No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effect of Initial Conditions on the Development of Two-Phase Jets
Abstract
The results of an experimental investigation into the behavior of an unconfined, steady, fully turbulent, two-phase jet of diameter of 12.7 mm at the exit, with an exit flow velocity of 50 m/s and containing particles with a mass density of loading of 1.5% is described. The second phase consisted of glass beads 80 microns in diameter. Velocity profiles in a plane parallel to the exit of the jet at several downstream stations, as well as the rms values, turbulent intensity and velocity cross correlations were measured for both phases. The radial rms velocities of the particles, although similar to those of the fluid, were found to be surprisingly higher than for a jet of 25.4 mm in diameter with a lower exit velocity. Measurements of the particle velocities were extremely sensitive to changes in the upstream boundary conditions. Keywords: Laser doppler anemometry; Two phase flow.
... An interesting aspect of two phase jets is the spreading of particles beyond the expected jet envelope. Accumulating evidence, such as those of Hardalupas et al. (1989), Zoltani and Bicen (1990a) suggests that the observed levels of high fluctuations of the particulate velocity in the streamwise direction in the near field of particle laden two-phase jets are due to "fan-spreading". This is a phenomenon whereby some particles at the exit of a jet take trajectories at angles greater than the expected extent of the carrier jet. ...
The results of a flow visualization study of the behavior of an unconfined, steady, fully turbulent, two phase jet of diameter 12.7 mm at the exist with velocities up to 25 m/s and containing particles with a mass density of loading up to 5% are described. The significant result is the demonstration of fan spreading, whereby some of the particulates carried by the jet take paths outside of the expected envelope of an equivalent single-phase jet. Measurements of the path angles and a new theory to explain the reason for fan spreading is reported.
A new approach to the calculation of turbulent flows is presented. Variational principles are introduced into the statistical theory of turbulence enabling the determination of correlation functions by extremizing certain functionals. To demonstrate the efficiency of the technique a sample calculation of a mean flow profile and certain two point correlation functions of a cylindrically symmetric free jet were carried out using the Rayleigh-Ritz method. A judicious choice of the trial functions leads to the determination of the correlation functions with a modest amount of computation. The results are in reasonable agreement with experimental data.
Variational principles are introduced In the statistical theory of turbulent two-phase flows. With the help of these, correlation functions can be calculated by means of extremizing certain functionals. We carry out a sample calculation of the mean flow profile and correlation functions of a cylindrically symmetric two-phase jet. A Rayleigh-Ritz method is used for the determination of the correlation functions. There is a reasonable agreement between the theoretical calculation and experimental data even with a rather simple choice of the trial functions.
The velocity and mass flux characteristics in the non-self-similar region of a round turbulent bead-laden jet for three bead diameters (200, 80, and 40 microns), at two mass loadings, are described. The mean velocity of the 200-micron beads is virtually constant, with little influence of mass loading on the mean motion of the beads because the mean Stokes number is small. The centerline velocity of the 80-micron beads decays but not as a function of mass loading, at least up to 86 percent (mass/mass). For the 40-micron beads, the rate of decay of the centerline bead velocity decreases with increasing mass loading. The rate of spreading of 40-micron beads decreases with increasing loading, but the opposite is true for the 80-micron beads. The 'fan-spreading' model for the motion of the beads is considered, which refers to quasi-unidirectional trajectories of the beads from the exit of the jet up to about 20 diameters downstream for the 40-micron diameter beads, and farther for the larger beads.
Over the past two decades, several two-phase-flow interior ballistic codes have been developed. Generally, they have treated ignition-induced pressure waves as a hydrodynamic problem which arises from the ignition stimulus, the propellant geometry, the path of flame-spreading in the propellant bed, and the interaction of charge and chamber. Ignition and combustion have been treated as a simple process, with convectively-driven inert heating of the propellant until a surface-temperature criterion is reached, at which time an aP superscript n burning law describes the propellant surface regression, and all of the energy contained in the burned propellant is released immediately. The effects of propellant grain fracture, caused either by grain stress due to propellant bed compaction or by impact with fixed boundaries, has been outside the scope of the several codes. While the codes have incorporated interphase heat transfer and drag, they have been called inviscid, as the conservation laws are formulated to neglect the efforts of viscosity and heat conduction in the gas phase. This report describes, for the NOVA family of codes, (a) the recent inclusion of finite-rate chemistry and grain fracture, (b) planned efforts to improve the propellant near-field combustion model further, and (c) ongoing efforts to formulate a viscid/inviscid model to permit a linkage of effects with widely differing scales of heterogeneity. (jhd)