Gurney襟翼对双三角翼气动特性影响的低速风洞实验研究

通过低速风洞实验研究了Gurney襟翼对双三角翼气动特性的影响,结果表明Gurney襟翼可以提高双三角翼的升力系数、最大升力系数以及中高升力系数情况下的升阻比。此外,进一步证实了Gurney襟翼的有效迎风面积是影响增升效果的主要因素。     

Structural design and model fabrication of cable-rib tensioned deployable parabolic cylindrical antenna

Deployable mechanisms with light weight and high storage ratio have received considerable attention for space applications. To meet the requirements of space missions, a parabolic cylindrical deployable antenna based on cable-rib tension structures is proposed and verified by a physical prototype. The parabolic cylindrical antenna adopts simple parallel four-bar mechanisms to construct the basic deployable unit, and the cylindrical direction dimension can be easily extended by modularization, which has obvious advantages in storage ratio and area density. Considering the complexity of the entire antenna structure design, including cable networks and flexible trusses, the form-finding design optimization model of a parabolic cylindrical antenna is established using the force density sensitivity method, and then the kinematics analysis of the deployable mechanism is carried out. Finally, a single-module prototype with a deployable diameter of 4 m × 2 m was designed and fabricated. The results of the ground deployment process test and surface accuracy measurements show that the antenna has good feasibility and practicability.     

Experimental study on transfer functions of an active rotor under different flight conditions

Vibrations impose negative impacts on the effectiveness and public acceptance of helicopters. Active rotors with trailing-edge flaps have been proved to be an effective way to actively eliminate helicopter vibrations. For the existing control algorithm based on offline system identification, the transfer functions of an active rotor under different flight conditions are pre-requisites to implement closed-loop vibration control. In this study, a three-bladed active rotor with improved trailing-edge flaps is designed, and wind-tunnel tests are conducted to identify the transfer functions of this active rotor using frequency sweep and phase sweep methods. The experimental results demonstrate that these transfer functions are insensitive to the variation of flight speeds: the amplitude of the transfer function varies slightly, while the phase delay almost remains unchanged. In addition, this finding is validated through closed-loop vibration control tests with the active rotor. The transfer function obtained from the hover test results is also applicable to closed-loop vibration control tests under the forward flight conditions. This will dramatically simplify the implementation and operation of an active rotor.