Search

Airflow in the atmospheric surface layer over nonhomogeneous surfaces with discontinuities in surface roughness and temperature is investigated by numerical techniques. A computational scheme is developed for solving the steady state two-dimensional boundary layer equations. Several theorems of convergence are proved. A successful numerical test, which has been compared to the exact solution, is achieved. Some iterative schemes, which have already enjoyed considerable success without theoretical support are here shown to be convergent. The variations in pressure and buoyancy force associated with changes in surface roughness have been neglected by previous investigators whose work is included in the present study. The numerical results of velocity and shear stress are compared with wind tunnel and field data. The roughness and temperature discontinuities are shown to have an effect on the upstream as well as the downstream flow conditions. (Author)

The structure of the turbulent boundary layer on a flat plate consisting of alternate, longitudinal strips of smooth and rough (Sand paper, Grit 4) surfaces parallel to the direction of the flow has been investigated. Measurements of mean velocity, wall shear stress, turbulent intensities, turbulent shear stresses and energy spectra of the streamwise turbulent velocity were obtained. (Author)

A wind tunnel study has been carried out in order to simulate mean flow conditions and turbulence characteristics in the vicinity of the Tower Grid at Dugway Proving Ground. Significant modifications of the upstream flow conditions were found to occur primarily in the region between the Grid Center and the Downstream meteorological tower where the turbulence increased and local accelerations of the flow occurred. (Author)

Measurements of mean velocity, mean-square turbulent velocity, turbulent shear stress, one-dimensional spectrum, and mass concentration distributions following a step increase in surface roughness of a wind-tunnel boundary-layer flow are presented. The mean velocity distributions agree well with Nickerson's numerical calculations for a small roughness change. The mixing-length distribution in the 'transitory' region is not experimentally consistent with that established for fully-developed turbulent boundary layer. Turbulent intensity and shear stress are generated progressively towards the upper layer as one moves downstream from the roughness discontinuity. The high frequency end of the spectra in the 'transitory' region can be exactly represented by the high frequency shape of the undisturbed turbulent boundary layer. Self-preserving mass concentration profiles are in general possible for both the vertical and horizontal distributions. The adjustment of the mean motion to the roughness change is more rapid than that of the turbulence. (Author)

A summary of accomplishments is given of both an experimental and analytical nature in the following specific studies: (1) Airflow in simulated temperate and tropical forest canopy. (2) Methods of modeling diffusion tests ahead of time to design most efficient and economical field experiments. (3) Use of controlled models of field tests to extend empirical data on CB transport and diffusion. (4) Extend wind tunnel investigation to thermally stratified boundary layers and broader ranges of surface roughness. (5) Investigation of longitudinal dispersion through both shear flow and turbulence. (6) Extend the Lagrangian similarity hypothesis considering a more realistic probability function. (7) Model Dugway Proving Ground and study mean wind patterns near the ground when flow aloft is oriented SW-SE. (Author)