• Journal of Advanced Marine Engineering and Technology
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• v.27 no.4
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• pp.511-519
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• 2003

A stratified flow is simulated using the finite difference lattice Boltzmann method (FDLBM). The effect of body force (gravity) in a simple one-dimensional model with the lattice BGK 9 velocity is examined. The effect of body force in the compressible fluid is greatly different from that of the incompressible fluid In a compressible fluid under gravitational force, the density stratification is not sufficient and the entropy stratification is essential. The numerical simulation of a line sink compressible stratified flow in two-dimensional channel is also carried out. The results show that selective withdrawal is established when the entropy of the upper part increases. and the simulated results using FDLB method are satisfactory compared with the theoretical one.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.113-118
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• 2004

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.381-390
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• 2016

In this study, aeroacoustic characteristics of combined fan are investigated and noise was reduced by applying Serrated Trailing Edge which is known as the method to reduce fan noises. Unsteady CFD (Computational Fluid Dynamics) analysis was carried out using Lattice Boltzmann Method(LBM) to figure out the combined fan's aeroacoustics and experimental results was used to verify simulation results. Results show that different BPFs are generated at the each inner fan and outer fan on the different frequency while Blade Passing Frequency(BPF) of general fans is constant on the entire frequency range. Boundary vortex and vortex shedding are suppressed or dispersed by applying the Serrated Trailing Edge to the inner fan. Furthermore, broadband noise and fan's torque are reduced.

• Journal of Mechanical Science and Technology
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• v.19 no.11
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• pp.2032-2039
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• 2005

The lattice Boltzman method (LBM) and the finite difference-based lattice Boltzmann method (FDLBM) are quite recent approaches for simulating fluid flow, which have been proven as valid and efficient tools in a variety of complex flow problems. They are considered attractive alternatives to conventional finite-difference schemes because they recover the Navier-Stokes equations and are computationally more stable, and easily parallelizable. However, most models of the LBM or FDLBM are for incompressible fluids because of the simplicity of the structure of the model. Although some models for compressible thermal fluids have been introduced, these models are for monatomic gases, and suffer from the instability in calculations. A lattice BGK model based on a finite difference scheme with an internal degree of freedom is employed and it is shown that a diatomic gas such as air is successfully simulated. In this research we present a 2-dimensional edge tone to predict the frequency characteristics of discrete oscillations of a jet-edge feedback cycle by the FDLBM in which any specific heat ratio $\gamma$ can be chosen freely. The jet is chosen long enough in order to guarantee the parabolic velocity profile of a jet at the outlet, and the edge is of an angle of $\alpha$=23$^{o}$. At a stand-off distance w, the edge is inserted along the centerline of the jet, and a sinuous instability wave with real frequency is assumed to be created in the vicinity of the nozzle exit and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations resulting from periodic oscillation of the jet around the edge.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.570-575
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• 2008

Flows are studied to understand the flow structure in the narrow region that any experimental approaches are hard to access, Effects on the vehicle commodities from the flows are anticipated in the point of aerodynamics and aero-acoustics. PowerFLOW, which was well validated commercial software, was used to simulate the flow field in the small region, for example, the inner region of the fender panel, the inner region around the front door and the inner region of the trunk lid. Flows in the narrow region could be origins of door sealing problem and dust piling problem.