Download or read book Calculations of Unsteady Turbulent Boundary Layers with Flow Reversal written by John F. Nash and published by . This book was released on 1975 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: The results are presented of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method developed earlier was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degrees of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. A singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations. A tentative hypothesis was advanced in an attempt to predict the appearance of the singularity, and is shown to be consistent with the calculated results.
Download or read book Computation of Unsteady Turbulent Boundary Layers with Flow Reversal and Evaluation of Two Separate Turbulence Models written by Tuncer Cebeci and published by . This book was released on 1981 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently a new procedure, which solves the governing boundary-layer equations with Keller's box method, has been developed for calculating unsteady laminar flows with flow reversal. In this report, we extend this method to turbulent boundary layers with flow reversal. Using the algebraic eddy viscosity formulation of Cebeci and Smith, we consider several test cases to investigate the proposition that unsteady turbulent boundary layers also remain free of singularities. We also perform turbulent flow calculations by using the turbulence model of Bradshaw, Ferriss, and Atwell; we solve the governing equations for both models by using the same numerical scheme and compare the predictions with each other. The study reveals that, as in laminar flows, the unsteady turbulent boundary layers are free from singularities, but there is a clear indication of rapid thickening of the boundary layer with increasing flow reversal. The study also reveals that the predictions of both turbulence models are the same for all practical purposes. (Author).
Download or read book Calculations of Unsteady Turbulent Boundary Layes with Flow Reversal written by J.F. Nash and published by . This book was released on 1975 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Computation of Unsteady Turbulent Boundary Layers with Flow Reversal and Evaluation of Two Separate Turbulence Models written by Dhirendra Patel and published by . This book was released on 1980 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Further Studies of Unsteady Boundary Layers with Flow Reversal written by John F. Nash and published by . This book was released on 1976 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Calculation of Boundary Layers Near the Stagnation Point of an Oscillating Airfoil written by Tuncer Cebeci and published by . This book was released on 1983 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: The results of an investigation of boundary layers close to the stagnation point of an oscillating airfoil are reported. Two procedures for generating initial conditions - the characteristics-box scheme and a quasi-static approach - were investigated, and the quasi-static approach was shown to be appropriate provided the initial region was far from any flow separation. With initial conditions generated in this way, the unsteady boundary-layer equations were solved for the flow in the leading-edge region of a NACA 0012 airfoil oscillating from 0 degrees to 5 degrees. Results were obtained for both laminar and turbulent flow, and, in the latter case, the effect of transition was assessed by specifying its occurrence at different locations. The results demonstrate the validity of the numerical scheme and suggest that the procedures should be applied to calculation of the entire flow around oscillating airfoils. (Author).
Download or read book Calculations of Unsteady Turbulent Boundary Layers with Flow Reversal written by and published by . This book was released on 1975 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Standardization of Computational Experiments in Unsteady Turbulent Boundary layer Flow written by and published by . This book was released on 1977 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experiments on Controlled Unsteady Separated Turbulent Boundary Layers written by W. C. Reynolds and published by . This book was released on 1984 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments on turbulent boundary were layers subjected to controlled unsteadiness were performed in a special water channel. The flow is steady in the development section upstream of the unsteady test section where the boundary layer is subjected to an oscillating adverse free-stream velocity gradient sufficient to induce flow reversal near the wall. Measurements of the mean, oscillatory, and turbulence components of the streamwise velocity in the boundary layer indicate that the mean velocity and mean turbulent stresses are unaffected by the oscillations, whereas the periodic components of these quantities are strongly dependent upon frequency. At low frequencies the boundary layer behaves quasistaticly at intermediate frequencies the boundary layer behavior correlates with the Strouhal number based on the length of the unsteady region and at high frequencies the outer region of the boundary layer moves as a slug while the sublayer behaves as a Stokes layer described by laminar equations. Reverse flows occur in this Stokes layer, but the boundary layer remains thin and hence attached to the surface.
Download or read book Further Studies of Unsteady Turbulent Boundary Layers written by B. R. Ramaprian and published by . This book was released on 1986 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: Periodic turbulent boundary layers in zero and adverse time-mean pressure gradient have been studied. The study includes experimental, analytical and numerical investigations. The experiments were conducted in an unsteady-flow water tunnel, in which the freestream velocity varies sinusoidally with time around a mean value. Reduced frequencies up to about 25 and a relative oscillation amplitude of 40 per cent of the mean velocity were studied. Flow reversal occurred over a significant part of the oscillation cycle in the adverse pressure gradient experiments, though no mean-flow separation was observed. Data on turbulent stresses and wall shear stress were obtained using a two-component laser Doppler anemometry and a surface-mounted heat flux gage. A theory and calibration procedure were developed for the use of the latter in unsteady flow. All the experimental data were recorded on magnetic tape. A general asymptotic theory has been developed for unsteady turbulent boundary layers. This theory leads to the development of wall functions for these flows. Such wall functions have been developed and used in a calculation procedure based on the k-epsilon model of turbulence.
Download or read book Calculation of Boundary Layers of Oscillating Airfoils written by and published by . This book was released on 1984 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Prediction of Unsteady Turbulent Boundary Layers with Flow Reversal written by Tuncer Cebeci and published by . This book was released on 1979 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: The prediction of unsteady turbulent boundary layers with flow reversal is of importance in a number of aerodynamic problems, notably in dynamic stall, buffeting and gust studies. However, some of the more popular turbulence models implicity assume that the wall shear is positive and their extension to unsteady flows with flow reversal is not easy. It requires a modification of the functional form of the law of the wall and the manner in which the wall shear is determined. Two near-wall assumptions are considered here. In the first, the near wall grid point is located in the logarithmic region and the law of the wall is used to link the flow properties at this grid point to the wall. In the second, a Van Driest formulation due to Cebeci and Smith is used and implies that the grid point closest to the wall will occur in the viscous sublayer.
Download or read book Prediction of Periodic Boundary Layers written by A. N. Menendez and published by . This book was released on 1984 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: A relatively simple, yet efficient and accurate finite difference method is developed for the solution of the unsteady boundary layer equations for both laminar and turbulent flows. The numerical procedure is subjected to rigorous validation tests in the laminar case, comparing its predictions with exact analytical solutions, asymptotic solutions, and/or experimental results. Calculations of periodic laminar boundary layers are performed from low to very high oscillation frequencies, for small and large amplitudes, for zero as well as adverse time-mean pressure gradients, and even in the presence of significant flow reversal. The numerical method is then applied to predict a relatively simple experimental periodic turbulent boundary layer, using two well-known quasi-steady closure models. The predictions are shown to be in good agreement with the measurements, thereby demonstrating the suitability of the present numerical scheme for handling periodic turbulent boundary layers. The method is thus a useful tool for the further development of turbulence models for more complex unsteady flows. (Author).
Download or read book Unsteady Turbulent Boundary Layer Analysis written by and published by . This book was released on 1973 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Unsteady Turbulent Shear Flows written by R. Michel and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 445 pages. Available in PDF, EPUB and Kindle. Book excerpt: It was on a proposal from the "Comite National Fran.
Download or read book Analysis of Dynamic Stall Using Unsteady Boundary layer Theory written by Roy Mac Scruggs and published by . This book was released on 1974 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Analysis of Dynamic Stall Using Unsteady Boundary layer Theory written by R. M. Scruggs and published by . This book was released on 1974 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt:
