A DETAILED EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FLOW STRUCTURES IN A TURBINE TIP GAP WITH PASSIVE INJECTION

摘要

An experimental and numerical study of the flow in the tip gap of a linear turbine blade cascade has been performed. Be-sides the plain tip gap flow, a passive injection with a single injection hole at the blade tip near the pressure side has been considered. Detailed measurements of the static pressure distribution on the cascade end wall and on the blade surface are conducted. The pressure measurements are supported by surface oil flow visualizations of the blade tip and suction side surface to get qualitative insights into the underlying flow structures. The experimental data is compared to highly resolved unsteady RANS simulations. Previous investigations on the same cascade have shown, that flow separation phenomena on the suction side surface play an important role on this blade profile, hence the transition model by Menter was used for all simulations. It was found, that the influence of a single passive injection hole is limited to a narrow region downstream. The additional injection jet leads to a changed pressure distribution, indicating a lower velocity level and a weakened tip gap vortex.