Research on the numerical simulation of aerodynamic noises of shear flow based on linearized Euler equations

This paper numerically simulated the propagation of different sound sources in inhomogeneous media through solving linearized Euler equations (LEE). In space, dispersion-relation-preserving (DRP) scheme and compact difference scheme of high-order accuracy were used for dispersion. In time, Runge-Kutta (Low Dispersion and Dissipation Runge-Kutta) method with low-dispersion and low-dissipation was applied to push ahead. Nonreflecting boundary condition was adopted at the far-field boundary. In the meanwhile, numerical filtering was conducted for numerically computational results. The scattering of Gaussian pulse source around a cylinder was taken as a verification example. Numerical simulation results were compared with theoretical solutions to verify the correctness of numerical simulation method of aerodynamic noises in this paper. Numerical simulation was conducted for the sound propagation of monopole sound source in the shear layer and the sound propagation of different modes of sound sources in and out the tailpipe nozzle of engines. Numerical simulation results showed: The treatment for dispersion schemes and boundary conditions in this paper could well simulate the propagation process of aerodynamic noises in the shear layer; the shear flow would have an impact on the amplitude and propagation direction of aerodynamic noises in the flow field; for different modes of pipe sound sources, the shear layer would cause different refraction effects; the direction of sound radiation was rather centralized for the single pipe mode and dispersive for the multi-pipe mode. In addition, the dispersive-ness of sound radiation became stronger and stronger with the increased pipe modes. Namely, the directivity of sound presented to be a petal. The shear layer would reduce the dispersion effect of multi-pipe modes in the direction of sound radiation

Numerical modelling of fluid-induced noise from lifting surfaces at moderate Reynolds numbers

Fluid-induced noise from lifting surface flows occurs in a wide variety of industrial applications and, despite decades of research, there are still many open questions relating to the underlying physics of how different flows produce particular acoustic signatures. Predicting fluid-induced noise is challenging and requires a detailed understanding of the underlying fluid flow. At moderate Reynolds numbers, the transitional nature of the flow makes the acoustic field very sensitive to small changes in the flow conditions, making predictions particularly difficult. This thesis presents a numerical study of fluid-induced noise over lifting surfaces. A hybrid aero-acoustic model is developed that is capable of resolving the acoustic field resulting from the turbulent flow over an arbitrary body or bodies. The methodology leads to a flexible and robust model that allows for both the fluid and acoustic fields to be resolved simultaneously on separate, partially overlapping domains, allowing for the separation of turbulent and acoustic scales to be handled in an efficient manner. The model is used, together with large eddy and direct numerical simulations, to investigate the fluid dynamics and fluid-induced noise of flows over lifting surfaces at moderate Reynolds numbers (o 10^5). The acoustics of finite and infinite span lifting surfaces are investigated, with a particular focus on trailing edge noise and its relationship to a transitional boundary layer. Multi-body interaction noise is also considered, with results comparing favourably with experimental data, providing a high degree of confidence in the predictive capabilities of the model

Modelling Seismic Wave Propagation for Geophysical Imaging

International audienceThe Earth is an heterogeneous complex media from the mineral composition scale (10−6m) to the global scale ( 106m). The reconstruction of its structure is a quite challenging problem because sampling methodologies are mainly indirect as potential methods (Günther et al., 2006; Rücker et al., 2006), diffusive methods (Cognon, 1971; Druskin & Knizhnerman, 1988; Goldman & Stover, 1983; Hohmann, 1988; Kuo & Cho, 1980; Oristaglio & Hohmann, 1984) or propagation methods (Alterman & Karal, 1968; Bolt & Smith, 1976; Dablain, 1986; Kelly et al., 1976; Levander, 1988; Marfurt, 1984; Virieux, 1986). Seismic waves belong to the last category. We shall concentrate in this chapter on the forward problem which will be at the heart of any inverse problem for imaging the Earth. The forward problem is dedicated to the estimation of seismic wavefields when one knows the medium properties while the inverse problem is devoted to the estimation of medium properties from recorded seismic wavefields

Gaussian Process Modeling for Upsampling Algorithms With Applications in Computer Vision and Computational Fluid Dynamics

Across a variety of fields, interpolation algorithms have been used to upsample lowresolution or coarse data fields. In this work, novel Gaussian Process based methodsare employed to solve a variety of upsampling problems. Specifically threeapplications are explored: coarse data prolongation in Adaptive Mesh Refinement(AMR) in the field of Computational Fluid Dynamics, accurate document imageupsampling to enhance Optical Character Recognition (OCR) accuracy, and fastand accurate Single Image Super Resolution (SISR). For AMR, a new, efficient,and “3rd order accurate” algorithm called GP-AMR is presented. Next, a novel,non-zero mean, windowed GP model is generated to upsample low resolution documentimages to generate a higher OCR accuracy, when compared to the industrystandard. Finally, a hybrid GP convolutional neural network algorithm is used togenerate a computationally efficient and high quality SISR model

Seismic Wave Simulation for Complex Rheologies on Unstructured Meshes

The possibility of using accurate numerical methods to simulate seismic wavefields on unstructured meshes for complex rheologies is explored. In particular, the Discontinuous Galerkin (DG) finite element method for seismic wave propagation is extended to the rheological types of viscoelasticity, anisotropy and poroelasticity. First is presented the DG method for the elastic isotropic case on tetrahedral unstructured meshes. Then an extension to viscoelastic wave propagation based upon a Generalized Maxwell Body formulation is introduced which allows for quasi-constant attenuation through the whole frequency range. In the following anisotropy is incorporated in the scheme for the most general triclinic case, including an approach to couple its effects with those of viscoelasticity. Finally, poroelasticity is incorporated for both the propagatory high-frequency range and for the diffusive low-frequency range. For all rheology types, high-order convergence is achieved simultaneously in space and time for three-dimensional setups. Applications and convergence tests verify the proper accuracy of the approach. Due to the local character of the DG method and the use of tetrahedral meshes, the presented schemes are ready to be applied for large scale problems of forward wave propagation modeling of seismic waves in setups highly complex both geometrically and physically