Numerical Investigation of Rotation Effects on Anti-vortex Film-Cooling Holes

The anti-vortex film-cooling technique under rotating conditions is investigated using large eddy simulation (LES) due to its complex mixture between the main stream flow, film-cooling flow, and the flow through the anti-vortex holes. The film-cooling was enhanced by placing two small injection holes (anti-vortex holes) just downstream of the main cooling hole in order to modify the approaching boundary layer flow and its interaction with the film-cooling jet. A geometry of a single row of rectangular holes inclined normally on a flat plate is used as the baseline case. The finite volume method and the unsteady SIMPLE algorithm were applied on a non-uniform staggered grid. The simulations were performed for four different values of rotation number (Ro) of 0.0, 0.03021, 0.06042, and 0.12084 and a jet Reynolds number of 4,700. Three different values of velocity ratio (coolant jets / main jet velocity), namely 0.5, 1, and 1.5, were studied. One position of the anti-vortex holes is investigated with density ratio (coolant density / main stream density), namely 1.04. The present simulation is carried out using an in-house FORTRAN code. Numerical calculations of flow field and film-cooling effectiveness are validated with reported LES results. It was shown that the rotational speed is the dominant factor in determining the cooling effectiveness level. The jet footprint of the anti-vortex is broader than for the single jet case and increases as Ro increases. Furthermore, it was also found that the anti-vortex technique used in this study reduces the mixing of the main stream and the coolant jets and improves the film-cooling effectiveness using the same amount of coolant fluid as was used in the case of a single jet. It was also shown that the anti-vortex holes create reverse vortices against the main vortices that are created by the main hole. These reverse vortices help to keep the coolant jet flow near the wall.