Experimental study of swirling flow characteristics in a semi cylinder vortex cooling configuration

This study utilised planar Particle Image Velocimetry (PIV) to investigate the flow characteristics in a semi cylindrical confinement with 2 jet inlets. The water based experimental study aims to understand the basic flow behaviour in a gas turbine leading edge vortex cooling configuration. The time averaged and fluctuating flow fields were collected at 3 cross sections and 1 longitudinal section at 3 different inlet Reynolds numbers. The snapshot based Proper Orthogonal Decomposition (POD) was applied to extract the coherent flow characteristics. Results showed that the vortex flow consists a large-scale vortex in the chamber with a small recirculating corner vortex. The core vortex is similar to the Rankine vortex with a near solid body rotating vortex, surrounded by a jetting vortex layer and a boundary layer along the chamber wall. The jetting vortex layer featuring a proportional decline of circumferential velocity is different to the potential layer in a typical Rankine vortex. The jetting vortex at a high velocity level is mainly responsible for the high heat transfer rate for vortex cooling. A turning region at theta approximate to 170 degrees separating the circumferential velocity behaviour was noticed, which provides a flow dynamic explanation to the heat transfer intensity along the surface wall for vortex cooling. The region at the interface between the solid body rotating vortex and the jetting vortex features with relatively low velocity magnitude but strong shear and large fluctuating velocity intensity. The longitudinal section has a low average velocity (approximately 10% of that in the cross sections in magnitude), indicating the vortex flow is strongly rotational but weakly helical. However, the fluctuating velocity intensity has a comparative level to cross sections. POD analysis reveals that the first 4 modes contain about 23.2% of the fluctuating velocity energy. In nozzle cross sections, the coherent vortex near the surface wall dominates the fluctuation energy and is responsible for the heat transfer enhancement. In the cross section between nozzles, the coherent flow structure displays a vortex pair in the core and a minor corner vortex.