bluuebunny/crossref_metadata_2025_split huggingface dataset:
Static and Rotordynamic Characteristics of Liquid Annular Seals With a Circumferentially-Grooved Stator and Smooth Rotor Using Three Levels of Circumferential Inlet-Fluid Rotation
Authors: Childs Dara W. , Torres Jose M. , Bullock Joshua T. 
Published: August 2018

Test results are presented for a smooth-rotor/circumferentially-grooved, annular pump seal. The seal’s geometry and operating conditions are representative of electrical submersible pumps (ESPs) as used for oil recovery; however, most ESPs use grooved rotors instead of grooved stators. Test results include static and rotordynamic data at speeds ω of 2, 4, 6 krpm, axial pressure drops ΔP of 2.1, 4.1, 6.2, 8.3 bars. The grooved seal has a length-to-diameter ratio L/D of 0.5 and a minimum radial clearance Cr of 203 μm. It employs 15 circumferential grooves with a length Gl, and depth Gd of 1.52 mm, which are equally-spaced by a land length of 1.52 mm. Tests are conducted for eccentricity ratios ϵ0 of 0.00, 0.27, 0.53, 0.80. Three different inlet-fluid prerotation inserts are used upstream of the test seals to create a range of inlet preswirl ratios. Pitot tubes are used to measure the circumferential velocity at one location immediately upstream of the test seal and one downstream location near the seal exit. The test fluid is ISOVG2 oil @ 46 °C.
Test results for the grooved seal are compared to test results for a smooth annular seal with the same L, D, and minimum Cr. The grooved-seal’s leakage rate Q̇, ranges from a low 15.64 LPM at ω = 6 krpm, and ΔP = 2 bar, to a high 56.36 LPM at ω = 2 krpm, and ΔP = 8 bar. When compared to the smooth seal, the grooved seal provides a 20% Q̇ reduction at ω = 2 krpm, and a 6% reduction at ω = 6 krpm.
The grooved seal’s rotordynamic coefficients are generally not sensitive to changes in ϵ0. The smooth seal’s stiffness and damping coefficients are not very sensitive to changes in ϵ0 in moving from ϵ0 = 0 to 0.5, but typically increase dramatically in magnitude in moving from ϵ0 = 0.5 to 0.8.
From a rotordynamic viewpoint, the major difference between the two seals concerns the direct stiffness coefficients, with the grooved seal having near zero to negative values and the smooth seal having larger positive values, particularly at increased ϵ0 values. The grooved seal generally produces lower-magnitude cross-coupled stiffness and direct damping coefficient values than the smooth seal.
A Simple (1-Flexible Rotor) Model That Shows Bull Gear Runout As a Source of Subsynchronous, Lateral, Vibration in Integrally Geared Compressor (IGC) Pinions
Authors: Childs Dara , Crandall Andrew 
Published: August 2018

A new flexible-pinion-shaft rotor model is presented to predict the response of the pinion shaft of an integrally geared compressor (IGC). The motion of the pinion shaft is driven by: (1) its own imbalance and (2) the axial reaction force developed by relative axial motion at the thrust collar (TC) that connects it to the pinion. The axial reaction force at the TC arises because of the relative axial motion between the pinion shaft and the bull gear (BG) at the overlapping area of the TC. The relative axial motion arises because of: (1) absolute axial motion of the pinion (assumed to be a rigid body), (2) pitch and yaw motion of the pinion at the TC, and (3) absolute axial motion of the BG at the TC overlap area. Because the axial reaction force acts at a radial distance from the mass center of the TC disk, it creates moments that couple the relative axial motion of the pinion and BG shafts to the radial motion of the pinion. The present model includes the local flexural stiffness of the BG.
Excitation for the model is provided by: (1) runout from the BG at its running speed, Ω, acting through the axial reaction force of the TC, (2) runout from the pinion at its running speed, ω, acting through the axial reaction force of the TC, and (3) pinion TC mass imbalance at ω. Measured axial runouts of the BG and TC were taken from a test rig at the authors’ laboratory. Predictions for the TC oil-film axial stiffness and damping come from a proprietary Reynolds equation solution to the TC oil-film. The local axial stiffness of the BG at the overlap area was obtained from a finite element analysis of the authors’ test rig. The base rotordynamic model for the pinion was provided for a production IGC pinion by an IGC manufacturer including the bearings and structural dynamics model.
Waterfall plots are presented from the model’s predictions of radial motion at the IGC’s Stage 1 compressor impeller. The response is dominated by synchronous response at the pinion speed, ω, and tracking subsynchronous response at the BG speed, Ω. The response at ω comes from the pinion’s imbalance, not the pinion runout at the TC. The response at Ω comes from the BG runout acting across the TC. The IGC manufacturer’s representatives state that predictions from the model are consistent with measurements from real IGCs, particularly in regard to the presence (and amplitudes) of tracking subsynchronous response amplitudes at the BG frequency.
Obviously, more detailed models can be developed for the rotordynamics of IGCs, but the authors feel that this relatively simple, one-rotor model, is adequate to predict the observed tracking phenomena in IGCs. The analysis can be produced by modifying an existing rotor code or by simply downloading the rotor’s [M], [K], and [C] matrices over a range of speeds and then using MATLAB or similar codes.
Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD
Authors: Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni , Holst David , Church Benjamin , Wegner Felix , Pechlivanoglou George , Nayeri Christian Navid , Paschereit Christian Oliver , Ferrari Lorenzo 
Published: August 2018

The wind industry needs airfoil data for ranges of Angle of Attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 degree are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and post stall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design.
Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140k and Re = 180k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies.
Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behaviour. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.
Axial Compressor Performance Prediction Using Improved Streamline Curvature Approach
Authors: Li Tao , Wu Yadong , Ouyang Hua , Qiang Xiaoqing 
Published: August 2018

This paper presents in detail the improved streamline curvature approach (SLC) to the performance evaluation and internal flow field calculation of subsonic and transonic axial compressors. Based on previous research, the diverse incidence, deviation and total pressure loss models, generally existing in the form of fitting curves and semi-empirical correlations, are discussed respectively. Typically, transonic flow in axial compressor results in the variation of several flow parameters and particularly the appearance of shock waves compared with subsonic flow. In this paper, the revision and improvement of loss models are applied to reach higher accuracy, especially considering the loss component due to actual incidence angle. Several modifications have been made as well considering the influence of three-dimensional flow.
For the purpose of validating this approach, two test cases, including a single-stage transonic axial compressor NASA Stage37 and a 3-stage subsonic axial compressor P&W 3S1, are calculated. The overall characteristics and spanwise aerodynamic parameters for blade rows are demonstrated at both design and off-design conditions. Furthermore, the results agree well with both experimental data and computational fluid dynamic (CFD) results. This throughflow method is verified as an applicable and convenient tool for aerodynamic analysis and performance prediction of subsonic and transonic axial compressors.
Formation and Evolution of Rayleigh-Bénard Streaks in Rotating Cavities
Authors: Puttock-Brown M. R. , Rose M. G. 
Published: August 2018

This paper presents numerical investigation into the phenomena of so-called Rayleigh-Bénard streaks inside rotating-cavities. Experimental data from the University of Sussex Multiple Cavity Rig (MCR) has been used as boundary conditions for Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculation using the k-ω SST turbulence model on a three cavity model of the MCR. A four-point validation is presented using comparison to experimental and historical data sets and shows encouraging agreement.
The Rayleigh-Bénard streaks develop along the periphery of the rotating cavity (shroud) and are only associated with flow involved in cyclonic circulation due to the circumferential pressure gradient. These streaks modify the local Nusselt number by as much as 40% above the surface average and, given the contribution of the shroud to the total heat transfer, upwards of 60%, may be a significant factor in further work concerning rotating cavities in aero-engines. However experimental confirmation is required to ratify the existence of the structures.
Design Point Efficiency of Radial Turbines
Authors: Cox Graham D. 
Published: August 2018

Results are presented from CFD calculations on a large database of 3D, radially-stacked, radial turbine geometries. The database covers a comprehensive range of basic geometrical features allowing the most appropriate geometry to be selected for optimum efficiency over extensive ranges of blade-speed-ratio, flow coefficient and specific speed.
Initial studies considered the wheel only and used 78 geometries for low Mach number applications and 102 geometries for high Mach number applications. Each was run over a range of blade-speed-ratios and inlet flow angles to generate preliminary results. Designs that did not contribute to the optimum efficiency trends were discarded. The remaining 17 low Mach number and 24 High Mach number wheels were recalculated with a range of nozzle guide vanes and back-face cavities to provide increased fidelity numerical solutions.
The calculated optimum efficiency is presented on charts of blade-speed-ratio against flow coefficient, against specific speed and against non-dimensional mass-flow. The effect of exducer trim reduction, as often required for mechanical reasons, is demonstrated. The charts can be used for preliminary design of new applications.
Gas Turbine Fouling Offshore: Effective Online Water Wash Through High Water-to-Air Ratio
Authors: Madsen Stian , Bakken Lars E. 
Published: August 2018

Optimized operation of gas turbines is discussed for a fleet of eleven GE LM2500PE engines at a Statoil North Sea offshore field in Norway. Three engines are generator drivers and eight engines are compressor drivers. Several of the compressor drive engines are running at peak load (T5.4 control), hence production rate is limited by the available power from these engines. The majority of the engines discussed run continuously without redundancy, hence gas turbine uptime is critical for the field’s production and economy. The performance and operational experience with online water wash at high water-to-air ratio, as well as successful operation at longer maintenance intervals and higher average engine performance are described.
This work is based on long-term operation with online washing, where operational data are collected and performance is analyzed over a 10-year period. Today, all engines are operated with 6-month intervals between maintenance stops, where offline crank wash is performed as well as other necessary maintenance and repairs. Online washing is performed daily between the maintenance stops at full load (i.e. normal operating load for the subject engine). To keep the engine as clean as possible and reduce degradation between maintenance stops, both an effective online water wash system and an effective air intake filter system are critical factors. The overall target is to maintain high engine performance, and extend the interval between maintenance stops through effective online washing.
Water-to-air ratio is significantly increased compared to the OEM limit (OEM limit is 17 l/min which yields approx. 0.5% water-to-air ratio). Today the engines are operated at a water rate of 50 l/min (3 times the OEM limit) which yields a 1.4% water-to-air ratio. Such a high water-to-air ratio has been proven to be the key parameter for obtaining good online water wash effectiveness. Possible downsides of high water-to-air ratio have been thoroughly studied.
The effect of optimized online water wash for the subject engines is longer intervals between maintenance stops, higher power availability, lower engine performance deterioration and reduced emissions (CO2 and NOx). The operating intervals are now extended to six months (4,000 hours), from initially two months (1,500 hours, early 1990s) followed by four months (3,000 hours, mid-2000s). Other installations operated as low as 750 hours between offline washes in the 1980s and 1990s. Of a total efficiency deterioration improvement of 6% over each 6-month operating period, the deterioration is reduced by an estimated 3% related to online water wash.
Low Order Modelling for Fan and Outlet Guide Vanes in Aero-Engines
Authors: Cui Jiahuan , Watson Rob , Tucker Paul , Wilson Mark 
Published: August 2018

Intakes of reduced length have been proposed with the aim of producing aero-engines with higher efficiency and reduced weight. As the intake length decreases, it is expected that stronger effects of the fan on the flow over the intake lip will be seen. If the effects of the fan cannot be ignored, a low-cost but still accurate fan model is of great importance for designing a short-intake.
In this paper, a low order rotor/stator model — the immersed boundary method with smeared geometry (IBMSG), has been further developed and validated on a rig test case. The improved IBMSG is more robust than the original. The rig test case used for validation features a low-pressure compression system with a non-axisymmetric inflow, which is representative of the inlet condition of an aero-engine at its cruise condition. Both the fan and the Outlet Guide Vanes (OGV) are modelled using IBMSG. Detailed analysis is carried out on the flow both upstream and downstream of the fan. After validating the IBMSG method against the rig test case, a short-intake case, coupled with a fan designed for the next generation of aero-engines, is further investigated. It is found that, compared with the intake-alone case, the inflow distortion at the fan face is significantly reduced by the presence of fan. Due to this increased interaction between the fan and the flow over the intake lip, accounting for the effects of the downstream fan is shown to be essential when designing a short intake.
Study of the Impact of Multi-Row Interaction on Flutter Analysis for a Representative LPT Geometry
Authors: Sotillo Adrian , Gallardo Juan Manuel 
Published: August 2018

Acoustic reflections and multiple blade-row effects have an impact on aeroelastic behavior, which can change the aerodynamic damping by a significant amount. However, conventional flutter analyses neglect these effects as they ignore any information about the multistage unsteady interaction. In order to capture them, the authors of this paper have developed a multistage coupling methodology for ITP’s in-house unsteady 3D frequency-domain linearized RANS solver. The current approach allows carrying out CFD simulations on a multistage environment built upon an arbitrary number of blade-rows; each one of them could also have an arbitrary number of frequencies and/or interblade phase angles. The coupling mechanism between consecutive blade-rows arises in a somewhat straightforward way after the solutions are decomposed as the sum of several spinning modes in the inter-row boundaries and the continuity of acoustic, vortical and entropic waves is enforced. This method is suitable for flutter and forced response computations, and also for tonal noise propagation.
The focus of this paper is on the study of multiple blade-row effects on flutter stability margin. A brief analysis of results for a couple of simple test cases is presented to demonstrate the correctness of the method. Then, a detailed flutter analysis for a representative LPT geometry is performed and the results are compared with a single row conventional analysis. The impact of neighboring and further blade-rows, as well as spinning modes scattered from the fundamental circumferential mode, are accounted for in the unsteady aerodynamic loading of the excited blade.
HRSG Duct Firing Revisited
Authors: Gülen S. Can 
Published: August 2018

Duct firing in the heat recovery steam generator (HRSG) of a gas turbine combined cycle power plant is a commonly used method to increase output on hot summer days when gas turbine airflow and power output lapse significantly. The aim is to generate maximum possible power output when it is most needed (and, thus, more profitable) at the expense of power plant heat rate.
In this paper, using fundamental thermodynamic arguments and detailed heat and mass balance simulations, it will be shown that, under certain boundary conditions, duct firing in the HRSG can be a facilitator of efficiency improvement as well. When combined with highly-efficient aeroderivative gas turbines with high cycle pressure ratios and concomitantly low exhaust temperatures, duct firing can be utilized for small but efficient combined cycle power plant designs as well as more efficient hot-day power augmentation. This opens the door to efficient and agile fossil fuel-fired power generation opportunities to support variable renewable generation.
Emulsion Jet in Crossflow Atomization Characteristics and Dynamics
Authors: Leask Scott B. , McDonell Vincent G. , Samuelsen Scott 
Published: August 2018

This work presents the atomization characteristics and dynamics of water-in-heptane (W/H) emulsions injected into a gaseous crossflow. W/H mixtures were tested while varying momentum flux ratios and aerodynamic Weber numbers. Different injector orifice diameters and orifice length-to-diameter ratios were used to test the generality of the results.
The atomization properties of W/H mixtures were compared with properties of neat water and neat heptane to evaluate the effect of an emulsion on droplet sizing, cross-sectional stability and dispersion, and jet penetration depth. Liquid dynamics were extracted through analyzing instantaneous spray measurements and dynamic mode decomposition (DMD) on high-speed video recordings of the atomization processes. Correlations were proposed to establish preliminary relationships between fundamental spray processes and test conditions. These correlations allowed for emulsion behavior to be compared with neat liquid behavior.
The use of emulsions induces greater spray instability than through using neat liquids, likely due to the difficulty in injecting a stable emulsion. Neat liquid correlations were produced and successfully predicted various spray measurements. These correlations, however, indicate that injector geometry has an effect on spray properties which need to be addressed independently. The emulsions are unable to adhere to the neat liquid correlations suggesting that an increased number of correlation terms are required to adequately predict emulsion behavior.
Application and Experience of the SSS (Synchro-Self-Shifting) Clutch for High Speed Gas Turbine Marine Propulsion Systems
Authors: Hendry Morgan L. 
Published: August 2018

Synchro-Self-Shifting (SSS) Overrunning Clutches are used in a myriad of propulsion system configurations for naval and commercial vessels powered by gas turbines and/or combined gas turbine and cruise engines worldwide. Of these, much has been written about high power gas turbine propulsion clutches for large naval vessels (frigates, destroyers, cruisers, etc.), whereas less has been published about the application and experience of the propulsion machinery with Synchro-Self-Shifting Clutches for hydrofoils, hovercraft, fast patrol boats, fast ferries, yachts, etc. Space, weight, and high-speed constraints can be different for high speed gas turbine propulsion systems used in these smaller types of vessels, and can therefore provide gearing challenges, including system design challenges for these clutches.
A comparison between Synchro-Self-Shifting overrunning clutches and other types of freewheels will be given discussing the advantages and disadvantages of each, particularly as they relate to high speed gas turbine marine propulsion applications. Lastly, this paper will give some history of a number of high speed gas turbine driven marine propulsion applications with clutches from the early 1960’s until the present, describe various gearing arrangements that were used in particular vessels, articulate where these clutches are incorporated, and discuss the application experience of these clutch installations.
Measurements of the Leakage and Rotordynamic Performance of Interlocking Labyrinth Seals
Authors: Gary Keith , Childs Dara W. , Ramirez Mauricio A. 
Published: August 2018

Leakage and rotordynamic measurements are presented for an interlocking-labyrinth gas seal. Magnetic bearings and differential-pressure transducers are used to measure dynamic forces in the labyrinth seal following the approach of Wagner et al. in 2009. Magnetic bearings precess the rotor creating a dynamic pressure wave that is measured and integrated to find the reaction forces. The interlocking seal has 3 teeth on the stator and 2 teeth on the rotor creating 4 cavities. Each cavity has an axial length of 6 mm, and all teeth have a 5 mm height. Teeth on the rotor and stator, respectively, create a 0.2 mm radial clearance with respect to the stator and rotor. All tests are conducted at ∼ 167 Hz (10 krpm) rotor speed with, and without, swirl brakes for a range of precession frequencies from 10–50 Hz forward and backward. Inlet pressure is varied between 2.75 ∼ 4.83 bar, and pressure ratios vary between 0.5 ∼ 0.8.
Static results are presented for leakage, inlet preswirl, and cavity pressure. Dynamic results are presented for rotordynamic coefficients. Dynamic results show behavior that is unique to each cavity and are presented for the entire seal as well as for each cavity individually. Cross-coupled stiffness of the entire seal increases with increasing precession frequency, yet all other rotordynamic coefficients are frequency independent. The seal shows improved stability via increased effective damping with the use of swirl brakes when considering the entire seal. Negative direct damping values are seen in all but the third cavity.