基于Theodorsen理论的新型动态失速预测模型及其应用

风力机叶片动态失速时的非定常气动特性及严重的迟滞现象使得风力机功率实测值严重偏离其静态预测值。鉴于此,基于Theodorsen理论、基尔霍夫势流理论,在忽略低阶附加质量引起的下洗气流加速度项及状态变量转换后,提出一种包括翼型附着流和后缘动态分离流的新型动态失速模型。利用该模型分析NREL 5 MW海上风力机叶片6种翼型的非定常动态失速特性得出：通过翼型的气流在完全附着流与完全分离流之间不断转换,受附着流脱落尾诱导的动态下洗气流影响及边界层动态分离产生的压力滞后的双重作用,动态升力系数变化曲线和静态升力现象曲线偏差较大,6种翼型动态升力系数变化曲线均呈非常明显的迟滞环现象。DU40、DU35、DU30、DU25、DU21和NACA64这6种翼型动态升力系数增幅明显,分别达17.6%、60.9%、60.7%、55.1%、63.7%和40.8%。动态失速攻角极大地超过静态失速攻角,分别增大到36.53°、21.40°、20.20°、17.68°、16.97°和21.42°。6种翼型动态失速预测结果与公开实验数据结论一致,证实所提出的动态失速气动模型计算结果准确可信,具有较强通用性。

NOVEL DYNAMIC STALL PREDICTION MODEL BASED ON THEODORSEN THEORY AND ITS APPLICATION

The unsteady aerodynamic characteristics and serious time-lag of wind turbine blades during dynamic stall made the actual measured value of rotor power seriously deviate from its static prediction value. Therefore, ignoring the acceleration term of downwash flow caused by low-order added mass and undergoing state variable transformation, a novel dynamic stall prediction model including airfoil attachment flow and dynamic separation flow of trailing edge was proposed based on Theodorsen theory and Kirchhoff potential flow theory. The model was used to analyze the unsteady dynamic stall characteristics of six airfoils from NREL 5 MW offshore wind turbine blades. The conclusions were as follows. The airflow through the airfoil continuously varied between the fully attached flow and the fully separated flow. Due to the dual effects of the dynamic downwash flow induced by the shedding trailing edge vortex of the attached flow and the pressure lag caused by the dynamic separation of the boundary layer, the variation curve of the dynamic lift coefficient and the static lift phenomenon curve deviated greatly. The dynamic lift coefficient curves of six airfoils showed a very obvious time-lag phenomenon. The dynamic lift coefficients of DU40, DU35, DU30, DU25, DU21 and NACA64 airfoils increased significantly, reaching 17.6%, 60.9%, 60.7%, 55.1%, 63.7% and 40.8% respectively. The dynamic stall angle of attack greatly exceeded the static stall angle of attack, increasing to 36.53°, 21.40°, 20.20°, 17.68°, 16.97° and 21.42° respectively. The prediction values of six airfoils were consistent with the conclusions of public experimental data, which proved that the calculation results of the proposed model were accurate, reliable and universal.