Film cooling effectiveness enhancement on wall surface with crater hole and SDBD plasma actuation

At three blowing ratios ( M = 0.5, 1, and 1.5), film cooling effectiveness on plain wall surface with designed contoured crater cooling hole was numerically investigated. With variable crater depth (0.4 D≤ d≤2.7 D) and crater expansion angle (18°–30°), the optimal crater hole was determined and then combined with SDBD plasma actuation further. Effects of SDBD plasma actuation frequency (0≤ D θ ≤11.25) and actuation strength (0≤ D s ≤100) were analyzed, and the cases of the conventional cylindrical holes (i.e. baseline cases) were also conducted for comparison. The results showed that the wall film cooling effectiveness gradually rises with increased crater depth and remains stable with crater depth up to 2.3 D. Compared to the baseline case, the laterally averaged wall film cooling effectiveness of the contoured crater hole of d = 2.3 D is increased by over 55%, 500%, and 700% near the hole ( X/ D<3), and nearly 45%, 300%, and over 850% downstream region (3< X/ D<10) at M = 0.5, 1 and 1.5 respectively. Increasing the crater expansion angle also improves the wall film cooling effectiveness by expanding the coolant coverage area and strengthening the coolant attachment onto the wall. Compared with the baseline case, the overall laterally averaged wall film cooling effectiveness is improved by nearly 450% for the crater hole with a 30° outward expansion angle at M = 1. As SDBD plasma actuation frequency and intensity increase, the wall film cooling effectiveness increases and remains stable at D θ = 6.25 and D s = 60. The benefits of the contoured crater hole configuration and plasma actuation mainly result from the generation of anti-kidney vortex pair, which can effectively suppress the development of the existing kidney vortex pair and restrain the coolant rising. Compared with the baseline case, the optimized contoured crater hole combined with the plasma actuation at D θ = 6.25 and D s = 60 increases the laterally averaged wall film cooling effectiveness by nearly 1200% near the hole ( X/ D<3), and over 600% in the downstream region ( X/ D>3) at M =1.