Rotordynamic characteristics of a novel pocket damper seal with self-regulated injection

Wanfu Zhang,Pengbo Qin,Xiaobin Zhang,Kai Ma,Lu Yin,Chun Li 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.8

The conventional fully partitioned pocket damper seal (FPDS) was improved by introducing several nozzles on the first seal tooth, which generates a reverse injection fluid suppressing the cavity flow in the circumferential direction. Computational fluid dynamics (CFD) models of the conventional FPDS and current novel FPDS were established. An infinitesimal theory was employed to identify the rotordynamic coefficient of the FPDS. The influence of nozzle types (negative, straight, positive), inlet/outlet areas, deflection angles (θ) on the rotordynamic performance was comprehensively analyzed. It was found that reducing the circumferential flow in the first seal cavity is crucial for increasing the stability of the FPDS. A negative nozzle angle can restrict the circumferential flow effectively and significantly improve the effective damping and system stability. The crossover frequency for the novel FPDS with θ = -10° is ~62 Hz, which is much lower than that for the conventional FPDS (~85 Hz). The increasing inlet/outlet area ratio of the nozzle can also enhance the seal stability. Increasing the negative nozzle angle (θ = none, -10°, -15°, -20°) can effectively increase the effective damping and reduce the crossover frequency from ~85 Hz to ~38 Hz. However, the novel FPDS with three kinds of nozzles shows a slight increase (< 2.5 %) in the leakage flow rate compared with the conventional FPDS.

Annular seal rotordynamic stability enhancement with circumferential spiral flow control using helical deflectors

Mingjie Zhang,Jian Gang Yang,Wanfu Zhang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.3

Rotordynamic instability problem caused by seal force widely exists in turbomachines. The fluid-induced force in the seal is determined by the pressure distribution associated with the flow field structure, particularly with the circumferential flow characteristics. In the previous study, the authors found that the helix-comb seal can effectively change the circumferential flow field. The specially designed helical deflectors can reverse the circumferential flow direction of the fluid inside the seal. A considerable static stability enhancement is obtained. However, the transient rotordynamic characteristics of the helix-comb seal are not reported. In the present study, the transient rotordynamic characteristics of the helix-comb seal are investigated further. The rotordynamic coefficients, effective damping, and aerodynamic work of the helix-comb seal are calculated and compared with those of the labyrinth seal. Results reveal that compared with the labyrinth seal, the helix-comb seal considerably improves rotordynamic stability, particularly at a high preswirl ratio. The desirable rotordynamic stability can be obtained with flow field control.

Disassembly Line Balancing Optimization Method for High Efficiency and Low Carbon Emission

Lei Zhang,Xikun Zhao,Qingdi Ke,Wanfu Dong,Yanjiu Zhong 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.1

Disassembly is the first step in product recycling and remanufacturing. When disassembling large quantities of products, the disassembly efficiency is crucial for enterprises. Thus, disassembly line is the best choice for automated disassembly of disposal products. Disassembling products, especially complex structure of products, consume a lot of resources and energy and produce large amounts of carbon emissions. So, it is essential for disassembly line to work efficiently and environmentally. In this paper, the hybrid graph is proposed to express the direct and indirect constraint relationship among components. Then, the mathematical model of carbon emission is built by quantifying the carbon emissions in the process of product disassembly. Taking into account the basic disassembly time, direction change time and tool change time, the mathematical model of high efficiency is presented for optimizing disassembly time. Additionally, based on the traditional multi-objective disassembly line balancing problem (DLBP), a novel multi-objective optimization model of the DLBP with shortest disassembly time and minimum carbon emissions is proposed for improving disassembly efficiency and reducing the carbon emissions in the process of disassembly. Furthermore, genetic algorithm is presented for optimizing the disassembly sequence. Finally, an automobile engine is given as an example to confirm the practicality of the proposed model in solving the DLBP.

A multi-objective optimization for HAWT blades design by considering structural strength

Yang Yang,Chun Li,Wanfu Zhang,Jun Yang,Zhou Ye,Weipao Miao,Kehua Ye 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.8

The challenge of wind turbine blade design is to balance the conflict between high capacity and heavy system loads introduced by the large scale rotor. To solve this problem, we present a multi-objective optimization method to maximize the Annual energy production (AEP) and minimize the blade mass. The well-known Blade element momentum (BEM) theory is employed to predict the aerodynamic performance and AEP of the blade. The blade is simplified as a thin Bernoulli beam. The cross section is modelled as a combination of composite layer, shear webs and spar caps typically. The strain of every cross section has been considered as a constraint to minimize the spar cap thickness for minimizing the blade mass. An improved genetic algorithm (NSGA-II) is applied to obtain the Pareto front set. Several solutions of the Pareto set are selected to compare with the reference blade (NREL 5MW blade). Performance of the rotors on design condition is simulated by STAR-CCM+ to verify the results of BEM theory. Optimal results show that the present blade, which is fully superior to the reference blade, can be selected from the Pareto set. The optimization design method can provide a superior blade with an increase by 2.48% of AEP and a reduction by 5.52% of the blade mass. It indicates the present optimization method is effective. Results of numerical simulations show that the spanwise flow would be increased obviously in tip region of the reference blade. The reason is that chord length variation in blade tip affects the flow and causes minor stall. The abrupt change of chord distribution in blade tip should be avoided to reduce the spanwise flow in initial blade design.

Investigation on aerodynamics and active flow control of a vertical axis wind turbine with flapped airfoil

Yang Yang,Chun Li,Wanfu Zhang,Xueyan Guo,Quanyong Yuan 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.4

A 2D unsteady numerical simulation with dynamic and sliding meshing techniques was conducted to solve the flow around a threeblade Vertical axis wind turbine (VAWT). The circular wakes, strip-like wakes and the shedding vortex structures interact with each other result in an extremely unstable performance. An airfoil with a trailing edge flap, based on the NACA0012 airfoil, has been designed for VAWT to improve flow field around the turbine. Strategy of flap control is applied to regulate the flap angle. The results show that the flapped airfoil has an positive effect on damping trailing edge wake separation, deferring dynamic stall and reducing the oscillating amplitude. The circular wake vortices change into strip vortices during the pitch-up interval of the airfoils. Examination of the flow details around the rotating airfoil indicates that flap control improves the dynamic stall by diminishing the trend of flow separation. Airfoil stall separation has been suppressed since the range of nominal angle of attack is narrowed down by an oscillating flap. Vortices with large intensity over rotational region are reduced by 90 %. The lift coefficient hysteresis loop of flapped airfoil acts as an O type, which represents a more stable unsteady performance. With flap control, the peak of power coefficient has increased by 10 % relative to the full blade VAWT. Obviously, the proposed flapped airfoil design combined with the active flow control significantly has shown the potential to eliminate dynamic stall and improve the aerodynamic performance and operation stability of VAWT.

Comparative analysis of bovine maternal corpus luteum microRNAs with aberrant and normal developed cloned fetus at late gestation

Xiaohu Su,Shenyuan Wang,Guangqi Gao,Xinyu Zho,Lidong Han,Guanghua Su,Jiaqi Zhang,Wanfu Bai,Xiuying Wang,Guangpeng Li,Li Zhang 한국유전학회 2020 Genes & Genomics Vol.42 No.3

Background The development efficiency of cloned cattle is extremely low (< 5%), most of them were aborted at late gestation. Based on our previous studies, some recipient cows with a cloned fetus would present as engorged uterine vessels and enlarged umbilical vessels randomly. Abortion involves both maternal and fetal factors. Objective Our aim was to explore this phenomenon by microRNAs expression profile analysis of maternal corpus luteum (CL), which was related to pregnancy maintenance. Methods The present study provided the comparison of maternal CL miRNAs expression of abnormally and normally developed cloned bovine fetus at late gestation (~ 210 days) using RNA-Seq technology. Results We selected two abnormally pregnant cows (abnormal group, AG) and three normally pregnant cows (normal group, NG) and acquired valid reads of 9317,261–12,327,185 (~ 84.53–91.28%) from five libraries. In total, we identified 981 conserved miRNAs and 223 novel miRNAs. 1052 miRNAs were co-expressed, 124 miRNAs were uniquely expressed in AG, and 93 miRNAs were uniquely expressed in the NG. Compared with NG, 11 were significantly overexpressed, and 22 were downregulated (p < 0.05) at AG among 1052 co-expressed miRNAs. The differentially expressed miRNAs-targeted genes were further analyzed by Gene Ontology and KEGG pathway analysis. Notably, the steroid biosynthesis pathway was a significantly enriched term (p < 0.01), which may affect the secretion of progesterone. Conclusion Our research suggested that abnormal miRNAs expression of bovine maternal CL may affect the pregnant status at late gestation.