TY - JOUR

T1 - A preliminary numerical study on the time-varying fall attitudes and aerodynamics of freely falling conical graupel particles

AU - Chueh, Chih Che

AU - Wang, Pao K.

AU - Hashino, Tempei

N1 - Funding Information:
This study is partially supported by the US NSF grant AGS-1219586 and research fund provided by Academia Sinica, Taiwan . Any opinions, findings and conclusions for recommendations given in this article are those of the authors and don't necessarily reflect the viewpoints of the National Science Foundation (NSF).

PY - 2017/1/1

Y1 - 2017/1/1

N2 - The flow fields and dynamic motions of conical graupel of diameters 0.5–5 mm falling in air of 800 h Pa and − 8 °C are studied by solving the transient Navier-Stokes equations numerically for flow past the conical graupel and the body dynamics equations representing the 6-degrees-of-freedom motion that determines the position and orientation of the graupel in response to the hydrodynamic force of the flow fields. The shape of conical graupel made through a simple but practical existing mathematical equation allows us to have an uneven mass distribution, which is generally believed to have great influence on ice particles’ orientations while falling when inertial force becomes increasingly dominant over other effects. The simulated motions include vertical fall, lateral translation, sailing, rotation and pendulum swing. The computed flow fields are characterized in terms of streamtrace patterns as well as the vorticity magnitude fields, and the corresponding motions of the conical graupel is physically featured by looking upon the graupel surface distributions of pressure coefficient, torques contributed by both pressure as well as viscous effects. Tumbling doesn't occur when an initial orientation of the graupel is either 20° or 160° about Y axis, and the torque contributed by the pressure effect is dominant over that contributed by the viscous effect.

AB - The flow fields and dynamic motions of conical graupel of diameters 0.5–5 mm falling in air of 800 h Pa and − 8 °C are studied by solving the transient Navier-Stokes equations numerically for flow past the conical graupel and the body dynamics equations representing the 6-degrees-of-freedom motion that determines the position and orientation of the graupel in response to the hydrodynamic force of the flow fields. The shape of conical graupel made through a simple but practical existing mathematical equation allows us to have an uneven mass distribution, which is generally believed to have great influence on ice particles’ orientations while falling when inertial force becomes increasingly dominant over other effects. The simulated motions include vertical fall, lateral translation, sailing, rotation and pendulum swing. The computed flow fields are characterized in terms of streamtrace patterns as well as the vorticity magnitude fields, and the corresponding motions of the conical graupel is physically featured by looking upon the graupel surface distributions of pressure coefficient, torques contributed by both pressure as well as viscous effects. Tumbling doesn't occur when an initial orientation of the graupel is either 20° or 160° about Y axis, and the torque contributed by the pressure effect is dominant over that contributed by the viscous effect.

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U2 - 10.1016/j.atmosres.2016.08.017

DO - 10.1016/j.atmosres.2016.08.017

M3 - Article

AN - SCOPUS:84983616724

VL - 183

SP - 58

EP - 72

JO - Atmospheric Research

JF - Atmospheric Research

SN - 0169-8095

ER -