圆形坚冰影响翼型气动性能的数值分析

本文用FLUENT软件模拟了结冰后NACA 0012翼型周围流场的变化,并与结冰前NACA 0012翼型的气动性能进行了对比.工作中首先以未结冰的NACA 0012翼型(干净翼型)为标准模型进行了数值验证计算,再以经过检验的方法计算结冰模型,并与结冰风洞试验数据进行了对比.本文计算攻角为0°～20°,温度为250.37K,雷诺数为2,400,000,冰型为圆形坚冰.通过对比升力阻力性能,发现与干净翼型相比,结冰翼型的最大升力系数大约减少了50%,阻力系数增加了约65%,失速攻角降低了4°.结冰后翼型提前失速是造成气动性能恶化的主要原因.     

Effects of Gurney Flaps on a NACA0012 Airfoil

Experimental measurements of surface pressure distributions and wake profiles were obtained for a NACA0012 airfoil to determine the lift, drag, and pitching-moment coefficients for various configurations. The addition of a Gurney flap increased the maximum lift coefficient from 1.37 to 1.74, however there was a drag increment at low-to-moderate lift coefficient. In addition, the boundary layer profile measurements were taken using a rake of total pressure probes at the 90% chord location on the suction side. The effective Gurney flap height is about 2% of chord length, which provides the highest lift-to-drag ratio among the investigated configurations when compared with the clean NACA0012 airfoil. In this case, the device remains within the boundary layer. This revised version was published online in July 2006 with corrections to the Cover Date.     

A comparative investigation of hydrofoil at angles of attack

In this paper, a numerical investigation of incompressible flow around a hydrofoil is presented. The laminar flow was modeled at different angles of attack. Momentum and continuity equations were coupled by the artificial compressibility scheme. In finite‐volume method, convective fluxes were calculated and compared by four schemes. Flux averaging with pressure correction was used. The other characteristic‐based (CB) methods consisted of Roe scheme and original CB scheme. A revised CB scheme was implemented in this research, which demonstrated very accurate solutions with respect to others. The results confirmed the superiority of the revised upwind scheme regarding accuracy and convergence without any requirement to artificial viscosity. The problem was studied at high Reynolds numbers at the onset of turbulence. For time discretization, the fifth‐order Runge–Kutta scheme was used. Results were compared with those of others in which good agreement was observed. Numerical experiments were performed on the NACA0012 hydrofoil. Copyright © 2011 John Wiley & Sons, Ltd.     

Self-sustained aeroelastic oscillations of a NACA0012 airfoil at low-to-moderate Reynolds numbers

A wind tunnel experimental investigation of self-sustained oscillations of an aeroelastic NACA0012 airfoil occurring in the transitional Re regime is presented. To the authors’ knowledge this is the first time that aeroelastic limit cycle oscillations (LCOs) associated with low Re effects have been systematically studied and reported in the public literature. While the aeroelastic apparatus is capable of two-degree-of-freedom pitch-plunge motion, the present work concerns only the motion of the airfoil when it is constrained to rotate in pure pitch. The structural stiffness is varied as well as the position of the elastic axis; other parameters such as surface roughness, turbulence intensity and initial conditions are also briefly discussed. In conjunction with the pitch measurements, the flow is also recorded using hot-wire anemometry located in the wake at a distance of one chord aft of the trailing edge. It is observed that for a limited range of chord-based Reynolds numbers, 4.5×10⁴Re_c1.3×10⁵, steady state self-sustained oscillations are observed. Below and above that range, these oscillations do not appear. They are characterized by a well-behaved harmonic motion, whose frequency can be related to the aeroelastic natural frequency, low amplitude (θ_max<5.5°) and some sensitivity to flow perturbations and initial conditions. Furthermore, hot-wire measurements for the wing held fixed show that no periodicity in the undisturbed free-stream nor in the wake account for the oscillations. Overall, these observations suggest that laminar separation plays a role in the oscillations, either in the form of trailing edge separation or due to the presence of a laminar separation bubble.