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Liu Z.,China Agricultural University | Xiao R.,China Agricultural University | Lu T.,China Agricultural University | Li S.,Aviation Key Laboratory of Science and Technology on Aerospace Electromechanical System Integration
Paiguan Jixie Gongcheng Xuebao/Journal of Drainage and Irrigation Machinery Engineering | Year: 2012

A swept blade was designed based on changing the stacking line in the meridional plane of an axial flow pump impeller. The high speed fuel axial flow pumps, with swept blades and datum blades respectively, were simulated in the overall operation by the code of computational fluid dynamics (CFD) and the overall efficiency and pump head performance curves were obtained. Using the full cavitation model, the cavitation performances of pumps were predicted under the designed point condition and near stall point condition to investigate the effects of swept blade on the cavitation performance and distribution of pressure on blade surfaces of an axial flow pump. According to the numerical results, the swept blade changes the hump characteristic of the axial flow pump, controls the onset and growth of the secondary flows, and recovers the low-energy fluid on the endwalls. Therefore, the stability of operation in the hump zones is improved. Near stall point condition, the swept blade improves the cavitation characteristic of the pump, changes the pressure distribution on the impeller inlet, and avoids the separated flow on the endwalls. While under the design point condition, the swept blade reduces the cavitation characteristic, the blade surface pressure distribution also presents the pressure difference of the datum blade is higher than the swept blade, resulting in the ability of doing work of the former is better than the latter. Source

Ouyang X.-P.,Zhejiang University | Xue Z.-Q.,Zhejiang University | Peng C.,Zhejiang University | Zhou Q.-H.,Aviation Key Laboratory of Science and Technology on Aerospace Electromechanical System Integration | Yang H.-Y.,Zhejiang University
Zhejiang Daxue Xuebao (Gongxue Ban)/Journal of Zhejiang University (Engineering Science) | Year: 2015

A new cylinder seal was investigated to improve the performance of reciprocating seal installed in the aircraft hydraulic cylinder. Firstly, the analysis of the working principle of general hydraulic reciprocating seal pointed out the effect of contact pressure distribution on seal leakage and friction, and the most suitable contact pressure distribution method was obtained. Secondly, the VL seal was modeled and simulated, and the contact pressure distributions at different fluid pressures were obtained to reveal the relationship between the construction and contact pressure distribution during the process of building fluid pressure. The adaption of the seal structure against high fluid pressure and the principle of the special pressure distribution of the VL seal were pointed out. Finally, comparison among the VL seal, O-ring seal and step seal was carried out by analyzing their frictions and leakages, respectively. Results show that the VL seal has the best performance of leakage and liability. ©, 2015, Zhejiang University. All right reserved. Source

Wang Z.,Nanjing Southeast University | Liu B.,Nanjing Southeast University | Zhang Y.,Nanjing Southeast University | Cheng M.,Nanjing Southeast University | And 2 more authors.
Energies | Year: 2016

Three-port isolated (TPI) bidirectional DC/DC converters have three energy ports and offer advantages of large voltage gain, galvanic isolation ability and high power density. For this reason this kind of converters are suitable to connect different energy sources and loads in electric and hybrid vehicles. The purpose of this paper is to propose chaotic modulation and the related control scheme for TPI bidirectional DC/DC converters, in such a way that the switching harmonic peaks can be suppressed in spectrum and the conducted electromagnetic interference (EMI) is reduced. Two chaotic modulation strategies, namely the continuously chaotic modulation and the discretely chaotic modulation are presented. These two chaotic modulation strategies are applied for TPI bidirectional DC/DC converters with shifted-phase angle based control and phase-shifted PWM control. Both simulation and experiments are given to verify the validity of the proposed chaotic modulation-based control schemes. © 2016 by the authors. Source

Tian L.,Nanjing University of Aeronautics and Astronautics | Fu Y.,Nanjing University of Aeronautics and Astronautics | Yang L.,Nanjing University of Aeronautics and Astronautics | Xu J.,Nanjing University of Aeronautics and Astronautics | And 3 more authors.
Jixie Gongcheng Xuebao/Journal of Mechanical Engineering | Year: 2013

In order to investigate the influence law of chip formation process affected by grinding speed, the single-grain tests are carried out on the difficult to cut materials superalloy GH4169. The single-grain grinding forces are measured. The trances and chips morphologys of the single-grain grinding tests are observed and analyzed to calculate the critical thickness of chips formation. The speed effect on the grinding process scratches and grinding forces are studied systematically in the grinding wheel velocity range 20 m/s to 165 m/s. The results show that the grinding speed affects the division of grinding process and the critical thickness of chip formation, and the single-grain grinding forces first increase then decrease and increase finally with the increasing grinding velocity. Machinability changes due to the speed effect, and these changes caused by the alternative variation of the leading position between the strain rate strengthening effects and the thermal softening effects on the difficult to cut materials. Serrated chip occurs during single-grain grinding superalloy, as the grinding speed increases, the grade of serrated tooth grows and the pile up rate of the single-grain grinding grooves decrease first then increases, these phenomenon indicated that mechanism of chip formation due to the speed effect. © 2013 Journal of Mechanical Engineering. Source

Wang Z.,Beihang University | Xing Y.,Beihang University | Liu X.,Beihang University | Zhao L.,Beihang University | Ji Y.,Aviation Key Laboratory of Science and Technology on Aerospace Electromechanical System Integration
Applied Thermal Engineering | Year: 2016

The heat transfer process among droplet, film and bubble is selected as the local characteristic process of spray cooling to build a multiphase flow model. Volume of fluid (VOF) method is employed to simulate the transient process, in which single or multiple droplets impact on a liquid film with a vapor bubble growing, considering the effects of surface tension, gravity and vapor-liquid phase transition. The effect of vibration environment is analyzed by setting vibration boundary condition, and a far broader range of vibration condition is calculated in light spray and dense spray to identify the effect. Heat is mainly removed by strong convection due to the droplet impact. It is significant to form stabilized and intact film during spray cooling. Heat transfer process can be mainly separated into four stages: 1. before the impact; 2. droplet impacts on the surface and forms thinner film on the surface; 3. film extends outwards; 4. film breakage. In dense spray cases, the third stage is barely observed due to continuous impacting of droplets, and mainly all the cases show that vibration has invigorating effect on heat transfer. © 2016 Elsevier Ltd Source

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