Frictional Resistance of a Forest Edge

B. Shannak ； U. Corsmeier ； Ch. Kottmeier ； K. Träumner ； A. Wieser ； M. Al-Rashdan

《Development and Applications of Oceanic Engineering》 1卷1期 (2012/11) Pp. 12-23

並列摘要

The effect of vegetation on flow generally is expressed as an effect on hydraulic roughness. Based on wind velocity measurements using a Doppler, Wind LIDAR (Light Detection And Ranging), the resistance of forest edge and, hence, the velocity profile and friction coefficient were investigated. Against the sudden change in roughness height due to the existence of trees, the airflow streamlines are unable to follow the sharp angle of the forest. As a consequence, flow separation and contraction occur and cause the main friction losses. Considering the shape of the measured wind profiles flat, parabolic and wavy inflected profiles forms can be distinguished. Applying the conservation laws of mass, momentum, and energy, a new model was developed to determine the friction coefficient of forest. The experimental results demonstrate that at 30 m forest height and an average wind velocity from 3 up to 9 m/s the friction coefficient decreases with increasing pressure ratio and Froude number as well as Reynolds number and varies from 0.08 to 0.002. An empirical correlation was represented as a simplified form of the proposed model. The correlation includes the relevant primary parameters, fits the experimental data well, and is sufficiently accurate for engineering purposes. The results may be very useful for the most common flow dynamics problems in the atmosphere, environment, hydrology, metrology, and wind engineering.

並列關鍵字

Friction Coefficien ； Flow Resistance ； Forest ； Velocity Profile ； LIDAR