bluuebunny/crossref_metadata_2025 huggingface dataset:
Beamforming and Compressive Sensing Mode Detection of Duct Acoustic Source by Sensor Array
Authors: Yu Wenjun , Bu Huanxian , Huang Xun
Published: August 2018

Low noise design and testing methods for aeroengine are indispensable for civil aviation industry with the public environmental convern growing and the stringent regulations established. A novel array testing approach is proposed to reconstruct spinning modal fan noise amplitude from scattered sound wave measurements outside the jet flow downstream to an unflanged duct. The proposed approach relies on the forward propagation model based on the Wiener-Hopf method. The key contribution of this work is the development of the inverse acoustic scattering methods using a non-classical beamforming and a compressive sensing strategies. The performance of the proposed strategies are demonstrated with various numerical simulations, which show that the deconvolution method is more generic while the compressive sensing method is more efficient. The reconstruction results from both methods are comparable in terms of accuracy and dynamic range. Overall, the proposed testing approach should be able to extend the current duct acoustic array testing capability and help the design and evaluation of low-noise ducted fan system.
Rotational Speed-Dependent Contact Formulation for Nonlinear Blade Dynamics Prediction
Authors: Heinze Torsten , Panning-von Scheidt Lars , Wallaschek Jörg , Hartung Andreas
Published: August 2018

Considering rotational speed-dependent stiffness for vibrational analysis of friction-damped bladed disk models has proven to lead to significant improvements in nonlinear frequency response curve computations. The accuracy of the result is driven by a suitable choice of reduction bases. Multi-model reduction combines various bases which are valid for different parameter values. This composition reduces the solution error drastically. The resulting set of equations is typically solved by means of the harmonic balance method. Nonlinear forces are regularized by a Lagrangian approach embedded in an alternating frequency/time domain method providing the Fourier coefficients for the frequency domain solution.

The aim of this paper is to expand the multi-model approach to address rotational speed-dependent contact situations. Various reduction bases derived from composing Craig-Bampton, Rubin-Martinez, and hybrid interface methods will be investigated with respect to their applicability to capture the changing contact situation correctly. The methods validity is examined based on small academic examples as well as large-scale industrial blade models. Coherent results show that the multi-model composition works successfully, even if multiple different reduction bases are used per sample point of variable rotational speed. This is an important issue in case that a contact situation for a specific value of the speed is uncertain forcing the algorithm to automatically choose a suitable basis. Additionally, the randomized singular value decomposition is applied to rapidly extract an appropriate multi-model basis. This approach improves the computational performance by orders of magnitude compared to the standard singular value decomposition, while preserving the ability to provide a best rank approximation.
Effect of Pore Blockage on Transpiration Cooling With Additive Manufacturable Perforate Holes
Authors: Yang Li , Min Zheng , Parbat Sarwesh Narayan , Chyu Minking K.
Published: August 2018

Transpiration Cooling is an effective cooling technology to protect hot section components such as gas turbine airfoils, rocket heads and space craft. This external cooling method has much higher efficiency than film cooling with holes when consuming the same amount of coolant, due to the uniformity of coolant distribution. However, pore blockage, which frequently occur during the operation of transpiration cooled components, prevented its application in turbine components which require long term stability. Dust deposition was one the main reasons causing blockage of pores for transpiration cooling. A lot of effort was devoted into dust deposition and erosion while optimization for the components themselves were generally difficult as the blockage caused by dusts was unpredictable for traditional sintered porous media. Additive manufacturing, with capability to precisely construct structures in small scales, is a considerable tool to enhance the controllability of porous media, and furthermore, to find a good solution to minimize the blockage disadvantage. Present study selected a cooling configurations containing perforate straight holes with an additive manufacturable diameter of 0.4 mm. Computational Fluid Dynamics (CFD) methods were utilized to model the pore blockage and its effect on heat transfer. A scripting code in addition to the ANSYS CFX solver was utilized to simulate the random blockage conditions of the holes. Two hundred numerical cases with four different blockage probabilities were calculated and statistically evaluated to quantify the disadvantage of pore blockage on the cooling effectiveness. Results obtained from the numerical analysis indicated that the overall blockage ratio was a dominating parameter for the cooling effectiveness. Upstream regions of the cooled surface were more sensitive to local blockage compared to downstream regions. Randomness of the cooling effectiveness increased with the increase of blockage probability. Present study provided a quantitative understanding of the random blockage disadvantage on the specific transpiration cooling configuration, and could benefit further optimization effort to reduce the blockage disadvantage of transpiration cooling using additive manufacturing.
Static and Rotordynamic Characteristics of Liquid Annular Seals With a Circumferentially-Grooved Stator and Smooth Rotor Using Three Levels of Circumferential Inlet-Fluid Rotation
Authors: Childs Dara W. , Torres Jose M. , Bullock Joshua T.
Published: August 2018

Test results are presented for a smooth-rotor/circumferentially-grooved, annular pump seal. The seal’s geometry and operating conditions are representative of electrical submersible pumps (ESPs) as used for oil recovery; however, most ESPs use grooved rotors instead of grooved stators. Test results include static and rotordynamic data at speeds ω of 2, 4, 6 krpm, axial pressure drops ΔP of 2.1, 4.1, 6.2, 8.3 bars. The grooved seal has a length-to-diameter ratio L/D of 0.5 and a minimum radial clearance Cr of 203 μm. It employs 15 circumferential grooves with a length Gl, and depth Gd of 1.52 mm, which are equally-spaced by a land length of 1.52 mm. Tests are conducted for eccentricity ratios ϵ0 of 0.00, 0.27, 0.53, 0.80. Three different inlet-fluid prerotation inserts are used upstream of the test seals to create a range of inlet preswirl ratios. Pitot tubes are used to measure the circumferential velocity at one location immediately upstream of the test seal and one downstream location near the seal exit. The test fluid is ISOVG2 oil @ 46 °C.

Test results for the grooved seal are compared to test results for a smooth annular seal with the same L, D, and minimum Cr. The grooved-seal’s leakage rate Q̇, ranges from a low 15.64 LPM at ω = 6 krpm, and ΔP = 2 bar, to a high 56.36 LPM at ω = 2 krpm, and ΔP = 8 bar. When compared to the smooth seal, the grooved seal provides a 20% Q̇ reduction at ω = 2 krpm, and a 6% reduction at ω = 6 krpm.

The grooved seal’s rotordynamic coefficients are generally not sensitive to changes in ϵ0. The smooth seal’s stiffness and damping coefficients are not very sensitive to changes in ϵ0 in moving from ϵ0 = 0 to 0.5, but typically increase dramatically in magnitude in moving from ϵ0 = 0.5 to 0.8.

From a rotordynamic viewpoint, the major difference between the two seals concerns the direct stiffness coefficients, with the grooved seal having near zero to negative values and the smooth seal having larger positive values, particularly at increased ϵ0 values. The grooved seal generally produces lower-magnitude cross-coupled stiffness and direct damping coefficient values than the smooth seal.
A Simple (1-Flexible Rotor) Model That Shows Bull Gear Runout As a Source of Subsynchronous, Lateral, Vibration in Integrally Geared Compressor (IGC) Pinions
Authors: Childs Dara , Crandall Andrew
Published: August 2018

A new flexible-pinion-shaft rotor model is presented to predict the response of the pinion shaft of an integrally geared compressor (IGC). The motion of the pinion shaft is driven by: (1) its own imbalance and (2) the axial reaction force developed by relative axial motion at the thrust collar (TC) that connects it to the pinion. The axial reaction force at the TC arises because of the relative axial motion between the pinion shaft and the bull gear (BG) at the overlapping area of the TC. The relative axial motion arises because of: (1) absolute axial motion of the pinion (assumed to be a rigid body), (2) pitch and yaw motion of the pinion at the TC, and (3) absolute axial motion of the BG at the TC overlap area. Because the axial reaction force acts at a radial distance from the mass center of the TC disk, it creates moments that couple the relative axial motion of the pinion and BG shafts to the radial motion of the pinion. The present model includes the local flexural stiffness of the BG.

Excitation for the model is provided by: (1) runout from the BG at its running speed, Ω, acting through the axial reaction force of the TC, (2) runout from the pinion at its running speed, ω, acting through the axial reaction force of the TC, and (3) pinion TC mass imbalance at ω. Measured axial runouts of the BG and TC were taken from a test rig at the authors’ laboratory. Predictions for the TC oil-film axial stiffness and damping come from a proprietary Reynolds equation solution to the TC oil-film. The local axial stiffness of the BG at the overlap area was obtained from a finite element analysis of the authors’ test rig. The base rotordynamic model for the pinion was provided for a production IGC pinion by an IGC manufacturer including the bearings and structural dynamics model.

Waterfall plots are presented from the model’s predictions of radial motion at the IGC’s Stage 1 compressor impeller. The response is dominated by synchronous response at the pinion speed, ω, and tracking subsynchronous response at the BG speed, Ω. The response at ω comes from the pinion’s imbalance, not the pinion runout at the TC. The response at Ω comes from the BG runout acting across the TC. The IGC manufacturer’s representatives state that predictions from the model are consistent with measurements from real IGCs, particularly in regard to the presence (and amplitudes) of tracking subsynchronous response amplitudes at the BG frequency.

Obviously, more detailed models can be developed for the rotordynamics of IGCs, but the authors feel that this relatively simple, one-rotor model, is adequate to predict the observed tracking phenomena in IGCs. The analysis can be produced by modifying an existing rotor code or by simply downloading the rotor’s [M], [K], and [C] matrices over a range of speeds and then using MATLAB or similar codes.
Effect of Shelf Squealer Tip Configurations on Film Cooling Effectiveness
Authors: Kim JeongJu , Seo Wonjik , Bang Minho , Kim Seon Ho , Choi Seok Min , Cho Hyung Hee
Published: August 2018

Film cooling effectiveness and heat transfer were measured in squealer tip configurations on the blade tip surface. Three different shelf squealer tip geometries were studied: conventional, vertical, and inclined. The experiment was carried out in a wind tunnel with an inlet mainstream Reynolds number, based on the axial chord length of the blade, of 140,000. The experiments were conducted in five blades in linear cascade with an averaged turbulence intensity of 8.5%. The film cooling effectiveness and heat transfer coefficient on the tip surface were obtained using the transient IR thermography technique. For the pressure side film cooling holes, averaging blowing ratios (M) of 1.0 and 2.0 were set. The results showed the film cooling effectiveness distributions on the tip surface. Owing to the mainstream, the cooling effect appeared after x/Cx = 0.15 and the film cooling effectiveness tended to increase toward downstream of the trailing edge. Additionally, the heat transfer distributions were investigated regarding the film cooling holes. In the presence of film cooling holes, the heat transfer distribution had more uniformity than without them on the pressure side. As the blowing ratio increased from 1 to 2, the heat transfer was decreased on the tip surface. The heat transfer ratio represented the change of heat transfer distribution with and without film cooling holes. Those of results were compared in three squealer tip geometries. The overall area-averaged net heat flux reduction (NHFR) levels on the tip surface were enhanced as the blowing ratio increased. The NHFR of the shelf squealer tip configurations was better than that with the conventional squealer tip.
Aerodynamic Effects in a Transonic Compressor With Nonaxisymmetric Tip Clearance
Authors: Jüngst Maximilian , Liedtke Samuel , Schiffer Heinz Peter , Becker Bernd
Published: August 2018

Future axial compressor designs tend to be built with larger relative tip gaps and eccentricity, since the core engines are reduced in size. Our knowledge of the aerodynamic effects due to eccentric tip gaps is largely based on low-speed work. The aim of this study is to widen current knowledge by using the 1.5 stage Darmstadt Transonic Compressor, which is representative of the front stage of a high pressure compressor. Efficiency, peak pressure rise and stability margin of the compressor are reduced linearly at design speed when the tip clearance is increased from 0.9% to 2.5% tip chord length. This holds true for configurations with eccentric rotor tip gap, if their circumferentially averaged gaps are considered. For a compressor with 96% eccentricity and 1.7% average tip clearance, corrected mass flow at rotor exit varies locally with up to ±20% and ±10% at stator exit, which can result in inlet distortions for subsequent stages in a multi-stage configuration. Also, the redistribution of flow massively influences stall inception during throttling at constant speed. Propagating disturbances are damped in sectors with higher inlet mass flow and lower incidence. Thus, overall operation remains stable, even though some sectors are highly disturbed. Consequently, the maximum clearance of an eccentric stage is not limiting the stable operation of the whole stage.
Static and Dynamic Analysis of a NACA 0021 Airfoil Section at Low Reynolds Numbers Based on Experiments and CFD
Authors: Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni , Holst David , Church Benjamin , Wegner Felix , Pechlivanoglou George , Nayeri Christian Navid , Paschereit Christian Oliver , Ferrari Lorenzo
Published: August 2018

The wind industry needs airfoil data for ranges of Angle of Attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 degree are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and post stall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design.

Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140k and Re = 180k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies.

Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behaviour. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs.
Studies on Cooling Performance of Round Cooling Holes With Various Configurations on a High-Pressure Turbine Vane
Authors: Funazaki Ken-ichi , Kikuchi Fumiya , Tashiro Issei , Ideta Takeomi , Tanaka Yuhi
Published: August 2018

This study deals with detailed experimental investigations on cooling performance of round cooling holes with three hole configurations on the pressure surface of a large-scale test model of a high-pressure turbine vane for gas turbines, where one configuration is a conventional one and the other two are newly designed through a GA (Generic Algorithm) optimization. The purpose of this study is to see how those new hole configurations perform under realistic flow conditions. A blow-down type wind tunnel is used in this study, where IR camera-based transient method is applied to the measurement of film effectiveness and heat transfer distributions on the test model. Numerical simulations using a commercial software are also carried out to enhance the understanding of the cooling performance of each of the hole configurations.
Axial Compressor Performance Prediction Using Improved Streamline Curvature Approach
Authors: Li Tao , Wu Yadong , Ouyang Hua , Qiang Xiaoqing
Published: August 2018

This paper presents in detail the improved streamline curvature approach (SLC) to the performance evaluation and internal flow field calculation of subsonic and transonic axial compressors. Based on previous research, the diverse incidence, deviation and total pressure loss models, generally existing in the form of fitting curves and semi-empirical correlations, are discussed respectively. Typically, transonic flow in axial compressor results in the variation of several flow parameters and particularly the appearance of shock waves compared with subsonic flow. In this paper, the revision and improvement of loss models are applied to reach higher accuracy, especially considering the loss component due to actual incidence angle. Several modifications have been made as well considering the influence of three-dimensional flow.

For the purpose of validating this approach, two test cases, including a single-stage transonic axial compressor NASA Stage37 and a 3-stage subsonic axial compressor P&W 3S1, are calculated. The overall characteristics and spanwise aerodynamic parameters for blade rows are demonstrated at both design and off-design conditions. Furthermore, the results agree well with both experimental data and computational fluid dynamic (CFD) results. This throughflow method is verified as an applicable and convenient tool for aerodynamic analysis and performance prediction of subsonic and transonic axial compressors.
Interaction Phenomena of High Frequency Pulsed Blowing in LP Turbine-Like Boundary Layers at High Speed Test Conditions
Authors: Bettrich Valentin , Bitter Martin , Niehuis Reinhard
Published: August 2018

The use of fluidic oscillators for active flow control applications is a proven and efficient concept. For the well-known highly loaded LP turbine profile T161, the total pressure losses could already reduced by 40% at low Reynolds numbers, were usually flow separation occurs. For further improvements of the active flow control concept, it is essential to understand the driving flow phenomena responsible for the loss reduction mechanism, which are discussed in this paper. The results presented are based on experimental investigations on a flat plate with pressure gradient, imposed with an aerodynamically highly loaded low pressure turbine suction side flow and equipped with active flow control. The analogy to the suction side of the T161 is shown and validated against former cascade measurements. Based on the T161 equivalent operating point of Re = 70,000 and a theoretical out flow Mach number of Ma2,th = 0.6, the focus is set on the interaction of the boundary layer flow with high frequency actuation. The chosen actuator, a high frequency coupled fluidic oscillator, is designed to independently adjust mass flow and frequency. The flat plate is equipped with an array of high frequency actuators to control the flow separation. For this study one oscillator operating point at 6.7kHz is presented and the influence on transition and loss reduction compared to the non-actuated case is discussed. This oscillator operating point was found to be most efficient and the steady and unsteady mixing behavior of the high frequency actuator impact and the low pressure turbine like suction side boundary layer flow is investigated in much detail. Depending on the measurement technique, the isentropic Mach number distribution, frequency spectra, standard deviation, skewness and kurtosis are evaluated. The most important results are on the one hand, that the chosen concept is more efficient compared to former studies in means of mass flow investment, which is mainly based on the chosen oscillator outlet position and frequency. On the other hand, in a transonic flow the mixing and interaction of the high frequency pulses and the boundary layer flow require about 10% of the surface length to even establish and about to 30% to be completed. These results of the mixing behavior between actuator and boundary layer for compressible flow conditions help to attain a fundamental understanding for future designs of active flow control concepts.
Formation and Evolution of Rayleigh-Bénard Streaks in Rotating Cavities
Authors: Puttock-Brown M. R. , Rose M. G.
Published: August 2018

This paper presents numerical investigation into the phenomena of so-called Rayleigh-Bénard streaks inside rotating-cavities. Experimental data from the University of Sussex Multiple Cavity Rig (MCR) has been used as boundary conditions for Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculation using the k-ω SST turbulence model on a three cavity model of the MCR. A four-point validation is presented using comparison to experimental and historical data sets and shows encouraging agreement.

The Rayleigh-Bénard streaks develop along the periphery of the rotating cavity (shroud) and are only associated with flow involved in cyclonic circulation due to the circumferential pressure gradient. These streaks modify the local Nusselt number by as much as 40% above the surface average and, given the contribution of the shroud to the total heat transfer, upwards of 60%, may be a significant factor in further work concerning rotating cavities in aero-engines. However experimental confirmation is required to ratify the existence of the structures.
A Novel Evaluation Procedure for the Prediction and Assessment of Diffuser Humming in Steam Turbines
Authors: Tusche Johannes , Musch Christian
Published: August 2018

The mechanical integrity of turbine blade rows might be compromised by transient aerodynamic effects that occur in interaction with the diffuser. Effectively addressing this issue requires the prediction of the effects and the creation of a basis for their evaluation. This paper focuses on the specific case of diffuser humming in steam turbines. The paper describes the results obtained from two turbine diffusers with different pulsation frequencies calculated and tested under identical conditions. One diffuser forced a resonance of the last-stage blade row, while the other diffuser ensured the absence of resonance. The basic principles are described that allow estimating and quantifying the pulsation frequencies of the fluctuating pressure. To evaluate the developed approach comprehensive test runs were conducted using a Siemens low-pressure turbine test rig. These measured results are shown to provide validation of the calculation method.
Impact of a Combination of Micro-Vortex Generator and Boundary Layer Suction on Performance in a High-Load Compressor Cascade
Authors: Ma Shan , Chu Wuli , Zhang Haoguang , Liu Chuanle
Published: August 2018

The performance of a compressor cascade is considerably influenced by flow control methods. In this paper, the synergistic effects of combination between micro-vortex generators (MVG) and boundary layer suction (BLS) are discussed in a high-load compressor cascade. Seven cases, which are grouped by a kind of micro-vortex generator and boundary layer suction with three locations, are investigated to control secondary flow effects and enhance the aerodynamic performance of the compressor cascade. The MVG is mounted on the end-wall in front of the passage. The rectangle suction slot with three radial positions is installed on the blade suction surface near the trailing edge. The numerical results show that: at the design condition, the total pressure loss is effectively decreased as well as the static pressure coefficient increase when the combined MVG and SBL method (COM) is used, which is superior to MVG in an aerodynamic performance. At the stall condition, the induced vortex coming from MVG could mix the low-energy fluid and mainstream, which result in the reduced separation, and the total pressure loss decreased by 11.54% when the suction flow ratio is 1.5%. The total pressure loss decreases by 14.59% when the COM control methods are applied.
Comparison of Various CFD Codes for LES Simulations of Turbomachinery: From Inviscid Vortex Convection to Multi-Stage Compressor
Authors: Brunet Vincent , Croner Emma , Minot Alexandre , de Laborderie Jérôme , Lippinois Eric , Richard Stéphane , Boussuge Jean-François , Dombard Jérôme , Duchaine Florent , Gicquel Laurent , Poinsot Thierry , Puigt Guillaume , Staffelbach Gabriel , Segui Luis , Vermorel Olivier , Villedieu Nadège , Cagnone Jean-Sébastien , Hillewaert Koen , Rasquin Michel , Lartigue Ghislain , Moureau Vincent , Couaillier Vincent , Martin Emeric , de la Llave Plata Marta , Le Gouez Jean-Marie , Renac Florent
Published: August 2018

Some possible future High Fidelity CFD codes for LES simulation of turbomachinery are compared on several test cases increasing in complexity, starting from a very simple inviscid Vortex Convection to a multistage axial experimental compressor. Simulations were performed between 2013 and 2016 by major Safran partners (Cenaero, Cerfacs, CORIA and Onera) and various numerical methods compared: Finite Volume, Discontinuous Galerkin, Spectral Differences. Comparison to analytical results, to experimental data or to RANS simulations are performed to check and measure accuracy. CPU efficiency versus accuracy are also presented. It clearly appears that the level of maturity could be different between codes and numerical approaches. In the end, advantages and disadvantages of every codes obtained during this project are presented.
Design Point Efficiency of Radial Turbines
Authors: Cox Graham D.
Published: August 2018

Results are presented from CFD calculations on a large database of 3D, radially-stacked, radial turbine geometries. The database covers a comprehensive range of basic geometrical features allowing the most appropriate geometry to be selected for optimum efficiency over extensive ranges of blade-speed-ratio, flow coefficient and specific speed.

Initial studies considered the wheel only and used 78 geometries for low Mach number applications and 102 geometries for high Mach number applications. Each was run over a range of blade-speed-ratios and inlet flow angles to generate preliminary results. Designs that did not contribute to the optimum efficiency trends were discarded. The remaining 17 low Mach number and 24 High Mach number wheels were recalculated with a range of nozzle guide vanes and back-face cavities to provide increased fidelity numerical solutions.

The calculated optimum efficiency is presented on charts of blade-speed-ratio against flow coefficient, against specific speed and against non-dimensional mass-flow. The effect of exducer trim reduction, as often required for mechanical reasons, is demonstrated. The charts can be used for preliminary design of new applications.
Intelligent Reasoning for Gas Turbine Fault Isolation and Ambiguity Resolution
Authors: Tang Liang , Volponi Allan J.
Published: August 2018

An engine health management (EHM) system typically consists of automated logic for data acquisition, parameter calculation, anomaly detection and eventually, fault identification (or isolation). Accurate fault isolation is pivotal to timely and cost effective maintenance but is often challenging due to limited fault symptom observability and the intricacy of reasoning with heterogeneous parameters. Traditional fault isolation methods often utilize a Single Fault Isolator (SFI) that primarily relies on gas path performance parameters. While effective for many performance related faults, such approaches often suffer from ambiguity when two or more faults have signatures that are very similar when monitored by a rather limited number of gas path sensors. In these cases, the ambiguity often has to be resolved by experienced analysts using additional information that takes many different forms, such as various non-gas path symptoms, FADEC fault codes, comparisons with the companion engine, maintenance records, and quite often, the analyst’s gas turbine domain knowledge. This paper introduces an intelligent reasoner that combines the strength of an optimal, physics-based SFI and a fuzzy expert system that mimics the analytical process of human experts for ambiguity resolution. A prototype diagnostic reasoner software has been developed and evaluated using existing flight data. Significant performance improvements were observed as compared with traditional SFI results. As a generic reasoning framework, this approach can be applied not only to traditional snapshot data, but to full flight data analytics as well.
A Sensitivity Based Heuristic for Optimal Blade Arrangement in a Linear Mistuned Rotor
Authors: Mitra Mainak , Bayrak Alparslan Emrah , Zucca Stefano , Epureanu Bogdan I.
Published: August 2018

This paper investigates methodologies for finding optimal or near-optimal blade arrangements in a bladed disk with inserted blades for minimizing or maximizing blade response amplification due to mistuning in material properties of the blades. The mistuning in the blades is considered to be known, and only their arrangement is modifiable. Hence, this is a problem in discrete optimization, particularly combinatorial optimization where the objective of response amplification is a nonlinear function of the blade arrangement. Previous studies have treated mistuning as a continuous parameter to analyze its effects on the response amplification. Sensitivity metrics have proven to be an important tool in quantifying the effects of mistuning. One such sensitivity metric is used here to formulate an iterative heuristic approach to solve the optimization problem. A component mode mistuning reduced order model is used for fast evaluations of the dynamic responses of a bladed disk with a given blade arrangement. At any iteration the sensitivity of the maximum response of the current rotor design to changes in blade stiffnesses due to changes in the blade arrangement is used to predict the arrangement for the following iteration. In addition to the proposed sensitivity-based approach, we use genetic algorithms to find optimal arrangements and compare results with the heuristic approach.
Aeroderivative Engines in LNG Liquefaction Mechanical Drive Applications
Authors: Meher-Homji Cyrus B. , Taher Matt , Meher-Homji Feroze J. , Pillai Pradeep
Published: August 2018

Over the last 50 years of the LNG industry, there has been a significant evolution in the drivers used to power liquefaction compressors. For several decades, steam turbines were utilized and the first gas turbines were deployed in 1969. In a LNG liquefaction plant, the gas turbine drivers and refrigeration compressors strongly influence overall plant performance and efficiency. After the first Aeroderivative solution was applied at Darwin LNG in 2006, there has been a significant growth in the application of these engines for LNG mechanical drive. This trend is driven by the need to reduce greenhouse gas emissions, and fuel auto-consumption, which in a feed gas constrained situation, boosts LNG output. Aeroderivatives tends to increase plant availability. This paper reviews the market penetration of Aeroderivatives into the LNG liquefaction sector highlighting the fundamental differences between Aeroderivative, and heavy duty engines. The background, historical deployment and technical issues relating to the use of Aeroderivative engines for LNG mechanical drive are addressed. Qualification programs for new engines and technologies such as inlet chilling for power augmentation as implemented in LNG plants are reviewed.
Comparing Jet-A and JP-10 Ignition Performance in a Swirl-Stabilized Combustor at High Mach Conditions
Authors: Gross Justin T. , Huelskamp Bethany C. , Neuroth Craig , Caswell Andrew W.
Published: August 2018

The capability of current turbomachinery-based engines limit the obtainable altitude and flight Mach number of modern aircraft. Maturing hypersonic technologies such as ram and scramjets allow greatly increased flight velocity but are not able to power themselves from the ground and, thus, rely on lift aircraft. Combined-cycle engines incorporate turbomachinery and ramjet technologies to allow both high and low flight Mach numbers. These high Mach capable systems are typically flown using specialty fuels such as JP-7 that are more applicable to hypersonic applications than conventional gas-turbine fuels such as JP-8/Jet A or JP-5. Potential issues exist, however, when operating a combined cycle that employs a legacy main combustor since these platforms were not designed for operation with these fuels. Of particular concern is the re-ignition performance of the turbomachinery core. The relight of the gas-turbine combustor occurs at high altitudes and relatively high vehicle speeds, yielding low pressure and temperature in the combustor as well as high combustor-dome velocities. All of these conditions are unfavorable for ignition. Additionally, heavy fuels require more energy for atomization and vaporization, which increases the probability that ignition will become a problem in a turbine-based combined-cycle (TBCC) system. Successful demonstration of legacy main-combustor technologies in hypersonic combined-cycle applications will eliminate the need for costly design of new main-burner technology. The literature does not provide information on the effects of running specialty fuels such as JP-7 and JP-10 in burners with conventional aerodynamic features. To fill that gap, a three-cup sector of a conventional fighter-class swirl-stabilized combustor configured to provide optical access through the sidewall was used in the study. Two test conditions representative of varying flight Mach number and altitude are evaluated. For each flight condition, the combustor pressure drop is varied to characterize ignition as a function of burner inlet velocity. Data are correlated by loading parameter and equivalence ratio at ignition, and at each test point the conditions are varied until ignition cannot be achieved.
Study on Subsynchronous Vibration With Tilting Pad Journal Bearing Under Starved Lubrication
Authors: Kawashita Rimpei , Nishioka Tadasuke , Yokoyama Shimpei , Iwasaki Makoto , Isayama Shuichi , Waki Yuichiro
Published: August 2018

Industrial machines such as gas and steam turbines require high efficiency and reliability. Direct lubricated bearings have been developed and installed to reduce mechanical losses. In recent years, it has been reported in the literature that subsynchronous vibration can occur to rotor shafts with direct lubricated tilting pad journal bearings under reduced oil flow rate conditions. In this study, a test rig with a 200 mm diameter and 3.5 meter long rotor supported by a direct lubricated tilting two pad journal bearing was constructed. The primary critical speed is 2100rpm and rotational speed is 3600rpm. The oil-starved area, the non-oil film layer region at the leading edge of the bearing pads, was measured by observing oil film pressure in the bearing clearance with pressure transducers on the rotor surface. A sine sweep excitation test was carried out by using an inertial shaker installed on the bearing housing and the damping ratio of the rotor system was measured. Measured data showed that a larger starved area at the leading edge of the bearing pads due to reduced oil feeding results in a smaller damping ratio, and an increase in the natural frequency of the rotor. Experimental results of two types of oil feeding nozzles were compared with respect to the correlation between starved area and damping ratio of the rotor system, and a relationship between oil flow rate and starved area was discussed. A method for modeling bearing coefficients under starved lubrication has been proposed based on thermo-hydrodynamic lubrication (THL) analysis. A numerical analysis of a finite element-transfer matrix model of the test rotor with the bearing coefficients calculated by the proposed method is carried out, and it is found that the analytical results are in broad agreement with the experimental results.
Gas Turbine Fouling Offshore: Effective Online Water Wash Through High Water-to-Air Ratio
Authors: Madsen Stian , Bakken Lars E.
Published: August 2018

Optimized operation of gas turbines is discussed for a fleet of eleven GE LM2500PE engines at a Statoil North Sea offshore field in Norway. Three engines are generator drivers and eight engines are compressor drivers. Several of the compressor drive engines are running at peak load (T5.4 control), hence production rate is limited by the available power from these engines. The majority of the engines discussed run continuously without redundancy, hence gas turbine uptime is critical for the field’s production and economy. The performance and operational experience with online water wash at high water-to-air ratio, as well as successful operation at longer maintenance intervals and higher average engine performance are described.

This work is based on long-term operation with online washing, where operational data are collected and performance is analyzed over a 10-year period. Today, all engines are operated with 6-month intervals between maintenance stops, where offline crank wash is performed as well as other necessary maintenance and repairs. Online washing is performed daily between the maintenance stops at full load (i.e. normal operating load for the subject engine). To keep the engine as clean as possible and reduce degradation between maintenance stops, both an effective online water wash system and an effective air intake filter system are critical factors. The overall target is to maintain high engine performance, and extend the interval between maintenance stops through effective online washing.

Water-to-air ratio is significantly increased compared to the OEM limit (OEM limit is 17 l/min which yields approx. 0.5% water-to-air ratio). Today the engines are operated at a water rate of 50 l/min (3 times the OEM limit) which yields a 1.4% water-to-air ratio. Such a high water-to-air ratio has been proven to be the key parameter for obtaining good online water wash effectiveness. Possible downsides of high water-to-air ratio have been thoroughly studied.

The effect of optimized online water wash for the subject engines is longer intervals between maintenance stops, higher power availability, lower engine performance deterioration and reduced emissions (CO2 and NOx). The operating intervals are now extended to six months (4,000 hours), from initially two months (1,500 hours, early 1990s) followed by four months (3,000 hours, mid-2000s). Other installations operated as low as 750 hours between offline washes in the 1980s and 1990s. Of a total efficiency deterioration improvement of 6% over each 6-month operating period, the deterioration is reduced by an estimated 3% related to online water wash.
Assessment of a Finite-Rate-Chemistry Model for ANSYS® CFX® Using Experimental Data of a Downsized Gas Turbine Combustor
Authors: Fiolitakis A. , Lückerath R. , Lammel O. , Schmitz G. , Ax H. , Stöhr M. , Arndt C. , Noll B. , Kluß D.
Published: August 2018

In this work the implementation and validation of a finite-rate-chemistry (FRC) combustion model for ANSYS® CFX® 15.0 is presented. For the solution of the stiff system of species transport equations a splitting scheme is used where transport processes and chemical reactions are solved numerically in separate steps. In this splitting scheme the software Cantera is used for the integration of the chemistry sub-step. It is coupled via user-defined-functions (“USER-Fortran”) to ANSYS® CFX® 15.0. To provide validation data for this model under gas turbine relevant conditions, a down sized version of an industrial burner is investigated experimentally at different operating conditions and with different fuels. The burner is operated in a high-pressure combustion test rig with optical access at technically relevant pressures. Data for emissions of nitric oxide and carbon monoxide are obtained along with OH* chemiluminescence images of the flame. Additionally, investigations are made on the risk of flashback in this burner. The operating points are simulated using the FRC model developed in this work. It is demonstrated that this model approach can predict carbon monoxide and nitric oxide emissions very well, despite the simplistic treatment of turbulence-chemistry interaction. Moreover, it is shown that this model approach can also predict the onset of flashback: the change in flame shape, which is an indicator for flashback, can be well reproduced with this model.
Low Order Modelling for Fan and Outlet Guide Vanes in Aero-Engines
Authors: Cui Jiahuan , Watson Rob , Tucker Paul , Wilson Mark
Published: August 2018

Intakes of reduced length have been proposed with the aim of producing aero-engines with higher efficiency and reduced weight. As the intake length decreases, it is expected that stronger effects of the fan on the flow over the intake lip will be seen. If the effects of the fan cannot be ignored, a low-cost but still accurate fan model is of great importance for designing a short-intake.

In this paper, a low order rotor/stator model — the immersed boundary method with smeared geometry (IBMSG), has been further developed and validated on a rig test case. The improved IBMSG is more robust than the original. The rig test case used for validation features a low-pressure compression system with a non-axisymmetric inflow, which is representative of the inlet condition of an aero-engine at its cruise condition. Both the fan and the Outlet Guide Vanes (OGV) are modelled using IBMSG. Detailed analysis is carried out on the flow both upstream and downstream of the fan. After validating the IBMSG method against the rig test case, a short-intake case, coupled with a fan designed for the next generation of aero-engines, is further investigated. It is found that, compared with the intake-alone case, the inflow distortion at the fan face is significantly reduced by the presence of fan. Due to this increased interaction between the fan and the flow over the intake lip, accounting for the effects of the downstream fan is shown to be essential when designing a short intake.
On the Evaluation and Consideration of Fracture Mechanical Notch Support Within a Creep Fatigue Lifetime Assessment
Authors: Kontermann Christian , Almstedt Henning , Müller Falk , Oechsner Matthias
Published: August 2018

Changes within the global energy market and a demand for a more flexible operation of gas- and steam-turbines leads to higher utilization of main components and raises the question how to deal with this challenge. One strategy to encounter this is to increase the accuracy of the lifetime assessment by quantifying and reducing conservatisms. At first the impact of considering a fracture mechanical notch support under creep-fatigue loading is studied by discussing the results of an extensive experimental program performed on notched round-bars under global strain control. A proposal how to consider this fracture mechanical notch support within a lifetime assessment is part of the discussion of the second part. Here, a theoretical FEM-based concept is introduced and validated by comparing the theoretical prediction with the results of the previously mentioned experimental study. Finally, the applicability of the developed and validated FEM-based procedure is demonstrated.
Experimental Characterisation of Acoustic Damping Generated by Perforated Screens at High Frequencies
Authors: Jurisch M. , Szeponik M. , Paschereit C. O. , Flohr P. R. , Huth M. , Panek L. , Moeck J. P.
Published: August 2018

Modern low-emission gas turbine combustion systems often experience thermo-acoustic instabilities at certain operating conditions, which adversely affect the performance of the engine. One way to mitigate the detrimental effect of such instabilities is to place passive damping devices along the wall of the combustion chamber. To achieve greatest overall damping requires good understanding of the acoustic properties of the damping devices at engine conditions and determination of the undesired acoustic mode shapes for optimal placement at the wall. This paper presents an experimental study which characterises the acoustic properties of bias flow liners operating at frequencies in the low kilohertz regime (> 1 kHz). The engine conditions are simulated in the experiment at ambient conditions by maintaining dynamic similarity, i.e. by matching a number of non-dimensional parameters in the experiment which characterise the engine conditions. The present experimental study contributes to the existing measurement database by taking into account the strong gradient in characteristic impedance between grazing and bias flow medium. The acoustic properties of the investigated damper configurations are assessed in terms of the surface impedance at the interface between grazing and bias flow. An impedance model is suggested which accounts for the strong gradient in characteristic impedance between grazing and bias flow medium. The impedance model may serve conveniently as input to an acoustic mode shape prediction in the combustion chamber to identify the optimal placement of the damping devices.
Adjoint Methods for Elimination of Thermoacoustic Oscillations in a Model Annular Combustor via Small Geometry Modifications
Authors: Aguilar José G. , Juniper Matthew P.
Published: August 2018

In gas turbines, thermoacoustic oscillations grow if moments of high fluctuating heat release rate coincide with moments of high acoustic pressure. The phase between the heat release rate and the acoustic pressure depends strongly on the flame behaviour (specifically the time delay) and on the acoustic period. This makes the growth rate of thermoacoustic oscillations exceedingly sensitive to small changes in the acoustic boundary conditions, geometry changes, and the flame time delay. In this paper, adjoint-based sensitivity analysis is applied to a thermoacoustic network model of an annular combustor. This reveals how each eigenvalue is affected by every parameter of the system. This information is combined with an optimization algorithm in order to stabilize all thermoacoustic modes of the combustor by making only small changes to the geometry. The final configuration has a larger plenum area, a smaller premix duct area and a larger combustion chamber volume. All changes are less than 6% of the original values. The technique is readily scalable to more complex models and geometries and the inclusion of further constraints, such that the combustion chamber itself should not change. This demonstrates why adjoint-based sensitivity analysis and optimization could become an indispensible tool for the design of thermoacoustically-stable combustors.