マイクロバースト下降流の力学的特性付け

概要

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The air downdraft which is caused by an ensemble of falling condensed particles is analyzed on the basis of a two-dimensional prototype model to characterize the dynamics of microburst downdrafts. It is assumed that the identical particles are initially suspended in otherwise quiescent atmosphere, with a uniform number density in a rectangular region located above the ground surface. The analysis satisfactorily identifies the only dynamic dimensionless parameter which yields the criterion of microburst onset σ=(pmg/n_oH)^<1/2>/D<1, where no is the number density of condensed particle with weight mg and drag coefficient D, p the air density and H the initial height of condensed particle ensemble column. The magnitude of downdraft velocity is scaled by (n_omgH/p)^<1/2>. The underlying physics are interpreted in terms of vortex dynamics. The conventional physical model of microburst, described in terms of a vortex ring colliding a plane surface, is found to be valid only for the later stage of diverging flow on the ground surface because the vorticity sheet produced along the particle ensemble column perimeter can not roll up into a vortex ring during the downdraft stage.
一般社団法人日本機械学会の論文
1999-08-25