Time accurate numerical simulations were conducted to investigate the effect of triangular cavities on the unsteady aerodynamic characteristics of NACA 0012 airfoil at a Reynolds number of 50,000. Right-angled triangular cavities are placed at 10%, 25% and 50% chord location on the suction and have depths of 0.025c and 0.05c, measured normal to the surface of the airfoil. The second-order accurate solution to the RANS equations is obtained using a pressure-based finite volume solver with a four-equation transition turbulence model, γ–Re_θt, to model the effect of turbulence. The two-dimensional results suggest that the cavity of depth 0.025c at 10% chord improves the aerodynamic efficiency (l/d ratio) by 52%, at an angle of attack of α = 8°, wherein the flow is steady. The shallower triangular cavity when placed at 25%c and 50%c enhances the l/d ratio by only 10% and 17%, respectively, in the steady-state regime of angles of attack between α = 6° and 10°. The deeper cavity also enhances the l/d ratio by up to 13%, 22% and 14% at angles of attack between α = 6° and 10°. Even in the unsteady vortex shedding regime, at α =12° and higher, significant improvements in the time-averaged l/d ratios are observed for both cavity depths. The improvements in l/d ratio in the steady-state, pre-stall regime are primarily because of drag reduction while in the post-stall, unsteady regime, the improvements are because of enhancements in time-averaged C_l values. The current finding can thus be used to enhance the aerodynamic performance of MAVs and UAVs that fly at low Reynolds numbers.

进行时间精确的数值模拟以研究三角形腔对雷诺数为 50,000 的 NACA 0012 翼型的非定常气动特性的影响。直角三角形腔位于吸力的 10%、25% 和 50% 弦位置，深度为 0.025c 和 0.05c，垂直于翼型表面测量。RANS 方程的二阶精确解是使用基于压力的有限体积求解器获得的，该求解器具有四方程过渡湍流模型γ–Re _θt，以模拟湍流的影响。二维结果表明，10%弦长处深度为0.025c的空腔提高了气动效率（l/dratio) 增加 52%，攻角为 α = 8°，其中流动是稳定的。在 α = 6° 和 10° 之间的攻角的稳态范围内，当放置在 25%c 和 50%c 时，较浅的三角形腔使l/d比分别提高了10% 和 17%。在 α = 6° 和 10° 之间的攻角下，更深的空腔还将l/d比提高了 13%、22% 和 14%。即使在不稳定的涡旋脱落状态下，在 α = 12° 和更高时，对于两个腔深度，时间平均l/d比也有显着改善。l/d的改进比在稳定状态下，预失速制度是减阻，主要是因为，而在后失速，非定常制度，所述改进是因为在时间上平均的增强Ç_升值。因此，当前的发现可用于提高以低雷诺数飞行的 MAV 和 UAV 的空气动力学性能。