A snow accretion simulation method considering precipitation types based on the liquid water fraction of falling snowflakes

摘要

A numerical model for evaluating liquid water fraction of falling snowflakes is presented and is implemented into a snow accretion simulation code for overhead transmission lines,named SNOVAL(R)R(Ver.3).The new model allows to predict surface precipitation types(dry snow,wet snow,and rain)from averaged value of liquid water fraction of snowflakes with different size and density.It is shown that the averaged liquid water fraction of melting snowflakes depends not only on surface air temperature and relative humidity but also on the vertical temperature profile and precipitation intensity.By comparing temporal changes of observed snow load accreted on conductor samples with those of calculated liquid water fraction of snowflakes,it is found that snow accretion starts when the liquid water fraction is less than approximately 0.5.This condition based on the liquid water fraction is more accurate than using temperature or wet bulb temperature.