Unsteady Validation of a Mean Flow Boundary Condition for Computational Aeroacoustics

For flow noise simulations, the nonreflecting boundary condition (NRBC) is significant to confine the computational domain to a small domain. Lattice Boltzmann method (LBM) has advantages for noise because of its low dissipation, but is limited to the uniform grid. In this paper, an absorbing boundary condition (ABC) based on perfectly matched layer (PML) technique is introduced to LBM. Then PML stability is analyzed and a new strategy is developed to achieve robustness. Invoking the decoupling time integration, the underlying equation for streaming is solved with the nodal discontinuous Galerkin method. Benchmark acoustic problems were used to demonstrate the PML absorption. Moreover, PML parameters, long time behavior and inhomogeneous pseudo mean flow are discussed. The methodology appears to work very well and would be hoped for practical flow noise computation.

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Numerical Analysis on Outflow Boundary Condition of Vortex Convection with Uniform Mean Flow.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.58.313 ◽

1992 ◽

Vol 58 (546) ◽

pp. 313-320 ◽

Cited By ~ 3

Author(s):

Yi DAI ◽

Toshio KOBAYASHI

Keyword(s):

Boundary Condition ◽

Numerical Analysis ◽

Mean Flow ◽

Outflow Boundary Condition ◽

Outflow Boundary

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Review of Two Numerical Approaches to Predict Nonlinear Airfoil Response to High-Amplitude Incident Gust

Noise Control and Acoustics ◽

10.1115/imece2004-61407 ◽

2004 ◽

Author(s):

Vladimir V. Golubev

Keyword(s):

Unsteady Aerodynamics ◽

High Amplitude ◽

Finite Amplitude ◽

Computational Aeroacoustics ◽

Mean Flow ◽

Linear Superposition ◽

Perturbation Field ◽

Unsteady Aerodynamic ◽

The Mean ◽

Numerical Approaches

In this work, two different numerical methods of time-accurate nonlinear analysis are reviewed and compared in application to the problem of nonlinear unsteady aerodynamic and aeroacoustic airfoil responses to a high-intensity impinging gust. The incident perturbation field is of finite amplitude relative to the mean flow so that in general, no assumption of a linear superposition of responses from each individual harmonic can be made. Thus, in addition to providing a comparison of two different approaches in computational aeroacoustics, the paper achieves the objective of obtaining verified solutions determining the limits of validity for linearized methods, universally accepted in studies of unsteady aerodynamics and aeroacoustics. The work investigates nonlinear near- and far-field responses of a Joukowksi airfoil in the parametric space of gust intensity and frequency.

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COMPUTATIONAL FLUID DYNAMICS STUDY OF PULL AND PLUG FLOW BOUNDARY CONDITION ON NASAL AIRFLOW

Biomedical Engineering Applications Basis and Communications ◽

10.4015/s1016237213500440 ◽

2013 ◽

Vol 25 (04) ◽

pp. 1350044 ◽

Cited By ~ 3

Author(s):

Mohammed Zubair ◽

Vizy Nazira Riazuddin ◽

Mohammad Zulkifly Abdullah ◽

Ismail Rushdan ◽

Ibrahim Lutfi Shuaib ◽

...

Keyword(s):

Fluid Dynamics ◽

Boundary Condition ◽

Computational Fluid Dynamics ◽

Boundary Conditions ◽

Comparative Study ◽

Flow Model ◽

Plug Flow ◽

Maximum Velocity ◽

Nasal Valve ◽

Flow Boundary

The recent advances in the computer based computational fluid dynamics (CFD) software tools in the study of airflow behavior in the nasal cavity have opened an entirely new field of medical research. This numerical modeling method has provided both engineers and medical specialists with a clearer understanding of the physics associated with the flow in the complicated nasal domain. The outcome of any CFD investigation depends on the appropriateness of the boundary conditions applied. Most researchers have employed plug boundary condition as against the pull flow which closely resembles the physiological phenomenon associated with the breathing mechanism. A comparative study on the effect of using the plug and pull flow boundary conditions are evaluated and their effect on the nasal flow are studied. Discretization error estimation using Richardson's extrapolation (RE) method has also been carried out. The study is based on the numerical model obtained from computed tomographic data of a healthy Malaysian subject. A steady state Reynold averaged Navier–Stokes and continuity equations is solved for inspiratory flow having flow rate 20 L/min representing turbulent boundary conditions. Comparative study is made between the pull and plug flow model. Variation in flow patterns and flow features such as resistance, pressure and velocity are presented. At the nasal valve, the resistance for plug flow is 0.664 Pa-min/L and for pull flow the value is 0.304 Pa-min/L. The maximum velocity at the nasal valve is 3.28 m/s for plug flow and 3.57 m/s for pull flow model.

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