Civil Engineering Reports
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From 1947 to 1996, the Colorado State University Department of Civil Engineering issued reprints of engineering papers, bulletins, and documents as the series Civil Engineering Reports. University faculty and students authored most reports, and the department assigned report numbers in order of acquisition for each year. The series grew to more than 2,000 reports, of which nearly 1,300 are available in this digital collection.
Other CERs may be found in Mountain Scholar - Archives and Special Collections and in the Groundwater Data Collection.
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Browsing Civil Engineering Reports by Subject "Air flow -- Mathematical models"
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Item Open Access An investigation of flow over high roughness(Colorado State University. Libraries, 1971-08) Kawatani, Takeshi, author; Sadeh, Willy Z., author; Colorado State University, publisherAn experimental investigation of the atmospheric boundary-layer flow on high roughness was conducted by simulating the flow over a forest canopy in a meteorological wind tunnel. The model forest canopy used consisted of plastic simulated-evergreen trees. The measurements were carried out at constant free-stream velocity and under thermally neutral conditions. Two canopy densities were tested to explore the effects of the roughness density on the flow. One roughness density was half of the other. The results indicate that the mean velocity profiles within the fully developed flow region can be described by generalized logarithmic relationships. For the flow in the inner zone, the free-stream velocity and the roughness height are the similarity parameters for the velocity and the vertical distance, respectively. In the outer zone the freestream velocity and the momentum thickness are the scaling parameters. The roughness density has a strong influence on the momentum loss and the upward flow displacement in the transition region. The shape of the roughness element affects the mean velocity distribution inside the canopy, i.e., jetting effect. The internal boundary-layer thickness was determined based on the turbulent shear-stress distribution. It is found that the flow near the canopy leading edge has two-dimensional wake-like characteristics. The latter are due to the canopy frontal area which is a drastic step obstruction. The existence of an inertial subrange in the fully developed flow region is doubtful although local isotropy occurs for eddies smaller than 2% of the total boundary-layer thickness. The evolution of turbulent energy associated with various size eddies along the canopy can be successfully described by a discretized-energy analysis.Item Open Access Interaction of a wall-jet with a shear flow(Colorado State University. Libraries, 1972-05) Mukherji, Sanjib K., author; Sadeh, Willy Z., author; Fluid Dynamics and Diffusion Laboratory, Fluid Mechanics Program, Department of Civil Engineering, Colorado State University, publisherAn experimental investigation of a flow field resulting from the interaction between a spreading turbulent wall jet on a smooth surface and a shear flow was conducted. The combined flow was formed by a downward circular jet penetrating perpendicularly a moving shear stream confined within a constant-area open channel. A hot-wire survey of mean velocity and turbulence intensity was carried out. A similar variation of mean velocity was found to exist on either side of the axis of the impinging jet, provided that appropriate characteristic scales were used. Similarity was obtained by dividing the flow into an inner and an outer layer, and by subdividing the latter into two zones of equal thickness. This partition into three distinct regions was deduced from the velocity change with height and, particularly, from the existence of a local characteristic maximum velocity. Within each region, velocity and length scales were formulated. The former was defined in terms of the local maximum velocity for the inner layer. In the two zones of the outer layer the velocity scales were defined in terms of the zonal maximum excess velocities. The excess velocity was computed with respect to the local free-stream velocity characteristic to this flow. In all three regions, the thicknesses of the layers were utilized as the length scale. The similarity in mean velocity variation is corroborated by the computed constant values of the shape factor for each particular region of the flow. The use of analogous scales led to similarity in the change of mean energy. Furthermore, it was found that the turbulence intensity variation exhibited similarity when the same scales used for the velocity were employed.Item Open Access Numerical simulation of wind, temperature, shear stress and turbulent energy over nonhomogeneous terrain(Colorado State University. Libraries, 1972-03) Huang, Chin-hua, author; Nickerson, Everett C., author; Colorado State University, Fluid Dynamics and Diffusion Laboratory, College of Engineering, publisherAirflow 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. Significant variations in the horizontal velocity, vertical velocity and shear stress profiles near the roughness discontinuity occurred between those cases neglecting and those retaining the pressure terms in the governing equations. The predicted physical quantities for diabatic conditions also show significant differences in those two cases; thus, the pressure terms should be retained in the governing equations. No inflection point in the wind profile for neutral conditions has been observed in the mixing length model; however, it has been observed in both the turbulent energy model and the model presented in this study. The field and wind tunnel observations also confirm the presence of an inflection point. The inflection point is less visible in the presented model as compared with the turbulent energy model. For a small change in surface roughness, the wind profiles simulated by the numerical method are in good agreement with wind tunnel data. The distribution of the surface shear stress predicted by the presented theory is in better agreement with Bradley's field data than previously existing theories. A proposed mechanism of turbulent energy transfer is developed, based upon the results of numerical experiments that explain the distribution of shear stress, and, hence, the distribution of velocity profiles in the atmospheric surface layer. Two different theories, the mixing length theory and the turbulent energy theory, are modified, and examined in detail; a theory is developed to remove some weaknesses of previously existing theories.