Institute Of Mechanics,Chinese Academy of Sciences
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High-amplitude wall heat flux events in an impinging shock wave/turbulent boundary layer interaction
No full textThis study focuses on High-Amplitude Wall Heat Flux events (HAWHFs) occurring during the interaction between a supersonic flat-plate Turbulent Boundary Layer (TBL) at a Mach number of 2.25 and an oblique shock wave impinging at 33.2 degrees. A database from a validated direct numerical simulation is analyzed using conditional averaging and a two-dimensional clustering methodology to elucidate the statistical characteristics of both positive and negative HAWHFs within the interaction region. The results reveal that the interaction considerably affects the temporal attributes of the HAWHFs, leading to an extended lifespan for the positive HAWHFs and an increased interval between the occurrences of negative HAWHFs. The structural characteristics of the identified HAWHFs are delineated based on the evolution of population density, aspect ratio, and both absolute and relative distances throughout the interaction. The joint probability density functions of the relative positioning of two adjacent structures indicate that, away from the reattachment point, the positive HAWHFs align in the spanwise direction, displaying similarities with the negative HAWHFs. Moreover, a conditional analysis of flow structures associated with HAWHFs is conducted. This analysis of the conditionally averaged three-dimensional fields reveals that the interaction fosters larger-scale organizational patterns in the downstream region. However, the formation of positive and negative HAWHFs remains largely unaffected by the interaction, with the former predominantly linked to a two-layer temperature structure and the latter primarily associated with a pair of oblique vortices. (c) 2025 The Author(s). Published by Elsevier Ltd on behalf of Chinese Society of Aeronautics and Astronautics. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/)
Modulation of the instability growth at sequential heavy-light interfaces in a shocked dual layer
No full textWe present a theoretical framework and validation for manipulating instability growth in shock-accelerated dual-layer material systems, which feature a light-heavy interface followed by two sequential heavy-light interfaces. An analytical model is first developed to predict perturbation evolution at the two heavy-light interfaces, explicitly incorporating the effects of reverberating waves within the dual-layer structure. The model identifies five distinct control regimes for instability modulation. Shock-tube experiments and numerical simulations are designed to validate these regimes, successfully realising all five predicted states. Notably, the selective growth stagnation of a perturbation at either the upstream or downstream heavy-light interface is realised numerically by tuning the initial separation distances of the three interfaces. This work elucidates the critical role of the wave dynamics in governing interface evolution of a shocked dual layer, offering insights for mitigating hydrodynamic instabilities in practical scenarios such as inertial confinement fusion
Direct numerical simulation of inflow boundary-layer turbulence effects on cavity flame stabilisation in a model scramjet combustor
No full textSupersonic lean premixed hydrogen/air combustion stabilised by a cavity-flame holder within a model scramjet, characterized by a Mach 1.5 inflow at 1000 K and 50 kPa, is investigated via direct numerical simulation. By separately implementing wall-bounded turbulent and laminar inlet conditions, this work analysis various physical processes of flame stabilization and turbulence-flame interactions to study the influence of inflow boundary layer conditions. Findings indicate that combustion occurred within the cavity shear layer in both cases and propagated downstream along the lower wall. Also, the server impingement at the rear wall in the case with laminar inflow leads to greater cavity resistance. Furthermore, the studies on gas exchange and transport process indicates that with laminar inflow the entered gas accumulates in the back part of the cavity via the intensive mass exchange process and weaker interaction between the primary and secondary vortices. Flame stretch and thickness are further investigated to shed light into turbulence-flame interaction in supersonic flows. Results show that the interaction between the cavity shear layer and the aft wall leads to the increase of flame surface and weaken the correlation between S-d and del . n in both cases. After that, the analysis on flame thickness indicate that the tangential strain rate serves as a dominant factor influencing flame thickness within the preheat layer. In contrast to the case with wall-bounded turbulence inflow, the specific roll-up vortex observed in the cavity shear layer of case with laminar inflow bring different physical phenomenon. Also, the collision at the aft wall exerts a much more significant influence on thickening the flame within oxidation layer due to the intense turbulent effects and increasing the flame stretch in regions characterized by large positive curvature in this case.</p
A spatio-temporal fusion method for non-destructive testing using infrared thermography
No full textThe infrared thermography, as a non-contact and highly sensitive non-destructive testing (NDT) method, has been extensively applied in various fields such as aerospace, construction, and industrial manufacturing industry. Current post-processing of dynamic thermal sequences relies mainly on thermal images' spatial information without incorporating temporal data, compromising defect detection accuracy and efficiency. To address this challenge, we propose a spatio-temporal fusion thermography (STFT) method that enables high-precision of surface defects detection. The method primarily establishes a theoretical model by integrating spatial and temporal gradient information from dynamic thermal sequences, with thermal propagation being estimated using optical flow method. The verification experiment on metal surface defects indicates that the STFT method is capable of reliably detecting surface microcracks as small as 3 mu m in width. And it can effectively eliminate the impact of uneven temperature distribution on the test specimens and significantly improves the signal-to-noise ratio (SNR) of the defect images. The proposed method holds great potential for broad application in the field of industrial non-destructive testing, such as detecting surface or near surfac cracks and pitting defects in gears
Research on Lateral Dynamics Characteristics and Adaptive Control Strategies of EMU with Motor Active Suspension
No full text高速铁路动车组因其高运行速度、强运载能力、低能源消耗、弱环境影响以及显著的经济和社会效益，获得了诸多国家的重视与发展。运行速度的提升是高速动车组技术发展的重要目标。制约运行速度提升的关键问题是车辆横向动力学特性。车辆横向动力学特性与车辆悬挂装置密切相关。以补偿车辆悬挂参数为出发点的半主动、主动控制策略可以有效地改善车辆横向动力学特性。因此，研究车辆系统的横向动力学特性并提出有效的控制策略对动车组在高速下的稳定运行具有重要意义。然而，现有研究所建立的整车系统动力学模型并未考虑电机的弹性架悬和自旋蠕滑的影响，且以往的控制策略均未考虑减振器的动态特性。
为此，本文围绕电机主动架悬动车组的横向动力学特性展开研究，旨在设计出合理的控制策略以改善车辆系统的蛇行稳定性。首先，本文基于Kalker线性轮轨滚动接触理论并考虑电机主动架悬，建立了一个考虑自旋蠕滑效应的23自由度电机主动架悬动车组整车系统动力学模型，并在Simpack平台中搭建了对应的多体动力学仿真模型。随后，通过Sobol全局敏感性分析与Pearson相关性分析方法，识别出二系横向刚度Ksy、二系横向阻尼Csy与电机横移频率fmy是影响横向稳定性与运行平稳性的关键因素。在此基础上，进一步分析了电机架悬参数对线性临界速度和系统最小阻尼比的具体影响规律。同时，通过与高精度Simpack仿真模型及已有文献复现模型的对比，验证了本文所建模型在引入自旋蠕滑项后，在物理合理性与工程适用性方面具备更高的一致性。基于敏感性与相关性分析结果，本文设计了一种基于状态反馈的自适应主动控制方法，结合车辆蛇行频率的实时检测，对抗蛇行减振器的动态刚度与阻尼进行更新，并据此通过作动器输出控制力，实现对关键悬挂参数的在线优化调节。联合仿真结果表明，本文所提出的控制策略不仅能显著提升车辆系统的临界速度，还能提高车辆对外界激扰的响应抑制能力，同时降低构架的横移加速度，从而有效改善电机主动架悬动车组的蛇行稳定性。
综上所述，本文的研究为主动悬架在高速动车组中的应用提供了完整的建模流程、关键参数识别方法与控制策略设计依据，对提升高速动车组的横向动力学特性具有重要理论价值与工程推广意义。</p
空间变重力在轨流体管理实验箱
No full text本发明公开了空间变重力在轨流体管理实验箱， 包括实验箱， 以及安装于实验箱内的实验贮箱、受热模拟装置和流体观测装置；实验箱安装在变重力离心平台， 变重力离心平台用于向实验贮箱提供离心加速度， 实验贮箱的长轴是沿变重力离心平台的径向布置的；实验箱还设置有：用于驱动实验贮箱旋转旋转机构， 用于驱动实验贮箱、旋转机构和流体观测装置同时进行直线往复运动的振动机构， 变重力离心平台、旋转机构与振动机构协同作用， 能够对实验贮箱模拟集旋转与平动组合运动的空间变重力在轨运动
微重力金属熔丝增材熔体定向转移及液桥过渡保持装置及方法
No full text本发明提供一种微重力金属熔丝增材熔体定向转移及液桥过渡保持装置及方法， 成形基板安装在多轴运动平台上；多轴运动平台根据增材制造中的三维数据定制三维运动轨迹路径；2个电流夹分别固定在金属丝材和成形基板之间， 通过直流电源在金属丝材和成形基板之间形成电流通路， 同时在电流通路中串联电流表；金属丝材的周向布置电磁线圈， 导磁棒与电磁线圈连接， 并分布在金属丝材的端部两侧对称位置；交流电源为电磁线圈提供交变电场；送丝机构及驱动电机定量定速地将金属丝材送至激光源发射的光斑的作用范围内；激光作用在成形基板上， 在成形基板上形成液态熔池；金属丝材和成形基板通过液态熔体形成液桥连接模式。本发明能够减小构件的气孔缺陷
一种多孔流道换热器及加工方法
No full text本发明提供了一种多孔流道换热器及加工方法， 加工方法中， 在换热器板片上机械加工制成上壁面流道；将多孔介质颗粒制成具有粘性的混合颗粒粉体；将混合颗粒粉体填充满整个上壁面流道， 以在上壁面流道内粘合形成颗粒多孔粘合层；将单个换热器板片进行热压烧结， 以使混合颗粒粉体中多孔介质颗粒间， 以及多孔介质颗粒与上壁面流道内壁间均产生冶金结合， 以制得单层的多孔流道换热器。本发明也提供了制备多层的多孔流道换热器的方法， 本发明提供的加工方法， 可以同时完成多孔介质颗粒内部和换热器板片相互之间等组成的热压烧结， 以解决现有技术通过小的单个流道尺寸设计来提高比表面积和换热效率的方案而增加加工难度， 乃至于难以实现的问题
一种铂膜传感器的批量质量检测装置及检测方法
No full text本发明公开了一种铂膜传感器的批量质量检测装置检测方法， 包括：传感器批量送料单元， 用于向老化检测仪依次输入定量的铂膜传感器；老化检测仪， 用于依次与每个铂膜传感器连接， 并向铂膜传感器定时通入恒定电流以模拟铂膜传感器的使用过程， 老化检测仪通过分析铂膜传感器的模拟使用过程中的特征参数来筛选合格的铂膜传感器。本发明检测准确， 检测效率高
一种用于非均质材料的剪切失稳判据的方法
No full text本发明提供了一种用于非均质材料的剪切失稳判据的方法， 其具体包括以下步骤：(1)在多种动态条件下对射流材料进行力学性能测试， 获得非均质材料的JC动态本构关系；(2)在JC动态本构关系基础上对材料进行扰动分析， 以获得材料的剪切失稳判据；(3)将JC动态本构参数代入剪切失稳判据， 即可获得材料剪切失稳的临界应变。本发明构思合理， 充分考虑了材料多相夹杂及应变梯度效应对剪切失稳的影响， 可以广泛地应用于各种新型非均质材料， 能够低成本、高效、准确地获得剪切失稳判据