The Experts below are selected from a list of 1434 Experts worldwide ranked by ideXlab platform
Mark C Thompson - One of the best experts on this subject based on the ideXlab platform.
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three dimensional instabilities in the boundary layer flow over a Long Rectangular Plate
Journal of Fluid Mechanics, 2011Co-Authors: Hemant Kumar Chaurasia, Mark C ThompsonAbstract:A detailed numerical study of the separating and reattaching flow over a square leading-edge Plate is presented, examining the instability modes governing transition from two- to three-dimensional flow. Under the influence of background noise, experiments show that the transition scenario typically is incompletely described by either global stability analysis or the transient growth of dominant optimal perturbation modes. Instead two-dimensional transition effectively can be triggered by the convective Kelvin–Helmholtz (KH) shear-layer instability; although it may be possible that this could be described alternatively in terms of higher-order optimal perturbation modes. At least in some experiments, observed transition occurs by either: (i) KH vortices shedding downstream directly and then almost immediately undergoing three-dimensional transition or (ii) at higher Reynolds numbers, larger vortical structures are shed that are also three-dimensionally unstable. These two paths lead to distinctly different three-dimensional arrangements of vortical flow structures. This paper focuses on the mechanisms underlying these three-dimensional transitions. Floquet analysis of weakly periodically forced flow, mimicking the observed two-dimensional quasi-periodic base flow, indicates that the two-dimensional vortex rollers shed from the recirculation region become globally three-dimensionally unstable at a Reynolds number of approximately 380. This transition Reynolds number and the predicted wavelength and flow symmetries match well with those of the experiments. The instability appears to be elliptical in nature with the perturbation field mainly restricted to the cores of the shed rollers and showing the spatial vorticity distribution expected for that instability type. Indeed an estimate of the theoretical predicted wavelength is also a good match to the prediction from Floquet analysis and theoretical estimates indicate the growth rate is positive. Fully three-dimensional simulations are also undertaken to explore the nonlinear development of the three-dimensional instability. These show the development of the characteristic upright hairpins observed in the experimental dye visualisations. The three-dimensional instability that manifests at lower Reynolds numbers is shown to be consistent with an elliptic instability of the KH shear-layer vortices in both symmetry and spanwise wavelength.
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sources of acoustic resonance generated by flow around a Long Rectangular Plate in a duct
Journal of Fluids and Structures, 2003Co-Authors: Boon Thong Tan, Mark C Thompson, Kerry HouriganAbstract:This paper describes a numerical investigation of the acoustic resonance occurring at specific flow speeds when a Long two-dimensional Rectangular Plate is placed on the centre-line of a duct. The flow Mach number is sufficiently small that the flow and acoustic fields can be modelled separately; however, the effect of the acoustic field in modifying the flow field is accounted for and, in turn, the flow field solution determines the time-dependent source distribution for the acoustic model. This allows the range of flow speeds, or equivalently the associated Strouhal numbers, where resonance is possible to be predicted. It is shown that the Strouhal number based on Plate chord (or length) displays a stepping behaviour as the Plate length is increased. The main source or sink region where energy is transferred between the acoustic and flow fields is shown to be immediately downstream of the trailing edge of the Plate. Visualizations of the numerical solution show that the timing when the vortices enter this region relative to the phase of the acoustic cycle is crucial in determining if resonance can occur and is the cause of the observed stepwise increase. Comparison is made with previous physical experiments.
Kerry Hourigan - One of the best experts on this subject based on the ideXlab platform.
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sources of acoustic resonance generated by flow around a Long Rectangular Plate in a duct
Journal of Fluids and Structures, 2003Co-Authors: Boon Thong Tan, Mark C Thompson, Kerry HouriganAbstract:This paper describes a numerical investigation of the acoustic resonance occurring at specific flow speeds when a Long two-dimensional Rectangular Plate is placed on the centre-line of a duct. The flow Mach number is sufficiently small that the flow and acoustic fields can be modelled separately; however, the effect of the acoustic field in modifying the flow field is accounted for and, in turn, the flow field solution determines the time-dependent source distribution for the acoustic model. This allows the range of flow speeds, or equivalently the associated Strouhal numbers, where resonance is possible to be predicted. It is shown that the Strouhal number based on Plate chord (or length) displays a stepping behaviour as the Plate length is increased. The main source or sink region where energy is transferred between the acoustic and flow fields is shown to be immediately downstream of the trailing edge of the Plate. Visualizations of the numerical solution show that the timing when the vortices enter this region relative to the phase of the acoustic cycle is crucial in determining if resonance can occur and is the cause of the observed stepwise increase. Comparison is made with previous physical experiments.
Boon Thong Tan - One of the best experts on this subject based on the ideXlab platform.
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sources of acoustic resonance generated by flow around a Long Rectangular Plate in a duct
Journal of Fluids and Structures, 2003Co-Authors: Boon Thong Tan, Mark C Thompson, Kerry HouriganAbstract:This paper describes a numerical investigation of the acoustic resonance occurring at specific flow speeds when a Long two-dimensional Rectangular Plate is placed on the centre-line of a duct. The flow Mach number is sufficiently small that the flow and acoustic fields can be modelled separately; however, the effect of the acoustic field in modifying the flow field is accounted for and, in turn, the flow field solution determines the time-dependent source distribution for the acoustic model. This allows the range of flow speeds, or equivalently the associated Strouhal numbers, where resonance is possible to be predicted. It is shown that the Strouhal number based on Plate chord (or length) displays a stepping behaviour as the Plate length is increased. The main source or sink region where energy is transferred between the acoustic and flow fields is shown to be immediately downstream of the trailing edge of the Plate. Visualizations of the numerical solution show that the timing when the vortices enter this region relative to the phase of the acoustic cycle is crucial in determining if resonance can occur and is the cause of the observed stepwise increase. Comparison is made with previous physical experiments.
Hemant Kumar Chaurasia - One of the best experts on this subject based on the ideXlab platform.
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three dimensional instabilities in the boundary layer flow over a Long Rectangular Plate
Journal of Fluid Mechanics, 2011Co-Authors: Hemant Kumar Chaurasia, Mark C ThompsonAbstract:A detailed numerical study of the separating and reattaching flow over a square leading-edge Plate is presented, examining the instability modes governing transition from two- to three-dimensional flow. Under the influence of background noise, experiments show that the transition scenario typically is incompletely described by either global stability analysis or the transient growth of dominant optimal perturbation modes. Instead two-dimensional transition effectively can be triggered by the convective Kelvin–Helmholtz (KH) shear-layer instability; although it may be possible that this could be described alternatively in terms of higher-order optimal perturbation modes. At least in some experiments, observed transition occurs by either: (i) KH vortices shedding downstream directly and then almost immediately undergoing three-dimensional transition or (ii) at higher Reynolds numbers, larger vortical structures are shed that are also three-dimensionally unstable. These two paths lead to distinctly different three-dimensional arrangements of vortical flow structures. This paper focuses on the mechanisms underlying these three-dimensional transitions. Floquet analysis of weakly periodically forced flow, mimicking the observed two-dimensional quasi-periodic base flow, indicates that the two-dimensional vortex rollers shed from the recirculation region become globally three-dimensionally unstable at a Reynolds number of approximately 380. This transition Reynolds number and the predicted wavelength and flow symmetries match well with those of the experiments. The instability appears to be elliptical in nature with the perturbation field mainly restricted to the cores of the shed rollers and showing the spatial vorticity distribution expected for that instability type. Indeed an estimate of the theoretical predicted wavelength is also a good match to the prediction from Floquet analysis and theoretical estimates indicate the growth rate is positive. Fully three-dimensional simulations are also undertaken to explore the nonlinear development of the three-dimensional instability. These show the development of the characteristic upright hairpins observed in the experimental dye visualisations. The three-dimensional instability that manifests at lower Reynolds numbers is shown to be consistent with an elliptic instability of the KH shear-layer vortices in both symmetry and spanwise wavelength.
L V Molchenko - One of the best experts on this subject based on the ideXlab platform.
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numerical solution of the nonlinear problem of motion of a Long Rectangular Plate in a variable magnetic field
Journal of Mathematical Sciences, 1994Co-Authors: A A Balyunov, L V MolchenkoAbstract:The coupled problem of motion of a Long Rectangular Plate in a variable magnetic field is analyzed in the framework of the geometrically nonlinear theory of thin shells. The proposed numerical procedure is applied to estimate the effect of external electromagnetic and mechanical fields on the stress- strain state of the Plate.
