Investigation of forests as factor of aerodynamic protection of settlements from dust storms and industrial polution

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

The paper presents the results of the experimental research on the aerodynamic resistance forces of different types of the forest plantations and the types of tree planting under the air mass motion. The results of mathematical modeling of moving a dust cloud filled with different sized particles in a forest massif are shown with account of sizes and the mass of the crown elements, the resistance forces of separate elements of tree crowns. While investigating branch resistances as dimensionless parameters one can separate the two Reynolds numbers: one of them is calculated by the diameter of a needle, the other by the diameter of a branch – base to which the needles are attached. As a method to determine the resistance forces of the treetops, in this paper a hydrodynamic approach is applied where the authors propose to investigate the resistance coefficient of the branch (being investigated) when it is moving in water. On this grounds in order to investigate the resistance coefficients of the woodland a setting was assembled, it was based on the study of falling these elements into a transparent pool of water under the action of gravity produced by special cargoes. It was revealed that the resistance coefficient of the conifer crowns greatly depends on the velocity of a climbing stream. Thus, at high Reynolds numbers a well-known effect of "folding" of the crown elements is observed and the resistance coefficient of the whole crown tends to the resistance coefficient of the needleless branches. With the flows up to 20 m/s the main parameter which determines the flow past the bodies with the predetermined geometry is the Reynolds number. On the basis of the data obtained from the experiment a mathematical modeling of a dust cloud was carried out in a stand of forest. The propagation of the wind in the stand of forest is described by three-dimensional equations of gas dynamics. To describe the dust cloud the continuum model consisting of dust particles was adopted as a mathematical model. It takes into account the forces acting on the particles from the air, as well as the sizes of dust particles and the change of momentum of particles in collisions with the elements of trees. In this case it is assumed that in such collisions a dust mass falls on the trees and it is proportional to the surface of these elements, to the dust flow on them and to a certain coefficient of the particle capture which can vary from zero to unity. The simulation of the dust particles is based on the Eulerian approach, the movement of the mass is modeled in the volume. The influence of different types of forests and forms of the forest plantations on the process of distribution of the dust cloud of particles was also investigated. To protect from a dust cloud a series of computational experiments of comparing the efficiency of certain variants of the forest protection zones has been carried out. The results can be used while designing the measures to protect the settlements from the harmful ejections and emissions of the industrial enterprises. In this paper the results of the parametric investigation for different types of particles have been presented, the conclusions as regards the efficiency of some types of the forest protecting belts have been made. The problem of modeling the distribution of the dust cloud with the account of the viscosity forces recorded in the approximation of the boundary layer in the forest belt has been solved.