CFD Analysis of Flow in High-Radius Pre-Swirl Systems

Abstract

Pre-swirl systems of gas turbines are utilized to reduce the temperature of the cooling air during the transfer from the stationary into the rotating system of the turbine. The amount of temperature decrease between the pre-swirl nozzle and the receiver holes depends on many geometrical and operational parameters. For the design process of a cooling air system, simple but general 1D (one-dimensional) calculation methods are required. These models must comprise correlations describing all dominant flow effects in order to provide the most accurate results. For the development of such models, a good understanding of the flow behavior in the system is indispensable. In this contribution, a pre-swirl scheme consisting of the three main components: pre-swirl nozzle, pre-swirl cavity and receiver hole is investigated numerically for different configurations. The cavity of the system is described as a rotorstator system and as a rotor-rotor system. With both configurations, CFD (Computational Fluid Dynamics) simulations with the same set of boundary conditions are performed. The evaluation of the results shows the influence of each component on the three-dimensional structure of the flow. For different operating conditions, the flow inside the cavity is represented by streamlines and discussed in detail. In the cavity, the swirl distribution is shown for all configurations and compared to free vortex behavior. For some regions, where a strong decrease of total pressure is present, the flow pattern is described in detail. In view of the development of a 1D design method for a pre-swirl system, the described flow effects give some important hints.