Vibration Characteristics of a 75kW Turbo Machine With Air Foil Bearings

2006 ◽  
Vol 129 (3) ◽  
pp. 843-849 ◽  
Author(s):  
Kyeong-Su Kim ◽  
In Lee
Keyword(s):  
High Speed ◽  
Performance Test ◽  
Pressure Ratio ◽  
Vibration Characteristics ◽  
Operating Conditions ◽  
Maximum Pressure ◽  
Stable Operation ◽  
Foil Bearings ◽  
Wide Range ◽  
Free Environment

Air foil bearings are very attractive bearing systems for turbomachinery because they have several advantages over conventional bearings in terms of oil-free environment, low power loss, long life, and no maintenance. However, most of the developed machines using air foil bearings are limited to small and high-speed rotors of 60,000–120,000 rpm, since the increase in power of turbomachinery requires lower rotor speed and greater loading in bearings, which makes it difficult to use air foil bearings for large machines. In this paper, a 75 kW turboblower using air foil bearings is introduced, and the vibration characteristics of the machine have been investigated experimentally under a wide range of operating conditions, including compressor surge in the performance test. The machine is designed to be fully air lubricated and air cooled, and its operating speed is 20,000–26,000 rpm with maximum pressure ratio of 1.8. The results show that the air foil bearings offer adequate damping to ensure dynamically stable operation in the whole range.

Analysis of Thermal Damage in the High-Speed Foil Bearing

2017 ◽  
Vol 260 ◽  
pp. 266-277 ◽  
Author(s):  
Grzegorz Żywica ◽  
Paweł Bagiński ◽  
Artur Andrearczyk
Keyword(s):  
High Speed ◽  
Thermal Analyses ◽  
Experimental Tests ◽  
Significant Rise ◽  
Operating Conditions ◽  
Factors Affecting ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Wide Range ◽  
Heavy Loads

The article discusses experimental research and simulation testing on prototypical foil bearings. All experimental tests were conducted on a special test rig which makes it possible to operate in various conditions and within a wide range of speeds. As a result of the study, it turned out that adverse operating conditions caused almost instant bearing damage, accompanied by a significant rise in temperature. The main factors affecting the durability of foil bearings were material covering mating surfaces, bearing geometry, way of assembling the bearing, rotational speed and load. To better understand the physical phenomena occurring in foil bearings, a numerical model has been developed which allowed carrying out thermal analyses. The analysis of heat flow in the bearing's structure showed that, because of the system geometry, significant problems with proper removal of large amounts of heat continued to be experienced, which may have led to an accelerated rate of fatigue damage and shorter bearing life. This phenomenon can occur in bearings operating under tough conditions (e.g. at low speeds or under heavy loads). The research showed that the development of a new foil bearing is a very difficult task and requires many aspects to be taken into account, including the aspects directly related to the operation of the bearing itself, as well as those related to the rotor's operation and characteristics of the machine.

Flutter Generation and Control Using Mistuning in a Turbine Rotating Rig

2016 ◽  
Author(s):  
Roque Corral ◽  
Josu Beloki ◽  
Paolo Calza ◽  
Robert Elliot
Keyword(s):  
Rotor Blade ◽  
Vibration Amplitude ◽  
High Speed ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Density Level ◽  
Shaft Speed ◽  
Air Density ◽  
Wide Range ◽  
Bladed Rotor

The paper describes a free-flutter experiment on a stand-alone low-pressure turbine bladed rotor in a high-speed rotating wind tunnel together with the most relevant design decisions and solutions obtained for a low-reduced frequency cantilever shrouded rotor blade design. The test rotor underwent an experimental campaign with independent control of the shaft speed, pressure ratio and air density levels. Measurements were obtained entirely by means of non-intrusive techniques such as blade tip timing optical probes, and unsteady pressure transducers located in the outer casing of the rig downstream of the rotor. The bladed rotor was designed to flutter under a wide range of operating conditions. The independent effects of the shaft speed and the air density level were thoroughly investigated. It was concluded that, firstly, the higher the density level the higher the level of instability and, secondly, that the vibration amplitude of the rotor blade exhibits a maximum with the shaft speed. In addition the rotor blades were designed in such a way that additional masses could be mounted in the tip-shrouds to create arbitrary mistuning patterns. Two different mistuning patterns were tested, the first consisted of a classical alternate mistuning pattern designed to suppress flutter whereas a second pattern was designed to halve the vibration amplitude of the tuned bladed-disk. Both objectives were successfully achieved during the experiment.

Characteristics of air entrainment during dynamic wetting failure along a planar substrate

2014 ◽  
Vol 747 ◽  
pp. 119-140 ◽  
Author(s):  
E. Vandre ◽  
M. S. Carvalho ◽  
S. Kumar
Keyword(s):  
High Speed ◽  
Water Solution ◽  
Air Entrainment ◽  
Dynamic Contact ◽  
Operating Conditions ◽  
Dynamic Wetting ◽  
Glycerol Water ◽  
Planar Substrate ◽  
Wide Range ◽  
Stationary Plate

AbstractCharacteristic substrate speeds and meniscus shapes associated with the onset of air entrainment are studied during dynamic wetting failure along a planar substrate. Using high-speed video, the behaviour of the dynamic contact line (DCL) is recorded as a tape substrate is drawn through a bath of a glycerol/water solution. Air entrainment is identified by triangular air films that elongate from the DCL above some critical substrate speed. Meniscus confinement within a narrow gap between the substrate and a stationary plate is shown to delay air entrainment to higher speeds for a wide range of liquid viscosities, expanding upon the findings of Vandre, Carvalho & Kumar (J. Fluid Mech., vol. 707, 2012, pp. 496–520). A pressurized liquid reservoir controls the meniscus position within the confinement gap. It is found that liquid pressurization further postpones air entrainment when the meniscus is located near a sharp corner along the stationary plate. Meniscus shapes recorded near the DCL demonstrate that operating conditions influence the size of entrained air films, with smaller films appearing in the more viscous solutions. Regardless of size, air films become unstable to thickness perturbations and ultimately rupture, leading to the entrainment of air bubbles. Recorded critical speeds and air-film sizes compare well to predictions from a hydrodynamic model for dynamic wetting failure, suggesting that strong air stresses near the DCL trigger the onset of air entrainment.

Characteristics of Stable Rotating Stall Cells in an Axial Compressor

2017 ◽  
Author(s):  
Adam R. Hickman ◽  
Scott C. Morris
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Axial Compressor ◽  
Field Measurements ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Stable Operation ◽  
Double Phase

Flow field measurements of a high-speed axial compressor are presented during pre-stall and post-stall conditions. The paper provides an analysis of measurements from a circumferential array of unsteady shroud static pressure sensors during stall cell development. At low-speed, the stall cell approached a stable size in approximately two rotor revolutions. At higher speeds, the stall cell developed within a short amount of time after stall inception, but then fluctuated in circumferential extent as the compressor transiently approached a stable post-stall operating point. The size of the stall cell was found to be related to the annulus average flow coefficient. A discussion of Phase-Locked Average (PLA) statistics on flow field measurements during stable operation is also included. In conditions where rotating stall is present, flow field measurements can be Double Phase-Locked Averaged (DPLA) using a once-per-revolution (1/Rev) pulse and the period of the stall cell. The DPLA method provides greater detail and understanding into the structure of the stall cell. DPLA data indicated that a stalled compressor annulus can be considered to contained three main regions: over-pressurized passages, stalled passages, and recovering passages. Within the over-pressured region, rotor passages exhibited increased blade loading and pressure ratio compared to pre-stall values.

Influence of operating conditions on population dynamics in nitrifying biofilms

1999 ◽  
Vol 39 (7) ◽  
pp. 5-11 ◽  
Author(s):  
Valentina Lazarova ◽  
Danièle Bellahcen ◽  
Jacques Manem ◽  
David A. Stahl ◽  
Bruce E. Rittmann
Keyword(s):  
Population Dynamics ◽  
Ammonia Oxidation ◽  
Biofilm Reactor ◽  
Operating Conditions ◽  
Stable Operation ◽  
N Removal ◽  
Wide Range ◽  
Total Nitrogen Removal ◽  
Nitrite Oxidizers

TURBO N® is a circulating-bed biofilm reactor that provides stable operation and high N removal for a wide range of N and BOD loadings. This paper describes the influence of operating conditions on biofilm composition and population dynamics when the TURBO N® is operated to achieve tertiary nitrification, simultaneous carbon and ammonia oxidation and total nitrogen removal when coupled with a pre-denitrification fixed floating bed reactor. In situ specific nitrification rates and respiration tests showed that ammonium and nitrite oxidizers became less active in the biofilm once oxidation of influent BOD became important. Analyses of community structure with oligonucleotide probes targeted to the 16S rRNA showed the same general trends for nitrifiers, but also suggested shifts in the makeup of the ammonium and nitrite oxidizers that could not be detected with respirometry or specific nitrification rates.

Subsynchronous Vibration Patterns Under Reduced Oil Supply Flow Rates

2017 ◽  
Author(s):  
B. R. Nichols ◽  
R. L. Fittro ◽  
C. P. Goyne
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Operating Conditions ◽  
System Stability ◽  
Supporting Evidence ◽  
Test Rig ◽  
Flow Rates ◽  
Oil Supply ◽  
Bending Mode ◽  
Wide Range

Many high-speed, rotating machines across a wide range of industrial applications depend on fluid film bearings to provide both static support of the rotor and to introduce stabilizing damping forces into the system through a developed hydrodynamic film wedge. Reduced oil supply flow rate to the bearings can cause cavitation, or a lack of a fully developed film layer, at the leading edge of the bearing pads. Reducing oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses due to shear forces. While machine efficiency may be improved with reduced lubricant flow, little experimental data on its effects on system stability and performance can be found in the literature. This study looks at overall system performance of a test rig operating under reduced oil supply flow rates by observing steady-state bearing performance indicators and baseline vibrational response of the shaft. The test rig used in this study was designed to be dynamically similar to a high-speed industrial compressor. It consists of a 1.55 m long, flexible rotor supported by two tilting pad bearings with a nominal diameter of 70 mm and a span of 1.2 m. The first bending mode is located at approximately 5,000 rpm. The tiling-pad bearings consist of five pads in a vintage, flooded bearing housing with a length to diameter ratio of 0.75, preload of 0.3, and a load-between-pad configuration. Tests were conducted over a number of operating speeds, ranging from 8,000 to 12,000 rpm, and bearing loads, while systematically reducing the oil supply flow rates provided to the bearings under each condition. For nearly all operating conditions, a low amplitude, broadband subsynchronous vibration pattern was observed in the frequency domain from approximately 0–75 Hz. When the test rig was operated at running speeds above its first bending mode, a distinctive subsynchronous peak emerged from the broadband pattern at approximately half of the running speed and at the first bending mode of the shaft. This vibration signature is often considered a classic sign of rotordynamic instability attributed to oil whip and shaft whirl phenomena. For low and moderate load conditions, the amplitude of this 0.5x subsynchronous peak increased with decreasing oil supply flow rate at all operating speeds. Under the high load condition, the subsynchronous peak was largely attenuated. A discussion on the possible sources of this subsynchronous vibration including self-excited instability and pad flutter forced vibration is provided with supporting evidence from thermoelastohydrodynamic (TEHD) bearing modeling results. Implications of reduced oil supply flow rate on system stability and operational limits are also discussed.

Performance of Strongly Bowed Stators in a Four-Stage High-Speed Compressor

2004 ◽  
Vol 126 (3) ◽  
pp. 333-338 ◽  
Author(s):  
Axel Fischer ◽  
Walter Riess ◽  
Joerg R. Seume
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Maximum Pressure ◽  
Controlled Diffusion ◽  
Stage 4 ◽  
The University

The FVV sponsored project “Bow Blading” (cf. acknowledgments) at the Turbomachinery Laboratory of the University of Hannover addresses the effect of strongly bowed stator vanes on the flow field in a four-stage high-speed axial compressor with controlled diffusion airfoil (CDA) blading. The compressor is equipped with more strongly bowed vanes than have previously been reported in the literature. The performance map of the present compressor is being investigated experimentally and numerically. The results show that the pressure ratio and the efficiency at the design point and at the choke limit are reduced by the increase in friction losses on the surface of the bowed vanes, whose surface area is greater than that of the reference (CDA) vanes. The mass flow at the choke limit decreases for the same reason. Because of the change in the radial distribution of axial velocity, pressure rise shifts from stage 3 to stage 4 between the choke limit and maximum pressure ratio. Beyond the point of maximum pressure ratio, this effect is not distinguishable from the reduction of separation by the bow of the vanes. Experimental results show that in cases of high aerodynamic loading, i.e., between maximum pressure ratio and the stall limit, separation is reduced in the bowed stator vanes so that the stagnation pressure ratio and efficiency are increased by the change to bowed stators. It is shown that the reduction of separation with bowed vanes leads to a increase of static pressure rise towards lower mass flow so that the present bow bladed compressor achieves higher static pressure ratios at the stall limit.

scholarly journals The Design and Evaluation of a High Pressure Ratio Radial Turbine

1992 ◽  
Author(s):  
K. R. Pullen ◽  
N. C. Baines ◽  
S. H. Hill
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Pressure Ratio ◽  
Performance Measurements ◽  
Turbine Engine ◽  
High Pressure Ratio ◽  
Turbine Efficiency ◽  
Wide Range ◽  
Dimensional Parameters ◽  
Very High

A single stage, high speed, high pressure ratio radial inflow turbine was designed for a single shaft gas turbine engine in the 200 kW power range. A model turbine has been tested in a cold rig facility with correct simulation of the important non-dimensional parameters. Performance measurements over a wide range of operation were made, together with extensive volute and exhaust traverses, so that gas velocities and incidence and deviation angles could be deduced. The turbine efficiency was lower than expected at all but the lowest speed. The rotor incidence and exit swirl angles, as obtained from the rig test data, were very similar to the design assumptions. However, evidence was found of a region of separation in the nozzle vane passages, presumably caused by a very high curvature in the endwall just upstream of the vane leading edges. The effects of such a separation are shown to be consistent with the observed performance.

Assessment of engine combustion network recommendations for measurement of ignition and lift-off length

2020 ◽  
pp. 146808742092264
Author(s):  
Boni F Yraguen ◽  
Farzad Poursadegh ◽  
Caroline L Genzale
Keyword(s):  
Ignition Delay ◽  
High Speed ◽  
Operating Conditions ◽  
Bias Error ◽  
Ambient Conditions ◽  
Intensity Histogram ◽  
Wide Range ◽  
Engine Combustion ◽  
Length Measurements ◽  
Lift Off

The engine combustion network recommends two different imaging-based diagnostics for the measurement of diesel spray ignition delay and lift-off length, respectively. To measure ignition delay, high-speed imaging of broadband luminosity, spectrally filtered to limit collected wavelengths below 600 nm, is recommended. This diagnostic is often referred to as broadband natural luminosity. For lift-off length measurements, the engine combustion network recommends imaging of OH* chemiluminescence. This diagnostic requires using an image-intensified camera to detect narrowly filtered light around 310 nm. Alternatively, it has been shown that the lift-off length can be measured using broadband natural luminosity, avoiding the need for an intensifier and ultraviolet-transmitting optics. However, care is needed in the collection and processing of this diagnostic to accurately isolate the chemiluminescence signal. Particularly, standard intensity thresholding techniques are not sufficient for isolating the chemiluminescence signal in broadband natural luminosity images. Thus, an intensity-histogram-based thresholding method is introduced. This article assesses the feasibility and practicality of measuring lift-off length using broadband natural luminosity using a detailed comparison to OH* chemiluminescence measurements. It is shown that lift-off length measurements using broadband natural luminosity are prone to user bias error in the optical setup and data processing, especially under moderate- to high-sooting conditions. We conclude that while OH* imaging provides the most reliable and accurate measurement of lift-off length at a wide range of ambient conditions, an intensity-histogram analysis can help discriminate the high-temperature chemiluminescence signal from others in a broadband natural luminosity image at higher-sooting operating conditions than demonstrated in current literature.

Theory Versus Experiment for the Effects of Pressure Ratio on the Performance of an Orifice-Compensated Hybrid Bearing

1998 ◽  
Vol 120 (4) ◽  
pp. 930-936 ◽  
Author(s):  
P. Mosher ◽  
D. W. Childs
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Load Capacity ◽  
Dynamic Stiffness ◽  
Pressure Ratio ◽  
Navier Stokes ◽  
Rotordynamic Coefficients ◽  
Wide Range ◽  
Bearing Load ◽  
Hybrid Bearing

This research investigates the effect of varying the concentric recess pressure ratio of hybrid (combination hydrostatic and hydrodynamic) bearings to be used in high-speed, high-pressure applications. Bearing flowrate, load capacity, torque, rotordynamic coefficients, and whirl frequency ratio are examined to determine the concentric, recess-pressure ratio which yields optimum bearing load capacity and dynamic stiffness. An analytical model, using two-dimensional bulk-flow Navier-Stokes equations and anchored by experimental test results, is used to examine bearing performance over a wide range of concentric recess pressure ratios. Typically, a concentric recess pressure ratio of 0.50 is used to obtain maximum bearing load capacity. This analysis reveals that theoretical optimum bearing performance occurs for a pressure ratio near 0.40, while experimental results indicate the optimum value to he somewhat higher than 0.45. This research demonstrates the ability to analytically investigate hybrid bearings and shows the need for more hybrid-bearing experimental data.

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