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中文核心期刊

自由涡尾迹方法中涡核尺寸对风力机气动计算的影响

INFLUENCE OF VORTEX CORE SIZE ON AERODYNAMIC CALCULATION OF WIND TURBINE IN FREE VORTEX WAKE METHOD

  • 摘要: 涡核模型中的涡核尺寸对自由涡尾迹(free vortex wake,FVW)方法准确预估风力机气动特性至关重要,涡核尺寸包括初始涡核半径和由于耗散效应涡核半径在尾迹中的增长.FVW方法中涡线控制方程离散采用三步三阶预估校正格式,涡核模型采用经典Lamb-Oseen模型,并考虑了涡耗散效应和拉伸效应.首先,通过气动载荷和叶尖涡涡量平均值的分析得到初始涡核半径的取值范围;然后,根据叶尖涡耗散特性的分析,确定体现涡黏性耗散效应涡核半径增长的经验常数的取值;最后,分析了涡核尺寸对叶尖涡结构的影响,进一步验证初始涡核半径和涡黏性耗散经验常数的取值对风力机气动计算的影响.结果表明:当初始涡核半径大于50%弦长时,FVW方法收敛稳定且能准确预估风轮气动载荷;综合风轮气动载荷和叶尖涡耗散特性,初始涡核半径取60%到70%弦长为宜,且对应的涡黏性耗散经验常数取值也不同;风轮气动载荷和叶尖涡结构的准确预估主要受初始涡核半径影响,经验常数对其影响不大,而经验常数主要影响风轮下游尾流场叶尖涡的耗散特性.

     

    Abstract: The vortex core size in the vortex core model is very important for the accurate prediction of aerodynamic characteristics of wind turbines by the free vortex wake (FVW) method. The vortex core size includes the initial radius of the vortex core and the radius variation due to the viscous dissipation effect. In the FVW method, to solve the convection equation of the vortex filaments numerically, the three-step and third-order predictor-corrector scheme was used to approximate the derivatives. The classical Lamb-Oseen model was adopted as the vortex core model in which the effects of viscous diffusion and stretching were taken into account. Firstly, the initial radius of the vortex core was determined through the analysis of the airload and the mean value of the tip vortex vorticity. Secondly, the empirical constant that reflects the increase of the vortex core radius was determined based on the tip vortex dissipation characteristics. Finally, the effect of vortex core size on the shape of tip vortex line was analysed to further verify the influence of the initial radius of the vortex core and the empirical constant that reflects the increase of the vortex core radius on aerodynamic calculation of wind turbine. The results show that when the initial vortex core size is greater than 50% of the chord length, the FVW model can produce a stabler convergent wake system and can accurately predict the blade airload. About 60% to 70% of the chord length is recommended as the initial vortex core size in order to take into account both the airload prediction and the wake dissipation characteristics. Different empirical constants of the viscous dissipation effect correspond to different initial vortex core sizes. The blade airload and the wake geometry are mainly affected by the initial vortex core size, rather than the empirical constant of the viscous dissipation effect. However, the empirical constant mainly affects the vortex disspiation characteristics in the downstream wake field.

     

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