Details and Complexities of Boundary Conditions in Turbulent Piloted Dilute Spray Jets and Flames

Abstract

AbstractA good understanding of the details and sensitivities to boundary conditions is essential for the development of reliable predictive tools for turbulent spray flows. This chapter presents a comprehensive account of the boundary conditions relevant to dilute spray jets issuing in a co-flowing stream of air. The flames are stabilized with an annular pilot to prevent lift-off. Radial profiles of the velocity and turbulence fields as well as droplets size distributions and number densities are presented at the jet exit plane of a range of non-reacting and reacting jets of acetone and ethanol fuels. A non-reacting spray jet of mineral turpentine has been used as a base case to validate the liquid flux measurements. Laser-Phase Doppler Velocimetry (LDV/PDA) is employed for the measurements of velocity and droplet fluxes while Mie scattering is used for the high-speed laser imaging of droplets at the jet exit plane. The probability density function of the droplet size distribution measured at the exit plane is shown to be best represented by the Nukiyama-Tanisawa fit. Droplets less than 10 μm in diameter are shown to be adequate representatives of the gaseous flow. Larger droplets tend to exit the nozzle with mean axial velocities lower than those of the gas (and hence negative slip velocities). The rms fluctuations of the axial velocities of large droplets are found to be higher than those of small droplets. High-speed imaging of Mie scattering from sprays at the jet exit plane reveal that this anomaly is due to droplet shedding from the liquid film that develops on the inner wall of the pipe.KeywordsDroplet SizeDroplet Size DistributionExit PlaneCarrier VelocityNozzle Exit PlaneThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.