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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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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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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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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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