bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Impeller Outflow Conditions on the Performance of Vaned Diffusers
Authors: Everitt Jonathan , Spakovszky Zoltán , Rusch Daniel , Schiffman Jürg
Published: September 2016

Highly-loaded impellers, typically used in turbocharger and gas turbine applications, exhaust an unsteady, transonic flow that is non-uniform across the span and pitch and swirling at angles approaching tangential. With the exception of the flow angle, conflicting data exist regarding whether these attributes have substantial influence on the performance of the downstream diffuser.

This paper quantifies the relative importance of the flow angle, Mach number, non-uniformity and unsteadiness on diffuser performance, through diffuser experiments in a compressor stage and in a rotating swirling flow test rig. This is combined with steady and unsteady Reynolds-Averaged Navier Stokes computations. The test article is a pressure ratio 5 turbocharger compressor with an airfoil vaned diffuser. The swirling flow rig is able to generate rotor outflow conditions representative of the compressor except for the periodic pitchwise unsteadiness, and fits a 0.86 scale diffuser and volute. In both rigs, the time-mean impeller outflow is mapped across a diffuser pitch using miniaturized traversing probes developed for the purpose.

Across approximately two-thirds of the stage operating range, diffuser performance is well correlated to the average impeller outflow angle when the metric used is effectiveness, which describes the pressure recovery obtained relative to the maximum possible given the average inflow angle and Mach number and the vane exit metal angle. Utilizing effectiveness captures density changes through the diffuser at higher Mach numbers; a 10% increase in pressure recovery is observed as the inlet Mach number is increased from 0.5 to 1. Further, effectiveness is shown to be largely independent of the time-averaged spanwise and unsteady pitchwise non-uniformity from the rotor; this independence is reflective of the strong mixing processes that occur in the diffuser inlet region. The observed exception is for operating points with high time-averaged vane incidence. Here, it is hypothesized that temporary excursions into high-loss flow regimes cause a nonlinear increase in loss as large unsteady angle variations pass by from the rotor.

Given that straight-channel diffuser design charts typically used in preliminary radial vaned diffuser design capture neither streamtube area changes from impeller exit to the diffuser throat nor vane incidence effects, their utility is limited. An alternative approach, utilizing effectiveness and vane leading edge incidence, is proposed.
Adjoint-Response Surface Method in Aerodynamic Shape Optimization of Turbomachinery Blades
Authors: Tang Xiao , Luo Jiaqi , Liu Feng
Published: September 2016

An adjoint-response surface method is developed to give global representation of cost function in a parametrized design space for turbomachinery blades. Radial basis function (RBF) based and quadratic polynomial (QP) based response surface models are constructed using both the values of cost function and its adjoint gradients with respect to geometry control parameters. The method is tested on a quasi-three dimensional NACA0012 blade row, then applied to the transonic Rotor 67. In preliminary design optimization stage, when the number of undetermined control parameters is large, the QP based model can provide a global image of the cost function in high dimensional design space with a small amount of sample points. In two-parameter fine optimization stage, high resolution can be achieved with the RBF based models. This gradient-enhanced response surface method is useful in guiding designers to discover the global optimum which may be missed by local gradient methods in a complicated design space. It may also be used as substitute of CFD flow solver in time consuming iterative design and optimization.
Comparison of the Combustion Characteristics of Liquid Single-Component Fuels in a Gas Turbine Model Combustor
Authors: Grohmann Jasper , O’Loughlin William , Meier Wolfgang , Aigner Manfred
Published: September 2016

Alternative production pathways for liquid fuels provide the opportunity to adjust the chemical composition of the product in order to improve combustion performance. In this study, flame characteristics of selected single-component fuels were investigated to provide a basis for a better understanding of the influence of specific fuel components on the combustion behaviour. The measurements were performed in a redesigned gas turbine model combustor for swirl-stabilised spray flames under atmospheric pressure. The combustor features a dual-swirl geometry and a prefilming airblast atomiser. The combustion chamber provides good optical access and yields well-defined boundary conditions. As part of different projects in the field of alternative fuels, two liquid single-component fuels (n-hexane, n-dodecane) and kerosene Jet A-1 were investigated. Flow fields of the nonreacting and reacting flow were measured using stereo particle image velocimetry. The flame structure and spray distribution were derived from CH* chemiluminescence and Mie scattering respectively. Lean blowout limits were measured. Results show noticeable differences in combustion behaviour of the chosen fuels at comparable flow conditions. Furthermore, the results provide a detailed data base for the validation of numerical models.
Development of a Centrifugal Compressor Facility for Performance and Aeromechanics Research
Authors: Lou Fangyuan , Harrison Herbert M. , Fabian John C. , Key Nicole L. , James Darrell K. , Srivastava Rakesh
Published: September 2016

This paper details the development of a Single Stage Centrifugal Compressor (SSCC) research facility at Purdue University in collaboration with Honeywell. The research vehicle is a Honeywell experimental compressor that has been specifically outfitted with a variety of instrumentation for research purposes. Both steady-state and fast-response instrumentation will be used to provide benchmark experimental data for performance and aeromechanics tool development and validation. Some unique facility aspects include real-time clearance control, active bleed flow management, fast-response pressure sensors embedded in the impeller, and a full circumferential traverse at the compressor inlet to facilitate inlet distortion quantification. The details of the facility and baseline results are presented.
Minimisation of Ducted Flow Non-Uniformity Caused by Downstream Blockages
Authors: Rife M. E. , Barbarossa F. , Parry A. B. , Green J. S. , di Mare L.
Published: September 2016

Flow in annular ducts is sensitive to the presence of downstream blockages which can cause flow non-uniformities propagating far upstream of the blocking body. These effects can be exacerbated in swirling flows where a cascade of uniform guide vanes is present upstream of the blockage. This work uses two- and three-dimensional boundary singularity methods to model and optimise a guide vane cascade geometry to minimise the upstream velocity distortion. Starting from a uniform cascade, the geometry is modified to provide a uniform upstream velocity distribution and minimised blade-to-blade loading in two dimensions. The new geometry is then extrapolated to a three-dimensional annulus. A three-dimensional tool is used to further modify the geometry in three dimensions to minimise the velocity distortion in the whole annulus upstream of the cascade.
Investigation of Engine Distortion Interaction
Authors: Wartzek Fabian , Schiffer Heinz-Peter , Haug Jakob P. , Niehuis Reinhard , Bitter Martin , Kähler Christian J.
Published: September 2016

Inflow distortions in the compression system of a jet engine are becoming increasingly important for research focus. The investigation of the emergence of a distortion, its interaction with the rotor and the resulting impact on the rotor flow is challenging. In this work a separation in the inflow of a transonic compressor was created and the impact on stage aerodynamics investigated. The separation resulted in a total pressure distortion close to the casing within a sector of 120°. Effects were studied both numerically and experimentally in a joint collaboration project. The numerical model consisted of the full rotor-stator compressor stage, the inlet duct and the distortion generator upstream of the stage. This enables both an accurate validation of the numerical results and contributes to a deeper understanding of the flow. The results of both the numerical and experimental studies were in good agreement. The rotor is locally throttled by the inlet separation, resulting in the formation of an additional loss core at the stability limit due to a local aerodynamic overload. Considering classic distortion descriptors like the DC60, it is shown that they are not able to adequately assess the impact of a strong, but small distortion close to the tip of the rotor. The data can be considered as test case for future numerical models as well as for the validation of new analytical models. Furthermore, the results of this study reveal effects in both experimental and numerical studies that would not be realized if only a model of the separation was analyzed.
A Mutual Nearest Neighbours Based Chaotic Synchronization Index to Detect Thermo-Acoustic Coupling in Gas Turbine Combustion Instabilities
Authors: Chiocchini S. , Pagliaroli T. , Camussi R. , Giacomazzi E.
Published: September 2016

The characterization of unstable combustion regimes is often performed in the light of the Rayleigh Criterion, in the frequency domain, employing the Power Spectral Analysis of pressure (p′) and heat-release (q′) fluctuations. Equally often, it is assumed a priori that the thermo-acoustic oscillations are periodic, with a dominant frequency and a fixed amplitude (Period-1Llimit Cycle Oscillations). However one has to consider that: 1) p′ and q′, involved in the Rayleigh instability index, are governed by the Linearized Acoustic Energy Perturbation Balance Equations; 2) in the frequency domain any interdependence is measured by the coherence function, based on cross spectral densities, or Fourier spectra of cross-correlations, that in turn suppose a linear interdependence between sampled quantities. Conversely, recent experiments reveal that even simple thermo-acoustic systems exhibit nonlinear behaviour, far more elaborate than period-1 limit cycle oscillations. Therefore, in addition to the conventional linear analysis, a new approach based on Nonlinear Dynamics will be required to characterize the unstable regimes in lean gas-turbine combustors. With such approach, one may avoid the risk of misunderstanding the Deterministic Chaos, underlying in the measured signals also during stable combustion regimes, as stochastic noise. The preserved information will be thus available to analytically formulate an index acting as the earliest warning signal of an impending oscillatory combustion instability.

In the light of this, we have applied the Interdependence Index E, based on chaotic synchronization theory, to pressure and radiant energy signals sampled from an industrial combustor. The index was found: 1) low computationally demanding, since based on quantities already calculated for the phase space reconstruction; 2) really effective in the early detection of self sustained (chaotic or not) thermo-acoustic oscillations; 3) valid for a range of coupling strength, and thus smoothly increasing at the instability onset, as requested by the control system time response; 4) unaffected by the non linear relationship between heat release an chemiluminescence, that may make invalid the pseudo-Rayleigh index, computed from pressure and radiant energy fluctuations; 5) asymmetric and thus able to identify the driven and driver (sub)systems, as in combustion instabilities with no thermo-acoustic feed-back.
Influence of Tip Clearance on the Performance and Matching of Multistage Axial Compressors
Authors: Zheng Xinqian , Yang Heli
Published: September 2016

Tip clearance has great influence on the performance of multistage axial compressors including efficiency, pressure rise, mass flow, as well as matching. This paper reports a study into the influence of tip clearance on the performance and matching of a 5-stage axial compressor by a numerical method. Different tip clearances from 0% to 5.0% span which represents the typical range of tip clearance in modern multistage axial compressors were simulated and analyzed. The results show that as tip clearance increases from 0% to 5.0% span, the choked mass flow decreases by about 21.8%, the peak pressure ratio decreases by about 43.1% and the peak efficiency decreases about 14.3 percents. As tip clearance increases, the efficiency of the whole compressor decreases in a parabolic manner not linearly as previous suggested, which is partially attributable to the cantilevered stators considered in this paper and primarily due to the mismatching of different stages. It is of great importance to control the tip clearance. When tip clearance increases, the front stage tends to work near surge condition and the rear stage tends to work near choke condition, which leads to lower efficiency than in the middle stages. A weight was defined to evaluate each stage’s contribution to the whole compressor’s efficiency deficit caused by the increase of tip clearance. Front and rear stages contribute more to the efficiency deficit than the middle stages, which indicates that more attention should be paid on front and rear stages to improve the performance of multistage axial compressors. In order to evaluate the matching of multistage axial compressors with a quantified method, a new parameter named “Peak Efficiency Deviation (PED)” was defined based on the difference between each stage’s operating efficiency and its peak efficiency. The mass flow of multistage axial compressors should be well considered to make the PED parameter to be close to zero as possible. In the most commonly used range of tip clearance from 0.5% to 3.0% span, the PED varies little within 0.4 percent, which is only about 8.4% of the peak efficiency deficit at 1.5% span tip clearance. So, the PED could be small within a wide range of tip clearances if the matching of the compressor is perfect at design tip clearance.
Electric Power Generation From Low-Enthalpy Heat Recovery in FPSOs Using Kalina Cycle
Authors: Campos Rodríguez Carlos Eymel , Gotelip Correa Veloso Thiago , Rodríguez Sotomonte Cesar Adolfo , Alves de Moura Junior Antônio , Coronado Rodríguez Christian Jeremi , Rosa do Nascimento Marco Antônio
Published: September 2016

The present work aims to study, by mean of the First and Second Law the Thermodynamic, the performance of a Kalina Cycle (KCS-34) using low-temperature waste heat recovery in the fourth stage of compression in the CO2 Compression Unit on a Floating Production, Storage and Offloading System (FPSO). Different parameters are evaluated associated with the evaporator to improve the heat absorption of the cycle and taking into account the area of the system too. Three different concentrations of ammonia water mixture are studied, between 65% and 85% of ammonia mass fraction, the CO2 acting as a hot fluid, entry to the evaporator of the Kalina Cycle at 135.2 °C. Some other parameters taking into account in this work are: evaporation pressure, pinch point temperature and terminal temperature differential (TTD) to reach the maximum power production and first and second law efficiency. The Aspen-Hysys software V. 8.6 is used as a tool to simulate the thermal system and Peng-Robinson Stryek-Vera (PRSV) equations of state (EoS). A power output gain in the cycle is obtained with a higher ammonia mass fraction, reaching a maximum net power output of 598 kW using 85% of ammonia mass fraction, a pinch point of 2 °C, a terminal temperature differential of 10 °C and 3500 kPa of the working pressure. Ending, a total heat exchange area calculation is determined in order to have an idea of how big the system is for the different design projects.
Flame Holding in the Premixing Zone of a Gas Turbine Model Combustor After Forced Ignition of H2-NG-Air-Mixtures
Authors: Utschick Matthias , Sattelmayer Thomas
Published: September 2016

Flashback and self-ignition in the premixing zone of typical gas turbine swirl combustors in lean premixed operation are immanent risks and can lead to damage and failure of components. Thus, steady combustion in the premixing zone must be avoided under all circumstances. This study experimentally investigates the flame holding propensity of fuel injectors in the swirler of a gas turbine model combustor with premixing of H2-NG-air-mixtures under atmospheric pressure and proposes a model to predict the limit for safe operation.

The A2EV swirler concept exhibits a hollow, thick walled conical structure with four tangential slots. Four fuel injector geometries were tested. One of them injects the fuel orthogonal to the air flow in the slots (jet-in-crossflow-injector, JICI). Three injector types introduce the fuel almost isokinetic to the air flow at the trailing edge of the swirler slots (trailing edge injector, TEI). A cylindrical duct and a window in the swirler made of quartz glass allow the application of optical diagnostics (OH* chemiluminescence and Planar Laser Induced Fluorescence of the OH radical (OH-PLIF)) inside the swirler. The fuel-air-mixture was ignited with a focused single laser pulse during steady operation. The position of ignition was located inside the swirler in proximity to a fuel injection hole. If the flame was washed out of the premixing zone not later than four seconds after the ignition the operation point was defined as safe. Operation points were investigated at three air mass flows, three air ratios, two air preheat temperatures (573 K, 673 K) and 40 to 100 percent per volume hydrogen in the fuel composed of hydrogen and natural gas.

The determined safety limit for atmospheric pressure yields a similarity rule based on a critical Damköhler number. Application of the proposed rule at conditions typical for gas turbines leads to these safety limits for the A2EV burner: With the TEIs the swirler can safely operate with up to 80 percent per volume hydrogen content in the fuel at an air ratio of two. With the JIC injector safe operation at stoichiometric conditions and 95 percent per volume hydrogen is possible.
Implementation and Validation of the Harmonic Balance Method for Temporally Periodic Non–Linear Flows
Authors: Jasak Hrvoje , Cvijetić Gregor
Published: September 2016

An efficient method for tackling non-linear, temporally–periodic incompressible flows is presented in this paper. Assuming temporally fully periodic flow, Harmonic Balance method deploys Fourier transformation in order to formulate transient problem as a multiple quasi-steady state problems. The method is implemented in OpenFOAM and developed for a general transport equation and incompressible Navier–Stokes equations. Validation is presented on three test cases: oscillating scalar case for scalar transport validation, a flow around a 2D NACA airfoil and a 3D Onera M6 wing for turbulent incompressible Navier–Stokes validation. For all test cases Harmonic Balance results are compared to transient simulation results. Verification of the model is performed by changing the number of harmonics for all test cases.
Optimization of a Two-Stage Transonic Axial Fan to Enhance Aerodynamic Stability
Authors: Ma Sang-Bum , Afzal Arshad , Kim Kwang-Yong , Choi Jaeho , Lee Wonsuk
Published: September 2016

In this paper, a multi-objective optimization of a transonic axial fan to enhance aerodynamic stability has been conducted using three-dimensional Reynolds-Averaged Navier-Stokes equations, surrogate modeling and multi-objective genetic algorithm (MOGA). Hub radius and first rotor chord length of the axial fan were chosen as design variables for the optimization. Peak adiabatic efficiency of the axial fan and stall margin at 60% of the designed rotational speed, were used as objective functions. Latin Hypercube Sampling (LHS) method was used to select design points in the design space. The objective functions were formulated using the response surface approximation (RSA) model. Three LHS samples with different distributions of twelve design points were tested to study their effects on prediction accuracy of the RSA model and optimization results. MOGA with the RSA models based on the best LHS sample, was used to obtain the Pareto-optimal front. As a result of optimization, an improvement of 17.2% in the stall margin at 60% of the designed rotational speed and 2.96% in peak adiabatic efficiency were obtained compared to the reference design. It was also found that distribution of the design points generated by LHS affects the effectiveness of the surrogate-based optimization.
Aerodynamic Optimization of a Winglet-Shroud Tip Geometry for a Linear Turbine Cascade
Authors: Zhang Min , Liu Yan , Zhang Tian-long , Zhang Meng-chao , Li Hong-kun
Published: September 2016

This paper presents a continued study on a previously investigated novel winglet-shroud (WS) (or partial shroud) geometry for a linear turbine cascade. Various width of double-side winglets and different locations of a partial shroud are considered. In addition, both a plain tip and a full shroud tip are applied as the datum cases which were examined experimentally and numerically. Total pressure loss and viscous loss coefficients are comparatively employed to execute a quantitative analysis of the aerodynamic performance.

The effectiveness of various width (w) of double-side winglets (DSW) involving 3%, 5%, 7% and 9% of the blade pitch (p) is numerically investigated. Skin-friction lines on the tip surface indicate that the different DSW cases do not alter flow field features including the separation bubble and reattachment flow within the tip gap region, even for the case with the broadest width (w/p = 9%). However, the pressure side extension of the DSW exhibits the formation of the separation bubble, while the suction side platform of the DSW turns the tip leakage vortex away from the suction surface. Meanwhile, the horse-shoe vortex near the casing is not generated even for the case with the smallest width (w/p=3%). As a result, both the tip leakage and the upper passage vortices are weakened and further dissipated with wider w/p in the DSW cases.

Larger width of the DSW geometry is indeed able to improve the aerodynamic performance, but in a slight degree. With the w/p increasing from 3% to 9%, the mass-averaged total pressure loss coefficient over an exit plane is just reduced by 2.61%. Therefore, considering both the enlarged (or reduced) tip area and the enhanced (or deteriorated) performance compared to the datum cases, a favorable width of w/p=5% is chosen to design the WS structure. Three locations of the partial shroud (linkage segment) are devised, which are located near the leading edge, the middle and close to the trailing edge respectively. Results illustrates that all three cases of the WS have advantages in lessening the aerodynamic loss over the DSW arrangement, but with the linkage segment located in the middle having optimal effect. This conclusion verifies the feasibility of the previously studied WS configuration.
Influence of Topology on Heat Transfer in a Double Wall Cooling Channel: Potential of Series-Linked Jets
Authors: Yang Li , Li Weihong , Ren Jing , Chyu Minking , Jiang Hongde
Published: September 2016

Impingement cooling has been widely used in turbine components, including endwalls, vanes and blades. Numerous investigations focus on single or multiple arrays of jets, which are typically in parallel connection. Very few studies considered jets in series connection, except for some impingement structures used in the trailing edge.

Present study selected a series of double wall cooling structures using impinging jets both in series connection and parallel connection. Structures with different connections and geometry parameters were located inside a piece of super alloy to protect the substrate from the high temperature on the external side. Conjugate heat transfer simulation was implemented in this paper with a CFX solver to get the aero-thermal characteristics of the cooling channels. Work condition with power plant operating temperature and pressure was applied. Results indicate that jets linked in series enhance the heat transfer on the target surface both upstream and downstream. The increase of pressure drop induced by series-linked jets is slower than the increase of heat transfer. Conjugate heat transfer analysis implies a potential of coolant saving and pressure saving for series-linked jets.
Experimental Investigation of Pressure Side Flow Separation on the T106C Airfoil at High Suction Side Incidence Flow
Authors: Stotz Stephan , Niehuis Reinhard , Guendogdu Yavuz
Published: September 2016

The objective of this work is to study the influence of a pressure side separation bubble on the profile losses and the development of the bubble in the blade passage. For the experimental investigations the T106 profile is used, with an increased loading due to an enlarged pitch to chord ratio from 0.799 to 0.95 (T106C). The experiments were performed at the high-speed cascade wind tunnel of the Institute of Jet Propulsion at the University of the Federal Armed Forces Munich. The main feature of the wind tunnel is to vary Reynolds and Mach number independently to achieve realistic turbomachinery conditions. The focus of this work is to determine the influence of a pressure side separation on the profile losses and hence the robustness to suction side incidence flow. The cascade is tested at four incidence angles from 0° to −22.7° to create separation bubbles of different sizes. The influence of the Reynolds number is investigated for a wide range at constant exit Mach number. Therefore a typical exit Mach number for low pressure turbines in the range of 0.5–0.8 is chosen in order to consider compressible effects. Furthermore, two inlet turbulence levels of about 3% and 7.5% have been considered. The characteristics of the separation bubble are identified by using the profile pressure distributions, whereas wake traverses with a five hole probe are used to determine the influence of the pressure side separation on the profile losses. Further, time-resolved pressure measurements near the trailing edge as well as single hot wire measurements in the blade passage are conducted to investigate the unsteady behavior of the pressure side separation process itself and also its influence on the midspan passage flow.
Impact of Enhanced GT Air Filtration on Power Output and Compressor Efficiency Degradation
Authors: Schirmeister Ulf , Mohr Frederick
Published: September 2016

Power output and compressor efficiency of the gas turbine decrease over time due to compressor fouling. A major part of this power and compressor efficiency loss can be recovered by compressor online and offline washing. Nevertheless, with an enhanced filtration in the EPA class, it is possible to reduce the deployment of degradation and the necessity of washings to a minimum. After providing an overview of published research work from the past, this paper presents a thorough investigation and quantification of the effect of different air filter classes on degradation based on fleet wide analysis.

The operating data of a total of 12 gas turbines (Alstom’s GT13E2, GT24 and GT26) from 6 power stations in 5 different countries are analyzed, giving a sum of 34 filter cycles for evaluation (1 cycle represents the time period between two filter exchanges or compressor offline washings). The filter houses of the assessed plants are equipped with 2- or 3-stage filtration systems with filter classes ranging from G4 to E11 and various combinations thereof. The relevant data for power output and compressor efficiency together with the exchange history of the air filters is used to determine the degradation as a function of the last filter stage class, which allows for a quantification of the degradation and reveals a clear correlation.

As it is shown that not only the last stage filter with the highest filter class determines the degradation, but the filter system with all stages as a combination, this paper additionally evaluates the effect of the second-last filter class on the degradation.

Due to more and more challenging market environments for the plant owners, the decision to opt for highly efficient EPA filters must be well-considered: more efficient filters generally have a higher pressure loss with a negative influence on power output and are generally more expensive. Nevertheless, EPA filtration can be a strong business case when all factors such as prices for electricity and gas, operating regime of the plant, pressure loss and exchange scenarios of the filters, necessity for compressor washing etc. are considered. An exemplary profitability analysis considering all the above mentioned factors is presented in this paper. The insights of this paper shall be used as a basis for decision making when it comes to the question of how to lay out the project specific GT air inlet filtration system, as well as of how to modify the existing GT air inlet filtration for improved performance and economics.
Experimental and Numerical Investigations on Oil Leakage Across Labyrinth Seals in Aero Engine Bearing Chambers
Authors: von Plehwe Felix C. , Krug Matthias B. , Höfler Corina , Bauer Hans-Jörg
Published: September 2016

This paper presents experimental and numerical investigations of oil leakage across a conventional labyrinth seal commonly found in aero engine bearing chambers. Measurements and simulations were carried out in order to investigate the influence of chamber geometry and operating conditions on the reliability of the oil seal against leakage.

The main goal of the experiments was to determine a minimum required pressure difference Δpleak to prevent oil from leaving the bearing chamber for any given operating point. To determine this variable, the pressure inside the test rig was continuously lowered from a high pressure difference until oil was found to leave the bearing chamber. Using two pressure supplies, this pressure could be negative or positive. The results show that the minimum pressure depends on component design and rotational speed. While certain component designs may increase this pressure at low rotational speeds, thereby creating a safety margin for oil leakage, the opposite effect can manifest itself at higher rotational speeds.

Selected operating points were simulated using computational fluid dynamics employing the Volume-of-Fluid (VoF) approach. A comparison of the experimental and numerical results shows good qualitative agreement of the two phase flow phenomena inside the bearing chamber.
Auxiliary Bearing System Optimization for AMB Supported Rotors Based on Rotor Drop Analysis: Part II — Optimization for Example Vertical and Horizontal Machines
Authors: Cao Jianming , Allaire Paul , Dimond Timothy , Dousti Saeid
Published: September 2016

This paper forms Part II of the rotor drop analysis, focusing on the auxiliary bearing system design and optimization based on the rotor drop analysis methods, as introduced in Part I. Optimization focuses on shaft orbit, maximum ball bearing stress, and how to avoid possible ball bearing damage due to impact loading during rotor drop by optimizing auxiliary design including bearing selection, preload method, radial and axial damping element, and flexible bearing support. Using the detailed rotor drop model and time transient method, a variety of simulations are presented for 1) an energy storage vertical flywheel system, and 2) an 8-stage horizontal centrifugal compressor, are conducted to investigate the effects of auxiliary bearing design and to optimize the auxiliary system. Axial drops, radial drops and combination of radial/axial drops are all evaluated considering angular contact auxiliary bearing size, number of rows, preload, and flexible damped bearing supports in the axial and radial directions. The rotor drop analysis method introduced in this paper may be used as a design toolbox for the auxiliary bearing system.
3D Viscous Inverse Design of Turbomachinery Using One-Equation Turbulence Model
Authors: Yang Jinguang , Liu Yan , Wang Xiaofang , Wu Hu
Published: September 2016

Inverse method is a very efficient method in turbomachinery aerodynamic design. It takes blade aerodynamic loading as input, and the blade shape and the flow field are computed when calculation converged. However most current inverse methods model turbulent eddy viscosity by Baldwin-Lomax (BL) model or similar approximation, which does not involve local wall distance as a model parameter. Most one- and two-equation turbulence models are not that case, and local wall distance is needed in turbulent work variable(s) transport equation formulation.

The usual wall distance computing procedure is the so called “exhaustive search method”, which is a time-consuming process. When a flow solver running in analysis mode, the wall distance calculation is not a problem, it can be computed once and stored for subsequent use. But for design mode, this computation intensive process becomes a big challenge. For an inverse design run, the blade shape is updated periodically for about 400 times, if wall distances is re-computed for each blade shape update, the time cost is very appreciable. That is the reason that prohibits the application of higher order (one- and two-equation, compared to BL model) turbulence models in inverse method.

In this paper, a novel wall distance calculation method is proposed. The new method transforms the distance searching problem into a length optimization problem, and the steepest descent method is used to find the minimal length from a target point to a wall face. Numerical experiments show that the method can reduce the computing time to approximately 1/10 of the exhaustive search method. Based on this, together with an enhanced blade update method and Spalart-Allmaras turbulence model, a 3D viscous redesign of an axial fan rotor is conducted. Final results demonstrate the effectivity of the proposed method.
Introduction of a New Numerical Simulation Tool to Analyze Micro Gas Turbine Cycle Dynamics
Authors: Henke Martin , Monz Thomas , Aigner Manfred
Published: September 2016

Micro gas turbine (MGT) technology is evolving towards a large variety of novel applications, like weak gas electrification, inverted Brayton cycles and fuel cell hybrid cycles; however, many of these systems show very different dynamic behaviors compared to conventional MGTs. In addition, some applications impose more stringent requirements on transient maneuvers, e.g. to limit temperature and pressure gradients in a fuel cell hybrid cycle. Besides providing operational safety, optimizing system dynamics to meet the variable power demand of modern energy markets is also of increasing significance.

Numerical cycle simulation programs are crucial tools to analyze these dynamics without endangering the machines, and to meet the challenges of automatic control design. For these tasks, complete cycle simulations of transient maneuvers lasting several minutes need to be calculated. Moreover, sensitivity analysis and optimization of dynamic properties like automatic control systems require many simulation runs. To perform these calculations in an acceptable timeframe, simplified component models based on lumped volume or one-dimensional discretization schemes are necessary. The accuracy of these models can be further improved by parameter identification, as most novel applications are modifications of well-known MGT systems and rely on proven, characterized components.

This paper introduces a modular in-house simulation tool written in Fortran to simulate the dynamic behavior of conventional and novel gas turbine cycles with real-time calculation speed. Thermodynamics, gas composition, heat transfer to the casing and surroundings, shaft rotation and control system dynamics as well as mass and heat storage are simulated together to account for their interactions.

The simulation tool is explained in detail, including a description of all component models, coupling of the elements and the ODE-solver. Finally, validation results of the simulator based on measurement data from the DLR Turbec T100 recuperated MGT test rig are presented, including cold start-up and shutdown maneuvers.
Application of an Overset Grid Method to the Large Eddy Simulation of a High-Speed Multistage Axial Compressor
Authors: de Laborderie Jerome , Duchaine Florent , Vermorel Olivier , Gicquel Laurent , Moreau Stephane
Published: September 2016

The present study aims at evaluating the feasibility and the accuracy of the Large-Eddy Simulation of an actual high-pressure multistage compressor, performed with the TurboAVBP numerical method. TurboAVBP relies on the coupling of several domains via an overset grid method. The latter is demonstrated to keep the order of accuracy of the numerical scheme across six successive rotor-stator interfaces. The simulated configuration corresponds to the 3.5 stage axial compressor CREATE. Three unstructured grids of CREATE, with different resolutions, are generated. They contain 37 blades, the actual rotor tip clearances and a recirculating cavity. The predictions of the global aerodynamic performances and of the radial profiles are found to agree well with experimental data. The analysis of the flow shows that the finest grid exhibits the turbulent flow structures expected in such a configuration, including the blade and vane wakes and the rotor tip leakage vortices.
Effect of Aft Rotor on the Inter-Rotor Flow of an Open Rotor Propulsion System
Authors: Slaboch Paul E. , Stephens David B. , Van Zante Dale E.
Published: September 2016

The effects of the aft rotor on the inter-rotor flow field of an open rotor propulsion rig were examined. A Particle Image Velocimetry (PIV) dataset that was acquired phase locked to the front rotor position has been phase averaged based on the relative phase angle between the forward and aft rotors. The aft rotor phase was determined by feature tracking in raw PIV images through an image processing algorithm. The effects of the aft rotor potential field on the inter-rotor flow were analyzed and shown to be in reasonably good agreement with Computational Fluid Dynamics (CFD) simulations. The aft rotor position was shown to have a significant upstream effect, with implications for front rotor interaction noise. It was found that the aft rotor had no substantial effect on the position of the forward rotor tip vortex but did have a small effect on the circulation strength of the vortex when the rotors were highly loaded.
Effects of Oscillations in the Main Flow due to Thermo Acoustic Fields in a Gas Turbine Combustor on Film Cooling
Authors: Baek Seung Il , Yavuzkurt Savas
Published: September 2016

The objective of this study is to understand the effects of oscillations in the main flow and the film cooling jets caused by the thermoacoustic fields formed in a gas turbine combustor on film cooling. As a first step, CFD simulations are performed for the case of steady mainstream and steady film cooling jets for validation of models and simulations and compared with other studies trying to predict adiabatic effectiveness under similar operating conditions. Based on the knowledge gained on the capability and limitations of different turbulence models for the steady simulations, simulations were extended to unsteady main flow and unsteady cooling jets. The unsteady simulations are performed using URANS-realizable k-ε turbulence model and LES-Smagorinsky-Lilly model. Initially, oscillations due to the combustion instabilities are approximated to be in sinusoidal form. For unsteady main flow and cooling jet simulations, results from the Seo et al. [3] experimental study were selected for comparison with CFD results. The effects of different frequencies (2, 16, 32 Hz) on film cooling are investigated. In each case, average blowing ratio was M=0.5. The results show that if the frequencies of the main flow and the cooling jet flow are increased, the adiabatic centerline effectiveness is decreased and the heat transfer coefficient is increased. Some representative results are: if the frequency of the main flow is increased from 0 Hz to 2 Hz, 16 Hz, or 32 Hz for L/D=1.6, the centerline effectiveness is decreased about 10%, 12%, or 47% and the spanwise-averaged heat transfer coefficient is increased around 1%, 2%, or 4% respectively. If the frequency of the mainstream and the jet flow is increased, the amplitude of the pressure difference between the mainstream and the plenum is increased and the amplitude of coolant flow rate oscillation is increased. Additionally, rectangular or triangular wave forms are used for mainstream and coolant jet flow in order to see the effect on the results and total 36 cases are simulated and effects of changing wave form are investigated. In each case, coolant flow rate was the same as sinusoidal wave forms. It seems like rectangular wave form for main flow at 2 Hz has a negative effect on film cooling performance whereas the same wave form for coolant jet at 32 Hz has a positive effect.
Large-Eddy Simulation and Linear Acoustic Analysis of a Diffusion Swirling Flame Under Forcing and Self-Excitation
Authors: Zhang Man
Published: September 2016

A diffusion swirling flame under external forcing and self-excitation within a single swirler combustor have been studied in this paper with the large-eddy simulation and linear acoustic method. The combustor features pre-vaporized kerosene as the fuel, a single radial air swirler for flame stabilization and a square cross section chamber with adjustable length. Firstly, self-sustained pressure oscillation has been achieved by using of a chocked nozzle on the chamber outlet with large-eddy simulation. Dynamic pressure oscillations are analyzed in frequency domain through Fast Fourier Transform. The major pressure oscillation is identified as the 1st order longitudinal mode of the chamber. Further, the same frequency in the form of harmonic velocity oscillation is imposed on the inlet of the combustor while the chamber length has been changed. Based on this approach, a comparative study of the flame response with different excitation method but same frequency is carried out.

In both self-excited and forced cases, global and local flame responses as well as Rayleigh index have been analyzed and compared. With the flame response function, the excited acoustic modes under the influence of dynamic heat release have been predicted with linear acoustic method and compared with the results obtained from large-eddy simulation. Results show that the flame response presents a great difference in the spacial distribution with different excitation approaches. Thermo-acoustic interaction distributes along the flame front with the expansion of the flame under self-excitation while it damps with the acoustic propagating downstream under forcing condition. As the ratio of flame length to acoustic wave length could not be neglected for the diffusion swirling flame, the global flame response under forcing cannot represent the local response feature of the flame accurately, thus influencing the instability prediction.
Subsonic Flow Over Open Cavities: Part 1 — Analytical Models and Numerical Investigations
Authors: Shao Weidong , Li Jun
Published: September 2016

The aeroacoustical oscillation and acoustic field generated by subsonic flow grazing over open cavities has been investigated analytically and numerically. The tone generation mechanism is elucidated with an analytical model based on the coupling between shear layer instabilities and acoustic feedback loop. The near field turbulent flow is obtained using two-dimensional Large Eddy Simulation (LES). A special mesh is used to absorb propagating disturbances and prevent spurious numerical reflections. Comparisons with available experimental data demonstrate good agreement in both the frequency and amplitude of the aeroacoustical oscillation. The physical phenomenon of the noise generated by the feedback loop is discussed. The correlation analysis of primitive variables is also made to clarify the characteristics of wave propagation in space and time. The effects of free-stream Mach number and boundary layer thickness on pressure fluctuations within the cavity and the nature of the noise radiated to the far field are examined in detail. As free-stream Mach number increases velocity fluctuations and mass flux into the cavity increase, but the resonant Strouhal numbers slightly decrease. Both the resonant Strouhal numbers and sound pressure levels decrease with the increase of boundary layer thickness. Results indicate that the instability of the shear layer dominates both the frequency and amplitude of the aeroacoustical oscillation.
NovaLT16 Bearing #2 Oil System Design: Test Rig Architecture, Functional Tests and Design Challenges
Authors: Mazzola Manfredi , Signori Andrea , Evangelisti Silvia , Di Sisto Paolo
Published: September 2016

This paper describes the test rig and the functional tests that have been carried out to define a satisfying solution for the bearing #2 of NovaLT16, the GE Oil & Gas latest high-efficiency Gas Turbine.

The bearing #2 is a journal bearing located inside the compressor discharge casing and for this reason it is exposed to high temperatures. As a consequence, the lube oil provided to the bearing should not only lubricate the bearing pads but also cool the bearing housing and for this reason it should be more than what required by the pads. This large amount of oil is gathered by two bearing housing sumps and then drained by gravity through two pipes. Scavenge pumps are not required. The bearing housing also includes two circumferential labyrinth seals able to prevent oil leakage through the gap between the bearing housing and rotor. Both seals are purged by air extracted from the gas turbine compressor; the air not only creates a barrier to oil leakage but facilitate the draining inside the sumps.

An insufficient draining system may increase the oil levels in the bearing housing sumps above the safety limit and therefore it may generate oil leakage through the labyrinth seals. If the leakage reaches the external high-temperature zone then it can lead to oil degradation, decrease in GT performances and engine tripe due to smoke in the GT package in the worst case.

The draining system was therefore tested with an advanced test rig. The test rig was a 1:1 scale including the bearing housing, the bearing with its pads and also a mock-up of the shaft. The shaft was driven by an electric motor and therefore it was possible to verify the full operating speed range of the gas turbine. The gas turbine discharge compressor casing environment was simulated through electric resistances able to provide heat all around the bearing housing.

During the functional tests there have been simulated design and off-design conditions including extreme values of oil pressure, oil temperature, pitch and roll angles (for offshore application), shaft speed and buffering air. The results were mainly evaluated in terms of sump oil levels, shaft temperatures and bearing housing temperatures.

The full test campaign allowed to identify and validate a satisfying configuration both for on-shore and off-shore applications and to properly tune all the main bearing parameters in order to guarantee a robust configuration.

The NovaLT16 test campaign is part of the continue evolution in the GE O&G bearing #2 area design, started with the previous gas turbines (such as MS5002E and GE10).