Using linear stability theory (LST) and direct numerical simulation (DNS), the linear evolution and oblique breakdown of Mack's second mode in Mach 4.5 boundary layer flows over convex walls are investigated through comparative analyses with flat plate boundary layer flows, revealing the influence mechanism of convex curvature on different stages of the second mode transition. Analysis of the linear growth stage indicates that convex curvature significantly suppresses linear disturbance growth, with the suppression intensity increasing as the radius of curvature decreases; convex curvature shifts the unstable frequency band of the second mode upward, but reduces the maximum growth rate; LST can qualitatively reflect the change of stability through the influence of curvature on basic flow. For the analysis of nonlinear saturation and breakdown, convex curvature has almost no suppression effect on disturbance amplitudes at the nonlinear saturation stage, but prolongs this stage, thereby delaying breakdown; meanwhile, convex curvature promotes the generation of higher-order harmonics at the nonlinear saturation stage. Furthermore, statistical analysis indicates that from the nonlinear saturation stage to the turbulent stage, convex curvature significantly weakens the intensity of Reynolds shear stress and turbulent kinetic energy generation, and simultaneously reduces skin friction.
The novel ground-based magnetically levitated electromagnetic propulsion high-speed scientific research and test facility (referred to as the electromagnetic sled) provides a new approach for aerodynamic tests of high-speed equipment such as aircraft. To address the core key issue of mathematical characterization of aerodynamic drag, lift and pitching moment of the electromagnetic sled vehicle body, this paper conducts a systematic analysis on the aerodynamic characteristics of the facility’s vehicle body under subsonic and transonic operating conditions based on the three-dimensional viscous compressible Navier–Stokes equations. By analyzing flow field contours and comparing aerodynamic forces, the influences of operating speed, ground effect and pitching angle variation on the aerodynamic characteristics of the electromagnetic propulsion facility are investigated.The results show that the ground effect significantly increases the aerodynamic lift of the vehicle body, and a reasonably designed vehicle fairing can effectively reduce aerodynamic lift and balance the pitching moment. When the vehicle operates at supersonic speed, obvious shock waves are generated at the head; the aerodynamic drag increases significantly with the increase of Mach number, the aerodynamic lift first decreases and then increases with increasing Mach number, and the pitching moment exhibits complex variation characteristics. The numerical simulation results can provide important technical support for the optimal design of super-high-speed maglev electromagnetic propulsion facility.
To improve the efficiency and flexibility of airfoil design, this paper proposes an airfoil generation method based on denoising diffusion probabilistic models (DDPM), named Airfoil-DDPM. This method does not rely on traditional parameterization methods. It uses a diffusion model to directly learn airfoil geometric features and generate airfoils. Thus, it avoids the limitation of preset parameter functions on shape diversity. By combining U-Net and an attention mechanism, the model accurately captures the geometric details of training samples. The generated airfoils have smooth surfaces and continuous curvature. Experimental results on the UIUC airfoil dataset show that the geometric error of the airfoils generated by Airfoil-DDPM is less than 5u00D710u22123. When generating airfoils, the method not only reproduces the geometric features of NACA 0012 and RAE 2822 airfoils with high accuracy, but also meets their aerodynamic performance requirements. Principal component analysis visualization and target space analysis further show that the samples generated by Airfoil-DDPM cover the entire feature space of the UIUC dataset. They are also distributed over a wider range of lift and drag coefficients. This demonstrates its significant advantage in design diversity. This study provides an efficient and flexible parameterization-free solution for airfoil generation. It is helpful for promoting research on aircraft design and optimization.
As one of the core components in wind-to-electric energy conversion systems, wind turbine generators are rapidly expanding in global deployment. Blade icing, a phenomenon that severely compromises operational efficiency, has emerged as a critical challenge for the industry. With the growing demand for wind energy, turbine sizes have increased significantly, yet research on full-scale turbine icing characteristics and anti-icing strategies remains limited. Therefore, this study employs numerical simulations to investigate the icing distribution characteristics of a three-dimensional, large-scale wind turbine with a 200 m rotor diameter. The simulation results are compared with natural icing observations from unmanned aerial vehicles to analyze the aerodynamic impact of icing on large-scale wind turbines, and to determine the anti-icing zones and strategies. Results indicate that ice accretion predominantly occurs along the leading edge, and minor ice accretion can also be observed at the tipu2019s trailing edge due to local airfoil geometry. The maximum ice thickness decreases from the blade tip toward the root, and remains comparable at radial positions below 40% (r/Ru226440%) under different icing conditions. Based on these accretion patterns, the anti-icing zone is determined as s/clocalu22640.25. Within this zone, the blade leading edge is divided into several heating zones along the spanwise direction, and the required heat-flux-density distribution is further analyzed. The results show that the closer the heating zone is to the blade tip, the higher the required heat flux density. For the same heating zone, the greater the temperature difference between the anti-icing temperature and the ambient icing temperature, the higher the required heat flux density. For example, at an ambient icing temperature of 255 K, zone1 near the blade tip requires 55 kW/m2 when the surface temperature is 318 K, but only 16 kW/m2 at 278 K. These findings provide a reference for determining anti-icing zones and designing anti-icing power for large-scale wind turbine blades.
To reveal the energy transport mechanisms over the compression ramp of a supersonic inlet under shock-wave/boundary-layer interaction (SBLI)
