Dynamics of ultra-high speed liquid jets in still gas

Instability of free liquid jets is an important fundamental problem rising from multiple engineering fields such as material processing, energy production, etc. Ultra-high speed condition brings new difficulties to stability research. This work demonstrates flow patterns of ultra-high speed liquid jet (UHSLJ) and points out the potential challenges in relevant investigation, from a turbulence point of view. A PDA measurement of flow velocity and droplet size on a cross-section of UHSLJ is present. Flow physics involved in the jet is discussed together with the limitation of this measurement. It is found that the velocity profile on the measured section obeys 1/7 power law. Concentration of droplets has an inverse gradient (from outer region of a jet pointing to the inner region) in the breakup section. Flow properties hold an axisymmetric distribution in the atomization section while this section itself has an evident two-layer (core-outer) structure. The length scales (size of drop) that be resolved by the present experiment is estimated to be only 0.1% of the entire scales.