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Numerical and wind tunnel simulation of stratified shear layers to nonhomogeneous surface features




Yamada, Tetsuji, author
Meroney, Robert N., author
Colorado State University, publisher

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Two-dimensional airflows over various nonuniform surfaces in a stratified atmosphere are studied both numerically and experimentally. Three problems are investigated, classified by the effect of the external forcing functions upon the basic airflow. They are: 1) mountain lee waves, 2) heat islands (sea breezes are included here), and 3) heated mountain phenomena in a stratified airflow. Both experiments and numerical analyses are conducted for each case. A wind tunnel was designed and constructed for these particular problems, since they require very small velocities and a strong temperature stratification. Both numerical and wind tunnel experiments succeed in producing clear lee waves behind the square obstacle. The amplitude of the first wave is about the same order of magnitude as the obstacle height, and wave length closely agrees with that predicted by the linear theory. Perturbations of a stratified shear flow by a heated boundary, which may represent a heated island or an urban region, are investigated experimentally and numerically. These experiments are apparently the first attempt to simulate the urban heat island effect in a wind tunnel facility. The results obtained by both numerical and experimental methods agree quantitatively. Several modifications of meteorological factors by urbanization are reproduced: a downward wind and acceleration of a horizontal velocity in the surface layer of an approach flow to a city, temperature cross over, and frequent elevated inversion but less frequent surface inversion over the city during the night. If the obstacle is heated, then the flow combines the features of the airflow over an obstacle and that over a heated island. A detailed examination of the results reveals a strong nonlinearity which does not allow one to utilize conventional linearization techniques as a first approximation of the phenomenon.


June 1971.
Includes bibliographical references (pages 153-164).
Prepared under Office of Naval Research contract no. N00014-68-A-0493-0001, Project No. NR 062-414/6-6-68(Code 438).
Project THEMIS, technical report no. 9.

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Dynamic meteorology
Convection (Meteorology)


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