Driver Gas Research Articles

Fluorescence Imaging of Rotational and Vibrational Temperature in Shock-Tunnel Nozzle Flow

Two-dimensional rotational and vibrational temperature measurements were made at the nozzle exit of a free-piston shock tunnel using planar laser-induced fluorescence. The Mach 7 flow consisted predominantly of nitrogen with a trace quantity of nitric oxide. Nitric oxide was employed as the probe species and was excited at 225 nm. Nonuniformities in the distribution of nitric oxide in the test gas were observed and were concluded to be due to contamination of the test gas by driver gas or cold test gas.The nozzle-exit rotational temperature was measured and is in reasonable agreement with computational modeling. Nonlinearities in the detection system were responsible for systematic errors in the measurements. The vibrational temperature was measured to be constant with distance from the nozzle exit, indicating it had frozen during the nozzle expansion.

Driver gas contaminationin a detonation-driven reflected-shock tunnel

A computational study has been carried out to examine the effects of driver gas contamination in the NASA HYPULSE facility at GASL when operating with a detonation driver in reflected-shock tunnel mode. Unlike high-enthalpy shock tunnels which use helium as a driver gas, the driver gas in a detonation driver consists of a mixture of water vapour and argon, which has very different chemical and thermodynamic properties than those of helium. The purpose of the present work is to quantitatively evaluate the effects of driver gas contamination on the flow properties in the test section. Two computational analyses have been performed. The first analysis examined the nozzle flow under the influence of a prescribed level of driver gas contamination. In the second analysis, the transient development of the driver gas leakage in the reflected-shock region in the shock tube is studied. The unique flow features brought about by the detonation-driver gas and the method for detecting the contamination are discussed.

3107 ドライバのアクセルペダル操作に基づく新しいブレーキ支援システム

3107 ドライバのアクセルペダル操作に基づく新しいブレーキ支援システム

Radiative interaction between driver and driven gases in an arc-driven shock tube

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.

3315 イクスパンション管有用性向上のための新たな試み

In order to improve the performance and usefulness of an expansion tube, a new trial of controlled diaphragm rupture has been examined. An 80 mm x 80 mm square duct is used as the driven section of a shock tube. The ambient air acts as the driver gas, and is separated with a single or a few layers of diaphragm made either of Mylar, cellophane or polyethylene. The diaphragm is ruptured by irradiating a single pulse laser beam of 380 J energy on to it. The results of the experiments are reported here.

Study on Performance of Detonation-Driven Shock Tube

A detonation-driven shock tube firstly designed by H.R. Yu is considered to be a useful apparatus for producing high-enthalpy flow. In this apparatus, a strong shock wave is generated by detonating an oxygen-hydrogen mixture (oxy-hydrogen) and the driver gas temperature and pressure are extremely high compared with those of a conventional shock tube. However, the structure of the detonation wave is not uniform, e.g., the detonation wave has three-dimensional cellular structures and multiple transverse waves. Furthermore, the detonation wave is followed by a Taylor expansion fan and the performance of detonation-driven shock tube is not well understood. In this preliminary study, a detonation-driven shock tube is constructed and its performance is experimentally investigated by measuring pressure histories and the profile of the ionization current behind the detonation wave

Numerical Analysis of Reducing Driver Gas Contamination in Impulse Shock Tunnels

A numerical analysis was carried out to study the interaction of the reflected shock with incident boundary layer and contact surface in reflected shock tunnels and the driver gas contamination of the hot flow, in tailored conditions. Navier-Stokes equations were solved with a multiblock finite volume method in a shock tube and a nozzle. Different suction devices, such as a corner slit, a corner slit prolongated by a sleeve, and a conical ring, were tested for their capability of delaying this contamination effect. The results show that the driver gas passes through a bifurcated shock foot as a jet and causes premature contamination of the driven gas. They also show why the suction induced by a corner slit is inefficient for delaying the contamination. Located just behind the bifurcated shock foot after the shock/interface interaction, the sleeve device captures driver gas upstream and leads to an improvement in the driver gas arrival time by a factor of 1.8. Finally, based on the present numerical investigation, a new conical ring device is proposed, with a horizontal and vertical suction, which further increases this factor to 2.5

Optimization of a compact two-stage light-gas gun aiming at a velocity of 9 km/s

We developed a compact two-stage light-gas gun and optimized several operating parameters for aiming at velocities higher than 9 km/s. A firing test achieved a velocity of 6.2 km/s using helium as driver gas with a projectile weighing 0.6 g and a piston weighing 430 g. In the case of firing tests using hydrogen, a velocity of 8.1 km/s was obtained under the same condition. Moreover, it was found that higher velocities could be achieved by using a lighter piston to increase piston velocities, and that the efficiency of acceleration strongly depended on the initial gas pressure for each piston. Finally, a projectile velocity of 8.9 km/s was achieved using a piston weighing 290 g.

Numerical analysis of reducing driver gas contamination in impulse shock tunnels

Numerical analysis of reducing driver gas contamination in impulse shock tunnels

Test Time Increase by Delaying Driver Gas Contamination for Reflected Shock Tunnels

A gasdynamical detectorhas been applied to measure thearrival timeof driver gas in a low concentration in the testsectionofa high-enthalpyshock tunnel. Thedetection determines theusefultesttimewith uncontaminated test gas for a wide range of specie c reservoir enthalpies. Effects of over- or undertailored interface condition on severe contaminationhavebeeninvestigated.Itisexperimentallydemonstratedthatovertailoredinterfaceoperationmust beavoided toachievethetestdurationnecessary foraerodynamicmeasurements,especially forhigh-enthalpy e ow. Theinterfacecondition isoptimized forthelongesttesttimeattainable. Asan activemethod fordelaying drivergas contamination,adevicetotrapthedrivergasattheendoftheshocktubehasbeentriedforanovertailoredcondition. The method, however, causes the contamination to occur earlier. A modie ed device using a sleeve to capture driver gas upstream has been developed. Results with the longest sleeve tested show that strong contamination is dramatically delayed and that the uncontaminated test time is signie cantly increased. Nevertheless, improved test times are still shorter than the test time without the device at a slightly undertailored condition.

Characteristics of an annular vertical diaphragmless shock tube

Abstract. This paper reports on the characteristics of a compact vertical diaphragmless shock tube, which was constructed and tested in the Shock Wave Research Center to study experimentally the behavior of toroidal shock waves. It is 1.15 m in height and has a self-sustained co-axial vertical structure consisting of a 100 mm i.d. outer tube and an 80 mm o.d. inner tube. To create a ring shaped shock wave between the inner and outer tubes, a rubber sheet is inserted to separate a high pressure driver gas from a test gas, which is bulged with auxiliary high pressure helium from the behind. When the rubber membrane is contracted by the sudden release of the auxiliary gas so as to break the seal, shock waves are formed. Special design features of the shock tube are described and their role in producing repeatable shock waves is discussed. Its special opening characteristics make possible the production of annular shaped shock waves that are unlikely met with a conventional tube that uses rupturing diaphragms. Performance of the shock tube is evaluated in terms of the shock wave Mach numbers and the measured flow properties. It eventually showed a higher degree of repeatability and the scatter in the shock wave Mach numbers Ms was found to be 0.2% for Ms ranging from 1.1 to 1.8. The shock wave Mach number so far measured agreed very well with the simple shock tube theory.

Unstarted Inlet for Direct-Connect Combustor Experiments in a Shock Tunnel

Despite the very short flow duration, it is possible to conduct direct-connect combustor experiments in impulse facilities by using an unstarted converging-diverging nozzle located in the freestream flow. Such an unstarted inlet contains a very large subsonic region, which would be expected to require considerable time to establish and reach steady flow. Pressure measurements indicate that steady flow was achieved after approximately 1.5 ms of freestream flow, which at low tunnel enthalpies leaves sufficient time for meaningful combustor measurements to be made before driver gas arrival.

Experimental study on the tuned operation of a free piston driver

An experimental study of the tuned operation of a free-piston driver is described. Two series of experiments were carried out. The first was performed to validate a theory which has been developed recently to predict the operation with a small free piston-driver named NAL-CTA. The driver has a transparent window at the end of the compression tube to allow observation of piston motion. In the second, a theoretically determined length of piston buffer was used to tune the operating condition. Piston collision speeds of less than 3 m/sec were observed. A quasi-one-dimensional numerical code including leakage of driver gas through the piston clearance gap was derived. The numerical result agreed well with the experimental result. It is concluded that tuned operation, by using an appropriate length of the piston buffer, can be extrapolated to large-size tunnels.

Test time increase by delaying driver gas contamination for reflected shock tunnels

Test time increase by delaying driver gas contamination for reflected shock tunnels

A Study on Performance of a Detonation-Driven Shock Tube.

A detonation-driven shock tube firstly designed by H.-R. Yu, is considered as a useful facilities capable of producing high-enthalpy flow. In this apparatus, a strong shock wave is generated by detonating oxygen-hydrogen (oxyhydrogen) mixture and has characteristics that temperature as well as pressure of driver gas is extremely high compared with conventional shock tubes. However, a structure of detonation wave is not uniform e.g., detonation wave has three-dimensional cellular structures and multiple transverse waves. Furthermore, the detonation wave is followed by a Taylor expansion fan and performance of detonation-driven shock tube is not well understood. In this preliminary study, a detonation-driven shock tube is constructed and its performance is experimentally investigated by measuring pressure histories and a profile of ionization current behind detonation wave. As a result, (i) the pressure histories of detonation wave is clarified and it shows reasonable agreement with a result obtained by KASIMIR shock tube simulation code. (ii) A propagation velocity of detonation wave is coincided well with theoretical predictions assuming Chapman-Jouguet detonation wave. (iii) An equivalence ratio of oxyhydrogen mixture to produce a highest Mach number of the shock wave is evaluated as 〓≃1.7.

A two-stage free-piston driver

The overall cost of free-piston driven facilities can be substantially reduced if the contraction between the compression and shock tubes is replaced with a constant area section. However, with such an implementation, a new driver concept is required in order to achieve a realistic facility length. This paper describes a new free-piston driver type for expansion tubes which satisfies the above criteria. The technique is known as the two-stage free-piston driver where the driver gas is compressed in two distinct stages with a unique compound piston design. A new facility has been constructed (X-2) which is described in some detail. A quasi-one-dimensional numerical model of the compression process is also developed which agrees well with driver tube experimental results. This new driver is coupled to an expansion tube arrangement where super-orbital test flows are generated. The results show that a two-stage free-piston driver is capable of driving hypervelocity expansion tubes and therefore new facilities of increased size but reduced cost are now possible.

高温衝撃風洞における駆動気体汚染の測定

Driver gas contamination in high-enthalpy shock tunnels has been detected using a gasdynamical device composed of a duct and a wedge. The detection technique was developed in the T 5 shock tunnel, and a detector has been newly designed for use in the HEK and HIEST shock tunnels with some modifications. Driver gas in low concentration is satisfactorily detected at the test sections of both shock tunnels. The detector allows the flow visualization of duct internal flow, and a sequence of Schlieren pictures during a shot gives a better understanding of unsteady duct choking phenomena. Futhermore, the useful test time is compared among three shock tunnels and the optimum length-to-diameter ratio of shock tube is discussed.

Three‐dimensional propagation of coronal mass ejections (CMEs) in a structured solar wind flow: 1. CME launched within the streamer belt

A three‐dimensional (3‐D) numerical hydrodynamic model is used to investigate the temporal and spatial evolution of large‐scale solar wind structures. A tilted‐dipole outflow configuration is specified at the inner boundary near the Sun, and a structured, corotating solar wind (SW) flow is established by dynamic relaxation. Time‐dependent variation of the pressure and velocity at the inner boundary is applied to generate transient structures within the streamer belt. The dynamical interaction of a coronal mass ejection (CME) with the corotating coronal streamer belt flow between 0.14 and 5.04 AU is then investigated. Numerical results show that the motion and appearance of a CME can be strongly affected by its interaction with the velocity and density structure of the background SW. The initial shape and density distribution of the CME is distorted in all dimensions; it is compressed where, the CME is trapped between slow streamer belt and high‐speed coronal hole flows, and it is distended where the CME penetrates into the trailing edge of the preceding high‐speed stream. Thus a given CME can be observed with substantially different properties at different locations; the shock strength as well as the stand‐off distance between the shock front and the CME driver gas can vary considerably across the structure, and the density profile through the disturbance can adopt different forms depending on location. Merging of CME and corotating interaction region shocks and thermodynamic structures as demonstrated in this simulation complicate the interpretation of single‐spacecraft observations.

The converging gas flow driven by metal jets

Abstract The converging gas flows induced by the explosion of a cylindrical explosive shell produce high pressure conditions near the focusing point. After the imploding shocks reflect at the center, the compressed gas diverges outwards and the energy density is suddenly reduced. This is caused by the driver gas density being too low to confine the high pressure gas in a small area. In this paper, the focusing method utilizing the shaped charges is described and the results of the converging run are presented. The metal jet generated by the shaped charge worked as well as a converging piston.

Microwave detection of molecules formed by shock wave induced reactions

The paper describes experimental investigations in a shock tube concerning the formation of new molecules using He as a driver gas and a mixture of Kr, CH\(_4\) and NH\(_3\) as driven gas, where Kr serves as diluant. By microwave absorption technique it was possible to detect HCN, CH\(_2\)O and CH\(_3\)NH\(_2\) as reaction products. Obviously, these molecules were formed in the plasma behind the shock wave. In addition, the “swan bands” of C\(_2\) have been observed with optical methods.