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Renormalized droplet theory is applied to study the influence
of convective flow and short range drop-drop interaction on the
aerodynamic drag of a droplet. Based on the renormalized
droplet theory, the influence of convective flow on the
aerodynamic drag of a droplet could be decomposed into five
principal mechanisms : (1) the variations in pressure of the
flow field, (2) the viscous effects, (3) the variations in
momentum of the flow field, (4) the thrust drag of the test
droplet caused by droplet vaporization, (5) the effects of
unsteadiness. It is found that for a single droplet in hot
convective flow, the aerodynamic drag is decreased as the
environment temperature is increased. At lower Reynolds number,
the aerodynamic drag of a combustion droplet is higher than a
vaporizing droplet due to the existence of the envelope flame.
As the effects of drop-drop interaction are considered, the
aerodynamic drag of the test droplet at lower environment
temperature is increased as the number density of field
droplets is increased.On the other hand, when the environment
temperature is higher, the drag coefficient of the test droplet
is decreased as the number density of field droplets is
increased.Furthermore,according to the renormalized theory, it
is found that the pressure variations dominate the drag
coefficient of the test droplet, as the drop-drop interaction
effects are considered. The viscous effects are further
important as the number density of neighboring droplets is
decreased. The variations in momentum of the flow field would
produce negative effects on the drag coefficient. As to the
thrust drag of the test droplet is almost negligible in our
calculation.
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