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Aeroacoustics using LES of Turbulent Flows around an Airfoil
Takeo Kajishima,Changhwa Han 한국전산유체공학회 2014 한국전산유체공학회 학술대회논문집 Vol.2014 No.11
To development an efficient indirect method for aeroacoustic field, a numerical method for turbulent flows at low Mach number and a sound source model are discussed. The time marching method for the usual incompressible scheme is modified to account for the weak compressibility. A one-equation subgrid scale model (SGS) for the large-eddy simulation (LES) is improved to deal with high Reynolds number flows appropriately. The reproduced turbulent flow around NACA0012 airfoil is in good agreement with experimental data The sound source formulation is derived by rearranging the continuity and Navier-Stokes equations to the wave motion equation. The investigation using LES database of flow around NACA0012 airfoil suggests that the material derivative of the velocity divergence plays a dominant role as a sound source. The distribution of the sources is consistent with of the classical sound source model such as Lighthill or Powell in case of very low fluctuation of density. The sound pressure level predicted based on the above-mentioned LES and newly derived sound source model is in reasonable agreement with experimental data.
박용찬,Takeo Kajishima 한국자원공학회 2010 Geosystem engineering Vol.13 No.4
Traditionally, the gas-lift pump has been used to lift corrosive or toxic liquid due to its simple structure and maintenance. It is also considered as a technically feasible system for the development of deep-ocean minerals and as a means to sequestrate CO2 gas into the ocean. Donor-cell scheme or Forward-Time and Backward- Space (FTBS), which is commonly used in solving advection equation such an air-lift system, is very stable but causes numerical diffusion. In order to reduce numerical diffusion or dissipation by the first-order upwind scheme, CIP (Cubic-Interpolated Propagation/Constrained Interpolation Profile) has been applied to bubble and slug flows in a gas-lift pumping system. The GLAD (Gas-Lift Advanced Dissolution) model using CIP method were validated by comparison with gas-liquid two-phase experiments and the effectiveness of the CIP method over the typical one has been demonstrated from the simulation of gas-liquid two-phase slug flow.
Sound Source Detection in Turbulent Flows Around an Airfoil at Low Mach Number
Changhwa HAN,Takeo KAJISHIMA 한국전산유체공학회 2014 한국전산유체공학회 학술대회논문집 Vol.2014 No.10
The purpose of our study is a sound source detection in turbulent flows. To this end, we rearrange the continuity and Navier-Stokes equations to have a wave equation with a lump of source terms which include the velocity divergence. As a result of investigation of turbulent flows around NACA0012 airfoil at low Mach number, it becomes evident that the material derivative of the velocity divergence plays an important role in the sound field. That distribution is corresponding to the classical sound source such as Lighthill or Powell, and the sound pressure level is in agreement with the experimental data by Miyazawa et al. Our acoustic theory clarifies the meaning of sound which is not fully understood in traditional indirect methods using incompressible flows. We think that it provides the basis of a new indirect method which can treat a wide range of sound sources.
Park, Yong-Chan,Kajishima, Takeo 한국암반공학회 2010 Geosystem engineering Vol.13 No.4
Traditionally, the gas-lift pump has been used to lift corrosive or toxic liquid due to its simple structure and maintenance. It is also considered as a technically feasible system for the development of deep-ocean minerals and as a means to sequestrate $CO_2$ gas into the ocean. Donor-cell scheme or Forward-Time and Backward- Space (FTBS), which is commonly used in solving advection equation such an air-lift system, is very stable but causes numerical diffusion. In order to reduce numerical diffusion or dissipation by the first-order upwind scheme, CIP (Cubic-Interpolated Propagation/Constrained Interpolation Profile) has been applied to bubble and slug flows in a gas-lift pumping system. The GLAD (Gas-Lift Advanced Dissolution) model using CIP method were validated by comparison with gas-liquid two-phase experiments and the effectiveness of the CIP method over the typical one has been demonstrated from the simulation of gas-liquid two-phase slug flow.