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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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Měřicí řetězec aerodynamického profilu se dvěma stupni volnosti
Štěpán, M. ; Šidlof, P. ; Vlček, Václav
Příspěvek je zaměřen na měření vibračního pohybu aerodynamického profilu v aerodynamickém tunelu Ústavu termomechaniky AV ČR. Fyzikální model NACA 0015 profilu byl navržen a vyroben, umožňuje pohyb se dvěma stupni volnosti: vertikální pohyb a otáčení kolem elastické osy. Pohyb profilu byl registrován optickým inkrementálním čidlem, nezávisle též vysokorychlostní kamerou se synchronním měřením tlaků na povrchu profilu. Zesílené signály ze snímačů tlaku a tenzometrů byly získány pomocí datových karet National Instruments a Dewesoft měřícího programu. Výsledky měření jsou zde uvedeny.
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Parallel numerical simulation of airflow past an oscillating NACA0015 airfoil
Řidký, Václav ; Šidlof, Petr ; Vlček, Václav
This paper focuses on 3D and 2D parallel computation of pressure and velocity fields around an elastically supported airfoil self-oscillating due to interaction with the airflow The results of numerical simulations are compared with data measured in a wind tunnel, where physical model of a NACA0015 airfoil was mounted and tuned to exhibit the flutter instability. The experimental results were obtained previously in the Institute of Thermomechanics by interferometric measurements in a subsonic wind tunnel in Nový Knín. For the numerical solution is implemented in OpenFOAM, an open-source software package based on finite volume method. In the numerical solution is prescribed displacement of the airfoil, which corresponds to the experiment.
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Computational aeroacoustics of human phonation
Šidlof, Petr ; Zörner, S.
The current paper presents a CFD model of flow past vibrating vocal folds coupled to an acoustic solver, which calculates the sound sources from the flow field in a hybrid approach. The CFD model is based on the numerical solution of 3D Navier-Stokes equations on a time-dependent domain, solved by cell-centered finite volume method. To capture the fine turbulent scales important for the acoustic source calculations, the equations are discretized and solved on large computational meshes up to 3.2M elements. The CFD simulations were run in parallel using domain decomposition method and OpenMPI implementation of the MPI standard. Aeroacoustic simulations are calculated in a separate step by Lighthill’s acoustic analogy, which determines the acoustic sources based on the fluid field. This is done with the research code CFS++ which employs the finite element method (FEM).
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Numerical simulations of the flow with the prescribed displacement of the airfoil and comparison with experiment
Řidký, Václav ; Šidlof, Petr ; Vlček, Václav
The work is devoted to comparing measured data with the results of numerical simulations. As mathematical model was used mathematical model whitout turbulence for incompressible flow In the experiment was observed the behavior of designed NACA0015 airfoil in airflow. For the numerical solution was used OpenFOAM computational package, this is open-source software based on finite volume method. In the numerical solution is prescribed displacement of the airfoil, which corresponds to the experiment. The velocity at a point close to the airfoil surface is compared with the experimental data obtained from interferographic measurements of the velocity field. Numerical solution is computed on a 3D mesh composed of about 1 million ortogonal hexahedron elements. The time step is limited by the Courant number. Parallel computations are run on supercomputers of the CIV at Technical University in Prague and on a computer cluster of the Faculty of Mechatronics of Liberec . Run time is fixed at five periods, the results from the fifth periods and average value for all periods are then be compared with experiment.
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Computational aeroacoustics of human phonation
Šidlof, Petr ; Zoerner, S.
The current paper presents a CFD model of flow past vibrating vocal folds coupled to an acoustic solver, which calculates the sound sources from the flow field in a hybrid approach. The CFD model is based on the numerical solution of 3D Navier-Stokes equations on a time-dependent domain, solved by cell-centered finite volume method. To capture the fine turbulent scales important for the acoustic source calculations, the equations are discretized and solved on large computational meshes up to 3.2M elements. The CFD simulations were run in parallel using domain decomposition method and OpenMPI implementation of the MPI standard. Aeroacoustic simulations are calculated in a separate step by Lighthill’s acoustic analogy, which determines the acoustic sources based on the fluid field. This is done with the research code CFS++ which employs the finite element method (FEM).
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Coherent turbulent structures in flow through the human vocal tract
Šidlof, Petr ; Doaré, O. ; Cadot, O. ; Čejka, J.
This paper presents experimental and computational data on the coherent turbulent structures in flow through the human vocal tract. The experimental results were obtained using a 4:1 scaled self-oscillating physical model of vocal folds. Flow velocity fields in the coronal plane were visualized and measured using a PIV system phase-synchronized with vocal fold vibration. Computational results originate from finite volume discretizations of viscous incompressible Navier-Stokes equations in 2D and 3D. The results reveal flow separation in the divergent part of glottis and formation of a planar jet. Vortex structures are shed from the shear layer of the jet and convected further downstream. The computational model helps to assess the influence of the ventricular folds on the flow patterns.
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Matematické a fyzikální modelování prouděním vyvolaného kmitání lidských hlasivek
Šidlof, Petr ; Doaré, O. ; Cadot, O. ; Chaigne, A. ; Horáček, Jaromír
Práce je věnována výpočtům tlakového a rychlostního pole v okolí kmitajících hlasivek metodou konečných prvků. Tvar hlasivek byl specifikován podle měření excizovaných hrtanů ve fonačním postavení. Matematický model je založen na 2D nestlačitelných Navier-Stokesových rovnicích v ALE-formulaci, která umožňuje pracovat v časově proměnlivé oblasti. Výsledky numerických simulací demonstrují odtrhávání proudu v hlasivkách, Coandův efekt a odtrhávání vírů. Numerické výsledky byly ověřeny experimentálně pomocí metody PIV na fyzikálním modelu hlasivek. Kromě akustických, tlakových a dynamických měření byly zaznamenány proudová pole v oblasti bezprostředně za hlasivkami. Analýza PIV záznamu z průběhu 25 fází jednoho oscilačního cyklu hlasivek poskytuje základní vhled do dynamiky supraglotického proudění
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