Early stage gas turbine blades feature complicated internal geometries in order to enhance internal heat transfer and to supply coolant for film cooling. Most film cooling experiments decouple the effect of internal coolant feed from external film cooling effectiveness, even though engine parts are commonly fed by cross-flow and feature internal rib turbulators which can affect film cooling. Experiments measuring adiabatic effectiveness were conducted to investigate the effects of turbulated perpendicular cross-flow on a row of 45 deg compound angle cylindrical film cooling holes for a total of eight internal rib configurations. The ribs were angled to the direction of prevailing internal cross-flow at two different angles: 45 deg or 135 deg. The ribs were also positioned at two different spanwise locations relative to the cooling holes: in the middle of the cooling hole pitch and slightly intersecting the holes. Experiments were conducted at a density ratio of DR = 1.5 for a range of blowing ratios including M = 0.5, 0.75, 1.0, 1.5, and 2.0. This study demonstrates that peak effectiveness can be attained through the optimization of cross-flow direction relative to the compound angle direction and rib configuration, verifying the importance of hole inlet conditions in film cooling experiments. It was found that ribs tend to reduce adiabatic effectiveness relative to a baseline, smooth-walled configuration. Rib configurations that directed the internal coolant forward in the direction of the mainstream resulted in higher peak adiabatic effectiveness. However, no other parameters could consistently be identified correlating to increased film cooling performance. It is likely that a combination of factors is responsible for influencing performance, including internal local pressure caused by the ribs, the internal channel flow field, in-hole vortices, and jet exit velocity profiles. This study also attempted to replicate the possibility that film cooling holes may intersect ribs and found that a hole which partially intersects a rib still maintains moderate levels of effectiveness.

The effectiveness of film cooling from short cooling holes, scaled to engine conditions, has been shown to be dependent on the nature of the internal coolant feed. A common method of supplying coolant to film cooling holes in engine components is through an internal cross-flow, which causes skewed effectiveness profiles on the surface of film cooled parts. For round axial holes, this effect causes coolant jets to more effectively spread across the surface. Additionally, for compound angle round holes, the direction of the cross-flow relative to the direction of injection has a substantial effect on film cooling effectiveness. A cross-flow directed counter to the span-wise direction of coolant injection has previously been shown to cause greater lateral jet spreading than cross-flow directed in-line with the span-wise injection direction. To better understand the phenomena responsible for the improved coolant spreading, two-dimensional thermal field profiles were measured downstream of compound angle film cooling holes fed by an internal cross-flow. A smooth-walled rectangular channel was used to produce an internal cross-flow in both a counter and in-line flow direction. Thermal field cross-section data was collected at three stream-wise locations: 0.7, 3.4, and 8.8 diameters downstream of the holes. Blowing ratios of 0.75 and 1.00 were studied at a density ratio of 1.5. Experiments were performed in a low speed recirculating wind tunnel at high mainstream turbulence with a thick approach boundary layer relative to the film cooling holes. It was found that the improved lateral spreading observed in the coolant jets fed by a counter cross-flow occurred due to the formation of a bulge on the downstream side of the jet.Copyright © 2015 by ASME

CFD simulations were performed to study the film cooling of a flat plate from one row of compound-angles holes fed by an internal-cooling passage that is perpendicular to the hot-gas flow. Parameters examined include direction of flow in the internal cooling passage and blowing ratios of 0.5, 1.0, and 1.5 with the coolant-to-hot-gas density ratio kept at 1.5. This CFD study is based on steady RANS with the shear-stress transport (SST) and realizable k-ε turbulence models. To understand the effects of unsteadiness in the flow, one case was studied by using large-eddy simulation (LES). Results obtained showed an unsteady vortical structure forms inside the hole, causing a side-to-side shedding of the coolant jet. Values of adiabatic effectiveness predicted by CFD simulations were compared with the experimentally measured values. Steady RANS was found to be inconsistent in its ability to predict adiabatic effectiveness with relative error ranging for 10% to over 100%. LES was able to predict adiabatic effectiveness with reasonable accuracy.

In gas turbine engines, film cooling holes are often fed by an internal cross-flow, with flow normal to the direction of the external flow around the airfoil. Many experimental studies have used a quiescent plenum to feed model film cooling holes and thus do not account for the effects of internal cross-flow. In this study, an experimental flat plate facility was constructed to study the effects of internal cross-flow on a row of cylindrical compound angle film cooling holes. Operating conditions were scaled, based on coolant hole Reynolds number and turbulence level, to match realistic turbine engine conditions. A cross-flow channel allowed for coolant to flow alternately in either direction perpendicular to the mainstream flow. Film cooling holes were operated at blowing ratios ranging from 0.5 to 2.0 at a density ratio of 1.5. There are relatively few studies available in literature that focus on the effects of cross-flow on film cooling performance, with no studies examining the effects of internal cross-flow on film cooling with round, compound angled holes. This study showed that significantly greater adiabatic effectiveness was achieved for cross-flow in the opposite direction of the span-wise direction of the coolant holes and provides possible explanations for this result.