Computation of Unsteady Turbulent Boundary Layers with Flow Reversal and Evaluation of Two Separate Turbulence Models PDF Download
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Author: Tuncer Cebeci
Publisher:
ISBN:
Category : Turbulent boundary layer
Languages : en
Pages : 55
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Book Description
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: Tuncer Cebeci
Publisher:
ISBN:
Category : Turbulent boundary layer
Languages : en
Pages : 55
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Book Description
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:
ISBN:
Category : Turbulent boundary layer
Languages : en
Pages : 134
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Author: R. Michel
Publisher: Springer Science & Business Media
ISBN: 3642817327
Category : Science
Languages : en
Pages : 445
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Book Description
It was on a proposal from the "Comite National Fran.
Author:
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ISBN:
Category : Science
Languages : en
Pages : 220
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Author:
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Category :
Languages : en
Pages : 60
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Author: Tuncer Cebeci
Publisher:
ISBN:
Category :
Languages : en
Pages : 22
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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: W. H. Shafer
Publisher: Springer Science & Business Media
ISBN: 1468442295
Category : Science
Languages : en
Pages : 311
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Book Description
Masters Theses in the Pure and Applied Sciences was first conceived, published, and dis seminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS) * at Purdue University in 1957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dissemination phases of the ac tivity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the thought that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this joint undertaking we had concluded that it was in the interest of all concerned if the printing and distribution of the volume were handled by an international publishing. house to assure improved service and broader dissemination. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Corporation of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 25 (thesis year 1980) a total of 10,308 theses titles from 27 Canadian and 214 United States universities. We are sure that this broader base for theses titles reported will greatly enhance the value of this important annual reference work. While Volume 25 reports theses submitted in 1980, on occasion, certain universities do report theses submitted in previous years but not reported at the time.
Author:
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Category : Mechanics, Applied
Languages : en
Pages : 568
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Author:
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Category : Aeronautics
Languages : en
Pages : 464
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Author: Yue Zhang
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ISBN:
Category :
Languages : en
Pages :
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"Employing the advection-diffusion-reaction equation as a model problem, a multiscale stable finite element formulation is presented for the Spalart-Allmaras turbulence model, and for the Zonal Detached-Eddy Simulation (ZDES) with a vorticity-based subgrid length scale. The multiscale method arises from a decomposition of the scalar field into coarse (resolved) and fine (unresolved) scales. Modeling of the unresolved scales corrects the lack of stability of the standard Galerkin formulation. The proposed method possesses superior properties like those of the Streamline Upwind/Petrov-Galerkin method and the Galerkin/Least-Squares method. The stabilization terms appear naturally and are effective for turbulent computations in which reaction-dominated effects strongly influence the boundary layer prediction.Validation of the method is accomplished via a two-dimensional problem in which skewed advection goes through a unit square, and a three-dimensional problem where turbulent unsteady flow passes over tandem cylinders. The boundary layer separation, free shear layer roll-up, vortex shedding from the upstream cylinder, and interaction with the downstream cylinder, are well reproduced. Good agreement with experimental measurements gives credence to the accuracy of ZDES in modeling turbulent separated flows.Following validation, two problems related to turbulent flows in aerospace and wind engineering applications are investigated. The first study is the evaluation of the performance degradation of ice-contaminated airfoils, including a NACA 23012 airfoil with a spanwise ice ridge, and a GLC-305 airfoil with a leading edge horn-shape glaze ice. Appropriate spanwise domain size and sufficient grid density are determined to enhance the reliability of the simulations. A comparison of lift coefficient and flow field variables demonstrates the added advantage of the ZDES model for the standard Spalart-Allmaras turbulence model, as illustrated by massively separated flows at pre-stall conditions of an icing airfoil. The vorticity-based subgrid length scale in ZDES prevents the delayed development of instabilities in the shear layer and a subsequent late transition to a fully turbulent flow. Spectral analysis and instantaneous visualization of turbulent structures are also highlighted.Another application of interest is wind-induced vibrations of tall buildings. In this numerical procedure, the natural unsteady wind in the atmospheric boundary layer is modeled with artificial inflow turbulence generation. The turbulent flow is simulated by the stabilized ZDES model, and a conservative quadrature-projection scheme is adopted to transfer unsteady loads from fluid to structural nodes. The aerodynamic damping that represents the fluid-structure interaction mechanism is determined by empirical functions extracted from wind tunnel experiments. Eventually, the unsteady motion of the building is solved via a structural modal analysis. The flow solutions and the structural responses in terms of mean and root mean squared quantities are compared with experimental measurements, over a wide range of reduced velocities. The significance of turbulent inflow conditions and aeroelastic effects is highlighted. This numerical procedure provides predictions of good accuracy and can be considered a preliminary design tool to evaluate unsteady wind effects on tall buildings." --
