Robert Krewinkel

Conjugate Simulation of the Effects of Oxide Formation in Effusion Cooling Holes on Cooling Effectiveness

Within Collaborative Research Center 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants” at RWTH Aachen University an effusion-cooled multi-layer plate configuration with seven staggered effusion cooling holes is investigated numerically by application of a 3-D in-house fluid flow and heat transfer solver, CHTflow. The effusion-cooling is realized by finest drilled holes with a diameter of 0.2 mm that are shaped in the region of the thermal barrier coating. Oxidation studies within SFB 561 have shown that a corrosion layer of several oxides with a thickness of appoximately 20μm grows from the CMSX-4 substrate into the cooling hole. The goal of this work is to investigate the effect this has on the cooling effectiveness, which has to be quantified prior to application of this novel cooling technology in real gas turbines. In order to do this, the influence on the aerodynamics of the flow in the hole, on the hot gas flow and the cooling effectiveness on the surface and in the substrate layer are discussed. The adverse effects of corrosion on the mechanical strength are not a part of this study. A hot gas Mach-number of 0.25 and blowing ratios of approximately 0.28 and 0.48 are considered. The numerical grid contains the coolant supply (plenum), the solid body for the conjugate calculations and the main flow area on the plate. It is shown that the oxidation layer does significantly affect the flow field in the cooling holes and on the plate, but the cooling effectiveness differs only slightly from the reference case. This seems to justify modelling the holes without taking account of the oxidation.Copyright

Three-dimensional numerical analysis of curved transpiration cooled plates and homogenization of their aerothermal properties

Three different designs of a transpiration cooled multilayer plate-plane, convex, and concave-are analyzed numerically by application of a 3D conjugate fluid flow and heat transfer solver. The geometrical setup and the fluid flow conditions are derived from modern gas turbine components. The conjugate analysis of these designs focus on the influence of the surface curvature, the cooling film development on the plate surface, the fluid structure in the cooling channels, and on the cooling efficiency of the plate. Moreover, to predict the effective thermal properties and the permeability of these multilayer plates, a multiscale approach based on the homogenization technique is employed. This method allows the calculation of effective equivalent properties either for each layer or for the multilayer of superalloy, bondcoat, and thermal barrier coating (TBC). Permeabilities of the different designs are presented in detail for the TBC layer. The influence of the plate curvature and the blowing ratio on the effective orthotropic thermal conductivities is finally outlined.

The Effects of Unintentional Deviations Due to Manufacturing of Cooling Holes and Operation on Transpiration Cooling Efficiency

A full-coverage cooled multi-layer plate configuration is investigated numerically by application of a 3-D conjugate fluid flow and heat transfer solver, CHTflow. The geometrical setup and the fluid flow conditions derive from modern gas turbine combustion chambers and bladings. The numerical grid contains the coolant supply (plenum), the solid body and the main flow area on the plate. The full-coverage cooling is realized by finest drilled holes with a diameter of 0.2 mm that are shaped in the region of the thermal barrier coating. Two different effects will be considered in this paper. First, the effects of deviations in the cooling hole geometry due to the manufacturing process will be discussed, then the effects of an obstruction in one of the cooling holes will be looked at. The numerical investigation focuses on the cooling efficiency on the plate surface and on the cooling hole surface as well as the aerodynamics in the main flow. The scientific work is embedded in the Collaborative Research Center 561 at RWTH Aachen University.Copyright

Conjugate Calculation of Effusion Cooling With Realistic Cooling Hole Geometries

Within Collaborative Research Center 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants” at RWTH Aachen University an effusion-cooled multi-layer plate configuration with seven staggered effusion cooling holes is investigated numerically by application of a 3-D in-house fluid flow and heat transfer solver, CHTflow. The effusion-cooling is realized by finest drilled holes with a diameter of 0.2 mm that are shaped in the region of the thermal barrier coating. The geometry of the cooling holes is not symmetrical, due to the manufacturing process. Furthermore, the inlet of the cooling holes in the plenum shows no sharp edges, which has a significant influence on the formation of the kidney-vortices within the cooling hole. The impact of this geometry on the cooling effectiveness has to be quantified prior to application. A hot gas Mach-number of 0.25 and blowing ratios of approximately 0.28 and 0.48 will be considered. The numerical grid contains the coolant supply (plenum), the solid body for the conjugate calculations and the main flow area on the plate. The form of the hole, especially that of the diffuser, leads to a skewered mass flow from the hole and a non-symmetric temperature distribution on the plate surface. Therefore, neither the flow field on the hot gas surface nor the temperature distribution can be compared with the usually investigated idealised hole geometries.Copyright

Influence of a Broken-Away TBC on the Flow Structure and Wall Temperature of an Effusion Cooled Multi-Layer Plate Using the Conjugate Calculation Method

Within Collaborative Research Center 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants” at RWTH Aachen University an effusion-cooled multi-layer plate configuration is investigated numerically by application of a 3-D in-house fluid flow and heat transfer solver, CHTflow. Previous conjugate calculations have shown a considerably decreased surface temperature for a hole geometry with a broken-away TBC, but could not attribute this effect conclusively to the decreased surface or the changed fluid flow conditions resulting from the changed outlet geometry. For this work, both conjugate calculations and calculations with adiabatic wall temperatures are conducted to analyse the flow in and around a hole with a fan-shaped outlet. The adiabatic calculations will exclude the effect of the solid body, making a quantification of its effects possible. The geometrical setup and the fluid flow conditions derive from modern gas turbine combustion chambers and bladings and are the same for both types of calculations. The numerical grid contains the coolant supply (plenum), the solid body for the conjugate calculations and the main flow area on the plate. The effusion-cooling is realized by finest drilled holes with a diameter of 0.2 mm that are shaped in the region of the thermal barrier coating. The flow field and the resulting temperature distributions on the hot gas surface will be discussed in detail for the two approaches, two blowing ratios and two different fan-shapes. Finally, the results will be discussed from the point-of-view of optimising the cooling effectivenss for effusion cooling geometries. The results will show that only for the smallest blowing ratio and the largest cooling hole exit area the decreased surface area of the TBC is the dominant factor.© 2008 ASME

Influence of the Radial and Axial Gap of the Shroud Cavities on the Flowfield in a 2-Stage Turbine

An important goal in the development of turbine bladings is to improve their efficiency for an optimized usage of energy resources. This requires a detailed insight into the complex 3D-flow phenomena in multi-stage turbines. In order to investigate the flow characteristics of modern highly loaded turbine profiles a test rig with a two stage axial turbine has been set up at the Institute of Steam and Gas Turbines, RWTH Aachen University. The test rig is especially designed to investigate the influence of different cavity sizes. In order to analyze the influence of the cavity size on the secondary flow and to discuss the effects of the blade loading, the 3D flow through the 2-stage turbine with shrouded blades is investigated numerically, using the steady Navier-Stokes inhouse computer code, CHT-Flow. The turbine blading is designed to concentrate the mass flow in the middle of the passage in order to keep the main flow away from the secondary flow regions at the endwalls of the blade. The simulations include a comparison of a configuration without cavities (design case) and two configurations, where the axial gap between the shroud and the endwalls is about 5 mm and the radial gap between the shroud and the endwall is varied between 0.8 mm (open radial gap) and radial gaps “near zero” (closed radial gap). The investigations are done with focus on the secondary flow phenomena in the second guide vane. For a detailed analysis of the blade load the design point and an off-design point are simulated for each blading. The flow conditions are taken from experimental investigations performed at the Institute of Steam and Gas Turbines, Aachen University. In the experimental setup, the turbine is operated at a low pressure ratio of 1.4 with an inlet pressure of 3.2·105 Pa. The numerical results will also be compared to the corresponding experimental data at the outlet of the second stage.© 2006 ASME

3-D Numerical Analysis of Curved Transpiration Cooled Plates and Homogenization of Their Aerothermal Properties

Three different designs of a transpiration cooled multilayer plate — plane, convex and concave — are analysed numerically by application of a 3-D conjugate fluid flow and heat transfer solver. The geometrical setup and the fluid flow conditions are derived from modern gas turbine components. The conjugate analysis of these designs focus on the influence of the surface curvature, the cooling film development on the plate surface, the fluid structure in the cooling channels and on the cooling efficiency of the plate. Moreover, to predict the effective thermal properties and the permeability of these multilayer plates, a multiscale approach based on the homogenization technique is employed. This method allows the calculation of effective equivalent properties either for each layer or for the multilayer of superalloy, bondcoat and thermal barrier coating (TBC). Permeabilities of the different designs are presented in detail for the TBC layer. The influence of the plate curvature and the blowing ratio on the effective orthotropic thermal conductivities is finally outlined.Copyright