Institute Of Mechanics,Chinese Academy of Sciences
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Numerical Investigation of the Influence of Fuselage Corner Bluntness on a High-Pressure Capturing Wing Configuration
No full textUnder beneficial aerodynamic interference, the innovative high-pressure capturing wing (HCW) configuration exhibits remarkable aerodynamic performance at hypersonic speeds. At the same time, the additional lifting surface of the HCW may significantly improve the lift at subsonic speeds, which makes the configuration a promising concept for air vehicle design covering a wide speed range. Recent research has shown that the HCW can generate flow separations on the upper surface of the fuselage in certain subsonic flow conditions, which considerably deteriorates aerodynamic performance of the air vehicle. In this paper, a hybrid configuration combining HCW with a cone-truncated cone fuselage is studied. Numerical simulations are conducted to examine the impact of fuselage corner bluntness on flow characteristics and aerodynamic performances in typical subsonic (Mach 0.7) and hypersonic (Mach 7) flow conditions. The results show that at Mach 0.7, with the increase of blunt radius at the fuselage corner, the flow separations on the upper surface of the fuselage can be effectively restrained. The lift coefficient of the vehicle remains virtually unchanged, while the drag coefficient decreases significantly by 69% when the blunt radius is 600 mm. At Mach 7, the fuselage corner bluntness leads to a slight drop of 9% and 8% in the lift and drag coefficient of the vehicle, respectively, while the lift-to-drag ratio remains virtually unchanged
Effect of curvature on the hypersonic turbulent boundary over the curved compression ramp
No full textDirect numerical simulation of the shock wave/turbulent boundary layer interaction on a compression ramp and curved compression ramps with different radii of the curvature at the Mach number Ma=5.0 and Reynolds number Re=16 800/mm is performed, and the purpose of the study is to investigate the impact of different radii of the curvature on the development of the flow. The flow structure and turbulence properties are analyzed. As the curved angle radius increases, the range of flow deceleration and the impact of the shock wave interaction on the turbulent boundary layer gradually decrease, and the peak value of turbulent pulsation amplification in the interaction zone becomes smaller. Mean skin friction decomposition is carried in upstream undisturbed region and reattachment region. The skin friction coefficient in the upstream is primarily composed of the viscous dissipation term C-f,C-V and the turbulent kinetic energy production term C-f,C-T. While in the reattachment zone, it is mainly balanced by the term C-f,C-T and the spatial growth term C-f,C-G. Bidimensional empirical mode decomposition is applied to further study the contribution of the turbulent motion at different scales to C-f,C-T, and the result shows that for the compression ramp, C-f,C-T is mainly contributed by the large-scale vortex structure generated in the interaction zone, while for the curved compression ramp, it is mainly contributed by the rapid amplification of turbulent pulsations caused by the shock wave interaction. This study is not only a new parametric study of the shock wave/turbulent boundary interaction but also provides a reference for the aerodynamic design of hypersonic vehicles
Over 200 times current enhancement via buckling triboelectric nanogenerator at ultra-low speed for monitoring the swelling of lithium ion batteries
No full textA lightweight prosthetic hand with 19-DOF dexterity and human-level functions
No full textA human hand has 23-degree-of-freedom (DOF) dexterity for managing activities of daily living (ADLs). Current prosthetic hands, primarily driven by motors or pneumatic actuators, fall short in replicating human-level functions, primarily due to limited DOF. Here, we develop a lightweight prosthetic hand that possesses biomimetic 19-DOF dexterity by integrating 38 shape-memory alloy (SMA) actuators to precisely control five fingers and the wrist. The prosthetic hand features real-time sensing of joint angles in each finger, feeding data into a control module for selectively heating or cooling SMA actuators in a closed-loop manner, mimicking the functioning of human muscles. Enabled by the high-power density of SMAs, the hand part (from the wrist to the fingertip) only weighs 0.22 kg, much lower than existing products. We also integrate an onboard power management module that provides electricity for operating the entire system. In addition to 33 standard grasping modes, this prosthetic hand supports 6 advanced grasping modes designed for enhanced dexterity evaluation, expanding the range of achievable ADLs for amputees while facilitating standard prosthesis function tests and validation in real-world scenarios. This innovation offers a significant advancement in prosthetic hand functions, promising improved quality of life for users
Characterization of reflected shock tunnel freestream in carbon dioxide
No full textIn this study, the JFX reflected shock tunnel freestream is characterized using pitot probes, laser absorption spectroscopy, and high-speed schlieren for shock stand-off distances over a sphere. The experiment employed two driver gases: a mixture of H2 and CO2, and pure He. Three lasers, operating at wavelengths around 2.0 mu m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\upmu \mathrm{m}\end{document} and 1.4 mu m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\upmu \mathrm{m}\end{document} with a scanning frequency of 50 kHz, were utilized to measure the properties of CO2 and H2O. Computational fluid dynamics simulations showed near thermo-equilibrium conditions, supporting the use of an equilibrium model to determine the temperature and partial pressure of the two species. Isentropic calculations indicate that there is no significant thermodynamic nonequilibrium in the freestream. During the effective test time, the measured and simulated results were in good agreement for both the shock stand-off distance and CO2 partial pressure. However, the detection of H2O indicated contamination from the driver gas, with early onset leading to an increase in the shock stand-off distance. The uncontaminated time is around 700-800 mu s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\upmu \mathrm{s}\end{document} for both conditions, and the contamination onset time falls between the predicted values using different nozzle conditions, which also indicates a certain degree of contamination
Development and application of a 3D GPU-parallelized CDEM for blasting induced rock fractures
No full textThe study has developed a three-dimensional, GPU-parallelized Continuum-Discontinuum Element Method (CDEM) program, utilizing the CUDA C/C++ programming model on GPUs to simulate rock deformation, fracturing, and movement. Initially, the paper outlines the theory and algorithms of the 3D Graphics Processing Units (GPU) - parallelized CDEM, focusing particularly on parallelization and optimization. Performance tests indicate that the 3D GPU-parallelized CDEM achieves a computational speed 645.31 times faster than a single-core serial CDEM code, significantly boosting computational efficiency. The simulation results of rock fracturing were demonstrated through a single-borehole blasting simulation in granite. Material parameters for granite were calibrated using 3D Brazilian and uniaxial compression tests. Comparisons with experimental data demonstrated that the simulation effectively replicated the observed crack patterns. However, discrepancies were noted in stress wave attenuation, and significant errors in crack density were observed across different sections, which may be attributed to variations in loading methods. These comparisons indicate that the proposed model can simulate the entire process of explosive-induced fracturing with substantial improvements in computational efficiency. Nonetheless, further enhancements in accuracy are necessary. These findings underscore the advantages of the 3D GPU-parallelized CDEM in enhancing computational speeds and its potential in geotechnical engineering, especially for simulating rock fractures under quasi-static and explosive dynamic conditions
Reconfiguration and drag reduction of flexible beam with point buoyancy in oscillatory flow
No full textFlexible structures with point buoyancy widely exist in nature and engineering. Under the action of oscillating flow, it usually has a large geometric nonlinear dynamic response. However, the dynamic response and drag reduction of flexible structures with point buoyancy have not been studied. Therefore, the numerical method in this paper investigates the dynamic response and drag reduction of point buoyant flexible structures under oscillatory flow. Firstly, complex spatial curvilinear coordinates establish the dynamic partial differential equations of flexible structures with point buoyancy. Then, the implicit finite-difference time-domain method is used to discretize the partial differential equation in space and time to form an algebraic equation. Finally, the dynamic response and drag reduction of flexible structures under non-buoyancy, uniform buoyancy, and point buoyancy are numerically analyzed. The results show that with the increase of Cauchy number CY, the deformation of the flexible structure becomes larger and larger, and a local bending point appears. The dimensionless vibration frequency numbers explain the occurrence of local bending points. Unlike no buoyancy, uniform buoyancy and point buoyancy make the flexible structure smaller and more symmetrical. Uniform buoyancy and point buoyancy can increase the Reconfiguration number R. The greater the buoyancy and buoyancy position, the greater the Reconfiguration number R. The load on the flexible structure under oscillating flow is still less than that on the rigid structure. The Vogel exponent is calculated by fitting the Reconfiguration number R. The drag reduction is directly proportional to the Vogel exponent v, that is, the greater the Vogel exponent v, the greater the drag reduction. When the Cauchy number CY is large, the Vogel exponent v of uniform buoyancy and point buoyancy is smaller than that of non-buoyancy. The greater the point buoyancy and buoyancy position, the smaller the deformation of the flexible structure, the greater the Reconfiguration number R, and the greater the Vogel exponent v. When the buoyancy position is small, the influence of point buoyancy on the flexible structure can be ignored
Computational investigation on the formation of liquid-fueled oblique detonation waves
No full textUtilizing a two-phase supersonic chemically reacting flow solver with the Eulerian-Lagrangian method implemented in OpenFOAM, this study computationally investigates the formation of liquid-fueled oblique detonation waves (ODWs) within a pre-injection oblique detonation wave engine operating at an altitude of 30 km and a velocity of Mach 9. The inflow undergoes two-stage 12.5 degrees compression, followed by uniform mixing with randomly distributed n-heptane droplets before entering the combustor. The study examines the effects of droplet breakup models, gas-liquid ratios, and on-wedge strips on the ODW formation. Results indicate that under the pure-droplet condition, the ODW fails to form within the combustor, irrespective of the breakup models used. However, increasing the proportion of n-heptane vapor in the fuel/air mixture facilitates the ODW formation, because the n-heptane vapor rapidly participates in the gaseous reactions, producing heat and accelerating the transition from low- to intermediate-temperature chemistry. Additionally, the presence of onwedge strips enhances ODW formation by inducing a bow shock wave within the combustor, which significantly increases the temperature, directly triggering intermediate-temperature chemistry and subsequent heatrelease reactions, thereby facilitating the formation of ODW
Non-inertial computational framework for long-distance shock-driven object dynamics
No full textIn the realm of dynamic separation problems, the motion of a body triggered by shock interactions is a common phenomenon. This is particularly important in terms of the safe separation of two-stage-to-orbit vehicles, where the motion must remain stable despite long-distance disturbances from shock waves. The flow field in these cases is complex, marked by interactions between hypersonic shock waves and a moving boundary. This leads to significant unsteady effects due to the body's translation and rotation over extended distances. Existing simulation techniques fall short in rapidly and accurately predicting the aerodynamic force and thermal properties for these problems, largely due to the overwhelming computational demands that result from oversize computational domains and the necessity of grid deformation. This paper presents a novel non-deforming grid method to address these challenges. The central concept is to anchor the reference frame to the moving object itself and to approach the problem from a non-inertial frame perspective. This accounts for the motion of the object solely via the inertial source term, circumventing the complexities of mesh manipulation typically required to link flow and motion equations. The moving shock boundary is designed to be closely compatible with selected shock-captured schemes, which reduces non-physical oscillations compared to the traditional method of direct assembly with theoretical shock relations. Other boundary conditions and the solution process are also refined to specifically target the unsteady, shock-dominated flow. These modifications significantly alleviate the computational burden. The effectiveness of the proposed method is demonstrated through several test cases. To showcase the method's practical application, a scenario is simulated wherein an ellipse is dislodged from a wedge by an incident shock wave, covering a long distance. These tests confirm the method's feasibility in aerospace engineering problems
Enabling quantitative analysis of<i> in</i><i> situ</i> TEM experiments: A high-throughput, deep learning-based approach tailored to the dynamics of dislocations
No full textIn situ TEM is by far the most commonly used microscopy method for imaging dislocations, i.e., line-like defects in crystalline materials. However, quantitative image analysis so far was not possible, implying that also statistical analyses were strongly limited. In this work, we created a deep learning-based digital twin of an in situ TEM straining experiment, additionally allowing to perform matching simulations. As application we extract spatio-temporal information of moving dislocations from experiments carried out on a Cantor high entropy alloy and investigate the universality class of plastic strain avalanches. We can directly observe "stick- slip motion"of single dislocations and compute the corresponding avalanche statistics. The distributions turn out to be scale-free, and the exponent of the power law distribution exhibits independence on the driving stress. The introduced methodology is entirely generic and has the potential to turn meso-scale TEM microscopy into a truly quantitative and reproducible approach