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Numerical study of particle dispersion from a power plant chimney
심정보,유동현,Shim, Jeongbo,You, Donghyun Korean Association for Particle and Aerosol Resear 2017 Particle and Aerosol Research Vol.13 No.4
An Eulerian-Lagrangin approach is used to compute particle dispersion from a power plant chimney. For air flow, three-dimensional incompressible filtered Navier-Stokes equations are solved with a subgrid-scale model by integrating the Newton's equation, while the dispersed phase is solved in a Lagrangian framework. The velocity ratios between crossflow and a jet of 0.455 and 0.727 are considered. Flow fields and particle distribution of both cases are evaluated and compared. When the velocity ratio is 0.455, it demonstrates a Kelvin-Helmholtz vortex structure above the chimney caused by the interaction between crossflow and a jet, whereas the other case shows flow structures at the top of the chimney collapsed by fast crossflow. Also, complex wake structures cause different particle distributions behind the chimney. The case with the velocity ratio of 0.727 demonstrates strong particle concentration at the vortical region, whereas the case with the velocity ratio of 0.455 shows more dispersive particle distribution. The simulation result shows similar tendency to the experimental result.
압축성 유동 모사를 위한 셀중심 유한체적 기법용 출구 무반사 특성경계조건에 관한 연구
강명석(Myeongseok Kang),유동현(Donghyun You) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.3
A non-reflecting boundary condition is known to be an essential element for compressible flow simulations unless the computational domain is infinitely large. Practical engineering applications involve a finite domain yet complex nature of which discretization favors a finite-volume method (FVM) over a finite-difference method (FDM) in terms of computational cost and efficiency. A non-reflecting characteristic boundary condition (CBC) is implemented in a cell-centered compressible finite-volume solver. While the CBC is well-suited for FDM and vertex-based FVM, the implementation in a cell-centered FVM causes a subtlety due to the mistmatch between the cell-center and the boundary face center. Motivated by Nordström & Björck (2001, Applied Numerical Mathematics), we first introduce the data node at the boundary face center, and then integrate the governing equations modified by the characteristic approach as Granet et al. (2010, AIAA) used for the vertex-based FVM. An alternative approach similar to Motheau et al. (2017, AIAA) that utilizes spatial derivatives modified by the characteristic approach instead of time-integration is also implemented. Two different implementations are compared for a canonical convecting inviscid vortex problem and the effect of numerical dissipation of boundary fluxes and grid resolution sensitivity on the test are also examined. Finally CBC implementations are tested on the VKI turbine cascade against the experimental data.
VOF기법 및 식별 알고리즘을 이용한 쇄파에서의 기포 크기 분포도 분석
문호준(Hojun Moon),유동현(Donghyun You) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.3
A numerical simulation of a three-dimensional breaking wave is conducted using a VOF (volume-of-fluid) method to investigate the wave breaking dynamics and the bubble size distribution. The wave is initialized using the third-order Stokes wave solution. The initial wave slope and velocity fields generate turbulent wave breaking. Various interfacial phenomena are observed including a jet forming, a jet impacting to the free-surface, ejecting spray, entraining air pocket, and breakup. Bubbles with various sizes are formed from turbulent breakup of the air pocket during active breaking time. To obtain the bubble size distribution, an identification algorithm is proposed to accurately count independent bubbles. The proposed algorithm successfully identified independent bubble structures. A joining algorithm is also introduced to consider bubble structures spanning multiple blocks for parallel computations. The obtained bubble size distribution averaged during active breaking time is proportional to r<SUP>-10/3</SUP> for radii larger than the Hinze scale and shows good agreement with previous experiment and simulation results as well as the theoretical model.
가상경계기법을 통한 협착된 미세혈관에서 적혈구 분포의 수치 해석
윤대근(Daegeun Yoon),유동현(Donghyun You) 한국전산유체공학회 2019 한국전산유체공학회지 Vol.24 No.2
In order to investigate the distribution of red blood cells in a stenosed microvessel, three-dimensional blood flow simulations are conducted using immersed boundary methods. To treat deformable structures like blood cells, a continuous-forcing immersed boundary method is employed. Also, a ghost-cell immersed boundary method is employed to treat rigid and complex structures like a stenosed vessel. In the present study, two immersed boundary methods are integrated into a single computational framework by treating each structure separately. The present framework is validated through the simulation of blood flow in a straight microvessel compared with related previous studies. Present simulations of blood flow in a stenosed microvessel reveal that distribution of RBCs passing the stenosis is changed uniformly and the cell-free layer has significant spatial variation across the stenosis, which might induce the change of wall shear stress and flow resistance.