Study On Characteristics Of Inner Flow And Impinging Pressure Of Swirling Water Jet Nozzle

Aiming at the special demands for material breaking, swirl generating method ofswirling ?ow equipment is analysed, and a new type of nozzle is designed in orderto avoid the existence of low axial velocity and low pressure area at the center of theswirling jet produced by the traditional guide vane nozzle. The new type of nozzlecalled Combinative Swirling Water Jet Nozzle (CSWJN) employs tangential injectingand axial injecting to generate swirling ?ow and strengthen the impact force of the jetrespectively.In the present dissertation, hydrodynamic characteristics of CSWJN are investi-gated in detail with experiments and numerical simulation under di?erent in?ow con-ditions. The velocity field in the nozzle is measured with the two-dimensional digitalparticle image velocimetry (PIV), and the impact pressure produced by the nozzle insubmerged condition is measured by continuous shooting of the piezometer tubes usinga camera and obtaining the pressure automatically based on computer image process-ing technology. Numerical simulation is conducted by using di?erent turbulent mod-els, and comparison between the simulated results and the measured ones shows thatthe large eddy simulation (LES) is one of the most suitable turbulent models for theswirling ?ow simulation with both enough precision and e?ciency. The whole ?owand pressure information inside and outside the nozzle are obtained based on LES,which reveals the regular patterns of the swirl generation and development.Stable swriling water jet can be produced by CSWJN, and the swirling ?ow at thenozzle outlet maintains its stability even with high swirl intensity. Swirl momentumof the nozzle ?ow comes from the tangential in?ow, and is gradually transported tothe aixal in?ow as the ?ow runs downstream. The transport can be accelerated by thethe increment of i, the ratio of the tangential in?ow rate to axial in?ow rate, and therewould be a fully developed swirling ?ow at the nozzle outlet when i = 1.00. Thetangential velocity increases first and then decreases along the radial direction, and it can be enhanced by the increment of both the ratio i and the total ?ow rate Q. Themaximum value of the axial velocity appears at the axis of the swirling jet, and there isno low velocity area at the center of the jet. The swirl intensity of the jet increases withthe ratio i, and the swirl number S at the nozzle outlet is approximatively propotionalto (i / i + 1)~2.The impact pressure of the swirling water jet is dependent of the in?ow conditionas well as the inner ?ow of the nozzle. The increment of the total ?ow rate Q results inincreasing of the impact pressure, and the increment of the ratio i results in increasingof impact area and ?attening of the impact pressure distribution. The impact pressureunder di?erent in?ow conditions decreases along the radial direction, and there is nolow pressure area at the center of impact zone. The response of the wall impacted bythe water jet is also studied, and the surface layer of the elastical wall can ?atten thespacial distribution and suppress the temporal ?uctuation of the impact pressure. It isshown that the newtype nozzle structure is of favorable hydrodynamic characteristics.