Hyeon-Seok Shim

Three-objective optimization of a centrifugal pump with double volute to minimize radial thrust at off-design conditions:

Optimization of a centrifugal pump with double volute was performed using surrogate modeling and a multi-objective genetic algorithm to minimize the radial thrust at off-design conditions with minimal loss in hydraulic efficiency. Both steady and unsteady numerical analyses were conducted using three-dimensional Reynolds-averaged Navier–Stokes equations with a shear stress transport turbulent model. The three objective functions are hydraulic efficiency at the design flow rate, and radial thrust coefficient at 70% and 120% of the design flow rate. In addition, three geometric parameters related to the surface curve and the locations of both ends of the rib structure were selected as the design variables for optimization. The Latin hypercube sampling method was used to choose the design points in the design space. The three objective functions were approximated using response surface approximation models. Pareto-optimal solutions representing the trade-off between the objective functions were obtained using a genetic algorithm. Representative optimal designs show that the optimized double volutes significantly reduce both the radial force and the amplitude of the radial force fluctuation with small loss in hydraulic efficiency.

Effects of Geometric Parameters of a Bobsleigh on Aerodynamic Performance

* Dept. of Mechanical Engineering, Undergraduate school, Inha Univ., ** Dept. of Mechanical Engineering, Graduate school, Inha Univ., *** Dept. of Mechanical Engineering, Inha Univ. (Received January 29, 2015 ; Revised May 4, 2015 ; Accepted August 4, 2015)Key Words: Aerodynamic Performance(공력성능), Bobsleigh(봅슬레이), Drag Coefficient(항력계수), Reynolds-Average Navier-Stokes Equations(레이놀즈 평균 나비어-스톡스 방정식) 초록: 본 연구에서는 다양한 형상변수들이 봅슬레이의 공력성능에 미치는 영향을 평가하기 위하여 삼차원 Reynolds-averaged Navier-Stoke 해석을 수행하였으며, 난류모델로는 표준 k-e 모델이 사용하였다. 격자계로는 비정렬 사면체 격자를 사용하였다. 성능 평가를 위한 형상변수로는 전방범퍼의 장축의 길이, 범퍼의 높이, 그리고, 카울링 측면과 정면 각각에서의 곡률반경 등 네가지 변수를 설정하였으며. 이들이 공력성능으로 선정된 항력계수에 미치는 영향을 평가하였다. 해석결과, 범퍼의 높이와 카울링 측면의 곡률반경이 항력계수에 민감한 영향을 미침을 알 수 있었다. Abstract: Analysis of the aerodynamic performance of a bobsleigh has been performed for various types of bobsleigh body shape. To analyze the aerodynamic performance of the bobsleigh, three-dimensional Reynolds-averaged Navier-Stoke equations were used with the standard k-e model as a turbulence closure. Grid structure was composed of unstructured tetrahedral grids. The radii of curvature of cowling, and height and length of front bumper at the tip on the drag coefficient were selected as geometric parameters. And, the effects of these parameters on the aerodynamic performance, i.e., the drag coefficient, were evaluated. The results shows that the aerodynamic performance is significantly affected by the height of front bumper and radius of curvature.

Aerodynamic Performance Analysis of a Bobsleigh Body Shape

Aerodynamic performance of a bobsleigh is one of the most important factors in reducing the race time. In this study, an investigation on the aerodynamic characteristics of a bobsleigh has been performed using three-dimensional Reynolds-averaged Navier-Stokes equations with the k-e turbulence model. An unstructured tetrahedral grid system was constructed in the computational domain, and the optimal number of grids was selected through a grid-dependency test. The major axis length and thickness of ellipse-shaped front bumper, and the radii of the cowling on side and front views, were selected as four geometric parameters to be tested, and the drag coefficient was considered as an aerodynamic performance parameter. It was found that the drag coefficient was more sensitive to the thickness of the front bumper and the radius of the cowling on side view of the bobsleigh than on the other parameters.Copyright