First Results of a New Test Rig for the Research on the Internal Air System of an Industrial Gas Turbine

Abstract

Improvement of the internal air system has great impact on the efficiency and power of gas turbines. This paper describes a new two-stage test rig for research on the cooling air supply of industrial gas turbines. The design is modeled on a simplified geometry of the internal cavities of the high pressure turbine with receiver holes simulating the restriction imposed by internal blade cooling flow circuits. The test rig consists of a rotor-stator cavity and a full rotating cavity. The Stage One supply and the Stage Two supply are separated inside the rotorstator cavity. The intended aim of the research is the branched cooling air supply. The rim seal flow, which effect on cavity flows is known to be non-trivial, is outside the scope of this area of interest. This paper concentrates on the flow path supplying the Stage Two. Variations of the axial gap size and the radial location of the connecting holes respectively the outlets of the rotor-stator cavity are described here. The air enters axially without pre-swirl at the outer radius of the stator and leaves the rotor-stator cavity through three rotating, axially directed connecting holes at a radius depending on the investigated case, which causes axial throughflow in Case 1 and radial inflow in Case 2. The experimental results show that the net cavity mass flow, presented in terms of a reduced mass flow parameter, increases with increasing pressure ratio, rotational Reynolds number and gap size. The increase due to a larger gap size depends on the rotation and is less prominent at higher rotational Reynolds numbers. An axial throughflow at the outer radius results in higher values of the reduced mass flow parameter, as compared to the case with radial inflow. The difference between the two cases increases with increasing rotational Reynolds number. Measured static pressure fluctuations inside the rotor-stator cavity due to the rotating nozzles can be raised up to ± 4% of the mean in the case with the small gap and the outlet at outer radius. The Pitot probe measurements show a low swirl ratio, radial outflow near the rotor and radial inflow close to the stator, which is consistent with Batchelor-type flow.