphragm. Shock tube test times are determined from calculations of the perturbed shock and interface trajectories. In the second method a constant velocity shock is assumed and test times are determined by approximately satisfying only the condition of mass continuity between the shock and the interface. A critical comparison is made between this and previous theories which assume a constant velocity shock. Test times predicted by the constant shock speed theory are generally in agreement with those predicted by the unsteady theory, although the latter predicts a transient maximum test time in excess of the final asymptotic value. Shock tube test times have also been measured over a wide range of operating conditions and these measurements, supplemented by those reported elsewhere, are compared with the predictions of the theories; good agreement is generally obtained. Finally, a simple method of estimating shock tube test times is outlined, based on self similar solutions of the constant shock speed analysis.
TL;DR: In this paper, high frequency net ionization rates in hot air were determined as a function of field strength by measurements in a shock tube and the equilibrium air temperature was 3350°K±350°.
Abstract: High‐frequency net ionization rates in hot air were determined as a function of field strength by measurements in a shock tube. The equilibrium air temperature was 3350°K±350°. The rates were deduced from time‐resolved measurements of the electron density in hot air when exposed to the pulsed fields on microwave slot antennas. The rates in equilibrium hot air were found to be higher than the rates in room‐temperature air by more than a factor of ten. The ionization rates are shown to increase from the room‐temperature values to the equilibrium hot‐air values during the first few mean free paths behind the shock front.
TL;DR: In this article, the results of an experimental investigation of the reflection of strong shocks in xenon from the end wall of a shock tube are presented. But the results are limited to the case of a single tube.
Abstract: The results of an experimental investigation of the reflection of strong shocks in xenon from the end wall of a shock tube are presented. The reflection of the incident shock structure, consisting of a frozen shock front, a region of relatively uniform frozen flow, and an ionization front, was observed with a fast‐rise (0.3 μsec) pressure gauge mounted in the shock‐tube end wall. The incident shock Mach number was varied from 11‐20, and the initial pressure was varied from 0.1‐1.5 mm Hg. The interaction between the reflecting shock and the ionizing gas in the incident shock structure produces a complicated series of shock and rarefaction waves; those waves that propagate back to the end wall were observed with the pressure gauge. A simple model which includes the gross features of the shock reflection process is used to calculate end wall pressures. The calculated pressures agree well with the experimental observations. In addition, ionization relaxation times for xenon behind the incident and reflected s...
TL;DR: In this paper, the authors measured the total pressure and static pressure in a magnetically driven shock tube at an initial pressure range of 50-200 μHg and found that the static pressure was approximately equal to the drive magnetic pressure.
Abstract: Measurements of total pressure and static pressure were taken in a magnetically driven shock tube at an Alfven Mach number of M1≈0.66 in air at an initial pressure range of 50–200 μHg. Total pressure measurements ranged from 0.3–0.8 of the Newtonian pressure based on an equilibrium real gas density ratio. A small separation between the shock and drive current sheet was detected over the range of initial pressures, but was not always repeatable. The static pressure was measured and found to be approximately equal to the drive magnetic pressure.
TL;DR: Quantitative determination of reentry shock precursor absorption level and effect on surface radiation heating, calculating radiative flux from shock layer enthalpy distribution is presented in this paper, where the authors also consider the effect of surface radiation on reentry.
Abstract: Quantitative determination of reentry shock precursor absorption level and effect on surface radiation heating, calculating radiative flux from shock layer enthalpy distribution
TL;DR: Flow fields construction for normal shock waves with nonequilibrium chemical reactions reflected from shock tube end wall is described in this article, where the authors propose a flow field construction method for normal wave propagation.
Abstract: Flow fields construction for normal shock waves with nonequilibrium chemical reactions reflected from shock tube end wall
TL;DR: In this article, an inverse pinch electromagnetic shock tube was used to measure the current sheet and the shock wave trajectories of argon, helium, and hydrogen in an inverse-pinch electromagnetic tube, and the electron number density was determined by using the Stark broadening effect on spectral lines.
Abstract: Experiments were performed in argon, helium, and hydrogen in an inverse pinch electromagnetic shock tube The current sheet and shock wave trajectories were measured by using magnetic pickup coils and piezoelectric pressure probes, respectively, and the electron number density was determined from electrostatic probes and by using the Stark broadening effect on spectral lines The experimental parameters vary from conditions where the dominant heating mechanism in Ohmic dissipation to those where shock heating is greater Snowplow speed for the current sheet is measured in all cases and low levels of ionization within the sheet were observed for the conditions where Ohmic dissipation was the only heating mechanism A description of how a current sheet with a low degree of ionization can sweep up the gas it encounters (snowplow) is given
TL;DR: In this paper, the gas phase oxidation of n-pentane was investigated in a chemical shock tube and the formation of peroxidic products was determined as a function of time, reaction temperature and mixture composition.
TL;DR: In this article, a series of shock-tube experiments was carried out to determine the evaporation rate of submicron platinum particles suspended in xenon-argon and pure xenon carrier gases.
Abstract: A series of shock‐tube experiments was carried out to determine the evaporation rate of submicron platinum particles suspended in xenon‐argon and pure xenon carrier gases. The particle suspensions were produced by electrically exploding platinum wire in the carrier gases in a chamber attached to the end of the shock tube. Visible radiation from the shock‐heated aerosols was recorded by a drum camera viewing a strip along the centerline of the shock tube and by a photomultiplier viewing a point near the shock‐tube end wall. The duration of the short pulse, ∼100 μsec, of intense continuum radiation behind the reflected shock was used to determine approximately the evaporation time of the particles and, more precisely, the temperature dependence of the particle‐evaporation time. The experimental results confirmed an analytical prediction that the platinum particles could be vaporized readily in the short high‐temperature residence time available in a shock tube. Furthermore, since the experimental temperatur...
24 Jun 1968
TL;DR: In this paper, a chemical kinetic model describing photochemical reactions that are likely to be important in "cold" argon ahead of a strong shock wave is examined on a quantitative basis, including the propagation of resonance radiation far from the nucleus, the shock front in the wings of the resonance absorption line, partial trapping of the absorbed resonance, subsequent photoionization of excited atoms, photoionisation of ground state argon, and certain recombination and deexcitation processes.
Abstract: A chemical kinetic model describing photochemical
reactions that are likely to be important
in "cold" argon ahead of a strong shock wave is examined
on a quantitative basis. The model includes
the propagation of resonance radiation far from the
shock front in the wings of the resonance absorption
line, partial trapping of the absorbed resonance
radiation, subsequent photoionization of excited
atoms, photoionization of ground state argon,
and certain recombination and deexcitation processes.
Specific consideration is given to shock
tube geometry, the occurrence of both nonequilibrium
and equilibrium regions of variable lengths
behind the pressure discontinuity, and the (experimentally)
known shock tube wall reflectivity. Theoretical
predictions of electron and excited atom
concentrations ahead of the shock wave are presented
for typical shock tube operating conditions.