Field measurements of windbreak effects on airflow, turbulent exchanges and microclimates

被引:26
作者
Cleugh, HA [1 ]
机构
[1] CSIRO Land & Water, Pye Lab, Canberra, ACT 2600, Australia
来源
AUSTRALIAN JOURNAL OF EXPERIMENTAL AGRICULTURE | 2002年 / 42卷 / 06期
关键词
shelter; windbreaks; wind; evaporation fluxes; microclimate;
D O I
10.1071/EA02004
中图分类号
S [农业科学];
学科分类号
09 ;
摘要
While there has been considerable research into airflow around windbreaks, the interaction of this airflow with the exchanges of heat and water vapour has received far less attention. Yet, the effects of windbreaks on microclimates, water use and agricultural productivity depend, in part, on this interaction. A field and wind tunnel experimental program was conducted to quantify the effects of windbreaks on microclimates and evaporation fluxes. This paper describes the field measurements, which were conducted over a 6-week period at a tree windbreak site located in undulating terrain in south-east Australia. The expected features of airflow around porous windbreaks were observed despite the less than ideal nature of the site. As predicted from theory, the air temperature and humidity were elevated, by day, in the quiet zone and the location of the peak increase in temperature and humidity coincided with the location of the minimum wind speed. However, this increase in temperature and humidity was small in size and restricted to the zone within 10 windbreak heights (H) of the windbreak. This pattern contrasts with that for the near surface wind speeds, which were reduced by up to 80% in a sheltered zone that extended from 5 H upwind to over 25 H downwind of the windbreak. Similar differences were found between the turbulent scalar (heat, water vapour) and velocity terms. While both are reduced in the quiet zone, the turbulent scalar terms near the surface were substantially enhanced at the location where the wake zone begins. Here the mean wind speed is reduced by 50% and the turbulent velocity terms return to their upwind values. Wind speed reductions varied linearly with [cos (90-alpha)], where is the incident angle of the wind, for sites located 6 H downwind. This means that the spatial pattern of wind speed reduction applies to all wind directions, provided that distance downwind is expressed in terms of streamwise distance. However, shelter in the near-break region is slightly increased as the wind blows more obliquely towards the windbreak. The atmospheric demand in the quiet zone was reduced when the humidity of the upwind air was low. In such conditions, windbreaks can 'protect' growing crops from the impact of dry air with high atmospheric demand. The corollary is that in humid conditions, the atmospheric demand in the quiet zone can be increased as a result of shelter.
引用
收藏
页码:665 / 677
页数:13
相关论文
共 14 条
[1]  
AYOTTE KW, 1995, J ATMOS SCI, V52, P3523, DOI 10.1175/1520-0469(1995)052<3523:AMSFDM>2.0.CO
[2]  
2
[3]   The Australian National Windbreaks Program: overview and summary of results [J].
Cleugh, H ;
Prinsley, R ;
Bird, RP ;
Brooks, SJ ;
Carberry, PS ;
Crawford, MC ;
Jackson, TT ;
Meinke, H ;
Mylius, SJ ;
Nuberg, IK ;
Sudmeyer, RA ;
Wright, AJ .
AUSTRALIAN JOURNAL OF EXPERIMENTAL AGRICULTURE, 2002, 42 (06) :649-664
[4]   Impact of shelter on crop microclimates: a synthesis of results from wind tunnel and field experiments [J].
Cleugh, HA ;
Hughes, DE .
AUSTRALIAN JOURNAL OF EXPERIMENTAL AGRICULTURE, 2002, 42 (06) :679-701
[5]   Effects of windbreaks on airflow, microclimates and crop yields [J].
Cleugh, HA .
AGROFORESTRY SYSTEMS, 1998, 41 (01) :55-84
[6]   A 3-COMPONENT SONIC ANEMOMETER THERMOMETER SYSTEM FOR GENERAL MICROMETEOROLOGICAL RESEARCH [J].
COPPIN, PA ;
TAYLOR, KJ .
BOUNDARY-LAYER METEOROLOGY, 1983, 27 (01) :27-42
[7]   A wind tunnel study of turbulent flow around single and multiple windbreaks .1. Velocity fields [J].
Judd, MJ ;
Raupach, MR ;
Finnigan, JJ .
BOUNDARY-LAYER METEOROLOGY, 1996, 80 (1-2) :127-165
[8]   EFFECTS OF WINDBREAKS ON TURBULENT TRANSPORT AND MICROCLIMATE [J].
MCNAUGHTON, KG .
AGRICULTURE ECOSYSTEMS & ENVIRONMENT, 1988, 22-3 :17-39
[9]   Large-eddy simulation of windbreak flow [J].
Patton, EG ;
Shaw, RH ;
Judd, MJ ;
Raupach, MR .
BOUNDARY-LAYER METEOROLOGY, 1998, 87 (02) :275-306
[10]  
Seginer I., 1975, Boundary-Layer Meteorology, V8, P383, DOI 10.1007/BF02153559