A numerical study of the flow fields around falling hails

- Numerical solutions of unsteady fields past spherical hails of diameters 1-10 cm.
- Reynolds numbers range from 6000 to 250,000.
- Flow regime changed from semi-turbulent for smaller hails to complete turbulent for large hails.
- Numerical results exhibit similar flow characteristics as experimental results.

The characteristics of the flow fields around falling hailstones of diameters 1 to 10 cm are studied. The flow fields are obtained by numerically solving the time-dependent Navier-Stokes equations for flow past hails which are assumed to be smooth spheres. The fall velocities of the hails are based on observational derived values. The Reynolds numbers of these flow fields range from 5780 to 206,000. The characteristics of these fields are discussed according to the streamtrace pattern, pressure deviation, z-velocity and vorticity fields. While the upstream flow remains quasi-steady, the wakes of these fields are increasingly turbulent and the maximum velocity region flanking the recirculation bubble exhibits a ring-shedding phenomenon as the Reynolds number increases. The eddy length and drag coefficient for each cases are also calculated and empirical relations are provided. Potential impacts of these characteristics to the cloud physical of hail are also discussed. An outlook of future works is also given.