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Chen X.,PLA Air Force Aviation University | Chen X.,Northwestern Polytechnical University | Chen X.,Co Innovation Center for Advanced Aerospace Engine | Li Y.,Northwestern Polytechnical University | And 2 more authors.
International Journal of Impact Engineering

Our paper investigates the dynamic tensile properties of 2D-C/SiC composites at elevated temperatures of 800°C and 1000°C by means of SHTB. The temperature and strain rate effects of the composite are found and discussed. Then the morphology of fracture surface of coated and uncoated composites at elevated temperature is examined by SEM, and it was found that the uncoated specimen was much more severely oxidized. Thus we conclude that coated composite displays a better tensile property. In other words, it displays excellent tensile property at 800°C and some tensile property at 1000°C. © 2014 Elsevier Ltd. All rights reserved. Source

Yi K.,Ecole Centrale Lyon | Collet M.,Ecole Centrale Lyon | Ichchou M.,Ecole Centrale Lyon | Li L.,Beihang University | Li L.,Co Innovation Center for Advanced Aerospace Engine
Smart Materials and Structures

In this paper, we designed and analyzed a piezo-lens to focus flexural waves in thin plates. The piezo-lens is comprised of a host plate and piezoelectric arrays bonded on the surfaces of the plate. The piezoelectric patches are shunted with negative capacitance circuits. The effective refractive indexes inside the piezo-lens are designed to fit a hyperbolic secant distribution by tuning the negative capacitance values. A homogenized model of a piezo-mechanical system is adopted in the designing process of the piezo-lens. The wave focusing effect is studied by the finite element method. Numerical results show that the piezo-lens can focus flexural waves by bending their trajectories, and is effective in a large frequency band. The piezo-lens has the ability to focus flexural waves at different locations by tuning the shunting negative capacitance values. The piezo-lens is shown to be effective for flexural waves generated by different types of sources. © 2016 IOP Publishing Ltd. Source

Gao X.,Northwestern Polytechnical University | Chu W.-L.,Northwestern Polytechnical University | Chu W.-L.,Co Innovation Center for Advanced Aerospace Engine
Hangkong Dongli Xuebao/Journal of Aerospace Power

For the study object of a subsonic axial-flow compressor rotor of Northwestern Polytechnical University, a reliable numerical simulation method was presented, and then axisymmetric contouring optimization for the casing under the condition of peak efficiency was conducted with the module DESIGN/3D in software package NUMECA, and the optimal rotor was obtained finally. The optimal rotor pushed the tip clearance leakage vortex away from the suction side at the leading edge of the blade. Although this led to an increase of the magnitude of leakage vortex and flow loss at the first 30% axial chord, the magnitude of leakage vortex and flow loss were greatly reduced at the last 70% axial chord of the blade, thus reducing the total loss, and increasing the peak efficiency and absolute total pressure at the outlet. The efficiency of the optimal rotor increases about 0.36% under the peak efficiency condition, which increases more under large mass flow rate condition, but under the near stall condition, the optimal rotor forms low velocity zone earlier at the blade tip area, leading to an earlier stall and making the stability margin of the optimal rotor smaller. Source

Yu J.,Beihang University | Yu J.,Co Innovation Center for Advanced Aerospace Engine | Chen Z.,Beihang University
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica

Blade is easily affected by clamping, cutting force and residual stress which result in warp and torsion due to thin-walled and free surface of blade. In this paper, a new method for the control of machining distortion that eliminates surface errors by using an adaptive dual-arm fixture is presented. Firstly, the sources of distortion in different machining methods are discussed. Secondly, after the detailed analysis of unstressed fixing and stress releasing, the engineering design and mechanism analysis of the adaptive mechanism are shown. Finally, a control process of machining distortion is obtained based on the adaptive dual-arm fixture. Machining distortion can be eliminated without multiple repairing datum and changing machine. The experimental results show that the adaptive dual-arm fixture can effectively eliminate surface errors by 50% in machining, and the precision of test blade machined in this way is improved obviously. © 2016, Press of Chinese Journal of Aeronautics. All right reserved. Source

Zhang C.,Nanjing University of Aeronautics and Astronautics | Hu J.,Nanjing University of Aeronautics and Astronautics | Hu J.,Co Innovation Center for Advanced Aerospace Engine | Wang Z.,Nanjing University of Aeronautics and Astronautics
Journal of Engineering for Gas Turbines and Power

To clearly clarify the effects of different upstream boundary layer thickness and tip clearance size to the detailed tip flow field and flow mechanism, numerical simulations are performed on a subsonic compressor rotor, which is used for low-speed model testing of a rear stage embedded in a modern high-pressure compressor. First, available experimental data are adopted to validate the numerical method. Second, comparisons are made for tip leakage vortex (TLV) structure, the interface of leakage flow/mainflow, endwall loss, isentropic efficiency and pressure-rise among different operating conditions. Then, effects of different clearance sizes and inflow boundary layer thicknesses are investigated. Finally, the self-induced unsteadiness at one near-stall (NS) operating condition is studied for different cases. Results show that the increment of tip clearance size has a deleterious effect on rotor efficiency and pressure-rise performance over the whole operating range, while thickening the inflow boundary layer is almost the same except that its pressure-rise performance will be increased at mass flow rate larger than design operating condition. Self-induced unsteadiness occurs at NS operating conditions, and its appearance largely depends on tip clearance size, while the effect of upstream boundary layer thickness is little. Copyright © 2014 by ASME. Source

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