Three-dimensional direct numerical simulation of infrasound propagation in the Earth’s atmosphere

2018 ◽  
Vol 859 ◽  
pp. 754-789 ◽  
Author(s):  
R. Sabatini ◽  
O. Marsden ◽  
C. Bailly ◽  
O. Gainville
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Lower Thermosphere ◽  
Three Dimensional ◽  
Stratified Medium ◽  
Horizontal Wind ◽  
Physical Analysis ◽  
Strong Impact

A direct numerical simulation of the three-dimensional unsteady compressible Navier–Stokes equations is performed to investigate the infrasonic field generated in a realistic atmosphere by an explosive source placed at ground level. To this end, a high-order finite-difference method originally developed for aeroacoustic applications is employed. The maximum overpressure and the main frequency of the signal recorded at 4 km distance from the source location are about 4000 Pa and 0.2 Hz, respectively. The atmosphere is parametrized as a vertically stratified medium, constructed by specifying vertical profiles of the temperature and the horizontal wind which reproduce measurements. The computation is carried out up to 140 km altitude and 450 km range. The goal of the present paper is twofold. On the one hand, the feasibility of using a direct numerical simulation of the three-dimensional fluid dynamic equations for the detailed description of long-range propagation in the atmosphere is proven. On the other hand, a physical analysis of the infrasonic field is realized. In particular, great attention is directed towards some important phenomena which are not taken into account or not well predicted by classical propagation models. To begin with, the present study clearly demonstrates that the weakly nonlinear ray theory may lead to an incorrect evaluation of the waveform distortion of high-amplitude waves propagating towards the lower thermosphere. In addition, signals recorded in the shadow zones are investigated. In this regard, the influence on the acoustic field of temperature and wind inhomogeneities of length scale comparable with the acoustic wavelength is analysed. The role of diffraction at the thermospheric caustic is finally examined and it is pointed out that the amplitude of the source may have a strong impact on the length of the shadow zone.

Direct Numerical Simulation of Effects of Small Angle of Incidence on Honji Instability

2011 ◽  
Author(s):  
Kun Yang ◽  
Liang Cheng ◽  
Hongwei An ◽  
Ming Zhao
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Oscillatory Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Angle Of Incidence ◽  
Navier Stokes Equations ◽  
Small Incidence ◽  
Inclination Angles

This paper concerns Honji instability generated around a circular cylinder in an oscillatory flow with a small oblique angle. In this study, direct numerical simulation has been conducted for an oscillatory flow past a stationary cylinder with small incidence angles (α) of 5° and 10° at KC number of 2 and β number of 200. The three-dimensional Navier-Stokes equations are solved using the Petrov-Galerkin finite element method. Flow structures around the cylinder are visualized through using streamlines, velocity vectors and vorticity contours. Honji instability has been captured at both chosen inclination angles. However Honji vortex pairs are asymmetric at α = 5° and 10° due to the inclination of the oscillation direction and can only be observed during the flow reversal. It is also found that the flow inclination appears to suppress the three-dimensional instability.

Local Mesh Refinement and Penalty Methods Dedicated to the Direct Numerical Simulation of Incompressible Multiphase Flows

2003 ◽  
Author(s):  
Ste´phane Vincent ◽  
Jean-Paul Caltagirone ◽  
Pierre Lubin ◽  
Nirina Randrianarivelo
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Multiphase Flows ◽  
Stokes Equations ◽  
Mathematical Formulation ◽  
Mesh Refinement ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Local Mesh Refinement

Recent advances in numerical methods for the direct numerical simulation (DNS) of multiphase flows are presented. The mathematical formulation is based on an eulerian discretisation of the navier-stokes equations on fixed staggered curvilinear grids where the media are located thanks to volume of fluid functions. An adaptative and local mesh refinement method (AMR) is proposed to allow multi-space scale solutions in three dimensions and a tensorial penalty (or fictious domain) approach is detailed for the numerical modelling of incompressibility, velocity/pressure coupling and liquid/solid interactions in multi fluid flows. The article is focussed on three-dimensional applications of the direct numerical simulation. The DNS tool is applied to the mould filling under unstable viscous jet conditions, the stoke’s flow induced by a solid particle in a tube and the turbulent wave breaking in deep water. These flows are chosen to highlight the abilities of the numerical model for characterising unsteady incompressible multiphase flows.

scholarly journals Direct numerical simulation of ‘short’ laminar separation bubbles with turbulent reattachment

2000 ◽  
Vol 403 ◽  
pp. 223-250 ◽  
Author(s):  
M. ALAM ◽  
N. D. SANDHAM
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Laminar Boundary Layer ◽  
Stokes Equations ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Wall Turbulence ◽  
Mean Flow ◽  
Laminar Separation

Direct numerical simulation of the incompressible Navier-Stokes equations is used to study flows where laminar boundary-layer separation is followed by turbulent reattachment forming a closed region known as a laminar separation bubble. In the simulations a laminar boundary layer is forced to separate by the action of a suction profile applied as the upper boundary condition. The separated shear layer undergoes transition via oblique modes and Λ-vortex-induced breakdown and reattaches as turbulent flow, slowly recovering to an equilibrium turbulent boundary layer. Compared with classical experiments the computed bubbles may be classified as ‘short’, as the external potential flow is only affected in the immediate vicinity of the bubble. Near reattachment budgets of turbulence kinetic energy are dominated by turbulence events away from the wall. Characteristics of near-wall turbulence only develop several bubble lengths downstream of reattachment. Comparisons are made with two-dimensional simulations which fail to capture many of the detailed features of the full three-dimensional simulations. Stability characteristics of mean flow profiles are computed in the separated flow region for a family of velocity profiles generated using simulation data. Absolute instability is shown to require reverse flows of the order of 15–20%. The three-dimensional bubbles with turbulent reattachment have maximum reverse flows of less than 8% and it is concluded that for these bubbles the basic instability is convective in nature.

Direct Numerical Simulation of Gas-Solids Flow Based on the Immersed Boundary Method

2010 ◽  
pp. 245-276 ◽  
Author(s):  
Rahul Garg ◽  
Sudheer Tenneti ◽  
Jamaludin Mohd. Yusof ◽  
Shankar Subramaniam
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Immersed Boundary Method ◽  
Stokes Equations ◽  
Particle Surface ◽  
Three Dimensional ◽  
Immersed Boundary ◽  
Navier Stokes Equations ◽  
Boundary Method ◽  
Coarse Grained Simulations

In this chapter, the Direct numerical simulation (DNS) of flow past particles is described. DNS is a first-principles approach for modeling interphase momentum transfer in gas-solids flows that does not require any further closure as the flow around the particles is fully resolved. In this chapter, immersed boundary method (IBM) is described where the governing Navier-Stokes equations are modeled with exact boundary conditions imposed at each particle surface using IBM and the resulting three dimensional time-dependent velocity and pressure fields are solved. Since this model has complete description of the gas-solids hydrodynamic behavior, one could extract all the Eulerian and Lagrangian statistics for validation and development of more accurate closures which could be used at coarse-grained simulations described in other chapters.

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