Experimental investigations of a full model with adaptive elasto-flexible membrane wings

The morphing wing concept aims to constantly adapt the aerodynamics to different flight stages. The wing is able to adapt to different flight conditions by an adjustable Aspect Ratio (AR) and sweep. A high AR configuration provides high aerodynamic efficiency, while a low AR configuration, with highly swept wings offers a good maneuverability. Additionally, the flexible membrane allows the wing surface to stretch and contract in-plane as well as the airfoil to adapt to different aerodynamic loads. In the context of this work, the aerodynamic characteristics of a full model with form-adaptive elasto-flexible membrane wings are investigated experimentally. The focus is on the high-lift regime and on the analysis of the aerodynamic coefficients as well as their sensitivities. Especially, the lateral aerodynamic derivatives at asymmetric wing positions are of interest.     

A review of numerical analyses and experimental characterization methods for forming of textile reinforcements

The forming of textile reinforcements is an important stage in the manufacturing of textile composite parts with Liquid Composite Molding process. Fiber orientations and part geometry obtained from this stage have significant impact on the subsequent resin injection and final mechanical properties of composite part. Numerical simulation of textile reinforcement forming is in strong demand as it can greatly reduce the time and cost in the determination of the optimized processing parameters, which is the foundation of the low-cost application of composite materials. This review presents the state of the art of forming modeling methods for textile reinforcement and the corresponding experimental characterization methods developed in this field. The microscopic, mesoscopic and macroscopic models are discussed. Studies concerning the simulation of wrinkling are also presented since it is the most common defect occurred in the textile reinforcement forming. Finally, challenges and recommendations on the future research directions for textile reinforcement modeling and experimental characterization are provided.     

Experimental study on impact of roller imbalance on cage stability

This study presents a method for measuring the imbalance in a small-sized cylindrical roller. The roller imbalance was calibrated on the built static-pressure-air flotation measurement machine. The impact of the roller imbalance on the dynamic characteristics of a cage were then studied on the aero-bearing test rig. The displacement spectrums with different roller imbalance of the obtained cage orbits under various bearing speed and radial load were used to evaluate the cage stability. The results show that the cage cannot form a stable operating state at a lower bearing speed with or without the unbalanced rollers. The cage with balanced rollers gradually develops stable motion with the increase of the bearing speed. The existence of a small roller imbalance causes the stability of the cage to deteriorate. With an increase in the bearing speed and radial load, the cage with the unbalanced rollers runs unsteadily accompanied by a high-frequency vibration when the roller imbalance is large enough. The vibration amplitude of the cage in the horizontal direction is greater than that in the vertical direction during an unstable operation, which is similar in the stable status.     

基于壁面压力的试验参数分析方法

为了在冲压发动机试验过程中丰富试验参数类别和提高参数分析速度,针对直连式超燃冲压发动机,原创性地提出了基于壁面压力测量结果的试验参数分析方法。该方法引入原子流量守恒方程 构建了封闭方程组,在无需任何额外测量仪器的条件下,以壁面压力、来流参数和燃烧室面积变化律为输入,求解方程组可快速获得超燃冲压发动机的马赫数、温度、速度、组份浓度、燃烧效率等参数。结合三维数值计算和地面试验,通过两个算例对该方法的可行性进行了验证。结果表明,该算法可以获得较高的精度,在燃烧室出口,速度、温度等误差均在5%以内,组份浓度分布和数值结果非常吻合。     

CFD/CSD-based flutter prediction method for experimental models in a transonic wind tunnel with porous wall

To predict the flutter dynamic pressure of a wind tunnel model before flutter test, an accurate Computational Fluid Dynamics/Computational Structural Dynamics (CFD/CSD)-based flutter prediction method is proposed under the conditions of a 2.4 m × 2.4 m transonic wind tunnel with porous wall. From the CFD simulations of the flows through an inclined hole of this wind tunnel, the Nambu’s linear porous wall model between the flow rate and the differential pressure is extended to the porous wall with inclined holes, so that the porous wall can be conveniently modeled as a boundary condition. According to the flutter testing approach for the current wind tunnel, the steady CFD calculation is conducted to achieve the required inlet Mach number. A time-domain CFD/CSD method is then employed to evaluate the structural response of the experimental model, and the critical flutter point is obtained by increasing the dynamic pressure step by step at a fixed Mach number. The present method is applied to the flutter calculations for a vertical tail model and an aircraft model tested in the current transonic wind tunnel. For both models, the computed flutter characteristics agree well with the experimental results.     

A dynamic modeling approach for nonlinear vibration analysis of the L-type pipeline system with clamps

There exists a lot of research on the nonlinear vibration of the pipeline system with different boundary conditions. To the best of our knowledge, little research on the actual constraint of the clamp has been performed. In this paper, according to hysteresis loops of the clamp obtained from experimental test, the simplified bilinear stiffness and damping model is proposed. Then the Finite Element (FE) model of L-type pipeline system with clamps is established using Timoshenko beam theory in combination with aforementioned stiffness-damping model. Both hammering and shaker tests verify the FE model via the comparisons of natural frequencies and vibration responses. The results show that the maximum errors of natural frequencies and vibration responses are about 8.31% and 17.6%, respectively. The proposed model can simulate the dynamic characteristics of the L-type pipeline system with clamps well, which is helpful to provide some guidance for the early design stage of pipeline in aero-engine.     

复合材料风扇叶片力学性能试验研究与有限元分析

依照制定的规范化试验流程,进行额定工况和二倍超载工况下的静力加载试验和全寿命周期疲劳试验,以验证复合材料风扇叶片运转工况所需的力学性能试验,结果表明复合材料风扇叶片满足使用强度要求,具有足够疲劳寿命。试验流程制定和具体试验方法可为同类产品力学性能检测提供参考。提出一种曲面外形构件复合材料属性设置方法,基于该方法建立复合材料叶片有限元模型,应用该模型对复合材料叶片在额定工况离心力作用下的载荷-位移响应进行计算。计算所得载荷-位移曲线与试验结果基本吻合,验证了计算方法的合理性。     

Experimental study of single-row chevron-jet impingement heat transfer on concave surfaces with different curvatures

To address the curvature effect on single-row chevron-nozzle jet impingement heat transfer on concave surface, a series of experiments are conducted in the present investigation.Four concave surfaces including one semi-cylindrical concave surface and three parabolic concave surfaces with different width-to-depth ratios are tested under three typical Reynolds numbers(Re = 5000,10000 and 15000) and several dimensionless nozzle-to-surface distances ranging from 1 to 8.The results show that the concave curvature has a clear impact on chevron-nozzle jet impingement heat transfer, tightly dependent on jet Reynolds number and impinging distance.In general, the semicylindrical concave surface produces the highest longitudinally-averaged Nusselt number at the leading line of concave surface.Under a low jet Reynolds number, the parabolic concave surface with a highly curved curvature produces higher longitudinally-averaged Nusselt number at the leading line and more uniform longitudinally-averaged Nusselt number distribution along the curvilinear direction.However, the longitudinally-averaged Nusselt number at the leading line of concave surface is the lowest for the highly curved surface under a high jet Reynolds number and large impinging distance.In comparison with the round-nozzle, chevron nozzle plays a more significant role on improving jet impingement heat transfer at small impinging distances.     

LHT-100霍尔推力器宽功率范围工作实验研究

为了研究兰州空间技术物理研究所口径为100mm的LHT-100霍尔推力器宽功率范围工作性能,从实验的角度研究了放电电压100~400V、放电功率500~1800W时LHT-100霍尔推力器的工作性能。实验结果表明,LHT-100霍尔推力器可以在较宽功率范围内正常工作,放电特性和推力性能稳定,推力变化范围为30~95mN,比冲变化范围为600~1950s,推力效率变化范围为18%~53%,功率推力比变化范围为14.3~18.4W/mN。