Detached-eddy simulation of flow past a pitching NACA 0015 airfoil with pulsed actuation

作者：Wang, Liang; Fu, Song^*

来源：Aerospace Science and Technology, 2017, 69: 123-135.

DOI：10.1016/j.ast.2017.06.002

• SEPARATION

This study conducted Detached-Eddy Simulations (DES) of actively controlled flow over a 0.35 m chord NACA0015 airfoil at an incidence angle of 11 degrees and a chord Reynolds number of I million. The uncontrolled, natural flow were simulated by using DES-type methods, with a comparison of different underlying RANS models and subgrid-scale stress models in LES mode. Results from these computations were compared with experimental observations, enabling their reliable assessment through the detailed investigation of the Reynolds stresses as well as the separation and reattachment. It was found that among all five DES-type methods, only the Spalart-Allmaras-based Improved Delayed DES (IDDES-SA) captured the separation point as measured in the experiments. The classical vortex-shedding and the shear-layer flapping modes for airfoil flows with shallow separation were also extracted from the IDDE-SA results by using Dynamic Mode Decomposition. With better understanding of unsteady flow features, effective control practices were illustrated. The pulsed blowing actuation was adopted according to the experimental settings. The flow-field around jet orifices was resolved, instead of the use of actuation boundary conditions. It was found that for all actuation frequencies investigated in this article, the saturation of lift-to-drag ratio was yielded already at intermediate momentum coefficients, two-fifths of the actuation amplitude used in the experiment; the optimal actuation frequency was 0.6 among all cases, consistent with the dominant frequency of the baseline flow. The suppression of separation bubble led to a maximum lift-to-drag ratio enhancement of 194%, as well as a sharp decrease of all Reynolds stress components. To further reduce the strong unsteadiness introduced by excitation, a phase shift among jet orifices was applied and evaluated. The pulsed blowing with the jet orifices in an anti-phased manner was found to be very effective to damp the fluctuations of the lift around its mean value, though it led to a small decrease in mean lift.

• 出版日期2017-10
• 单位清华大学