農耕地における熱的現象の模型実験
(1) 防風垣後方の気温の分布
1972 年 27 巻 4 号 p. 153-158
詳細
1972 年 27 巻 4 号 p. 153-158
In order to make clear the influence of shelter-hedge upon thermal conditions of cultivated fields, measurements of wind and temperature profiles were made in the lee of model windbreaks. Experiments were made in a wind tunnel as shown in Fig. 1 and on a plowed field. The geometrical sizes of model shelter-hedges and the hydraulic charactriestics of underlying surfaces are shown in Table 1. The results obtained are summarized as follows:
1. The similitude between phenomena observed in the wind tunnel and field experiments was examined by the following relations proposed by Inoue (1959) and Nemoto (1961, 1967) for wind profile in the surface air layer
HN/HM=ZON/ZOM, UN/UM=(HN/HM)1/3
Relationships among wind speed, roughness and height of shelter-hedge used in the experiments satisfied approximately the relations mentioned above, indicating that the results obtained in wind tunnel experiments may be applicable to field conditions.
2. Fig. 4 indicates clearly that the vertical distribution of air temperature in the lee of the shelter-hedge (closeness 100%) is not very affected by thermal stratification in air flow. However, the distribution pattern of air temperature in the lee of the shelter-hedge (closeness 100%) changed considerbly by wind speed as shown in Fig. 5. Especially, the temparature profiles observed in field experiments (N) was much affected by wind speed.
3. The temperature rising effect of shelter-hedge was studied in relation to the closeness of sheter-hedge in the wind tunnel. The model shlter-hedges with the closeness of 100, 60, 50, 40 and 30% were set in the wind tunnel and temperature profles in the lee of these shelter-hedges were measuried by using thermocouples. Two-dimensional distributions of air temperature as shown in Fig. 7 indicate that the temperature rising effect is highest in the lee of shelter-hedge with closeness of 60%.
