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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 2034-2041 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data obtained from the two-dimensional numerical simulation of a plane mixing layer have been used to study the feasibility of tagging one side of the flow by a passive scalar and using the instantaneous concentration of the scalar to detect the typical coherent events in the flow. The study has shown that this technique works quite satisfactorily and yields results similar to those obtained by using the instantaneous vorticity as a detection criterion. The contribution from the coherent events to the time-averaged turbulent momentum and scalar transport has been estimated. It is found that this contribution is of the same order as the time-mean transport during most of the dynamical evolution of the coherent structure. However, it may attain very large values for short periods of time in the neighborhood of pairing. The increase is particularly spectacular in the case of the Reynolds shear stress. While the present findings obtained from a two-dimensional simulation seem to support earlier results obtained from actual experiments, it is desirable to conduct additional studies with three-dimensional simulations when they become available.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 784-791 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mean and fluctuating pressure and skin friction around a circular cylinder in cross-flow were studied in the subcritical Reynolds number range, 104–105. Results are presented for two cases, namely, with and without a splitter plate behind the cylinder. The splitter plate was used to suppress vortex shedding. The nonlinear dynamics of the flow around the cylinder was examined to characterize the process of laminar separation in terms of the number of degrees of freedom, and to determine whether the process is chaotic. For this purpose, the Grassberger–Procaccia correlation dimension and the largest Lyapunov exponent were estimated from the time series of the pressure data. The results indicate a correlation dimension of the order of 10–12 both in the presence and absence of the splitter plate. The largest Lyapunov exponent was found to be positive in both cases, suggesting that the process of laminar separation is chaotic. These results are new and are significant from the point of view of modeling and controlling the phenomenon of laminar separation in the future.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 331-338 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple heat-tagging technique was used to isolate and analyze the large-scale coherent structures present in the two-dimensional wake of a flat plate. The results indicate the presence of these coherent structures even at 250 momentum thicknesses downstream of the trailing edge. These structures have a vortexlike topology and carry a significant amount of the total shear stress. The present results for the flat-plate wake seem to be in general agreement with those that have been obtained in cylinder wakes by other contemporary investigators using more complex techniques of eduction and signal enhancement.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 4 (1984), S. 781-800 
    ISSN: 0271-2091
    Keywords: Unsteady Flows ; Periodic Boundary Layers ; Laminar Boundary Layers ; Turbulent Boundary Layers ; Finite-Difference Methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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