CFD INVESTIGATION OF THE PURGE AIR INFLUENCE ON THE FLOW STRUCTURE AND BEHAVIOUR OF GAS TURBINE STAGE AND ROTOR-STATOR DISC CAVITY SYSTEM

Abstract: Gas turbines operate with medium of very high temperatures, which requires using advanced materials for vanes and blades and sophisticated methods of their cooling. Other parts of the turbine have to be protected from contact with hot gases. Discs that hold vanes and blades are especially exposed to this danger. In order to avoid it certain improvements have to be applied: providing sealing air and adjusting geometry of the hub to make the ingress to the cavity (space between discs)more difficult. This thesis concerns CFD investigation of the influence of the amount of sealing air on sealing efficiency and on the flow in the main annulus. The first part concerned literature study. Phenomena of ingress and interaction between main flow and sealing air were described. Different methods of estimating efficiency were shown. The second part focused only on the main path of the gas, modeling secondary air as constant and uniform outflow through the opening. The aim was to investigate how the power and reaction rate depend on the secondary air. The results were also exported to be used as boundary condition in the second part of the thesis. The last part concerned only the cavity – conditions at the main annulus were taken from the main annulus solution. Pressure in specified locations was measured and used to calculate sealing efficiency. Results were compared with the theoretical equations from the literature study. A structure of the flow inside the cavity was analyzed for several different amounts of the sealing flow. A method of unsteady flow analysis was developed and described. It was successfully implemented which proves that the method is promising. However, some improvements are necessary to obtain stable solution and research in this field should be continued.