Chinese Journal of Aeronautics最新文献

An electromagnetic coil topology and its control strategy, which can be incorporated into the electromagnetic docking device, have been proposed for the relative roll control of two satellites in space. The target satellite and the chaser satellite are respectively embarked with four and six coils evenly arranged around the docking axis. All the coils on the target satellite are Direct Current (DC) energized, while the currents in the coils of the chaser satellite are regulated to achieve the relative roll control. The electromagnetic force/torque model is built by utilizing the frequently-used far field model. Based on the fundamental components extracted from that model, this paper proposes a real-time magnetic moment vector distribution formula that simply generates a constant roll torque. This paper not only presents an equation for calculating the relative roll angle through the Euler angles of two satellites, but also an equation that converts the roll torque setpoint to the setpoints of the coil currents. A 3-closed-loop positioning controller composed of angle, angular velocity, and current loop is developed. The proposed topology is verified by finite element simulation, and the control strategy is validated by dynamics simulation and ground-based tests.

The internal friction of floating spline can cause self-excited vibration of a supercritical flexible rotor system. To address this issue, a high-efficiency dynamic modeling method is proposed to investigate the self-excited vibration behavior and instability evolution of the rotor. Experiments are conducted to validate the theoretical results. The coupled dynamic equations for the rotor system connected with the floating spline are derived through the combination of finite element method and lumped parameter model. A hybrid numerical approach of precise integration and Runge-Kutta method is adopted to examine the effects of the friction coefficient of spline’s tooth surface, torque, and eccentricity on the self-excited vibration of the rotor system. The results show that the spline friction leads to negative damping and inputs energy into the rotor system under supercritical conditions, triggering self-excited vibration when the input energy exceeds a specific level. With the same parameters, the experimentally obtained axial trajectory and primary frequency components are consistent with the theoretical results, verifying the accuracy of the proposed theoretical model. This study can serve as a useful theoretical guide for the dynamic stability design of flexible rotor systems with the floating spline.

For the second-order finite volume method, implicit schemes and reconstruction methods are two main algorithms which influence the robustness and efficiency of the numerical simulations of compressible turbulent flows. In this paper, a compact least-squares reconstruction method is proposed to calculate the gradients for the distribution of flow field variables approximation. The compactness of the new reconstruction method is reflected in the gradient calculation process. The geometries of the face-neighboring elements are no longer utilized, and the weighted average values at the centroid of the interfaces are used to calculate the gradients instead of the values at the centroid of the face-neighboring elements. Meanwhile, an exact Jacobian solving strategy is developed for implicit temporal discretization. The accurate processing of Jacobian matrix can extensively improve the invertibility of the Jacobian matrix and avoid introducing extra numerical errors. In addition, a modified Venkatakrishnan limiter is applied to deal with the shock which may appear in transonic flows and the applicability of the mentioned methods is enhanced further. The combination of the proposed methods makes the numerical simulations of turbulent flow converge rapidly and steadily with an adaptive increasing CFL number. The numerical results of several benchmarks indicate that the proposed methods perform well in terms of robustness, efficiency and accuracy, and have good application potential in turbulent flow simulations of complex configurations.

Space truss structures are essential components for space-based remote sensing loads with high spatial and temporal resolutions. To achieve high-precision vibration control, an accurate and efficient dynamics model is essential. In addition to the current equivalent beam model (EBM) based on the classical continuum theory, an improved equivalent beam model (IEBM) is proposed that considers the impact of the distinction between trusses and beams on torsional and shear deformations, as well as the impact of shear deformation on flexural rigidity. According to the displacement expressions of spatial beams, torsional, shear, and bending correction coefficients are introduced to derive expressions of strain energy and kinetic energy. The energy equivalence principle is then utilized to calculate the elasticity and inertia matrices, and dynamics equations are established using the finite element method. Subsequently, an IEBM is constructed by employing the particle swarm optimization approach to determine the correction coefficients with the truss natural frequency as the optimization target. The natural vibration characteristics of the structure are estimated for various material properties. Compared with the full-scale finite element model, the EBM reaches a maximum error of 80% for a low modulus of elasticity, while the maximum error of the IEBM is less than 2% for any given parameters, indicating its superior accuracy to the EBM.

Scallop ice is a special phenomenon that occurs during swept wing aircraft passing through icing clouds. It poses a great challenge for the icing safety assessment that the complex scallop ice shape feature and its mechanism are still unclear. In this work, a large-scale icing wind tunnel experiment of swept wing designed by NACA0012 airfoil is conducted in the Icing Wind Tunnel of China Aerodynamics Research and Development Center. The detailed three-dimensional ice shapes under 0°, 15°, 30° and 45° swept angles are obtained by laser scanning technology. The experimental results show that with the swept angle increasing from 0° to 45°, the 2D double ice horn structures show certain spanwise variation, and finally transform into complete scallop ice with ice thickness greatly enhanced in the stagnation line region. The empirical mode decomposition of the spanwise ice curve captures the high-frequency fluctuation on the scallop ice caused by the small-scale roughness element, while the trend with low frequency is not obvious. Based on the experimental data, a new complete scallop ice geometric model, named 5Points-5Lines-2Arcs (5P-5L-2A) model, is proposed, which can provide important basis for the quantitative description of complex scallop ice shape.