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1.
We have investigated the evolution of cellular detonation-wave structure as a gaseous detonation travels along a round tube
and measured cell lengths as a function of the initial pressure of the gas. We have tested acetylene-containing combustible
gas mixtures with different degrees of regularity. Along with the smoked-foil technique, an emission method has been used
to the measure current and average values of the detonation cell length. The method is based on the detection of an emission
spectrum behind the detonation front in the spectral range corresponding to local gas temperatures that are much higher than
those for the Chapman-Jouguet equilibrium condition. This technique provides quasi-continuous cell-length measurements along
the normal to the detonation front over the length of several factors of ten times the tube.
Our study has experimentally identified the steady states of detonation structure in round tubes, referred to here as the
single detonation modes. When the state of a single mode is fully established, then both the flow structure and the energy
release at detonation front develop strictly periodically along the tube at a constant frequency inversely proportional to
the cell length of the mixture. The mixture regularity has had no influence on the occurrence of the detonation mode, which
is defined by the value of initial pressure or the total energy release of the mixture. Outside of the pressure range where
a detonation mode was most likely to occur, the detonation front is unstable and may exhibit an irregular cellular pattern.
Monitoring the evolution of cells over a long distance revealed that the local gas emissivity, which is time dependent and
corresponds to axial pulsations of the detonation structure, has the appearance of a superposition of separate harmonics describing
the states of emissivity oscillations and cell structure of single detonation modes.
Received 18 October 1999 / Accepted 10 June 2001 相似文献
2.
Detonation in gaseous nitromethane (NM) and mixed with O2 has been studied. Experiments were performed in a preheated steel tube at an initial temperatureT
0∼=390 K for different initial pressuresP
0 (1.7≥P
0≥5 10−2 bar). Different selfsustained detonation regimes were obtained, from multiheaded mode to spinning and galloping mode in marginal
conditions. These chemical systems were characterized by a specific detonation cellular structure very different from that
currently observed with classical gaseous C
n
H
m
/O2/N2 mixtures. All modes of detonation propagation in rich NM/O2 mixtures exhibit a double scale cellular structure. The pattern of this double scale structure is particularly clear in the
case of spinning mode.
An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Boulder, Colorado, from July 30 to August 4, 1995 相似文献
3.
Numa Manson on velocity deficits and detonation stability 总被引:1,自引:0,他引:1
S. B. Murray 《Shock Waves》2008,18(4):255-268
This memorial paper pays tribute to Professor Numa Manson’s contributions to the understanding of detonation velocity deficits
and wave stability. Manson and his colleague Guénoche postulated that a velocity deficit exists in a tube because the chemical
reactions are inhibited in a thin layer adjacent to the tube walls. The hydrodynamic theory of detonation was modified to
account for this, and it was shown that the deficit varies inversely with the tube diameter. Manson and his students measured
detonation velocities in tubes of various diameter. An estimate of the detonation velocity for an infinite tube diameter was
obtained by plotting the velocity against the reciprocal of the tube diameter, , and extrapolating the line through the data to . The relative contributions of tube geometry and surface roughness to the deficits were systematically studied. Manson was
also one of the early investigators to shed light on the cellular structure of detonation by reporting “vibratory phenomena”
seen as striations in streak schlieren photographs. An attempt was made to relate this phenomenon to “dispersions” in the
propagation velocity and hence the wave stability. The author has extended Manson’s work by investigating detonations in tubes
with yielding walls. Whereas boundary layers were responsible for the gasdynamic expansion and deficits in Manson’s rigid
tubes, it was the moving boundaries that caused similar effects in the author’s investigations. The author has repeated the
“nozzle” analysis of Fay and Dabora using the detonation cell length as the relevant chemical kinetic length scale, and found
reasonable agreement between his experimental results and the model. When the Poitiers data are reinterpreted in light of
the modified model, the trends are described quite well. More recent studies have shown that the measured deficits for mixtures
characterized by irregular cellular structures do not agree with the Fay–Dabora model. Possible reasons for the discrepancy
are discussed.
This paper is based on the invited lecture that was presented at the 21st International Colloquium on the Dynamics of Explosions
and Reactive Systems, Poitiers, France, July 23-27, 2007. 相似文献
4.
Recent work on gaseous detonations 总被引:1,自引:0,他引:1
M.A. Nettleton 《Shock Waves》2002,12(1):3-12
The paper reviews recent progress in the field of gaseous detonations, with sections on shock diffraction and reflection,
the transition to detonation, hybrid, spherically-imploding, and galloping and stuttering fronts, their structure, their transmission
and quenching by additives, the critical energy for initiation and detonation of more unusual fuels. The final section points
out areas where our understanding is still far from being complete and contains some suggestions of ways in which progress
might be made.
Received 9 September 1999 / Accepted 10 May 2001 相似文献
5.
To interpret the results of direct numerical simulations for the one-dimensional pulsating detonation, a nonlinear oscillator
model is proposed based on the integral conservation considerations. A gauging procedure is suggested in which the results
from the direct numerical simulation are used to compute the coefficients of the oscillator equation. Various terms of the
oscillator equation obtained are compared with those of mechanical nonlinear oscillators in order to illustrate their analogy.
Among many important features captured by this nonlinear oscillator equation, the oscillatory behavior of the detonation wave
front can be interpreted as resonant excitation of the chemical energy release.
Received 24 March 1997 / Accepted 7 May 1998 相似文献
6.
Three-dimensional numerical simulation of detonations in both a circular tube and a coaxial tube are simulated to reveal characteristics
of single spinning and two-headed detonations. The numerical results show a feature of a single spinning detonation which
was discovered in 1926. Transverse detonations are observed in both tubes, however, the single spinning mode maintains the
complex Mach reflection whereas the two-headed mode develops periodically from the single Mach reflection to the complex one.
The calculated cell aspect ratio for the two-headed mode changes from 1.09 to 1.34 as the radius of axial insert increases
from r
1/R = 0.1 to 0.9. The calculated cell aspect ratio for r
1/R = 0.1 is close to the experimental results without an axial insert. The formation of an unreacted gas pocket behind the detonation
front was not observed in the single spinning mode; however, the two-headed mode has unreacted gas pocket behind the front
near the axial insert.
相似文献
7.
Effect of scale on the onset of detonations 总被引:6,自引:0,他引:6
S.B. Dorofeev V.P. Sidorov M.S. Kuznetsov I.D. Matsukov V.I. Alekseev 《Shock Waves》2000,10(2):137-149
Critical conditions for onset of detonations are compared at (1) two significantly different scales, (2) for a range of -air mixtures diluted with C, O, and (3) for two types of geometry – one a long obstructed channel and the other a room with a relatively small aspect ratios.
For the range of scales, mixtures, and initial conditions tested, the detonation cell size was shown to be a reliable scaling parameter for characterization of detonation onset conditions. An experimental correlation
is suggested for the critical detonation onset conditions. This correlation is based on a wide variety of available experimental
data on DDT in mixtures of hydrogen and hydrocarbon fuels with air and on the use of detonation cell size as a scaling parameter characterizing the mixture.
Received 14 November 1999 / Accepted 16 February 2000 相似文献
8.
This investigation deals with the two-dimensional unsteady detonation characterized by the cellular structure resulting from
trajectories of triple-shock configurations formed by the transverse waves and the leading shock front. The time-dependent
reactive shock problem considered here is governed by a system of nonlinear hyperbolic conservation laws coupled to a polytropic
equation of state and a one-step Arrhenius chemical reaction rate with heat release. The numerical solution obtained allowed
us to follow the dynamics of the cellular detonation front involving the triple points, transverse waves and unreacted pockets.
The calculations show that the weak tracks observed inside the detonation cells around the points of collision of the triple-shock
configurations arise from interactions between the transverse shocks and compression waves generated by the collision. The
unreacted pockets of gas formed during the collisions of triple points change form when the activation energy increases. For
the self-sustained detonation considered here, the unreacted pockets burn inside the region independent of the downstream
rarefaction, and thus the energy released supports the detonation propagation. The length of the region independent of the
downstream is approximately the size of one or two detonation cell.
Received 13 February 1998 / Accepted 13 August 1998 相似文献
9.
S. B. Dorofeev V. P. Sidorov M. S. Kuznetsov A. E. Dvoinishnikov V. I. Alekseev A. A. Efimenko 《Shock Waves》1996,6(1):21-28
Large scale experiments were carried out to study the effect of fuel concentration on air blast parameters and heat radiation
from gaseous detonations. Hemispheric plastic envelope (4 meters in radius) was used with propane-air mixtures containing
from 4 to 7 vol. % of fuel. The expressions for overpressures and impulses were determined in Sachs variables. The effect
of fuel concentration on blast parameters is shown to be insignificant for the same amount of oxygen in the mixture volume.
Thus the blast wave parameters can be described as for stoichiometric mixtures using additional scaling for the explosion
energy according to oxygen content (cloud volume). The results of large scale experiments with fuel spray clouds containing
0.16–100 tons of fuel with mean concentration from stoichiometric () up to are reconsidered. These results confirm the proposed scaling of air blast parameters for a wide range of fuel types, cloud
volumes and fuel concentrations. Detonations of fuel rich gaseous mixtures result in a strong heat radiation. Heat radiation
energy, time and size of the fireball formed are studied as a function of fuel concentration.
Received March 10, 1995 / Accepted March 12, 1995 相似文献
10.
11.
Analysis of the shock structures in a regular detonation 总被引:1,自引:0,他引:1
Time-dependent two-dimensional numerical simulations have been used to investigate the detailed shock structures and patterns of energy release in the regions of the triple points and transverse waves in a planar detonation. As the system of shock triple points evolves between collisions, they trace a well shaped cellular pattern characteristic of detonations in argon-diluted, low-pressure mixtures of hydrogen and oxygen. In the region of the triple points, the shock structure evolves continuously from a single Mach structure to a double Mach structure and finally to a complex Mach structure characteristic of spinning detonations. Most of the energy released in the region of the triple points. The amount of energy release increases as the triple point comes closer to a collision with a wall or another triple point. Just before the collision, there is a large region of energy release that covers the length of the interacting transverse waves. The result is a rectangular high-energy region which boosts the propagation of the new detonation cell. 相似文献
12.
Fundamentals of rotating detonations 总被引:17,自引:0,他引:17
A rotating detonation propagating at nearly Chapman–Jouguet velocity is numerically stabilized on a two-dimensional simple
chemistry flow model. Under purely axial injection of a combustible mixture from the head end of a toroidal section of coaxial
cylinders, the rotating detonation is proven to give no average angular momentum at any cross section, giving an axial flow.
The detonation wavelet connected with an oblique shock wave ensuing to the downstream has a feature of unconfined detonation,
causing a deficit in its propagation velocity. Due to Kelvin–Helmholtz instability existing on the interface of an injected
combustible, unburnt gas pockets are formed to enter the junction between the detonation and oblique shock waves, generating
strong explosions propagating to both directions. Calculated specific impulse is as high as 4,700 s.
相似文献
13.
Reignition of detonations by reflected shocks 总被引:2,自引:0,他引:2
Numerical simulations are used to study the diffraction, decay, and reignition that occurs when a detonation propagates past
an increase in cross-sectional area in a rectangular tube. The computations solve the time-dependent two-dimensional equations
describing a reactive flow in an argon-diluted stoichiometric hydrogen-oxygen mixture at atmospheric pressure. Previous studies
have shown that soon after transmission to a larger area, the reaction front decouples from the leading shock and forms a
decaying blast wave (“bubble”) in the larger tube. Then, depending on the initial conditions, the detonation either continues
to decay or is reignited as the bubble reflects off confining surfaces. For a strongly overdriven initiating detonation, reignition
occurs through an interaction between the bubble and the original contact surface. For a more weakly driven system, reignition
can occur in two ways: either in the slip line and Mach stem of the Mach reflection formed when the bubble reflects off the
bottom surface of the tube, or by multiple shock interactions that occur when the reflected bubble overtakes the initial detonation
front. The computations show the evolution and development of the cellular structure of the steady detonation front.
Submitted to the 14th International Colloquium on the Dynamics of Energetic and Reactive Systems, Coimbra, Portugal, August,
1993 相似文献
14.
In this paper,detonation parameters of fuel cloud,such as propylene oxide(PO),isopropyl nitrate(IPN),hexane,90 # oil and decane were measured in a self-designed and constructed vertical shock tube.Results show that the detonation pressure and velocity of PO increase to a peak value and then decrease smoothly with increasing equivalence ratio.Several nitrate sensitizers were added into PO to make fuel mixtures,and test results indicated that the additives can efficiently enhance detonation velocity and pressure of fuel cloud and one type of additive n-propyl nitrate(NPN) played the best in the improvement.The critical initiation energy that directly initiated detonation of all the test liquid fuel clouds showed a U-shape curve relationship with equivalence ratios.The optimum concentration lies on the rich-fuel side(φ > 1).The critical initiation energy is closely related to molecular structure and volatility of fuels.IPN and PO have similar critical values while that of alkanes are larger.Detonation cell sizes of PO were respectively investigated at 25 C,35 C and 50 C with smoked foil technique.The cell width shows a U-shape curve relationship with equivalence ratios at all temperatures.The minimal cell width also lies on the rich-fuel side(φ > 1).The cell width of PO vapor is slightly larger than that of PO cloud.Therefore,the detonation reaction of PO at normal temperature is controlled by gas phase reaction. 相似文献
15.
The cellular detonation structure has been recorded for hybrid hydrogen/air/aluminium mixtures on 1.0 m 0.110 m soot plates. Addition of aluminium particles to the gaseous mixture changes its detonation velocity. For very fine
particles and flakes, the detonation velocity is augmented and, in the same time, the cell width diminishes as compared with the characteristic cell size of the mixture without particles. On the contrary, for large particles, the detonation velocity decreases and the cell size
becomes larger than . It appears that the correlation law between the cell size and the detonation velocity in the hybrid mixture is similar to
the correlation between the cell size and the rate of detonation overdrive displayed for homogeneous gaseous mixtures. Moreover,
this correlation law remains valid in hybrid mixtures for detonation velocities smaller than the value D of the mixture without particles.
Received 10 May 2001 / Accepted 12 August 2002 Published online 19 December 2002
Correspondence to: B. Veyssiere (e-mail: veyssiere@lcd.ensma.fr) 相似文献
16.
17.
Experimental results presented in this work enable us to classify the three-dimensional structure of the detonation into
two fundamental types: a rectangular structure and a diagonal structure. The rectangular structure is well documented in the
literature and consists of orthogonal waves travelling independently from each another. The soot record in this case shows
the classical diamond detonation cell exhibiting ‘slapping waves’. The experiments indicate that the diagonal structure is
a structure with the triple point intersections moving along the diagonal line of the tube cross section. The axes of the
transverse waves are canted at 45 degrees to the wall, accounting for the lack of slapping waves. It is possible to reproduce
these diagonal structures by appropriately controlling the experimental ignition procedure. The characteristics of the diagonal
structure show some similarities with detonation structure in round tube. Pressure measurements recorded along the central
axis of the cellular structure show a series of pressure peaks, depending on the type of structure and the position inside
the detonation cell. Pressure profiles measured for the whole length of the two types of detonation cells show that the intensity
of the shock front is higher and the length of the detonation cell is shorter for the diagonal structures.
Received 17 May 2000 / Accepted 29 November 2000 相似文献
18.
We present two-dimensional numerical simulations of the transmission of detonation from a rectangular channel into a larger
volume. The simulations solve the Euler equations on a Cartesian grid using the method of Flux-Corrected Transport for the
fluid equations and a two-step induction parameter model for the chemistry. We simulate detonation in a H2/O2/Ar mixture and use sufficient grid resolution to resolve the cellular structure of the detonation. When a planar detonation
front without a resolved cellular structure expands into the larger volume, the reaction front separates from the shock front
and the detonation fails. When the planar front is perturbed to induce a quasi-regular cellular structure in the detonation,
it again initially begins to fail, but now the presence of the transverse waves leads to reignition of the detonation in the
larger volume. The form of this reignition shows striking similarities to the reignition of detonation which has been seen
experimentally in H2/O2 mixtures. We describe this reignition mechanism in detail, and also investigate the dependence of the reignition on the number
of cells in the detonation front.
An abridged version of this paper was presented at the 15th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Boulder, Colorado, from July 30 to August 4, 1995 相似文献
19.
旋转爆轰胞格结构的实验和数值研究 总被引:6,自引:0,他引:6
对爆轰波在环形圆管(预混气体为2H2/O2/Ar)内的传播分别进行了实验和数值研究。实验研究
采用烟迹板记录了环形圆管内爆轰波的胞格结构。数值计算利用二阶附加半隐的Runge-Kutta法和五阶
WENO格式分别离散欧拉方程的时间和空间导数项,采用基元反应简化模型描述化学反应过程,得到了旋转
爆轰的流场及数值胞格结构。实验和数值模拟结果表明:爆轰波在圆环管中传播时,由于圆环的内壁发散、外
壁收敛,圆环内侧爆轰强度小于外侧,胞格尺寸较大;内侧OH 的分布区域大于外侧,浓度较低。旋转爆轰的
这种性质,使爆轰波能以稳定的角速度绕轴旋转。 相似文献
20.
Large scale experiments on detonation initiation in gasoline-air by two different sources were carried out at stoichiometric
conditions. Unconfined clouds of volume generated by a special facility had a shape of semicylinder of 15–17 m in length and 6–8 m in radius. Both the charge
of condensed HE and the charge of stoichiometric propane-air were used to initiate detonation in the mixture. In case of initiation
by a propane-air charge the critical initiation energy was up to 7 times as large as that for HE initiation. The detonation
cell size for gasoline-air was determined as 0.04–0.05 m. It was shown, that the well-known correlation between the critical
energy of point blast initiation and the cell size failed for this system. The cell size obtained is close to one of propane-air,
but no direct transfer of detonation from one mixture to another was observed.
Received 10 March 1995 / Accepted 12 March 1995 相似文献