bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamic Damping Predictions for Oscillating Airfoils in Cascades Using Moving Meshes
Authors: Ni Ron Ho , Humber William , Ni Michael , Capece Vincent R. , Ooten Michael , Clark John
Published: September 2016

This paper presents a numerical analysis of oscillating airfoils in turbomachinery cascades using the unsteady nonlinear Reynold’s Averaged Navier-Stokes (URANS) equations. The periodic unsteady flow solutions are determined using a conventional time marching method (DTS) and the Nonlinear Harmonic Balance method (NHB). Mesh motions, using a weighted distortion procedure and a linear elastic method, are described. Comparison of computed results are made with the Eleventh Standard Test Configuration (STC11) experimental data for subsonic and transonic exit flow conditions. The solutions for the NHB and DTS methods exhibit excellent correlation with each other and good correlation with the experimental data on the pressure surface. The numerical solutions deviate from the experimental data on the suction surface especially in the vicinity of the shock wave for the transonic exit flow case. A numerical influence coefficient modeling method is shown for airfoil cascades that can be used to calculate unsteady aerodynamic loading over a range of interblade phase angles. Application to the STC11 illustrates that a cascade of five airfoils is sufficient to provide accurate unsteady aerodynamic loading predictions for the modeled flow conditions.
Sensitivity Study of S-CO2 Compressor Design for Different Real Gas Approximations
Authors: Lee Jekyoung , Cho Seong Kuk , Cha Jae Eun , Lee Jeong Ik
Published: September 2016

With the efforts of many researchers and engineers on the Supercritical CO2 (S-CO2) Brayton cycle technology development, the S-CO2 Brayton cycle is now considered as one of the key power technologies for the future. Since S-CO2 Brayton cycle has advantages in economics due to high efficiency and compactness of system, various industries have been trying to develop technologies on the design and analysis of S-CO2 Brayton cycle components. Among various technical issues on the S-CO2 Brayton cycle technology development, treatment of thermodynamic property near the critical point of S-CO2 is very important since the property shows non-linear variation which causes large error on design and analysis results for ideal gas based methodologies.

Due to the special behavior of thermodynamic property of CO2 near the critical point, KAIST research team has been trying to develop a S-CO2 compressor design and analysis tool to reflect real gas effect accurately for better design and performance prediction results. The main motivation for developing an in-house code is to establish turbomachinery design methodology based on general equations to improve accuracy of design and analysis results for various working fluids including S-CO2. One of the key improvements of KAIST_TMD which is an in-house tool for S-CO2 turbomachinery design and analysis is the conversion process between stagnation condition and static condition. Since fluid is moving with high flow velocity in a compressor, the conversion process between stagnation and static condition is important and it can have an impact on the design and analysis results significantly. A common process for the conversion is based on the specific heat ratio which is typically a constant from ideal gas assumption. However, specific heat ratio cannot be assumed as a constant for the case of S-CO2 compressor design and analysis because it varies dramatically near the critical point.

Thus, in this paper, sensitivity study results on the state condition conversion between stagnation and static conditions with different approaches will be presented and further analysis on impact of the selected approaches on the final impeller design results will be discussed.
Numerical Optimization and Manufacturing of the Impeller of a Centrifugal Compressor by Variation of Splitter Blades
Authors: Moussavi Torshizi S. Abolfazl , Hajilouy Benisi Ali , Durali Mohammad
Published: September 2016

Design and optimization of centrifugal compressors, based on main blades configuration of impeller have been vastly discussed in open literature, but less researches have addressed splitters. In this research, the impeller of a commercial turbocharger compressor is investigated. Here, profiles of main blades are not changed while the effect of changing the configuration of splitters is studied. An optimization study is performed to find the best configuration using genetic algorithm over a complete operating curve of the compressor. CFD codes with experimental support are used to predict the compressor performance. Quantumetric tests beside destructive analysis of two impellers are implemented for material identification and selection which is necessary for manufacturing. After taking into account structural considerations and approving the safety by numerical simulation, the new impeller is manufactured using 5 axis CNC machine. Non destructive tests are performed for identification of any structural defects. The new impeller is then mounted on a turbocharger shaft and tested experimentally in a wide range of operating conditions, which leads to a design having 2.3% improvement in efficiency. This is an important achievement in all applications of centrifugal compressors, especially in turbochargers.
2nd Quadrant Centrifugal Compressor Performance: Part I
Authors: Belardini Elisabetta , Rubino Dante Tommaso , Tapinassi Libero , Pelella Marco
Published: September 2016

Performance curves in 2nd quadrant are important to size protection equipment of both compressor and surrounding system. With reverse flow also the level and frequency of pressure fluctuations in different operating points is important to estimate blade loading and possible presence of excitation frequencies. The capability of performance predictive tools (either CFD or correlations based methods) as also mechanical design criteria are generally poor in 2nd quadrant and suffer for the scarcity and inadequacy of validation data.

The second quadrant branch for a centrifugal compressor has been experimentally tested after the standard characterization in direct flow. A test arrangement has been designed, with a booster compressor connected in parallel with the tested stage, forcing the flow to be stable in reverse flow. The compressor characteristics have been measured with static and dynamic instrumentation. Present experience showed that when machine is operated in the stable reverse flow condition, pressure fluctuations and vibration are higher with respect to the values measured in nominal direct flow operating conditions. The increase is in the order of 10–20% of the corresponding value in direct flow. The same can be stated also for axial thrust and secondary flows that increase when the gas flows in reverse direction but the increase is in the order of 10–15%. Thus in 2nd quadrant, compressor equipment (in particular impeller blades) and all other system devices experience unusual loading levels but the additional loads are not big enough to cause relevant damaging if sustained for limited time periods. This result may allow simplifying the design of system layout: in particular, if during ESD no surging cycle is expected but only a reverse flow sustained steadily by the system (which is actually the most typical experience), the additional ASV’s, such as hot or cold gas by-pass valves, may be reduced in size or eventually removed optimizing the plant BOP.
Low Pressure Steam Turbine Exhaust Flow: Part 1 — CFD Coupling of LP Turbine and Condenser Neck
Authors: Stein Peter , Telschow Dirk , Lamarque Frederic , Colitto Nuncio
Published: September 2016

Since many years the diffuser and exhaust of low pressure (LP) turbines have been in the focus of turbine development and accordingly broadly discussed within the scientific community. The pressure recovery gained within the diffuser significantly contributes to the turbine performance and therefore plenty of care is taken in investigations of the flow as well as optimization within this part of the turbine. However on a plant level the component following the LP turbine is the condenser, which is connected by the condenser neck. Typically the condenser neck is not fully designed to provide additional enthalpy recovery. Due to plant arrangement reasons, often it is full of built-ins like stiffening struts, feed-water heaters, extraction pipes, steam dump devices and others. It is vital to minimize the pressure losses across the condenser neck, in order to keep performance benefit, previously gained within the diffuser. As a general rule, each mbar of total pressure loss in a condenser neck may reduce the gross power output up to 0.1%.

While turbines usually follow a modular approach, the condenser is typically designed plant specific. Therefore, on a plant level it is crucial to identify and evaluate the loss contributors and develop processes and tools which allow an accurate and efficient design process for an optimized condenser neck design. This needs to be performed as a coupled modelling approach, as both, turbine and condenser flow interact with each other. 3-D CFD tools enable a deep insight into the flow field and help to locally optimize the design, as they help to identify local losses and this even for small geometrical design changes. Unfortunately these tools are costly with respect to computational time and resources, if they are used to analyze a full condenser neck with all built-ins. Here 1-D modelling approaches can help to close the gap, as they can provide fast feedback, e.g. in a project tender phase, or can allow to quickly analyze design changes. For this they need a proper calibration and validation. This publication discusses the CFD modelling of a LP steam turbine coupled to a condenser neck and the validity of such calculations against measurement data. In the second publication (Part 2) a simplification of the gained information to a 1-D modelling approach will be discussed.
Low Pressure Steam Turbine Exhaust Flow: Part 2 — Investigation of the Condenser Neck Flow Field and 1D Modelling
Authors: Telschow Dirk , Stein Peter , Wolf Hartwig , Sgambati Alessandro
Published: September 2016

Since many years the diffuser and exhaust of low pressure (LP) turbines are in focus of turbine development and accordingly broadly discussed within the scientific community. The pressure recovery gained within the diffuser significantly contributes to the turbine performance and therefore care is taken in flow investigation as well as optimization within this part of the turbine. However, on a plant level the component following the LP turbine is the condenser, which is connected by the condenser neck. Typically the condenser neck is not designed to provide additional enthalpy recovery. For plant design reasons, often numerous built-ins like stiffening struts, extraction pipes, steam dump devices and others are placed into the neck. Here it is vital to keep the pressure losses low, in order not to deteriorate performance, previously gained within the diffuser. Each mbar of total pressure loss in a condenser can reduce the plant power output up to 0.1%.

As discussed in the first publication (Part 1), 3D CFD enables a deep insight into the flow field, which is costly with respect to computational time and resources. But there are phases during project execution, when geometry and/or boundary conditions are not fixed and quick estimation of pressure loss and recovery in the condenser neck is needed for benchmark of designs or design changes (e.g. tender phase). Here 1D modelling approaches can help to close the gap.

Analysis of available 1D correlation of flow around obstacles has shown that these need to be adapted to the flow conditions in a condenser neck of a steam, nuclear or combined-cycle power plant. Therefore, the fluid fields, calculated and discussed in the first publication (Part 1), were analyzed regarding pressure loss created by single obstacles and interaction of built-ins of different size, number and shape. Furthermore, a 1D velocity to be used for 1D calculation was derived from the 3D velocity field. In addition, vacuum-correction-curves were implemented to cover the range of possible operating conditions.

This publication discusses the development of a 1D model for calculation of pressure loss in a condenser neck and the validity of such calculations against measurement and 3D CFD data.
Effect of Air-Curtains on Labyrinth Seal Performance
Authors: Rai Aakash C. , Prabhudharwadkar Deoras , Murthy Sunil , Giametta Andrew , Johns David
Published: September 2016

Labyrinth seals are used in many key sealing locations in gas turbines to control various leakage flows, e.g., to control the secondary air-flow from the compressor (bypassing the combustor), the turbine inter-stage leakages and blade tip leakages. This study was performed to assess the improvement in the performance of a labyrinth seal by using an air-curtain (cross-flow jet(s)) from the stator. Detailed parametric studies were performed to study the effect of the air-curtain jet pressure, location, and the number of jets on the seal performance with respect to the leakage flow. The analysis was done using 2-dimensional axisymmetric CFD simulations.

It was found that in the case of a labyrinth seal with a flat stator (without a honeycomb attached to the stator) the air-curtain design can reduce the seal leakage by about 30% over the baseline seal design without air-curtains. This reduction happened because the air-curtain jet deflected the main seal jet away from the seal clearance. A similar conclusion was also obtained in case of a labyrinth seal with a honeycombed stator. Furthermore, our parametric studies with different air-curtain designs parameters implemented over a honeycombed labyrinth seal showed that the air-curtain jet pressure, location, and the number of jets were crucial factors governing the seal leakage. Amongst the air-curtain designs studied, it was found that implementing three air-curtains in the 1st pocket gave the maximum leakage reduction (by about 50%) over the baseline design.
Investigation of Cross Flow in Double Entry Turbocharger Turbines
Authors: Lückmann Dominik , Stadermann Max , Aymanns Richard , Pischinger S.
Published: September 2016

The downsizing of combustion engines has become the major strategy within the automotive industry to meet the increasing demands in terms of fuel economy and harmful emissions. Furthermore, it is important to fulfil the customers expectations in terms of drivability by increasing the power density and transient performance of the engines. The key technology to reach these ambitious targets is the enhanced utilization of exhaust pulses on turbocharged engines. In four cylinder gasoline engine applications this is mainly realized by the use of double entry turbines or variabilities in the exhaust valve train. During the designing and matching process of double entry turbines it is still a major challenge to predict the turbine power output and accurately model its interaction with the engine. In the past few years, several authors have published measurement and simulation technologies aimed at enhanced modelling quality. Most of these approaches are based on the introduction of different flow conditions which help to describe the thermodynamic performance under various pulsating boundary conditions. Within an average engine cycle, the turbine operates under equal, single and unequal admissions. Furthermore, the evaluation of a turbine interacting with a four cylinder gasoline engine shows that cross flow between both turbine scrolls can occur during the blow-down phase of the cylinders. In this phase, the temperature and pressure upstream of the turbine reach their peak values within the complete engine cycle. Therefore, this phase is most crucial for the conversion of the exhaust energy into mechanical energy, which drives the compressor impeller of the turbocharger.

This work focuses on the results of stationary hot gas measurements and 3D CFD simulations of the cross flow phenomena to gain a deeper understanding of the scroll interaction in double entry turbines and its impact on engine performance. The findings were used to improve the modeling quality of double entry turbines in 1D engine process simulations, especially during the exhaust blow down where cross flow between the dividing wall and the turbine wheel occurs. The new methodology to quantify the amount of cross flow with a hot gas test has shown that the cross flow rate of a twin scroll turbine can reach values as high as 35% of the overall flow rate entering the turbine housing, whereas this value can be significantly reduced by using a segment turbine housing. The new map based turbine model, which enables predictive simulations, covers all engine relevant flow conditions of the turbine including cross flow. This is important because the cross flow has a large impact on the exhaust pulse separation and thus on the residual gas fraction of the cylinders after the gas exchange.
Investigation of Damping Potential of Strip Damper on a Real Turbine Blade
Authors: Afzal M. , Arteaga I. Lopez , Kari L. , Kharyton V.
Published: September 2016

This paper investigates the damping potential of strip dampers on a real turbine bladed disk. A 3D numerical friction contact model is used to compute the contact forces by means of the Alternate Frequency Time domain method. The Jacobian matrix required during the iterative solution is computed in parallel with the contact forces, by a quasi-analytical method. A finite element model of the strip dampers, that allows for an accurate description of their dynamic properties, is included in the steady-state forced response analysis of the bladed disk. Cyclic symmetry boundary conditions and the multiharmonic balance method are applied in the formulation of the equations of motion in the frequency domain. The nonlinear forced response analysis is performed with two different types of boundary conditions on the strip: (a) free-free and (b) elastic, and their influence is analyzed. The effect of the strip mass, thickness and the excitation levels on the forced response curve is investigated in detail.
Conjugate Heat Transfer Analysis for Laminated Cooling Effectiveness: Part B — Effects of Film Hole Incline Angle
Authors: Deng Qinghua , Zhou Weilun , Feng Zhenping
Published: September 2016

The laminated cooling or multi-layered impingement-effusion cooling, which originates from combustion liner cooling, is believed to be an advanced and promising gas turbine blade cooling technique. Previous authors’ works have found that surface curvatures have different influences on overall cooling effectiveness of laminated cooling. To determine the optimal configuration of laminated cooling for various surface curvatures respectively, the conjugate heat transfer approach that has been validated by the experimental data was employed to study numerically the effects of streamwise incline angles (including 15, which was 20 degree for flat plate and concave surface, 30, 60 and 90 degree) on overall cooling effectiveness with different surface curvatures. The results show that the shallower film holes restrain the liftoff of the coolant ejection, and lead to a higher overall cooling effectiveness. However, shallower injection angle causes higher pressure loss. The relationship between injection angle and overall cooling effectiveness for different curvature is illustrated in the paper. The results indicate that shallower injection angle provides more than 10% improvement of cooling effectiveness compared to that of 90° injection angle for flat plate, concave surface and convex surface with smaller curvature at high blowing ratio. But for convex surface with large curvature, blowing ratio of 0.7 to 0.9 is better for overall cooling effectiveness, and shallower injection angle has little effect on cooling effectiveness. Moreover, additional pressure loss occurs to shallower injection angle because of the serious flow separation.
Experimental Investigation of a Low Pressure Model Steam Turbine With Supporting Rib in Close Vicinity to the Last Stage Rotor Blades at Varying Operating Conditions
Authors: Müller Fabian F. , Schatz Markus , Vogt Damian M. , Rehnsch Andreas
Published: September 2016

Steam turbine retrofits often result in an increase of turbine size, aiming for more power and higher efficiency. As the existing LP steam turbine exhaust hoods are generally not modified, the last stage rotor blades frequently move closer to installations within the exhaust hood, such as baffles or ribs.

To assess the influence of supporting ribs on the vibration behavior of the last stage rotor blades, tests with two rib configurations were performed in a single stage LP model steam turbine at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) at the University of Stuttgart, Germany.

At design load and overload operating conditions no significant change in blade vibration amplitudes is observed in case of a supporting rib in close vicinity to the rotor blades compared to the reference case without installations. However, at part load operating conditions a remarkable reduction in blade amplitudes is found rather unexpectedly.

The present work shows that changes in the pattern and the frequency content of the flow within the diffuser, caused by the interaction between supporting rib and steam flow is evidently responsible for this.
The Low Reduced Frequency Limit of Vibrating Airfoils: Part IIIB — Numerical Quantification and Influence of Unsteady Loading
Authors: Vega Almudena , Corral Roque
Published: September 2016

This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced frequency regime with special emphasis on its impact on the work per cycle curves. Simulations using a frequency domain linearized Navier-Stokes solver have been carried out on rows of a low-pressure turbine airfoil section, the NACA65 section and a flat plate, to show the correlation between the actual value of the unsteady loading parameter (ULP), theoretically derived in Part IIIa, and the flutter characteristics, for different airfoils, operating conditions and mode-shapes. Both, the traveling-wave and influence coefficient formulations of the problem are used in combination to increase the understanding of the ULP influence in different aspects of the unsteady flowfield. It is concluded that, for a blade vibrating in a prescribed motion at design conditions, the ULP can quantitatively predict the effect of loading variations due to changes in the incidence, and also in the mode shape. It is also proved that the unsteady loading parameter can be used to compare the flutter characteristics of different airfoils.
Development and Test of Oxide/Oxide CMC Combustor Liner Demonstrators for Aero Engines
Authors: Behrendt Thomas , Hackemann Stefan , Mechnich Peter , Shi Yuan , Hönig Sandrine , Hofmann Severin , Koch Dietmar
Published: September 2016

Ceramic matrix composites (CMC) offer the potential of increased service temperatures and are thus an interesting alternative to conventional combustor alloys. Tubular combustor liner demonstrators made of an oxide/oxide CMC were developed for a lean combustor in a future aero-engine in the medium thrust range and tested at engine conditions. During the design various aspects like protective coating, thermo-mechanical design, development of a failure model for the CMC as well as design and test of an attachment system were taken into account. The tests of the two liners were conducted at conditions up to 80% take-off. A new protective coating was tested successfully with a coating thickness of up to t=1 mm. Different inspection criteria were derived in order to detect crack initiation at an early stage for a validation of the failure model. With the help of detailed pre- and post-test computer tomography scans to account for the micro structure of the CMC the findings of the failure model were in reasonable agreement with the test results.
Estimation of the Particle Deposition on a Subsonic Axial Compressor Blade
Authors: Suman Alessio , Morini Mirko , Kurz Rainer , Aldi Nicola , Brun Klaus , Pinelli Michele , Spina Pier Ruggero
Published: September 2016

The quality and purity of the air entering a gas turbine is a significant factor influencing its performance and life. Foulants in the ppm range which are not captured by the air filtration system usually cause deposits on blading, which results in a severe drop in the performance of the compressor.

Through the interdisciplinary approach proposed in this paper, it is possible to determine the evolution of the fouling phenomenon through the integration of studies in different research fields: (i) numerical simulation, (ii) power plant characteristics and (iii) particle-adhesion characteristics. In fact, the size of the particles, their concentrations and adhesion ability, and filtration efficiency represent the major contributors to performing a realistic quantitative analysis of fouling phenomena in an axial compressor. The aim of this work is the estimation of the actual deposits on the blade surface in terms of location and quantity. This study combines the impact/adhesion characteristic of the particles obtained through a CFD and the real size distribution of the contaminants in the air swallowed by the compressor.

The blade zones affected by deposits are clearly reported by using easy-to-use contaminant maps realized on the blade surface, in terms of contaminant mass.

The analysis has shown that particular fluid-dynamic phenomena and airfoil shape influence the pattern deposition. The use of a filtration system decreases the contamination of the blade and the charge level of the electrostatic seems to be less important than the air contaminant concentration. From these analyses, some guidelines for proper installation and management of the power plant (in terms of filtration systems and washing strategies) can be drawn up. Characterization of the air contaminants in the power plant location represents the most important step in improving the management of the gas turbine power plant.
Performance Measurements of Gas Bearings With High Damping Structures of Polymer and Bump Foil via Electric Motor Driving Tests and 1-DOF Shaker Dynamic Loading Tests
Authors: Sim Kyuho , Park Jisu
Published: September 2016

This paper presents comprehensive test measurements for gas journal bearings with damping structures of a bump foil layer and/or a polymer layer. A one-pad top foil forms the bearing surface, under which the bearing structure and a bearing housing are located. Test bearings include gas foil bearings (GFBs), gas polymer bearings (GPBs), and gas foil-polymer bearings (GFPBs). In addition, three metal shims were employed to create wedge effects in the GFPBs. Firstly, static load-deflection tests of test bearings estimate the radial assembly clearance, which is measured to be ∼200 μm. Secondly, shake dynamic loading tests identify frequency-dependent dynamic characteristics. An electromagnetic shaker provides flat bearing specimens with one-degree-of-freedom vertical dynamic loading at excitation frequencies reaching 800 Hz. The bearing structures of GFB, GPB, and GFPB were measured to have resonance frequencies near 200 Hz. The GFPB has the lowest stiffness coefficients, which also increased with increasing excitation frequency. In addition, it has higher loss factor than those of GFB, which decreases with increasing excitation frequency. Therefore, GFPB was measured to exhibit a higher structural damping and lower stiffness than GFB. Lastly, the electric motor driving tests examine the rotordynamic stability performance. A permanent magnet (PM) synchronous motor drives a PM rotor supported on a pair of test journal bearings. The rotor has a diameter of 40 mm, length of 240 mm, and weight of 19.6 N. Two orthogonally positioned displacement sensors record the horizontal and vertical rotor motions. Test results indicate that sub-synchronous rotor motions for GFPBs showed the lowest amplitudes < 28 μm with the WFRs ∼0.14, and operated up to the highest rotating speed of 85 krpm with the OSS of 69 krpm, compared to GFBs and GPBs. In addition, the effects of mechanical preload and bearing clearance on the rotordynamic performance are examined for GFPBs. As a result, the GFPBs with mechanical preloads enhanced the rotordynamic performance with no subsynchronous motions up to the maximum rotor speed of 88 krpm, and the bearing friction characteristics as well. Furthermore, they showed comparable rotordynamic performance to three-pad GFBs from a past literature, even with larger bearing clearances and small mechanical preloads.
Variable Inlet Guide Vane Effect on Centrifugal Compressor Performance in Wet Gas Flow
Authors: Vigdal Levi André B. , Bakken Lars E.
Published: September 2016

The introduction of variable inlet guide vanes (VIGVs) upfront of a compressor stage affects performance and permits tuning for off-design conditions. This is of great interest for emerging technology related to subsea compression. Unprocessed gas from the wellhead will contain liquid condensate, which affects the operational condition of the compressor. To investigate the effect of guide vanes on volume flow and pressure ratio in a wet gas compressor, VIGVs are implemented upfront of a centrifugal compressor stage to control the inlet flow direction. The guide vane geometry and test rig setup have previous been presented. This paper documents how changing the VIGV setting affects compressor performance under dry and wet operating conditions. The reduced performance effect and operating range at increased liquid content are of specific interest. Also documented is the change in the VIGV effect relative to the setting angle.
Increased Load Carrying Capacity of Large Tilting-Pad Journal Bearings by Injection of Cold Oil
Authors: Buchhorn Nico , Kukla Sebastian , Bender Beate
Published: September 2016

In this paper a theoretical study with the aim to achieve higher load capacity of large tilting-pad turbine bearings is presented. The main focus is set on the reduction of thermal gradients inside the pad and thus, of adverse thermomechanical deformations. This allows for the increase of either the load carrying capacity, minimum film thickness hmin, and/or decrease maximum pad temperature Tmax.

Subject of the investigation is a 5-pad tilting-pad bearing with rocker pivots. Each pad arc measures 56° and the pivot is positioned at 60 %. By having a 500mm inner diameter the 350mm long bearing features a relative clearance of 1.28% and nominal preload of 0.23.

It is shown that the axial pad bending Δh (crowning) has a major impact on film thickness and pressure distributions and thus on the operational safety parameters.

In order to reduce this effect, radial bores through the pad supplying pressurized cold oil (Tinj = 50 °C) are simulated. Despite the evident increase in oil film pressure, the primary purpose of the injection is to rinse away the layer of hot oil sticking to the pad surface. The maximum pad temperature and the overall pad temperature gradients are thereby decreased.

The code used for simulation solves Reynolds and energy equations and computes thermomechanical deformations simultaneously. However, the simulations are carried out for one single pad only and are therefore supported by boundary conditions taken from experiments.

In order to determine the impact of the approach on the static bearing characteristics, diameter and location of the bores are varied (0.3mm ≤ db ≤ 0.5mm). It is shown that pad crowing can be reduced significantly: The axial deviation of the film thickness Δh can be decreased from Δh = 47 μm to Δh = 31 μm, while the maximum temperature Tmax can be decreased by 20 K. Further, the minimum film thickness hmin can be increased by 16 μm. Subsequently, allowing the same limits for hmin and Tmax for the new design, the load capacity can be raised by up to 1.21MPa ≙ 44 %.
Influence of Turbulence Modelling to Condensing Steam Flow in the 3D Low-Pressure Steam Turbine Stage
Authors: Patel Yogini , Patel Giteshkumar , Turunen-Saaresti Teemu
Published: September 2016

With the tremendous role played by steam turbines in power generation cycle, it is essential to understand the flow field of condensing steam flow in a steam turbine to design an energy efficient turbine because condensation at low pressure (LP) turbine introduces extra losses, and erosion in turbine blades. The turbulence has a leading role in condensing phenomena which involve a rapid change of mass, momentum and heat transfer. The paper presents the influence of turbulence modelling on non-equilibrium condensing steam flows in a LP steam turbine stage adopting CFD code. The simulations were conducted using the Eulerian-Eulerian approach, based on Reynolds-averaged Navier-Stokes equations coupled with a two equation turbulence model, which is included with nucleation and droplet growth model for the liquid phase. The SST k-ω model was modified, and the modifications were implemented in the CFD code. First, the performance of the modified model is validated with nozzles and turbine cascade cases. The effect of turbulence modelling on the wet-steam properties and the loss mechanism for the 3D stator-rotor stage is discussed. The presented results show that an accurate computational prediction of condensing steam flow requires the turbulence to be modelled accurately.
An Academic Test Rig for Industrial Centrifugal Compressor Stages: A Design Approach
Authors: Bianchini Alessandro , Ferrari Lorenzo , Ferrara Giovanni
Published: September 2016

Due to the huge amount of power connected to centrifugal compressors’ applications, even small rangeability increases of the stages would provide significant energy and money savings. In particular, industrial manufacturers pay lot of interest in better understanding the instabilities that in many cases define the minimum flow limit of their stages, but they are often hampered in the research by the short time-to-market. On the other hand, academia has historically found difficulties in approaching the problem due to the lack of dedicated experimental facilities.

In this study, the concept design of a new research test rig is presented. The rig will be able to test impellers in field-like conditions (original mass flow and peripheral Mach numbers up to 0.7), operating in open-loop configuration with ambient inlet conditions. In view of systematic test campaigns, a modular design will allow to easily replace any component of the asset and even to modify the flowpath after the impeller, so that the influence of each component can be estimated. As a research academic facility, the rig is characterized by some new design solutions, oriented to minimize the mechanical complexity, the energy consumption, the overall dimensions, and, finally, the cost. Moreover, it will be equipped with advanced experimental measurement instrumentation, e.g. a PIV system or fast response aerodynamic pressure probes.

The paper illustrates the conceptual design of the rig, including the selection of the best architecture and layout, the drivetrain assessment and the rotordynamic verification. Computational fluid-dynamic analyses are also presented, aimed at verifying the flow uniformity in the discharge sections and the thermal stability of the system during the tests.
Small Horizontal Axis Wind Turbines: Current Status and Future Challenges
Authors: Van Treuren Kenneth W.
Published: September 2016

The category of small wind turbines is a rapidly growing market. The U. S., Europe (UK), and China are of particular interest and seeing the most growth. This paper examines the category of small wind starting with the variety of definitions found in the literature. Growth world-wide, with an emphasis on these major markets, is analyzed for trends and predicted development. The focus is on fixed pitch, small horizontal axis wind turbines, with a direct drive DC generator in the 1–10 kW class. To understand small wind turbines it is necessary to discuss design tools available for design. Included in this design discussion is the necessity for computational fluid dynamic models as well as experimentally testing both open rotors and wind tunnel models. In order for small wind turbines to continue to improve, better technologies are necessary. For design, wind turbines must be optimized for peak performance to include startup/cut-in speeds and other modifications. These wind turbines will rely on new and purposely designed airfoils; however, for low Reynolds number conditions actual airfoil data are needed as many of the computational tools do not accurately predict separation. Increasingly, noise is an issue, especially if these wind turbines will be sited in populated urban areas. An analysis of noise generation as well as design techniques for reducing noise is necessary for future designs. Important discussions on the technologies particular to small wind turbines should include the topics of aerodynamics and structures/materials. Future applications of small wind turbines seem bright. Small wind turbines are contributing to the concept of distributed generation and helping to reduce the carbon footprint. Urban environments are becoming more accepted for small wind turbines which lead to studies of flow fields in and around buildings. Of particular note are hybrid systems which combine wind with other energy generation systems such as solar, internal combustion engines, and diesel engines to name a few. These systems are advantageous for the homeowner, small business, cell phone towers, remote locations, and backup emergency power systems (to include lighting). Lastly, the concept of energy storage must be addressed in the context of small wind turbines, especially those turbines used in an isolated application. Permitting and government incentives are critical to the future success of these wind turbines.
Unsteady Effects in the Heat Load Predictions for a Two-Stage Compressor Turbine
Authors: Farhanieh Arman , Mau Christoph , Annerfeldt Mats , Nadali Najafabadi Hossein , Karlsson Matts
Published: September 2016

Heat load analysis play an important role in the estimation of hot gas components’ lifetime. To achieve a high level of accuracy in heat load analysis, predicting the temperature distribution on the vane and blades is one area where further development is needed. Due to strong flow unsteadiness and mixing effects from blade row interactions and cooling injections, accurate heat load predictions have become an engineering challenge. This study uses both steady and time-accurate computational fluid dynamics (CFD) simulations to investigate the unsteady and mixing effects in a two-stage compressor turbine. The commercial code ANSYS CFX-15 is utilized to evaluate the performance of the steady state, mixing plane (MP) method, versus time-accurate, profile transformation (PT) and time transformation (TT) methods. The presence or absence of the rotor-stator cavities from which purge or cooling air is entering the main flowpath can also play an important role in the unsteadiness and mixing properties. Therefore the unsteady effects have been examined for two cases; a simplified model without any cavity and a detailed geometry with all the cavities included. In the simplified case, the cooling has been implemented as local patches. The results are then compared with gas temperature measurements from the real engine tests using thermo-crystals. The measurements include temperature profiles in front of the leading edge of each stator and rotor for both stages.

The findings suggest that including cooling cavities may not improve the results in steady state simulations, however their presence in transient simulations can lead to mixing prediction improvements. Moreover, the results indicate that the transient simulations will improve the mixing predictions mainly in the second stage of the turbine. The results also indicate that in transient simulations, number of passages and pitch ratio between the stators of consecutive stages directly affect the results regardless of which transient method is used.
Non-Realizability Problem With Quadrature Method of Moments in Wet-Steam Flows and Solution Techniques
Authors: Afzalifar Ali , Turunen-Saaresti Teemu , Grönman Aki
Published: September 2016

The quadrature method of moments (QMOM) has recently attracted much attention in representing the size distribution of liquid droplets in wet-steam flows using the n-point Gaussian quadrature. However, solving transport equations of moments using high-order advection schemes is bound to corrupt the moment set, which is then termed a non-realizable moment set. The problem is that the failure and success of the Gaussian quadrature is unconditionally dependent on the realizability of the moment set. First, this article explains the non-realizability problem with the QMOM. Second, it compares two solutions to preserve realizability of the moment sets. The first solution applies a so-called “quasi-high-order” advection scheme specifically proposed for the QMOM to preserve realizability. However, owing to the fact that wet-steam models are usually built on existing numerical solvers, in many cases modifying the available advection schemes is either impossible or not desired. Therefore, the second solution considers correction techniques directly applied to the non-realizable moment sets instead of the advection scheme. These solutions are compared in terms of accuracy in representing the droplet size distribution. It is observed that a quasi-high-order scheme can be reliably applied to guarantee realizability. However, as with all numerical models in an Eulerian reference frame, in general its results are also sensitive to the grid resolution. In contrast, the corrections applied to moments either fail in identifying and correcting the invalid moment sets, or distorts the shape of the droplet size distribution after the correction.
Acoustically Induced Vibration Mitigations in Compressor Piping Systems
Authors: Allison Timothy C. , Bennett Jeffrey
Published: September 2016

Acoustically induced vibration (AIV) is a high-frequency vibration phenomenon that can occur downstream of pressure-reducing devices such as control valves, restriction orifices, and pressure relief or safety valves in compressor piping systems. These vibrations can lead to high cycle fatigue failures of downstream piping at side branches or welded supports. Existing methods for screening and analyzing acoustically induced vibration are not well-grounded in the underlying physics and thus do not provide a methodology for evaluating a variety of mitigation strategies. Modeling of acoustically induced vibration is computationally challenging, as it requires the interaction between tens or hundreds of higher-order acoustic modes with a similar number of piping shell modes.

In order to obtain better insight into the underlying physics of AIV and to characterize the effectiveness of several mitigation methods, full-scale blow-down testing was performed at Southwest Research Institute. Tests were performed using 20 MPa nitrogen gas vented at 28 kg/s through a 3×4” pressure safety valve and multiple header pipe sizes ranging from 12” to 36”. Test configurations included baseline piping geometry at each size and several AIV mitigations including stiffening rings, viscous damping wrap, and internal acoustic mode disruptors. Test results from strain gauges, accelerometers, and dynamic pressure transducers show a broadband multimodal response with dynamic stresses up to 3 kHz near the safety valve tailpipe connection to the test header, and various mitigations reduced dynamic stresses by 8–52% depending on the piping and type of mitigation.

Acoustic and structural finite element models were analyzed in order to determine the coincident modes that match in both axial/circumferential shape and natural frequency and compare coincident frequencies with measure stresses. The results show that observed peak stress frequencies do not generally correlate well with predicted coincident modes, and that flow-induced turbulence excites frequencies below piping shell modes that can also result in significant stresses that combine with AIV.
Development and Testing of a 333 Kilowatt Industrial Gas Turbine
Authors: Armstrong Jeffrey , Bolin Christopher , Ebrahim Mohammed , Carney Michael
Published: September 2016

The development of a derivative small industrial gas turbine, sometimes termed a “microturbine”, is described. The target markets were the oil and gas upstream and midstream markets, and combined heat and power applications. These applications defined the product objectives. A general description is presented of the baseline recuperated gas turbine from which the new gas turbine is derived. The new gas turbine is a 333kWe recuperated gas turbine with a modernized compressor, variable inlet guide vanes for improved part-power efficiency and emissions, and an improved hot-section. The applicability and advantages of the GT333S features are compared with the market requirements. The development program included compressor rig testing, inlet guide vane development and testing, and engine testing. For the new product, a large number of components remained unchanged from GT250S, including most of the drivetrain. This provided confidence that the reliability of the GT333S, based on the millions of successful operating hours accrued on the GT250S, would translate into good GT333S reliability and availability. Extensive factory testing was performed to demonstrate the robustness of the new engine. The final performance results showed that the gas turbine achieved the program objectives. Some lessons learned from the development program are described.