Permeable Surface Corrections for Ffowcs Williams and Hawkings Integrals

Lockard, David P.; Casper, Jay

doi:10.2514/6.2005-2995

Cited by 34 publications

(40 citation statements)

References 24 publications

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“…There are only minor differences between the solutions for the permeable and solid surfaces, most likely caused by vortices crossing the downstream portions of the porous surfaces. 21,22 At this low frequency with a Helmholtz number kD = 0.19, it is very unlikely that there are any flow effects on the radiated noise. Therefore, only results for the solid surfaces will be presented in the remainder of the paper.…”

Section: Ivd Acoustic Radiationmentioning

confidence: 99%

Tandem Cylinder Noise Predictions

Lockard

Khorrami

Choudhari

et al. 2007

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

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In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters.Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 × 10 5 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow.The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to capture the complete decay in the spanwise correlation, thereby producing reasonable noise radiation levels.

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Section: Ivd Acoustic Radiationmentioning

confidence: 99%

Tandem Cylinder Noise Predictions

Lockard

Khorrami

Choudhari

et al. 2007

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

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“…The surfaces were extracted from the CFD multi-block structured grid used for the CFD. A first set of rigid surfaces includes the wall surfaces on the wing leading edge (1-7) and on the slat pressure side (8)(9)(10)(11). Then, three sets of porous surfaces are available near the external boundary of the computational domain.…”

Section: American Institute Of Aeronautics and Astronauticsmentioning

confidence: 99%

Slat noise measurement and numerical prediction in the VALIANT programme

Manoha¹,

Terracol²,

Lemoine

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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In the context of the on-going EC research program VALIANT, mechanisms of slat noise generation are studied on the basis of a simple but representative 2-element (slat and main body) airfoil, for which a detailed experimental aerodynamic/acoustic database has been collected in the open jet facility at Ecole Centrale de Lyon (ECL) at a Reynolds number, based on the airfoil chord, of about one million. Then several CFD/CAA prediction methods have been compared, improved and validated against this database.The airfoil shape has been optimized by Onera with the objectives of isolating the slat noise sources from other spurious sources, while minimizing the airfoil total lift and the wind tunnel mean flow deflection. The tests at ECL provided aerodynamic data (static and unsteady wall pressure data, hot-wire probe measurements) and farfield noise acquisitions, including directivity characterization and noise sources localization using Onera's microphone antenna. Then an unsteady zonal hybrid RANS/LES simulation has been performed using Onera's FUNk solver, providing a comprehensive description and physical analysis of the unsteady flow inside the slat cove. The computed and measured wall pressure spectra are in fair qualitative and quantitative agreement, both being characterized by several tonal peaks emerging from a global broadband content. The noise maps confirmed that these peaks are actually generated by the slat cove region. These tones are attributed to a cavity feedback loop mechanism involving the impact of the main shear layer on the slat pressure side, and a theoretical law predicting the tone frequencies has been proposed. Finally, a farfield noise prediction is achieved, using a Ffowcs Williams-Hawking integration (Onera's MIA solver), from CFD unsteady data stored on a porous surface located at the external boundaries of the CFD domain. Corrections are proposed to account for (i) the difference between experimental and computational airfoil spans, based on un-correlated spanwise duplication of the CFD domain, (ii) the acoustic installation effects, studied via BEM computations using Onera's Bemuse solver, due to the test set-up side plates and the airfoil surfaces which were not included in the CFD domain. With these corrections, measured and predicted farfield noise spectra and overall sound pressure levels are in fair agreement. I ContextIn the on-going EC research program VALIANT (VALidation and Improvement of Airframe Noise prediction Tools) coordinated by the Von Karman Institute (Brussels, Belgium) basic mechanisms of airframe noise (AFN) are studied through a dual approach, • to generate a detailed, accurate experimental database on broadband noise associated with simple but representative configurations, including the turbulent flow sources causing the noise and, • to validate and improve CFD/CAA tools for prediction of the corresponding type of broadband AFN and generate a detailed numerical database. The following specific flow configurations revealing the basic mechanisms of AFN generated by ...

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“…It has been shown that escaping eddies through an integration surface can generate spurious noise. 7,8 This issue makes it difficult to attribute additional noise contributions, as compared to solid surface predictions, to quadrupole sources or spurious noise generated numerically. Since it is still computationally infeasible to resolve and propagate the effect of all relevant quadrupole sources in a realistic engineering problem, we turn to a model problem that captures the salient physics but at a cost that allows the opportunity to address the questions at hand.…”

Section: Introductionmentioning

confidence: 98%

Quadrupole Noise in Turbulent Wake Interaction Problems

Wolf

Lele

2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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A 3-D model airframe noise interaction problem is proposed to investigate source term effects in different flow configurations. Simulations of the model problem were conducted to assess the relative importance of quadrupole noise. In these simulations, a cylinder is placed in the vicinity of the trailing edge of a NACA 0012 airfoil at incidence. LES is performed to compute the noise source field while the far-field noise is computed using a fast Ffowcs Williams-Hawkings solver with the ability to directly include quadrupole terms. 2-D results have shown that, for the flow parameters studied, the inclusion of quadrupole sources is necessary for reasonable agreement with direct noise predictions. 3-D simulations were run in this study to determine if the same finding holds for turbulent wake interactions between the bodies. The Reynolds number for these simulations was chosen to be high enough to ensure turbulent breakdown at the trailing edge of the airfoil and in the near wake of the cylinder. Several cases were run to parameterize the problem, including variations in Mach number as well as variations in gap spacing between the cylinder and airfoil. Results show that the effect of quadrupoles is much more pronounced in the presence of turbulence and excluding their contribution severely detriments acoustic predictions at the nominal Mach number of 0.3. At lower Mach number, as expected, the effect of quadrupoles is less severe but their exclusion still modifies the far-field radiation pattern significantly. Ongoing work is being performed to directly include the quadrupole terms in the acoustic analogy prediction as well as to evaluate possible errors introduced by commonly used porous surface analogy methods.

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Permeable Surface Corrections for Ffowcs Williams and Hawkings Integrals

Cited by 34 publications

References 24 publications

Tandem Cylinder Noise Predictions

Tandem Cylinder Noise Predictions

Slat noise measurement and numerical prediction in the VALIANT programme

Quadrupole Noise in Turbulent Wake Interaction Problems

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