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Li P.,Northwestern Polytechnical University | Li W.-L.,Xian Aerospace Propulsion Institute | He G.-Q.,Northwestern Polytechnical University
Guti Huojian Jishu/Journal of Solid Rocket Technology | Year: 2012

A numerical calculation on the flow field of mixing combustion chamber without chemical reaction was carried out for hydrazine monopropellant air-turbo-rocket under uniform inlet flows. The induction and decay evolution of streamwise and normal vortices were obtained, and an analysis was made on the influence of this course on turbulent mixing efficiency of the bypass and core flows. A quantitative analysis revealed that streamwise vortices induced by a spanwise array of large scale secondary flows at trailing edge play a dominant role in the downstream mixing process of the bypass and core flows. It is preferable to employ scarfed lobed mixers with large lobe penetration rate. A preliminary analysis of turbulent mixing efficiency was also made between computational and experimental data for two mixing schemes including three kinds of lobed mixer, and results show that nonuniform inlet flow conditions have a significant impact upon turbulent mixing and combustion efficiency for small dimension air-turbo-rocket.

Wang X.M.,Northwestern Polytechnical University | Wang Y.F.,Avic The First Aircraft Institute | Lu Z.Z.,Northwestern Polytechnical University | Deng C.H.,Xian Aerospace Propulsion Institute | Yue Z.F.,Northwestern Polytechnical University
Mechanics of Materials | Year: 2010

This paper presents the results of a series of experiments to investigate the superelastic cyclic stress-strain responses of NiTi shape memory alloys under tension-torsion biaxial loading conditions. The uniaxial tension and torsion experiments were also conducted to make comparisons. Experiments were controlled by axial displacement and torsional angle in sine wave form with fixed maximum values. Saturation is reached after 30 cycles. The evolutions of equivalent stress-strain curves as well as the separated tensile and shear stress-strain curves during cycling are analyzed. Dissipated energy density, characteristic stresses and strains as functions of deformation cycles are paid attention. Results show that the mechanical responses are significantly affected by the loading path. The stress-strain behaviors under proportional loading are similar to those under uniaxial loading. With the increase of the out-of-phase angle during the non-proportional loading, the special phase transformation exhibition totally disappears in the equivalent stress-strain curves. © 2009 Elsevier Ltd. All rights reserved.

Ma A.-J.,Xian Technological University | Li H.,Xian Aerospace Propulsion Institute | Chen W.,Xian Technological University | Hou Y.,Xian Technological University
Polymer - Plastics Technology and Engineering | Year: 2013

The surface functionalized silicon carbide/carbon fiber (SiC/CF) hybrid fillers were introduced to improve the thermal conductivities and mechanical properties of the epoxy resin composites. Results revealed that, the thermal conductivities of epoxy resin composites were increased with the increasing volume fraction of SiC, and a higher thermal conductivity of 1.226 W/mK could be achieved with 28 vol% treated SiC/CF hybrid fillers (25 vol% treated SiC +3 vol% treated CF), about 6 times higher than that of native epoxy resin (0.202 W/mK). Both the flexural strength and impact strength of the epoxy resin composites increased up to 5 vol% incorporation, but decreased with the further addition of SiC. However, the electrical conductivity was decreased with the increasing volume fraction of SiC. For a given SiC/CF hybrid fillers loading, the surface functionalized SiC/CF hybrid fillers exhibited a positive effect on the thermal conductivities and mechanical properties of the epoxy resin composites. © 2013 Copyright Taylor and Francis Group, LLC.

Gao Y.-S.,Beihang University | Gao Y.-S.,Xian Aerospace Propulsion Institute | Jin P.,Beihang University | Cai G.-B.,Beihang University
Tuijin Jishu/Journal of Propulsion Technology | Year: 2013

In order to obtain the differences and connections of the GO2/CH4 and GH2/GO2 combustion characteristics, to provide experience of the GH2/GO2 injector for guiding GO2/CH4 injector design, comparison of GO2/CH4 and GH2/GO2 combustion characteristics for shear-coaxial injectors was conducted in the same combustion chamber by numerical simulation and experiment. The results show that under the similar design parameters, the size of GO2/CH4 injector is almost equal to that of GH2/GO2 injector. On condition that the pressure at design point and dimensions are the same, in order to produce the same thrust, the mass flow rate of GO2/CH4 (mixture ratio 3.5) is about 1.27 times as GH2/GO2 (mixture ratio 6.0). Furthermore, combustion characteristic length of GO2/CH4 is approximately 1.48 times as much as GH2/GO2 combustion chamber, and the thermal load of the GO2/CH4 combustion chamber is about half of the GH2/GO2 combustion chamber.

Li X.-J.,Xidian University | Xu L.-P.,Xidian University | Zheng W.-S.,Xian Aerospace Propulsion Institute
Yuhang Xuebao/Journal of Astronautics | Year: 2012

The performance of PMF-FFT code acquisition algorithm under different frequency offsets is analyzed in this paper. Focusing on the detection performance degradation under partial frequency offset caused by the low frequency estimation accuracy, an improved code phase and Doppler shift united acquisition method is proposed. First, a set of matched filter outputs are obtained based on the partial matching filter (PMF) algorithm; then a low complexity and high-accuracy iterative frequency estimation algorithm is proposed by using the magnitude difference of the PMF-FFT output, and the frequency offset estimation is used to compensate the PMF output, thus improving the accuracy of frequency estimation and signal detection probability at the same time. Simulation results show that the algorithm can effectively improve the frequency estimation accuracy and the detection probability, and has very low complexity.

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