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Validace CFD výpočtů s experimentálními daty, metody a jejich přesnost
Uruba, Václav
Validace a verifikace výsledků CFD jsou procesy, které virtuální realitu získanou pomocí daného software přibližují fyzikální realitě. Klíčovou roli v těchto procesech hraje metoda kvantifikace blízkosti různých situací v proudovém poli, tedy metrika, kterou je třeba vhodně zvolit. V procesu verifikace je dále důležitá strategie modifikací numerického modelu, u validace potom kvalita a vhodná volba experimentálních dat, která jsou k validaci použita. Experimentální data jsou dále použita k určení okrajových podmínek pro CFD. Předkládaný příspěvek se zabývá právě těmito aspekty.
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Physical modelling axisymmetric diffusors by plane models
Uruba, Václav
Diffusers with axisymmetric geometry are used very often in technical applications, they are characterized by circular cross-section along the flow axis. Such geometry is not suitable for application of optical methods, so the plane model with rectangular cross-section is used instead very often. However the flow inside such model could be significantly different as for velocity and pressure fields. The physical similarity of 1D flow in axisymmetric diffusers and plane models will be studied in details. The plane model opening angle is suggested to optimize velocity and pressure distributions in the model.
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Simulation of Transonic Flow Through a Mid-span Turbine Blade Cascade for Various Mach Numbers
Straka, P. ; Příhoda, Jaromír ; Fenderl, D.
The contribution deals with the numerical simulation of 2D transonic flow through a mid-span turbine blade cascade for several Mach numbers by means of the EARSM turbulence model of Hellsten (2004) connected with the algebraic bypass transition model of Straka and Příhoda (2014). Both models are implemented into an in-house numerical code based on the finite volume method. The gamma-transition model of Menter et al. (2015) with SST turbulence model accessible in the commercial code ANSYS Fluent was used for the comparison.
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Modelling of Flow in Linear Blade Cascade with Thick Trailing Edge at a Lower Reynolds Number
Straka, P. ; Příhoda, Jaromír
In the paper there are compared results of numerical simulation of compressible turbulent flow through a low-pressure turbine blade cascade with relatively thick trailing edges for various physical models. Steady, unsteady, fully turbulent, transitional, two-dimensional and three-dimensional models are compared. Results show that: a) steady simulation gives an incorrect prediction of the boundary layer development, b) two-dimensional unsteady simulation leads to inaccurate prediction of the far wake development and c) only three-dimensional unsteady transitional simulation gives sufficiently accurate prediction. Results of numerical simulations are compared with the experimental data.
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Simulation of Transonic Flow Through a Mid-Span Turbine Blade Cascade with the Separation-Induced Transition
Straka, P. ; Příhoda, Jaromír ; Fenderl, D.
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.
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Coanda effect in valves
Uruba, Václav ; Procházka, Pavel P. ; Skála, Vladislav
Coanda effect takes place in flow within valves diffuser for certain conditions. The valve plug in\nhalf-closed position forms wall-jet, which could be stable or instable, depending on geometry and other\nconditions. This phenomenon was subject of experimental study using time-resolved PIV technique. For the acquired data analysis the special spatio-temporal methods have been used.
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On stability of 2D flow-field
Uruba, Václav
Stability of a 2D flow-field generated under 2D boundary conditions will be analyzed using various methods. The most practical cases of such flows are found to be highly instable and thus unphysical. The presented paper analyses the situation with help of experiments and mathematical modelling from literature defining an interesting areas for future experimental research, which could extend the published experimental studies and/or verify some recent results of mathematical modelling.
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