Akinori Tamura

Direct Simulation of Acoustic Waves Emitted from Moving Bodies by the Finite Difference Lattice Boltzmann Method

Direct simulation of acoustic waves emitted from rotating elliptic cylinder has been performed by the finite difference lattice Boltzmann method (FDLBM) formulated by the arbitrary Lagrangian Eulerian (ALE) scheme. The flow field is almost periodic after the calculation fully develops. The large vortexes appear outside of the elliptic cylinder, and move slowly to the same direction as the cylinder’s rotation. The positive and negative vorticity is alternately generated at the edge by those large vortexes. The acoustic waves propagate synchronizing with the rotation. The acoustic waves consist of those whose frequency is two and four times that of the rotation. One of the sound sources is the potential like doublet due to the motion of the edge and the other is the doublet that is formed by the interaction between the above-mentioned vortexes and the surface of the edge. The bladevortex interaction is also directly simulated. The wave patterns of the acoustic waves by the simulation are compared with those by the experimental result, and both agree well qualitatively.

Direct simulation of Aeolian tones emitted from a circular cylinder in transonic flows using the finite difference lattice Boltzmann method

We present an application of the finite difference lattice Boltzmann method to direct simulations of aerodynamic sound in transonic flows. The arbitrary Lagrangian Eulerian formulation is introduced and the Aeolian tones emitted from a moving circular cylinder are successfully simulated. It is shown that the sound sources change depending on the flow Mach numbers as follows: the oscillating flow just behind the cylinder is the sound source for low Mach number flows. For flow of Mach numbers about 0.7, in which the supersonic region appears without shock waves, an additional source, interaction between the vortices, becomes significant. For Mach numbers about 0.9, a shock wave appears and interaction between the vortex and the weak shock wave is shown to be the sound source.

A Study of BVI Noises by the Finite Difference Lattice Boltzmann Method

Noises caused by parallel blade-vortex interaction have been calculated using the finite difference lattice Boltzmann method of the compressible Euler model. The perturbed discrete Boltzmann equation based on a prescribed vortex method has been proposed in order to prevent a vortex from diffusing by numerical dissipation. The discretization of the governing equation is based on a second order accurate Runge-Kutta time integration and a fifth order accurate upwind scheme which includes dissipative terms to clearly capture shock waves. Numerical simulations of unsteady two-dimensional inviscid blade-vortex interaction have been carried out by proposed method as a simple model of parallel bladevortex interaction. An instantaneous pressure coefficient, a time history of a lift coefficient and patterns of acoustic waves were compared with the other results, and agreed with them very well. Mechanism of noise generation was also investigated from numerical results. Three-dimensional calculations of parallel blade-vortex interaction have also performed using present numerical procedure. Good agreements between numerical results and experimental ones have been obtained in comparisons of instantaneous pressure coefficient.

Simulation of Transonic Flows Past a Body by Finite Difference Lattice Boltzmann Method Using ALE Formulation

Compressible transonic flows around a circular cylinder are simulated by the finite difference lattice Boltzmann method using the Arbitrary Lagrangian Eulerian formulation. High speed compressible flow is successively calculated by giving the local equihirium distribution function in Eulerian form and moving the body and grids in Lagrangean manner. By this technique, the Navier-Stokes equations are recovered and the fluid velocity is kept small in the equilibrium distribution functions and the calculation becomes stable. Patterns of compressible waves and expansion waves agree well with experimental results. The Rankine-Hugoniots relation is also recovered for the shock waves appearing on the lee-side of the cylinder.