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.
Trends in turbomachinery turbulence treatments
Abstract General forms of turbulence models are outlined along with their defects and palliatives for these in relation to turbomachinery. The turbulence modelling hierarchy available in turbomachinery is set out, moving from RANS (Reynolds Averaged Navier–Stokes) to the eddy resolving DNS (Direct Numerical Simulation) approach. New vistas for techniques are discussed. A modular RANS turbulence modelling strategy is outlined. Simple scaling arguments for Unsteady RANS (URANS) spectral gaps in turbomachinery are presented and the presence of such gaps shown not always to be guaranteed. The power of computers continues to steadily rise. Hence, the use of eddy resolving simulations in their various forms is expected to increase and also their use for the refinement of lower order models. Current examples for the latter are given. The use of eddy resolving simulations in the coupled and sometimes multi-physics turbomachinery environment is considered. The need for improved measurements with well defined boundary conditions that have Reynolds stress and even spectral information, at Reynolds and Mach numbers that connect with typically powerful turbomachinery systems is identified. This is necessary to refine both RANS and eddy resolving strategies. Most available ‘Best Practices’ are centred on RANS. Hence, new guidance needs to be developed for eddy resolving methods. Expert systems, based around flow taxonomies, that can assist with for example making initial grid estimates and guiding aerodynamicists through the eddy resolving simulation process are discussed. The need for more turbomachinery relevant strategies for generating turbulence inflow is identified.
Effect of a new inhibitor of cholesterol biosynthesis (AY 9944) on serum and tissue sterols in the rat.
AY 9944 is a novel inhibitor of cholesterol biosynthesis which appears to act on the Delta 7-reductase enzyme, interfering with the conversion of 7-dehydrocholesterol to cholesterol. In all tissues studied, with the exception of the lens, there was a reduction in cholesterol and a marked accumulation of 7-dehydrocholesterol. Isotope studies showed a reduced uptake of acetate into cholesterol, and an increased uptake into 7-dehydrocholesterol, in various tissues in vivo and by skin samples in vitro. There was no apparent accumulation of lanosterol or of the methostenols in the rat skin.