Modelling and analysis of initial icing roughness with fixed-grid enthalpy method based on DPM-VOF algorithm

Ice particles could form under the continuous impingement of incoming supercooled droplets in icing conditions, which will change the surface roughness to enhance the further heat and mass transfer during icing process. A fixed-grid porous enthalpy method based on the improved Discrete Phase Model(DPM) and Volume of Fluid(VOF) integrated algorithm is developed to solve the multiphase heat transfer problem to give more detailed demonstration of the formation of initial ice roughness. The algorith...     

中心支板参数对RBCC发动机性能影响研究

针对某宽域加速飞行任务下RBCC发动机中心支板主要几何参数设计问题，采用全流道一体化数值模拟方法，在Ma 0.4-6速域内研究支板阻塞比、顶角及长宽比等参数对发动机引射、亚/超燃模态的性能影响规律。结果表明，随着阻塞比增大，各模态下空气流动受压缩作用增强，燃烧反应更加充分，发动机总推力有0.13%-5%的提升；随着顶角增大，除Ma 2.5工况由流道截面构型变化引起激波形成外，增强的支板前缘激波使得燃烧反应位置较为集中，燃料喷注贯穿主流深度提高，较为充分的燃烧释热使得发动机总推力有2.2%-5.7%的提升；随着长宽比减小，在Ma 0.4-4条件下，增大的流道面积有利于煤油横向扩展，较好的氧燃掺混使得发动机总推力有2%-4.8%的提升，而在Ma 6条件下，支板前缘激波的减速增压作用逐渐减弱，发动机总推力可降低5.2%-7.1%。所得结论可为RBCC发动机中心支板设计参数选择提供依据。     

Vector deflection stability control of aero-engine based on linear active disturbance rejection

Aimed at the problem of instability in engine control caused by vector deflection in experiment of turbofan engines with Axisymmetric Vectoring Exhaust Nozzle (AVEN), a vector deflection stability control method of aero-engine based on Linear Active Disturbance Rejection Control (LADRC) is proposed. Firstly, based on CFD numerical simulation, aerodynamic performance model of AVEN is established, and the aerodynamic load change rule of the nozzle throat area actuator during vector deflection is revealed. Subsequently, the integrated model of AVEN/turbofan engine is established by Simulink/AMESim co-simulation. Finally, the nozzle throat area control loop based on LADRC is designed. The simulation results show that the integrated model can reflect the influence of vector deflection on the stability of the control system. The accuracy comparison between the fan rotor speed and the test data during vector deflection is larger than 1%, indicating a high degree of confidence. Compared with the conventional PID control, the designed LADRC control loop reduces the speed of the low-pressure rotor during vector deflection by 70%, which effectively improves the control stability of the vector deflection. Meanwhile, the fuel flow ratechange during the vector deflection process is smaller and more economical, which provides an important reference for engineering applications.     

SiC_(f)/SiC复合材料铣削加工表面质量北大核心CSCD

使用PCD立式铣刀对聚合物浸渍裂解法(PIP)制备的SiC_(f)/SiC复合材料开展单因素铣削试验,通过对加工中产生的切削力和加工后的表面粗糙度进行测量,分析了铣削工艺参数对其的影响;对加工表面、纤维断口进行SEM分析,讨论了SiC_(f)/SiC复合材料加工表面的形成。研究结果表明,表面粗糙度与切削力的变化趋势相同,高主轴转速和小切削宽度有利于得到表面粗糙度较小的加工表面;近孔洞区域与远离孔洞区域的材料去除方式不同;材料中纤维发生面内偏移和层间屈曲,纤维存在多种去除方式。     

表面粗糙度对高辐射涂层发射率的影响

以氧化铁、碳化硅和氧化钴为高辐射填料,通过控制涂层浆料固含量和喷涂次数制备出了不同表
面粗糙度的高辐射涂层。用AE 辐射计测试了不同表面粗糙度高辐射涂层的室温发射率,根据GB/ T 7287—
2008 测试了涂层的800℃高温发射率,用扫描电子显微镜和光学显微镜观察了涂层表面形貌,用扫描探针显微
镜测试了涂层的表面粗糙度。结果表明,在辐射换热条件下高辐射涂层表面粗糙度在2. 75 ~225. 70 μm 变化
时,其室温发射率发生了0. 02 ~ 0. 05 的变化。而在导热换热条件下高辐射涂层表面粗糙度在2. 75 ~ 36. 99
μm 变化时,其高温发射率没有变化。     

干式铣削Al-50wt%Si高硅铝合金刀具磨损与表面粗糙度评价

本文以Al-50wt%Si高硅铝合金为研究对象，采用单因素试验方法进行无涂层硬质合金刀具干式铣削试验，分析切削参数对刀具磨损和表面粗糙度的影响。结果表明：表面粗糙度受每齿进给量的影响最显著，随每齿进给量的增加而增加，当每齿进给量从0.07 mm/z增加到0.16 mm/z时，表面粗糙度增加2倍；刀具磨损受切削速度的影响最显著，随切削速度的增加而增加，当切削速度从140 m/min增加到260 m/min时，切削总长度降低3倍，而刀具后刀面磨损量仅是260 m/min速度下的0.8倍；表面粗糙度随刀具磨损的增加呈现先增加后降低的变化趋势，切削长度从350 mm增加到1 750 mm，刀具磨损量平均增加4.5倍，而表面粗糙度却下降2倍；硬质合金刀具主要的磨损形式为磨粒磨损、崩刃。     

Effects of surface topography and specimen thickness on high-speed raindrop impact damage of CFRP laminates

Raindrop impact erosion has been observed since early days of aviation, and can be catastrophic for exposed materials during supersonic flight. A single impact waterjet apparatus is established for mimicking drop impacts at the velocities between 350 m/s and 620 m/s. Carbon Fiber Reinforced Polymer(CFRP) laminates with three different surface morphologies and specimen thicknesses are tested here. A central region with no visible damage has been noticed, surrounded by a “failure ring” with common...