COMPARISON OF THE COOLING PERFORMANCE OF CYLINDRICAL AND FAN-SHAPED COOLING HOLES WITH SPECIAL EMPHASIS ON THE EFFECT OF INTERNAL COOLANT CROSS-FLOW

Cooling holes in real gas turbine applications are prevalently exposed to cross-flow in the coolant passage. The majority of the studies available in literature do not consider the effects of flow in the coolant passage. Our own studies however reveal that especially diffuser holes are very susceptible in respect to cross-flow at the hole entrance, if the orientation of the cross-flow is perpendicular to the symmetry plane of the cooling hole. The effect of coolant cross-flow will be discussed in detail. The superordinate target is to identify the dominating mechanisms, which determine the flow field within the diffuser hole and hence limit the potential of cooling performance augmentation. For this reason a fan-shaped hole with 14 expansion angle will be compared to a simple cylindrical hole. Both holes have a length-to-diameter ratio of 6 and an inclination angle of 30. The comparison will be performed by means of experimentally gained discharge coefficients, local and laterally averaged adiabatic film cooling effectiveness, and heat transfer coefficients. Numerical simulations of the cooling flow will support the interpretation of the experimental results.