Group-based multiple pipe routing method for aero-engine focusing on parallel layout

External pipe routing for aero-engine in limited three-dimensional space is a typical nondeterministic polynomial hard problem, where the parallel layout of pipes plays an important role in improving the utilization of layout space, facilitating pipe assembly, and maintenance. This paper presents an automatic multiple pipe routing method for aero-engine that focuses on parallel layout. The compressed visibility graph construction algorithm is proposed first to determine rapidly the rough path and interference relationship of the pipes to be routed. Based on these rough paths, the information of pipe grouping and sequencing are obtained according to the difference degree and interference degree, respectively. Subsequently, a coevolutionary improved differential evolution algorithm, which adopts the coevolutionary strategy, is used to solve multiple pipe layout optimization problem. By using this algorithm, pipes in the same group share the layout space information with one another, and the optimal layout solution of pipes in this group can be obtained in the same evolutionary progress. Furthermore, to eliminate the minor angle deviation of parallel pipes that would cause assembly stress in actual assembly, an accurate parallelization processing method based on the simulated annealing algorithm is proposed. Finally, the simulation results on an aero-engine demonstrate the feasibility and effectiveness of the proposed method.     

刷式密封高温摩擦磨损行为*

刷式密封能够提升各类透平机械的性能,近年来航空发动机对刷式密封提出了更高的工作温度要求。为研究高温条件下跑道对刷丝尖端的磨损作用,针对性地研制基于电磁加热原理的刷式密封高温磨损试验设备,并成功完成 GH5605 材料的刷封试样与转子跑道之间的高温高速磨损试验,试验温度达到 700 ℃,试验线速度达到 100 m / s。为研究刷丝柱面的高温摩擦磨损行为,基于 SRV 摩擦磨损试验机开展刷丝柱面模拟磨损试验。研究结果表明：刷丝尖端与跑道耐磨涂层之间的磨损机理以磨粒磨损为主,随着跑道温度升高,刷丝尖端附着的氧化物增加,并可使刷丝柱面产生粗糙氧化层;温度对刷丝柱面的磨损行为有显著影响,常温条件下刷丝柱面呈现出显著的黏着磨损特征,在 300 ℃和 700 ℃的试验温度条件下,氧化现象削弱了刷丝柱面的黏着磨损作用,并使其摩擦因数和磨损速率降低。研究结果揭示了刷式密封的磨损机理及高温条件对其磨损行为的影响,可为提升刷式密封的磨损性能提供理论指导。     

High temperature anti-oxidative and tunable wave absorbing SiC/Fe3Si/CNTs composite ceramic derived from a novel polysilyacetylene

With the rapid development of high power electromagnetic (EM) equipment and high-speed aircraft, the powerful and high oxidation-resistance absorbers are fundamentally desirable for the EM field. Herein, a novel high temperature anti-oxidative SiC/Fe₃Si/CNTs composite is synthesized by a facile polymer derived ceramic (PDC) route from a Fe-containing polysilyacetylene (PSA). The microstructure of as-prepared SiC/Fe₃Si/CNTs composite absorber is featured by micro-sized SiC ceramic grains with spherical Fe₃Si nanoparticles and carbon nanotubes (CNTs) attached to. The vector network analyzer tests show a tunable wave-absorbing performance by adjusting the thickness of layer, and the effective bandwidth (the reflection loss < −10 dB) is 3.3–16.8 GHz for the sample S-1400 (heat treatment at 1400 °C in nitrogen flow). The minimal RL value is −41.2 dB at 10.5 GHz at a thickness of 2 mm and an effective bandwidth is nearly 4 GHz (12.9–16.9 GHz) at the thickness of only 1.5 mm. Moreover, after the oxidation treatment at 800 °C in the air, this absorber maintains the main structure and shows a good high temperature oxidation resistance. This absorber still remains excellent wave absorption property, in view of a minimal RL value of −40 dB at the thickness of 3 mm and a bandwidth of 4.8 GHz (10.4–15.2 GHz) at the thickness of 2.5 mm. The mechanism of high EM wave absorption performance is studied and attributed to the impendence matching, polarization, and the magnetic properties. Thus, the SiC/Fe₃Si/CNTs composite is a promising EM absorber for high-temperature EM wave-absorbing applications.     

可变几何部件对某增能涡扇发动机性能的影响

基于某无人战斗机用增能小涵道比混排涡扇发动机计算模型,选取3个典型工况,开展风扇进口整流叶片角度、压气机进口整流叶片角度和喷管喉道面积等对发动机推力性能影响的研究.计算结果表明:调开风扇整流叶片1°与缩小喷管喉道面积1％后,0 km、0.2 M工况点推力分别增加0.55％和0.48％;5 km、0.9 M工况点推力增加...     

变循环发动机中倒流现象的稳态建模与仿真

变循环发动机根据模式选择机构的打开和关闭有两种工作状态,在模态转换过程中,可能出现经过核心机驱动风扇压缩的气体一部分重新流回到核心机驱动风扇进口的现象.为分析变循环发动机中倒流现象对整机的影响规律,采用稳态性能仿真方法进行性能分析,完成了模拟稳定倒流现象的变循环发动机稳态模型建模.通过研究相关文献对倒流现象描述,从倒流...     

Failure of connecting pins of a compressor disc in an aero engine

This paper describes the failure analysis of pins connecting the second and third stage compressor discs in an aero-engine that had failed after 46,000 h of service. The investigation included metallography, microscopy (SEM), hardness and fractographic examination. Analysis revealed that failure was due to overloading by bending stresses and fretting owing to improper riveting of the pins. There was no indication of fatigue failure in these pins.     

A windmill with cam-articulated blades

The design is described of a windmill with blades articulated by means of cam contours. The choice of a suitable cam contour is discussed, and several alternatives are presented. Performance predictions are described for a six-flap, horizontal-axis windmill model with a selected cam contour. Windtunnel experiments have been conducted on this model and performance improvements are suggested. Predictions and experimental findings agree well.     

Co substituted BaFe12O19 ceramics with enhanced magnetic resonance behavior and microwave absorption properties in 2.6 – 18 GHz

BaFe_12-xCo_xO₁₉ (BFCO, x ≤ 0.4) ceramics with superior magnetic and electromagnetic (EM) properties were prepared using Co³⁺ substituted BaFe₁₂O₁₉ (BFO) in 2.6–18 GHz. Compared with the ceramics without Co³⁺, the incorporation of 40 mol% Co³⁺ enhances magnetic properties; the saturation magnetization (M_S) is improved by about 55.6 emu·g⁻¹ due to the variety of magnetocrystalline anisotropy. The resonance behaviors of complex permeability are observed and resonance frequency shifts to lower frequency range from 6 to 3 GHz. The minimum reflection loss (RL) of −32.1 dB (<−10 dB) is obtained at 11.2 GHz in 8.5–13.5 GHz at 2.0 mm thickness in the sample with x = 0.4, which suggests that such ceramics is highly promising as effective microwave absorbers for EM applications.     

Fabrication of SiCf/SiC-mullite composite with improved pretreatment condition via precursor infiltration-sintering combined with infiltration-pyrolysis process

SiC fiber/ceramic matrix composite has potential applications in military and civil fields due to their excellent microwave absorption performances, light weight and oxidation resistance. In this work, the SiC_f/SiC-mullite composite with improved pretreatment condition was fabricated via precursor infiltration-sintering combined with infiltration-pyrolysis process for achieving excellent mechanical and microwave absorption performances. Results indicated that different dehydrations of matrix precursor influenced ultimate mechanical properties of the composites. At the same time, SiC derived from polycarbosilane had significantly improved several properties of the composite. The flexural strength and failure displacement reached 266 MPa and 0.46 mm, respectively. The high loss tangent was related with the interfacial polarization. In addition, a prominent reflection loss value of −45 dB was observed at 9 GHz. What's more, the maximum absorption bandwidth reached 2.9 GHz (from 8.2 to 11.1 GHz). The SiC_f/SiC-mullite composite with improved pretreatment condition is expected to be an excellent structural-functional material.     

3D printing of bioactive macro/microporous continuous carbon fibre reinforced hydroxyapatite composite scaffolds with synchronously enhanced strength and toughness

Continuous carbon fibre (CF) reinforced HA (CF/HA) composite scaffolds were prepared using a self-designed and manufactured 3D printer. The optimised design of nozzle structure and the tailored viscoelastic property of HA inks ensured compound extrusion of monofilament and multifilament CF with HA rod. The composite scaffolds designed using the CAD programme and sintered via a suitable process exhibited a hierarchical macro/microporous structure and contained approximately 50% HA and 50% β-TCP. The continuous CF synchronously enhanced the strength and toughness of the scaffolds. The compressive strengths of 1CF/HA and 5CF/HA were 11.4 ± 1.7 MPa and 16.3 ± 2.6 MPa, respectively, which were approximately double and triple compared with that of HA scaffolds. The fracture toughness of 1CF/HA was approximately double that of HA scaffolds and close to that of cortical bone. In vitro and in vivo studies demonstrated that 1CF/HA also had apatite formation capability and adequate bone regeneration capacity.