Auxiliary hole influence on internal flow characteristics in bend region of a real investment-casting blade coolant channel

Abstract

For modern investment-casting turbine blades, auxiliary holes (AHs) are unavoidable to be generated near internal coolant channels; however, the additional effect of AH is usually ignored. In this work, the AH-injection influence on the flow characteristics in a round bend was studied, using a planar Time-resolved Particle Image Velocimetry (TRPIV) system. The main feature of this experiment was the application of a ribbed channel with the real blade geometry as the specimen. At first, in the real bend, different flow phenomena from those in the simplified models reported in the past literature can be observed, i.e. asymmetrical mainstream near two sides of blade and a superposition of secondary vortices downstream of bend. Subsequently, the AH influences on the special flow mentioned above were discussed at an inlet Reynolds number (Rein) of 21,500 and five AH-to-inlet mass flow ratios (MFRs = 0–10%). The conditions at MFR larger than 5% can obviously change the original flow at MFR = 0 and due to the real blade geometry, the various influences can be observed in different planes. In general, the sizes of separation bubble and corner vortex can be suppressed by the AH-injection; however, the AH-injection effects on the flow impingement are complex, i.e. enhancement on suction side but reduction on pressure side. Finally, through the increase of Rein from 21,500 to 39,000, it can be found that at a given MFR, the flow impingement and turbulent kinetic energy can be simultaneously enhanced by Rein.