trees

Reports daily run-of-wind measurements, made for 3 years at distances of 3.5 h and 7 h to leeward of a 7-row shelterbelt about 6m.high. After elimination of variations in wind direction, the monthly values of relative shelter at these positions showed no evidence of an increase with time. The variations in wind direction were eliminated by regressions of monthly values of relative shelter on the monthly percentage frequency of effective winds, i.e. winds from the normal windward side of the shelterbelt.

Describes experiments aiming to estimate the protection afforded by a shelterbelt on the plains area of America. Describes three test houses and gives test results. The three houses were unprotected, partially protected and closely protected by a slat fence. Gives basic data in the form of fuel use, wind and temperature. Concludes that the reduction in wind speed by windbreaks is of the general order of 35% with a proportional saving in fuel. Finds that the area of tree shelterbelts has themost important effect on the degree of wind reduction.

Discusses the need for shelterbelts over farmland and gives expression for drag force exerted by a barrier in terms of air density, wind speed, barrier height and ratio of wind speed in the shelter to that in the open. Describes field study to determine the effect of a shelterbelt on vertical wind profiles. Presents two-dimensional wind reduction patterns in the lea of the shelterbelt. Calculates drag coefficients for the shelterbelt. Concludes that a shelterbelt can be very effectivein a very short period after planting.

Describes experiment to determine the effect of an evergreen windbreak on residential heat losses attributable to air infiltration. Eight-meter tall pines were arranged as an experimental windbreak to shelter a townhouse for nine weeks Air infiltration was measured continuously using SF6 as a tracer gas to compare air change rates before and after the windbreak. A dimensionless parameter was derived to distinguish between wind-and temperature-produced air infiltration and to determine the effects of wind direction.

States that porosity is the most important single parameter describing shelterbelts but is very difficult to measure or define. Describes a method for categorizing wind breaks in terms of porosity using only measured minimum leeward-wind velocity. Gives theoretical expressions for the flow through a porous shelterbelt. Describes experiment to measure wind velocities around shelterbelts of low, medium and high porosity. Shows that wind measurements could be made any height without affecting relative reduction in velocity.

Refers to earlier work by Mattingly, Peters, Harrje and Heisler which indicated the possibility of reducing air infiltration by using sheltering devices such as fences, neighbouring buildings and trees. Reports use of wind tunnel air infiltration model to explore the effect of trees in a windbreak on a model home. Presents results of tests determining the effect on wind-induced air infiltration of the variation of various windbreak layout parameters. Introduces concept of turbulence generation as the mechanism of tree wind sheltering.