Experimental And Numerical Investigation On Sprays Of Hollow-Cone Pressure Nozzle

The objective of this thesis was to investigate the atomization characteristics of hollow-cone pressure nozzle through experiments and numerical simulations. A general experimental rig for sprays has been designed in the Turbo Machinery Institute (TMI) of Shanghai Jiao Tong University. The experimental rig enables the production of steady sprays with pressure ranging from 0 to 20 bar,and flow rate from 0 to 1000 kg/h using a centrifugal pump. A fan was employed to create steady air flow under the spray in order to reduce recirculation effects.Based on the general experimental rig for sprays, the pressure-flow rate curves of the hollow-cone pressure nozzles were obtained, which offers important data for further experiments and numerical simulation.The investigation is categorized into two parts as follows.1. Experimental and Numerical Investigation on the Sprays of a Single Hollow-cone Pressure NozzleSteady two-dimensional sprays of a single hollow-cone pressure nozzle were investigated.The droplet velocity distributions on the plane through the axis of the nozzle were measured using a PIV system. Several spray characteristics, which include droplet axial velocity distributions, radial velocity distributions and vortices stemming from entrainment between droplets and the air, are discussed in terms of injection pressure P=4,8,12,16 bar. At the lowest pressure, PIV outcomes do not demonstrate hollow-cone spray behaviors; however, other sprays show hollow-cone spray behavior under the nozzle because of the measurable changes in injection pressure.PTV analyses based on the droplet photos of PIV measurements at the injection pressure P=4, 8bar were implemented, which provides valid droplet velocity but does not provide valid data for droplet diameter because of the resolution of CCD digital camera and other reasons.Employing a coupled Eulerian-Lagrangian approach for the gas-droplet flow, applying the LISA model for the formation of droplets,four cases with the same conditions as the experiments'were modeled with the FLUENT software. Several spray features, which involve droplet axial velocity distributions, radial velocity distributions and DSD at X=10, 20, 40, 80 mm, were presented and discussed. It is shown that numerical simulation is capable of modeling the atomization characteristics of hollow-cone pressure nozzle. Compared to the PTV results, the numerical simulations are validated.2. Experimental and Numerical Investigation of Two Interacting Hollow-cone Pressure Nozzle SpraysThe atomization characteristics of two interacting sprays were investigated by DualPDA, PIV, CFD, respectively.Both droplet size and velocity distributions on a plane perpendicular to the axes of the nozzles were quantified using a DualDPA system. Several spray properties, for example, droplet axial velocity distribution, radial velocity distribution, and average diameter distribution, Sauter average diameter distribution etc, were fully discussed. Particular attention was paid to the discrete numerical probability distribution of the droplet average diameter and quantitative dependency between droplet axial velocity and average diameter.A factorial design of the experiments was adopted to explore the influence of the injection pressure (P=8, 16 bar) and the distance of axes (D=40, 50 mm) of sprays on the intersection area. Varying values of these parameters, the features of the intersection area were discussed.Interacting sprays of two hollow-cone pressure nozzles installed side by side were simulated numerically with a three-dimensional model. Particular attention was given to the examination of the features in the intersection area of sprays at four different times t=0.0025, 0.0050, 0.0075, 0.0100 s.