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During pumped energy storage using abandoned mines, coal pillars are not only affected by monotonic loads, but also suffer from frequent stress disturbances. The strength and deformation characteristics as well as the failure mode of the coal specimens under the influence of monotonic loading (stress path 1), multilevel constant-amplitude cyclic loading (stress path 2) and multilevel increasing cyclic loading (stress path 3) were studied using the coal samples from Hepan Coal Mine, Shaanxi Province, as the research object. The test results showed that the stress-strain curves of the coal specimens under cyclic loading formed obvious hysteresis loops, and the area of hysteresis loops increased significantly with the rise of stress level; compared with the axial strain, the circumstantial strain was more sensitive to the stress path; the peak strength and peak axial strain of the coal samples were the largest under monotonic loading, and the peak strength and axial strain of the specimens decreased by 22.12% and 18.35% (path 2) and 5.30% and 10.34% (path 3) under multi-level cyclic loading, respectively; the tangent modulus of the specimens under stress path 2 was significantly higher than the other stress paths; the stress paths had not changed the macroscopic failure mode of the coal specimens, but the cyclic loading caused the number and size of cracks on the specimen’s surface to become larger.

The aircraft wake vortex is an important factor affecting flight safety; as an important part of the aircraft, the powered nacelle will inevitably have an important impact on the aircraft wake vortex, so it is of great practical significance to research it. The present study focused on the numerical simulation of the wake flow of large aircraft (as the front aircraft) and the comparative analysis of the influence of engine jets on the wake flow. In order to meet the accuracy requirements and control the consumption of computing resources, LES and RANS methods were compared, and the RANS method was finally selected for subsequent calculation. The dynamic effect of jet flow was simulated by simplifying the boundary conditions of the inlet fan and outlet bypass as the mass flow boundary condition. The simulation results showed that the engine nacelle will have a significant impact on the morphology of the aircraft wake flow (position and strength of the main vortex in the wake flow system), which is caused by the vortices formed under the shear flow and separated flow of the nacelle. However, the nacelle will not significantly change the total strength of the wake vortex (half-plane circulation). The engine jet intensity causes additional turbulent mixing, which will accelerate the fusion of the nacelle vortex and ultimately change the intensity ratio of the inner wing vortex and the wingtip vortex, affecting the trajectory of the wake of the mean vortex. The study provides a corresponding reference for the following research on a wake vortex by a powered nacelle.

The characteristic of delayed airfoil stalls caused by the bio-inspired Wavy Leading-Edges (WLEs) has attracted extensive attention. This paper investigated the effect of WLEs on the aerodynamic performance and flow topologies of the airfoil through wind tunnel experiments, while also discussing the flow control mechanism of WLEs. The result shows that, at small Angle of Attack (AOA), the flow through the WLEs exhibits periodic and symmetrical characteristics, where flow vortices upwash at the trough and downwash at the crest, resulting in flow from the crest to the trough. Upwash leads to the formation of a localized three-dimensional laminar separation bubble (LSB) structure at the leading edge of the trough section. At large AOA after baseline airfoil stall, the flow on the airfoil surface of WLEs presents a two-period pattern along the spanwise direction, and the separation zone and the attachment zone appear alternately, indicating that the control effect of delayed stall is accomplished by reducing the separation zone on the airfoil surface. The alternating occurrence of the separation and attachment zones is the result of intricate interactions among flows passing through multiple WLEs. This interaction causes the convergence of high-momentum attached airflows on both sides, thereby constraining the spread of the separation from the leading edge and enabling the re-attachment of separated air. The research results of this paper provide a reference for researchers to reveal the flow control mechanism of WLEs more comprehensively.

At cryogenic temperatures, gases exhibit significant deviations from ideal behaviour, and the commonly employed gas model may inadequately represent the thermodynamic properties of cryogenic gases, subsequently impacting numerical simulations using various thermodynamic and transport models at cryogenic temperatures. The findings of this study reveal that the relative errors in aerodynamic characteristics obtained through different isentropic relations are noteworthy, with the maximum relative error in the drag coefficient reaching 16%. The impact of the equation of state, viscosity model, and thermal conductivity model is relatively minor, with relative errors in the pressure drag coefficient and viscous drag coefficient remaining well below 1%. Nevertheless, the relative error in the skin friction coefficient cannot be ignored due to transonic shock wave/boundary layer interactions. Consequently, when conducting numerical simulations of cryogenic flow, it is imperative to select appropriate gas models to attain precise results.

This research investigated the impact of complex low-speed wake flow structures on the aerodynamic characteristics of objects downstream. It employed the proper orthogonal decomposition (POD) method and the domain precursor simulation method to compare traditional methods and validate this approach. The study generated several flow structures of parallel dual-cylinder wakes with different scales and spacing. The variations in the aerodynamic coefficient of three downstream objects at various times passing through wakes of varying scales were appropriately compared and analyzed. The study established that the wake with a cylinder spacing of G = 1.5 has a more compact and concentrated modal structure than that with a cylinder spacing of G = 0.35. Smaller objects were more responsive to the wake flow structure with a spacing of G = 1.5, whereas larger objects responded more to the flow structure with a spacing of G = 0.35. The achieved results also revealed that the aerodynamic force coefficients of objects passing through the wakefield at different times were closely related to the temporal characteristics of the wake flow structure with different scales.

Transonic buffet is a phenomenon of large self-excited shock oscillations caused by shock wave-boundary layer interaction, which is one of the common flow instability problems in aeronautical engineering. This phenomenon involves unsteady flow, which makes optimal design more difficult. In this paper, aerodynamic shape optimization design is combined with reinforcement learning to address the problem of transonic buffet. Using the deep deterministic policy gradient (DDPG) algorithm, a reinforcement learning-based design framework for airfoil shape optimization was constructed to achieve effective suppression of transonic buffet. The aerodynamic characteristics of the airfoil were calculated by the computational fluid dynamics (CFD) method. After optimization, the buffet onset angles of attack of the airfoils NACA0012 and RAE2822 were improved by 2° and 1.2° respectively, and the lift-drag ratios improved by 83.5% and 30% respectively. Summarizing and verifying the optimization results, three general conclusions can be drawn to improve the buffet performance: (1) narrowing of the leading edge of the airfoil; (2) situating the maximum thickness position at approximately 0.4 times the chord length; (3) increasing the thickness of the trailing edge within a certain range. This paper established a reinforcement learning-based unsteady optimal design method that enables the optimization of unsteady problems, including buffet.

Lossy dielectric bars have potential applications in high power microwave (HPM) radiation-effect experiments performed in wind tunnels. Under plane excitation, beat wave patterns are observed along lossy and lossless dielectric bars in 3-D electromagnetic simulation results. Mode analysis is performed to clarify the two main modes in the beat waves—the leaky and guided modes. Comparisons are made between the theoretical and simulated results and acceptable agreements are obtained. The absorbing array of lossy dielectric bars is further investigated. The array can attenuate 90% of the microwave power at 10 GHz when a ten-meter series of such arrays is arranged. It is expected that the proposed absorbing array can achieve the required attenuation, considering that the testing object under microwave radiation is also an absorbing structure itself.

W-NiTi tungsten heavy alloys were prepared by an infiltration process using submicron W powders, and the effect of sintering temperatures on grain-coarsening behaviors and the mechanical properties of W-NiTi tungsten heavy alloys were investigated. The microstructures and mechanical properties were investigated using scanning electron microscopy, X-ray diffraction and compression tests. The results showed that tungsten particles were uniformly distributed in the NiTi binder. The W-NiTi tungsten heavy alloys consisted of B19′-NiTi and body-centered cubic W phases. The average tungsten particle sizes of W-NiTi tungsten heavy alloys sintered at 1400 °C, 1480 °C and 1560 °C were 2.62 μm, 4.04 μm and 5.20 μm, respectively. The average tungsten particle size increased with sintering temperatures, while the densities decreased at higher temperatures. The cavities retained in the W-NiTi tungsten heavy alloy sintered at 1560 °C, which degraded the mechanical properties. The calculated grain growth activation energy of W particles in the NiTi binder was 330 kJ/mol, which was higher than those in conventional W-NiFe and W-NiCo tungsten heavy alloys. The higher activation energy means more difficult diffusion process of W atoms in NiTi binders during sintering. Therefore, finer-grained heavy tungsten alloys were more easily obtained by using NiTi binders. Yield strength of W-NiTi tungsten heavy alloys decreased with increasing sintering temperatures due to coarsened tungsten particles.

The effect of the Reynolds number on the flying wing common research model with a large sweep angle and small aspect ratio is studied by numerical simulation. The helicity cross-flow transition correction of the Langtry–Menter model is established in view of the deficient prediction accuracies of existing transition prediction models in simulating cross-flow transition, and the helicity parameters are calibrated to improve the prediction accuracy of the numerical method. The transition prediction method is verified by the test results of the standard model transition of the DLR-F5 wing and small-aspect-ratio flying wing. At the same time, the numerical method is effectively verified by comparing it to the aerodynamic/torque results of the standard model of the small-aspect-ratio flying wing. On this basis, the variation laws with the Reynolds number are analyzed for the aerodynamic and flow field characteristics of the flying wing common research model with a large sweep angle and small aspect ratio. The numerical simulation is mainly carried out in the high subsonic speed range (M = 0.9), and the simulated Reynolds number range is from 2 × 106 to 80 × 106, which includes the test Reynolds number and flight Reynolds number. The influence of turbulence on the surface flow pattern and drag characteristics of the small-aspect-ratio standard model is analyzed. Calculation results show that when the turbulence is greater than 0.4%, it has a considerable influence on the surface laminar flow range and total drag coefficient. The results reveal that the Reynolds number mainly affects the magnitude of friction in the cruise state (small angle of attack). The problem of the Reynolds number in the self-aligning region of the flying wing standard model with a small aspect ratio is further studied, and the Reynolds number is found to be greater than 10 × 106. The drag and lift coefficients after the approach are close to the Reynolds number in the self-aligning region of the flying wing standard model with a small aspect ratio.