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예조건화 압축성 알고리즘에 의한 저마하수 유동장 해석기법
고현(Hyun Ko),윤웅섭(Woong-Sup Yoon) 한국전산유체공학회 1998 한국전산유체공학회 학술대회논문집 Vol.1998 No.-
Time marching algorithms applied to compressible Navier-Stokes equation have a convergence problem at low Mach number. It is mainly due to the eigenvalue stiffness and pressure singularity as Mach number approaches to zero. Among the several methods to overcome the shortcomings of time marching scheme, time derivative preconditioning method have been used successfully. In this numerical analysis, we adopted a preconditioner of K.H. Chen and developed a two-dimensional, axisymmetric Navier-Stokes program. The steady state driven cavity flow and backward facing step flow problems were computed to confirm the accuracy and the robustness of preconditioned algorithm for low Mach number flows. And the transonic and supersonic flows insice the JPL axisymmetric nozzle internal flow is exampled to investigate the effects of preconditioning at high Mach number flow regime. Test results showed excellent agreement with the experimental data.
DPF의 PM 포집효율 예측을 위한 다양한 다공성 매질 유동장 모델 해석
정승채(Seung-chai Jung),윤웅섭(Woong-sup Yoon) 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.1
In the present study a detailed examination of various porous media models for predicting filtration efficiency and pressure drop of diesel particulate filter (DPF), such as sphere-in-cell and constricted tube models, are attempted. In order for demonstrating their validities of correct estimation on permeability, geometry of property configurations common in commercial cordierite DPFs are correlated to the porous media flow models, and validations of predicted filtration efficiencies due to the use of different unit collectors are made with experiments. The result shows that the porosity, pore size and permeability of cordierite DPF can be successfully correlated by Kuwabara flow field with correction factor of 0.6. The unit collector efficiency predicted by sphere-in-cell model agrees very well with measurements in accumulation mode, whereas that by constricted tube model with significant prediction error.
NH₃-SCR 방법에 의한 디젤 배기 내 De-NO<SUB>x</SUB> 과정에서의 DOC에 의한 영향과 거감 성능 변화 해석
정승채(Seung-chai Jung),윤웅섭(Woong-sup Yoon) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
A positive influence of oxidation precatalyst on the NOx reduction by NH₃-SCR was analytically investigated. Physicochemical processes in regard to NOx reduction by NH₃-SCR and NO-NO₂ conversion by the oxidation catalyst are formulated with proper models for individual physics. A unified model is correctly validated with experimental data in terms of NOx reduction efficiency for SCR and NO-NO₂ conversion efficiency for DOC. The model equipped with rate expressions of Langmuir-Hinshelwood type reaction scheme is deterministic and finds a conversion extent directly. A series of numerical experiments were carried out and parametric analysis of the NOx reduction was conducted. NOx reduction is expedited in proportion to DOC volume at lower temperatures, whereas deactivated with increasing DOC volume when the space velocity is lower at intermediate temperature regime. At intermediate temperatures, NOx conversion is proportionally increasing with the space velocity. NOx conversion is a weak function of the space velocity and DOC volume at higher exhaust temperatures. In DOC-SCR system, the NOx reduction efficiency is gradually increasing with NH₃/NOx ratios.