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전산유체역학을 위한 일반 곡률좌표계에서 운동량 방정식의 종속변수 선정에 관한 연구
김원갑,최영돈,Kim, Won-Kap,Choi, Young Don 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.2
This study reports the selection of dependent variables for momentum equations in general curvilinear coordinates. Catesian, covariant and contravariant velocity components were examined for the dependent variable. The focus of present study is confined to staggered grid system Each dependent variable selected for momentum equations are tested for several flow fields. Results show that the selection of Cartesian and covariant velocity components intrinsically can not satisfy mass conservation of control volume unless additional converting processes ore used. Also, Cartesian component can only be used for the flow field in which main-flow direction does not change significantly. Convergence rate for the selection of covariant velocity component decreases quickly as with the increase of non-orthogonality of grid system. But the selection of contravariant velocity component reduces the total mass residual of discretized equations rapidly to the limit of machine accuracy and the solutions are insensitive to the main-flow direction.
김원갑,강신형,Kim, Won-Kap,Kang, Shin-Hyoung 한국유체기계학회 2000 한국유체기계학회 논문집 Vol.3 No.1
This paper reports the impeller performance of centrifugal pump, modified HES65-250. Developed CFD code uses SIMPLE algorithm, power-law scheme, standard $k-{\espilon}$ turbulence model in curvilinear coordinate system. The calculations are conducted for 5 cases, from 0.6 to 1.4 of flow rate ratio with 0.2 increment. The flow characteristics inside of impeller are analysed. The results show that reversal flows exist at the inlet of impeller which have small rotary stagnation pressure. The obtained results are compared with the experimental data at impeller exit and shows good qualitative agreement.
Level Set Method에 의한 2 차원 결정성장에 관한 연구
김원갑(Won-Kap Kim),정재동(Jae-Dong Jung) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Numerical simulations for dendritic growth of crystals are conducted in this study. The level set method is used to update the moving interface so that the topological changes can be handled easily. The governing equations are solved on a fixed Cartesian mesh. The 2nd and 4th order Runge-Kutta scheme are used for time discretization and 1st order upwind scheme and 2nd and 3rd order WENO(weighted essentially nonoscillatory) schemes are used for space discretization. Also, sharp interface model for temperature field is used to treat the phase boundary accurately. Test problems for the validation of the code are calculated and compared to exact solution and results in the literature. Finally, process of the dendritic growth of crystals are calculated and the effect of the parameters are concerned.
김원갑(Won-Kap Kim),강신형(Shin-Hyoung Kang) 한국유체기계학회 1999 유체기계 연구개발 발표회 논문집 Vol.- No.-
This paper reports the impeller performance of centrifugal pump, modified HES65-250. Developed CFD code uses SIMPLE algorithm, power-law scheme, standard k-ε turbulence model in curvilinear coordinate system. The calculations are conducted for 5 cases, from 0.6 to 1.4 of flow rate ratio with 0.2 increment. The flow characteristics inside of impeller are analysed. The results show that reversal flows exist at the inlet of impeller which have small rotary stagnation pressure. The obtained results are compared with the experimental data at impeller exit and shows good qualitative agreement.
김원갑(Won-Kap Kim),한성호(Seong-Ho Han),최영돈(Young-Don Choi) 대한설비공학회 2007 설비공학 논문집 Vol.19 No.2
It was noted by the several researchers that the voltage outputs in response to a single yawed hot-wire sensor in a flow perpendicular to the axis deviate from the theoretical voltage output by King's law and Jorgensen's relation. This study noticed that the calibration coefficients of original Grande's method are not constant and fairly sensitive to the radial angle (α<SUB>R</SUB>). For more accuracy, this study interpolated the parameters of the Grande relation as a function of radial angle and compared velocity components with ones by Jorgensen and original Grande relation in the calibration jet flow. Finally, as a test case, 3-dimensional turbulent flows of the inlet plane of 180 degree bend are measured and compared the velocity components by above three methods and showed the characteristics of the flows.
글라이딩 하는 잠자리 날개 주름의 영향에 대한 수치해석적 연구
김원갑(Won-Kap Kim),변도영(Do-Young Byun),박훈철(HoonCheol Park) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.9
단면상에 주름이 있는 잠자리 날개의 공기역학적 성능을 검토하기 위해 정지상태에 있는 2차원 비정상 수치해석을 수행하였다. 해석 조건으로서 레이놀즈수는 150과 1400, 10,000이며 받음각은 0도에서 40도까지 변화시켰다. 해석 결과 임계각 이상의 받음각에서는 주름에 의한 양력의 증가량은 거의 일정하게 유지되며 또한 날개 윗면의 주름은 양력의 증가에 거의 영향이 없음을 알 수 있었다. We investigate the aerodynamic performance of the dragonfly wing which has the cross-sectional corrugation by using the static 2-dimensional unsteady simulation. Computational condition is at Re=150, 1400 and 10,000 with the angles of attack from 0 to 40 degrees. As computational results, the increment of the lift coefficient by corrugation is nearly constant over the critical angle of attack. Also, upper side corrugation of the wing have very little influence on increase of the lift coefficient.
글라이딩 하는 잠자리 날개 주름의 영향에 대한 수치해석적 연구
김원갑(Won-Kap Kim),변도영(Do-Young Byun),박훈철(HoonCheol Park) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
We investigate the aerodynamic performance of the dragonfly wing which has the cross-sectional corrugation by using the static 2-dimensional unsteady simulation. Computational condition is at Re=150, 1400 and 10,000 with the angles of attack from 0 to 40 degrees. As computational results, lift coefficients are increased by the wing corrugation at all Reynolds number. But corrugation have little influence on the drag coefficients. The flow such as vortex in the valley of corrugation and near the edge of corrugation are locally different from the elliptic wing. But such local flow have little influence on the time averaged wing performance. From the numerical experiment in this study, suction side corrugation of the wing have very little influence on increase of the lift coefficient at the positive angle of attack.
Level Set Method 의 재초기화에 대한 연구
김원갑(Won-Kap Kim),정재동(Jae-Dong Jung) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
The advantage of the level set method is the robustness of the topological changes such as merging and formation of pores without special treatment. Although the level set method is a useful interface-capturing method, there is a problem of reinitialization error as noted by Kensuke[1]. This error is the distortion of interface position by reinitialization equation and accumulation of this error with time can be a serious problem in cases of complex moving boundaries. In this study, the effect of order of difference and effect of schemes are tested for reinitializatin error in simple problem. It is founded in case of 1st order of difference that very fine grids have to be used to minimize the error and higher order of difference is desirable to minimize the reinitialization error if the coarser grids are used. The 2nd and 4th order Runge-Kutta scheme in time and from 1st to 5th order of difference except 4th order are tested with several scheme such as Hamilton-Jacobi type and Godunov’s scheme etc. Especially, 3rd and 5th order of differencing areapplied with WENO schemes with Godunov scheme are used for space discretization.