3D numerical simulation of the long range propagation of acoustical shock waves through a heterogeneous and moving medium

Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a...

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Bibliographic Details
Main Authors: Luquet, David, Marchiano Régis, Coulouvrat François
Format: Conference Proceeding
Language:English
Subjects:
ABSORPTION
Acoustic noise
Aerodynamics
AMPLITUDES
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
Computational fluid dynamics
COMPUTERIZED SIMULATION
DIFFRACTION
Distributed memory
Engine noise
Explosions
Fan blades
Finite element method
Human influences
Message passing
NOISE
NONLINEAR PROBLEMS
Plane waves
Propagation
Scattering
Shear flow
Shock wave propagation
SHOCK WAVES
Sonic booms
SOUND WAVES
Supersonic aircraft
Supersonic speed
Three dimensional flow
THREE-DIMENSIONAL CALCULATIONS
TURBINE BLADES
TURBOMACHINERY
Turbulence
TURBULENT FLOW
Variation
VELOCITY
Wave diffraction
WAVE EQUATIONS
WIND
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Summary:Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D aspect, the code was massively parallelized using the single program, multiple data paradigm with the Message Passing Interfaces (MPI) for distributed memory architectures. This allows us to handle problems in the order of a thousand billion mesh points in the four dimensions (3 dimensions of space plus time). The validity of the method has been thoroughly evaluated on many cases with known solutions: linear piston, scattering of plane wave by a heterogeneous sphere, propagation in a waveguide with
ISSN:0094-243X
1551-7616
DOI:10.1063/1.4934447