Sintering Behavior of Plasma-Sprayed Sm2Zr2O7 Coating

Plasma-sprayed thermal barrier coating (TBC) systems are widely used in gas turbine blades to increase turbine entry temperature (TET) and better efficiency. Yttria stabilized zirconia (YSZ) has been the conventional thermal barrier coating material because of its low thermal conductivity, relative high thermal expansion coefficient and good corrosion resistance. However the YSZ coatings can hardly fulfill the harsh requirements in future for higher reliability and the lower thermal conductivity at higher temperatures. Among the interesting TBC candidates, materials with pyrochlore structure show promising thermo-physical properties for use at temperatures exceeding 1200 °C. Sm2Zr2O7 bulk material does not only have high temperature stability, sintering resistance but also lower thermal conductivity and higher thermal expansion coefficient. The sintering characteristics of ceramic thermal barrier coatings under high temperature conditions are complex phenomena. In this paper, samarium zirconate (Sm2Zr2O7, SZ) powder and coatings were prepared by solid state reaction and atmosphere plasma spraying process, respectively. The microstructure development of coatings derived from sintering after heat-treated at 1200–1500 °C for 50 h have been investigated. The microstructure was examined by scanning electron microscopy (SEM) and the grain growth was analyzed in this paper as well.

Factors Affecting Oil Removal From an Aeroengine Bearing Chamber

Aeroengines incorporate various bearing chambers that house the shaft bearings and the oil used to cool and lubricate these bearings must subsequently be recovered from these chambers. Effective oil removal (scavenge) is essential to avoid heat generation through unnecessary working of the oil which can lead to excessive heat generation and reduced overall efficiency. Therefore the design of the scavenge region (sump) in a bearing chamber, as well as the ability to assess its performance is very important. An ongoing research program into bearing chamber scavenge comprising experimental and computational components is being conducted at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems. This program is enhancing understanding of sump performance and design. In this paper an experimental study into a simplified but representative scavenge is reported. This experimental work helps to further understanding of the complex two-phase flow physics in a bearing chamber, particularly in the scavenge region, by means of various measurements and flow visualization. For the study a bespoke test rig has been built. It consists of a simplified, generic bearing chamber with simple sump geometry constructed entirely of Perspex to allow visualization. A shaft in the centre of the chamber capable of rotating up to 15,000 rpm is employed to introduce a windage flow in the chamber. Water (the working fluid) is fed to the chamber via an inlet pump and an outlet pump removes liquid from the chamber, closing the circuit. Several pneumatic pinch valves are installed in the flow circuit to allow residence volume measurement. A completely air-tight reservoir with internal baffle functions as a simple liquid-gas separator, allowing measurement of gas volumetric flow rate in the off-take pipe; hence the scavenge ratio (ratio of total exit volume to liquid volume) can be obtained. Residence volume measurements highlight the importance of sump geometry as an ill-designed sump can lead to an undesirable increase in residence volume.

Mechanical Design of a Variable Pitch Fan for Turbofan Engines

The mechanical design of a new variable pitch fan system for high bypass turbofan engines is presented, offering 10–14% fuel savings for next generation turbofan engines. Comparable in weight to current fans, the new design incorporates a compact pitch change mechanism that fits within a current fan’s center body. The key to compactness is the use of multiple high strength tension/torsion straps, which support blade centrifugal loads with unique structural efficiency and redundancy, while allowing ten to fifteen degrees of blade pitch rotation. The new retention system also offers significant reduction of pitch control forces by balancing blade centrifugal twisting loads with strap restoring moments, achieving a desired pitch setting. The use of a pin root fan blade facilitates on-wing blade replacement. Fan blade incidence angles are decreased at low aircraft speeds to avoid fan stall flutter problems. Therefore, advanced engines no longer need the addition of a variable area nozzle to the exit of the fan duct to prevent flutter, saving additional weight, complexity, and cost. This new fan system offers the best solution for achieving a major improvement in turbofan engine efficiency, at the lowest weight.

Vapor Phase Deposition Using a Plasma Spray Process

Plasma spray - physical vapor deposition (PS-PVD) is a low pressure plasma spray technology recently developed by Sulzer Metco AG (Switzerland) to deposit coatings out of the vapor phase. PS-PVD is developed on the basis of the well established low pressure plasma spraying (LPPS) technology. In comparison to conventional vacuum plasma spraying (VPS) and low pressure plasma spraying (LPPS), these new process use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and electron beam - physical vapor deposition (EB-PVD) coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated with columnar thermal barrier coatings using PS-PVD. Even shadowed areas and areas which are not in the line of sight to the coating source can be coated homogeneously. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase. Columnar thermal barrier coatings made of Yttria stabilized Zircona (YSZ) are optimized to serve in a turbine engine. This includes coating properties like strain tolerance and erosion resistance but also the coverage of multiple air foils.

Further Computational Investigations Into Aero-Engine Bearing Chamber Off-Take Flows

Within an aero-engine bearing chamber oil is provided to components to lubricate and cool. This oil must be efficiently removed (scavenged) from the chamber to ensure it does not overheat and degrade. Bearing chambers typically contain a sump section with an exit pipe leading to a scavenge pump. In this paper a simplified geometry of a sump section, here simply made of a radial off-take port on a walled inclined plane, is analysed computationally. This paper follows on work presented within GT2008-50634. In the previous paper it was shown that simple gravity draining from a static head of liquid cold be modelled accurately, for what was akin to a deep sump situation fond in integrated gear boxes for example. The work within this paper will show that the draining of flow perpendicular to a moving film can be modelled. This situation is similar to the arrangements found in transmission bearing chambers. The case modelled is of a walled gravity driven film running down a plane with a circular off-take port, this replicates experimental work similar to that reported in GT2008-50632. The commercial computational fluid dynamics (CFD) code, Fluent 6 [1] has been employed for modelling, sing the Volume of Fluid (VOF) approach of Hirt and Nichols [2, 3] to capture the physics of both the film motion and the two phase flow in the scavenge pipe system. Surface tension [4] and a sharpening algorithm [5] are used to complement the representation of the free surface and associated effects. This initial CFD investigation is supported and validated with experimental work, which is only depicted briefly here as it is mainly sued to support the CFD methodology. The case has been modelled in full as well as with the use of a symmetry plane running down the centre of the plane parallel to the channel walls. This paper includes details of the meshing methodology, the boundary conditions sued, which will be shown to be of critical importance to accurate modelling, and the modelling assumptions. Finally, insight into the flow patterns observed for the cases modelled are summarised. The paper further reinforces that CFD is a promising approach to analysing bearing chamber scavenge flows although it can still be relatively costly.

Characteristics of Preheated Bio-Oil Sprays Produced by an Air-Blast Injector

In this study the vegetable oil (VO) is preheated to reduce the kinematic viscosity, and thus, improve atomization. A commercial air-blast atomizer is used to produce the VO spray at ambient conditions of temperature and pressure. Characteristics of the resulting spray are measured using a laser sheet visualization system and a Phase Doppler Particle Analyzer system. Experiments are conducted for VO temperatures varying from 40 C to 100 C and air to liquid mass ratio (ALR) of 2.0 and 4.0. Results show a decrease in Sauter Mean Diameter with an increase in VO temperature, regardless of the ALR. Radial profiles show larger droplets migrating towards the edge of the spray and smaller droplets in the interior spray region. Results show a significant difference in distributions of mean and root mean square axial velocity profiles as the VO inlet temperature is increased for a fixed ALR. Higher VO inlet temperature and higher ALR produced a narrower spray with smaller diameter droplets and higher peak axial velocities. Overall, this study has shown that preheating VO improves atomization by producing spray with smaller diameter droplets.

Heavy Duty Gas Turbine Simulation: A Compressor IGV Airfoil Off-Design Characterization

The correct simulation of power plant behavior over a variety of operating conditions has to be extremely detailed in order to provide reliable help to the turbomachinery developers. The latter instance implies for designers and commercial personnel to be equipped with reliable calculation tools (in-house developed or commercial). In particular, Performance Analysis Codes (PACs) allow the designers to analyze different system configurations. To predict off-design behavior, these codes need to be not limited to thermodynamic analysis, but also able to perform a simplified description of each component that require a specific set of correlations. The selection of suitable correlation sets for compressor IGV airfoils could be very difficult. This paper deal with a procedure based on 2D-CFD analysis to provide a reliable evaluation of compressor IGV airfoils deviation and profile loss coefficients in a wide range of operating condition. The analysis were set up on the IGV of the Ansaldo Energia AE94.3A compressor and the developed correlations were successfully implemented in an in-house PAC called ESMS.

On the Performance of Porous Sound Absorbent Material in High Temperature Applications

This paper discusses the use of novel porous sound absorbent ceramic tiles as heat shields in combustion chambers with respect to their sound absorption. For this purpose a theory describing the bulk properties of a homogeneous porous absorber layer was combined with a transfer matrix approach to account for the temperature gradient within the absorber. By means of a high temperature scenario, the maximum absorption performance and the required microscale properties of the absorber are presented.

Ultra Low Emissions Combustion and Control Systems: Installation Into Mature Power Plant Gas Turbines

The search for power plant sustainability options continues as regulating agencies exert more stringent industrial gas turbine emission requirements on operators. Purchasing power for resale, de-comissioning current capabilities altogether and repowering by replacing or converting existing equipment to comply with emissions standards are economic-driven options contemplated by many mature gas turbine operators. One Las Vegas Nevada, USA operator, NV Energy, with four (4) natural gas fired W501B6 Combined Cycle units at their Edward W. Clark Generating Station, was in this situation in 2006. The units, originally configured with diffusion flame combustion systems, were permitted at 103 ppm NOx with regulatory mandates to significantly reduce NOx emissions to below 5ppm by the end of 2009. Studies were conducted by the operator to evaluate the economic viability of using a Selective Catalytic Reduction (SCR) system, which would have forced significant modifications to the exhaust system and heat recovery steam generator (HRSG), or convert the turbines to operate with dry low-emissions combustion systems. Based on life cycle cost and installation complexity, the ultra-low emission combustion system was selected. This technical paper focuses on a short summary of the end user considerations in downselecting options, the ultra low emissions technology and key features employed to achieve these low emissions, an overview of the conversion scope and a review and description of the control technology employed. Finally, a technical discussion of the low emissions operational flexibility will be provided including performance results of the converted units.

Performance Study for the Benefits of a Variable Pitch Composite Fan

This paper describes the installed performance potential for a recently patented new design concept for a variable pitch composite fan blade [1,2]. The unique characteristic of this design is the compactness and light weight of the assembly of fan plus variable pitch mechanism. This design enables turbofan engine cycles with higher propulsive efficiency that previously were not viable due to high installation weight and performance penalties. As part of its mandate to support new technology that improves fuel efficiency, the Connecticut Coalition for the Advancement of Technology (CCAT) sponsored a study to quantify the potential savings. A comparison is made between a current high bypass ratio engine and an advanced very high bypass ratio engine both configured to deliver approximately 30,000 lbs of thrust at the sea level static takeoff (SLTO) power setting. These engines are evaluated to determine the installed thrust and fuel consumption characteristics over the full spectrum of flight operation, enabling fuel burn to be evaluated for any aircraft mission. For a nominal mission profile considered in this paper, the advanced engine cycle enabled by the use of the variable pitch composite fan blade provided more than 12% reduction in fuel burn.