EXPERIMENTAL CHARACTERIZATION OF AN INTERMITTENT GASOLINE SPRAY IMPINGING UNDER CROSS-FLOW CONDITIONS

摘要

This article reports an experimental study on an intermittent gasoline spray impinging onto a flat surface in the presence of a cross flow.The experiments include detailed phase Doppler anemometry (PDA) measurements of droplet size,velocity,and volume flux to quantify the time-dependent fluid dynamic interactions between the spray and the cross flow.The analysis is performed in terms of the expected influence on the outcome of impact.Interposition of the wall decreases the penetration rate of the spray,and therefore the energy available at impact is smaller than would be expected from the analysis of the free spray.However,the main effect of the wall is due to the formation of a three-dimensional time-varying vortical structure in the vicinity of the wall,which entrains reatomized droplets to reimpinge with smaller Reynolds numbers,thus contributing to the formation of the wall liquid film.Although spray/wall interaction is altered due to deviation of the impinging spray by the cross flow,the main effect is due to drag of small droplets from the vortical structure,thus reducing the number of droplets predicted to stick at the wall.However,it is suggested that the cross flow enhances the interaction between crowns at the target surface and impinging droplets,in such a way that the volume flux of small droplets flying way from the surface may overcome the volume flux of impinging droplets.