ON THE WINDBREAK IN THE FIELD. : (II) Systematic Studies in Windbreak by Windtunnel Experiment Method (No.1)

[摘要] The present model experiments were carried out by the windtunnel experiment method in order to know the relation between the clearance ratio of the fence and the breaking effect, using a great number of lattice fences which have different amount of crevices. The wind velocity was measured with the Pitot tube putting it 5 cm apart from the board floor. The standard wind velocity V was 10 or 20 m/s. The curves of wind velocity ratio in the figures in this paper are shown v/V×100 (V: the standard wind velocity, v: local wind velocity). The results cbtained were as follows: 1. A lattice fence with a few crevices has a large vortex region where severe adverse wind is created on the leeward near the fence and the wind regains its strength quickly after passing the fence. On the contrary it has been known that a lattice fence with too many crevices are useless for weakening the wind force. Accordingly the ideal fence for breaking the wind strength is the one where the crevices occupy 40∼50% of the surface of the fence. 2. A little difference exists between the cylindrical lattice bolt and oblong lattice bolt concerning the clearance ratio. The former flows out air more easily than the latter. Therefore in order to get the perfect effect, the clearance ratio of the former should be lower than that of the latter. 3. The curve of wind velocity ratio in the leeward has nothing to do with the strength of the standard wind velocity.

[学科分类] 农业科学（综合）