bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Investigation of Small Scale Tesla Turbines
Authors: Renuke Avinash , Vannoni Alberto , Pascenti Matteo , Traverso Alberto
Published: November 2019

Interest in small scale turbines is growing mainly for small scale power generation and energy harvesting. Conventional bladed turbines impose manufacturing limitations and higher cost, which hinder their implementation at small scale. This paper focuses on experimental and numerical performance investigation of Tesla type turbines for micro power generation. A flexible test rig for Tesla turbine fed with air as working fluid has been developed, of about 100W net mechanical power, with modular design of two convergent-divergent nozzles to get subsonic as well as supersonic flow at the exit. Seals are incorporated at the end disks to minimize leakage flow. Extensive experiments are done by varying design parameters such as disk thickness, gap between disks, radius ratio and outlet area of exhaust with speeds ranging from 10000 rpm to 40000 rpm. A quasi-1D model of the whole setup is created and tuned with experimental data to capture the overall performance. Major losses, ventilation losses at end disks, nozzle and exhaust losses are evaluated experimentally and numerically. Effect of design parameters on the performance of Tesla turbines is discussed.
Evaluating Splitter Blade Designs to Avoid Impeller Failure in a High-Speed Unshrouded Centrifugal Compressor
Authors: Curtin Alex , Berdanier Reid A. , Kunz Robert F. , Jonson Michael L.
Published: November 2019

This study investigates splitter blade failures experienced during testing of an unshrouded transonic centrifugal compressor. Specifically, when the impeller was deeply throttled using an upstream inlet guide vane to introduce significant pre-swirl, the splitter blades exhibited cracking near the root of the leading edge. The observed failures are of particular interest because the impeller does not exhibit a mode shape typical of this type of failure corresponding to either the upstream IGV or downstream diffuser vane count, nor the anticipated surge frequencies. Accordingly, modal analysis and CFD modeling were performed leading to an understanding of the failure mechanism, and a successful splitter blade cut-back solution was implemented. Specifically, excitation sources developed from a CFD model of the IGV and impeller were used in a blade flutter calculation, in order to determine the aerodynamic damping and unsteady loading on the blade. The CFD model indicates that shockwaves arise near the splitter leading edge for this off-design condition. Due to interactions with the high incidence/separated boundary layer, these shockwaves exhibit streamwise unsteadiness, thereby leading to the observed failure mechanisms. It was determined that by cutting back the splitter blade at the leading edge, the failure could be avoided while minimally affecting the overall stage performance.
Study on Effect of Axial Overlap on Tip Leakage Flow Structure in Tandem Bladed Low Speed Axial Flow Compressor
Authors: Singh Ajey , Mistry Chetan S.
Published: November 2019

This paper discusses the effect of axial overlap on tip leakage flow behavior in a low speed tandem bladed axial compressor. Tandem bladed axial flow compressors provide an efficient way of obtaining a higher pressure rise with minimum number of stages as compared to a conventional design. The single stage tandem rotor compressor is designed to achieve a stage loading coefficient of 1.04 and flow coefficient of 0.9. A tip clearance of 3% (of span) is provided for the current study and it is maintained constant for all axial overlap configuration studies. A computational study of the designed stage was performed to investigate the behavior of tip leakage flow with different axial overlap and its effect on the overall performance of the stage. The application of tandem blading is only justified by prescribing high aerodynamic loading on both blades which increases the concern for associated tip leakage and corner separation losses. The study reveals the interaction of tip leakage flow from the fore and aft blade with the end wall flow and its influence on the main stream flow. The presence of an aft blade behind the fore seeks additional caution for optimum management of tip leakage flow. The leakage flows from the individual blades tend to roll up along with the shroud boundary layer resulting in the formation of momentum deficit fluid in the flow passage and at exit of rotors. The penetration of momentum deficit fluid in the main stream flow is directly related to the leakage flow structure from the fore and aft blade and also their interaction with the end wall flow. The axial overlap is seen to influence the leakage flow structure in two different ways. Firstly, it is observed that the initiation of tip leakage vortex of aft blade shifts from 30% to 10% of chord measured from leading edge, as axial overlap varies from 5% to −5% of chord in the tip region respectively. Secondly, a change in axial overlap also causes a change in passage geometry of the tandem blade interaction zone which has a first order influence on the mass flow rate through it. The accelerated flow through the passage geometry sustains high loading on the aft blade. It can also be utilized for mitigating the low momentum incoming fluid resulting from the mixing of tip leakage and end wall flow. The appropriate realization of these two effects has a potential to minimize the losses occurring due to tip leakage flow in the tandem compressor rotor and to achieve the benefit of higher loading with minimum number of stages.
Evaluating the Aerodynamic Impact of Circumferentially Grooved Fan Casing Treatments With Integrated Acoustic Liners on a Turbofan Rotor
Authors: Bozak Richard F. , Podboy Gary G.
Published: November 2019

NASA is investigating the potential of integrating acoustic liners into fan cases to reduce fan noise, while maintaining the fans aerodynamic performance. An experiment was conducted to quantify the aerodynamic impact of circumferentially grooved fan cases with integrated acoustic liners on a 1.5 pressure ratio turbofan rotor. In order to improve the ability to measure small performance changes, fan performance calculations were updated to include real gas effects including the effect of humidity. For all fan cases tested, the measured difference in fan isentropic efficiency was found to be less than the measurement repeatability for a torque-based efficiency calculation (≈ 0.2%), however, an unintended tip clearance difference between configurations makes it difficult to determine if circumferentially grooved fan cases degraded fan performance. Fan exit turbulence measurements showed a 1.5% reduction in total turbulence intensity between hardwall and circumferentially grooved fan cases in the tip vortex region, which is attributed to a disruption in the formation of the tip leakage vortex. This decrease in fan exit turbulence could potentially lead to a 1–2dB reduction in broadband rotor-stator interaction noise. Reduced aerodynamic performance losses associated with over-the-rotor liners could enable further fan noise reduction.
Dynamic Response of Acoustically Forced Turbulent Premixed Biogas Flames
Authors: Ajetunmobi Oluwaseun , Talibi Midhat , Balachandran Ramanarayanan
Published: November 2019

Increasing demand for energy and the need for diversification of fuels used in gas turbine power generation is continuing to drive forward the development of fuel-flexible combustion systems, with particular focus on biomass derived sustainable fuels. The technical challenges arising from burning sustainable fuels are largely associated with the change in the chemical, thermal and transport properties of these fuels due to the variation of the constituents and their impact on the performance of the combustor including emissions, static and dynamic stabilities. There is a lack of detailed understanding on the effect of fuel composition on the flame sensitivity to acoustic and flow perturbations.

This paper describes an experimental study investigating the acoustic flame response of simulated biogas (methane/carbon dioxide/air mixtures) turbulent premixed flames. The effect of variation in carbondioxide, CO2, content on the flame response was quantified. Special emphasis was placed on understanding the dependence of this flame response on the amplitude of the acoustic forcing. The flame was subjected to strong velocity perturbations using loud speakers.

It was observed that the addition of CO2 had considerable influence on the magnitude of heat release response. The magnitude and the phase of flame describing function indicated that the mechanism of saturation in these flames for all conditions tested were the same. The difference in magnitude could been attributed to dilution effect and hence further investigation were carried out with N2 and Ar to clarify the role of CO2. The results indicate that the thermal capacity of the diluent gases could be playing a significant role in nonlinear flame dynamics.
Comparative Analysis of Detailed and Reduced Chemical Models of N-Dodecane
Authors: Zheng Chenwei , Eldeeb Mazen A. , Coombs Deshawn , Akih-Kumgeh Benjamin
Published: November 2019

For the purposes of combustion analysis, n-dodecane is used as the surrogate or a surrogate component for biodiesel and jet fuel. In order to capture kinetic effects in computational combustion, detailed and reduced models of n-dodecane are therefore used. This paper presents a comparative analysis of selected detailed chemical kinetic models of n-dodecane as well as reduction of these detailed models to more compact skeletal versions. The selected models are compared based on their ability to predict ignition phenomena. Measured ignition delay times from the literature are used as references. Both low- and high-temperature ignition simulations are considered. To further facilitate future computational combustion analysis, the detailed models are reduced using the Alternative Species Elimination (ASE) approach reported by Akih-Kumgeh and Bergthorson (Energy & Fuels, 2316–2326, 2013). The resulting skeletal models are compared in terms of their retained species, ranked species sensitivities, and kinetic parameters of the key reactions. Furthermore, within the framework of this paper, another model reduction technique is explored. The aim of this method is to further decrease model reduction time since this is often considered as a weakness of the otherwise effective ASE method. The resulting models from this exploratory reduction approach are compared with those obtained from the ASE method in terms of species retained and the accuracy with which combustion properties from the detailed models are predicted. Further chemical kinetic analysis of the reduced models is carried out with the aim of explaining observed similarities and differences.
Effect of Deterministic and Continuous Design Space Resolution on Multiple-Objective Combustor Optimization
Authors: Briones Alejandro M. , Rumpfkeil Markus P. , Thomas Nathan R. , Rankin Brent A.
Published: November 2019

A supervised machine learning technique namely an Adaptive Multiple Objective (AMO) optimization algorithm is used to divide a continuous and deterministic design space into non-dominated Pareto frontier and dominated design points. The effect of the initial training data quantity, i.e., computational fluid dynamics (CFD) results, on the Pareto frontier and output parameter sensitivity is explored. The optimization study is performed on a subsonic small-scale cavity-stabilized combustor. A parametric geometry is created using CAD that is coupled with a meshing software. The latter automatically transfers meshes and boundary conditions to the solver, which is coupled with a post-processing tool. Steady, incompressible three-dimensional simulations are performed using a multi-phase realizable k-ε Reynolds-averaged Navier-Stokes (RANS) approach with an adiabatic flamelet progress variable (FPV). Scalable wall functions are used for modeling turbulence near the wall. For each CFD simulation four levels of adaptive mesh refinement (AMR) are utilized on the original cut-cell grid. The mesh is refined where the flow exhibits large progress variable curvature. There are fifteen geometrical input parameters and three output parameters, viz., a pattern factor proxy (maximum exit temperature), a combustion efficiency proxy (averaged exit temperature), and total pressure loss (TPL). The Pareto frontier and the input-to-output parameter sensitivities are reported for each meta-model simulation. For the investigated design space, three times the number of input parameters plus one (48) yields an optimization independent of the initial sampling. This conclusion is drawn by comparing the Pareto frontiers and global sensitivities. However, the latter provides a better metric. The relative influence of the input parameters on the outputs is assessed by using both a Spearman’s order-rank correlation approach as well as an active subspace analysis. In general, non-dominated design points exhibit persistent geometrical features such as offset opposed cavity forward and aft driver jet alignment. Larger cavities necessitate larger chutes and smaller outer liner jet diameters, whereas smaller cavities require smaller chutes and larger outer liner jet diameters. The fuel injector radial location varies, but can be located either radially inward or outward with respect to the forward dilution jet radial locations. For these non-dominated designs there is substantial burning inside and outside of the cavity. The downstream dilution jets quench the upstream hot gases.
An Investigation of Laminar Flame Speed of CH4-O2-CO2 Mixtures
Authors: Turner Mattias A. , Paschal Tyler , Kulatilaka Waruna D. , Petersen Eric L.
Published: November 2019

The push for lower carbon emissions in power generation has driven interest in methods of carbon capture and sequestration. One such promising method involves the supercritical CO2 (sCO2) power cycle, a system which is powered by oxy-fuel combustion where supercritical carbon dioxide is used as the working fluid. The high CO2 concentration in the combustion products allows for relatively simple extraction of CO2 from the system. Although this is an active field of research, the design of such a combustor requires continued study of oxy-fuel combustion in high levels of CO2 diluent. With that objective in mind, laminar flame experiments were conducted for CH4-O2-CO2 mixtures at one atmosphere and room temperature, where the relative concentrations of O2 and CO2 in the oxidizer mixture were 34.0% and 66.0% by mole, respectively. These concentrations were chosen to ensure the flame would propagate quickly enough to overcome the effects of buoyancy, which were observed to become significant below laminar flame speeds of roughly 15 cm/s. A high-speed chemiluminescence imaging diagnostic was employed in place of the traditional schlieren technique. Laminar flame speed was measured from OH* emission at 306 nm for a full range of equivalence ratios, varying from 15.2 cm/s at 0.7 to 24.8 cm/s at stoichiometric. Additionally, images of OH* chemiluminescence of turbulent CH4-O2-CO2 flames and of quiescent, 5-atm CH4-O2-CO2 flames at stoichiometric concentration are also presented. These experiments provide useful data for validation of chemical kinetics models for oxy-methane combustion in a CO2 diluent, which can be applied to the modeling of oxy-methane combustion for supercritical CO2 power cycles.
Strongly Coupled Thermo-Mechanical Casing/Abradable Model for Rotor/Stator Interactions
Authors: Nyssen Florence , Vadcard Thibaut , Piollet Elsa , Batailly Alain
Published: November 2019

Modern turbomachine designs feature reduced nominal clearances between rotating bladed-disks and their surrounding casings in order to improve the engine efficiency. Unavoidably, clearance reduction increases the risk of contacts between static and rotating components which may yield hazardous interaction phenomena. In this context, the deposition of an abradable coating along the casing inner surface is a common way to enhance operational safety while mitigating interaction phenomena thus allowing for tighter clearances. Nonetheless, interactions leading to unexpected wear removal phenomena between a bladed-disk and a casing with abradable coating have been observed experimentally. Beside of blade damages such as cracks resulting from high amplitudes of vibration, experimental observations included very significant temperatures increase, particularly within the abradable coating, to a point that thermo-mechanical effects may not be neglected anymore. The aim of this work is to investigate the numerical modeling of thermal effects in the abradable coating and the casing due to contact interactions. In particular, the proposed model provides insight on the sensitivity of engines to contact events when the plane had reduced tarmac times between two consecutive flights.

A strongly coupled thermo-mechanical model of the casing and its abradable coating is first described. A 3D cylindrical mesh is employed, it may be decomposed in two parts: (1) along the casing contact surface, a cylindrical thermal mesh is constructed to compute the temperature elevation and heat diffusion in the three directions of space within the abradable coating, and (2) the casing itself is represented by a simplified cylindrical thermo-mechanical mesh to compute both temperature elevation and the induced deformations following temperature changes. This 3D hybrid mesh is combined with a mechanical mesh of the abradable layer, dedicated to wear modeling and the computation of normal and tangential contact forces following blade/abradable coating impacts. The heat flux resulting from contact events is related to the friction forces and only heat transfer by conduction is considered in this work. In order to reduce computational times, the time integration procedure is twofold: the explicit time integration scheme featuring reduced time steps required for contact treatment is combined with a larger time step time integration scheme used for the casing thermo-mechanical model. An extensive validation procedure is carried out from a numerical standpoint, it underlines the convergence of the model with respect to time and space parameters.
Strain Gage Ramifications on Mistuning in As-Manufactured Models and Experimental Testing
Authors: Gillaugh Daniel L. , Kaszynski Alexander A. , Brown Jeffrey M. , Beck Joseph A. , Slater Joseph C.
Published: November 2019

Blade mounted strain gages are vital during rig and engine development to ensure safe engine operation. However, they also enable a change in dynamics of integrally bladed rotors (IBR). State-of-the-art IBR dynamic response predictions are accomplished using as-manufactured models (AMM) generated via optical topography measurements and mesh morphing. Two AMM finite element models (FEMs) are created of a 20 bladed IBR. One FEM has no strain gages present, where the second FEM includes strain gages on six blades. Traditionally, strain gages and lead wires are treated as the same material property as the IBR itself. It will be shown that the inclusion of strain gages in AMM’s using this method changes the IBR’s predicted mistuning. An alternative AMM approach is developed that changes the material properties of the finite elements attributed to the strain gages. The predicted mistuning for each AMM is accomplished using the Fundamental Mistuning Model (FMM ID), where the predicted mistuning will be compared to both Traveling Wave Excitation (TWE) experiments and a rotating, single stage compressor rig. Findings show mistuning predictions of the non-strain gaged AMM compare far better to the experiments compared to the inclusion of the strain gages in the AMM. Additionally, altering material properties of the strain gages in the AMM improves mistuning prediction compared to treating the strain gages as the parent IBR material. Therefore, AMM should be acquired using clean, non-strain gaged rotors or the material properties of strain gaged elements need to be altered to more accurately model the component.
CFD Investigation of the Multiple Rotors Darrieus Type Turbine Performance
Authors: Mohamed Omar Sherif , Ibrahim Ahmed , El Baz Ahmed M. R.
Published: November 2019

The last few years have witnessed researches concerned by vertical axis wind turbine (VAWT) performance considering its advantages compared to the horizontal axis wind turbines, as it can be operated in urban areas without producing noise, ease of maintenance and simple construction, in addition to its low cost. More interest is growing in developing efficient clusters of VAWT in order to increase power generation at specific sites by using multiple turbines. In the present work, the performance of various configurations of Darrieus type VAWT clusters is examined using computational fluid dynamics (CFD) simulations. The objective of this work is to increase the overall power coefficient of the turbines cluster compared to single rotor performance. This objective shall be achieved by examining mutual interactions between rotors arranged in close proximity and examining the effect of oblique angle between rotors on overall performance of the cluster of rotors. The performance is assessed by observing the overall power coefficient of the cluster. Also, the velocity wake of the simulated three rotors turbine cases was analyzed and compared to the that of the single rotor.
Leakage and Cavity Pressures in an Interlocking Labyrinth Gas Seal: Measurements vs. Predictions
Authors: San Andrés Luis , Wu Tingcheng , Barajas-Rivera Jose , Zhang Jiaxin , Kawashita Rimpei
Published: November 2019

Gas labyrinth seals (LS) restrict secondary flows (leakage) in turbomachinery and their impact on the efficiency and rotordynamic stability of high-pressure compressors and steam turbines can hardly be overstated. Amongst seal types, the interlocking labyrinth seal (ILS), having teeth on both the rotor and on the stator, is able to reduce leakage up to 30% compared to other LSs with either all teeth on the rotor or all teeth on the stator. This paper introduces a revamped facility to test gas seals for their rotordynamic performance and presents measurements of the leakage and cavity pressures in a five teeth ILS. The seal with overall length/diameter L/D = 0.3 and small tip clearance Cr/D = 0.00133 is supplied with air at T = 298 K and increasing inlet pressure Pin = 0.3 MPa ∼ 1.3 MPa, while the exit pressure/inlet pressure ratio PR = Pout/Pin is set to range from 0.3 to 0.8. The rotor speed varies from null to 10 krpm (79 m/s max. surface speed). During the tests, instrumentation records the seal mass flow (ṁ) and static pressure in each cavity. In parallel, a bulk-flow model (BFM) and a computational fluid dynamics (CFD) analysis predict the flow field and deliver the same performance characteristics, namely leakage and cavity pressures. Both measurements and predictions agree closely (within 5%) and demonstrate the seal mass flow rate is independent of rotor speed. A modified flow factor Φ¯=m.T/PinD1-PR2 characterizes best the seal mass flow with a unique magnitude for all pressure conditions, Pin and PR.
A Constitutive Model for Predicting Modified Creep Strain Rates due to Cyclic Loading of Gas Turbine Components
Authors: Green Richard , Douglas Jonathan , Moffat Andrew , Scaletta Brent
Published: November 2019

The traditional approach to the design of industrial Gas Turbines considers base load operation. This assumption is no longer applicable as owner operators require more operational flexibility and increased availability and reliability. Flexibility in operation manifests as increased cyclic loading and variations in on and off load dwell periods and thermal loads. These complex loading profiles inevitably lead to damage from both creep and fatigue, and interaction of these two damage mechanisms over the duration of the service interval. These interactions can result in higher average creep rates and more damage than expected.

Robust, path dependent modeling approaches are required to better understand the effects of flexible operation on material response and subsequent damage. Moreover, a unified approach to creep-fatigue is significantly more effective at capturing this behavior.

There are several types of interactions that can drive additional damage. These include relatively well understood mechanisms, such as the effect of plasticity on primary creep and the effect of creep dwells on cyclic material properties. Other interactions that are less well understood include interruptions to the load during creep dwells and the effects of off-load periods on the overall creep rate.

This paper considers a constitutive approach to predict the modified creep rate due to load interruptions and off-load dwells using a backstress model. The backstress model is included in the calculation of inelastic strain rate equations, using a Chaboche type formulation. The model has been fitted to conventional material test data for typical superalloys used in gas turbine applications. To validate the approach, forward creep tests were conducted with varying interruptions to the load during the creep dwell period. These tests show a reduction in creep life and an increase in overall creep rate, when compared with the results for a constant stress and temperature condition. Previous work, presented by the authors [1], outlined a hypothesis that attributes the increase in overall creep rate to the influence of a recovery potential stress. This paper presents the subsequent work which demonstrates that the recovery potential stress can be defined by the difference between the applied stress and the backstress. It is shown that the dwell period between reload cycles is critical for calculating the recovery potential and overall creep rate.
NASA’s Role in Gas Turbine Technology Development: Accelerating Technical Progress via Collaboration Between Academia, Industry, and Government Agencies
Authors: Suder Kenneth L.
Published: November 2019

Given the maturity of the gas turbine engine since its invention and also considering the limited and flattened level of resources expected to be allocated for NASA aeronautics research and development, we ask the question are NASA technology investments still needed to enable future turbine engine-based propulsion systems? If so, what is NASA’s unique role to justify NASA’s investment? To address this topic, we will first review the accomplishments and the impact that NASA Glenn Research Center has made on turbine engine technologies over the last 78 years. Specifically, this paper discusses NASA’s role and contributions to turbine engine development, specific to both 1) NASA’s role in conducting experiments to understand flow physics and provide relevant benchmark validation experiments for Computational Fluid Dynamics (CFD) code development, validation, and assessment; and 2) the impact of technologies resulting from NASA collaborations with industry, academia, and other government agencies. Note that the scope of the discussion is limited to the NASA technology contributions with which the author was intimately associated, and does not represent the entirety of the NASA contributions to turbine engine technology. The specific research, development, and demonstrations discussed herein were selected to both 1) provide a comprehensive review and reference list of the technology and its impact, and 2) identify NASA’s unique role and highlight how NASA’s involvement resulted in additional benefit to the gas turbine engine community.

Secondly, we will discuss current NASA collaborations that are in progress and provide a status of the results. Finally, we discuss the challenges anticipated for future turbine engine-based propulsion systems for civil aviation and identify potential opportunities for collaboration where NASA involvement would be beneficial. Ultimately, the gas turbine engine community will decide if NASA involvement is needed to contribute to the development of the design and analysis tools, databases, and technology demonstration programs to meet these challenges for future turbine engine-based propulsion systems.
A Critical Plane Approach for LCF Evaluation of Gas Turbine Disks and Rotors
Authors: Riva Andrea , Riazantsev Sergei , Foletti Stefano , Beretta Stefano
Published: November 2019

In order to safely increase gas turbine efficiency without issues of early damage and failures, component life evaluation must neither be too conservative nor too optimistic. The method used for designing the parts is supposed to be as accurate as possible, so that the subsequent application of the appropriate statistically defined safety factors will not excessively reduce the component life estimation. In order to achieve such important targets, all phenomena that can be detrimental for fatigue damage, such as multiaxiality and non-proportionality, need to be properly addressed by the Low Cycle Fatigue (LCF) assessment method. In particular, high temperature gas turbine rotating parts are characterized by a superposition of thermal and centrifugal stresses, which act in the same location but along different directions (i.e. multiaxiality) in different moments of the start-up/base-load/shut-down cycle (i.e. non-proportionality).

In this framework, critical plane approaches are the most appropriate methods for an accurate and reliable low cycle fatigue life estimation. These methods search the most critical plane where the greatest damage will be accumulated by defining a damage parameter that is calculated for all planes. Among several methods developed in the academic community and considered in this work, the Fatemi-Socie method was identified as the most effective for the studied materials and components. The Fatemi-Socie damage parameter is a combination of in-plane shear strain and normal stress, which accounts for the fact that fatigue damage (of the materials object of the study) is developed along shear strain with an important contribution of tensile normal stress, which is responsible for crack opening and propagation.

An extensive testing campaign was performed to identify the most appropriate approach for the studied materials and to accurately fit all the model parameters. The testing campaign therefore included high temperature LCF tests and several types of multiaxial tests (tension-torsion, notched specimens, etc.).

Since the search for the critical plane can be demanding from the point of view of computing resources, an in-house software was developed with the scope of reducing the calculation time consistently with the speed required by the industrial design loops.

This paper will cover the background and the assumptions behind the development of a complete industrial workflow for the evaluation of LCF life of rotors and disks, prior to its systematic application for a significant number of Ansaldo components.
New Possibilities for Analyzing Complex Asynchronous Blade Vibrations From Tip-Timing Data Using a Sparse Spectral Analysis Method
Authors: Bouchain Antoine , Picheral José , Lahalle Elisabeth , Vercoutter Agathe , Burgardt Bertrand , Talon Arnaud
Published: November 2019

Measurements in engine operation provide key information for understanding the blades vibrating behaviors, especially while observing complex asynchronous vibrations, such as flutter. The studied vibration is performed by the spectral analysis of the measured vibrating mechanical responses. In this context, tip-timing measurement technology enables to get a large amount of information as it monitors all the blades. However, tip-timing technology generates sub-sampled and non-uniform sampled signals. Thus, conventional spectral estimation methods lead to aliased frequency components on the spectrum. Therefore, specific estimation methods have been developed to overcome this issue.

This paper presents the tip-timing measurements analysis of a non synchronous vibration test case. It uses a new sparse method with block-OMP algorithm in order to estimate time-frequency diagrams of each blade separately. The results are compared to the results of the well-known asynchronous tip-timing method, called All Blade Spectrum. This real test case highlights the limitations of the latter method, as it involves too much uncertainty, while the sparse method with block-OMP enables to characterize these complex asynchronous blade vibrations.
Evaluating the Effect of Vane Trailing Edge Flow on Turbine Rim Sealing
Authors: Monge-Concepción Iván , Berdanier Reid A. , Barringer Michael D. , Thole Karen A.
Published: November 2019

Modern gas turbine development continues to move toward increased overall efficiency, driven in part by higher firing temperatures that point to a need for more cooling air to prevent catastrophic component failure. However, using additional cooling flow bled from the upstream compressor causes a corresponding detriment to overall efficiency. A primary candidate for cooling flow optimization is purge flow, which contributes to sealing the stator-rotor cavity and prevents ingestion of hot main gas path flow into the wheelspace. Previous research has identified that the external main gas path flow physics play a significant role in driving rim seal ingestion. However, the potential impact of other cooling flow features on ingestion behavior, such as vane trailing edge (VTE) flow, is absent in the open literature. This paper presents experimental measurements of rim cavity cooling effectiveness collected from a one-stage turbine operating at engine-representative Reynolds and Mach numbers. Carbon dioxide (CO2) was used as a tracer gas in both the purge flow and vane trailing edge flow to investigate flow migration into and out of the wheelspace. Results show that the vane trailing edge flow does in fact migrate into the rim seal and that there is a superposition relationship between individual cooling flow contributions. Radial and circumferential traverse surveys were performed to quantify cooling flow radial migration through the main gas path with and without vane trailing edge flow. The surveys confirmed that vane trailing edge flow is entrained into the wheelspace as purge flow is reduced. Local CO2 measurements also confirmed the presence of VTE flow deep in the wheelspace cavity.
Effect of a Premixed Pilot Flame on the Velocity-Forced Flame Response in a Lean-Premixed Swirl-Stabilized Combustor
Authors: Li Jihang , Peluso Stephen , Santavicca Domenic , Blust James
Published: November 2019

The effect of a fully-premixed pilot flame on the velocity-forced flame response of a fully premixed flame in a single-nozzle lean-premixed swirl combustor operating on natural gas fuel is investigated. Measurements of the flame transfer function show that as the percent pilot is increased there is a decrease in the flame transfer function gain at all frequencies, a decrease in the frequencies at which the gain minima and maxima occurred, and a decrease in the flame transfer function phase at high frequencies.

High-speed CH* chemiluminescence flame imaging is used to gain a better understanding of the mechanism(s) whereby the pilot flame affects flame dynamics and thereby the flame transfer function.

Time-averaged flame images show that the location of the maximum heat release rate does not change with forcing frequency or percent pilot, although the flame extends further upstream into the inner shear layer with increasing percent pilot.

Heat release rate fluctuation images show that significant heat release rate fluctuations occur in the inner shear layer, the outer recirculation zone, and the near wall region and that the primary effect of increasing the forcing frequency or the percent pilot is a shift of the heat release rate fluctuation from the near wall region to the inner shear layer. In addition, an increase in the percent pilot results in lengthening and narrowing of the inner shear layer and the near wall regions.

The phase images show that the phase is less uniform as the frequency or percent pilot increase, resulting in greater interference between in phase and out of phase fluctuations which reduces the FTF gain. The phase images also show that the wavelength of the heat release rate perturbation travelling through the inner shear layer decreases with increasing frequency and percent pilot which suggests that the pilot flame alters the recirculation flow field.

Flame transfer functions calculated for the heat release rate fluctuations in the inner shear layer, the near wall region and the outer recirculation zone show that the inner shear layer is the largest contributor to the global heat release rate fluctuation in the unpiloted flame and that the primary effect of the pilot flame on the reduction of the global FTF gain is a result of the pilot flame’s effect on the inner shear layer.
Thermal-Fluid and Mechanical Investigations of Additively Manufactured Geometries for Transpiration Cooling
Authors: Min Zheng , Parbat Sarwesh Narayan , Yang Li , Chyu Minking K.
Published: November 2019

Transpiration cooling has always been the dream of gas turbine high temperature component design. The uniform coolant coverage and enhanced heat transfer in porous wall provided by this cooling technique can significantly reduce the base metal temperature which is essential for improving working efficiencies and operation life of gas turbine. Recently, with the capability of the innovative powder bed direct metal laser sintering (DMLS) additive manufacturing technology, the complex geometries of transpiration cooling part could be precisely fabricated and endued with improved mechanical strength. In the present study, five different schemes of transpiration cooling including (1) round holes with 1.5d in-line pitch, (2) round holes with 2d in-line pitch, (3) round holes with 3d in-line pitch, (4) round holes with 2d staggered pitch, (5) inclined holes (20° inclination towards the main stream direction) with 2d in-line pitch in In718 superalloy plates were fabricated by direct metal laser sintering (DMLS) printer. Temperature measurements of the hot side surfaces with coolant coverage were conducted to evaluate the cooling performances of those structures. Tensile bars containing the same designed structure as the heat transfer test coupons in the gauge part were printed as well for the evaluation of the ultimate tensile strength. The test results showed that the coupons with smaller pore size had higher cooling effectiveness but lower tensile strength. The smaller pitch value (P = 1.5D) and the staggered pattern could enhance the cooling performance but decrease the mechanical strength as well. Taking both cooling efficiency and mechanical strength into consideration, the 0.3mm pore size coupon with 3d in-line pitch round holes is considered to be the optimal design with cooling effectiveness of 0.48 at the injection ratio of 2.5% and ultimate tensile strength of 775.9MPa. The present research work demonstrated the potential of additive manufacturing to design and fabricate the transpiration cooling structure with high cooling efficiencies and desired tensile strength.
A Multi-Dimensional Extension of Balje Chart for Axial Flow Turbomachinery Using Artificial Intelligence Based Meta-Models
Authors: Angelini Gino , Corsini Alessandro , Delibra Giovanni , Tieghi Lorenzo
Published: November 2019

The main intent of this work is the exploration of the rotor-only fan design-space to identify correlations between fan performance and enriched geometric and kinematic parameters. In particular, the aim is to derive a multidimensional “Balje chart”, where the main geometric and operational parameters are taken into account in addition to the specific speed and diameter, to guide a fan designer towards the correct choice of parameters such as hub solidity, blade number, hub-to-tip ratio. This multidimensional chart was built using performance data derived from a quasi-3D in-house software for axisymmetric blade analysis and then explored by means of machine learning techniques suitable for big data analysis. Principal Component Analysis (PCA) and Projection to Latent Structure (PLS) allowed finding optimal values of the main geometric parameters required by each specific speed/specific diameter pair.
Towards Large Eddy Simulation of Rotating Turbomachinery for Variable Speed Gas Turbine Engine Operation
Authors: Jain Nishan , Bravo Luis , Kim Dokyun , Murugan Muthuvel , Ghoshal Anindya , Ham Frank , Flatau Alison
Published: November 2019

In this work, massively parallel wall-modeled Large Eddy Simulations (LES) are conducted to simulate flow through a single stage power turbine sector of a gas-turbine engine under realistic operating conditions. The numerical framework in the current work uses finite volume based compressible CharLES solver that utilizes a moving Voronoi diagram based grid generation. To test grid sensitivity and evaluate the capability of the solver in predicting turbomachinery flows, three grids of varying resolution are used to simulate flow through the baseline gas-turbine under design operating conditions. After assessing the flow solution quality and establishing simulation parameters, LES simulations are conducted to investigate the performance of gas-turbine at off-design conditions. The conditions include the rotor design point at 100% speed, and off-design points at 75%, and 50% speeds subject to high temperatures from the combustor exit flow. The results showed that the internal flow becomes highly unsteady as the rotational speed of rotor deviates from the design point leading to reduced aerodynamic performance. This study demonstrates that the current framework is able to robustly simulate the unsteady flow in a three-dimensional moving rotor environment towards the design of variable speed gas-turbine engines for US Army Future Vertical Lift program.
Commercialization and Fleet Experience of the 7/9HA Gas Turbine Combined Cycle
Authors: Vandervort Christian , Leach David , Walker David , Sasser Jerry
Published: November 2019

The power generation industry is facing unprecedented challenges. High fuel costs and increased penetration of renewable power have resulted in greater demand for high efficiency and operational flexibility. Imperatives to reduce carbon footprint place an even higher premium on efficiency. Power producers are seeking highly efficient, reliable, and operationally flexible solutions that provide long-term profitability in a volatile environment. New generation must also be cost-effective to ensure affordability for both domestic and industrial consumers.

Gas turbine combined cycle power plants meet these requirements by providing reliable, dispatchable generation with a low cost of electricity, reduced environmental impact, and broad operational flexibility. Start times for large, industrial gas turbine combined cycles are less than 30 minutes from turning gear to full load, with ramp rates from 60 to 88 MW/minute.

GE introduced the 7/9HA industrial gas turbine product portfolio in 2014 in response to these demands. These air-cooled, H-class gas turbines (7/9HA) are engineered to achieve greater than 63% net combined cycle efficiency while delivering operational flexibility through deep, emission-compliant turndown and high ramp rates. The largest of these gas turbines, the 9HA.02, is designed to exceed 64% combined cycle efficiency (net, ISO) in a 1×1, single-shaft (SS) configuration.

As of December 2018, a total of 32 7/9HA power plants have achieved COD (Commercial Operation Date) while accumulating over 220,000 hours of operation. These plants operate across a variety of demand profiles including base load and load following (intermediate) service. Fleet leaders for both the 7HA and 9HA have exceeded 12,000 hours of operation, with multiple units over 8,000 hours.

This paper will address four topics relating to the HA platform: 1) gas turbine product technology, 2) gas turbine validation, 3) integrated power plant commissioning and operating experience, and 4) lessons learned and fleet reliability.
Modelica and Functional Mock-Up Interface: Open Standards for Gas Turbine Simulation
Authors: Sielemann Michael , Thorade Matthis , Claesson Jim , Nguyen Anh , Zhao Xin , Sahoo Smruti , Kyprianidis Konstantinos
Published: November 2019

This paper introduces two physical modeling standards in the gas turbine and cycle analysis context. Modelica is the defacto standard for physical system modeling and simulation. The Functional Mock-Up Interface is a domain-independent standard for model exchange (“engine decks”). The paper summarizes key language concepts and discusses important design patterns in the application of gas turbine simulation concepts to the acausal modeling language. To substantiate how open standards are applicable to gas turbine simulation, the paper closes with two application examples, a conventional unmixed turbofan thermodynamic cycle and weight analysis as well as an electrically boosted geared turbofan.
Adjoint Based Aerodynamic Optimization of a Multi-Splitter Turbine Vane Frame
Authors: Russo Vincenzo , Orsenigo Simone , Mueller Lasse , Verstraete Tom , Lavagnoli Sergio
Published: November 2019

This work presents a 2D optimization of a multi-body turbine vane frame (TVF), a particular configuration that can lead to considerable shortening of the aero-engine shaft as well as weight reduction. Traditionally, the turbine vane frame is used to guide the flow from the high pressure (HP) turbine to the low pressure (LP) turbine. Current designs have a mid turbine frame equipped with non lifting bodies that have structural and servicing functions, while multi-body configurations are characterized by the fact that, in order to shorten the duct length, the mid turbine struts are merged with the LP stator vanes, traditionally located downstream. This design architecture consists therefore of a multi-body vane row, where lifting long-chord struts replace some of the low pressure vane airfoils. However, the bulky struts cause significant aerodynamics losses and penalize the aerodynamics of the small vanes. The objective of the present work is to numerically optimize a TVF geometry with multi-body architecture using a gradient based algorithm coupled with the adjoint approach, enabling the use of a rich design space. Steady-state CFD simulations have been used to this end. The aim of this study is to reduce the total pressure losses of the TVF, while imposing several aerodynamic and structural constraints. The parametrization of the TVF geometry represents the airfoil shapes and their relative pitch-wise positions. The outcome of the optimization is to evaluate the potential improvements introduced by the optimized TVF geometry and to quantify the influence of the different design parameters on the total pressure losses.