bluuebunny/crossref_metadata_2025 huggingface dataset:
Derivative Design of Axial Fan Range: From Academia to Industry
Authors: Bonanni Tommaso , Cardillo Lucio , Corsini Alessandro , Delibra Giovanni , Sheard Anthony G. , Volponi David
Published: September 2016

The work presented in this paper concerns a useful method for axial fans preliminary design based on the “Derivative Design” concept. The emphasis is, on one side, on education and, on the other, on the practical help that such method can provide in the early preliminary design process.

A complete data set of an axial fan measured with ISO 5801 standards is the start point for the investigation and the prediction of the multiple possible performance that different fan configurations can provide, in terms of dimensionless duty coefficients. In particular, configurations with different number of blades, and hence of solidity, are studied. The typical options of derivative design are explored and relations for performance prediction are presented.

A detailed description of the derivative design methodology is followed by tests and validation. The tools employed are a fully three dimensional code, the Advanceded Actuator Disk Mode (AADM), and two other in-house codes, the Meanline Axisymmetric Calculation (MAC) and Axisymmetric Laboratory (AXLAB).

Results of the derivative design method are reported, showing a good accuracy against the AADM data. The MAC and AXLAB ensure still acceptable results when increasing the solidity of the machine. On the contrary, a decrease of solidity leads to higher relative errors in the prediction of the load coefficient.

In conclusion, an exploration of the possible fields of operation of a blade profile can be carried out by a correct prediction of the stage diffusion factor.
Influence of Honeycomb Land Geometry on Seal Performance
Authors: Frączek Daniel , Bochon Krzysztof , Wróblewski Włodzimierz
Published: September 2016

The aim of this study was to identify the best structures of the honeycomb (or structures used instead of it) that can be applied to a seal cavity labyrinth in order to improve the sealing performance. The problem was investigated numerically using the ANSYS CFX commercial software.

The paper presents geometrical data concerning the proposed solutions to the labyrinth seal land structure. A simple straight-through labyrinth geometry with two leaned fins is analysed. Such a simple structure of the flow conditions was chosen to reduce the influence of other effects on the seal performance. Three-dimensional models of the labyrinth seal were elaborated for each honeycomb or honeycomb-like land structure. The following concepts were analysed: an inclination of the honeycomb cells, a land with different cell shapes (squeezed honeycomb) and honeycomb cells filled with a porous material. The labyrinth seals with different land structures were compared with two reference cases: a seal with a standard honeycomb land (with 1/8-inch cell size) and a seal with a smooth land. Calculations were performed for the pressure ratio values ranging from 1.08 to 1.8 and for varied sizes of the clearance.

Main parameters of the leakage flows are discussed. Additionally, the influence of the inlet narrowing on the seal performance is investigated. A qualitative assessment of the seal concepts is made and the most promising solutions are pointed out.
An Improved Test Facility for Studying Deposit Fouling on Steam Turbine Blades
Authors: May Estebaranz Alan R. , Williams Richard J. , Hogg Simon I. , Dyer Philip W.
Published: September 2016

A laboratory scale test facility has been developed to investigate deposition in steam turbines under conditions that are representative of those in steam power generation cycles. The facility is an advanced two-reactor vessel test arrangement, which is a more flexible and more accurately controllable refinement to the single reactor vessel test arrangement described previously in ASME Paper No. GT2014-25517 [1]. The commissioning of the new test facility is described in this paper, together with the results from a series of tests over a range of steam conditions, which show the effect of steam conditions (particularly steam pressure) on the amount and type of deposits obtained. Comparisons are made between the test results and feedback/experience of copper fouling in real machines.
Non-Invasive Parameter Identification in Rotordynamics via Fluid Film Bearings: Linking Active Lubrication and Operational Modal Analysis
Authors: Santos Ilmar Ferreira , Svendsen Peter Kjær
Published: September 2016

In recent years, theoretical and experimental efforts have transformed the conventional tilting-pad journal bearing (TPJB) into a smart mechatronic machine element. The application of electromechanical elements into rotating systems makes feasible the generation of controllable forces over the rotor as a function of a suitable control signal. The servovalve input signal and the radial injection pressure are the two main parameters responsible for dynamically modifying the journal oil film pressure and generating active fluid film forces in controllable fluid film bearings. Such fluid film forces, resulting from a strong coupling between hydrodynamic, hydrostatic and controllable lubrication regimes, can be used either to control or to excite rotor lateral vibrations. If non-invasive forces are generated via lubricant fluid film, in situ parameter identification can be carried out, enabling evaluation of the mechanical condition of the rotating machine.

Using the lubricant fluid film as a non-invasive calibrated shaker is troublesome, once several transfer functions among mechanical, hydraulic and electronic components become necessary. In this framework the main original contribution of this paper is to show experimentally that the knowledge about the several transfer functions can be bypassed by using output-only identification techniques. The manuscript links controllable (active) lubrication techniques with operational modal analysis, allowing for in-situ parameter identification in rotordynamics, i.e. estimation of damping ratio and natural frequencies.

The experimental analysis is carried out on a rigid rotor-level system supported by one single pair of pads. The estimation of damping and natural frequencies is performed using classical experimental modal analysis (EMA) and operational modal analysis (OMA). Very good agreements between the two experimental approaches are found. Maximum values of the main input parameters, namely servovalve voltage and radial injection pressure, are experimentally found with the objective of defining ranges of non-invasive perturbation forces.
Evaluation of Recent Data From the Sandia National Laboratories Closed Brayton Cycle Testing
Authors: Pasch Jim , Carlson Matt , Fleming Darryn , Rochau Gary
Published: September 2016

At Sandia National Laboratories (SNL), The Nuclear Energy Systems Laboratory / Brayton Lab has been established to research and develop subsystems and demonstrate the viability of the closed Brayton cycles (CBC), and in particular, the recompression CBC. The ultimate objective of this program is to have a commercial-ready system available for small modular reactors. For this objective, R&D efforts must demonstrate that, among other things, component and the system behavior is understood and control is manageable, and system performance is predictable. Research activities that address these needs include investigating system responses to various anticipated perturbations, and demonstrating that component and system performance is understood. To these ends, this paper presents system response to a perturbation, and turbomachinery performance results during steady state operation. A long duration test, with an extensive period at steady state, was completed in the simple CBC configuration. During this period, a cooling perturbation was initiated. Data from this test are presented and evaluated to explain the sequence of events following the perturbation. It was found that a cascading series of events ensued, starting with the fluid condensing effect of the cooling perturbation. The explanation of events emphasizes the highly interactive and nonlinear nature of CBC’s. The comparisons of measured and predicted turbomachinery performance yielded excellent results and give confidence that the predictive methods originally envisioned for this system work well.
Mechanical Integrity and Design Analysis Suite (MIDAS): A Tool for Rapid Finite Element Analysis (FEA) of Steam Turbine Blades
Authors: Lolis Periklis , Guardino Cesare , Brown Trevor , Henson Jonathan
Published: September 2016

Even though Finite Element Analysis (FEA) is considered to be an accurate static and dynamic simulation method, it is used only to verify the Mechanical Integrity (MI) of Steam Turbine (ST) blades, due to the time required to set up and perform a typical FEA. Furthermore, the complexity of the blade model results in convergence issues that further increase the analysis time, which can last several days. Instead, faster, lower order empirical tools with increased conservatism are preferred for the design phase.

Based on parametric steam turbine blades definition, the Mechanical Integrity and Design Analysis Suite (MIDAS) provides a platform for rapid, fully-automated 3D model generation and FEA. The analysis applies simplified contact interactions on a fully structured mesh, aiming primarily for model convergence in a short time, whilst maintaining the required accuracy. In order to verify that, an extended comparison of MIDAS static and vibrational analysis results with the state-of-the-art FEA and experimental measurements is performed.

Therefore, with MIDAS an accurate full FEA is completed within few minutes for each blade, speeding up the MI validation process and enabling its use at the design of every ST blade. Furthermore, the use of FEA contributes to an extended blade application envelope and optimised blade geometry. As a result, MIDAS presents several benefits to new and existing ST customers including increased operational flexibility, extended blade life, faster delivery of the ST cylinders at a lower acquisition cost and extended outage intervals.
Steam Turbine Rotor Transient Thermo-Structural Analysis and Lifetime Prediction
Authors: Moroz Leonid , Frolov Boris , Kochurov Roman
Published: September 2016

Market requirements for faster and more frequent power unit start-up events result in a much faster deterioration of equipment, and a shorter equipment lifespan. Significant heat exchange occurs between steam and turbine rotors during the start-up process and even more intensive heat exchange takes place during the condensation phase in cold start-up mode, which leads to further thermal stresses and lifetime reduction. Therefore, the accuracy of lifetime prediction is strongly affected and dependent on the accuracy of transient thermal state prediction.

In this study, transient thermal and structural analyses of a 30 MW steam turbine for a combined High and Intermediate pressures (HPIP) rotor during a full cold start cycle is performed and special attention is paid to initial start-up phase with ‘condensation’ thermal BC. All steps for rotor design and the thermal model preparation were done using the AxSTREAM™* software platform. It included the development of a two dimensional model of the rotor, thermal zones and corresponding thermal boundary conditions (heat transfer coefficients and steam temperatures) calculation during turbine start-up and shut down operation. Rotor thermal and structural simulations were done using commercial FE analysis software to evaluate the thermo-stress-strain state of the turbine rotor. Calculation and validation of thermal and structural state of the rotor was done using actual start-up cycle and measured data from a power plant, and it showed good agreement of the calculated and the measured data. Based on the results of thermo-structural analysis, the evaluation of rotor lifetime by means of a low cycle fatigue approach was performed and presented in this paper.
Coupled Physics Performance Predictions and Risk Assessment for Dry Gas Seal Operating in MW-Scale Supercritical CO2 Turbine
Authors: Thatte Azam , Dheeradhada Voramon
Published: September 2016

U.S. Department of Energy (DOE) has recently sponsored research programs to develop megawatt scale supercritical CO2 (sCO2) turbine for use in concentrated solar power (CSP) and fossil based applications. To achieve the CSP goal of power at $0.06/kW-hr LCOE and energy conversion efficiency > 50%, the sCO2 turbine relies critically on extremely low leakage film riding seals like dry gas seal (DGS). Although DGS technology has been used in other applications before. making it successful for stringent conditions of an sCO2 turbo-expander is challenging. This paper presents results from a multi-scale coupled physics model that predicts the performance of DGS under a typical sCO2 turbine mission cycle and addresses some of the risks specific to operation in sCO2. Real gas equations of state are incorporated in the models to capture large discontinuities in fluid properties close to the critical point. A novel experimental setup is developed to observe and characterize transition of CO2 through liquid-vapor and supercritical phases. Coupled fluid-structure-thermal interaction model investigates the effect of aerodynamic and thermal perturbations on the structural and rotordynamic instabilities. Dynamic instabilities arising from sonic transition in thin sCO2 film of DGS pose additional challenges while the large surface roughness changes due to sCO2 corrosion warrant further design considerations. Effectiveness of features like spiral grooves in converting fluid momentum into pressure rise in the thin film and also in achieving local flow reversals is investigated. Effect of various design features on the optimal performance is quantified and insights for a successful DGS operation in a sCO2 turbomachine are provided.
Analysis and Comparison of the Performance of an Inverted Brayton Cycle and Turbo-Compounding With Decoupled Turbine and CVT Driven Compressor for Small Automotive Engines
Authors: Lu P. , Brace C. , Hu B. , Copeland C.
Published: September 2016

For an internal combustion engine, a large quantity of fuel energy (accounting for approximately 30% of the total combustion energy) is expelled through the exhaust without being converted into useful work. Various technologies including turbo-compounding and the pressurized Brayton bottoming cycle have been developed to recover the exhaust heat and thus reduce the fuel consumption and CO2 emission. However, the application of these approaches in small automotive power plants has been relatively less explored because of the inherent difficulties, such as the detrimental backpressure and higher complexity imposed by the additional devices. Therefore, research has been conducted, in which modifications were made to the traditional arrangement aiming to minimize the weaknesses. The turbocharger of the baseline series turbo-compounding was eliminated from the system so that the power turbine became the only heat recovery device on the exhaust side of the engine, and operated at a higher expansion ratio. The compressor was separated from the turbine shaft and mechanically connected to the engine via CVT. According to the results, the backpressure of the novel system is significantly reduced comparing with the series turbo-compounding model. The power output at lower engine speed was also promoted. For the pressurized Brayton bottoming cycle, rather than transferring the thermal energy from the exhaust to the working fluid, the exhaust gas was directly utilized as the working medium and was simply cooled by ambient coolant before the compressor. This arrangement, which is known as the inverted Brayton cycle was simpler to implement. Besides, it allowed the exhaust gasses to be expanded below the ambient pressure. Thereby, the primary cycle was less compromised by the bottoming cycle. The potential of recovering energy from the exhaust was increased as well. This paper analysed and optimized the parameters (including CVT ratio, turbine and compressor speed and the inlet pressure to the bottoming cycle) that are sensitive to the performance of the small vehicle engine equipped with inverted Brayton cycle and novel turbo-compounding system respectively. The performance evaluation was given in terms of brake power output and specific fuel consumption. Two working conditions, full and partial load (10 and 2 bar BMEP) were investigated. Evaluation of the transient performance was also carried out. Simulated results of these two designs were compared with each other as well as the performance from the corresponding baseline models. The system models in this paper were built in GT-Power which is a one dimension (1-D) engine simulation code. All the waste heat recovery systems were combined with a 2.0 litre gasoline engine.
Aerodynamics of Darrieus Wind Turbines Airfoils During Start-Up
Authors: Bianchini Alessandro , Balduzzi Francesco , Ferrara Giovanni , Ferrari Lorenzo
Published: September 2016

Recent studies have demonstrated that, when rotating around an axis orthogonal to the flow direction, airfoils are virtually transformed into equivalent airfoils with a camber line defined by their arc of rotation. In these conditions, the symmetric airfoils commonly used for Darrieus blades actually behaves like virtually cambered ones or, equivalently, rotors have to be manufactured with counter-cambered blades in order to have the performance of a symmetric airfoil.

To complete these analyses, the present study focuses the attention on the airfoils’ aerodynamics during the start-up of the rotors. This phase of turbines’ functioning is indeed of particular interest since it actually defines the cut-in speed of the rotors and then notably impacts on the annual energy production, especially in case of small-size machines.

In the work, unsteady CFD simulations have been carried out in start-up like conditions on three airfoils, i.e. a NACA 0018 and two modified profiles based on the same airfoil. The modified profiles have been conformally transformed to fit their camber lines to the arc of a circle, such that the ratio of the airfoil chord to the circle’s radius is 0.114 or 0.25.

The study demonstrates that all the conventional theories based on one-dimensional aerodynamic coefficients (e.g. blade element momentum models) are affected by an intrinsic error in evaluating the starting torque profiles. Symmetric airfoils in fact exhibit a counter-intuitive non symmetric starting torque over the revolution. Conversely, airfoils compensated for the virtual camber effect show a substantially different starting torque profile, with a more symmetric distribution between the upwind and the downwind halves. This behavior is due to the effect of the pitching moment, which is usually neglected in lumped parameters models. At very low revolution speeds, its contribution becomes significant due to the very high angles of attack experienced by the blade. In particular, the pitching moment is non symmetric between the upwind and the downwind halves of the revolution. For upwind azimuthal positions the pitching moment reduces the overall torque output, while it changes sign in the downwind section, increasing the torque.

The importance of accounting for the pitching moment contribution in low-order models (e.g. a blade element momentum model) is finally discussed by comparing the predicted torque profiles with those obtained by CFD.
Analysis of Heat Transfer in a Radial Turbine Wheel of Turbochargers and Prediction of Heat Transfer Coefficients With an Empirical Method
Authors: Rakut Christian , Diefenthal Mathias , Wirsum Manfred , Heuer Tom
Published: September 2016

The accurate prediction of the life cycle is one of the most challenging issues in turbomachinery design. Nowadays life cycle calculations for radial turbines focus on mechanical loads such as centrifugal and vibration forces. Because of enhanced turbine inlet temperatures with inevitably increasing thermal stress, the requirements in the design process of turbine wheels become higher. Therefore, it is desirable to know the temperature profile and thus the thermal stress in the turbine wheel as early as possible in the design process for steady state operating points and transient operation.

This paper reports the development of a fast empirical method to calculate the heat transfer coefficients on the surface of a radial turbine wheel for steady state operating points. In order to do this, steady state Conjugate Heat Transfer (CHT) investigations of a turbocharger turbine wheel for commercial application were performed to model the heat transfer between the fluid and the solid state. These investigations provide a basis for the analysis and characterization of the heat transfer distribution at the turbine wheel and the flow phenomena that cause these. The empirical method for determining heat transfer coefficients of a turbine wheel is developed based on the numerical results. To model the local different heat transfer coefficients the turbine wheel is divided in several surface segments which correspond to the geometry of a radial turbine wheel.

To validate the method the heat transfer coefficients from the empirical model are used as boundary conditions for a subsequent Finite Element Analysis (FEA). The calculated temperatures of the FEA results are compared to those of the CHT simulation and to the experimental data. For operating points with a circumferential velocity of u ≤ 0.75 u0 a good agreement are reached. The deviations increase for higher circumferential velocities. Furthermore the number of surface segments is varied to show the influence of the segmentation level to the temperature profile. It is also possible to reach a good agreement for operating points of u ≥ 0.75 u0 if the blade is segmented over its height. With the presented method a fast prediction of the heat transfer coefficients and the steady state temperature field of the turbine wheel are possible for steady state operating points.
Comparison Between Weak and Strong Coupling Modeling for Aeroelastic Stability of a Simple Sealing Device
Authors: de Cacqueray Nicolas , Seive Martin , Kernilis Alain
Published: September 2016

In the present paper, a strong coupling and two weak coupling approaches are compared to estimate the aeroelastic stability of a simple sealing system. This test configuration, directly inspired from clarinet modeling [19], combines a valve, represented by a single degree of freedom mechanical element, and an axial acoustic cavity. It displays aeroelastic instabilities due to interactions between mechanical and acoustic modes. The strong coupling (SC) computes directly the eigenmodes of the discrete problem and it is used as the reference solution. The numerical solver is based on low-dissipation and low-dispersion schemes combined with a selective filter. The first weak coupling approach presented here is named the flutter-like weak coupling (FWC), and it is derived from a blade flutter methodology employed in the industry. The second weak coupling method is called the resonator weak coupling (RWC), and it uses a coupling between the mechanical and the acoustic modes. The FWC fails to provide the stability of the present test configuration, whereas the RWC gives better results. However, the assumption made at the junction between the valve and the cavity is a critical issue for the RWC. The number of acoustic modes considered in this model can also impact the results.
Unsteady Flow Field and Coarse Droplet Measurements in the Last Stage of a Low Pressure Steam Turbine With Supersonic Airfoils Near the Blade Tip
Authors: Bosdas Ilias , Mansour Michel , Kalfas Anestis I. , Abhari Reza S. , Senoo Shigeki
Published: September 2016

The largest share of electricity production worldwide belongs to steam turbines. However, the increase of renewable energy production has led steam turbines to operate under part load conditions and increase in size. As a consequence long rotor blades will generate a relative supersonic flow field at the inlet of the last rotor. This paper presents a unique experiment work that focuses at the top 30% of stator exit in the last stage of an LP steam turbine test facility with coarse droplets and high wetness mass fraction under different operating conditions. The measurements were performed with two novel fast response probes. A fast response probe for three dimensional flow field wet steam measurements and an optical backscatter probe for coarse water droplet measurements ranging from 30 up to 110μm in diameter. This study has shown that the attached bow shock at the rotor leading edge is the main source of inter blade row interactions between the stator and rotor of the last stage. In addition, the measurements showed that coarse droplets are present in the entire stator pitch with larger droplets located at the vicinity of the stator’s suction side. Unsteady droplet measurements showed that the coarse water droplets are modulated with the downstream rotor blade-passing period. This set of time-resolved data will be used for in-house CFD code development and validation.
Three-Dimensional Character of VAWT Wakes: An Experimental Investigation for H-Shaped and Troposkien Architectures
Authors: Persico G. , Dossena V. , Paradiso B. , Battisti L. , Brighenti A. , Benini E.
Published: September 2016

In this paper the aerodynamics and performance of two Vertical Axis Wind Turbines are discussed, on the basis of a wide set of experiments performed at Politecnico di Milano (Italy). A H-shaped and a Troposkien Darrieus turbine for micro-generation, characterized by the same swept area and blade section, are tested in real-scale. Performance measurements show that the Troposkien rotor outperforms the H-shaped turbine, mostly related to the larger midspan section of the Troposkien rotor (resulting by the constraint of constant swept area) and to the non-aerodynamic struts of the H-shaped rotor. These features are consistent with the character of the wakes shed by the turbines, measured by means of hot wire anemometry on several surfaces downstream of the models. The morphology of H-shape and Troposkien rotor wakes exhibit relevant differences, especially in the three-dimensional character and time-periodic evolution in the blade tip region. In particular, large-scale vortices dominate the tip region of the wake shed by the H-shape turbine; these vortices pulsate significantly during the period, due to the periodic fluctuation of the blade aerodynamic loading. Conversely, the highly tapered shape of the Troposkien rotor prevents the onset of tip vortices, but also induces a dramatic spanwise reduction of tip speed ratio, promoting the onset of local dynamic stall marked by high periodic and turbulent unsteadiness in the tip region of the wake. The way in which these mechanisms affect the wake evolution and mixing process for the two classes of turbines is investigated for different tip speed ratios, highlighting some relevant implications in the framework of wind energy exploitation.
An Innovative Method for the Evaluation of Particle Deposition Accounting for the Rotor/Stator Interaction
Authors: Aldi Nicola , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Suman Alessio
Published: September 2016

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the micro-particles not captured by the air filtration system can cause deposits on blading and, consequently, result in a performance drop of the compressor.

This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0.15 μm – 1.50 μm) in a transonic axial compressor stage, carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase.

A particular computational strategy is adopted in order to take into account the presence of two subsequent annular cascades (rotor and stator) in the case of particle ingestion. The proposed strategy allows the evaluation of particle deposition in an axial compressor stage thanks to its capability of accounting for the rotor/stator interaction. NASA Stage 37 is considered as a case study for the numerical investigation. The compressor stage numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in literature.

The blade zones affected by particle impact and the kinematic characteristics of the impact of micrometric and sub-micrometric particles with the blade surface are shown. Both blade zones interested by particle impact and deposition are analyzed.

The particle deposition is established by using the quantity called sticking probability, adopted from literature. The sticking probability links the kinematic characteristics of particle impact on the blade with fouling phenomenon.

The results show that micro-particles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side of rotor blade and stator vane. Both rotor blade and stator vane suction side are affected only by the impact of smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, shock waves and tip leakage vortex, strongly influence the impact location of the particles. The kinematic analysis shows a high tendency of particle adhesion on the suction side of the rotor blade, especially for particles with a diameter equal to 0.15 μm.
Hermetic 40-kW-Class Steam Turbine System for the Bottoming Cycle of Internal Combustion Engines
Authors: Kraus Michael H. , Deichsel Michael , Hirsch Peter , Opferkuch Frank , Heckel Christoph
Published: September 2016

An entirely new 40-kW-class steam turbine prototype has been constructed and successfully tested for more than 6,500 hours. The two-stage Curtis wheel with a nominal pressure ratio of about 130 has been designed for applications in bottoming water/steam cycles. The axial turbine runs at a rated rotational speed of 36,000 rpm, utilizing magnetic bearings and a permanent magnet synchronous generator which is coupled to the grid by frequency inverters. The integral turbine-generator set has been designed as a hermetically sealed assembly group. The turbine design allows both the turbine’s oil supply system and the bottoming cycle’s feed-water treatment system to be eliminated. The turbine has been designed to allow unmanned operation of the entire cycle with minimum maintenance requirements and reduced costs.

Extensive turbine testing, including rated power, overload and load rejection tests was carried out to verify functionality. Long-term operational capability was also demonstrated, giving particular attention to generator performance. Exemplarily a bottoming cycle, utilizing the turbine, matching the exhaust conditions of internal combustion engines was designed, increasing electrical efficiency from 40.4% to 43.4%, which represents a relative net improvement of 7.5%. In this application a turbine isentropic efficiency of more than 55% is expected, based on the congruence of measurement and calculation.
A New Visualization Method for Harmonic Unsteady Flows in Turbomachinery
Authors: Gezork Tobias , Petrie-Repar Paul , Fransson Torsten
Published: September 2016

Understanding unsteady flow processes is key in the analysis of challenging problems in turbomachinery design such as flutter and forced response. In this paper a new visualization method for harmonic unsteady flow is presented. The method illustrates the direction in which unsteady waves are traveling and transporting energy by the direct visualization of the propagating pressure waves in terms of field lines constructed from the wave group velocity. The group velocity is calculated from the unsteady flow solution by assuming that the local unsteady pressure perturbation of interest can be represented by a single harmonic unsteady wave. The applicability of the method is demonstrated for three test cases including a linear cascade of two-dimensional flat plates and a linear cascade of two-dimensional compressor blade profiles.
An Integrated Software Tool for High Fidelity Probabilistic Assessments of Metallic Aero-Engine Components
Authors: McClung R. Craig , Wawrzynek Paul , Lee Yi-Der , Carter Bruce J. , Moody Jonathan P. , Enright Michael P.
Published: September 2016

Most current tools and methodologies to predict the life and reliability of fracture critical gas turbine engine components rely on stress intensity factor solutions that assume highly idealized component and crack geometries, and this can lead to highly conservative results in some cases. This paper describes a new integrated methodology to perform these assessments that combines one software tool for creating high fidelity crack growth simulations (FRANC3D) with another software tool for performing probabilistic fatigue crack growth life assessments of turbine engine components (DARWIN). DARWIN employs finite element models of component stresses, while FRANC3D performs automatic adaptive re-meshing of these models to simulate crack growth. Modifications have been performed to both codes to allow them to share and exchange data and to enhance their shared computational capabilities. Most notably, a new methodology was developed to predict the shape evolution and the fatigue lifetime for cracks that are geometrically complex and not easily parameterized by a small number of degrees of freedom. This paper describes the integrated software system and the typical combined work flow, and it shows the results from a number of analyses that demonstrate the significant features of the system.
On the Predicted Effect of Angular Misalignment on the Performance of Oil Lubricated Thrust Collars in Integrally Geared Compressors
Authors: Cable Travis A. , San Andrés Luis , Wygant Karl
Published: September 2016

Multiple-stage integrally geared compressors (IGCs) offer improved thermal efficiency and easier access for maintenance and overhaul than single-shaft centrifugal compressors. In an IGC, a main bull shaft drives pinion shafts, each having an impeller at its ends. The compression of process gas in the compressor stages induces axial loads along the pinion shafts that are transmitted via thrust collars (TCs) to the main bull gear (BG) shaft and balanced by a single thrust bearing. Manufacturing inaccuracies and a poor assembly process can lead to static angular misalignments of the TC and BG surfaces that affect the operating film thickness as well as the force and reaction moments of the lubricated mechanical element. In a follow up to Ref. [1], this paper presents an investigation of the performance of a single thrust collar configuration operating with increasing static angular misalignment of either the TC or BG. The flow model solves the Reynolds equation of hydrodynamic lubrication coupled to a thermal energy transport equation to determine the film pressure and bulk temperature fields, respectively. The model predicts performance parameters such as power loss and lubricant flow rate, and force and moment stiffness and damping coefficients. Predictions show that misaligning of either the thrust collar or bull gear alters the load carrying area in the lubricated zone, shifts the pressure field with peak magnitudes doubling or more depending on the degree and direction of TC or BG misalignment. Static angular misalignment does not significantly affect the power loss, temperature rise, etc., but does have an effect on the dynamic coefficients (both axial and angular). Finally, a reduced complex dynamic stiffness matrix for the lubricated TC shows that some cross coupled stiffness and moment coefficients are nonzero, indicating hydrodynamic coupling between axial and angular motions for the pinion and bull gear shafts. The coupling could affect the placement of the system natural frequencies and associated mode shapes as well as the system stability.
The Influence of Non-Equilibrium Wet Steam Effects on the Aeroelastic Properties of a Turbine Blade Row
Authors: Fuhrer Christopher , Grübel Marius , Vogt Damian M. , Petrie-Repar Paul
Published: September 2016

Turbine blade flutter is a concern for the manufacturers of steam turbines. Typically, the length of last stage blades of large steam turbines is over one meter. These long blades are susceptible to flutter because of their low structural frequency and supersonic tip speeds with oblique shocks and their reflections. Although steam condensation has usually occurred by the last stage, ideal gas is mostly assumed when performing flutter analysis for steam turbines.

The results of a flutter analysis of a 2D steam turbine test case which examine the influence of non-equilibrium wet steam are presented. The geometry and flow conditions of the test case are supposed to be similar to the flow near the tip in a steam turbine as this is where most of the unsteady aerodynamic work contributing to flutter is done. The unsteady flow simulations required for the flutter analysis are performed by ANSYS CFX. Three fluid models are examined: ideal gas, equilibrium wet steam (EQS) and non-equilibrium wet steam (NES), of which NES reflects the reality most.

Previous studies have shown that a good agreement between ideal gas and EQS simulations can be achieved if the prescribed ratio of specific heats is equal to the equilibrium polytropic index of the wet steam flow through the turbine.

In this paper the results of a flutter analysis are presented for the 2D test case at flow conditions with wet steam at the inlet. The investigated plunge mode normal to chord is similar to a bending mode around the turbine axis for a freestanding blade in 3D. The influence of the overall wetness fraction and the size of the water droplets at the inlet are examined. The results show an increase of aerodynamic damping for all investigated interblade phase angles with a reduction of droplet size. The influence of the wetness fraction is in comparison of less importance.
Forced Response Analysis of a Mistuned Compressor Blisk Comparing Three Different Reduced Order Model Approaches
Authors: Gutierrez Salas Mauricio , Bladh Ronnie , Mårtensson Hans , Petrie-Repar Paul , Fransson Torsten , Vogt Damian M.
Published: September 2016

Accurate structural modeling of blisk mistuning is critical for the analysis of forced response in turbomachinery. Apart from intentional mistuning, mistuning can be due to the manufacturing tolerances, corrosion, foreign object damage and in-service wear in general. It has been shown in past studies that mistuning can increase the risk of blade failure due to energy localization. For weak blade to blade coupling, this localization has been shown to be critical and higher amplitudes of vibration are expected in few blades. This paper presents a comparison of three reduced order models for the structural modeling of blisks. Two of the models assume cyclic symmetry while the third model is free of this assumption. The performance of the reduced order models for cases with small and large amount of mistuning will be examined. The benefits and drawbacks of each reduction method will be discussed.
Characterization of Brush Seal Permeability
Authors: Gresham Thomas G. , Weaver Brian K. , Wood Houston G. , Untaroiu Alexandrina
Published: September 2016

A basis for the study of flow through a brush seal is established by applying the fundamentals of porous media fluid mechanics. Permeability, the measure of a medium’s ability to transmit flow, is one of the most important factors needed to characterize a brush seal’s ability to reduce leakage. Previous studies have indicated that the performance of a brush seal is highly dependent on operating conditions. By investigating how the permeability is affected by the operating conditions (pressure ratio specifically), further understanding of the performance of this type of seal is developed. Experimental data in the literature was used in tandem with computational fluid dynamics (CFD) simulation results in order to characterize how the permeability of a single-stage brush seal changes as the pressure ratio changes. For each value of pressure ratio, the permeability of the CFD model was adjusted until the leakage calculated from the model matched experimentally measured values. The physical mechanisms behind the observed variations in permeability are discussed. Explanations are proposed based on flutter and deformation of the bristles and how these phenomena can affect the internal tortuosity of the bristle pack. As pressure across the bristles increases, it is expected that they will bend under the backing plate to align with the flow direction in the clearance region, but the increase in pressure will also act to compress the bristle pack in the flow direction, decreasing the spacing between bristles and reducing their ability to move relative to each other, thereby reducing the effective permeability of the bristle pack. By demonstrating the dependence of permeability on operating conditions, it is shown that the common assumption of constant permeability coefficients can often result in an insufficient model. Assumptions regarding the model of a bristle pack as an isotropic porous media are discussed, and the validity and utility of this model are assessed. This paper provides important insight into what a reasonable value of permeability of a typical brush seal is, and how that value may change as a function of operating conditions.
Investigations of Flutter and Aero Damping of a Turbine Blade: Part 1 — Experimental Characterization
Authors: Seeley Charles E. , Wakelam Christian , Zhang Xuefeng , Hofer Douglas , Ren Wei-Min
Published: September 2016

Flutter is a self-excited and self-sustained aero-elastic instability, caused by the positive feedback between structural vibration and aerodynamic forces. A two-passage linear turbine cascade was designed, built and tested to better understand the phenomena and collect data to validate numerical models. The cascade featured a center airfoil that had its pitch axis as a degree of freedom to enable coupling between the air flow and mechanical response in a controlled manner. The airfoil was designed to be excited about its pitch axis using an electromagnetic actuation system over a range of frequencies and amplitudes. The excitation force was measured with load cells and the airfoil motion was measured with accelerometers. Extraordinary effort was taken to minimize the mechanical damping so that the damping effects of the airflow over the airfoil, that were of primary interest, would be observable. Assembling the cascade required specialized alignment procedures due to the tight clearances and large motion. The aerodynamic damping effects were determined by observing changes in the mechanical frequency response of the system. Detail aero and mechanical measurements were conducted within a wide range of flow conditions. Experimental results indicate interesting changes in aerodynamic damping over a range of Mach numbers from 0.4 to 1.2. The aero damping was also found to be independent of displacement amplitude within the tested range, giving credence to linear numerical approaches.
Modeling a Spiral Groove Thrust Bearing Using 3-D, Two-Way Fluid Structure Interaction With Conjugate Heat Transfer
Authors: Hoopes Kevin , Wilkes Jason C. , Moore Jeff , Grieco Joseph , Passmore Kevin , Brady Jerry
Published: September 2016

In order to quantify the performance of a spiral groove thrust bearing at various operating conditions, a two-way fluid structure interaction model with conjugate heat transfer was created. In this model, the fluid passing through the rotating spiral grooves, as well as the fluid passing behind the bearing pads, was modeled with a Reynolds Averaged Navier-Stokes solver that included the effect of turbulence. This fluid simulation was coupled with a structural simulation of the runner and pads that included heat transfer. To simulate the effect of a thrust load, a force was applied to the structural side of the simulation that was, in turn, transferred to the fluid simulation by way of mesh deformation. The resultant data set includes details such as pad motion, temperature, pressure, and film-thickness profiles as a function of applied thrust load. This allows for the determination of the maximum allowable thrust load before contact occurs at some assumed film thickness. This paper outlines the setup procedure and includes a brief discussion of the simulation results. These results demonstrate that it is possible to use fluid structure interaction to predict the load capacity high speed spiral groove thrust bearing.
A Low Speed Compressor Test Rig for Flutter Investigations
Authors: Malzacher Leonie , Geist Silvio , Peitsch Dieter , Hennings Holger
Published: September 2016

A test facility for aereolastic investigations has been installed at the chair of Aero Engines at the Technische Universität Berlin. The test rig provides data for tool and code validation and is used for basic aeroelastic experiments. It is a low speed wind tunnel which allows free and controlled flutter testing. The test section contains a linear cascade with eleven compressor blades. Nine of them are elastically suspended. The paper presents a detailed description of the test facility, results to evaluate the overall flow quality and an aeroelastic model to predict the flutter velocity and critical interblade phase angles. Hot-wire anemometry has been applied to examine the inlet flow for several Mach- and Reynolds numbers. The results show small turbulence intensities. The blade surface pressure distribution and the flow field of the blade’s suction and pressure side has been accessed by oil flow visualization.