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Solution of flow and formation of vortex structures behind a free-standing pillar
Pluskal, Tomáš ; Pochylý, František (referee) ; Fialová, Simona (advisor)
The instability of the flow and the formation of vortices when surrounding free-standing pillars is a problem that has been solved for a long time. In most engineering applications we try to minimize their influence. However, some newer applications require them to be maximized. This deals with the study of these effects on the public street lamp using computer modelling in the Ansys Fluent and their use for the production of electricity. The information obtained in this way is then used for the design of a vibration generator, which is then used to transform the energy from mechanical vibrations to electricity.
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The Transitional Regime of Backward-Facing Step Flows
Tihon, Jaroslav ; Pěnkavová, Věra ; Havlica, Jaromír ; Šimčík, Miroslav
The backward-facing step flow is investigated experimentally (electrodiffusion technique) and numerically (CFD software Fluent) at moderate Reynolds numbers achieved in a water channel. The direction sensitive sensors are used to measure the wall shear rate behind the step and detect the near-wall extent of different flow-recirculation regions. 2D numerical simulations provide additional information on the global flow rearrangement caused by the change of operational parameters (channel expansion ratios, inlet flow conditions). At the transitional flow regime, the near-wall flow exhibits an unsteady character with a high sensitivity to external low-frequency perturbations (intrinsic flow instability). The inlet pulsatile forcing is found to affect strongly the overall flow structure behind the step, resulting in the reattachment length reduction and the reverse flow intensification.
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Dynamics of the Wavy Film Down an Inclined Plane. V. Newtonian Orr-Sommerfeld Problem Revisited
Wein, Ondřej ; Tihon, Jaroslav
Linear stability of the Newtonian film flow along an inclined plate is studied by treating the related 2D linearized equations of fluctuating motion (Orr-Sommerfeld). Quadratic character of the Orr-Sommerfeld (OS) equations and the corresponding multiplicity of solution (the regular and singular branch) is demonstrated. Region of validity of both the long-wave (20 terms) and short-wave (4 terms) analytic asymptotes to the regular branch is estimated by comparing it with numerical solution to the full Orr-Sommerfeld problem. In particular, the c1-stability criterion of the regular long-wave asymptote is confirmed. In addition to the basic wave characteristics of the inception region (celerity, growth rate, wavelength), the characteristics of the fluctuating wall shear rate are given.
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Stability of the Newtonian Film Flow Down an Oscillating Inclined Plane. II. The Related Orr-Sommerfeld-Floquet Problems in a Long-Wave Asymptote up to 3rd Order
Wein, Ondřej ; Tihon, Jaroslav
Linear stability of the film flow along an oscillating inclined plate is analyzed. Following the previous analyses by Yih (1968), Bajkov et al. (1982), Bauer and Kerczek (1991), Lin et al. (1996), the 2D linearized equations (Orr-Sommerfeld-Floquet) of fluctuating motion for a New-tonian fluid are treated. The long-wave (small wave number a ) asymptotic expansion for the complex-valued celerity coefficient, k = k(a) = R c(a), is solved analytically up to the or-der O(a3). In addition to well-known sufficient conditions for the wavy instability of the film under forced oscillation, the basic wave characteristics of the inception region are given: celer-ity, growth rate, and wavelength.
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