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CFD Analysis of Flow in a Blade Cascade Deformed Due to Forced Torsional Vibration
Vomáčko, V. ; Šidlof, P. ; Šimurda, David ; Hála, Jindřich
The paper presents a 3D numerical simulation of flow in a blade cascade, whose geometry models the test section of a new experimental facility for blade flutter research. In the experimental setup, the middle blade of the cascade undergoes high-frequency forced sinusoidal pitching oscillation. Due to inertial forces, the slender blade deforms elastically to certain degree. The goal of this study is to assess the influence of the elastic deformation on the flow field. To compute the deformed geometry, a transient structural analysis was performed. In the second part, the CFD model of flow past a 3D blade cascade with deformed and undeformed blade is presented and these two configurations are compared. For the deformed configuration the incidence angle increases along the blade span from -1.8° to -2.7°. However, the Mach number distribution along the span varies less than expected. blade cascade, flutter, turbomachinery, CFD
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Numerical simulation of dynamic loading of a test blade in forced torsional vibration
Šidlof, P. ; Vomáčko, V. ; Lepičovský, Jan ; Šimurda, David ; Štěpán, M. ; Luxa, Martin
Within a new project focused on blade flutter research, building on previous experience with the NASA Transonic Flutter Cascade facility, static blade cascade and airfoil flutter experiments realized in cooperation between the Institute of Thermomechanics and Technical University of Liberec, a new test facility is under development for the investigation of high subsonic and transonic flow in a blade cascade under forced torsional oscillation. Apart from aerodynamic loading of the blades, the oscillating blade will be exposed to significant structural stresses due to the highfrequency torsional vibration. In order to avoid structural integrity issues from high-cycle fatigue, a numerical simulation of the stress and displacement of the blade was realized. Regions where equivalent stress reaches maximum values were identified, and elastic deformations were computed. The limits in oscillation amplitude and frequency for the safe operation of the experimental setup were discussed.
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Aeroacoustic simulation of human phonation with the wale sub-grid scale model
Šidlof, Petr ; Lasota, M.
The paper reports on an aeroacoustic model of voice generation in human larynx, based on Large Eddy Simulation with the Wall-Adapting Local Eddy-Viscosity (WALE) sub-grid scale (SGS) model. The simulation uses a three-step hybrid approach, with an incompressible finite volume CFD computation providing the filtered velocity and pressure, evaluation of the aeroacoustic sources, and simulation of the sound propagation by finite element discretization of the Acoustic Perturbation Equations. The WALE SGS model is used to overcome the limitation of the classical Smagorinski SGS model, which overpredicts the SGS viscosity in regions of high shear, especially within the boundary layer in the glottal constriction. Results of the 3D CFD simulation, location of the aeroacoustic sources and the spectra of the radiated sound for two vowels are presented.
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Experimental and computer modelling study of glottal closing velocity during phonation
Horáček, Jaromír ; Radolf, Vojtěch ; Bula, Vítězslav ; Šidlof, P. ; Geneid, A. ; Laukkanen, A. M.
This preliminary study shows that the impact stress between the colliding vocal folds during phonation should not be evaluated from the maximum velocity of the glottal closing because the velocity of the closing diminishes just before the glottal closure. This phenomenon, which can be caused by a pressure cushion effect in the fast narrowing glottal gap, is demonstrated with measurements from high speed camera images recorded from human and on a physical laboratory model for vowel [u:] phonation and on a three-mass computer model employing a Hertz model of impact force. For a more detailed future study of this phenomenon a faster camera has to be used. \n
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Some experimentally determined properties of a profile in case of self-excited oscillations in subsonic flow
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan ; Šidlof, Petr ; Štěpán, M.
In the wind tunnel of the Institute of Thermomechanics of the AS CR,v .v. i., experiments were realized with the profile NACA0015 in the presence of the self-excited oscillation. The oscillation of the profile with pitch and plunge degrees of freedom was excited by the subsonic air flow. The plunge support had the same elasticity for all experiments, the pitch support had seven different values of elasticity. Within experiments different types of self-excited vibration (flutter, stall flutter, deep stall flutter) were realized. Range of Mach numbers were M=0.08–0.45, when the chord length is used as the characteristic dimension of the profile. The frequency and amplitude characteristics of the oscillating profile were experimentally determined.\n
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Evaluation of Interferograms of Unsteady Subsonic Airflow Past a Fluttering Airfoil
Šidlof, P. ; Riss, Š. ; Vlček, Václav
The paper reports on time-resolved interferometric measurements of unsteady ow elds around a uttering NACA0015 airfoil. A mechanical model with two degrees of freedom (pitch and plunge) has been designed and tested in a high-speed subsonic wind tunnel. Aeroelastic instability of the classical utter and dynamic stall type has been observed in the Mach number range M = 0.2 - 0.5. The interferograms were recorded using a Mach-Zehnder interferometer and a high-speed camera. An in-house software IFGPro was developed for the postprocessing and evaluation of the interferogram sequences, yielding pressure distribution, lift and drag force on the airfoil.
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Large eddy simulation of airflow in human vocal folds
Šidlof, Petr
Human phonation is a complex physiological process involving flow-induced oscillations of the vocal folds and aeroacoustic sound generation. The flow fields encountered in phonation are highly unsteady, feature massive flow separation and recirculation in the supraglottal spaces and generation of coherent vortex structures from the shear layer of the jet. For the sake of computational aeroacoustic modeling of human voice generation, an accurate resolution of the airflow through the vocal folds is essential. The Reynolds-averaged Navier-Stokes turbulence modeling is inappropriate, since it provides only the averaged flow field. The paper presents the first results obtained with a large-eddy simulation of flow through a model of human vocal folds using a second-order finite volume discretization of incompressible Navier-Stokes equations. In the first step, the flow field was resolved on a fine 2D mesh covering a short subglottal region, the glottis and a part of the supraglottal channel. The simulation was parallelized using domain decomposition method and run in parallel on a shared-memory supercomputer. The results compare two large eddy simulations using the algebraic Smagorinsky and one-equation sub-grid scale models against a simulation without turbulence model.
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