Different geometry patterns of the surface of thrust bearings have been proven very beneficial in terms of bearing loadcarrying capacity and friction coefficient. In this study, four different types of sector-pad thrust bearings have been crossevaluated for operation under realistic operating conditions: (a) an open pocket bearing, (b) a closed pocket bearing, (c) a tapered-land bearing, and (d) a bearing partially textured with rectangular dimples. Bearing performance has been computed by means of computational fluid dynamics simulations based on the numerical solution of the NavierStokes and energy equations for incompressible flow. Conjugate heat transfer at the bearing pad and rotor has been taken into account. Initially, for a reference design of each bearing, the effects of varying rotational speed and minimum film thickness have been investigated. Further, characterization of each bearing for a constant level of thrust load has been performed. Finally, the effects of varying the depth of each geometry pattern have been studied. The present results illustrate a superior performance of the open pocket bearing in comparison to the other bearing types.

Industrial gas turbines are susceptible to compressor fouling, which is the deposition and accretion of airborne particles or contaminants on the compressor blades. This paper demonstrates the blade aerodynamic effects of fouling through experimental compressor cascade tests and the accompanied engine performance degradation using turbomatch, an in-house gas turbine performance software. Similarly, on-line compressor washing is implemented taking into account typical operating conditions comparable with industry high pressure washing. The fouling study shows the changes in the individual stage maps of the compressor in this condition, the impact of degradation during part-load, influence of control variables, and the identification of key parameters to ascertain fouling levels. Applying demineralized water for 10 min, with a liquid-to-air ratio of 0.2%, the aerodynamic performance of the blade is shown to improve, however most of the cleaning effect occurred in the first 5 min. The most effectively washed part of the blade was the pressure side, in which most of the particles deposited during the accelerated fouling. The simulation of fouled and washed engine conditions indicates 30% recovery of the lost power due to washing.

On-line compressor washing for industrial gas turbine application is a promising method of mitigating the effects of compressor fouling degradation; however there are still few studies from actual engine experience that are inconclusive. In some cases the authors attribute this uncertainty as a result of other existing forms of degradation. The experimental approach applied here is one of the first of its kind, employing on-line washing on a compressor cascade and then relating the characteristics to a three-dimensional axial flow compressor. The overall performance of a 226MW engine model for the different cases of a clean, fouled and washed engine is obtained based on the changing compressor behavior. Investigating the effects of fouling on the clean engine exposed to blade roughness of 102μm caused 8.7% reduction in power at design point. This is equivalent, typically to 12 months degradation in fouling conditions. Decreases in mass flow, compressor efficiency, pressure ratio and unattainable design point speed are also observed. An optimistic recovery of 50% of the lost power is obtained after washing which lasts up to 10mins. Similarly, a recovery of all the key parameters is achieved. The study provides an insight into compressor cascade blade washing, which facilitates a reliable estimation of compressor overall efficiency penalties based on well established assumptions. Adopting Howell’s theory as well as constant polytropic efficiency, a general understanding of turbomachinery would judge that 50% of lost power recovered is likely to be the high end of what is achievable for the existing high pressure wash. This investigation highlights the obvious benefits of power recovery with on-line washing and the potential to maintain optimum engine performance with frequent washes. Clearly, the greatest benefits accrue when the washing process is initiated immediately following overhaul.

-In this paper, a computational investigation of thermohydrodynamic performance and mechanical deformations of a fixed-geometry thrust bearing with artificial surface texturing is presented. A parallel eight-pad bearing is considered; the surface of each pad is partially textured with square dimples. Here, a CFD-based thermohydrodynamic modeling approach, recently introduced by the authors, is used to calculate the performance of the bearing; the THD results are then used to quantify the deformations of the bearing mechanical parts. The bearing is modelled as a sector-shaped channel, consisting of a smooth rotating wall (thrust collar) and a partially textured stationary wall (bearing pad). The bearing performance characteristics are computed by means of numerical simulations, based on the numerical solution of the Navier-Stokes and energy equations for incompressible flow, as well as on the solution of the elasticity equations for the bearing solid parts. Here, a reference texture geometry is considered, while proper thermal and structural boundary conditions are implemented. For representative film thickness values, the effect of rotational speed and collar thickness on bearing performance is quantified, and the resulting pad and rotor deformation fields are computed. It is found that, due to oil heating, the load carrying capacity decreases with rotational speed for values higher that approximately 2000 rpm. The computed rotor deformation field is representative of a fixed support beam, characterized by substantially higher levels than those of the bearing pad. Rotor deformations increase substantially at low values of collar thickness.

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