2-D AND 3-D MODELING OF LOW-DENSITY ICE ACCRETION ON ROTATING WIRES WITH VARIABLE SURFACE IRREGULARITIES

New results on two stochastic models, a 2-D and 3-D one, developed to simulate ice accrection processes at low values of impaction parameter s are reported. The 2-D model of ice accretion on rotating cylindrical objects introduces fluid dynamics analytically by calculating the par ticle impaction direction as per the aerodynamic conditions; a polydis perse spectrum of particles is also used, Stokes numbers K in the rang e 1 less than or equal to K less than or equal to 7.8 were used in the numerical experiments. The numerical results on rotating collectors s uggested an original theory of lobe formation, being interpreted as th e outcome of an amplified growth of surface instabilities, An equation relating the angular frequency of lobes occurrence to the irregularit ies of the collector surface is introduced and tested for an experimen tal deposit with good result. A parameterization of the lobes growth i s given by means of the droplets aerodynamics. The 3-D model employs a monodisperse droplet spectrum: the dependence of the density on the a ngular position with respect to the stagnation line shows that angular dependence of some properties of the 2-D pure ballistic aggregate is kept even in the 3-D, The value at maximum density in the numerical de posits matches values found in experimental deposits.