bluuebunny/crossref_metadata_2025_split huggingface dataset:
Working Process Control in a Ship Gas Turbine Engine of Complex Cycle
Authors: Matviienko Valerii , Ocheretianyi Volodymyr , Andriets Oleksandr , Riznyk Sergiy 
Published: September 2016

Gas turbine engines (GTE) of complex cycles are more efficient in comparison to GTE of simple cycle, and they can be recommended for application in a ship propulsion complex. GTE’s representative of complex cycle is GTE with overexpansion turbine and heat regeneration, which has high efficiency, and which can provide heat energy to the consumers of specialized ships in co-generative mode of operation.
GTE with R and OT is adapted for used in different conditions of ships’ operation. It has high power efficiency at partial loads due to the working process control in the engine. There are two applicable methods of getting required engine’s characteristics of GTE with heat regeneration at partial loads.
If more constant production of heat energy is required at partial loads of the main engine, the method of air by-pass to the combustion chamber by recuperator is applied. Hereby, utilized heat is being redistributed towards the gas cooler boiler-utilizer increasing its power.
For the increase of efficiency of GTE with R and OT at partial loads it is used the method of GTE’s characteristics change by application of variable area nozzles (VAN) of power turbine. VAN in GTE with R allows keeping initial temperature of gas in the engine close to nominal value at partial loads. If the efficiency of GTE with R and OT at nominal load is 20 % relatively higher, in this case when power is equal to 50%, the efficiency of GTE with R and OT is 30% higher in relation to Brayton cycle. In GTE with R and OT it is possible to apply two methods of working process control simultaneously in various regimes of ship operation.
Performance Prediction and Early Design Code for Axial Turbines and its Application in Research and Predesign
Authors: Krumme Alexander 
Published: September 2016

This paper presents DLR’s in-house Performance prediction and Early Design Code for axial Turbines PrEDiCT. It is capable of designing multi-stage, multi-spool air-breathing turbines with consideration of coolant flows and different loading levels, relevant for energy, aircraft and general turbomachinery.
After pointing out the integration of PrEDiCT into the DLR predesign process and the role of each method involved, its iterative main calculation routine will be presented as well as its thermodynamic and geometrical methods to output a complete turbine annulus with preliminary blades, fulfilling power requirements and coming from a minimal input parameter set.
An important aspect is the developed concept for user-driven design work with PrEDiCT involving an interactive GUI and a built-in execution mode called ‘ReDesign’ that retains the design code nature of the program with geometry output, but still allows for effective evolution and tailoring of the global design down to each stage and blade row. The paper closes with the validation and results section, which highlights three examples where the code is applied to axial turbine predesign and research.
The intention of this paper is to encourage the use of early predesign methods even by non-OEM organizations, since the presented work has shown for DLR multiple benefits in terms of research work, cooperation with other departments and OEM industry as well as training of personnel. Furthermore the implementation of PrEDiCT facilitated the transition from pre- to detailed design (i.e. 3D CFD) to such an extent, that the still important role of 2D throughflow methods could be questioned, i.e. being less relevant in the future for some design tasks.
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.
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.
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.
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.
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.
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.