Testing and analysis of a profiled leading edge groove tilting pad journal bearing developed for light load operation is described. This bearing was designed for a generic, small, high speed steam turbine operating at projected loads of less than 25 psi (172.4 kPa) and journal surface speeds to 400 ft/s (122 m/s). On the second turbine application, a rotor instability was experienced with the oil flowrate reduced to optimize bearing steady state performance. This instability was eliminated by machining a taper on the exit side of the feed groove on each pad. At the reduced flowrate, the profiled groove bearing greatly improved the operating characteristics of the rotor system by reducing vibration amplitudes and stabilizing operation at speed. This paper is divided into two sections. The first section compares the rotordynamics analysis with test data that shows improved unbalance response and operating stability with the profiled groove bearing. The second section provides original insight of the effect of the profiled geometry on the bearing flow field using computational fluid dynamics models.
The amount of cooling air assigned to seal high pressure turbine rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk or cover plate life. Excessive purge air, on the other hand, adversely affects performance. This paper is Part-2 of the authors’ work on ingestion reported last year [1]. Whereas, the main focus of that investigation was to qualitatively describe ingestion driven by annulus circumferential pressure asymmetry under constant annulus conditions and rotational speed, in this paper, the research team investigated the variation of annulus circumferential pressure fluctuation and rotational speed on the double overlap platform rim seal cavity reported in Part-1, and mapped out the resulting non-dimensional minimum sealing flow (minimum value of Cw or Cw,min) as it relates to entrained ingestion in the absence of cavity cooling flow (Cw,ent). As was done in Part-1, the runs were made with 3D CFD in setup/run mode option using Fine/Turbo. At two rotational speeds, annulus conditions were varied by reducing turbine inlet pressure (i.e. mass flow) from the baseline operating condition, and the resulting pressure fluctuation was quantified. In addition, a preliminary investigation to assess the aft-located mixing plane steady state solution for this study was performed. The results yielded the linear decrease in Cw,ent at fixed rotational Reynolds number as annulus Reynolds number was decreased. Moreover, the rate of change in entrained flow sharply increases with increase in rotational Reynolds number. As annulus mass flow is reduced to a critical value defined by annulus-to-rotational Reynolds number ratio, the CFD prediction for Cw,ent converges to the turbulent boundary layer entrainment solution for the rotor, and Cw,min reverts to the rotational Reynolds number dominating region. The results from this study were compared to what has been observed by a previous study for a single overlap platform geometry. The resulting design curve allows insight in relating cavity purge flow requirements versus turbine cycle parameters which could lead to better efficiency.
The amount of cooling air assigned to seal high pressure turbine rim cavities is critical for performance as well as component life. Less air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk life. Excessive purge air adversely affects performance. The minimum purge (i.e. sealing) air requirement to control ingestion is also influenced by annulus circumferential pressure fluctuation present over the rim seal cavity. Its interaction with the platform gap resistance and the amount of purge air needs to be understood in order to reliably predict performance and component life. Work has commenced to investigate opportunities in reducing disk cavity purge flow requirements by studying ways to control ingestion. The study has been initiated with 3D CFD model setup/run mode options to benchmark main/cavity flow field interactions. The selection of the appropriate CFD model fidelity, however, is one of the main goals of this work. The CFD model phase has 3 options to be evaluated; 1) steady solution with mixing plane aft of the cavity, 2) steady solution with mixing plane forward of the cavity, 3) unsteady solution. Option 1 has been completed and is the subject of this paper. A reference HP turbine stage and disk cavity from an engine design was selected for the CFD study. The steady flow solution model captured the oscillatory movement and penetration depth of ingestion by varying purge flow rate and observing the impact on the mixing plane forward and aft of the disk cavity. Moreover, the influence of upstream stator vane airfoil fillet shape was also investigated. The entrained flow was established by starving the cavity and integrating the outflow along the disk. This value along with the nominal and intermediate cavity purge flows were validated against relevant sealing flow design correlations. At a radial location near the rim, an ingestion mixing efficiency value versus purge flow rate was obtained which correlates well with recent unsteady flow results from the literature.
This paper describes the experimental approach utilized to perform experiments using a fully cooled rotating turbine stage to obtain film effectiveness measurements. Significant changes to the previous experimental apparatus were implemented to meet the experimental objectives. The modifications include the development of a synchronized blowdown facility to provide cooling gas to the turbine stage, installation of a heat exchanger capable of generating a uniform or patterned inlet temperature profile, novel utilization of temperature and pressure instrumentation, and development of robust double-sided heat flux gauges. With these modifications, time-averaged and time-accurate measurements of temperature, pressure, surface heat flux, and film effectiveness can be made over a wide range of operational parameters, duplicating the nondimensional parameters necessary to simulate engine conditions. Data from low Reynolds number experiments are presented to demonstrate that all appropriate scaling parameters can be satisfied and that the new components have operated correctly. Along with airfoil surface heat transfer and pressure data, temperature and pressure data from inside the coolant plenums of the vane and rotating blade airfoils are presented. Pressure measurements obtained inside the vane and blade plenum chambers illustrate passing of the wakes and shocks as a result of vane/blade interaction. Part II of this paper (Haldeman, C. W., Mathison, R. M., Dunn, M. G., Southworth, S. A., Harral, J. W., and Heltland, G., 2008, ASME J. Turbomach., 130(2), p. 021016) presents data from the low Reynolds number cooling experiments and compares these measurements to CFD predictions generated using the Numeca FINE/Turbo package at multiple spans on the vanes and blades.
This paper presents measurements and the companion computational fluid dynamics (CFD) predictions for a fully cooled, high-work single-stage HP turbine operating in a short-duration blowdown rig. Part I of this paper (Haldeman, C. W., Mathison, R. M., Dunn, M. G., Southworth, S. A., Harral, J. W., and Heltland, G., 2008, ASME J. Turbomach., 130(2), p. 021015) presented the experimental approach, and Part II focuses on the results of the measurements and demonstrates how these results compare to predictions made using the Numeca FINE/Turbo CFD package. The measurements are presented in both time-averaged and time-accurate formats. The results include the heat transfer at multiple spans on the vane, blade, and rotor shroud as well as flow path measurements of total temperature and total pressure. Surface pressure measurements are available on the vane at midspan, and on the blade at 50% and 90% spans as well as the rotor shroud. In addition, temperature and pressure measurements obtained inside the coolant cavities of both the vanes and blades are presented. Time-averaged values for the surface pressure on the vane and blade are compared to steady CFD predictions. Additional comparisons will be made between the heat transfer on cooled blades and uncooled blades with identical surface geometry. This, along with measurements of adiabatic wall temperature, will provide a basis for analyzing the effectiveness of the film cooling scheme at a number of locations.
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