ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-2153
    Keywords: Cryogenic gaseous detonations ; H2-O2 detonability ; Critical energy ; Spherical detonation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Critical conditions for the direct initiation of self-sustained detonation in cryogenic hydrogen-oxygen mixtures are examined experimentally. These initial conditions are expected to depend mainly on four parameters: the equivalence ratio of the mixture, the amount of the initial energy deposition, the initial temperature and pressure of the mixture. These critical conditions are determined by fixing alternatively three of these parameters and varying the fourth one from subcritical to supercritical detonation conditions. Results are presented for initial pressuresP o and equivalence ratios Φ ranging from 0.3 to 1 bar and from 1 to 2 respectively, for the two initial temperaturesT o, 123 K and 293 K. These results indicate that for the lowest values of the initial pressure, a decrease of initial temperature may favour the onset of detonation. Whatever the initial conditions, the measured detonation pressures and velocities are in reasonably good agreement with the corresponding Chapman-Jouguet values computed using the ideal-gas equation of state.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Shock waves 4 (1995), S. 339-345 
    ISSN: 1432-2153
    Keywords: Supersonic combustions ; Oblique shocks ; Oblique detonations ; H2-Air combustion ; Flame stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract In order to study the mechanisms of initiation and stabilization of H2-Air combustions (stoechiometric mixture initially atT 0=293 K andp 0=0.5 bar) in supersonic flow conditions behind an oblique shock wave (OSW), an original technique is used where OSW is generated in this mixture by the lateral expansion of the burnt gas behind a normal CJ gaseous detonation propagating into a bounding reactive mixture. Four Mach numberM of propagation of OSW are considered in the study, namelyM=7.7-6.1-4.4 and 3. Depending on the Mach numberM and inclinaison angleθ of OSW different regimes of combustion may occur in the driven mixture. For high values ofM (6.1 and 7.7) delayed steady overdriven oblique detonation waves (SODW) were obtained with a near CJ detonation wave as the critical regime. It was found that SODW obtained correspond quite well to prediction of the polar method. When thermal conditions behind the OSW are lower, either for high Mach number 6.1 and 7.7 for smaller angleθ than the previous case, or for lower Mach number, 4.4 and 3, the flame initiated at the apex is stabilized as a turbulent oblique flame behind the OSW. With much lower conditions, no combustion appears in the H2-Air mixture.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1432-2153
    Keywords: Reduced reaction mechanism ; Reactive shock wave ; Blast wave flows ; Methane combustion ; Hydrocode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract A finite rate chemistry solver usually consumes the largest part of the computing time in the numerical simulation of reactive flows. To reduce these costs, a global simulation method has been developed for systematically simplifying detailed reaction mechanisms and a reduced reaction mechanism for CH4−O2 is presented. This reduced mechanism accurately replicates the associated detailed mechanism whilst significantly reducing the required computing time. A shock induced methane combustion problem is computed by coupling the reduced reaction mechanism to a 1-D viscous compressible flow solver. As a comparison, a simulation of non-reactive shock flow having the same initial conditions is also performed. These calculations reveal some of the key features found in reactive shock flows.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-2153
    Keywords: Detonations ; Velocity deficits ; Porous media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Experiments have been carried out to determine the dependence of the detonation velocity in porous media, on mixture sensitivity and pore size. A detonation is established at the top end of a vertical tube and allowed to propagate to the bottom section housing the porous bed, comprised of alumina spheres of equal diameter (1–32 mm). Several of the common detonable fuels were tested at atmospheric initial pressure. Results indicate the existence of a continuous range of velocities with change in Φ, spanning the lean and the rich propagation limits. For all fuels in a given porous bed, the velocity decreases from a maximum value at the most sensitive mixture near Φ≈1 (minimum induction length), toV/V CJ≈0.3 at the limits. A decrease in pore size brings about a reduction inV/V CJ and a narrowing of the detonability range for each fuel. For porous media comprised of spherical particles, it was possible to correlate the velocity data corresponding to a variety of different mixtures and for a broad range of particle sizes, using the following empirical expression:V/V CJ=[1–0.35 log(d c /d p)]±0.1. The critical tube diameterd c is used as a measure of mixture sensitivity andd p denotes the pore diameter. An examination of the phenomenon at the composition limits, suggests that wave failure is controlled by a turbulent quenching mechanism.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1432-2153
    Keywords: Detonation ; Ram accelerator ; Shock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Time-accurate numerical simulations are used to study the dynamic development of oblique detonations on accelerating projectiles in ram accelerators. These simulations show that the oblique detonation can be stabilized on the projectile. The high pressure generated behind the detonation can result in accelerations up to 106G and propel the projectile to velocities higher than 4.0 km/s. The detonation structure on the projectile is sensitive to the projectile geometry. A small change in the projectile shape is sufficient to alter the overall detonation structure and significantly affect the pressure distribution on the projectile. In order to maximize the thrust, an appropriate projectile shape has to be chosen to generate the detonation structure just behind the widest part of the projectile body. The projectile acceleration also has strong effects on the flow field and the detonation structure. During the acceleration, the location of the oblique detonation moves upstream from one reflected shock to another. However, one the detonation is stabilized behind the upstream shock, it remains at the new location until the transition to the next upstream shock occurs. In the simulations, the Non-Inertial-Source (NIS) technique was used to accurately represent of the projectile acceleration. Also, the Virtual-Cell-Embedding (VCE) method was employed to efficiently treat the complex projectile geometry on cartesian grids.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Shock waves 5 (1995), S. 103-108 
    ISSN: 1432-2153
    Keywords: dust flame acceleration ; transition to detonation ; dust explosion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract A new pneumatic dispersion system for obtaining a good quality uniform dust suspension in a horizontal dust combustion tube was developed. The effect of three different dispersion techniques on self-sustained dust flame acceleration in such a combustion tube was examined. The importance of the dispersion quality in the test tube for maintaining a self-sustained dust flame acceleration was demonstrated. A combustion tube for studies of flame acceleration in fine aluminum dust-air mixture and its transition to detonation under industrial ignition conditions was constructed in the course of the present study. It consists mainly of an initiation section and a test section. The initiation section must be equipped in a well-developed dispersion system for creating a good dispersion condition in the test tube. The length of this section is 3 meters. The test tube requires only to distribute uniformly the dust over the bottom of the tube prior to the experiment. The aluminum dust spherical in shape with 6 μm in diameter was used for tests. Experimental results demonstrated that the increase in flame velocity is roughly linear through the entire length of the test tube. The highest flame propagation velocity in fine aluminum dust-air mixture approaches some 1200m/s at a distance of 4.8m from the ignition plane.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Shock waves 3 (1993), S. 25-33 
    ISSN: 1432-2153
    Keywords: Compressible flow ; Fluctuation ; Interaction ; Shock oscillation ; Supersonic diffuser
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The present paper describes experimental investigations for shock oscillations caused by normal shock wave/turbulent boundary layer interaction in a supersonic diffuser. An array of wall-mounted transducers and especially a line image sensor for the nonintrusive detection of shock displacements were employed to investigate the interactions at low supersonic speeds. The line image sensor was collimated with a conventional schlieren optical system and was a good indicative of capturing the shock oscillating motions in the present configuration. This study shows that the amplitude of the shock motions increases with approaching flow Mach number, and the cause of oscillation of the shock wave can, however, be independent of the Mach number. In addition, the present system employed to determine the shock wave positions and displacements can be effectively applied to a variety of practical problems.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1432-2153
    Keywords: Laser-induced predissociation fluorescence ; Shock tunnel impurities ; Absolute intensity measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Absolute intensity measurements of impurity emissions in a shock tunnel nozzle flow are presented. The impurity emission intensities were measured with a photomultiplier and optical multichannel analyser and calibrated against an intensity standard. The various metallic contaminants were identified and their intensities measured in the spectral regions 290 to 330 nm and 375 to 385 nm. A comparison with calculated fluorescence intensities for predissociated laser-induced fluorescence signals is made. It is found that the emission background is negligible for most fluorescence experiments.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1432-2153
    Keywords: Rarefied gas dynamics ; Mach reflection ; DSMC method ; Smoothing technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The direct simulation Monte Carlo (DSMC) method is applied to simulation of nonstationary Mach reflection of strong shock waves. Normally the DSMC method is very time consuming in solving unsteady flow field problems especially for high Mach numbers, because of the necessity of iterative calculations to eliminate the inherent statistical fluctuation caused by a finite sample size. A central weighted smoothing technique is introduced to process the DSMC results, so that the iteration time can be significantly reduced. In spite of some relaxations of the shock wave structure, the smoothing technique is verified to be useful to estima te the flow fields qualitatively and even quantitatively by using a relatively small sample size. The comparison between the present approach and the kineticmodel approach (Xu et al. 1991a, 1991b) on the application to unsteady rarefied flow fields was also carried out.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 1432-2153
    Keywords: Piezoelectric polymer ; Porous solids ; Powders ; Pressure measurements ; PVDF gauge ; 5Ti+3Si ; Ni+Al ; TiO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract The response of highly porous powder compacts and powder mixtures to high pressure shock compression loading is of considerable interest for synthesis and processing of metals, ceramics and superhard materials. This technical note reports the first successful use of the Bauer piezoelectric polymer stress-rate gauge for measurements of shock wave velocity and stress-wave profiles in porous powder compacts. A powder mixture of 5Ti+3Si shows strong chemical reaction at a pressure of 2.5 GPa, while a powder mixture of 3Ni+Al shows no evidence for reaction at 4.7 GPa. A measurement of compaction of a powder compact of rutile at 5.5 GPa shows that it is not compacted to the solid density state. Although pressure increases due to chemical reaction products in condensed phases are modest and difficult to detect, shock wave velocities provide a sensitive measure of the existence of chemical reaction. The increase in shock speed can be described in terms of constant pressure processes which are descriptive of “ballotechnic” reactions, i.e. shock-induced reactions in heterogeneous material mixtures.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...