Wind tunnel simulation of atmospheric boundary layer flows

The present work shows how thick boundary layers can be produced in a short wind tunnel with a view to simulate atmospheric flows. Several types of thickening devices are analysed. The experimental assessment of the devices was conducted by considering integral properties of the flow and the spectra: skin-friction, mean velocity profiles in inner and outer co-ordinates and longitudinal turbulence. Designs based on screens, elliptic wedge generators, and cylindrical rod generators are analysed. The paper describes in detail the experimental arrangement, including the features of the wind tunnel and of the instrumentation. The results are compared with experimental data published by other authors and with naturally developed flows.Indisponível

Approximate Solutions to Singular Perturbation Problems: The Intermediate Variable Technique

AbstractThe intermediate variable technique, developed by S. Kaplun, “Fluid Mechanics and Singular Perturbations,” Academic Press, San Diego, 1967, and by P. A. Lagerstrom and R. G. Casten, Basic concepts underlying singular perturbation techniques, SIAM Rev. 14 (1972), 63–120, for the solution of singular perturbation problems, is applied to several problems which are normally solved by other perturbative methods. The objective of the present analysis is to obtain approximate solutions which are characterized by their domains of validity, so that the matching of adjacent solutions is promptly determined. The analysis also shows how the intermediate equations can be derived and how they play an important role in the determination of approximate Solutions

Wall function treatment for bubbly boundary layers at low void fractions

Abstract The present work investigates the role of different treatments of the lower boundary condition on the numerical prediction of bubbly flows. Two different wall function formulations are tested against experimental data obtained for bubbly boundary layers: (i) a new analytical solution derived through asymptotic techniques and (ii) the previous formulation of Troshko and Hassan (IJHMT, 44, 871-875, 2001a). A modified k-e model is used to close the averaged Navier-Stokes equations together with the hypothesis that turbulence can be modelled by a linear superposition of bubble and shear induced eddy viscosities. The work shows, in particular, how four corrections must the implemented in the standard single-phase k-e model to account for the effects of bubbles. The numerical implementation of the near wall functions is made through a finite elements code

Wall function treatment for bubbly boundary layers at low void fractions

<div><p>Abstract The present work investigates the role of different treatments of the lower boundary condition on the numerical prediction of bubbly flows. Two different wall function formulations are tested against experimental data obtained for bubbly boundary layers: (i) a new analytical solution derived through asymptotic techniques and (ii) the previous formulation of Troshko and Hassan (IJHMT, 44, 871-875, 2001a). A modified k-e model is used to close the averaged Navier-Stokes equations together with the hypothesis that turbulence can be modelled by a linear superposition of bubble and shear induced eddy viscosities. The work shows, in particular, how four corrections must the implemented in the standard single-phase k-e model to account for the effects of bubbles. The numerical implementation of the near wall functions is made through a finite elements code.</p></div