Author: Akamol ShavalikulPublisher:
ISBN:
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Languages : en
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Book Description
Abstract A time accurate prediction of the viscous flow in a turbine stage including a rotor in motion By Akamol Shavalikul The actual flow field in a turbine stage is extremely complex, three-dimensional, and unsteady, mainly due to interactions between the nozzle guide vanes (NGV) and the rotor vanes. A detailed understanding of turbine flow field characteristics, which is crucial for improving turbine performance, can be obtained using a computational fluid dynamics approach. In this current study, the flow field in the Pennsylvania State University Axial Flow Turbine Research Facility (AFTRF) was simulated using a three-dimensional Reynolds Averaged Navier-Stokes finite volume solver (RANS). This study examined four sets of simulations. The first set of flow simulations is an individual NGV passage flow field without the influence of a rotor blade row. The simulation results were used to produce the flow visualization in an NGV passage, which provide more detailed NGV flow characteristics. Secondly, a set of a rotor flow simulations was carried out to examine the flow fields associated with different pressure side tip extension configurations, which are designed to reduce the tip leakage flow. RANS based viscous flow simulations were used to compare a number of potential aerodynamic de-sensitization designs for blade tips. The last two sets use a multiple reference frames approach for a complete turbine stage with two different interface models. The first interface model is the circumferentially averaged mixing plane model. The quasi-steady state flow characteristics of the AFTRF can be obtained from this interface model. This model was not only used to investigate the flow characteristics in the turbine stage but also the effects of using pressure side rotor tip extensions. The tip leakage flow fields simulated from this model and from the linear cascade model show similar trends. More detailed understanding of unsteady characteristics of a turbine flow field can be obtained using the second type of interface model, the time accurate sliding-mesh model. The potential flow interactions, wake characteristics, their effects on secondary flow formation, and the wake mixing process in a rotor passage were examined using this model. A comparison between the results from the circumferential average model and the time accurate flow model results is presented. It was found that the circumferential average model cannot accurately simulate flow interaction characteristics on the interface plane between the NGV trailing edge and the rotor leading edge. However, the circumferential average model does give accurate flow characteristics in the NGV domain and the rotor domain with less computational time and computer memory requirements. In contrast, the time accurate flow simulation can predict all unsteady flow characteristics occurring in the turbine stage, but with high computational resource requirements.
