V. M. Boiko

INTERACTION OF A SHOCK WAVE WITH A CLOUD OF PARTICLES

The present paper is devoted to experimental and theoretical investigation of shock-wave propagation in a mixture of a gas and solid particles with clearly defined boundaries of the two-phase region (cloud of particles). The effect of qualitative transformation of supersonic flow behind a shock wave in a cloud of particles is shown experimentally and substantiated theoretically for volume concentrations of the dispersed phase of 0.1–3%.

Experimental study of two types of stripping breakup of the drop in the flow behind the shock wave

Results of an experimental study of two regimes of stripping breakup of low-viscosity liquid drops in the flow behind the shock wave in the range of Weber numbers from 200 to 8000 are reported. A phenomenological pattern of drop breakup is constructed on the basis of data on drop deformation and on the flow around the drop. A physical criterion of the change in stripping mechanisms of drop breakup is formulated.

MECHANISM OF DUST IGNITION IN INCIDENT SHOCK WAVES

A study is made of dust ignition during transient interaction of an incident shock wave with an extended dust cloud. It has been shown experimentally that in the presence of dispersed phase with volume concentration of ∼10−3 the temperature behind a shock wave with Mach number Ms=4.5 can exceed the ambient one by 400 K or more. A physical mechanism is proposed for carrier phase heating, based on the effect of supersonic flow braking behind the shock wave under constraints created by dust particles during velocity relaxation. The gasdynamic functions are obtained as analytic functions of the flow Mach number M. In particular, it is shown that the equation T/T0=M0/M is valid for the temperature. The form of M as a function of dispersed-phase parameters and the quantitative nonsteadiness criterion are found. The function M was found to agree well with experiment.

Measurement of gas velocity in a high-gradient flow, based on velocity of tracer particles

Methods of reconstruction of the gas flow velocity from the measured velocity of disperse phase particles are considered. It is demonstrated that available approaches are limited by the low velocity nonequilibrium of the phases. A method of correction of particle image velocimetry (PIV) data on the basis of measuring the parameters of velocity relaxation of particles is proposed for measuring the gas velocity in high-gradient flows. The method is experimentally tested in the flow behind a shock wave with submicron tracers. A possibility of using this method in flows with gas-dynamic discontinuities is demonstrated.

Effect of volatiles on ignition delay in coal dust gas suspensions within shock waves

We present the results from an experimental study into the dynamics involved in the formation and the unique features of ignition in shock gas suspensions of coal dust with a dispersion of<40 μm and a volatile content of 9, 26, and 55%. We have determined the ignition delays τig for coal dusts in air and in pure oxygen for a range of Mach numbers from 2.6 to 4.0 in an incident shock wave. We have established that the quantity τig as well as the nature of the function τig(1/T) are significantly affected by the kinetics of the volatile yield, in addition to the kinetics of volatile ignition. We have derived an approximation expression for τig as a function of the content of volatiles, the temperature of the medium, and the partial pressure of the oxygen.

Correction of PIV data for reconstruction of the gas velocity in a supersonic underexpanded jet

A method of correction of particle image velocimetry (PIV) data for reconstruction of the gas velocity based on the particle velocity in supersonic underexpanded jets is considered. The method is based on estimating the velocity lag of tracer particles on the basis of their velocity relaxation parameter as a correction to PIV data in the Newton approximation of interphase interaction. It is shown that the velocity relaxation parameter of tracer particles in flows with velocity jumps can be determined from the initial PIV data. Correction with the found parameter of velocity relaxation of the phases provides good accuracy.

Ignition of aluminum powders mixed with liquid hydrocarbon fuels in air

The feasibility of ignition of aluminum powders in air is studied by examining a number of hydrocarbon fuels, promoter additives in them, and hybrid systems of liquid mixtures and powders in shock waves. Data are obtained on the ignition delays for each of the components and mixtures of them. It is shown that for temperatures of 1000–2000 K, ignition is possible, with delays of less than 2 msec, in hybrid systems of Al powders having a dispersity of 5–10 μm with diesel fuel and added fatty-alcohol nitrates.

Influence of liquid hydrocarbons on the ignition of metal powders in shock waves

Ignition of mixtures of metal powders with liquid hydrocarbon fuels in an atmosphere of pure oxygen and air behind reflected shock waves is studied experimentally. It is shown that the ignition delays for the mixtures are determined by the liquid phase, and the times of combustion are primarily determined by the particle size of the solid phase.

Dynamics of the destruction of a liquid film behind a shock wavefront

The liquid film destruction in passing shock wavefront is examined in the range Mach number 2.0-3.0 and at an initial gas pressure of 0.1 MPa, obtained by the method of multiframe laser visualization, permitting observation of the dynamics of development of this process with a time resolution of approximately 30 nsec. A sample of shadow photographs illustrating the dynamic behavior of a film of VM-4 oil is shown. It is shown that the character of the interaction with the shoulder depends significantly on the properties of the liquid and is largely similar to the character of shock wavefront interaction with a drop.