Institute Of Mechanics,Chinese Academy of Sciences
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Heterogeneous detonation in gas-particle mixtures with full pattern flows: Numerical model, method, and verification
No full textIn practical engineering applications, heterogeneous detonation in gas-combustible particle mixtures often involves distinct flow regimes, including dilute, dense, dense-to-dilute transition patterns. This study aims to develop a numerical model and method suitable for heterogeneous detonation simulation of gas-particle systems with full pattern flows. First, based on the Eulerian-Lagrangian framework that is more consistent with particle dynamics, a numerical model for gas-particle detonation with four-way coupling of gas-particle and particle-particle interactions is established. For the gas phase, the governing equations are constructed on continuous Eulerian meshes, accounting for the effects of particle combustion, volume fraction, and interphase coupling. The dispersed particle phase is modeled in Lagrangian coordinates, with collisions among particles in the cloud resolved via a coarse-grained discrete element model. Particularly, the effect of mass transfer caused by particle combustion on the interphase momentum and energy coupling is carefully considered. Afterwards, a multiphase HLL/HLLC solver with high-order reconstruction scheme is employed to discretize the nozzling terms and convective fluxes of gas equations. To quickly solve for temperatures of the gas and particles (considering phase transition latent heat and realistic heat capacity), an efficient algorithm based on the Newtonian iterative method is proposed. To ensure the fidelity of two-phase interaction simulations in strong discontinuity and dense particle flow scenarios, an improved interphase coupling strategy with second-order accuracy is developed. Finally, a series of numerical verification and validation tests are conducted, covering key sub-models, interphase coupling algorithms, inert gas-particle flows and heterogeneous detonation across various flow patterns. Comparisons with theoretical solutions and experimental data demonstrate that the proposed numerical models and methods can accurately predict interphase coupling, shock interaction with particle clouds of different volume loadings, characteristic parameters of dilute heterogeneous detonation, and evolution of two-phase detonation in dense conditions
Unsteady flow characteristics of backflow vortices in an axial-flow pump at low flow rates
No full textAxial flow pumps are widely used in water conservancy, petrochemical and agricultural industries. Efficient operation is crucial for energy conservation and emission reduction. Improving efficiency under severe conditions requires studying the internal flow of axial-flow pumps, particularly at low flow rates where backflow vortices form near the impeller inlet. This study investigates the unsteady flow characteristics of backflow vortices at different flow rates in an axial-flow pump. Results show that backflow vortices form when the flow rate decreases to 0.59Qd. As the flow rate further declines, the backflow vortex progresses upstream, contracts, and rebounds. The flow rate range is divided into three stages: Stage I with no backflow vortex, stage II with initial vortex development extending upstream and relatively fragmented, and stage III with vortex contraction and rebound forming a more coherent structure. Besides, backflow vortices induce significant pressure fluctuations and velocity oscillations with the primary frequency being 0.5 fb. They exhibit a three-dimensional spiral motion involving changes in axial length, self-rotation, and revolution around the pump axis, with an angular velocity of approximately half the impeller's rotational speed. This work enhances insights into backflow vortex behaviors, which is essential for optimizing pump design and improving operational stability in challenging environments
Numerical Investigation of Freestream Composition Perturbations in a Scramjet Combustor
No full textThis study employs three-dimensional unsteady numerical simulations to analyze fluid-combustion interactions in a scramjet combustor under freestream oxygen perturbations at Mach 6 flight conditions. The combustor utilizes ethylene fuel injection, with systematic examinations of dynamic responses to abrupt reductions in freestream oxygen mole fractions from baseline 0.21 to 0, 0.05, and 0.10. A characteristic mode shift occurs from jet-wake stabilization to cavity shear-layer stabilization during oxygen depletion, followed by reversion to the original mode upon freestream recovery. This transition correlates strongly with perturbations in combustion intensity and heat release redistribution. Rapid alterations in shock train positioning and flow separation characteristics were observed, directly influencing static pressure distributions along the flowpath. The resultant pressure fluctuations exhibited temporal coherence with thrust variations. Thrust modulation magnitudes demonstrated linear dependence on oxygen depletion severity, while combustion sustainability remained intact during 0.2 ms perturbations. Prolonged perturbations can induce cumulative effects and are capable of altering hypersonic vehicle trajectories through thrust vectoring changes. These results highlight the critical time-dependent coupling between freestream composition transients and scramjet operability, providing quantitative benchmarks for robust combustor design in atmospheric disturbance scenarios
Experimental and numerical study on the chemical reactions of carbon dioxide-air mixtures behind high-speed shock waves
No full textThe ablation product carbon dioxide (CO2) around the hypersonic vehicle may become an important source of radiation. Accurate simulation of the chemical reaction process between CO2 and air is of great significance for the design of thermal protection systems. A combination of ground experiments and numerical simulations is used in this study to investigate the reaction process of CO2-air mixtures with different proportions behind shock waves with velocities ranging from 3.6 to 4.1 km/s. Flow parameters are simulated based on the two-temperature (2-T) model and the Lee and Park chemical reaction mechanism, and the laser absorption spectroscopy measurements are carried out on the Phi 800 mm shock tube at the Chinese Academy of Sciences, Institute of Mechanics, to obtain time-resolved post-shock gas temperatures and partial pressures of CO2 and carbon monoxide (CO). Measurement results indicate that the post-shock temperature is much higher than the equilibrium value when it is close to the shock front and then gradually develops towards equilibrium. The partial pressure of CO2 shows the same trend as temperature. Comparisons between experimental results and calculated results show that the used model can accurately predict the post-shock temperature. When the initial CO2 volume fraction is below 50%, the model underestimates the CO2 dissociation rate, meaning that the actual CO2 content is lower than the calculated value and the CO content is higher. Conversely, when the CO2 volume fraction is greater than or equal to 50%, the prediction of the CO2 dissociation rate tends to be overestimated
Improve wear resistance CoCrFeMnNiTix/WC high entropy alloy-ceramic composite coatings with hybrid ex/in-situ multi-scale reinforcement phase fabricating by laser cladding
No full textTo improve the hardness and wear resistance of high-entropy alloy coatings, laser cladding (LC) technology was successfully used to prepare CoCrFeMnNi high-entropy alloy coatings enhanced with multi-scale precipitations phases ranging from the nanometer to micron scale. The microstructure evolution of high entropy alloy matrix was investigated, with increasing Ti content, the high-entropy alloy matrix from an FCC solid solution to an FCC + BCC dual-phase structure. Simultaneously, sub-micron (Ti,W)C particles were formed in-situ. The volume fractions of BCC and (Ti,W)C gradually increase, and the (Ti,W)C particles exhibit aggregation, while the degree of WC melting increases. Specifically, in the CoCrFeMnNiTi1/WC coating, a very fine lamellar eutectic structure composed of alternating FCC and BCC phases was observed, with a layer spacing of 100-170 nm. In this coating, the interface relationship between high-entropy alloy matrix and (Ti,W)C was identified as a semi-coherent interface, with the orientation relationship between (Ti,W)C and FCC being (100)(Ti,W)C//(110)FCC and (020)(Ti,W)C//(111)FCC, with an interface energy of 0.71 J/m2. In local areas of CoCrFeMnNiTi1/WC coating, a rod-like eutectic structure and nanoscale BCC phase precipitation were observed. Furthermore, as the Ti content increased, the mechanical properties of the coating were significantly enhanced. The mechanical properties of the coatings are enhanced through a combination of multiple strengthening mechanisms. Compared to other coatings, the CoCrFeNiMnTi1.5/WC coating exhibits the highest microhardness (622.5 HV0.3) and the smallest wear volume of 6.16 x 10-6 mm3/(N & sdot;m), demonstrating the best wear resistance
一种考虑多因素影响的摩擦片疲劳寿命预测方法
No full text本发明公开了一种考虑多因素影响的摩擦片疲劳寿命预测方法，包括：获取摩擦片在实际工况下多因素影响的性能参数，引入平均摩擦系数计算关键参数；构建多维特征输入向量，基于深度神经网络模型建立摩擦片疲劳寿命与各影响因素之间的非线性映射关系；实时监测所述摩擦片的性能，获取对应的疲劳寿命预测值；采用模糊综合评判方法分析所述最优表征参数的变化趋势，建立状态评估的模糊评判模型，获取摩擦片磨损程度预测值；对所述擦片磨损程度预测值采用置信度分析模块，对所述摩擦片磨损程度预测值的预测结果进行置信度评估，生成包含误差范围的疲劳寿命预测区间，显著提升了预测精度和模型泛化能力，增强了预测结果的可信度和可解释性
高低温环境对剪切硬化胶改性乙烯-醋酸乙烯酯泡沫的防护性能影响
No full text乙烯-醋酸乙烯酯泡沫（ethylene-vinyl acetate foam,EVA）广泛应用于防弹衣缓冲层、护膝护肘中作为缓冲材料。文章利用剪切硬化胶（shear stiffening gel,SSG）对EVA进行改性，得到了具备更高冲击防护性能的EVA/SSG复合缓冲泡沫。为研究高低温环境对EVA/SSG泡沫材料缓冲性能的影响，利用动态热机械分析、万能压缩机对EVA/SSG泡沫在–50℃～50℃下的力学性能进行了研究，得到了EVA/SSG材料的损耗模量、储能模量、屈服强度随温度变化的规律；同时借助落球试验平台系统研究了高低温环境（–50℃～50℃）对EVA/SSG泡沫材料冲击防护性能的影响。通过分析落球冲击试验结果与材料的力学性能测试结果，系统总结了高低温环境对EVA/SSG复合泡沫材料防护性能的影响规律
Manipulating Wetting State of CFRP via One-Step Laser Micro/Nanostructuring
No full textThe wetting state is a fundamental property of a material surface, yet achieving precise control over this property remains a formidable challenge. Mastery of wetting behavior can impart tailored functionalities to surfaces, such as liquid repellency, anti-fouling, and directional liquid transport. Despite the potential benefits, strategies for rapid and reliable modulation of various wetting states have remained elusive until now. In this study, an innovative one-step laser-based strategy that enables precise and rapid manipulation of surface wetting states on carbon fiber reinforced plastic (CFRP) is presented. This approach allows for the creation of hydrophilic surfaces characterized by the Wenzel state, hydrophobic surfaces with a mixed Cassie-Baxter/Wenzel state, and robust superhydrophobic surfaces featuring a stable Cassie-Baxter state. The realization of a stable Cassie-Baxter state stems from the concurrent formation of hierarchical micro/nanostructures and the enrichment of low surface energy components. Critically, the resulting superhydrophobic CFRP surfaces with the Cassie-Baxter state exhibit exceptional stability, minimized adhesion, and superior anti-icing and de-icing properties. These findings provide both fundamental insights and a practical platform for the rapid development of non-wetting, multifunctional surfaces, significantly expanding the applicability of CFRP across diverse engineering domains
Manipulating Wetting State of CFRP via One-Step Laser Micro/Nanostructuring
No full textThe wetting state is a fundamental property of a material surface, yet achieving precise control over this property remains a formidable challenge. Mastery of wetting behavior can impart tailored functionalities to surfaces, such as liquid repellency, anti-fouling, and directional liquid transport. Despite the potential benefits, strategies for rapid and reliable modulation of various wetting states have remained elusive until now. In this study, an innovative one-step laser-based strategy that enables precise and rapid manipulation of surface wetting states on carbon fiber reinforced plastic (CFRP) is presented. This approach allows for the creation of hydrophilic surfaces characterized by the Wenzel state, hydrophobic surfaces with a mixed Cassie-Baxter/Wenzel state, and robust superhydrophobic surfaces featuring a stable Cassie-Baxter state. The realization of a stable Cassie-Baxter state stems from the concurrent formation of hierarchical micro/nanostructures and the enrichment of low surface energy components. Critically, the resulting superhydrophobic CFRP surfaces with the Cassie-Baxter state exhibit exceptional stability, minimized adhesion, and superior anti-icing and de-icing properties. These findings provide both fundamental insights and a practical platform for the rapid development of non-wetting, multifunctional surfaces, significantly expanding the applicability of CFRP across diverse engineering domains
Material frame formulation of the FE-based virtual fields method and applications to hyperelastic composites
No full textAs typical heterogeneous composites, traditional material parameter identification of the biological tissues has recently been challenged by the popularization of full-field measurements during experimental tests. The Finite Element Model Updating (FEMU) method, which is known for its robustness, has to face prohibitive computational costs with the massive data offered by full-field measurements. A promising alternative is the Virtual Fields Method (VFM) which is notably more efficient computationally when these full-field measurements are available. We recently proposed a general and robust VFM framework for identifying the material parameters of nonlinear elasticity. However, the framework was formulated with the spatial form of the principle of virtual power. In the current paper, we introduce a more concise formulation with the material form of the principle of virtual power, expanding the application to multiple measurement cases. Verification with analytical and numerical examples demonstrates its significant efficiency compared to the FEMU method as well as generality and robustness across various applications, including the noise sensitivity analysis and heterogeneous biological tissue cases. The accurate identification results highlight the significant potential of this method in nonlinear biological composites