Application of film cooling to an unshrouded HP turbine casing

In this paper we describe the design, modelling and experimental testing of a film cooling scheme employed on an unshrouded HP rotor casing. The casing region has high thermal loads at both low and high frequency, with the flow being dominated by the potential field of the rotor and over-tip leakage flows. Increasingly high turbine entry temperatures necessitate internal and film cooling of the casing to ensure satisfactory service life and performance. There are, however, very few published studies presenting CFD and experimental data for cooled rotor casings. Experimental testing was performed on a film cooled rotor casing in the Oxford Turbine Research Facility (OTRF) — a rotating transonic facility of engine scale. Unsteady CFD of a HP rotor blade row with a film cooled casing was performed with a domain utilizing a sliding interface in the tip gap. Specific advances in validation data and understanding include: 1. A discussion of the challenges faced in the design of a casing film cooling scheme. We show that the seemingly hostile film cooling environment can be managed with the use of holes shaped to utilize acoustic pressure wave reflections. 2. Time resolved and time averaged predictions of adiabatic film effectiveness on the rotor casing are presented. Mechanisms for interaction of the coolant with the rotor tip are proposed and discussed. 3. Acoustic effects due to the passing of the rotor are demonstrated on a 3D CFD geometry, supporting conclusions drawn by Collins and Povey [1] on the importance of this effect in a casing film cooling system. 4. Time-resolved and time-mean measurements of TAW and η’ taken using a high density array of thin film heat flux gauges are presented and compared to CFD predictions for the casing region (−30 % to +125 % CAX)