Relation between bagging of an apple and strong wind

Abstract

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 CD 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 CD. 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 CD 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 CD 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.

Keywords

• drag coefficient
• shear stress
• drag force
• apple drop
• bagging
• typhoon