等离子体激励对低雷诺数下翼型层流分离特性的影响及机理研究

There has been an increasing interest in the design and performance of airfoils operating in low Reynolds number flows. This interest has been a result of the desire to improve the low-speed performance of high-aspect-ratio sail plane wings, unmanned aerial vehicles, ultra-light micro-aircrafts, and wind turbine blades. Many significant aerodynamic problems including nonlinearities in the lift-curve characteristics, undesirable sharp decrease in lift-to-drag ratio, and static hysteresis in the section lift, drag and moment data appear to occur below chord Reynolds numbers of about 200,000. How the low Reynolds number performance of airfoils could be improved has been an urgent problem in the field of aeronautical engineering. Flow control with plasma has received growing attention because of its less space occupation, flexibility, broader frequency bandwidths, relatively low energy consumption and high efficiency. Based on the aforementioned background, the primary objective of the present research is to obtain the effects of dielectric barrier discharge plasma actuators on separation control of laminar boundary layer bubble over the specific airfoils with the wind tunnel testing methodology. Both Alternating Current (AC-) and Nanosecond Pulse (NS-) driven plasma will be examined in order to eliminate or control the laminar separation bubbles as well as improving the low Reynolds number performance of these specific airfoils. A deeper insight into the underlying physical mechanisms will be obtained by studying the time-averaged and instantaneous structure and dynamics of the laminar separation bubbles.

低雷诺数下翼型气动性能的改善对滑翔机、高空无人飞行器、直升机、微型飞行器、风力机等性能的提升有着重要的意义。当基于弦长的雷诺数低于200,000 时，翼型上会出现升力在零度附近随迎角非线性变化、最大升阻比迅速降低、力/力矩随迎角变化出现静态滞回等典型的低雷诺数空气动力学问题。当选取的翼型几何外形确定后，如何通过有效的流动控制技术来改善其在低雷诺数下的气动力特性是航空领域期待解决的问题。等离子体流动控制具有小体积、灵活多样、易于大面积放置的激励器，还具有宽频、小能量和高效率的电学特性。本项目通过正弦交流与纳秒脉冲两种不同介质阻挡放电等离子体激励，对选取的典型翼型进行流动控制风洞实验研究，通过对低雷诺数下翼型上广泛存在的前缘/后缘层流分离泡进行控制，期望对翼型气动力特性产生好的影响。通过对等离子体激励下层流分离泡的瞬时与时均形态的变化的研究给出流动控制机理解释。

低雷诺数下翼型气动性能的改善对滑翔机、高空无人飞行器、直升机、微型飞行器、风力机等性能的提升有着重要的意义。当基于翼型弦长的雷诺数低于200,000 时，翼型上会出现升力在零度附近随迎角非线性变化、最大升阻比迅速降低、力/力矩随迎角变化出现静态滞回等典型的空气动力现象。本项目研究目为通过有效的等离子体流动控制技术来改善其现有低雷诺数翼型的气动力特性，并对流动控制机制进行研究。..主要内容包括：（1）连续交流（AC-）与纳秒脉冲（NS-）介质阻挡放电（DBD）等离子体气动激励时产生的电磁学特性的研究；（2）典型对称、非对称翼型低雷诺数下的瞬时与时均气动特性研究；（3）等离子体定常与非定常激励下翼型层流分离、转捩、再附变化特性以及相应升/阻力、力矩变化特性研究。..研究结果发现：低雷诺数下，AC-DBD等离子体对于层流分离和气泡有着明显的影响，而NS-DBD主要的气动效应为瞬时压力波和时均热效应，其对低雷诺下的层流及转捩气泡影响很小。..对称椭圆翼型的AC-DBD等离子体流动控制研究结果表明：当翼型上表面仅发生层流分离时，等离子体激励和转捩带的作用类似，可以有效延迟或者消除后缘层流分离，从而增加升力；当翼型上表面出现层流分离气泡并发生再附现象时，等离子体可以有效减小或者消除层流分离泡的范围，从而减小升力；通过控制层流分离，占空循环等离子体激励可以实现对低雷诺数小迎角下的升力的线性控制。带弯度FX 63-137翼型的等离子体流动控制研究结果表明：上表面的层流分离气泡延迟了迎角上升过程的失速过程，而对于迎角的下降过程，流动无法建立与迎角上升过程相同的层流分离气泡，从而导致迎角增大与减小过程中升力和阻力的静态迟滞现象。等离子体激励可以显著影响层流分离气泡，从而可以消除和减小升力和阻力的静态迟滞现象。..本项目研究结果有助于细致了解低雷诺数范围内翼面层流气泡瞬时和时均特性、以及等离子体气动激励下诱导气流与分离气泡的相互作用机制，对于具有明显低雷诺数气动效应的飞行器的设计和优化有着重要的参考意义。