连续陶瓷纤维的制备、结构、性能和应用:研究现状及发展方向

连续陶瓷纤维是纤维增强陶瓷基复合材料的增强体,对提高陶瓷基复合材料的强度和韧性起关键作用,高损伤容限和高强度陶瓷纤维是阻止裂纹扩展实现陶瓷基复合材料强韧化的保障。本文对碳化硅、氮化硅、氮化硼、氧化铝和氧化锆等几种陶瓷纤维的制备方法、结构、性能和应用等方面进行了全面的综述,指出了今后的发展方向,期望为未来陶瓷纤维的研究、开发及应用提供参考。国家高技术研究发展计划(863)(2003AA305630);;国家自然科学基金(51472144);;山东省科技重大专项(2015ZDZX11003);;山东省青年学者未来计划(2016WLJH27

适用于流动转捩湍流连续模拟的大涡模拟模型研究

前期报告人提出的基于螺旋度的涡粘模型可以很好的预测不可压缩/可压缩湍流,相对传统的涡粘模型取得了明显的改进效果。与一般的涡粘模型的区别是:新模型能够很好的预测湍流,自动判断层流、转捩,涡粘系数是判断层流、转捩的开关。在对可压缩平板转捩流动的模拟中,预测的转捩位置、转捩峰与直接数值模拟结果高度吻合。在压缩折角这一包含转捩、湍流分离以及激波结构的流动中,新模型可以对这一典型流动做出正确的预测

适用于超声速边界层转捩的大涡模拟模型与方法

超/高超声速飞行器实际飞行控制中,边界层转捩对飞行器表面的气动力、气动热具有重要的影响,而现有的RANS模型只能给出转捩区域范围,不能准确预测转捩位臵,同时现有的大涡模拟模型面对预测转捩时也具有一定的局限性。本文针对超声速边界层中的转捩预测问题,提出了一种基于螺旋度的新型大涡模拟模型-螺旋度模型(HM),新模型包含了速度梯度张量和涡量梯度张量的对称部分,同时该模型在计算转捩问题上具有天然的优势,可以判别出层流和湍流,在不使用动态求解系数方法的情况下,也能准确预测转捩位臵。本文在超声速平板边界层下测试了4种工况,通过一些湍流平均量的对比,表明新模型在预测转捩上具有不错的潜力和优势

Study on turbulence drag reduction of riblet plate in hypersonic turbulent flows

This paper focuses on turbulence drag reduction of riblet plate in hypersonic turbulent flows. We use direct numerical simulation (DNS) and large eddy simulation (LES) to simulate three-dimensional spatially-developing boundary layer over the flat plate and riblet plate with a freestream Mach number Ma = 6. The results reveal the influence of different riblet heights h(w) and riblet distances lambda(w) on drag reduction effect. The drag reduction effect increases with the increase of riblet height and the decrease of riblet distance within suitable range of parameter values. Through analysis, it can be seen that the riblet plate affects the turbulent contribution of the skin friction by suppressing or destroying the large-scale vortex structure. Combined with the actual engineering design requirements, we can use the riblet plate with appropriate parameters to achieve the purpose of turbulence control

Subgrid-scale model for large-eddy simulation of transition and turbulence in compressible flows

This article focuses on a subgrid-scale (SGS) eddy viscosity model based on helicity which is derived from our previous research [Yu et al., "Subgrid-scale eddy viscosity model for helical turbulence," Phys. Fluids 25, 095101 (2013)] for large-eddy simulation of transition and turbulence in compressible flows. Based on the character of the compressible boundary layer over a flat plate, we obtain from theoretical analysis that this model can automatically distinguish laminar flow and turbulence and can also simulate turbulence well. Meanwhile, an a priori test using direct numerical simulation (DNS) data of a spatially developing flat-plate boundary layer at Ma = 2.25 shows that the helicity model can clearly differentiate laminar, transitional, and turbulent regions. Comparing the numerical simulation results with DNS and other SGS models in the spatially developing boundary-layer over a flat plate, we find that the suggested model could precisely predict the onset of transition, transition peak, skin-friction coefficient, mean velocity profile, mean temperature profile, and turbulence intensities. In the case of a compression ramp, the model can well simulate the bypass-type transition, the separated and reattached points, and the size of the separation bubble in the corner region. Furthermore, the prominent advantage of the proposed model can predict transitional flow exactly with no explicit filtering or dynamic procedure. Published under license by AIP Publishing

Heart chamber simulator driven by hydraulic or air-pressure artificial muscle

本发明公开了一种可真实反映心脏收缩和舒张跳动过程压力和腔室形变的液压或气压人工肌肉驱动的心脏腔室模拟器，所述模拟器包括外鞘层、心肌层、心脏瓣膜和构成于外鞘层与心肌层之间封闭的中空腔体；所述外鞘层的壁面上开有通孔，用于液（气）体在中空腔体内的输入或输出；通过改变中空腔体内的压力大小能够实现心脏模型的收缩和舒张。该模型能够克服在外部循环管路中使用泵带来的收缩和舒张压力错误的缺点，以及通过外部机械加载导致心腔形变与实际心肌收缩和舒张过程形变差距较大的问题，真实的反映了心腔跳动过程的形变及正确的循环压力关系