Analysis of flow transition and separation on oscillating airfoil by pressure signature

Binbin Wei,Yongwei Gao,Long Wang,Dong Li 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1

To have a better understanding of the unsteady aerodynamic characteristics of the airfoil which play important roles in wind turbine blade design, we investigated the boundary layer transition and separation on oscillating airfoil S809 using pressure signature captured in wind tunnel testing. The developed data processing technique of "sliding window" was applied to get useful transition and separation information. Meanwhile, the hysteresis effects of oscillation frequency on transition and separation were studied. It is found that (1) the root mean square (RMS) of pressure signature can indicate the transition and separation with the dimensionless window width of `m = 0.0015; (2) the transitional attack of angle in up stroke is larger than that in down stroke at the state of the relative chord length of x/c ≥ 0.14, while the situation is opposite at the state of the relative chord length of x/c ≤ 0.14; (3) the flow separation is advanced and the reattachment is delayed with the increase of the oscillation frequency, which results in a greater hysteresis effect. The sliding window technique, whose parameters were determined in this paper, is effective for detecting boundary layer transition and separation from pressure signature.

Physics of Dynamic Stall Vortex During Pitching Oscillation of Dynamic Airfoil

Binbin Wei,Yongwei Gao,Dong Li 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.6

Dynamic stall, which has a significant effect on the aerodynamic performances of dynamic airfoils, is closely related to the physics of the dynamic stall vortex (DSV). The physics of the DSV on the NACA 0012 airfoil was experimentally studied using unsteady pressure measurements with high time accuracy. The experimental Reynolds number was Re = 1.5 × 106, and the reduced frequency was k = 0.069. The propagation of the unsteady pressure field during the dynamic stall process was analyzed in detail. The motion characteristics of the DSV were examined, including its near-wall development characteristics and near-wall evolution velocity. Moreover, the frequency characteristics of the near-wall DSV were studied using wavelet analysis combined with proper orthogonal decomposition (POD) technology. In addition, the effects of the mean angle of attack (AoA) and the amplitude on the DSV motion and frequency characteristics were examined in detail. The effects of the mean AoA on the near-wall DSV strength and the propagation velocity were linear, while the effects of amplitude were nonlinear. The mean AoA and amplitude had a significant influence on the frequency of the leading-edge vortex (LEV) at the initial stage of the DSV development (x/c = 0.10–0.20). This work allows the DSV physics to be understood more deeply.

Reliability of electric power grids under tornadoes

Wei Liu,Binbin Zhou,Qianxiang Wu,Huiquan Miao 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.33 No.4

Strong wind disasters, especially tornadoes with high damage scales, constantly cause huge damage to electric power grids (EPGs). In this paper, a concept is presented to quantify the connectivity reliability of EPGs under tornadoes. First, a tornado wind field is established using a modified Rankine vortex model, which is a representative 2D tornado wind field model. Second, fragility models of grid components, including transmission substations, transmission support structures, distribution poles, distribution conductors, and local circuits, are introduced. Third, a Monte Carlo simulation is presented to evaluate the connectivity reliability of EPGs under tornadoes. Finally, the connectivity reliability is verified under different scales and propagation angles of tornadoes by taking an actual EPG in China as a case study. Results show that the connectivity reliability directly correlates with the maximum wind speed and the propagation angle of the tornado, and the EPG experiences severe damage when the tornado exceeds the Enhanced Fujita 3 scale.

A Novel Image Dehazing Algorithm Based on Dual-tree Complex Wavelet Transform

( Changxin Huang ),( Wei Li ),( Songchen Han ),( Binbin Liang ),( Peng Cheng ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.10

The quality of natural outdoor images captured by visible camera sensors is usually degraded by the haze present in the atmosphere. In this paper, a fast image dehazing method based on visible image and near-infrared fusion is proposed. In the proposed method, a visible and a near-infrared (NIR) image of the same scene is fused based on the dual-tree complex wavelet transform (DT-CWT) to generate a dehazed color image. The color of the fusion image is regulated through haze concentration estimated by dark channel prior (DCP). The experiment results demonstrate that the proposed method outperforms the conventional dehazing methods and effectively solves the color distortion problem in the dehazing process.

Measured and investigated nonlinear dynamics parameters on bolted flange joints of combined rotor

Tao Li,Dongjian Yang,Binbin Zhao,Qingchao Sun,Junzhou Huo,Wei Sun 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.5

The complex micro-slip phenomenon of the contact interface will lead to the nonlinear stiffness of the connection structure, as well as the structural damping and energy dissipation. As the most important connection structure of the combination rotor, the mechanical properties of bolted flange joint interface are needed in the dynamic analysis of the combined rotor. Therefore, it is urgent to model and test the friction contact interface in the nonlinear dynamic analysis of rotor. In this paper, two sets of mechanical characteristics test system were built to test the dynamic parameters of tangential and bending directions of the bolted flange joint interface. Then, the mechanical behavior and the change regularities of dynamics parameters were studied under different external excitation, bolt distribution and tightening torque. The results show that once the bolt preload is above the rated torque, stiffness softening behavior is not significant; and then the tangential stiffness of the joint interface tends to be stable, with the variation range of 8.08~8.96e8 N/m; the equivalent bending stiffness coefficient is about 3.38~3.83e6 N·m/rad. With the decrease of bolt preload, the external excitation and the number of bolts have a significant effect on the stiffness reduction of the joint. Finally, the change interval of the dynamics parameters of the interface obtained by the experiment provide basis for the uncertainty dynamic analysis and optimization of the rotor.

Application of the body force method in the rim driven thruster

Cai Boao,Tian Binbin,Qiu Liaoyuan,Xu Qing,Mao Xiaofei,He Wei,Chai Wei 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1

The Rim Driven Thruster (RDT) has become a popular ship propulsion system in recent years. Due to the complex structure of RDT, a great number of computational resources are required to study the interaction between RDT and hull by adopting the discretized propeller method. This research looks into a modified body force method which is suitable for the RDT. To simulate self-propulsion of a trawler with a rim driven thruster, the Reynolds-averaged NaviereStokes (RANS) solver is used. In the modified body force method, three virtual disks are adopted to replace the propeller and rim rotors. Before correction, the interactions among the duct, the rim rotors and the propeller were studied. Through the analysis, it is found that the most suitable scheme is to take the open water curves of the propeller, of the “rotors þ duct” and of the RDT as the references for modification. The ducted virtual disks open water curve is modified in open water simulations until the result is consistent with the RDT open water calculation results. When used to self-propulsion simulation, the modified body force method is accurate and can roughly characterize the flow fields. The modified body force method saves a huge number of grids when compared to the discretized propeller method. Furthermore, the interaction between the ship and the RDT can be accurately modeled, which is critical for quickly predicting self-propulsion in ships equipped with rim driven thrusters. Finally, the modified body force method in this work is named as the body force RDT method.

Experimental Investigation of Flow Separation Control over Airfoil by Upper Surface Flap with a Gap

Lishu Hao,Yongwei Gao,Binbin Wei 한국항공우주학회 2022 International Journal of Aeronautical and Space Sc Vol.23 No.5

This paper focused on the effects of the flap with a tiny gap on the flow separation over the NPU-WA-180 airfoil. The effects of the geometric parameters of the flaps, such as the flap gap height, angle, and position, were investigated. The study showed that the flap can significantly improve the stall features of airfoil in a limited phase of angle of attack (AoA), and increase lift and reduce drag at a high AoA. It can increase the lift coefficient and drag coefficient in the case of high AoAs, and the angle range of the lift augmentation and drag reduction can reach more than 9°. Furthermore, an excessively large gap is not conducive to the improvement of the airfoil stall performance. The flap angle plays a key role in the airfoil stall characteristic. As the flap angle decreases, the angle range of improving airfoil stall characteristics becomes larger, the pitching moment increment becomes smaller. However, the maximum lift increment and the effect of the drag reduction will decrease. And the effects of the position of the flap on the airfoil performance were also studied. Considering the maximum lift coefficient and drag coefficients in large AoA, the Type1 installed at the 0.7c position has the best effect; from the perspective of delayed stall, the Type1 installed at the 0.6c position has the best delay effect. These results can provide the data and theoretical support for the flap application in engineering.

Nuciferine modulates the gut microbiota and prevents obesity in high-fat diet-fed rats

Wang Yueping,Yao Weifan,Li Bo,Qian Shiyun,Wei Binbin,Gong Shiqiang,Wang Jing,Liu Mingyan,Wei Minjie 생화학분자생물학회 2020 Experimental and molecular medicine Vol.52 No.-

Gut microbiota dysbiosis has a significant role in the pathogenesis of metabolic diseases, including obesity. Nuciferine (NUC) is a main bioactive component in the lotus leaf that has been used as food in China since ancient times. Here, we examined whether the anti-obesity effects of NUC are related to modulations in the gut microbiota. Using an obese rat model fed a HFD for 8 weeks, we show that NUC supplementation of HFD rats prevents weight gain, reduces fat accumulation, and ameliorates lipid metabolic disorders. Furthermore, 16S rRNA gene sequencing of the fecal microbiota suggested that NUC changed the diversity and composition of the gut microbiota in HFD-fed rats. In particular, NUC decreased the ratio of the phyla Firmicutes/Bacteroidetes, the relative abundance of the LPS-producing genus Desulfovibrio and bacteria involved in lipid metabolism, whereas it increased the relative abundance of SCFA-producing bacteria in HFD-fed rats. Predicted functional analysis of microbial communities showed that NUC modified genes involved in LPS biosynthesis and lipid metabolism. In addition, serum metabolomics analysis revealed that NUC effectively improved HFD-induced disorders of endogenous metabolism, especially lipid metabolism. Notably, NUC promoted SCFA production and enhanced intestinal integrity, leading to lower blood endotoxemia to reduce inflammation in HFD-fed rats. Together, the anti-obesity effects of NUC may be related to modulations in the composition and potential function of gut microbiota, improvement in intestinal barrier integrity and prevention of chronic low-grade inflammation. This research may provide support for the application of NUC in the prevention and treatment of obesity.