Ghader Ghorbaniasl | Vrije Universiteit Brussel (original) (raw)

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Papers by Ghader Ghorbaniasl

Research paper thumbnail of Acoustic velocity formulation for Kirchhoff data surfaces

International Journal of Aeroacoustics, 2015

ABSTRACT This paper deals with the derivation of an analytical time-domain formulation for the pr... more ABSTRACT This paper deals with the derivation of an analytical time-domain formulation for the prediction of the acoustic velocity field generated by moving bodies in a medium at rest, according to the Kirchhoff method. The present formulation can be implemented in acoustic pressure codes based on the Farassat's Kirchhoff formula for arbitrary moving bodies, thus allowing direct and fast calculation of the acoustic velocity field in scattering problems. For validation purposes, four test cases are considered, namely a three-dimensional monopole, dipole and quadrupole source, as well as a monopole in uniform flow. Comparison of the results with the analytical solutions proves the remarkable accuracy of the present formulation.

Research paper thumbnail of Validation of a time domain formulation for propeller noise prediction

International Journal of Aeroacoustics, 2006

Research paper thumbnail of On the coupling between a high-order spectral difference method and large eddy simulation

Proc. V European Conference on Computational Fluid Dynamics ECCOMAS CFD, 2010

Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral ... more Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formula (BDF2). The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower-upper symmetric Gauss-Seidel (LU-SGS) ...

Research paper thumbnail of An implicit high-order spectral difference approach for large eddy simulation

Journal of Computational Physics, 2010

High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity mo... more High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity model Implicit LU-SGS algorithm a b s t r a c t

Research paper thumbnail of Validation and application of a far-field time domain formulation for fan noise prediction

11th AIAA/CEAS Aeroacoustics Conference, 2005

Research paper thumbnail of Sensitivity Study on Computational Parameters for the Prediction of Noise Generated by Counter-Rotating Open Rotors

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), 2011

Research paper thumbnail of Efficient Flow and Noise Prediction of Counter-Rotating Open Rotors

Research paper thumbnail of Verfication of Noise Prediction Through Acoustic Analogy

13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007

Research paper thumbnail of An implicit high-order spectral difference approach for large eddy simulation

Journal of Computational Physics, 2010

High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity mo... more High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity model Implicit LU-SGS algorithm a b s t r a c t

Research paper thumbnail of Analysis of the implicit LU-SGS algorithm for 3rd- and 4th-order spectral volume scheme for solving the steady Navier–Stokes equations

Journal of Computational Physics, 2011

Research paper thumbnail of An eddy interaction model for particle deposition

Journal of Aerosol Science, 2012

Deposition of mono-disperse aerosols is studied numerically on a simplified human upper airway mo... more Deposition of mono-disperse aerosols is studied numerically on a simplified human upper airway model (UAM). This paper presents new correction functions for eddy interaction model (EIM) in an attempt to improve the accuracy of predicting aerosol deposition in the UAM. Based on an Euler-Lagrange methodology, the fluid phase is solved using RANS (Reynolds Averaged Navier Stokes equation) and employing low-Reynolds SST k-o turbulence model. The particle phase is solved using Lagrangian approach and employing an EIM model. Mono-disperse particle sizes of 3 and 6 mm are considered for breathing rates of 30 and 60 L/min.

Research paper thumbnail of A stability analysis for the spectral volume method on tetrahedral grids

Journal of Computational Physics, 2009

Research paper thumbnail of Study of the sediment transport over flat and wavy bottom using large-eddy simulation

Journal of Turbulence, 2009

... Chang, YS and Scotti, A. 2003. Entrainment and suspension of sediments into a turbulent flow ... more ... Chang, YS and Scotti, A. 2003. Entrainment and suspension of sediments into a turbulent flow over ripples. ... [44. Nakagawa, S., Na, Y. and Hanratty, TJ 2003. Influence of a wavy boundary on turbulence. ... Direct numerical simulation of turbulent flow over a wavy wall. Phys. ...

Research paper thumbnail of A moving medium formulation for prediction of propeller noise at incidence

Journal of Sound and Vibration, 2012

This paper presents a time domain formulation for the sound field radiated by moving bodies in a ... more This paper presents a time domain formulation for the sound field radiated by moving bodies in a uniform steady flow with arbitrary orientation. The aim is to provide a formulation for prediction of noise from body so that effects of crossflow on a propeller can be modeled in the time domain. An established theory of noise generation by a moving source is combined with the moving medium Green's function for derivation of the formulation. A formula with Doppler factor is developed because it is more easily interpreted and is more helpful in examining the physic of systems. Based on the technique presented, the source of asymmetry of the sound field can be explained in terms of physics of a moving source. It is shown that the derived formulation can be interpreted as an extension of formulation 1 and 1A of Farassat based on the Ffowcs Williams and Hawkings (FW-H) equation for moving medium problems. Computational results for a stationary monopole and dipole point source in moving medium, a rotating point force in crossflow, a model of helicopter blade at incidence and a propeller case with subsonic tips at incidence verify the formulation.

Research paper thumbnail of On the coupling between a high-order spectral difference method and large eddy simulation

Proc. V European Conference on Computational Fluid Dynamics ECCOMAS CFD, 2010

Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral ... more Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formula (BDF2). The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower-upper symmetric Gauss-Seidel (LU-SGS) ...

Research paper thumbnail of On the coupling between a high-order spectral difference method and large eddy simulation

Proc. V European Conference on Computational Fluid Dynamics ECCOMAS CFD, 2010

Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral ... more Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formula (BDF2). The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower-upper symmetric Gauss-Seidel (LU-SGS) ...

Research paper thumbnail of Numerical Solution of the Linearized Euler Equations Using Compact Schemes

… Fluid Dynamics 2006, Jan 1, 2009

Research paper thumbnail of Quality of dynamic variational multiscale models on distorted grids

Journal of Turbulence, 2009

The present paper focuses on a dynamic version of the variational multiscale model and investigat... more The present paper focuses on a dynamic version of the variational multiscale model and investigates its performance in large eddy simulations (LES) of turbulent channel flow at Reynolds numbers (based on friction velocity) of 180, 395, and 590. The dynamic procedure was implemented for the variational multiscale model on the basis of the classical Smagorinsky model and the wall-adapting local

Research paper thumbnail of Prediction of Near- and Far-Field Noise Generated by Counter-Rotating Open Rotors

16th AIAA/CEAS Aeroacoustics Conference, 2010

Research paper thumbnail of Acoustic velocity formulation for Kirchhoff data surfaces

International Journal of Aeroacoustics, 2015

ABSTRACT This paper deals with the derivation of an analytical time-domain formulation for the pr... more ABSTRACT This paper deals with the derivation of an analytical time-domain formulation for the prediction of the acoustic velocity field generated by moving bodies in a medium at rest, according to the Kirchhoff method. The present formulation can be implemented in acoustic pressure codes based on the Farassat's Kirchhoff formula for arbitrary moving bodies, thus allowing direct and fast calculation of the acoustic velocity field in scattering problems. For validation purposes, four test cases are considered, namely a three-dimensional monopole, dipole and quadrupole source, as well as a monopole in uniform flow. Comparison of the results with the analytical solutions proves the remarkable accuracy of the present formulation.

Research paper thumbnail of Validation of a time domain formulation for propeller noise prediction

International Journal of Aeroacoustics, 2006

Research paper thumbnail of On the coupling between a high-order spectral difference method and large eddy simulation

Proc. V European Conference on Computational Fluid Dynamics ECCOMAS CFD, 2010

Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral ... more Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formula (BDF2). The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower-upper symmetric Gauss-Seidel (LU-SGS) ...

Research paper thumbnail of An implicit high-order spectral difference approach for large eddy simulation

Journal of Computational Physics, 2010

High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity mo... more High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity model Implicit LU-SGS algorithm a b s t r a c t

Research paper thumbnail of Validation and application of a far-field time domain formulation for fan noise prediction

11th AIAA/CEAS Aeroacoustics Conference, 2005

Research paper thumbnail of Sensitivity Study on Computational Parameters for the Prediction of Noise Generated by Counter-Rotating Open Rotors

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), 2011

Research paper thumbnail of Efficient Flow and Noise Prediction of Counter-Rotating Open Rotors

Research paper thumbnail of Verfication of Noise Prediction Through Acoustic Analogy

13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007

Research paper thumbnail of An implicit high-order spectral difference approach for large eddy simulation

Journal of Computational Physics, 2010

High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity mo... more High-order spectral difference method Large eddy simulation Wall-adapting local eddy-viscosity model Implicit LU-SGS algorithm a b s t r a c t

Research paper thumbnail of Analysis of the implicit LU-SGS algorithm for 3rd- and 4th-order spectral volume scheme for solving the steady Navier–Stokes equations

Journal of Computational Physics, 2011

Research paper thumbnail of An eddy interaction model for particle deposition

Journal of Aerosol Science, 2012

Deposition of mono-disperse aerosols is studied numerically on a simplified human upper airway mo... more Deposition of mono-disperse aerosols is studied numerically on a simplified human upper airway model (UAM). This paper presents new correction functions for eddy interaction model (EIM) in an attempt to improve the accuracy of predicting aerosol deposition in the UAM. Based on an Euler-Lagrange methodology, the fluid phase is solved using RANS (Reynolds Averaged Navier Stokes equation) and employing low-Reynolds SST k-o turbulence model. The particle phase is solved using Lagrangian approach and employing an EIM model. Mono-disperse particle sizes of 3 and 6 mm are considered for breathing rates of 30 and 60 L/min.

Research paper thumbnail of A stability analysis for the spectral volume method on tetrahedral grids

Journal of Computational Physics, 2009

Research paper thumbnail of Study of the sediment transport over flat and wavy bottom using large-eddy simulation

Journal of Turbulence, 2009

... Chang, YS and Scotti, A. 2003. Entrainment and suspension of sediments into a turbulent flow ... more ... Chang, YS and Scotti, A. 2003. Entrainment and suspension of sediments into a turbulent flow over ripples. ... [44. Nakagawa, S., Na, Y. and Hanratty, TJ 2003. Influence of a wavy boundary on turbulence. ... Direct numerical simulation of turbulent flow over a wavy wall. Phys. ...

Research paper thumbnail of A moving medium formulation for prediction of propeller noise at incidence

Journal of Sound and Vibration, 2012

This paper presents a time domain formulation for the sound field radiated by moving bodies in a ... more This paper presents a time domain formulation for the sound field radiated by moving bodies in a uniform steady flow with arbitrary orientation. The aim is to provide a formulation for prediction of noise from body so that effects of crossflow on a propeller can be modeled in the time domain. An established theory of noise generation by a moving source is combined with the moving medium Green's function for derivation of the formulation. A formula with Doppler factor is developed because it is more easily interpreted and is more helpful in examining the physic of systems. Based on the technique presented, the source of asymmetry of the sound field can be explained in terms of physics of a moving source. It is shown that the derived formulation can be interpreted as an extension of formulation 1 and 1A of Farassat based on the Ffowcs Williams and Hawkings (FW-H) equation for moving medium problems. Computational results for a stationary monopole and dipole point source in moving medium, a rotating point force in crossflow, a model of helicopter blade at incidence and a propeller case with subsonic tips at incidence verify the formulation.

Research paper thumbnail of On the coupling between a high-order spectral difference method and large eddy simulation

Proc. V European Conference on Computational Fluid Dynamics ECCOMAS CFD, 2010

Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral ... more Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formula (BDF2). The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower-upper symmetric Gauss-Seidel (LU-SGS) ...

Research paper thumbnail of On the coupling between a high-order spectral difference method and large eddy simulation

Proc. V European Conference on Computational Fluid Dynamics ECCOMAS CFD, 2010

Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral ... more Abstract. The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formula (BDF2). The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower-upper symmetric Gauss-Seidel (LU-SGS) ...

Research paper thumbnail of Numerical Solution of the Linearized Euler Equations Using Compact Schemes

… Fluid Dynamics 2006, Jan 1, 2009

Research paper thumbnail of Quality of dynamic variational multiscale models on distorted grids

Journal of Turbulence, 2009

The present paper focuses on a dynamic version of the variational multiscale model and investigat... more The present paper focuses on a dynamic version of the variational multiscale model and investigates its performance in large eddy simulations (LES) of turbulent channel flow at Reynolds numbers (based on friction velocity) of 180, 395, and 590. The dynamic procedure was implemented for the variational multiscale model on the basis of the classical Smagorinsky model and the wall-adapting local

Research paper thumbnail of Prediction of Near- and Far-Field Noise Generated by Counter-Rotating Open Rotors

16th AIAA/CEAS Aeroacoustics Conference, 2010