TY - JOUR

T1 - A numerical study on the ventilation coefficients of falling lobed hailstones

AU - Wang, Pao K.

AU - Chueh, Chih Che

PY - 2020/4

Y1 - 2020/4

N2 - The ventilation coefficients that characterize the enhancement of heat/mass transfer rate due to the falling motion of lobed hailstones created by a set of mathematical expressions in an atmosphere of pressure 460 hPa and temperature 248 K are computed by numerically solving the convective-diffusion water vapor transport equation while the local airflow velocities are obtained through the numerical solution of unsteady Navier-Stokes Equation around the falling hailstones. The atmospheric condition is chosen so that the hailstone is not growing wet and the ventilation coefficient represents dry hailstone condition. The diameters of the hailstones investigated here are 1, 3, 5, 7 and 10 cm with the Reynolds numbers ranging from 9560 to 388,000 respectively. The ventilation coefficients for all cases are nearly the same when the diameter is 1 cm. The difference becomes greater as the size increases. The highest ventilation coefficient calculated here is >500 for a 10 cm hailstone with 36 long lobes. We found that in general lobed hailstones have larger ventilation effect than spherical hailstones of the same size. We also report that the connection between basic geometry information (i.e. surface area and volume) and the ventilation coefficients. The larger surface area usually results in greater ventilation coefficient whereas no clear relation exists between the ventilation coefficient and volume for the stones investigated here. Empirical formulas for ventilation coefficient as a function of hailstone diameter and Schmidt numbers are given. Implications of these ventilation coefficients are discussed.

AB - The ventilation coefficients that characterize the enhancement of heat/mass transfer rate due to the falling motion of lobed hailstones created by a set of mathematical expressions in an atmosphere of pressure 460 hPa and temperature 248 K are computed by numerically solving the convective-diffusion water vapor transport equation while the local airflow velocities are obtained through the numerical solution of unsteady Navier-Stokes Equation around the falling hailstones. The atmospheric condition is chosen so that the hailstone is not growing wet and the ventilation coefficient represents dry hailstone condition. The diameters of the hailstones investigated here are 1, 3, 5, 7 and 10 cm with the Reynolds numbers ranging from 9560 to 388,000 respectively. The ventilation coefficients for all cases are nearly the same when the diameter is 1 cm. The difference becomes greater as the size increases. The highest ventilation coefficient calculated here is >500 for a 10 cm hailstone with 36 long lobes. We found that in general lobed hailstones have larger ventilation effect than spherical hailstones of the same size. We also report that the connection between basic geometry information (i.e. surface area and volume) and the ventilation coefficients. The larger surface area usually results in greater ventilation coefficient whereas no clear relation exists between the ventilation coefficient and volume for the stones investigated here. Empirical formulas for ventilation coefficient as a function of hailstone diameter and Schmidt numbers are given. Implications of these ventilation coefficients are discussed.

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U2 - 10.1016/j.atmosres.2019.104737

DO - 10.1016/j.atmosres.2019.104737

M3 - Article

AN - SCOPUS:85074447716

VL - 234

JO - Atmospheric Research

JF - Atmospheric Research

SN - 0169-8095

M1 - 104737

ER -