中低雷诺数翼型流动特征及气动噪声机理研究

THE AIRFOIL FLOW CHARACTERISTICS AND THE AERODYNAMIC NOISE MECHANISM AT LOW TO MEDIUM REYNOLDS NUMBERS

刘骁敏

11849099

硕士

航天工程

刘宇

2020-05-28

2020-05-28

哈尔滨工业大学

深圳

翼型的气动性能及噪声特征是飞机、发动机、风力机等各类流体机械设计的基本参数。小型风力机及微小型无人机通常在中低雷诺数下工作，且工作环境较为复杂，经常会遇到局部气流失速工况。另外，噪声性能目前也越来越受到人们的重视。因此，中低雷诺数下，从附着流动到失速流动状态的翼型流动特征及气动噪声机理的研究，对于这些相关气动部件的优化设计具有重要意义。本文选取了NACA 0012翼型作为研究对象，分析了其在不同攻角下的空气动力学特征、远场噪声特征、PIV可视化流场特征及其关联性。该研究在南方科技大学力学与航空航天工程系气动声学风洞开口测试段中进行。实验研究选取了来流速度10m/s和25m/s分别代表低雷诺数和中雷诺数工作点，攻角设置为递增及递减两个过程来研究翼型的迟滞效应，采用天平与PIV对翼型气动性能及流场进行了测试，采用麦克风对噪声特征进行了研究。最后，通过对远场噪声和流场特征进行同步采集，选取了若干代表性攻角，即有效攻角为0°、2.56°、4.90°、10.55°、14.28°、16.22°、23.21°对翼型噪声机理进行了分析。NACA 0012为典型的前缘失速翼型，有效攻角0°时流场呈现明显的对称结构。升力系数随攻角变化趋势与PIV测得的流场边界层速度变化及速度波动变化特征相一致。通过连续时刻的瞬时流场特征测量，可以清楚的观察到翼型表面涡结构的运动状态与轨迹。10 m/s时测得的远场噪声主要集中在100~1000 Hz的低频部分，中高频部分声压级始终维持在0 dB左右。有效攻角0°时即流场对称及小攻角时存在明显的纯音噪声。在有效攻角10.55°之后，总声压级随流速增大呈现明显的线性增加趋势。而25 m/s时有效攻角0°下不再存在纯音噪声，且大攻角时总声压级与升力系数的一致性较为明显。对来流速度10m/s时不同攻角下的翼型流场特征与远场噪声特征频谱进行了对比分析。比较了边界层法向速度波动频谱与同步采集的噪声频谱，发现小攻角时翼型的低频纯音噪声主要是由于尾缘处翼型表面气流速度波动造成的。在对称流动状态，翼型压力侧与吸力侧周期性流动对纯音噪声均有贡献。在非对称流动状态，翼型纯音噪声主要由压力侧周期性流动贡献。在翼型失速状态，翼型上没有纯音噪声，翼型前缘及尾缘附近只有湍流流动的宽频特征，没有观察到周期性流动特征。

The aerodynamic performance and aeroacoustic characteristics of the airfoil are the fundamental parameters for the design of various types of fluid machinery such as airplanes, engines, and wind turbines. Small scale wind turbines and micro-mini drones are popular in recent years, which are usually operated at low to medium Reynolds numbers and complex flow conditions, in which the arifoil encounters local stall. In addition, the noise performance has attracted more and more attention. Therefore, study of airfoil flow characteristics and aeroacoustic mechanism from attached to stall flow conditions at low-to-medium Reynolds numbers is of great significance for the optimal design of these related aerodynamic components.In this paper, the NACA 0012 airfoil is selected as the experimental model, and its aerodynamic characteristics, the far-field noise features, the flow field obtaiend by Particle Image Velocimetry (PIV), and the correlation between flow field and noise at different angles of attack are studied. The hysteresis effects of the airfoil was studied by increasing and decreasing the angle of attack. The experiments were conducted in the open-jet test section of the aeroacoustic wind tunnel at Mechanics and Aerospacer Engineering Department, Southern University of Science and Technology. The experiment surveyed the in the trend of the aerodynamic performance and aeroacoustic characteristics of the airfoil during versus the angle of attack at the inflow speed of 10 m/s and 25 m/s, and the effects of the inflow velocity on the noise characteristics of airfoil when the effective angle of attack is 0°, 2.56°, 4.90°, 10.55°, 14.28°, 16.22° and 23.21°. The far-field noise and flow field measurements were syschrolized and analized for the noise generation mechanism. NACA 0012 airfoil features the typical leading-edge stall characteristics. The flow structures show obvious symmetrical events when the effective angle of attack is 0°. The trend of lift coefficient versus angle of attack is consistent with that of the velocity measured by PIV around the airfoil. Through measurements of the instantaneous flow field, the convection and trajectory of the vortex structure on the airfoil surface can be clearly observed. The far-field noise measured at 10 m/s is mainly concentrated in the low-frequency part of 100 ~ 1000 Hz, and the sound pressure level in the middle and high-frequency part is always maintained at about 0 dB. There is obvious tonal noise when the effective angle of attack is 0° small angles of attack. After an effective angle of attack reaches 10.55 °, the overall sound pressure level shows a clear linear increasing trend versus the flow velocity. When the inflow velocity is 25m/s, there is no tonal noise observed at α_eff=0°, and the consistency between the overall sound pressure level and the lift coefficient at large angles of attack is more obvious. The frequency spectrum of the airfoil flow field characteristics and the far field noise characteristics under different conditions at an incoming flow velocity of 10 m/s were compared and analyzed. By comparing the velocity fluctuation spectrum to the noise spectrum, it was found that the low frequency tonal noise generated at a small angle of attack is mainly caused by the velocity fluctuation of the airflow near the trailing edge. In the symmetric flow conditon, the periodic flow on the pressure and suction sides of the airfoil both contribute to tonal noise. In the asymmetric flow condition, the airfoil tonal noise is mainly contributed by the periodic flow on the pressure side. During the airfoil stall condition, there is no tonal noise on the airfoil. consistently, only the broad-band characteristics of turbulent flow near the leading edge and trailing edge of the airfoil were observed, and no periodic flow characteristics were detected.

翼型附着流动噪声 翼型失速噪声 翼型气动性能 翼型噪声特征

airfoil noise during attached flow condition airfoil noise during stall condition aerodynamic performance of airfoil aeroacoustic characteristics of airfoil

中文

联合培养

南方科技大学

刘骁敏. 中低雷诺数翼型流动特征及气动噪声机理研究[D]. 深圳. 哈尔滨工业大学,2020.