bluuebunny/crossref_metadata_2025 huggingface dataset:
On Film Cooling Performance of a Turbine Vane Pressure Side: The Effect of Showerhead and Hole Alignment
Authors: Najafabadi Hossein N. , Karlsson Matts , Kinell Mats
Published: August 2017

This study uses transient IR-thermography to evaluate the effect of showerhead cooling and hole position on the performance of single-row cooling hole on the pressure side of a guide vane under engine representative conditions. The investigation includes both cylindrical and fan-shaped holes at two blowing conditions: 0.6 and 1.8. The influence of cooling hole alignment for these hole shapes in the performance of multiple row configurations was also studied in the presence of showerhead. For this purpose, double- and triple-row cases in staggered and non-staggered arrangements were considered for two blowing conditions, similar to the single row. The results are presented in terms of both adiabatic film effectiveness, AFE, and net heat flux reduction, NHFR. The showerhead effect was shown to be profound with regard to both AFE and NHFR for the cooling hole close to it. This holds for both hole shapes and blowing ratios. The overall film cooling performance, NHFR, of the rows further downstream of the showerhead and close to the trailing edge were affected marginally by the showerhead. The later cooling row showed superior performance compared to the other rows for fan-shaped holes in both presence and absence of shower-head at a low blowing ratio. For multiple row configurations, in general fan-shaped holes can maintain higher AFE in staggered alignment, while cylindrical holes benefit from consequent jet interaction between rows of cooling in a non-staggered arrangement. This holds for both investigated blowing ratios and double- and triple-rows. When considering NHFR, the results indicate that fan-shaped holes are less affected by the hole alignment. Cylindrical holes, however, can maintain superior performance in non-staggered alignment for all investigated cases except triple row under low blowing condition. The results also suggest that a double-row configuration in the presence of showerhead will benefit from an additional row mainly at high blowing ratios.
Complex Flow Generation and Development in a Full-Scale Turbofan Inlet
Authors: Guimarães Tamara , Lowe K. Todd , O’Brien Walter F.
Published: August 2017

The future of aviation relies on the integration of airframe and propulsion systems to increase fuel efficiency and improve the aerodynamic performance of aircraft. This need brings design challenges, such as the ingestion of non-uniform flows by turbofan engines. In this work, we seek to understand the behavior of a complex distorted inflow in a full-scale engine rig. A 21-inch diameter distortion screen previously designed is used to mimic the behavior of an adverse inlet flow encountered by a hybrid wing body type of aircraft. Three measurement planes along the inlet of the research engine are selected for the acquisition of data using particle image velocimetry at a duct diameter Reynolds number of 2.6 million. The resulting mean velocity profiles, velocity gradients and turbulent stresses are analyzed in order to describe the evolution of the flow along the inlet of the turbofan engine and as it approaches the fan face. As flow develops downstream, the vortex present in the profile migrates clockwise, opposite to the rotation of the fan, and towards the spinner of the engine. The turbulent stresses indicate that the center of the vortex meanders around a preferred location, and that location tightens as flow gets closer to the fan, yielding a smaller radius mean vortex near the fan. An analysis of velocity gradients shows the influence of the distortion screen in the flow, mainly in the streamwise direction, where signature features of the distortion device are observed, as an effect from the wakes of the vanes. The results obtained shed light onto the aerodynamics of swirling flows representative of distorted turbofan inlets, while further advancing the understanding of the complex vane technology presented herein for advanced ground testing of swirling inflows.
Improving Disturbance Compensation in Gas Turbines by Incorporating Event-Triggered Logic Signals From Switchgear
Authors: Moroto Robert H. , Bitmead Robert R. , Holcomb Chad M.
Published: August 2017

Traditional feedback control schemes perform well when the gas turbine (GT) is operating near steady state operating points. In the case of large and abrupt changes in shaft power demand, for example, a standard feedback controller cannot offer the same performance as a better informed controller with more rapid detection time and lesser measurement delays. This work seeks to improve the quality of the information available for use in feedback control by incorporating event-triggered logic signals from switchgear. In this paper, we consider a GT generating power for a microgrid in island mode operation. We seek to use more immediate, but logic-valued, signals available from switchgear monitoring equipment, such as circuit breakers, to improve transient load demand estimation and thereby control performance. Techniques are developed using ideas familiar from Kalman filtering for rapid acquisition of load estimates during transients, notably faults. The resulting approach yields a time-varying estimator which uses the breaker logic signals to augment the standard feedback signals to improve transient estimator response without a concomitant degradation of steady state response. An example is provided using an identified closed-loop GT model.
Robust Detection and Characterization of Cooling Holes Based on Surface Meshes of Turbine Blades
Authors: Knebel Sebastian , Baum Oliver , Högner Lars , Voigt Matthias , Mailach Ronald , Meyer Marcus
Published: August 2017

The present paper illustrates a robust way to extract relevant information of cooling holes from surface meshes of real turbine blades, which have been obtained by CT measurements. The X-ray based measurement technique results in low-quality meshes in certain regions of the component due to the very dense material of rotor blades. Thus the algorithms to extract cooling hole parameters must be robust for these low-quality meshes: The basic step of calculating the surface curvature information uses a regression based method that averages errors and provides a localized analytic surface description. Using geodesic distances as a node selection criterion for the surface function calculation, which is able to decouple curvature values from fluctuating node densities, is shown to improve the detection quality of the algorithm significantly. Based on characteristic curvature limits, clusters of cooling hole areas are distinguished. Finally, cylinders are fitted into the clustered mesh regions as a simple representation of the cooling holes. This procedure results in location and orientation parameters of the cylinders describing the general shape and location of the cooling holes of the investigated turbine blades.
Multi-Stage System Identification of a Gas Turbine
Authors: Pandey Amit , de Oliveira Maurício , Holcomb Chad M.
Published: August 2017

Several techniques have recently been proposed to identify open-loop system models from input-output data obtained while the plant is operating under closed-loop control. So called multi-stage identification techniques are particularly useful in industrial applications where obtaining input-output information in the absence of closed-loop control is often difficult. These open-loop system models can then be employed in the design of more sophisticated closed-loop controllers. This paper introduces a methodology to identify linear open-loop models of gas turbine engines using a multi-stage identification procedure. The procedure utilizes closed-loop data to identify a closed-loop sensitivity function in the first stage and extracts the open-loop plant model in the second stage. The closed-loop data can be obtained by any sufficiently informative experiment from a plant in operation or simulation. We present simulation results here. This is the logical process to follow since using experimentation is often prohibitively expensive and unpractical. Both identification stages use standard open-loop identification techniques. We then propose a series of techniques to validate the accuracy of the identified models against first principles simulations in both the time and frequency domains. Finally, the potential to use these models for control design is discussed.
Experimental Quantification of Fan Rotor Effects on Inlet Swirl Using Swirl Distortion Descriptors
Authors: Frohnapfel Dustin J. , O’Brien Walter F. , Lowe K. Todd
Published: August 2017

The prominence of highly integrated engine/airframe architectures in modern commercial aircraft design concepts has led to significant research efforts investigating the use of conventional turbofan engines in unconventional installations where severe inlet distortions can arise. In order to determine fan rotor capabilities for reducing or eliminating a complex inlet swirl distortion, an experimental investigation using a StreamVane™ swirl distortion generator was conducted in a turbofan engine research platform. Three-dimensional flow data collected at two discrete planes surrounding the fan rotor indicated that the intensity of the swirl distortion was decreased by the fan rotor; however, substantial swirl distortion effects remained in the fan exit flow. Flow angle magnitudes and swirl intensity decreased by approximately 30–40% across the fan rotor, while the presence of large-scale features within the distortion profile was nearly eliminated. Secondary flow streamlines indicated that small-scale features of the distortion were less affected by the rotating component and remained coherent at the fan rotor outlet plane. These results led to the conclusion that swirl distortion survived interactions with the fan rotor, leading to off-design conditions cascading through downstream engine components.
Validation of Transonic Axial Compressor Stage Unsteady-State Rotor-Stator Simulations
Authors: Galpin Paul , Hansen Thorsten , Scheuerer Georg , Kelly Ryan , Hickman Adam , Jemcov Aleksandar , Morris Scott C.
Published: August 2017

The paper describes the validation of steady-state and unsteady CFD simulations against experimental data from a single-stage, transonic axial compressor stage. The experimental data include overall compressor performance, high-resolution traverses of total pressure and total temperature, and unsteady-state total pressure measurements downstream of the rotor.

Various numerical rotor-stator interaction methods were applied across the operational speedline. These included a steady-state method mixing plane, and a transient time inclination method that accounts for the unsteady rotor to stator pitch change. Best practice procedures were employed to assess and quantify the sensitivity of the simulations to numerical error like mesh and timestep size, turbulence model error and systematic errors related to tip gap, and steady-state or unsteady-state flow assumptions. The effect of turbulence on the mean flow is modelled by a URANS approach based on the SST model and its extensions for laminar-turbulent transition and reattachment prediction.

The complex unsteady flow interactions between the rotor and stator were validated against steady-state and unsteady experimental data. The compressor flow is explained in detail including transonic flow features like shock boundary layer interactions. Comparisons are made between the various rotor-stator interaction simulation methods and the experimental data.
Multiscale Investigation of Strain Energy Density for Fatigue Life Prediction
Authors: Holycross Casey M. , Scott-Emuakpor Onome E. , George Tommy J. , Shen M.-H. H.
Published: August 2017

A fatigue life prediction method using strain energy density as a prediction parameter has had success predicting the lifetimes greater than 105 cycles for room and elevated temperatures under axial, bending, and shear loading for different material systems. This method uses monotonic strain energy density determined at the macroscale as a damage parameter for fatigue, despite the differences in damage behavior of static and dynamic loading. Recent studies have brought this method into question, as cyclic energy for low cycle fatigue loading has been found to be significantly greater. Amendments of the fatigue life model have addressed this discrepancy for continuum level measurements, but have yet to examine the localized effects of machined notches. This study investigates strain energy density for static and dynamic loading at cycle counts from one (monotonic) to 105 for plain and notched specimens, exposing the differences between damaging strain energy density at continuum and local length scales. Continuum level strain energy density is simply determined by using the load and strain feedback from a standard mechanical test procedure using a common extensometer and a servohydraulic load frame. Local strain energy density is determined more elaborately by using three methods. Localized energy is determined from compliance and a closed form relationship between stress intensity factor and strain energy density. The influence of the notch is considered in the stress intensity calculation, but its influence on stress concentration is disregarded. All calculations are based on the net section stress and linear elasticity is assumed. The analyses revealed two distinct groups, but one data set indicated coincidence with total accumulated strain energy density. These data also corroborate the theory that average strain energy density at the continuum level changes mechanisms governing damage evolution. Monotonic strain energy density is refuted as an appropriate damage parameter to predict fatigue lifetimes, and a statically equivalent strain energy density is proposed. An amended continuum level model is proposed, increasing prediction accuracy over fatigue lifetimes less than 106. Additionally, a localized model is proposed, expanding prediction capability to geometries with notch like features.
Experimental Analysis of Confinement and Swirl Effects on Premixed CH4-H2 Flame Behavior in a Pressurized Generic Swirl Burner
Authors: Runyon Jon , Marsh Richard , Pugh Daniel , Bowen Philip , Giles Anthony , Morris Steven , Valera-Medina Agustin
Published: August 2017

The introduction of hydrogen into natural gas systems for environmental benefit presents potential operational issues for gas turbine combustion and power generation applications; in particular acceptable blending concentrations are still widely debated. The use of a generic swirl burner under conditions pertinent to a gas turbine combustor is therefore advantageous to (i) provide evidence of potential design modifications to inform future gas turbine operation on hydrogen blends and (ii) validate numerical model predictions. Building on a previous experimental combustion database consisting of methane-hydrogen fuel blends under atmospheric and elevated ambient conditions, a new scaled generic swirl burner has been designed for experimental investigation of flame stability and exhaust gas emissions at combustor inlet temperatures to 573 K, pressures to 0.33 MPa, and thermal powers to 126 kW. The geometry downstream of the modular burner is developed further to enable separate investigation under isothermal and combustion conditions of the influence of combustor outlet geometry and the effect of changing geometric swirl number. The burner confinement is modified to include both a cylindrical exit quartz combustion chamber and a conical convergent exit quartz combustion chamber, designed to provide a more representative geometric and acoustic boundary at the combustor outlet. Two inlet geometric swirl numbers of industrial relevance are chosen; namely 0.5 and 0.8. Combustion stability and heat release locations of lean premixed CH4-air and CH4-H2-air combustion are evaluated by a combination of OH planar laser induced fluorescence, OH* chemiluminescence, and dynamic pressure measurements. Changes in flame stabilization location are characterized by the use of an OH* chemiluminescence intensity centroid. Notable upstream flame movement coupled with changes in acoustic response are evident, particularly near the lean operating limit as hydrogen blending shifts lean blowoff of methane flames to lower equivalence ratios with corresponding reduction in NOx emissions. The influence of increased pressure on the lean operating point stability and emissions appear to be small over the range considered, however a power law correlation has been developed for scaling combustion noise amplitudes with inlet pressure and swirl number. Indicators of flame flashback as well as combustor acoustic response are affected considerably when the convergent combustor outlet geometry is deployed. This has been shown to alter the influence of the central recirculation zone as a flame stabilizing coherent flow structure. Chemical kinetic modelling supports the experimental observations that stable burner operation can be achieved with blended methane-hydrogen up to 15% by volume.
Numerical and Experimental Evaluation of a Dual-Fuel Dry-Low-NOx Micromix Combustor for Industrial Gas Turbine Applications
Authors: Funke H. H.-W. , Beckmann N. , Keinz J. , Abanteriba S.
Published: August 2017

The Dry-Low-NOx (DLN) Micromix combustion technology has been developed originally as a low emission alternative for industrial gas turbine combustors fueled with hydrogen. Currently the ongoing research process targets flexible fuel operation with hydrogen and syngas fuel.

The non-premixed combustion process features jet-in-crossflow-mixing of fuel and oxidizer and combustion through multiple miniaturized flames. The miniaturization of the flames leads to a significant reduction of NOx emissions due to the very short residence time of reactants in the flame.

The paper presents the results of a numerical and experimental combustor test campaign. It is conducted as part of an integration study for a dual-fuel (H2 and H2/CO 90/10 Vol.%) Micromix combustion chamber prototype for application under full scale, pressurized gas turbine conditions in the auxiliary power unit Honeywell Garrett GTCP 36-300.

In the presented experimental studies, the integration-optimized dual-fuel Micromix combustor geometry is tested at atmospheric pressure over a range of gas turbine operating conditions with hydrogen and syngas fuel. The experimental investigations are supported by numerical combustion and flow simulations. For validation, the results of experimental exhaust gas analyses are applied.

Despite the significantly differing fuel characteristics between pure hydrogen and hydrogen-rich syngas the evaluated dual-fuel Micromix prototype shows a significant low NOx performance and high combustion efficiency. The combustor features an increased energy density that benefits manufacturing complexity and costs.
An Experimental Investigation of an Array of Inline Impinging Jets on a Surface With Varying Rib Orientations and Blockages
Authors: Hodges Justin , Osorio Andrea , Fernandez Erik J. , Kapat Jayanta S. , Gangopadhyay Tryambak , Sen Swarnendu , Mukhopadhyay Achintya
Published: August 2017

This investigation focuses on multi-jet impingement configurations for gas turbine geometries in which the objective is to understand the influence of the roughness elements (ribs) on a target surface to the heat transfer and flow field. Existing studies in literature show the implementation of roughness elements for impingement configurations prove to increase heat transfer by 10–30%. Three different surface configurations are chosen for this multi-jet array impingement study: smooth surface (no ribs), small perpendicularly oriented ribs, and large perpendicularly oriented ribs. These roughness elements are non-continuous, broken rib turbulators which are square in cross section and oriented orthogonally to the mean flow direction within the cross flow duct. The roughness elements are oriented perpendicular to the mean flow direction. For each of the ribs tested, the two blockages tested, based on rib-to-channel height, were 20.83% and 41.67%. The jet impingement arrays are of an inline configuration. The Reynolds numbers tested, based on jet diameter, include 4,600, 13,300, 20,600, 30,200. The x/D (streamwise direction), y/D (spanwise direction), z/D (channel height direction) for the impingement array considered are 5 and 10, 8, and 3, respectively. A temperature sensitive paint technique was used to measure the heat transfer at the target surface, in which the local temperature was measured to estimate area averaged heat transfer coefficient (HTC), row averaged HTC, and stagnation region HTC. The spent air is made to exit from one direction only, thus generating a maximum cross flow situation. Keeping the jet diameter fixed at 5.1 mm, the pitch in the streamwise direction is doubled (x/D = 10) to study the effect of reducing coolant flow on the Nusselt Number distribution. Direct comparisons for heat transfer augmentation were done for all test nodes, including baseline flat/smooth plate cases. From the local heat transfer distributions of the different array patterns of the roughness elements, this study aims to determine the effect of including these elements on the target surface by the increases seen in heat transfer compared to a flat/smooth target plate.
Reduced Order Modeling for Multi-Stage Bladed Disks With Friction Contacts at the Flange Joint
Authors: Battiato Giuseppe , Firrone Christian M. , Berruti Teresa M. , Epureanu Bogdan I.
Published: August 2017

Most aircraft turbojet engines consist of multiple stages coupled by means of bolted flange joints which potentially represent source of nonlinearities due to friction phenomena. Methods aimed at predicting the forced response of multi-stage bladed disks have to take into account such nonlinear behavior and its effect in damping blades vibration. In this paper a novel reduced order model is proposed for studying nonlinear vibration due to contacts in multi-stage bladed disks. The methodology exploits the shape of the single-stage normal modes at the inter-stage boundary being mathematically described by spatial Fourier coefficients. Most of the Fourier coefficients represent the dominant kinematics in terms of the well-known nodal diameters (standard harmonics), while the others, which are detectable at the inter-stage boundary, correspond to new spatial small wavelength phenomena named as extra harmonics. The number of Fourier coefficients describing the displacement field at the inter-stage boundary only depends on the specific engine order excitation acting on the multi-stage system. This reduced set of coefficients allows the reconstruction of the physical relative displacement field at the interface between stages and, under the hypothesis of the Single Harmonic Balance Method, the evaluation of the contact forces by employing the classic Jenkins contact element. The methodology is here applied to a simple multi-stage bladed disk and its performance is tested using as a benchmark the Craig-Bampton reduced order models of each single-stage.
The Effect of Lewis Number on Instantaneous Flamelet Speed and Position Statistics in Counter-Flow Flames With Increasing Turbulence
Authors: Salusbury Sean D. , Abbasi-Atibeh Ehsan , Bergthorson Jeffrey M.
Published: August 2017

Differential diffusion effects in premixed combustion are studied in a counter-flow flame experiment for fuel-lean flames of three fuels with different Lewis numbers: methane, propane, and hydrogen. Previous studies of stretched laminar flames show that a maximum reference flame speed is observed for mixtures with Le ≳ 1 at lower flame-stretch values than at extinction, while the reference flame speed for Le ≪ 1 increases until extinction occurs when the flame is constrained by the stagnation point. In this work, counter-flow flame experiments are performed for these same mixtures, building upon the laminar results by using variable high-blockage turbulence-generating plates to generate turbulence intensities from the near-laminar u′/SLo=1 to the maximum u′/SLo achievable for each mixture, on the order of u′/SLo=10. Local, instantaneous reference flamelet speeds within the turbulent flame are extracted from high-speed PIV measurements. Instantaneous flame front positions are measured by Rayleigh scattering. The probability-density functions (PDFs) of instantaneous reference flamelet speeds for the Le ≳ 1 mixtures illustrate that the flamelet speeds are increasing with increasing turbulence intensity. However, at the highest turbulence intensities measured in these experiments, the probability seems to drop off at a velocity that matches experimentally-measured maximum reference flame speeds in previous work. In contrast, in the Le ≪ 1 turbulent flames, the most-probable instantaneous reference flamelet speed increases with increasing turbulence intensity and can, significantly, exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction, with the PDF remaining near symmetric for the highest turbulence intensities.

These results are reinforced by instantaneous flame position measurements. Flame-front location PDFs show the most probable flame location is linked both to the bulk flow velocity and to the instantaneous velocity PDFs. Furthermore, hydrogen flame-location PDFs are recognizably skewed upstream as u′/SLo increases, indicating a tendency for the Le ≪ 1 flame brush to propagate farther into the unburned reactants against a steepening average velocity gradient.
Methods for the Calculation of Thermoacoustic Stability Margins and Monte Carlo-Free Uncertainty Quantification
Authors: Mensah Georg A. , Magri Luca , Moeck Jonas P.
Published: August 2017

Thermoacoustic instabilities are a major threat for modern gas turbines. Frequency-domain based stability methods, such as network models and Helmholtz solvers, are common design tools because they are fast compared to compressible CFD computations. Frequency-domain approaches result in an eigenvalue problem, which is nonlinear with respect to the eigenvalue. Nonlinear functions of the frequency are, for example, the n–τ model, impedance boundary conditions, etc. Thus, the influence of the relevant parameters on mode stability is only given implicitly. Small changes in some model parameters, which are obtained by experiments with some uncertainty, may have a great impact on stability. The assessment of how parameter uncertainties propagate to system stability is therefore crucial for safe gas turbine operation. This question is addressed by uncertainty quantification. A common strategy for uncertainty quantification in thermoacoustics is risk factor analysis. It quantifies the uncertainty of a set of parameters in terms of the probability of a mode to become unstable.

One general challenge regarding uncertainty quantification is the sheer number of uncertain parameter combinations to be quantified. For instance, uncertain parameters in an annular combustor might be the equivalence ratio, convection times, geometrical parameters, boundary impedances, flame response model parameters etc. Assessing also the influence of all possible combinations of these parameters on the risk factor is a numerically very costly task.

A new and fast way to obtain algebraic parameter models in order to tackle the implicit nature of the eigenfrequency problem is using adjoint perturbation theory. Though adjoint perturbation methods were recently applied to accelerate the risk factor analysis, its potential to improve the theory has not yet been fully exploited. This paper aims to further utilize adjoint methods for the quantification of uncertainties. This analytical method avoids the usual random Monte Carlo simulations, making it particularly attractive for industrial purposes. Using network models and the open-source Helmholtz solver PyHoltz it is also discussed how to apply the method with standard modeling techniques. The theory is exemplified based on a simple ducted flame and a combustor of EM2C laboratory for which experimental validation is available.
Identifying the Approach to Significantly Improve the Performance of NK-36ST Gas Turbine Power Plant
Authors: Baturin Oleg , Tkachenko Andrei , Krupenich Ilia , Popov Grigorii , Goryachkin Eugene
Published: August 2017

Collaboration between the Samara National Research University [1] and the JSC “KUZNETSOV” [2] included the research efforts in the field of increasing the performance of NK-36ST [3] gas turbine power plant intended for use as a driving unit of a gas compression station. The requirements included 3% increase in engine efficiency while keeping the maximum number of engine parts unchanged.

First, the thermogasdynamic simulator of the NK-36ST gas turbine power plant was developed and verified using the results of experimental investigations. The impact of various parameters of the engine upon its efficiency was thoroughly investigated and the approach to modernization preserving most of the engine parts was suggested. This approach included increasing the values of work process parameters, the hydraulic efficiency of turbomachinery and reducing the cooling air consumption.

Second, the analysis of the working process of turbomachinery was carried out. The air-gas channel in a meridional section was kept unchanged for the first iteration, thus keeping the parts of the initial engine unchanged, except for the blades and vanes of turbomachinery. For this variant, the parameters of compressors (head ratio and flow ratio) changed to more favorable values, supposedly providing 1–2% higher efficiency. Unfortunately, for this variant and the given restrictions the points, corresponding to the parameters of turbines moved at the Smith diagram to the unfavorable areas, thus making the increase in turbine efficiency very unlikely. The analysis had shown that to provide more convenient values of turbine parameters the blades should be shortened, and this decrease in blade length provides the possibility to increase the rotational speed of the rotor with the same strain levels of the blades and disks. As the result, the gas channel configuration and values of rotational speeds for the turbines providing the increase in their efficiency by 0.5%–1.0% were suggested. The suggested gas channel configuration preserves the same inner diameters thus keeping the disks layout the same.

At the next stage, the shapes of the low-pressure turbine and compressor blades and the blades of free turbine were optimized using the Profiler program (developed at the Samara University), the NUMECA [4] system and the IOSO [5] optimization package, providing the 0.5%–1.0% increase in the efficiency in comparison to the initial variant.

The results of the described research efforts provide the increase in engine efficiency of about 3% while providing the possibility to keep most of the rotor parts of the engine unchanged.
Flow Field and Wall Temperature Measurements for Reacting Flow in a Lean Premixed Swirl Stabilized Can Combustor
Authors: Park Suhyeon , Gomez-Ramirez David , Gadiraju Siddhartha , Kedukodi Sandeep , Ekkad Srinath , Moon Hee-Koo , Kim Yong , Srinivasan Ram
Published: August 2017

Designing gas turbine combustors requires accurate measurement and prediction of the violent, high-temperature environment in reacting flow. One important factor in combustor design is the heat load on the inner surface of the combustor liner during combustion. To properly analyze the heat load, the mechanisms of thermal energy transfer must be investigated. Of these, the convective heat transfer has not been fully characterized, representing an important challenge in the field of combustor research. The flow field is closely related to the combustion dynamics from the swirling flame in modern burners, and has a direct impact on the convective heat transfer. Most of the flow field measurements reported in the literature have relied on custom research nozzles. However, the development of modern low emission, lean-premixed combustors requires experimental results from realistic industrial fuel nozzles. This paper experimentally investigates the effects of combustor operating conditions on the reacting flow in an optical single can combustor. The swirling flow was generated by an industrial lean pre-mixed, axial swirl fuel nozzle manufactured by Solar Turbines Incorporated.

Planar particle image velocimetry (PIV) data were acquired and analyzed to understand the characteristics of the flow field. Experiments were conducted at Reynolds numbers ranging between 50000 and 110000 (with respect to the nozzle diameter, DN); equivalence ratios between 0.55 and 0.78; and pilot fuel split ratios of 0 to 6%. Characterizing the impingement location on the liner, and the turbulent kinetic energy (TKE) distribution were a fundamental part of the investigation. Self-similar characteristics were observed at reacting conditions. Jet impingement locations on the liner were at x ≈ 1.16 DN for seven different reacting cases, and it was observed that the impingement location was not significantly affected by the combustion parameters studied. However, non-reacting flow was significantly different in flame structure and impingement locations. Combustor liner wall temperature distributions were measured in reacting condition with an infrared camera for a single case. The temperature profile was explained qualitatively with the flow features measured with PIV. Peak wall temperature close to impingement location on the liner wall reached about 900 K, and peak heat flux was measured as ≈ 23 kW/m2 at x ≈ 2.3 DN.
Toward Affordable Uncertainty Quantification for Industrial Problems: Part II — Turbomachinery Application
Authors: Ghisu Tiziano , Shahpar Shahrokh
Published: August 2017

Uncertainty Quantification (UQ) is an increasingly important area of research. As components and systems become more efficient and optimized, the impact of uncertain parameters (such as boundary and operating conditions, geometrical variations due to manufacturing or in-service deterioration, etc.) is likely to become critical. It is therefore fundamental to consider the impact of these uncertainties as early as possible during the design process, with the aim of producing more robust designs (less sensitive to the presence of uncertainties). The cost of UQ with high-fidelity simulations becomes therefore of fundamental importance.

The companion part I paper presented an efficient approach for UQ based on Polynomial Chaos expansions, demonstrating its applicability to multi-fimensional uncertainty quantification problems. This paper focuses on the application of this approach to quantify the variability in the performance of two large bypass-ratio jet engine fans in the presence of shape uncertainty due to possible manufacturing processes. The impacts of shape uncertainty on the two geometries are compared, and sensitivities to the location of the blade shape variability are extracted. The mechanisms at the origin of the change in performance are analyzed in detail, as well as the differences between the two configurations. These results provide important information both for controling the manufacturing process, and for designing blades that are less sensitive to the presence of manufacturing uncertainties.
Effect of Acoustic Feedback on Lagrangian Coherent Structures in a Backward Facing Step Combustor With a Partially Premixed Flame
Authors: Sampath Ramgopal , Chakravarthy S. R.
Published: August 2017

The thermoacoustic oscillations of a partially premixed flame stabilized in a backward facing step combustor are studied at a constant equivalence ratio in long and short combustor configurations corresponding to with and without acoustic feedback respectively. We perform simultaneous time-resolved particle image velocimetry (TR-PIV) and chemiluminescence for selected flow conditions based on the acoustic characterization in the long combustor. The acoustic characterization shows a transition in the dominant pressure amplitudes from low to high magnitudes with an increase in the inlet flow Reynolds number. This is accompanied by a shift in the dominant frequencies. For the intermittent pressure oscillations in the long combustor, the wavelet analysis indicates a switch between the acoustic and vortex modes with silent zones of relatively low-pressure amplitudes. The short combustor configuration indicates the presence of the vortex shedding frequency and an additional band comprising the Kelvin Helmholtz mode. Next, we apply the method of finite-time Lyapunov exponent (FTLE) to the time-resolved velocity fields to extract features of the Lagrangian coherent structures (LCS) of the flow. In the long combustor post transition with the time instants with dominant acoustic mode, a large-scale modulation of the FTLE boundaries over one cycle of pressure oscillation is evident. Further, the FTLEs and the flame boundaries align each other for all phases of the pressure oscillation. In the short combustor, the FTLEs indicate the presence of small wavelength waviness that overrides the large-scale vortex structure, which corresponds to the vortex shedding mode. This behaviour contrasts with the premixed flame in the short combustor reported earlier in which such large scales were found to be seldom present. The presence of the large-scale structures even in the absence of acoustic feedback in a partially premixed flame signifies its inherent unstable nature leading to large pressure amplitudes during acoustic feedback. Lastly, the FTLE boundaries provide the frequency information of the identified coherent structure and also acts as the surrogate flame boundaries that are estimated from just the velocity fields.
Integration of CFD to Design Experiments for Enhanced Spatial and Temporal Discretization
Authors: De Maesschalck C. , Lavagnoli S. , Paniagua G.
Published: August 2017

The availability of high fidelity Computational Fluid Dynamics (CFD) suitable for turbomachinery design offers a powerful tool to define an effective experimental measurement campaign. This paper describes approaches to integrate Reynolds-Averaged Navier-Stokes simulations into experiment design. CFD simulations are used to a priori estimate the measurement errors induced by the finite spatial sampling and inherent limited sensor bandwidth for space-resolved and time-resolved turbine aerothermal measurements. The CFD predictions are employed to optimize the probe placement and traversing while minimizing the measurement errors associated with the finite spatial sampling. Additionally, time-resolved CFD traces serve to quantify the measurement errors as a function of the measurement chain bandwidth.

This approach was applied to a recent turbine test program, focused on the aerothermal characterization of the turbine over-tip casing endwall and downstream flow field. Based on the 3D simulations of the different rotor geometries, the discrete radial positions of the aerothermal probes located downstream of the stage were optimized to minimize the uncertainty on the individual aerodynamic quantities, as well as to mitigate the propagated uncertainty on the turbine loss coefficient. Furthermore, the effect of the implicit time-averaging of all sensors, due to the limited frequency response, was quantified.

This manuscript illustrates the benefits of CFD in the design and planning of a turbine experimental campaign. Based on the proposed procedure, the experimentalist can find the best compromise between measurement precision and instrumentation costs by establishing the minimum sensor performance requirements to obtain the target accuracies.
A Methodology for Variable Geometry Optimization of Multistage Axial Compressors
Authors: Lyall M. Eric , Eisert Fred J. , Rabe Douglas C. , Fleisher Patrick M.
Published: August 2017

This paper presents a procedure for experimentally optimizing a multistage axial compressor. Due to the usual proprietary nature of such tests, a mean-line model of a nine-stage compressor with three rows of variable geometry is used instead of a real machine as a testbed for explaining the optimization method. The compressor is optimized to achieve design-intent corrected flow and pressure ratio while achieving acceptable efficiency and stage matching. The optimization is performed using a response surface methodology that leverages a full factorial design of experiments approach. The resulting empirical models of compressor performance are of high quality, with coefficients of determination exceeding 0.99. An important finding of the work is that stage interactions are important for modeling both efficiency and stage matching, much more than for corrected flow and pressure ratio. Additionally the empirical equations resulting from the design of experiments analysis provide sensitivities due to changes in the variable geometry. These sensitivities can be applied to understanding the impact of uncertainties related to rigging the variable geometry and for assessing potential new or upgraded compressor designs.
Hydrogen-Enriched Methane Combustion Diluted With Exhaust Gas and Steam: Fundamental Investigation on Laminar Flames and NOx Emissions
Authors: Lhuillier Charles , Oddos Romain , Zander Lisa , Lückoff Finn , Göckeler Katharina , Paschereit Christian Oliver , Djordjevic Neda
Published: August 2017

Hydrogen utilization in conventional power plants can offer a possibility to cover the residual load of volatile renewable energies while at the same time reducing the carbon footprint of power production. The challenge here is the high reactivity of hydrogen posing a risk of flashback, whereas increased flame temperature may result in higher NOx emissions. A promising approach to overcome this challenges is the dilution of combustion mixtures by exhaust gas recirculation or by steam injection. The present paper provides experimental laminar burning velocities of hydrogen-enriched methane/air mixtures diluted with major components of exhaust gas and with steam. The corresponding numerical study based on a fictive species approach is used to quantify the chemical and physical effects of dilution on laminar burning velocities. The influence of hydrogen-enrichment and dilution on NOx formation is studied numerically. The results demonstrate high potential of dilution with steam or exhaust gas to ensure stable operation even for hydrogen-rich mixtures while maintaining low NOx emissions.
Experimental Investigation of Vibrational and Acoustic Phenomena for Detecting the Stall and Surge of a Multistage Compressor
Authors: Munari Enrico , D’Elia Gianluca , Morini Mirko , Mucchi Emiliano , Pinelli Michele , Spina Pier Ruggero
Published: August 2017

Nowadays, the operative range limit of compressors is still a key aspect of the research into turbomachinery. In particular, the study of the mass flow rate lower limit represents a significant factor in order to predict and avoid the inception of critical working conditions and instabilities such as stall and surge. The importance of predicting and preventing these dangerous phenomena is vital since they lead to a loss of performance and severe damage to the compression system and the compressor components. The identification of the typical precursors of these two types of compressor unstable behaviors can imply many advantages, in both stationary and aeronautic applications, such as i) avoiding the loss of production (in industry) and efficiency of systems and ii) reducing the cost of maintenance and repairing. Many approaches can be adopted to achieve this target, but one of the most fascinating is the vibro-acoustic analysis of the compressor response during operation. At the Engineering Department of the University of Ferrara, a test bench, dedicated to the study of the performance of an aeronautic turboshaft engine multistage compressor, has been equipped with a high frequency data acquisition system. A set of triaxle accelerometers and microphones, suitable for capturing broad-band vibration and acoustic phenomena, were installed in strategic positions along the compressor and the test rig. Tests were carried out at different rotational speeds, and with two different piping system layouts, by varying the discharge volume and the position of the electric control valve. Moreover, two different methodologies were adopted to lead the compressor towards instability. This experimental campaign allowed the inception of compressor stall and surge phenomena and the acquisition of a great amount of vibro-acoustic data which were firstly processed through an innovative data analysis technique, and then correlated to the thermodynamic data recorded. Subsequently, the precursor signals of stall and surge were detected and identified demonstrating the reliability of the methodology used for the study of compressor instability. The results of this paper can provide a significant contribution to the knowledge of the inception mechanisms of these instabilities. In particular, the experimental data can offer a valid support to the improvement of surge and stall avoidance (or control) techniques since it presents an alternative way of analyzing and detecting unstable compressor behavior characteristics by means of non-intrusive measurements.
Effectiveness Measurements of Additively Manufactured Film Cooling Holes
Authors: Stimpson Curtis K. , Snyder Jacob C. , Thole Karen A. , Mongillo Dominic
Published: August 2017

As additive manufacturing (AM) technologies utilizing metal powders continue to mature, the usage of AM parts in gas turbine engines will increase. Current metal AM technologies produce parts with substantial surface roughness that can only be removed from external surfaces and internal surfaces that are accessible for smoothing. Difficulties arise in making smooth the surfaces of small internal channels, which means the augmentation of pressure loss and heat transfer due to roughness must be accounted for in the design. As gas turbine manufacturers have only recently adopted metal AM technologies, much remains to be examined before the full impacts of applying AM to turbine parts are understood. Although discrete film cooling holes have been extensively studied for decades, this objective of this study was to understand how the roughness of film cooling holes made using AM can affect the overall cooling effectiveness. Coupons made from a high temperature nickel alloy with engine-scale film holes were tested in a rig designed to simulate engine relevant conditions. Two different hole sizes and two different build directions were examined at various blowing ratios. Results showed that the effectiveness is dependent on the build direction and the relative size of the hole. It was also discovered that commercially available AM processes could not reliably produce small holes with predictable behavior.
RT61 Power Turbine 100K MTBO Life Extension - Life Cycle Cost Reduction
Authors: Thirumurthy Deepak , Singh Jaskirat , Peng Mark
Published: August 2017

RT61 is a three-stage industrial power turbine which couples with industrial RB211-24GT gas generator. This power turbine was designed and developed by the turbomachinery group in Mount Vernon, Ohio. It was designed based on the 3-D vortex theory during the early 2000 for increased power output and efficiency. It was also designed for low weight with modular construction for ease in maintainability. The industrial RB211-GT61 product serves both oil & gas and power generation market.

Recent drop in crude oil prices has posed significant challenges to the oil & gas customers. To increase the profitability, the entire oil & gas industry (upstream, midstream, and downstream) is looking for opportunities to decrease the operating cost. This served as the main motivation for the life extension of the RT61 power turbine. In order to reduce customer life cycle cost, Siemens Energy, Inc., has extended the life of its most efficient power turbine from 50,000 hours to 100,000 hours.

This paper discusses the efforts taken in extending the meantime between overhaul lives of various RT61 industrial power turbine components from 50,000 hours to 100,000 hours. Measures taken to increase the reliability and minimize the product life cycle cost are presented. New coatings were incorporated for the stage 1 vane and blade for oxidation protection. The thermal characteristics of the power turbine were validated using a comprehensive thermocouple survey of the casings.