Measurements and Visualization of the Flow in a Turbine Blade Tip Gap With Passive Jet Injection

Results of detailed measurements of the flow in a turbine blade tip are presented. The blades of the linear cascade were made by means of 3D-printing technology. Different clearances and the impact of a passive jet injection on the gap flow were investigated. The resulting velocity profiles in the gap were measured by means of a miniaturized Pitot-probe. To gain qualitative insights into the flow details, surface oil flow visualizations were performed. This classical method was extremely helpful for obtaining and interpreting occurring flow structures. The effect of an additional passive blade tip injection was investigated in detail and compared with the results obtained for plain blade tips without an additional injection. It was found that the overall flow structure was not greatly affected by the additional jet injection. But in case of moderate or large tip clearances, a local reduction of the tip leakage flow was achieved. The surface oil flow visualizations indicated a complex interaction of the jet with the gap flow. Such vortex interactions are well known in case of gas turbine film cooling technologies, but here rather similar observations were made in case of a confined flow configuration, too.