Stability and receptivity characteristics of a laminar separation bubble on an aerofoil
Stability and receptivity characteristics of a laminar separation bubble on an aerofoil
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DOI：
10.1017/s0022112009993089
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发表时间：
2010-04-10
影响因子：
3.7
通讯作者：
Sandham, N. D.
中科院分区：
文献类型：
--
作者：
Jones, L. E.;Sandberg, R. D.;Sandham, N. D.
通过对时均速度剖面的线性稳定性分析和含时变强迫项的直接数值模拟，研究了翼型流动的稳定性特征。首先研究了翼型尾流，说明了用这些方法探测绝对不稳定性的可行性。NACA-0012翼型的时间平均流在发病率，然后研究其响应非常低的振幅水动力和声学扰动。从两个二维和三维模拟获得的流场进行了研究，其中翼型流动表现出层流分离泡。对流稳定性特征的文件，分离泡被发现没有表现出绝对的不稳定性在经典意义上，即没有增长的干扰与零群速度观察。然而，通过声反馈回路发现流动是全局不稳定的，声反馈回路涉及作为声激励源的翼型后缘和作为感受性部位的翼型前缘区域。有证据表明，反馈回路可能发挥重要作用，在频率选择的旋涡脱落，发生在两个维度。进一步的模拟研究的感受性过程中，声波产生的翼型边界层内的流体动力学不稳定性。接收过程的频率和源位置的依赖性进行了量化。结果发现，在充分发展的模拟后缘噪声的幅度是足够的，以促进过渡通过前缘感受性。
Stability characteristics of aerofoil flows are investigated by linear stability analysis of time-averaged velocity profiles and by direct numerical simulations with time-dependent forcing terms. First the wake behind an aerofoil is investigated, illustrating the feasibility of detecting absolute instability using these methods. The time-averaged flow around an NACA-0012 aerofoil at incidence is then investigated in terms of its response to very low-amplitude hydrodynamic and acoustic perturbations. Flow fields obtained from both two- and three-dimensional simulations are investigated, for which the aerofoil flow exhibits a laminar separation bubble. Convective stability characteristics are documented, and the separation bubble is found to exhibit no absolute instability in the classical sense; i.e. no growing disturbances with zero group velocity are observed. The flow is however found to be globally unstable via an acoustic-feedback loop involving the aerofoil trailing edge as a source of acoustic excitation and the aerofoil leading-edge region as a site of receptivity. Evidence suggests that the feedback loop may play an important role in frequency selection of the vortex shedding that occurs in two dimensions. Further simulations are presented to investigate the receptivity process by which acoustic waves generate hydrodynamic instabilities within the aerofoil boundary layer. The dependency of the receptivity process to both frequency and source location is quantified. It is found that the amplitude of trailing-edge noise in the fully developed simulation is sufficient to promote transition via leading-edge receptivity.