Institute Of Mechanics,Chinese Academy of Sciences
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Study on the effect of the fuselage profile on aerodynamic characteristics of HCW configuration
No full textThe High-pressure Capturing Wing aerodynamic configuration (abbreviated as HCW) can enhance the aircraft's lift and lift-to-drag ratio through the effective utilization of favourable aerodynamic interference between the fuselage and the capturing wing (abbreviated as CW). Consequently, the fuselage shape significantly influences not only the aerodynamic characteristics of the fuselage but also those of the CW. In this study, based on the concept of a fuselage of revolution combined with CW, the effects of different fuselage profile shapes-specifically, conical profile, 3/4-power profile, and Karman profile-on the aerodynamic characteristics of the HCW configuration are systematically investigated using a numerical simulation technique. The results indicate that while the 3/4-power and Karman configurations differ from the conical configuration by employing non-uniform compression, which increases the fuselage volumes by 18.5 % and 48.1 %, respectively, they achieve drag reductions of 6.7 % and 1.1 % under the design condition at Ma = 6. Moreover, due to the influence of different fuselage profiles on the flow characteristics, the peak pressure on the lower surface of the CW is reduced for both the 3/4-power and Karman configurations, while the area of the high-pressure zones is increased. Overall, compared to the conical configuration, the 3/4-power configuration exhibits a slight decrease in lift, whereas the Karman configuration demonstrates a significant increase in lift. Both configurations achieve an increase in the lift-to-drag ratio. Additionally, an analysis of the effects of different Mach numbers (Ma = 7, Ma = 8) that as the Mach number increases, the lift becomes more sensitive for both the 3/4-power and Karman configurations. However, compared to the conical configuration, both configurations keep exhibiting a decrease in overall drag and an increase in the lift-to-drag ratio. Furthermore, under different Mach number conditions, the centers of pressure for both configurations shift rearward
Nonlinear dynamic responses of wing flexible sealing undergoing flapping effect
No full textWith the increasing demands of higher performance of advanced aircrafts, the flexible sealing have been used to seal the gap between main wing surface and its movable control surface so as to improve stealth performance and control effectiveness. However, during whole flight process undergoing various operation states and severe loadings, the flexible sealing could be separated from control surface and consequently strongly vibrate under the disturbances coming from ambient airflow. In that case, "flapping" motions between flexible sealing and other wing components may cause complicated nonlinear dynamic structural response due to discontinuous boundary conditions along with impact effect. In this study, the static structural responses in multiple states, including original state, installation state and lifting process, are firstly examined based on FEM numerical simulations. The displacements and contact preloads that can influence the dynamic characteristics and responses, changing with flight states and speeds, are given so as to analyze and model the discontinuous boundary conditions. Furthermore, the dynamic responses of the flexible sealing during its flapping motions under these particular discontinuous constraints, considering combination actions of periodic excitation and intermittent impact forces, are comprehensively studied. Our numerical results show that the dynamic displacement amplitude and root moment of flapping motion increase respectively by 86.3 % and 177.9 % than static values. And, a mixing of standing waves and traveling waves of the acceleration and shear stress responses is observed through spatiotemporal evolutions. Generally speaking, the flapping is a dynamic response with broadband spectrum rather than a simple forced vibration, which include superharmonic frequencies of excitation frequency, natural frequency and high frequencies due to impact. More interestingly, significant nonlinear phenomena such as superharmonic resonance and chaos are found due to combination actions of discontinuous constraints and intermittent impacts. To deeply explore the nonlinear behaviors of this flapping motion, an analytical model including stiffness jump and impact force is developed, and the Runge-Kutta algorithm is used to obtain the solutions of the nonlinear system. The phase diagram and Poincare section of the analytical solutions give similar qualitative results with our numerical simulations
Nonlinear dynamic responses of wing flexible sealing undergoing flapping effect
No full textWith the increasing demands of higher performance of advanced aircrafts, the flexible sealing have been used to seal the gap between main wing surface and its movable control surface so as to improve stealth performance and control effectiveness. However, during whole flight process undergoing various operation states and severe loadings, the flexible sealing could be separated from control surface and consequently strongly vibrate under the disturbances coming from ambient airflow. In that case, "flapping" motions between flexible sealing and other wing components may cause complicated nonlinear dynamic structural response due to discontinuous boundary conditions along with impact effect. In this study, the static structural responses in multiple states, including original state, installation state and lifting process, are firstly examined based on FEM numerical simulations. The displacements and contact preloads that can influence the dynamic characteristics and responses, changing with flight states and speeds, are given so as to analyze and model the discontinuous boundary conditions. Furthermore, the dynamic responses of the flexible sealing during its flapping motions under these particular discontinuous constraints, considering combination actions of periodic excitation and intermittent impact forces, are comprehensively studied. Our numerical results show that the dynamic displacement amplitude and root moment of flapping motion increase respectively by 86.3 % and 177.9 % than static values. And, a mixing of standing waves and traveling waves of the acceleration and shear stress responses is observed through spatiotemporal evolutions. Generally speaking, the flapping is a dynamic response with broadband spectrum rather than a simple forced vibration, which include superharmonic frequencies of excitation frequency, natural frequency and high frequencies due to impact. More interestingly, significant nonlinear phenomena such as superharmonic resonance and chaos are found due to combination actions of discontinuous constraints and intermittent impacts. To deeply explore the nonlinear behaviors of this flapping motion, an analytical model including stiffness jump and impact force is developed, and the Runge-Kutta algorithm is used to obtain the solutions of the nonlinear system. The phase diagram and Poincare section of the analytical solutions give similar qualitative results with our numerical simulations
An arc-melted eutectic medium-entropy alloy with superior strength-ductility synergies at room and cryogenic temperatures
No full textThe cryogenic compressive mechanical properties of eutectic multi-principal alloys have rarely been reported. In this work, the superior fracture strength-fracture strain synergies at room and liquid nitrogen temperatures (RT and LNT) of the arc-melted Cr50Co25Ni25 eutectic medium-entropy alloy were found. These values were 1917 MPa and 39.1 % at RT, along with 1990 MPa and 26.1 % at LNT. The reduction of ductility at LNT was primarily attributed to the inferior deformation capability of the BCC phase containing HCP phase. The fracture mechanisms were dominated by ductile fracture of the FCC phase and brittle fracture of the BCC phase at both temperatures, while dislocation pile-ups and stacking faults were responsible for the deformation mechanisms
Prediction of mechanical properties of cross-linked polymer interface by graph convolution network
No full textMachine learning models have made significant advances in the establishment of structure-property relationships. However, it is still a challenge to predict the mechanical properties of the adhesive interface due to the complexity and randomness of the polymer topologies. In this paper, we employed a graph convolutional network (GCN) model to predict the mechanical properties of a specific cross-linked polymer interfacial system, including yield strength (sigma(y)), ultimate strength (sigma(u)), failure strain (epsilon(u)), and fracture toughness (Gamma) utilizing molecular dynamics simulations. The results showed that the adopted GCN model can predict the mechanical properties with over 88% accuracy. Furthermore, the prediction performances for epsilon(u) and sigma(u) are better than those for Gamma and sigma(y), with R-2 similar to 0.73 for epsilon(u), R-2 similar to 0.64 for sigma(u), R-2 similar to 0.51 for Gamma, and R-2 similar to 0.43 for sigma(y). It is worth noting that the GCN model with the sum aggregator slightly outperforms that with the mean aggregator, and that models with linear regression and fully connected neural network regression provide similar predictions. The influence of input node features on prediction performance was also investigated. It was observed that the node closeness centrality is an important graph parameter in prediction. Specifically, node closeness centrality presents a more significant influence on the global mechanical properties of the adhesive interface, such as epsilon(u), sigma(u), and Gamma. Additionally, sensitivity analysis demonstrated that appropriate hyperparameters can improve computational efficiency without losing accuracy on a restricted set of data. This paper demonstrated the capacity of the GCN model to predict the mechanical properties of the adhesive interface with diverse topologies and provided a possible pathway for improving the mechanical properties of the adhesive interface by tailoring polymer structures in the future
A numerical toolkit for the ignition delay time and ignition probability density predictions based on instantaneous mixing fields in OpenFOAM
No full textThe OpenFOAM built-in chemistry solver, chemFoam, is extended as multiMeshChemFoam to simultaneously calculate the zero-dimensional (0D) ignition processes on the entire computational domain of practical simulations. The instantaneous temperature, pressure, and species mass fractions of a mixing field are input for the ignition calculation. A solver termed idtFoam is then developed to extract the Ignition Delay Time (IDT) on all cells from the 0D calculations. Several ignition criterions including the temperature exceeds a threshold value, the peaks in heat release rate (or equivalently, the time derivative of temperature) and species mass fractions are available. Another solver denoted as ipdFoam is finally compiled to construct the Ignition Probability Density (IPD) on the entire domain for a certain period. A time series of transient data from the mixing field are necessitated for the ignition calculation, IDT extraction, and IPD construction on individual cells. The numerical toolkit is verified with chemFoam for the 0D ignitions of ethylene. It is then applied to the mixing fields of an ethylene-fueled model supersonic combustor. It is computationally-efficient to evaluate the ignition performance of practical combustion systems in the design phase. Furthermore, assessment on the ignition properties can be made prior to any detailed and computationally-expensive simulations on the reactive flow, since only mixing field is required for calculating the IDT and IPD
Elevated-temperature fatigue behavior and microstructure based cumulative damage evaluation of additive manufacturing superalloy under variable amplitude loading
No full textFatigue properties under service conditions are a critical barrier to the reliable application of additive manufacturing (AM) metals. Yet, the associated damage mechanisms and life evaluation approaches, particularly at long term, elevated temperature and variable amplitude (VA) loading, are almost unclear. To address these, high and very-high cycle fatigue VA tests and meso-microscale analyses were performed to investigate damage mechanism of a laser powder bed fused superalloy with heat treatment at service temperature of 650 degrees C, and a microstructure based cumulative damage evaluation approach was proposed. Results show that interior failures characterized by defect-assisted faceted cracking are predominant. VA loading tends to sequentially activate multiple defects, resulting in competitive multi-site crack nucleation. Increased stress levels accelerate crack growth, leading to the formation of localized rough growth areas and crack deflection. Both primary and secondary cracks grow transgranularly, with crack paths showing negligible dependence on grain orientation. The interior crack nucleation and growth mechanisms under VA loading are elucidated. A cumulative damage evaluation model incorporating the remaining life factor, correlation function transformation, and a reconstructed stress-life relationship was developed, with the prediction results being in close accord with the experimental data under VA loading. These findings provide new insights into the interior crack nucleation and growth mechanisms in AM superalloys and offer a predictive framework for fatigue life estimation under realistic service conditions
Linear stability of rotating pipe flow with non-ideal fluid
No full textA linear stability analysis is performed on rotating pipe flow with a non-ideal fluid. The study focuses on supercritical CO2 near its vapor-liquid critical point, where thermodynamic properties deviate significantly from ideal gas. Different wall temperatures are considered, ensuring centerline temperatures span subcritical, transcritical, and supercritical conditions. The modal analysis reveals that at low rotation speeds, unstable mode only exists at rotational speed Omega < 0. Also multiple unstable modes emerge, introducing a more complex instability mechanism compared to non-rotating pipe flow. As rotation speed increases, viscous dissipation plays a key role in flow stabilization, while thermodynamic effects remain secondary. The non-modal analysis further demonstrates that optimal system response under fixed-frequency forcing shifts due to rotation, with stronger deviations from incompressible behavior at high compressibility. In rotating pipe flow, the dependence of transient energy growth on the azimuthal wavenumber (n) is inherently nonlinear, which stands in stark contrast to the approximately linear relationship typically observed in non-rotating pipe flow. This nonlinearity arises primarily due to the influence of azimuthal velocity components introduced by rotation. These findings highlight the intricate coupling between rotation, compressibility, and thermodynamics, providing new insights into instability mechanisms in non-ideal fluid systems
Permeability anisotropy and non-Darcy effect of gas shale: A case study of S1l<sub>1-1</sub><SUP>1</SUP> sublayer of Longmaxi Formation in Sichuan Basin, China
No full textPermeability anisotropy and non-Darcy effect are critical factors in determing the production capacity of gas shale. Through combined testing using the cubic-block and crushed-particle sample methods, we systematically characterized the percolation characteristics of 27 samples from the main production layer (S1l(1-1)(1) sublayer) of the Longmaxi Formation. Results show the quartz matrix support system dominates percolation perpendicular to bedding, with permeability (K-V approximate to 1-500 nD) showing high consistency with crushed sample results (K-C), controlled by porosity-quartz content co-evolution. However, clay directional alignment significantly enhances bedding-parallel percolation advantage (K-P/K-V = 10(1)-10(3)), with every 5 % increase in clay content elevating K-P by approximately one order of magnitude. Based on Knudsen number (Kn), we demonstrate that Darcy flow and slip flow are the main flow forms while pure Knudsen flow is rare in shale gas development. Finally, an integrated evaluation framework of permeability to optimize shale gas exploration is developed by incorporating with actual well performance. From the perspective of permeability, reservoirs with Kn < 0.2 and K-P/K-V < 100 exhibit better exploration and development potential
Semi-analytical modeling of coating-crack-defect interactions using a combined distributed dislocation technique and numerical equivalent inclusion method
No full textCoatings play a critical role in controlling stress concentrations, mitigating crack-defect interactions, and enhancing the durability of tribological components under frictional loading. Understanding the interactions among cracks, coatings, and defects at the microscale is therefore critical for elucidating the underlying mechanisms and ensuring the design and reliability of coated materials in friction-related applications. This studyudy investigates the effect of coating on the interaction between a multi-branched crack and arbitrarily shaped inhomogeneities or voids. The governing equations for coatings, inhomogeneities, voids and cracks are fully coupled into a unified model. Furthermore, the stress solutions for the crack with multiple branches at any angle and length are innovatively derived in the half plane with the help of the Distributed Dislocation Technique (DDT). Based on the numerical equivalent inclusion method (NEIM) and Fast Fourier Transform (FFT) algorithms, a semi-analytical scheme with a multi-stage iterative procedure is presented to obtain the final stress solutions and the stress intensity factors (SIFs). Benchmark examples compared with finite element method (FEM) results validate the numerical implementation. The proposed semi-analytical method overcomes limitations related to crack branching, inhomogeneity shapes, and mesh complexity, offering enhanced flexibility and computational efficiency