Experiments in Fluids

, Volume 22, Issue 6, pp 463–472 | Cite as

The impact of a single drop on a wetted solid surface

  • G. E. Cossali
  • A. Coghe
  • M. Marengo


The impact of single drops on a thin liquid film was studied to understand the mechanism of secondary atomisation of sprays colliding on a wetted, cold, solid surface. To span a wide range of conditions various mixtures of water and glycerol were used. The use of Weber number, Ohnesorge number and non-dimensional film thickness to describe the peculiarities of the phenomenon allowed to carry out the experiments under appropriate similarity conditions. The impact of millimetric drops was analysed in detail by photographic means, using both still photography to study impact morphology, and laser sheet visualisation to investigate secondary droplet formation. Two mechanisms of splash were identified, depending essentially on the liquid viscosity (Ohnesorge number), a parameter which appears to play an important role also in defining the splash morphology. A photographic documentation is annexed. The characteristic times of the crown formation, the non-linear evolution of cusps (jet formation) and the surface roughness influence are further discussed. The experimental results allow to propose an empirical correlation for the splashing/deposition limit, for a wide range of conditions, and a comparison to available previous works is presented. The influence of the film thickness and liquid viscosity on the splash is confirmed and quantified.

List of Symbols


Bond number (= ρgh2/σ)


capillary number (= µV/σ)


nozzle diameter


impact frequency


non-dimensional impact frequency (=f φ/V)


Froude number (= V2φ/g)


film thickness


crown height


We Oh- 0.4


splashing/deposition limit


number of secondary droplets


number of jets detaching from the crown


Ohnesorge number (= µ/ φσρ 1/2)



Rc, nd

nondimensional crown radius (= Rc/φ)


crown radius


Reynolds number (= σVφ/µ)


non-dimensional roughness (= Ra/φ )




splash beginning time


gravitation potential energy


surface potential energy


terminal drop velocity


Weber number (= ρV2φ/σ)


critical Weber number


deposition Weber number


splash Weber number


splashing/deposition parameter

Greek symbols


drop impact angle


non-dimensional film thickness (= h/φ)


drop diameter


coalescence parameter


jet diameter


viscosity length ( = (µ/αf)1/2σρ/µ2)


liquid viscosity


liquid density


surface tension


non-dimensional time (= t φ/V)


splash time scale ( = φ/V)


nondimensional splash beginning time (= ts0)


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Copyright information

© Springer-Verlag 1997

Authors and Affiliations

  • G. E. Cossali
    • 1
  • A. Coghe
    • 2
  • M. Marengo
    • 2
  1. 1.Universita di BergamoDalmine, BergamoItaly
  2. 2.Politecnico di MilanoMilanoItaly

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