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- 2016
合成射流激励位置对控制翼型大攻角分离流动影响的数值研究
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Abstract:
针对合成射流的激励位置这一因素,以NACA0015翼型为研究对象,对大攻角(α=20°)下基于弦长的Re为8.96×105、单个合成射流激励位于翼型吸力面不同位置时的流场进行了二维非定常计算,并利用本征正交分解(POD)方法对计算结果进行了分析,阐释了相关控制机理。研究表明,合成射流的激励位置对翼型流动分离的控制效果有显著影响。当激励位置位于0.12至0.4倍弦长之间时,合成射流激励能有效抑制翼型流动分离,提升升力系数,降低阻力系数,升阻比最高提升293％,其中最优激励位置并不在普遍认为的控制前时均分离点附近,而在离分离点下游一定距离的分离区内部。对计算结果的POD分析表明,合成射流的引入改变了流场不同模态间的能量分配,能量由代表平均流动的一阶模态向代表流场中湍流大尺度结构的二阶及更高阶模态转移。合成射流的最佳激励位置与控制前流场二阶模态翼型吸力面附近的特征涡结构有关,要达到最佳的控制效果,合成射流激励应放置在特征涡结构的位置,若布置在下游或者较远的上游位置,则无控制效果。
For a NACA0015 airfoil, 2？？D unsteady flow fields are calculated when a synthetic jet is put at different locations on the suction surface at a large attack angle (α=20°) and Reynolds number of 8.96×105 based on chord length. POD (proper orthogonal decomposition) method is utilized to analyze the computation results, and relevant control mechanisms are explained. The results show that actuation location of a synthetic jet exerts significant influence on effects of flow separation control. When the actuator is located between 0.12 and 0.40 of chord length, flow separation on the airfoil is effectively suppressed, enhancing lift coefficient and reducing drag coefficient with lift to drag ratio increasing by 293％. The optimal location is not near the time？？averaged separation point as widely suggested but at some downstream locations inside the separation zone. POD analysis on computation results indicates that the introduction of synthetic jets would change the energy distribution among different modes, and that energy is transferred from 1st？？order mode representing mean flow to 2nd？？order mode or higher modes which represent large scale coherent structures. The best location for synthetic jet actuation is closely related to the site of a characteristic vortex on the suction side of the airfoil in 2nd？？order mode. In order to reach optimal control effects, synthetic actuation should be located within the covering range of the characteristic vortex. It is ineffective to put a synthetic jet at downstream or far upstream of the location of that vortex
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