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A Dynamic Globalization Model for Large Eddy Simulation of Complex Turbulent Flow
Haecheon Choi(최해천),Noma Park(박노마),Jinseok Kim(김진석) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
A dynamic subgrid-scale model is proposed for large eddy simulation of turbulent flows in complex geometry. The eddy viscosity model by Vreman [Phys. Fluids, 16, 3670 (2004)] is considered as a base model. A priori tests with the original Vreman model show that it predicts the correct profile of subgrid-scale dissipation in turbulent channel flow but the optimal model coefficient is far from universal. Dynamic procedures of determining the model coefficient are proposed based on the 'global equilibrium' between the subgrid-scale dissipation and viscous dissipation. An important feature of the proposed procedures is that the model coefficient determined is globally constant in space but varies only in time. Large eddy simulations with the present dynamic model are conducted for forced isotropic turbulence, turbulent channel flow and flow over a sphere, showing excellent agreements with previous results.
Haecheon CHOI,Jungil LEE 한국산업응용수학회 2011 한국산업응용수학회 학술대회 논문집 Vol.6 No.2
In Choi & Moin (2011), it was shown that the number of grid points (N) required for solving turbulent boundary layer flow using wall-modeled large eddy simulation (WMLES) is proportional to ReLx, but a wall-resolving LES requires N ∼ Re<SUP>13/7</SUP>Lx , where Lx is the flat-plate length in the streamwise direction. This grid-point requirement indicates the importance of WMLES for high Reynolds number flow. In this study, we provide the mean wall shear stress as a boundary condition for WMLES without any further modeling near the wall. The motivation of using this wall boundary condition for WMLES is such that in the framework of finite volume method, an accurate information of mean wall shear stress is the most important in the momentum transport near the wall, even if the first grid used in WMLES locates far away from the wall. For turbulent channel flow, the mean wall shear stress is balanced with the mean pressure gradient and thus is provided a priori during the simulation. DNS and LES with this boundary condition show that the results agree very well with those with no-slip boundary condition. WMLES up to Reτ = 2 × 10? (based on the wall shear velocity and boundary layer thickness) with current boundary condition predicts the log law very well.
Urea-SCR 적용을 위한 감압비등 와류 분무의 특성의 변화에 대한 실험적 연구
이해천(Haecheon Lee),윤웅섭(Woongsup Yoon) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
A Flash-boiling atomization is one of most device that generate fine droplet. The main features of the flash-boiling atomization are a finer diameter, better distribution and wider spray angle than mechanical atomizer. The flash-boiling is a atomization process that use a thermodynamic metastable state. The superheated liquid jet introduced at pressure place below the saturated vapor pressure rapidly evaporates and then shatters the adjacent liquid. This experiment is conducted in order to apply the flash-boiling swirl spray to the Urea-SCR(Selective Catalytic Reduction) system. The breakup length which is a macroscopic spray characteristic measured with CCD(Charge-Coupled Device) camera. SMD(Sauter mean diameter) and SMD distributions which are a microscopic spray characteristic measured with GSV(Global Sizing Velocimetry). The experiment is conducted varying three variable of pressure, temperature and velocity of convection.
Aerodynamics of Heavy Vehicles
Choi, Haecheon,Lee, Jungil,Park, Hyungmin Annual Reviews 2014 Annual review of fluid mechanics Vol.46 No.-
<P>We present an overview of the aerodynamics of heavy vehicles, such as tractor-trailers, high-speed trains, and buses. We introduce three-dimensional flow structures around simplified model vehicles and heavy vehicles and discuss the flow-control devices used for drag reduction. Finally, we suggest important unsteady flow structures to investigate for the enhancement of aerodynamic performance and future directions for experimental and numerical approaches.</P>