Effects of Realistic First-Stage Turbine Endwall Features
The modern gas turbine engine requires innovative cooling techniques to protect its internal components from the harsh operating environment typically seen downstream of the combustor. Much research has been performed on the design of these cooling techniques thus allowing for combustion temperatures higher than the melting point of the parts within the turbine. As turbine inlet temperatures and efficiencies continue to increase, it becomes vitally important to correctly and realistically model all of the turbine’s external cooling features so as to provide the most accurate representation of the associated heat transfer to the metal surfaces. This study examines the effect of several realistic endwall features for a turbine vane endwall. The first study addresses the effects of a mid-passage gap, endwall misalignment, and roughness on endwall film-cooling. The second study focuses on the effect of varying the combustor-to-turbine gap width. Both studies were performed in a large-scale low speed wind tunnel with the same vane geometry. Geometric and flow parameters were varied and the variation in endwall cooling effectiveness was evaluated. Results from these studies show that realistic features, such as surface roughness, can reduce the effectiveness of endwall cooling designs while other realistic features, such as varying the combustor-to-turbine gap width, can significantly improve endwall cooling effectiveness. It was found that, for a given coolant mass flowrate, a narrow combustor-turbine gap width greatly increased the coverage area of the leaked coolant, even increasing adiabatic effectiveness upstream of the vane stagnation point. The turbine designer can also more efficiently utilize leaked coolant from the combustor-to-turbine gap by controlling endwall misalignment, thereby reducing the overall amount of filmcooling needed for the first stage.
Flow Measurements in a First Stage Nozzle Cascade Having Leakage and Assembly Features: Effects of Endwall Steps and Leakage on Aerodynamic Losses
This work supports new gas turbine designs for improved performance by evaluating endwall leakage and assembly features in a cascade that is representative of a first stage stator passage. The present paper documents component misalignment and leakage flow effects on the aerodynamic losses within a passage having one contoured and one straight endwall. Steps on the endwall and leakage flows through the endwall can lead to thicker endwall boundary layers, stronger secondary flows and possibly additional vortex structures in the passage. The paper compares losses with steps of various geometries and leakage of various flow rates to assess their importance on aerodynamic losses in this contoured passage. In particular, features associated with the combustor-to-turbine transition piece and the slash-face gap, a gap between two vane segments on the vane platform, are addressed.Copyright © 2005 by ASME
Frequency selective surface design for blinds applications
In this paper, the reconfigurable blind structure with frequency selective surfaces(FSS) for the building applications are presented. Frequency transmission characteristics for different angles of the proposed blind-FSSs are investigated and verified through simulation and measurement. The simulation results show that we can implement the reconfigurable blind-FSS for multiband wireless applications. To verify the proposed paper, two kinds of blind-FSSs, crossed dipole FSS and circular ring FSS are fabricated and measurements are performed for different angles. The proposed structure in this paper which is very simple, can be easily applied to any planar surface for wireless security applications at low cost.