The typhoon often causes a serious damage of the apple before harvest. Many apples fall from trees by the strong wind. These apples are bagged to protect them from insects and control sun light for the apples coloring while they are ripening on the tree. We conceive that the wind-force acting on the bagging apple exceeds one without bag. Thus, we investigate the drag coefficient C D of the bagging apple by measuring drag force acting on an apple model experimentally. The shear stress on a stem under the typhoon is estimated for understanding one of mechanism for dropping apple due to the strong wind. The shear stress of a stem whose apple encounters the maximum velocity recorded at the past typhoon is estimated by the obtained C D. The drag force of the bagging apple becomes bigger than that of the apple without the bag. The bagging apple is not a rotational symmetry so that the C D is different with the different wind direction. The angle against the flow of model with the bag is changed from 0 deg. to 90 deg. to understand the influence of shape, since C D depends on the geometry. The shear force acting on the stem depends on the drag. Thus, the shear stress is larger if the drag is larger. The obtained shear stress is compared with allowable shear stress of a real tree. We suggest that there is possibility to decrease damage if we can decrease the drag of the bagging.

The drag on a cylinder with an apple-shaped cross section was studied numerically in this paper. This cross section is adopted because the drag on an apple is known to be lower than that of a sphere. Since the hollows of an apple seem to be points of drag reduction, two-dimensional numerical simulations of cylinders with hollows of several shapes are carried out at a Reynolds number of 6.7 × 10 4 by using the vortex method to check their effects. The cylinder with hollows like those of a real apple attained a 13% reduction in drag compared with a circular cylinder. Other geometrical hollow-shapes, namely, V-shaped and U-shaped grooves, also reduced drag from the circular model, but these effects were less pronounced than those of the apple-shaped cross section. It was concluded that an apple-like hollows were effective for drag reduction of a cylinder as well as a sphere.

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