ON SHELTER EFFICIENCY OF SHELTERBELTS IN OBLIQUE WIND

The changes of shelter effects in oblique flows are studied by numeric al simulations. The simulated results show that horizontal profiles of wind speed and the location of the minimum wind speed (i,e., maximum wind reduction) move toward the shelterbelt when approach flows depart from the normal, and wind speed may exceed the undisturbed wind speed in the middle lee because of the channeling effect of shelterbelts. W ith increasing wind incidence angle (IA), the minimum wind speed may d ecrease or increase, and the rate of decrease in the shelter distance may be faster or slower than cos(IA), both depending on the height of observation and the density and width of shelterbelts, The mean wind s peed reduction over 30H (H is shelterbelt height) leeward shows simila r characteristics to the shelter distance. The change of shelter effec ts in oblique flows may result from (i) change of effective shelterbel t density, (ii) different efficiencies in reducing wind speed in direc tions perpendicular and parallel to the belt, and (iii) change of hori zontal wind direction as the flow recovers to the undisturbed directio n. The relative importance of each factor, which depends on the height of observation and the density and width of shelterbelts, determines the variation of shelter effects. The simulations produced all the obs erved qualitative characteristics of shelter effects and for those pre vious reports giving measured values, the model produced results that are in good agreement.