Yes (81)
Number of found documents:
81
Published from
to
Impact of Turbulence Generators on Turbulent Characteristics and Structures
Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
2017 - English
The turbulent generators are routinely used to produce very turbulent flows. Special type of vertically slenderize spires are applied to enhance turbulent diffusion from the surface upwards in order to increase the boundary layer depth. This paper studies the influence of variable upstream distance of generators on formation of both vortical and non-vortical organized structures within a test section. The 2-component 2-dimensional time-resolved particle image velocimetry measurement of the flow was performed in the wind channel with very rough surface. Intermittent flow dynamics was evaluated by means of higher order moments, vorticity, quadrant and wavelet analysis. The downstream evolution of the flow suggests that equilibrium between roughness- and spires-produced turbulence was reached at the distance of 7 spires height.\n
Keywords:
turbulence generator; wind channel; vorticity; quadrant analysis
Fulltext is available at external website.
Impact of Turbulence Generators on Turbulent Characteristics and Structures
The turbulent generators are routinely used to produce very turbulent flows. Special type of vertically slenderize spires are applied to enhance turbulent diffusion from the surface upwards in order ...
CFD motivated applications of model order reduction
Isoz, Martin
2017 - English
The ongoing advances in numerical mathematics and available computing power combined with the industrial needs promote a development of more and more complex models. However, such models are, due to their complexity, expensive from the point of view of the data storage and the time necessary for their evaluation. The model order reduction (MOR) seeks to reduce the computational complexity of large scale models. We present an approach to MOR based on the proper orthogonal decomposition (POD) with Galerkin projection. The problems arising from the nonlinearities present in the original model are adressed within the framework of the discrete empirical interpolation method (DEIM). The main contribution of this work consists in providing a link between the POD-DEIM based MOR and OpenFOAM. OpenFOAM is an open-source CFD toolbox capable of solving even industrial scale processes. Hence, the availability of a link between OpenFOAM and POD-DEIM based MOR enables a direct order reduction for large scale systems originating in the industrial practice.
Keywords:
model order reduction; CFD; OpenFOAM
Fulltext is available at external website.
CFD motivated applications of model order reduction
The ongoing advances in numerical mathematics and available computing power combined with the industrial needs promote a development of more and more complex models. However, such models are, due to ...
Numerical Simulation of Laminar-Turbulent Transition in Accelerated Flows
Fürst, J.; Příhoda, Jaromír
2017 - English
The article deals with the evaluation of two RANS based models for simulation of transitional flows including heat transfer. The work is focused on the transition and heat transfer in cases of accelerated flows over a flat plate and through a test turbine cascade.
Keywords:
turbulence; laminar-turbulent transition; finite volume method
Fulltext is available at external website.
Numerical Simulation of Laminar-Turbulent Transition in Accelerated Flows
The article deals with the evaluation of two RANS based models for simulation of transitional flows including heat transfer. The work is focused on the transition and heat transfer in cases of ...
Simulation of Transonic Flow Through a Mid-Span Turbine Blade Cascade with the Separation-Induced Transition
Straka, P.; Příhoda, Jaromír; Fenderl, D.
2017 - English
The paper deals with the numerical simulation of the transonic flow through a mid-span turbine blade cascade by means of an in-house code based on the EARSM turbulence model of Hellsten [1] completed by the algebraic transition model of Straka and Příhoda [2]. The simulation using the transition model of Langtry and Menter [3] and Menter et al. [4] implemented in the commercial code ANSYS Fluent was used for the comparison. Simulations were carried out for the transonic regime close to the nominal regime. The flow separation on the suction side of the blade is caused by the interaction of the reflected shock wave with the boundary layer. The attention was focused on the modelling of the transition in the separated flow especially on the modelling of the length of the transition region. Numerical results were compared with experimental results.
Keywords:
mid-section blade cascade; boundary layer transition; shock wave interaction
Fulltext is available at external website.
Simulation of Transonic Flow Through a Mid-Span Turbine Blade Cascade with the Separation-Induced Transition
The paper deals with the numerical simulation of the transonic flow through a mid-span turbine blade cascade by means of an in-house code based on the EARSM turbulence model of Hellsten [1] completed ...
Transition Modelling on Separated Flow in Turbine Cascade
Louda, Petr; Příhoda, Jaromír; Kozel, K.
2017 - English
The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is gamma-zeta model based on transition criteria, second one algebraic transition model based on the concept of laminar uctuations energy (Kubacki, Dick 2016). The criterion for transition in separated state is re-formulated in order to remove stream-wise non-local formulation. The performance of the transition models is observed on the shock wave - boundary layer interaction on turbine blade.
Keywords:
turbine cascade; transition model; separation bubble; shock wave-boundary layer interaction
Fulltext is available at external website.
Transition Modelling on Separated Flow in Turbine Cascade
The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is ...
Vortex structures generated by dbd plasma actuator
Procházka, Pavel P.
2013 - English
This article deals with the research of vortex structures generated by a plasma actuator. Plasma actuators belong to devices that can be used for active flow control. Plasma actuator flow control has been in the center of interest for the last two decades. However, one can find only a limited amount of information dealing with the physical principal of this phenomenon. The conclusion of this article is formulated to give an explanation of physical laws acting during generating, evaluating and decay vortex structures in a complex way to ensure that results could be apply in the future for more applicable research.
Keywords:
plasma; actuation; DBD; vortex
Fulltext is available at external website.
Vortex structures generated by dbd plasma actuator
This article deals with the research of vortex structures generated by a plasma actuator. Plasma actuators belong to devices that can be used for active flow control. Plasma actuator flow control has ...
On the Reynolds number role in structure of recirculation zone b ehind backward facing step in a narow channel
Uruba, Václav
2013 - English
Topology of the time-mean flow-field behind the backward facing step in a narrow channel is presented for various Reynolds numbers. The flow-field is studied in planes close to the channel bottom and in the plane of symmetry. Special attention is devoted to the appearance of secondary and higher order structures defined on the time-mean basis. Experimental results are obtained from PIV measurements.
Keywords:
channel flow; backward facing step; Reynolds number; recirculation
Fulltext is available at external website.
On the Reynolds number role in structure of recirculation zone b ehind backward facing step in a narow channel
Topology of the time-mean flow-field behind the backward facing step in a narrow channel is presented for various Reynolds numbers. The flow-field is studied in planes close to the channel bottom and ...
On mathematical modelling of gust response using the finite element method
Sváček, P.; Horáček, Jaromír
2013 - English
In this paper the numerical approximation of aeroelastic response to sudden gust is presented. The fully coupled formulation of two dimensional incompressible viscous fluid flow over a flexibly supported structure is used. The flow is modelled with the system of Navier-Stokes equations written in Arbitrary Lagrangian-Eulerian form and coupled with system of ordinary differential equations describing the airfoil vibrations with two degrees of freedom. The Navier-Stokes equations are spatially discretized by the fully stabilized finite element method. The numerical results are shown.
Keywords:
aeroelasticity; Navier-Stokes equations for incompressible flow; airfoil section
Fulltext is available at external website.
On mathematical modelling of gust response using the finite element method
In this paper the numerical approximation of aeroelastic response to sudden gust is presented. The fully coupled formulation of two dimensional incompressible viscous fluid flow over a flexibly ...
Heterogeneous particles in steam turbines: measurements at power plant Prunéřov II and further development of measuring methods
Hrubý, Jan; Kolovratník, M.; Ždímal, Vladimír; Jiříček, I.; Bartoš, O.; Moravec, P.
2008 - English
The form in which various impurities and admixtures are transported in steam circuits of power plants is a missing piece of knowledge needed to fully understand the processes of liquid phase formation in the low-pressure stages of steam turbines and, consequently, to model these processes and suggest modifications of turbine operation and design. The existence of heterogeneous particles in the superheated steam has been proven by the present team using an original sampling device, enabling using standard aerosol instrumentation to characterize the heterogeneous particles in superheated steam. We report measurements at power plant Prunéřov II, where 5.6E9 particles per kilogram of dry steam was found. The Sauter diameter of the particles d32=30nm was determined. The mass balance indicates, that substantial part of the mass of impurities is contained in particles <3nm, the current detection limit. For this reason an expansion chamber is being developed with a goal of detecting particles down to 1nm. Stav aglomerace, ve kterém jsou nečistoty a příměsi transportovány v parních okruzích elektráren, je chybějící informací, potřebnou pro plné porozumění procesům tvorby kapalné fáze v nízkotlakých parních turbínách a následně pro modelování těchto procesů a návrh úprav provozu a konstrukce turbnín. Existence heterogenních částic v přehřáté páře byla dokázána tímto týmem pomocí originálního vzorkovacího přístroje, který umožňuje použití standardní aerosolové technologie pro charakterizaci heterogenních částic v přehřáté páře. Podáváme zprávu o měření na elektrárně Prunéřov II, kde bylo zjištěno 5.6E9 částic na kilogram suché páry. Byl určen Sauterův průměr těchto částic d32=30nm. Hmotnostní bilance naznačuje, že značná část hmoty nečistot je obsažena v částicích menších než 3nm, což je současný detekční limit. Z tohoto důvodu je vyvíjena expanzní komora, která by měla umožnit detekci do 1nm.
Keywords:
heterogeneous nucleation; steam turbine
Fulltext is available at external website.
Heterogeneous particles in steam turbines: measurements at power plant Prunéřov II and further development of measuring methods
The form in which various impurities and admixtures are transported in steam circuits of power plants is a missing piece of knowledge needed to fully understand the processes of liquid phase formation ...
Aerosoly v parních turbínách?
Kolovratník, Michal; Hrubý, Jan; Ždímal, Vladimír
2005 - Czech
Ačkoli parní oběhy klasických a jaderných elektráren pracují s velmi čistou vodou, existující malé množství příměsí má důležitý vliv na jejich životnost a energetickou účinnost. Je pravděpodobné, že netěkavé příměsi jsou v prostředí suché (přehřáté) páry transportovány ve formě suchých částic či koncentrovaných nanometrických kapiček, aerosolů. Pro detekci těchto částic je navržena nová vzorkovací trať, využívající aerosolovou technologii. Trať bude možno připojit na odběrová místa parní turbíny. The small amount of admixtures in steam circuits of power stations influences their life-expectancy and energetic efficiency. It is likely that non-volatile admixtures are in the environment of the dry (superheated) steam transported in the form lf dry particles or concentrated nanometric droplets, aerosols. For the detection of these particles a new sampling line is proposed, using the aerosol technology. It will be possible to connect the sampling line to sampling ports of a steam turbine.
Keywords:
aerosol; steam turbine
Fulltext is available at external website.
Aerosoly v parních turbínách?
Ačkoli parní oběhy klasických a jaderných elektráren pracují s velmi čistou vodou, existující malé množství příměsí má důležitý vliv na jejich životnost a energetickou účinnost. Je pravděpodobné, že ...
NRGL provides central access to information on grey literature produced in the Czech Republic in the fields of science, research and education. You can find more information about grey literature and NRGL at service web
Send your suggestions and comments to nusl@techlib.cz
Provider
Other bases