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Colloquium Fluid Dynamics 2014
Jonáš, Pavel ; Uruba, Václav
Selected results on theoretical and experimental fluid mechanics research at academic institutes, universities and other research and development establishments are presented in Colloquium Fluid Dynamics 2014 Proceedings. Seventeen contributions refer to the flow equations solutions, numerical calculations, flow visualization, investigations of shear flows dynamics, laminar turbulent transition, visualization in superfluid 4He, aerodynamic testing of supersonic blade cascades, fluidic oscillator etc.
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Dynamics of Recirculation Region Behind Backward-Facing Step
Uruba, Václav
Dynamics of the flow-field behind a backward-facing step in a narrow channel is studied experimentally using time-resolved PIV technique. Instability of the free shear layer of Kelvin-Helmholtz type is studied using simple averaging and Oscillation Pattern Decomposition (OPD) methods. Mean picture suggests existence of the classical recirculation zone. The OPD method reveals the structure of the instability consisting of a system of traveling vortical structures.
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Notes to Aerodynamic Testing of Supersonic Blade Cascades
Šimurda, David ; Luxa, Martin ; Šafařík, Pavel
Relatively narrow space for aerodynamic design of long rotor blades applied at last stages of large output steam turbines often results in blades with tips operating at supersonic regimes. This brings number of problems. Main of these are additional sources of loss and rather thin border between sections operating under turbine and compressor regimes one adding to performance and the other deteriorating it. Therefore, aerodynamic cascade data on turbine blading for a range of supersonic inlet and outlet conditions are needed. However, ensuring specified supersonic conditions in a high-speed wind tunnel for blade cascade tests is not an easy task and thus it deserves attention.
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Numerical and Experimental Studies of The Flow Through Narrow GAP
Hála, Jindřich ; Luxa, Martin
The flow in channels with characteristic dimension of the order of millimetres is of high importance for determination of losses of the devices such as small turbines, screw-type compressors and for investigation of the tip leakage flow. Since most of the contemporary studies deal with the micro or nano flows, the purpose of this work is to provide a reliable experimental data and to explore the possibilities of the numerical simulations of the present flow
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FEM solver for incompressible flow problems
Bauer, Petr ; Klement, V. ; Žabka, V.
We develop a FEM solver for flow problems based on incompressible Navier-Stokes equations. The discretization of the convective term is semi-implicit and the resulting linear systems are solved using multigrid techniques. The parallel implementations via OpenMP and NVidia CUDA are presented and their performance is compared.
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Fluidic oscillator with bistable turn-down amplifier
Tesař, Václav ; Smyk, E. ; Peszyński, K.
Search for new principles of no-moving-part fluidic oscillators suitable for operation at low frequency – and yet compact – has led to a design based on the amplifier configuration combining bistability (capability to remain in two alternative stable regimes) with capability to turn down the fluid flow passing through it. The feedback was arranged in a manner of recently introduced oscillators with resonator channel. Tests revealed the expected non-constant Strouhal number - but, rather strange, no dependence was found of oscillation frequency on the channel length.
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Control of flow separation by vestigial "synthetic jet"
Tesař, Václav ; Pavelka, Miroslav ; Smyk, E. ; Peszyński, K.
A useful aerodynamic control action may be causing a separation of flow from the wall past which the fluid flows. Several current research activities aim at doing so by oscillating zero-time-mean flow generated in a nozzle located in the wall. The effect is often described as “flow control by synthetic jet”, although it is obvious that the vortex rings generated in the outflow phase of the oscillation are deformed by the controlled flow and also are carried too far away so that they cannot form the classical synthetic jet configuration of vortex rings. Authors describe experiments with such a control applied successfully in an axisymmetric fluidic valve. Presented is a hypothesis explaining the separation mechanism.
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