The surface of stainless-steel (SS) mesh was modified by growing carbon nanotubes (CNTs) from ethanol flame. The CNT-modified SS mesh was then used as a heating element for the resistance welding of glass-fibre-reinforced polyetherimide (GF/PEI) laminates to improve the interfacial bond strength of SS wire and PEI resin. Interfacial microstructure, the mechanical properties of the welded joint and the effects of CNT growth time (t_g ) on the wettability of PEI resin solution to SS wire were investigated. The results indicate that the addition of CNTs increased wettability due to the capillary action of high-porosity CNT coating. The microstructure of the welded joints changed with t_g , and the thickness of the welding implant layer decreased below t_g = 10 min, and the maximum single lap shear strength (SLSS) value of the welded joint was 39.2 MPa when t_g = 10 min. The strengthening mechanism of CNTs and the failure modes of the welded joints were also elucidated in detail by the interfacial shear strength (IFSS) between SS wire, PEI resin and the fractography analysis.

The emphasis of this review is to discuss three peculiar phenomena of bubbles rising in viscoelastic fluids, namely, the formation of a cusp, negative wake, and velocity jump discontinuity, and to highlight the possible future directions of the subject. The mechanism and influencing factors of these three peculiar phenomena have been discussed in detail in this review. The evolution of the bubble shape is mainly related to the viscoelasticity of the fluid. However, the mechanisms of the two-dimensional cusp, tip-streaming, “blade-edge” tip, “fish-bone” tip, and the phenomenon of the tail breaking into two different threads, in some special viscoelastic fluids, are not understood clearly. The origin of the negative wake behind the bubbles rising in a viscoelastic fluid can be attributed to the synergistic effect of the liquid-phase viscoelasticity, and the bubbles are large enough; thus, leading to a very long relaxation time taken by the viscoelastic stresses. For the phenomenon of bubble velocity jump discontinuity, viscoelasticity is the most critical factor, and the cusp of the bubbles and the surface modifications play only ancillary roles. It has also been observed that a negative wake does not cause velocity jump discontinuity.

The unsteady motion behavior of oil/gas two-phase flow in a novel ventless bearing chamber has significant impacts on the lubrication and heat transfer efficiency of bearings due to the various advantages of lower pressure levels and weaker rotating airflow effects. In this paper, the unsteady motion behavior of oil/gas two-phase flow in a ventless aero-engine bearing chamber is investigated by three-dimensional numerical simulation through the volume of fluid (VOF) method, and the numerical method is verified using published experimental data. The flow characteristics of oil/gas two-phase in the secondary flow and three-dimensional flow are investigated. The results show the evolution of vortices and the transition of the driving mode in the unsteady motion of oil/gas two-phase flow, and a criterion for the shift of the driving mode at different rotor speeds is proposed. As the rotation speed increases, the variation trend of the velocity field and pressure field of oil/gas two-phase flow is consistent, and the accumulation region of oil becomes inconspicuous. The results indicate a reference for enhancing the performance of lubrication systems for aero-engines.

Helicopter trim models are multivariate nonlinear equations and it is difficult to determine these initial trim points comparable to flight conditions. To solve this question, a hybrid genetic algorithm is presented in this paper, that combines the quick convergence ability of the quasi-Newton method and the advantages of genetic algorithm, such as global convergence. The trim control vector and the constraint conditions were established in the coordinated-turn based on the helicopter flight dynamic model. The coordinated turn flight of a UH-60 A helicopter was taken as an example to simulate on the experimental platform. Comparisons were made between the trim results and flight test data and there is a good agreement among them, and the efficiency of the algorithm presented is verified. It is a general method that can be applied to trim the helicopter of different flight conditions.

To control precisely and investigate maneuverability of an underwater vehicle in a nuclear power pool this article presents a study on the mathematical model and the thrust characteristics of a ducted propeller under the quasi-cavitation effect by a numerical method. Firstly, a mathematical model of a ducted propeller including the quasi-cavitation effect term which is often ignored, is established based on the thrust performance under different quasi-cavitation distances and the revolution speed by CFD. Then the pressure field near the suction and pressure surface of blades are analyzed, which reveals that the thrust increases with a decrease of the quasi-cavitation distance. Finally, the thrust performances under different conditions are experimentally measured in an open-water pool, which can verify the reliability of the mathematical model below the error of 10%. The results demonstrates that the presented method can be used to evaluate the dynamic mechanism of a propeller, and hold a potential to improve the control strategy.