bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrodynamic Journal Bearings Optimization Considering Rotor Dynamics Restrictions
Authors: Moroz Leonid , Romanenko Leonid , Kochurov Roman , Kashtanov Evgen 
Published: August 2018

In this study, optimal designs of hydrodynamic journal bearings for 13.5 MW induction motor prototype is developed based on the design of experiment approach and best sequences method which involves entire rotor-bearing system multidisciplinary simulations. These simulations consist of bearing hydrodynamic characteristics calculation and optimization and rotor dynamics analyses for a rotor-bearing system. The results of rotor dynamics analyses are taken into account as the constraints during optimization.
Several journal bearings such as plain cylindrical with a different configuration of pockets, elliptical type, and 4-lobe fixed pad have been considered to select the most appropriate design for the application. The bearing clearance, length, diameter, pockets positions, lobe width, oil viscosity, are applied as design input variables. To find the bearing optimal design, following objective functions were considered:
1) Minimum oil film thickness. Optimal bearing clearance is designed to produce the maximum possible level of minimum oil film thickness in order to avoid or reduce possible metal-to-metal contact;
2) Maximization of the performance is done by minimization of friction power loss.
3) Rotor dynamics simulation for the rotor-bearing system is embedded in the optimization process in order to avoid resonances by providing sufficient critical speeds separation margins from operating speed.
The methodology for the bearing simulation is based on the mass-conserving mathematical model, proposed by Elrod & Adams and numerical solution for the equations is generated using finite difference method. Rotor dynamics analyses are performed using finite element method.
As the result of the study, optimized bearing designs for 13.5 MW induction motor were generated. Optimized bearings provide sufficient frequency margins for critical speeds for the rotor-bearing system and, at the same time, improved hydrodynamic bearing characteristics: maximized oil film thickness and increased efficiency compared to the starting design.
Through the considered bearings examples, the study shows how different parameters, such as bearing clearance, length, diameter, and etc., influence key performance characteristics like bearing minimum oil film thickness, friction power losses, rotor-bearing system critical speeds.
Demonstration of Bleed Air Recirculation System to Improve Part Load Efficiency of Solar Mars® 100 DLE Industrial Gas Turbine
Authors: Cowell Luke , Reynolds Simon , Caron Tim , Zhang Donghui 
Published: August 2018

On two-shaft DLE (Dry Low Emissions) gas turbines compressor air is often bled off the combustor housing to control the combustor flame temperature for part load emissions management. The bleed air is typically directed into the exhaust ducting, bypassing the turbine, causing engine efficiency to decrease. A prototype bleed air recirculation system was fitted onto a compressor package in the field that redirects bleed flow from the engine exhaust to the air inlet to raise the air temperature entering the engine. This system is designed to reduce the amount of bleed air required at a given ambient operating condition, while not compromising emissions, to increase part load efficiency.
The bleed air recirculation system was designed, built, installed, and tested on a Mars 16000S compressor package at a station in northern Pennsylvania. A control algorithm was developed and validated to control bleed air recirculation so that package durability was not impacted. Over an evaluation period of 12 months, no significant durability issues or degradation were noted.
The on-site evaluation indicated that the engine’s heat rate is significantly improved by using bleed air recirculation. The heat rate was reduced by as much as 7% during testing at site with a strong dependency on the engine operating load and ambient temperature. As predicted the best case was demonstrated at 50% load and at colder ambient conditions. The NOx emissions were also improved with bleed air recirculation. In addition, using this system extended the range of low emissions operation to lower loads. No effects on compressor surge or sound emissions were detected.
Capturing Radial Mixing in Axial Compressors With CFD
Authors: Cozzi Lorenzo , Rubechini Filippo , Giovannini Matteo , Marconcini Michele , Arnone Andrea , Schneider Andrea , Astrua Pio 
Published: August 2018

Due to the generally high stage and blade count, the current standard industrially adopted to perform numerical simulations on multistage axial compressors is the steady-state analysis based on the Reynolds-averaged Navier-Stokes approach (RANS), where the coupling between adjacent rows is handled by means of mixing planes. In addition to the well-known limitations of a steady-state picture of the flow, namely its inherent inability to capture the potential interaction and the wakes from the upstream blades, there is another flow feature which is lost through a mixing-plane, and which is believed to be a major accountable for the radial mixing: the transport of stream-wise vorticity. Streamwise vorticity arises throughout a compressor for various reasons, mainly associated with secondary and tip-clearance flows. A strong link does exist between the strain field associated with the transported vortices and the mixing augmentation: the strain field increases both the area available for mixing and the local gradients in fluid properties, which provide the driving potential for mixing itself.
Especially for the rear stages of a multistage axial compressor, due to high clearances and low aspect ratios, only accounting for the development along the meridional path of secondary and clearance flow structures it is possible to properly predict the spanwise mixing.
In this work, the results of steady and unsteady RANS simulations on the high-pressure section of an industrial heavy-duty axial compressor are presented and compared with experimental data acquired during a test campaign. Adopting an unsteady full-annulus URANS approach, the enhanced radial mixing in the rear stages of the compressor is properly captured, obtaining a really good agreement with experimental data both in terms of total temperature and pressure outlet radial distributions. On the contrary, with a steady-state modelling, the radial transport is strongly underestimated, leading to results with marked departures from experiments. Examining what occurs across the inter-row interfaces for RANS and URANS solutions, a possible explanation for this underestimation is provided. In particular, as the stream-wise vorticity associated with clearance flows is one of the main drivers of radial mixing, restraining it by pitch-averaging the flow at mixing planes of a steady-state analysis is the reason why this simplified approach is not able to properly predict the radial transport of fluid properties in the rear part of the axial compressor.
Performance Testing of an Axial Flow Fan Designed for Air-Cooled Heat Exchanger Applications
Authors: Wilkinson Michael B. , van der Spuy Johan , von Backström Theodor W. 
Published: August 2018

An axial flow fan developed in previous study is tested in order to characterise its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary CFD results obtained using an actuator disk model as well as a periodic three dimensional model indicate that the fan meets the specified performance targets, with an expected total-to-static efficiency of 59.4 % and a total-to-static pressure rise of 114.7 Pa at the operating point.
Experimental tests are performed on the M-fan in order to determine its performance across a full range of flow rates. A range of fan configurations are tested in order to ascertain the effect of tip clearance, blade angle and hub configuration on fan performance. Due to the lack of a suitable facility for testing a large diameter fan, a scaled 1.542 m diameter model is tested on the BS 848 (ISO 5801) type A fan test facility at Stellenbosch University. A RANS CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. The results of the CFD model will be validated using the experimental data obtained. Both the CFD results and the experimental data obtained are compared to the initial CFD results for the full scale fan, as obtained in the previous study, by means of fan scaling laws.
Experimental data indicates that the M-fan does not meet the pressure requirement set out in the initial study, at the design blade setting angle of 34 degrees. Under these conditions the M-fan attains a total-to-static pressure rise of 102.5 Pa and a total-to-static efficiency of 56.4%, running with a tip gap of 2 mm. Increasing the blade angle is shown to be a potential remedy, improving the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap, with larger tip gaps substantially reducing fan performance. The losses due to tip gap are also shown to be overestimated by the CFD simulations. Both experimental and numerically obtained results indicate lower fan total-to-static efficiencies than obtained in the initial CFD study. Results indicate that the M-fan is suited to its intended application, however it should be operated with a smaller tip gap than initially recommended and a larger blade setting angle. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.
On the Use of the Automatic Differentiation for Developing a Linear Harmonic Solver
Authors: Zhang Wei , Wang Dingxi , Huang Xiuquan , Yang Tianxiao , Yan Hong , Li Jianling 
Published: August 2018

The linear and nonlinear harmonic methods are efficient frequency domain methods for analyzing time periodic unsteady flow fields. They have been widely used in both academia and industry. But the cost and complexity of developing a linear harmonic solver has been limiting its wider applications. On the other hand, the automatic differentiation (AD) has long been used in the CFD community with a focus on generating adjoint codes in a reverse mode. All those AD tools can do a much better job in generating linearized codes in a tangent mode, but so far very little, if any, attention is paid to using AD for developing linear harmonic solvers.
The linear harmonic method, in comparison with the harmonic balance method, has its own advantages. For example, it can capture small disturbances very effectively, and avoids aliasing errors which can lead to solution instability since each wave component is solved for separately.
This paper presents the effort of using an AD tool to generate major source codes for the development of a linear harmonic solver for analyzing time periodic unsteady flows. It includes the procedures and advice of using AD for such a purpose. A case study is also presented to validate the developed linear harmonic solver.
Heavy Duty Gas Turbine Performance and Endurance Testing: The NovaLT™16 Experience
Authors: Asti Antonio , Gamberi Francesco , Del Vescovo Giuseppe , Carta Riccardo , Giannini Nicola , Ignesti Mirko , Orazi Claudio , Pieroni Nicola 
Published: August 2018

The NovaLT™16 gas turbine recently developed in Baker Hughes, a GE company (BHGE), is part of a larger class of gas turbines (LT class) aiming at covering a wide space in the small power range segment and at introducing in the market a state of the art technology engine for what concerns performance, emissions, operability, durability and maintainability.
The main purpose of this paper is to describe the entire validation campaign that was performed at BHGE facilities. This campaign can be divided into 3 different phases.
The first phase focused on measuring engine performance in a new, clean and unaltered configuration.
The second phase focused on emissions, vibration, thermal distribution, auxiliary system performances and the like, in order to validate the design assumption and calculation results across the full operational range. In this phase, more than 2000 sensors were installed across the entire engine, covering all modules, and all functional tests were performed (inside and outside of design space) to guarantee reliable engine behavior. At the end of this test phase, a full engine teardown was performed to allow a detailed parts inspection that confirmed the achievement of the design intent.
The standard maintenance plan of the engine requires 35Kh continuous running. Therefore, the third part of the test aimed at validating engine durability with a full endurance test that allowed the identification and correction of any possible remaining operation problem. In this phase, the engine was still equipped with more than 1000 sensors, and was operated continuously following a well-defined operating profile in order to simulate both mechanical drive and power generation modes. This campaign successfully allowed to fine tune several engine control logic details, to monitor emissions behavior across a wide range of ambient temperature and load condition (the test spans from hot to cold day), to analyze trends of standard engine parameters and special instrumentation and, through planned borescope inspection, to evaluate individual component status versus selected operating profile.
Data reported in this paper represent a summary of all the data acquired and post processing results, and illustrate how an endurance test can help tuning machine performance predictions in a wide operating range.
Numerical Investigation on Wide-Chord Fan Blade Forced Response due to Vortex Ingestion
Authors: Wang Zhonglin , Chen Yong , Ouyang Hua , Wang Anjenq 
Published: August 2018

When a turbofan engine is taxing or taking-off, a vortex can form between ground surface and the intake. As the diameters of engines increase, intakes are closer to the ground and as a result the possibility of vortex ingestion is increasing. The vortex starts from the ground surface and enters the inlet at high rotating speed. It is likely to draw in hard material or dust from the ground, which leads to blade erosion or impact damage. This is harmful to the engine durability and safety. Besides the vortex, inlet flow separation could induce high level of blade vibration, or aerodynamic instability, such as rotating stall. Cross wind may also lead to both vortex and flow distortion, which is more challenging for engine stability. Therefore, vibration characteristics and forced response under vortex ingestion should be evaluated to ensure the stability and safety of the engine in design phase.
This paper presents a computational study of the forced response of a wide-chord fan blade under vortex ingestion. A finite element model was built, and modal analysis was conducted to characterize the vibrating characteristics of the fan blade with a corresponding Campbell diagram. Transient simulations of vortex passing over the fan blade were conducted with and without the blade pre-vibration at the natural frequency of the first bending mode. The forced response level was evaluated under various conditions, including different hitting time and increasing intensity of vortex. Results showed that the ingested vortex is able to amplify the displacement and vibratory response to a significant level of 18% at most. Linear relation between vortex intensity and blade response was found. The results give a comprehensive prediction of forced response for a better blade design against vortex ingestion.
Second Law Analysis of Condensing Steam Flows
Authors: Grübel Marius , Schatz Markus , Vogt Damian M. 
Published: August 2018

A numerical second law analysis is performed to determine the entropy production due to irreversibilities in condensing steam flows. In the present work the classical approach to calculate entropy production rates in turbulent flows based on velocity and temperature gradients is extended to two-phase condensing flows modeled within an Eulerian-Eulerian framework. This requires some modifications of the general approach and the inclusion of additional models to account for thermodynamic and kinematic relaxation processes.
With this approach, the entropy production within each mesh element is obtained. In addition to the quantification of thermodynamic and kinematic wetness losses, a breakdown of aerodynamic losses is possible to allow for a detailed loss analysis. The aerodynamic losses are classified into wake mixing, boundary layer and shock losses.
The application of the method is demonstrated by means of the flow through a well known steam turbine cascade test case. Predicted variations of loss coefficients for different operating conditions can be confirmed by experimental observations. For the investigated test cases, the thermodynamic relaxation contributes the most to the total losses and the losses due to droplet inertia are only of minor importance. The variation of the predicted aerodynamic losses for different operating conditions is as expected and demonstrates the suitability of the approach.
A Comparative Study of Data and Physically Based Gas Turbine Modeling for Long-Term Monitoring Scenarios: Part II — Emission Prediction Utilizing Different Levels of Design Information
Authors: Lipperheide Moritz , Bexten Thomas , Wirsum Manfred , Gassner Martin , Bernero Stefano 
Published: August 2018

Reliable engine and emission models allow for an online monitoring of commercial gas turbine operation and help the plant operator and the original equipment manufacturer (OEM) to ensure emission compliance of the aging engine. However, model development and validation require fine-tuning on the particular engines, which may differ in a fleet of a single design type by production, assembly and aging status.
For this purpose, Artificial Neural Networks (ANN) offer a good and fast alternative to traditional physically-based engine modeling, because the model creation and adaption is merely an automatized process in commercially available software environments. However, ANN performance depends strongly on the availability of suitable data and a-priori data processing. The present work investigates the impact of specific engine information from the OEM’s design tools on ANN performance. As an alternative to a strictly data-based benchmark approach, engine characteristics were incorporated into ANNs by a pre-processing of the raw measurements with a simplified engine model. The resulting ‘virtual’ measurements, i.e. hot gas temperatures, then served as inputs to ANN training and application during long-term gas turbine operation. When processed input parameters were used for ANNs, overall long-term NOx prediction improved by 55%, and CO prediction by 16% in terms of RMSE, yielding comparable overall RMSE values to the physically-based model.
High Fidelity Modeling of the Acceleration of a Turboshaft Engine During a Restart
Authors: Ferrand Antoine , Bellenoue Marc , Bertin Yves , Cirligeanu Radu , Marconi Patrick , Mercier-Calvairac Fabien 
Published: August 2018

In order to decrease the fuel consumption, a new flight mode is being considered for twin-engine helicopters, in which one engine is put into sleeping mode (a mode in which the gas generator is kept at a stabilized, sub-idle speed by means of an electric motor, with no combustion), while the remaining engine operates at nominal load. The restart of the engine in sleeping mode is therefore deemed critical for safety reasons. This efficient new flight mode has raised the interest in the modeling of the restart of a turboshaft engine.
In this context, the initial conditions of the simulations are better known relative to a ground start, in particular the air flow through the gas generator is constant, the fuel and oil system states are known and temperatures of the casings are equal to ambient. During the restart phase of the engine, the gas generator speed is kept at constant speed until the light-up is detected by a rise in inter-turbine temperature, then the starter torque increases, accelerating the engine towards idle speed. In this paper, the modeling of the acceleration of the gas generator from light-up to idle and above idle speeds is presented. Details on the light-up process are not addressed here.
The study is based on the high-fidelity aero-thermodynamic restart model that is currently being developed for a 2000 horse power, free turbine turboshaft. In this case, the term high-fidelity refers not only to the modeling of the flow path components but it also includes all the subsystems, secondary air flows and controls with a high level of detail.
The physical phenomena governing the acceleration of the turboshaft engine following a restart — mainly the transient evolution of the combustion efficiency and the power loss by heat soakage — are discussed in this paper and modeling solutions are presented. The results of the simulations are compared to engine test data, highlighting that the studied phenomena have an impact on the acceleration of the turboshaft engine and that the model is able to correctly predict acceleration trends.
An Investigation on the Loss Generation Mechanisms Inside Different Centrifugal Compressor Volutes for Turbochargers
Authors: Tanganelli Andrea , Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni , Cencherle Francesco , De Luca Michele , Marmorini Luca 
Published: August 2018

In centrifugal compressor design, the volute plays a key role in defining the overall efficiency and operating range of the stage. The flow at the impeller outlet is indeed characterized by a high kinetic energy content, which is first converted to potential energy in the diffuser downstream. The compressed gas is then collected by the volute at the cylindrical outlet section of the diffuser and directed to the intake piping, possibly with a further pressure recovery to enhance the stage performance. Due to the high flow speed at the volute inlet, the capability of ensuring the lowest amount of total pressure loss is pivotal to prevent a detriment of the machine efficiency. Moreover, the flow conditions change when the volute operates far from its design point: at mass flow rates lower than the design one, the flow becomes diffusive, while at higher mass flow rates the fluid is accelerated, thus leading to different loss-generation mechanisms. These phenomena are particularly relevant in turbocharger applications, where the compressor needs to cover a wide functioning range; moreover, in these applications the definition of the volute shape is often driven also by space limitations imposed by the vehicle layout, leading to a variety of volute types.
The present paper reports an analysis on the sources of thermodynamic irreversibilities occurring inside different volutes applied to a centrifugal compressor for turbocharging applications. Three demonstrative geometrical configurations are analyzed by means of 3D numerical simulations using common boundary conditions to assess the overall volute performance and the different loss mechanisms, which are evaluated in terms of the local entropy generation rate. The modification of the loss mechanisms in off-design conditions is also accounted for by investigating different mass flow rates.
It is finally shown that the use of the entropy generation rate for the assessment of the irreversibilities is helpful to understand and localize the sources of loss in relation to the various flow structures.