Calculations Of Unsteady Turbulent Boundary Layers With Flow Reversal PDF Download
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| Author | : John F. Nash |
| Publisher | : |
| Total Pages | : 58 |
| Release | : 1975 |
| Genre | : Atmospheric turbulence |
| ISBN | : |
Download Calculations of Unsteady Turbulent Boundary Layers with Flow Reversal Book in PDF, ePub and Kindle
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.
| Author | : Tuncer Cebeci |
| Publisher | : |
| Total Pages | : 55 |
| Release | : 1981 |
| Genre | : Turbulent boundary layer |
| ISBN | : |
Download Computation of Unsteady Turbulent Boundary Layers with Flow Reversal and Evaluation of Two Separate Turbulence Models Book in PDF, ePub and Kindle
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).
| Author | : Dhirendra Patel |
| Publisher | : |
| Total Pages | : 134 |
| Release | : 1980 |
| Genre | : Turbulent boundary layer |
| ISBN | : |
Download Computation of Unsteady Turbulent Boundary Layers with Flow Reversal and Evaluation of Two Separate Turbulence Models Book in PDF, ePub and Kindle
| Author | : J.F. Nash |
| Publisher | : |
| Total Pages | : 46 |
| Release | : 1975 |
| Genre | : |
| ISBN | : |
Download Calculations of Unsteady Turbulent Boundary Layes with Flow Reversal Book in PDF, ePub and Kindle
| Author | : John F. Nash |
| Publisher | : |
| Total Pages | : 116 |
| Release | : 1976 |
| Genre | : Navier-Stokes equations |
| ISBN | : |
Download Further Studies of Unsteady Boundary Layers with Flow Reversal Book in PDF, ePub and Kindle
| Author | : Tuncer Cebeci |
| Publisher | : |
| Total Pages | : 22 |
| Release | : 1983 |
| Genre | : |
| ISBN | : |
Download Calculation of Boundary Layers Near the Stagnation Point of an Oscillating Airfoil Book in PDF, ePub and Kindle
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).
| Author | : |
| Publisher | : |
| Total Pages | : 60 |
| Release | : 1975 |
| Genre | : |
| ISBN | : |
Download Calculations of Unsteady Turbulent Boundary Layers with Flow Reversal Book in PDF, ePub and Kindle
| Author | : |
| Publisher | : |
| Total Pages | : 20 |
| Release | : 1977 |
| Genre | : |
| ISBN | : |
Download Standardization of Computational Experiments in Unsteady Turbulent Boundary-layer Flow Book in PDF, ePub and Kindle
| Author | : W. C. Reynolds |
| Publisher | : |
| Total Pages | : 7 |
| Release | : 1984 |
| Genre | : |
| ISBN | : |
Download Experiments on Controlled, Unsteady, Separated Turbulent Boundary Layers Book in PDF, ePub and Kindle
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.
| Author | : B. R. Ramaprian |
| Publisher | : |
| Total Pages | : 63 |
| Release | : 1986 |
| Genre | : |
| ISBN | : |
Download Further Studies of Unsteady Turbulent Boundary Layers Book in PDF, ePub and Kindle
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.
