scholarly journals Three-dimensional acoustic scattering by vortical flows. II. Axisymmetric scattering by Hill’s spherical vortex

2001 ◽  
Vol 13 (10) ◽  
pp. 2890-2900 ◽  
Author(s):  
Stefan G. Llewellyn Smith ◽  
Rupert Ford
Keyword(s):  
Three Dimensional ◽  
Acoustic Scattering ◽  
Vortical Flows ◽  
Axisymmetric Scattering ◽  
Spherical Vortex

Axisymmetric acoustic scattering by vortices

2002 ◽  
Vol 473 ◽  
pp. 275-294 ◽  
Author(s):  
Y. HATTORI ◽  
STEFAN G. LLEWELLYN SMITH
Keyword(s):  
Mach Number ◽  
Born Approximation ◽  
Acoustic Waves ◽  
Three Dimensional ◽  
Acoustic Scattering ◽  
Order Effects ◽  
Incoming Wave ◽  
Spherical Vortex ◽  
The Difference ◽  
Higher Order Effects

The scattering of acoustic waves by compact three-dimensional axisymmetric vortices is studied using direct numerical simulation in the case where the incoming wave is aligned with the symmetry axis and the direction of propagation of the vortices. The cases of scattering by Hill’s spherical vortex and Gaussian vortex rings are examined, and results are compared with predictions obtained by matched asymptotic expansions and the Born approximation. Good agreement is obtained for long waves, with the Born approximation usually giving better predictions, especially as the difference in scale between vortex and incoming waves decreases and as the Mach number of the flow increases. An improved version of the Born approximation which takes into account higher-order effects in Mach number gives the best agreement.

scholarly journals Three-dimensional acoustic scattering by vortical flows. I. General theory

2001 ◽  
Vol 13 (10) ◽  
pp. 2876-2889 ◽  
Author(s):  
Stefan G. Llewellyn Smith ◽  
Rupert Ford
Keyword(s):  
General Theory ◽  
Three Dimensional ◽  
Acoustic Scattering ◽  
Vortical Flows

Adaptivity and Three Dimensional Hierarchical Boundary Elements for Rigid Acoustic Scattering Problems

1995 ◽  
Author(s):  
Steven J. Newhouse ◽  
Ian C. Mathews
Keyword(s):  
Boundary Element ◽  
Acoustic Analysis ◽  
Three Dimensional ◽  
Acoustic Scattering ◽  
Error Estimator ◽  
Infinite Domain ◽  
Scattering Problems ◽  
Effective Form ◽  
Mesh Density ◽  
Acoustic Scattering Problems

Abstract The boundary element method is an established numerical tool for the analysis of acoustic pressure fields in an infinite domain. There is currently no well established method of estimating the surface pressure error distribution for an arbitrary three dimensional body. Hierarchical shape functions have been used as a highly effective form of p refinement in many finite and boundary element applications. Their ability to be used as an error estimator in acoustic analysis has never been fully exploited. This paper studies the influence of mesh density and interpolation order on several acoustic scattering problems. A hierarchical error estimator is implemented and its effectiveness verified against the spherical problem. A coarse cylindrical mesh is then refined using the new error estimator until the solution has converged. The effectiveness of this analysis is shown by comparing the error indicators derived during the analysis to the solution generated from a very fine cylindrical mesh.

Direct Simulation of Acoustic Scattering by Two- and Three-Dimensional Bodies

2000 ◽  
Vol 37 (1) ◽  
pp. 68-75 ◽  
Author(s):  
Olivier A. Laik ◽  
Philip J. Morris
Keyword(s):  
Three Dimensional ◽  
Acoustic Scattering ◽  
Direct Simulation

scholarly journals Cartesian Mesh Linearized Euler Equations Solver for Aeroacoustic Problems around Full Aircraft

2015 ◽  
Vol 2015 ◽  
pp. 1-18 ◽  
Author(s):  
Yuma Fukushima ◽  
Daisuke Sasaki ◽  
Kazuhiro Nakahashi
Keyword(s):  
Euler Equations ◽  
Complex Geometry ◽  
Time Integration ◽  
Three Dimensional ◽  
Acoustic Scattering ◽  
Shielding Effect ◽  
Immersed Boundary ◽  
Noise Propagation ◽  
Linearized Euler Equations ◽  
Cartesian Mesh

The linearized Euler equations (LEEs) solver for aeroacoustic problems has been developed on block-structured Cartesian mesh to address complex geometry. Taking advantage of the benefits of Cartesian mesh, we employ high-order schemes for spatial derivatives and for time integration. On the other hand, the difficulty of accommodating curved wall boundaries is addressed by the immersed boundary method. The resulting LEEs solver is robust to complex geometry and numerically efficient in a parallel environment. The accuracy and effectiveness of the present solver are validated by one-dimensional and three-dimensional test cases. Acoustic scattering around a sphere and noise propagation from the JT15D nacelle are computed. The results show good agreement with analytical, computational, and experimental results. Finally, noise propagation around fuselage-wing-nacelle configurations is computed as a practical example. The results show that the sound pressure level below the over-the-wing nacelle (OWN) configuration is much lower than that of the conventional DLR-F6 aircraft configuration due to the shielding effect of the OWN configuration.

Production and Development of Secondary Flows and Losses Within a Three Dimensional Turbine Stator Cascade

1985 ◽  
Author(s):  
A. Yamamoto ◽  
R. Yanagi
Keyword(s):  
Three Dimensional ◽  
Quantitative Information ◽  
Secondary Flows ◽  
Suction Surface ◽  
Trailing Edge ◽  
Loss Mechanism ◽  
Flow Measurements ◽  
Aerodynamic Loss ◽  
Vortical Flows ◽  
Turbine Stator

Using five-hole pitot tubes, detailed flow measurements were made before, within and after a low-speed three-dimensional turbine stator blade row to obtain quantitative information on the aerodynamic loss mechanism. Qualitative flow visualization tests and endwall static pressure measurements were also made. An analysis of the tests revealed that many vortical flows promote loss generation. Within a large part of the cascade, a major loss process could be explained simply as the migration of boundary layer low energy fluids from surrounding walls (endwalls and blade surfaces) to the blade suction surface near the trailing edge. On the other hand, complexity exists after the cascade and in the vortical flows near the trailing edge. The strong trailing shedding vortices affect upstream flow fields within the cascade. Detailed flow surveys within the cascade under the effects of blade tip leakage flows are also included.

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