Numerical investigation of jet-dispensed liquid spreading on a pre-wetted moving surface

• High-fidelity simulation of jet deposited film spread on pre-wetted moving surface • In-depth analysis of dynamics governing the hydraulic jump formation • Jet perturbed area decreases with increasing wall friction • Overall wall friction grows with surface velocity or liquid viscosity • Wall shear stress near impingement well predicted by self-similar solution The present work numerically investigates the spreading of a jet-dispensed liquid film on a linearly moving pre-wetted planar substrate with wall-to-jet impingement velocity ratios beyond unity ( U w / V imp ≥ 1), and jet Reynolds numbers varied as R e i m p = 4350 / 8700 / 13050 by assuming different viscosities. As the wave front comes closest to the jet for the largest considered ratio U w / V i m p = 2.5 , the big vortex otherwise governing the reversal of the dispensed liquid is completely suppressed. A similar transition from the impingement to wall motion dominated regime is seen for increasing viscosity. The transition is always accompanied by a marked rise of two distinct maxima in wall shear stress, occurring beneath the bow wave and very next to impingement at one jet radius upstream, which ultimately tend to merge. The realized gain in local wall shear stress is notably offset by the concurrently reduced jet-impacted area, as the lateral spreading of the wave front is weakened as well. The effectively obtained global wall friction force thus decreases for increasing wall velocity ratios U w / V imp . For increasing viscosity the trend is still not reversed. A closer proximity of the bow wave to impingement consistently provides a larger amount of redirected jet momentum, promoting break-off of droplets from the crest of the otherwise rather compact lamella, eventually constituting more than 20% of the total jet-dispensed mass. Two simple models based on self-similarity and superimposed flows, are proven as reliable in the impingement dominated regime, while their accuracy deteriorates as wall motion becomes dominant.