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Windbreak Function (How do they work?). Joe Zeleznik NDSU Extension Forester. Windbreak Function - Basics. They slow down the wind They re-direct the wind Which modifies the microclimate and environment in protected areas. Based on Structure. Based on Structure. Density - % solid.
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Windbreak Function(How do they work?) Joe Zeleznik NDSU Extension Forester
Windbreak Function - Basics • They slow down the wind • They re-direct the wind • Which modifies the microclimate and environment in protected areas
Based on Structure • Density - % solid
Based on Structure • Density - % solid • Height – changes over time – height of tallest row
Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length –
Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds
From Northerly or northwesterly Direction 12 out of 24 From Southeasterly or Easterly Direction 10 out of 24 From Southwesterly Direction 2 out of 24
Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds • Continuity
Based on Structure • Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds • Continuity • Species/Number of Rows
Windspeed in the open Fastest Slowest Ground
Windspeed in the open Fastest Slowest No turbulence over smooth ground Ground Turbulent flow over a rough surface
Windspeed in the open Fastest Turbulent - Random Slowest No turbulence over smooth ground Ground Turbulent flow over a rough surface Eddy – Circular, against main flow
Terms to know: H = height of object Upwind Windward Downwind Leeward
Pressure eddy Solid barrier 1-2H
Suction eddy Turbulent wake zone Resumption of open-field flow Solid barrier 1-3H 3-6H 6-8H
Porous barrier Lower effect of pressure eddy
Porous barrier Resumption of open-field flow Lower effect of suction eddy Turbulent wake farther downwind
Lower branches pruned Resumption of open-field flow Increased snow spreading? Even lower effect of suction eddy Turbulent wake even farther downwind
How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction (and length of protected zone)
Density Upwind Downwind
How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction (and length of protected zone) • Height – along with density, determines length of protected zone, upwind and downwind
WIND HEIGHT Protected Area 2-5 H 10-20 H Protected Area Protected Area
How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection
LENGTH End effect: Windspeeds increased around end of windbreak by 1.1-1.3 times
PROTECTED AREA Length:Height - > 10:1
How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection • Orientation – place perpendicular to prevailing winds
Wind ORIENTATION
? Wind
? PROTECTED AREA Wind
Wind PROTECTED AREA ? PROTECTED AREA
From Northerly or northwesterly Direction 12 out of 24 From Southeasterly or Easterly Direction 10 out of 24 From Southwesterly Direction 2 out of 24
How does structure affect wind speed and wind flow? • Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection • Orientation – place perpendicular to prevailing winds • Continuity