Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System—Part I: Measurements

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Luis San Andrés ◽  
Keun Ryu ◽  
Tae Ho Kim
Keyword(s):  
Thermal Management ◽  
Gas Turbines ◽  
Companion Paper ◽  
Outer Diameter ◽  
Predictive Tool ◽  
Heater Temperature ◽  
Foil Bearings ◽  
Cooling Flow ◽  
Limited Effectiveness ◽  
System Temperature

Implementation of gas foil bearings (GFBs) into micro gas turbines requires careful thermal management with accurate measurements verifying model predictions. This two-part paper presents test data and analytical results for a test rotor and GFB system operating hot (157°C maximum rotor outer diameter (OD) temperature). Part I details the test rig and measurements of bearing temperatures and rotor dynamic motions obtained in a hollow rotor supported on a pair of second generation GFBs, each consisting of a single top foil (38.14 mm inner diameter) uncoated for high temperature operation and five bump strip support layers. An electric cartridge (maximum of 360°C) loosely installed inside the rotor (1.065 kg, 38.07 mm OD, and 4.8 mm thick) is a heat source warming the rotor-bearing system. While coasting down from 30 krpm to rest, large elapsed times (50–70 s) demonstrate rotor airborne operation, near friction free, and while traversing the system critical speed at ∼13 krpm, the rotor peak motion amplitude decreases as the system temperature increases. In tests conducted at a fixed rotor speed of 30 krpm, while the shaft heats, a cooling gas stream of increasing strength is set to manage the temperatures in the bearings and rotor. The effect of the cooling flow, if turbulent in character, is most distinctive at the highest heater temperature. For operation at a lower heater temperature condition, however, the cooling flow stream demonstrates a very limited effectiveness. The measurements demonstrate the reliable performance of the rotor-GFB system when operating hot. The test results, along with full disclosure on the materials and geometry of the test bearings and rotor, serve to benchmark a predictive tool. A companion paper (Part II) compares the measured bearing temperatures and the rotor response amplitudes to predictions.

Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System: Part 1—Measurements

2010 ◽  
Author(s):  
Luis San Andre´s ◽  
Tae Ho Kim ◽  
Keun Ryu
Keyword(s):  
Thermal Management ◽  
Gas Turbines ◽  
Companion Paper ◽  
Predictive Tool ◽  
Heater Temperature ◽  
Foil Bearings ◽  
Cooling Flow ◽  
Limited Effectiveness ◽  
Reliable Performance ◽  
System Temperature

Implementation of gas foil bearings (GFBs) into micro gas turbines requires careful thermal management with accurate measurements verifying model predictions. This two-part paper presents test data and analytical results for a test rotor and GFB system operating hot (157°C max. rotor OD temperature). Part 1 details the test rig and measurements of bearing temperatures and rotor dynamic motions obtained in a hollow rotor supported on a pair of 2nd generation GFBs, each consisting of a single top foil (38.14 mm ID) uncoated for high temperature operation, and five bump strip support layers. An electric cartridge (max. 360°C) loosely installed inside the rotor (1.065 kg, 38.07 mm OD, and 4.8 mm thick) is a heat source warming the rotor-bearing system. While coasting down from 30 krpm to rest, large elapsed times (50∼70 s) demonstrate rotor airborne operation, near friction free; and, while traversing the system critical speed at ∼13 krpm, the rotor peak motion amplitude decreases as the system temperature increases. In tests conducted at a fixed rotor speed of 30 krpm, while the shaft heats, a cooling gas stream of increasing strength is set to manage the temperatures in the bearings and rotor. The effect of the cooling flow, if turbulent in character, is most distinctive at the highest heater temperature. For operation at a lower heater temperature condition, however, the cooling flow stream demonstrates a very limited effectiveness. The measurements demonstrate the reliable performance of the rotor-GFB system when operating hot. The test results, along with full disclosure on the materials and geometry of the test bearings and rotor, serve to benchmark a predictive tool. A companion paper (Part 2) compares the measured bearing temperatures and the rotor response amplitudes to predictions.

On the Failure of a Gas Foil Bearing: High Temperature Operation Without Cooling Flow

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Keun Ryu ◽  
Luis San Andrés
Keyword(s):  
High Temperature ◽  
Gas Turbine ◽  
Mechanical Energy ◽  
Test System ◽  
System Component ◽  
Outer Diameter ◽  
Foil Bearings ◽  
Cooling Flow ◽  
Thermal Growth ◽  
Reliability Issue

Implementing gas foil bearings (GFBs) in micro gas turbine engines is a proven approach to improve system efficiency and reliability. Adequate thermal management for operation at high temperatures, such as in a gas turbine or a turbocharger, is important to control thermal growth of components and to remove efficiently mechanical energy from the rotor mainly. The paper presents a test rotor supported on GFBs operating with a heated shaft and reports components temperatures and shaft motions at an operating speed of 37 krpm. An electric cartridge heater loosely inserted in the hollow rotor warms the test system. Thermocouples and noncontact infrared thermometers record temperatures on the bearing sleeve and rotor outer diameter (OD), respectively. No forced cooling air flow streams were supplied to the bearings and rotor, in spite of the high temperature induced by the heater on the shaft outer surface. With the rotor spinning, the tests consisted of heating the rotor to a set temperature, recording the system component temperatures until reaching thermal equilibrium in  ∼ 60 min, and stepping the heater set temperature by 200 °C. The experiments proceeded without incident until the heater set temperature equaled 600 °C. Ten minutes into the test, noise became apparent and the rotor stopped abruptly. The unusual operating condition, without cooling flow and a too large increment in rotor temperature, reaching 250 °C, led to the incident which destroyed one of the foil bearings. Post-test inspection evidenced seizure of the hottest bearing (closest to the heater) with melting of the top foil at the locations where it rests on the underspring crests (bumps). Analysis reveals a notable reduction in bearing clearance as the rotor temperature increases until seizure occurs. Upon contact between the rotor and top foil, dry-friction quickly generated vast amounts of energy that melted the protective coating and metal top foil. Rather than a reliability issue with the foil bearings, the experimental results show poor operating procedure and ignorance on the system behavior (predictions). A cautionary tale and a lesson in humility follow.

Prediction of Axial and Circumferential Flow Conditions in a High Temperature Foil Bearing With Axial Cooling Flow

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Keun Ryu
Keyword(s):  
Thin Film ◽  
High Temperature ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Thermal Management ◽  
Flow Rate ◽  
Successful Implementation ◽  
Flow Conditions ◽  
Cooling Flow ◽  
Limited Effectiveness

A successful implementation of gas foil bearings (GFBs) into high temperature turbomachinery requires adequate thermal management to maintain system reliability and stability. The most common approach for thermal management in a GFB-rotor system is to supply pressurized air at one end of the bearing to remove hot spots in the bearings and control thermal growth of components. This technical brief presents test data for a laboratory rotor-GFB system operating hot to identify the flow characteristics of axial cooling streams flowing through the thin film region and underneath the top foil. A bulk flow model is used for description of the fluid motion and includes the Hirs’ friction factor formulation for smooth surfaces. Laminar flow prevails through the thin film gas region; while for the cooling flow between the top foil and bearing housing, a transition from laminar flow to turbulent flow occurs as the cooling flow rate increases. Large cooling flow rate and the ensuing turbulent flow conditions render limited effectiveness in controlling temperatures in a test rotor-GFB system.

scholarly journals Effect of Cooling Flow on the Operation of a Hot Rotor-Gas Foil Bearing System

2012 ◽  
Author(s):  
Keun Ryu ◽  
Luis San Andrés
Keyword(s):  
Thermal Management ◽  
Flow Rate ◽  
System Integration ◽  
Damping Ratio ◽  
Temperature Drop ◽  
Test System ◽  
The Body ◽  
Air Cooling ◽  
Cooling Flow ◽  
Management Procedures

Gas foil bearings (GFBs) operating at high temperature rely on thermal management procedures that supply needed cooling flow streams to keep the bearing and rotor from overheating. Poor thermal management not only makes systems inefficient and costly to operate but could also cause bearing seizure and premature system destruction. This paper presents comprehensive measurements of bearing temperatures and shaft dynamics conducted on a hollow rotor supported on two first generation GFBs. The hollow rotor (1.36 kg, 36.51 mm OD and 17.9 mm ID) is heated from inside to reach an outer surface temperature of 120°C. Experiments are conducted with rotor speeds to 30 krpm and with forced streams of air cooling the bearings and rotor. Air pressurization in an enclosure at the rotor mid span forces cooling air through the test GFBs. The cooling effect of the forced external flows is most distinct when the rotor is hottest and operating at the highest speed. The temperature drop per unit cooling flow rate significantly decreases as the cooling flow rate increases. Further measurements at thermal steady state conditions and at constant rotor speeds show that the cooling flows do not affect the amplitude and frequency contents of the rotor motions. Other tests while the rotor decelerates from 30 krpm to rest show that the test system (rigid-mode) critical speeds and modal damping ratio remain nearly invariant for operation with increasing rotor temperatures and with increasing cooling flow rates. Computational model predictions reproduce the test data with accuracy. The work adds to the body of knowledge on GFB performance and operation and provides empirically derived guidance for successful rotor-GFB system integration.

Compliant Plate Seals: Design and Performance Simulations

2012 ◽  
Author(s):  
Hrishikesh V. Deo ◽  
Ajay Rao ◽  
Hemant Gedam
Keyword(s):  
Gas Turbines ◽  
Tip Clearance ◽  
Outer Diameter ◽  
Aircraft Engines ◽  
Steam Turbines ◽  
Flow Rates ◽  
Cfd Models ◽  
Low Leakage ◽  
And Performance ◽  
Large Rotor

Compliant Plate Seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines and oil & gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around a rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip–clearance. Due to this self–correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and non–contact operation even in the presence of large rotor transients. CFD models have been developed to predict the leakage flow rates and hydrostatic lift and blowdown forces, and a design philosophy is proposed to predict the feedback phenomenon from the CFD results.

Bearing Housing Design for Vibration Control, Using Tilting Pad Bearings Instead of Lemon-Bore Type on a Gas Turbine

2020 ◽  
Author(s):  
Chippa Anil ◽  
Aparna Satheesh ◽  
Babu Santhanagopalakrishnan ◽  
Marcin Bielecki
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Structural Integrity ◽  
Plane Surface ◽  
Rotor Dynamics ◽  
Turbine Rotor ◽  
Outer Diameter ◽  
Housing Design ◽  
Tilting Pad ◽  
And Performance

Abstract Heavy duty gas turbines are usually equipped with hydrodynamic bearings which are either lemon-bore or tilting pad type. Baker Hughes legacy gas turbines use these two types of bearings, and its selection is based on 1) considering pros & cons from Rotor dynamics, 2) bearing performance, 3) bearing housing stiffness, 4) vibration detection & control. Non-contact probes are used to monitor the vibrations of rotor. Majority of legacy gas turbines are not equipped with these probes. Due to this fact, over the years it resulted in non-detection of dynamics & vibration issue, which caused frequent bearing replacement. As the increase in industry demand to apply and measure vibrations using non-contact probes on bearings, an effort was made by Baker Hughes to implement these on existing fleet units. Also, in order to increase rotor dynamics stability of low-pressure rotor, to improve bearing life and performance, effort was made to replace lemon-bore bearings with tilting pad. This paper demonstrates efforts made to design the titling pad which would fit within envelop of already available bearing housing. Bearing/shaft clearance, bearing performance, modification of bearing retainer clearances are the mandatory tasks which would be dealt in this study. The swap of bearing type, and its effect on whole gas turbine rotor dynamic stability, checking the frequency crossovers with Campbell diagram would also be dealt in this paper. This paper also focuses on assessment on oil passage routing, temperature & proximity probe instrumentation routing design. Re-design is performed by analyzing various configuration, assessing different sensitivity studies & validation of modified bearing housing from structural integrity, ultimate load capability, & split plane oil leakage retention and its comparison with baseline are most important aspects of finalization of this change, which will be showcased in this paper. Instrumentation routing was a critical task when the considering bearing replacement from lemon-bore to tilting pad. As lemon-bore type bearings just have an elliptical inner surface, it’s quite easy to install the thermocouples into a simple hole. But as replacement has tilting pads, the challenge is to instrument the pads without effecting their movement and functionality. Such best practices are also dealt in this paper. Comparison of tilting-pad with lemon-bore, considering the fixed shaft diameter, the retainer outer diameter of tilting pad is higher than lemon-bore. This effect has a change in bearing seat on bearing housing, thereby reducing the effective stiffness of the housing, and the reduced split plane surface. To tackle this situation, several sensitivities were executed, by re-modifying the bolts and bolt holes on the existing housing, without modifying the housing envelop.

Time-Resolved Heat Transfer and Surface Pressure Measurements for a Fully Cooled Transonic Turbine Stage

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Jeremy B. Nickol ◽  
Randall M. Mathison ◽  
Malak F. Malak ◽  
Rajiv Rana ◽  
Jong S. Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Field ◽  
Surface Pressure ◽  
High Frequency ◽  
Gas Turbines ◽  
Pressure Measurements ◽  
Turbine Stage ◽  
Cooling Flow ◽  
Blade Cooling

The flow field in axial gas turbines is driven by strong unsteady interactions between stationary and moving components. While time-averaged measurements can highlight many important flow features, developing a deeper understanding of the complicated flows present in high-speed turbomachinery requires time-accurate measurements that capture this unsteady behavior. Toward this end, time-accurate measurements are presented for a fully cooled transonic high-pressure turbine stage operating at design-corrected conditions. The turbine is run in a short-duration blowdown facility with uniform, radial, and hot streak vane-inlet temperature profiles as well as various amounts of cooling flow. High-frequency response surface pressure and heat-flux instrumentation installed in the rotating blade row, stator vane row, and stationary outer shroud provide detailed measurements of the flow behavior for this stage. Previous papers have reported the time-averaged results from this experiment, but this paper focuses on the strong unsteady phenomena that are observed. Heat-flux measurements from double-sided heat-flux gauges (HFGs) cover three spanwise locations on the blade pressure and suction surfaces. In addition, there are two instrumented blades with the cooling holes blocked to isolate the effect of just blade cooling. The stage can be run with the vane and blade cooling flow either on or off. High-frequency pressure measurements provide a picture of the unsteady aerodynamics on the vane and blade airfoil surfaces, as well as inside the serpentine coolant supply passages of the blade. A time-accurate computational fluid dynamics (CFD) simulation is also run to predict the blade surface pressure and heat-flux, and comparisons between prediction and measurement are given. It is found that unsteady variations in heat-flux and pressure are stronger at low to midspan and weaker at high span, likely due to the impact of secondary flows such as the tip leakage flow. Away from the tip, it is seen that the unsteady fluctuations in pressure and heat-flux are mostly in phase with each other on the suction side, but there is some deviation on the pressure side. The flow field is ultimately shown to be highly three-dimensional, as the movement of high heat transfer regions can be traced in both the chord and spanwise directions. These measurements provide a unique picture of the unsteady flow physics of a rotating turbine, and efforts to better understand and model these time-varying flows have the potential to change the way we think about even the time-averaged flow characteristics.

Temperature-Based Optimization of Film Cooling in Gas Turbine Hot Gas Path Components

2013 ◽  
Author(s):  
Felipe A. C. Viana ◽  
Jack Madelone ◽  
Niranjan Pai ◽  
Genghis Khan ◽  
Sanghum Baik
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Optimization Design ◽  
Goal Attainment ◽  
High Efficiency ◽  
Cooling System ◽  
Computational Cost ◽  
Metal Temperature ◽  
Cooling Flow ◽  
Hot Gas

To achieve high efficiency, modern gas turbines operate at temperatures that exceed melting points of metal alloys used in turbine hot gas path parts. Parts exposed to hot gas are actively cooled with a portion of the compressor discharge air (e.g., through film cooling) to keep the metal temperature at levels needed to meet durability requirements. However, to preserve efficiency, it is important to optimize the cooling system to use the least amount of cooling flow. In this study, film cooling optimization is achieved by varying cooling hole diameters, hole to hole spacing, and film row placements so that the specified targets for maximum metal temperature are met while preserving (or saving) cooling flow. The computational cost of the high-fidelity physics models, the large number of design variables, the large number and nonlinearity of responses impose severe challenges to numerical optimization. Design of experiments and cheap-to-evaluate approximations (radial basis functions) are used to alleviate the computational burden. Then, the goal attainment method is used for optimizing of film cooling configuration. The results for a turbine blade design show significant improvements in temperature distribution while maintaining/reducing the amount of used cooling flow.

Test Evolution and Oil-Free Engine Experience of a High Temperature Foil Air Bearing Coating

2006 ◽  
Author(s):  
Daniel Lubell ◽  
Christopher DellaCorte ◽  
Malcolm Stanford
Keyword(s):  
High Temperature ◽  
Gas Turbines ◽  
Solid Lubricants ◽  
Deposition Process ◽  
Air Bearing ◽  
Free Gas ◽  
Foil Bearings ◽  
Start Up ◽  
High Temperature Operation

During the start-up and shut-down of a turbomachine supported on compliant foil bearings, before the bearings have full development of the hydrodynamic gas film, sliding occurs between the rotor and the bearing foils. Traditional solid lubricants (e.g., graphite, Teflon®) readily solve this problem at low temperature. High temperature operation, however, has been a key obstacle. Without a suitable high temperature coating, foil air bearing use is limited to about 300°C (570°F). In oil-free gas turbines, a hot section bearing presents a very aggressive environment for these coatings. A NASA developed coating, PS304, represents one tribological approach to this challenge. In this paper, the use of PS304 as a rotor coating operating against a hot foil gas bearing is reviewed and discussed. During the course of several long term, high cycle, engine tests, which included two coating related failures, the PS304 technology evolved and improved. For instance, a post deposition thermal treatment to improve dimensional stability, and improvements to the deposition process to enhance strength resulted from the engine evaluations. Largely because of this work, the bearing/coating combination has been successfully demonstrated at over 500°C (930°F) in an oil-free gas turbine for over 2500 hours and 2900 start-stop cycles without damage or loss of performance when properly applied. Ongoing testing at Glenn Research Center as part of a long term program is over 3500 hours and 150 cycles.

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