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Abstract
This paper aims to explore the effect of winglet equipped in blended wing body (BWB) underwater gliders.Com- putational fluid dynamics (CFD) method was used to obtain the fluid dynamic characters of BWB underwater gliders.The drag reduction efficient of different glider models with different height,sweep angle and slope angle under variable angles of attack were obtained and analyzed.Wake flow of different models was observed and the principles of drag reduction were analyzed.Comparisons between different models reveal that the vortex in wake flow is significantly affected by the winglet in a certain velocity.A proper winglet helps reducing the vortex magnitude and inhibits the occurrence of the vortex.As a result,the drag decreases in certain angles of attack. © 2018, Editorial Board of Journal of Huazhong University of Science and Technology. All right reserved.
... Gu (Gu et al., 2009) defined the shape and size parameters of the underwater glider as state variables, and directly drove CATIA parametric program to complete the geometric parametric modeling of the underwater glider. Lu (Lv et al., 2018) also used CAD software to carry out the parametric study of the underwater glider. However, CAD method needs use finite-difference method to compute the surface sensitivities, thus subjecting the sensitivities to truncation and round-off errors (Truong, 2014). ...
Lift-drag ratio has an important impact on the horizontal range of Blended-Wing-Body Underwater Glider (BWBUG). It is significant to increase the lift-drag ratio of BWBUG for a longer horizontal range. In this paper, a Kriging-based shape optimization framework for the BWBUG with NURBS-based parametrization is proposed to maximize the lift-drag ratio and to improve the optimization efficiency. In this framework, a shape parameterization method of BWBUG is presented based on the NURBS method, to precisely calculate the geometric constraints and their gradient information. The CFD method is applied to accurately compute the hydrodynamic parameters of BWBUG in the whole optimization design. A Kriging-based optimization framework is built with dynamically infilling sample points to update the Kriging model by the aid of the gradient information of geometric constraints, which further improves the optimization efficiency Finally, the effectiveness of the proposed optimization framework is verified by performing the shape optimization of a BWBUG.
... The shape of the leading edge and trailing edge are determined by the Bezier curve. The configuration design for BWBUG with and without winglet was finished previously and the drag reduction effect of single upper winglet on BWBUG was investigated (Lü et al., 2018). In this paper, the winglet configuration is adopted from the previous study. ...
Winglet has been widely used in aviation industries to improve the performance of aircraft. However, according to the authors' knowledge, the effect of winglet on underwater gliders has not been investigated in detail. This paper aims to investigate the impact of winglet on hydrodynamic performance and gliding trajectory of a blended-wing-body underwater glider (BWBUG). The hydrodynamic performance of the BWBUG without winglet (BWBUG-I) is firstly calculated. Then the hydrodynamic performance of BWBUG with winglet (BWBUG-II) is analyzed and compared. To estimate the influence of winglet on gliding trajectory, a dynamic model is established by considering the buoyancy and pitch regulating system. From the CFD results, the lift force acting on the glider is increased by the winglet, while the drag force remains at the same level. The lift-to-drag ratio is thereby improved. By comparing trajectories, the average gliding ratio for BWBUG-II is 5.10, 2.2% higher than 4.99 for BWBUG-I. With the winglet, the extreme attack angle is reduced from 7.2° to 6.1° when switching from rising to diving. The steady gliding speed is improved by 6.3%, and the squat depth is reduced by 11% under particular condition.
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