bluuebunny/crossref_metadata_2025 huggingface dataset:
On-Line Prediction of Temperature and Stress in Steam Turbine Components Using Neural Networks
Authors: Dominiczak Krzysztof , Rządkowski Romuald , Radulski Wojciech , Szczepanik Ryszard
Published: August 2015

Considered here are Nonlinear Auto-Regressive neural networks with exogenous inputs (NARX) as a mathematical model of a steam turbine rotor used for the on-line prediction of turbine temperature and stress. In this paper on-line prediction is presented on the basis of one critical location in a high pressure steam turbine rotor, according to power plant common measurements, i.e., turbine speed, turbine load as well as steam temperature and pressure before turbine control valve. In order to obtain neural networks that will correspond to the temperature and stress the critical rotor location, an FE rotor model was built. Neural networks trained using the FE rotor model not only have FEM accuracy, but also include nonlinearity related to nonlinear steam turbine expansion, nonlinear heat exchange inside the turbine and nonlinear rotor material properties during transient conditions. Simultaneous neural networks are algorithms which can be implemented in turbine controllers. This allows for the application of neural networks to control steam turbine stress in industrial power plants.
Externally Fired Micro Gas Turbine and ORC Bottoming Cycle: Optimal Biomass/Natural Gas CHP Configuration for Residential Energy Demand
Authors: Camporeale Sergio Mario , Ciliberti Patrizia Domenica , Fortunato Bernardo , Torresi Marco , Pantaleo Antonio Marco
Published: August 2015

Small scale Combined Heat and Power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly true when biomass fuels are used. In most cases, the use of both heat and electricity to serve on site energy demand is a key issue to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and is influenced by climatic conditions, in particular in the case of residential and tertiary end users. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small scale micro turbine for heat and power cogeneration, a bottoming ORC system can be coupled to the cycle, however this option reduces the temperature and quantity of cogenerated heat available to the load. In this perspective, the paper presents the results of a thermo-economic analysis of small scale CHP plants composed by a micro gas turbine (MGT) and a bottoming Organic Rankine Cycle (ORC), serving a typical residential energy demand. For the topping cycle three different configurations are examined: 1) a simple recuperative micro gas turbine fuelled by natural gas (NG), 2) a dual fuel EFGT cycle, fuelled by biomass and natural gas (50% energy input) (DF) and 3) an externally fired gas turbine (EFGT) with direct combustion of biomass (B). The bottoming cycle is a simple saturated Rankine cycle with regeneration and no superheating. The ORC cycle and the fluid selection are optimized on the basis of the available exhaust gas temperature at the turbine exit. The research assesses the influence of the thermal energy demand typology (residential demand with cold, mild and hot climate conditions) and CHP plant operational strategies (baseload vs heat driven vs electricity driven operation mode) on the global energy efficiency and profitability of the following three configurations: A) MGT with cogeneration; B) MGT+ ORC without cogeneration; C) MGT+ORC with cogeneration. In all cases, a back-up boiler is assumed to match the heat demand of the load (fed by natural gas or biomass). The research explores the profitability of bottoming ORC in view of the following tradeoffs: (i) lower energy conversion efficiency and higher investment cost of high biomass input rate with respect to natural gas; (ii) higher efficiency but higher costs and reduced heat available for cogeneration in the bottoming ORC; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid.
Numerical Investigation of Dynamic Characteristics of a Fluidic Device
Authors: Koli Bharat , Chew John W. , Hills Nick J. , Scanlon Timothy
Published: August 2015

Fluidic devices are of interest with turbomachinery internal air systems for modulation of cooling air and other applications. Generally, the flow states within a fluidic device are switched by control flow or flows. For most fluidic devices the switching procedure is almost instantaneous and hence it is difficult to characterize the performance of a device experimentally. The objective of this research is to numerically investigate the dynamic characteristics of a control flow operated fluidic device. In this study the dynamic characteristics of a nozzle during switching is considered. The simulations considered the unsteady interaction of the control flow with the nozzle jet for two different switching scenarios namely, switching of high to low flow state and vice versa. The magnitude of static pressure applied at the control port was identified as a controlling parameter and had to be below a critical value to achieve stable switching. The CFD solutions show that this is related to the flow physics and critical momentum flux ratios for switching are calculated for the present device.
CFD Investigation of Labyrinth Seal Leakage Performance Depending on Mushroom Shaped Tooth Wear
Authors: Doğu Yahya , Sertçakan Mustafa C. , Bahar Ahmet S. , Pişkin Altuğ , Arıcan Ercan , Kocagül Mustafa
Published: August 2015

Conventional labyrinth seal applications in turbomachinery encounter a permanent teeth tip damage and wear during transitional operations. This is the dominant issue that causes unpredictable seal leakage performance degradation. Since the gap between the rotor and the stator changes depending on engine transitional operations, labyrinth teeth located on the rotor/stator wear against the stator/rotor. This wear is observed mostly in the form of the labyrinth teeth becoming a mushroom shape. It is known that as a result of this tooth tip wear, leakage performance permanently decreases, which negatively affects the engine’s overall efficiency. However, very limited information about leakage performance degradation caused by mushroom wear is available in open literature.

This paper presents a study that numerically quantifies leakage values for various radii of mushroom shaped labyrinth teeth by changing tooth-surface clearance, pressure ratio, number of teeth, and rotor speed. Analyzed parameters and their ranges are mushroom radius (R=0–0.508mm), clearance (cr=0.254–2.032mm), pressure ratio (Rp=1.5–3.5), number of teeth (nt=1–12), and rotor speed (n=0–80krpm).

CFD analyses were carried out by employing compressible turbulent flow in 2-D axi-symmetrical coordinate system. CFD leakage results were also compared with well-known labyrinth seal semi-empirical correlations.

Given a constant clearance, leakage increases with the size of the mushroom radius that forms on the tooth. This behavior is caused by less flow separation and flow disturbance and the vena contracta effect for flow over the smoothly shaped mushroom tooth tip compared to the sharp-edged tooth tip. This leakage increase is higher when the tooth tip wear is considered as an addition to the unworn physical clearance, since the clearance dominates the leakage.

The leakage affected by the number of teeth was also quantified with respect to the mushroom radius. The rotational effect was also studied as a secondary parameter.
Aerodynamic Performances and Flow Fields of Pareto Optimal Solutions in an Aerodynamic Design of a Wind-Lens Turbine
Authors: Oka Nobuhito , Furukawa Masato , Yamada Kazutoyo , Oka Akihiro , Kurokawa Yasushi
Published: August 2015

The new type of shrouded wind turbine called “wind-lens turbine” has been developed. The wind-lens turbine has a brimmed diffuser called “wind-lens”, by which the wind concentration on the turbine blade and the significant enhancement of the turbine output can be achieved. A simultaneous optimization method for the aerodynamic design of rotor blade and wind-lens has been developed. The present optimal design method is based on a genetic algorithm (GA) which enables multi objective aerodynamic optimization. In the present study, aerodynamic performances and flow fields of the Pareto optimal solutions of wind-lens turbines designed by the present optimal design method have been investigated by wind-tunnel tests and three-dimensional Reynolds averaged Navier-Stokes (RANS) analyses. Output power coefficients obtained from the wind-tunnel tests in the optimal wind-lens turbine exceeded the Betz limit, which is the performance limitation for bare wind turbines. The numerical results and the experimental results show that the suppression of flow separations in the diffuser is important to achieve significant improvement in aerodynamic performances. As a result, it is found that the aerodynamic performance of wind-lens turbine is significantly affected by the interrelationship between the internal and external flow fields around the wind-lens.
Experimental Study of Heat Transfer Augmentation in High Aspect-Ratio Channels Featuring Different Dimple Configurations
Authors: Tyagi Kartikeya , Singh Prashant , Pandit Jaideep , Ramesh Sridharan , Ekkad Srinath V. , Tolpadi Anil
Published: August 2015

Transient liquid crystal technique was employed for experimental investigation of heat transfer distribution in high aspect ratio rectangular ducts featuring different dimple configurations. Four different dimple configuration shapes, viz. diamond, square, triangular and cylindrical, have been studied. This study also attempts to understand the dimple side wall heat transfer and correlate to the mechanisms of the flow inside the dimple. A brief numerical simulation study was also conducted to understand the vortex formation inside the dimples and how they affect the heat transfer on the dimple walls. Experiments were carried out at three different Reynolds number of 10,000, 16,000 and 21,000. Detailed normalized Nusselt number plots for different configurations has been presented. Pressure drop across each geometry was also recorded and a comparison of thermal–hydraulic performance is given. It was observed that heat transfer enhancement due to dimples was maximum for Re =10,000 case when compared to a flat plate scenario at the same Reynolds number. Thermal–hydraulic performance comparison showed that diamond and triangular dimples performed better due to lower pressure drop penalty.
Error Assessment of Blade Deformation Measurements on a Multi-Megawatt Wind Turbine Based on Digital Image Correlation
Authors: Winstroth Jan , Seume Joerg R.
Published: August 2015

Optical full-field measurement methods such as Digital Image Correlation (DIC) provide a new opportunity for measuring deformation and vibration in wind turbine rotor blades during operation, in high spatial and temporal resolution. Recent field tests on a multi-megawatt wind turbine have demonstrated the vast potential for full scale testing, however little is known about the overall accuracy of DIC measurements on wind turbines. The present work proposes using a virtual 3D wind turbine model for estimating the error associated with the optical measurements. The entire setup is simulated a priori and accurate error estimation becomes possible. The error estimation for a 3.2 MW wind turbine suggests that relative out-of-plane bending of the rotor blades can be measured with an accuracy of ±9.1 mm, relative in-plane bending of the rotor blades can be measured with an accuracy of ±10.2 mm, and relative blade torsion can be measured with an accuracy of ±0.07 deg. This corresponds to a relative error of 0.46% for out-of-plane bending, 1.11% for in-plane bending and 5.46% for blade torsion.
Flame Stability of Premixed Syngas-Air Flames Emitted From a Multi-Tube Fuel Injector
Authors: de La Torre Martin , Maldonado Sergio , Hossain Sarzina , Love Norman , Choudhuri Ahsan
Published: August 2015

Multi-tube injectors have been emerging as a component that has potential to mitigate flame stability (flashback and blowout) and emission issues (NOx) associated with quick-start and fuel-flexible operations in lean premixed applications. Although several designs currently exist in literature, there currently does not exist a large source of information on the design parameters and exact dimensional configurations for these existing injectors. One cause of this may be due to the proprietary nature of this component. Furthermore, most multiport injector designs involve complex tubing and typically significant pressure drops across the exit face. In the present study a fuel injector component was designed keeping in mind simple injector geometry, possible operability limits of the flame, and turbulence intensity expected at the exit of the injector. This work presents the final design and the flame stability results from a multi-tube fuel-air injector. The injector operates on simulated syngas mixtures of hydrogen and carbon monoxide including 20–80, 30–70, and 40–60% representing the variation in the hydrogen found in syngas mixtures. Tests were completed for lean conditions ranging from equivalence ratios between 0.6 and 0.9. The experimental results showed that for the current injector design at an equivalence ratio of 0.6 a stable flame was not achieved for any of the fuel mixtures tested. It was also observed that the stability region of the syngas flame increased as equivalence ratios above 0.7 and the hydrogen concentration in syngas fuel increases with the 40–60% hydrogen-carbon monoxide mixture demonstrating the greatest stability region which can accommodate more than three times the stability range of other conditions. Results from this study may benefit others who are currently designing such fuel injectors for lean premixed combustion applications.
Conjugate Scaling in the Presence of Bore Cooling
Authors: Dyson Thomas E. , Winka James R. , Helmer David B.
Published: August 2015

Many analyses in the literature have assessed the appropriate manner in which to scale an experimental test rig to represent film-cooled engine components. For conventional testing using low conductivity models, the key parameters are the mainstream Reynolds number, scaled coolant flow rate, and the adiabatic film effectiveness. The few studies that have sought scaling parameters for conjugate testing have identified that one must additionally match the heat transfer coefficient ratio between the internal and external surfaces and external Biot number. However, these analyses have focused on blade or nozzle regions with single or sparse film rows. The validity of this scaling approach to regions or components with substantial bore cooling contributions is unclear — for example the showerhead and/or platform of a blade or nozzle, or a component like a shroud. The present analysis outlines the drivers for potential departure from the accepted scaling. A numerical study is performed to assess potential errors due to the traditional scaling. The results of the analysis demonstrate that the additional parameter, the ratio of bore cooling to external heat transfer coefficient, is more appropriate in the near hole region especially in cases where film cooling is not significant.
Self-Excited Blade Vibration Experimentally Investigated in Transonic Compressors: Rotating Instabilities and Flutter
Authors: Holzinger F. , Wartzek F. , Jüngst M. , Schiffer H.-P. , Leichtfuß S.
Published: August 2015

This paper investigates the vibrations that occurred on the blisk rotor of a 1.5-stage transonic research compressor designed for aerodynamic performance validation and tested in various configurations at Technische Universität Darmstadt.

During the experimental test campaign self-excited blade vibrations were found near the aerodynamic stability limit of the compressor. The vibration was identified as flutter of the first torsion mode and occurred at design speed as well as in the part-speed region. Numerical investigations of the flutter event at design speed confirmed negative aerodynamic damping for the first torsion mode, but showed a strong dependency of aerodynamic damping on blade tip clearance.

In order to experimentally validate the relation between blade tip clearance and aerodynamic damping, the compressor tests were repeated with enlarged blade tip clearance for which stability of the torsion mode was predicted.

During this second experimental campaign, strong vibrations of a different mode limited compressor operation. An investigation of this second type of vibration found rotating instabilities to be the source of the vibration. The rotating instabilities first occur as an aerodynamic phenomenon and then develop into self-excited vibration of critical amplitude.

In a third experimental campaign, the same compressor was tested with reference blade tip clearance and a non-axisymmetric casing treatment. Performance evaluation of this configuration repeatedly showed a significant gain in operating range and pressure ratio. The gain in operating range means that the casing treatment successfully suppresses the previously encountered flutter onset. The aeroelastic potential of the non-axisymmetric casing treatment is validated by means of the unsteady compressor data.

By giving a description of all of above configurations and the corresponding vibratory behavior, this paper contains a comprehensive summary of the different types of blade vibration encountered with a single transonic compressor rotor. By investigating the mechanisms behind the vibrations, this paper contributes to the understanding of flow induced blade vibration. It also gives evidence to the dominant role of the tip clearance vortex in the fluid-structure-interaction of tip critical transonic compressors. The aeroelastic evaluation of the non-axisymmetric casing treatment is beneficial for the design of next generation casing treatments for vibration control.
Numerical Modeling of Soot Production in Aero-Engine Combustors Using Large Eddy Simulations
Authors: Franzelli B. , Riber E. , Cuenot B. , Ihme M.
Published: August 2015

Numerical simulations are regarded as an essential tool for improving the design of combustion systems since they can provide information that is complementary to experiments. However, although numerical simulations have already been successfully applied to the prediction of temperature and species concentration in turbulent flames, the production of soot is far from being conclusive due to the complexity of the processes involved in soot production. In this context, first Large Eddy Simulations (LES) of soot production in turbulent flames are reported in the literature in laboratory-scale configurations, thereby confirming the feasibility of the approach. However numerous modeling and numerical issues have not been completely solved. Moreover, validation of the models through comparisons with measurements in realistic complex flows typical of aero-engines is still rare.

This work therefore proposes to evaluate the LES approach for the prediction of soot production in an experimental swirl-stabilized non-premixed ethylene/air aero-engine combustor, for which soot and flame data are available. Two simulations are carried out using a two-equation soot model to compare the performance of a hybrid chemical description (reduced chemistry for the flame structure/tabulated chemistry for soot precursor chemistry) to a classical full tabulation method. Discrepancies of soot concentration between the two LES calculations will be analyzed and the sensitivity to the chemical models will be investigated.
A Semi-Empirical Model to Predict Aircraft Soot Emission in Rich Zone of RQL Combustor
Authors: Choo Kyung Hak , Lee Sangmin , Denney Russell K. , Mavris Dimitri N.
Published: August 2015

The reduction of particulate matter emissions is becoming a requirement for aircraft turbine engine combustor design. This requirement leads to the need to estimate particulate emissions during the conceptual design phase. Current prediction methods are based on detailed numerical simulation techniques such as CFD, which are unsuitable for conceptual design due to high computational cost.

This paper introduces a new approach employing a semi-empirical model for prediction of the soot emission indices of RQL combustors. The proposed approach dramatically improves computational efficiency by avoiding complex numerical calculations.

The model is based on the response surface developed from experimental data for turbulent non-premixed flames. The data has been extracted from the literature, employing statistical methods such as machine learning techniques and polynomial regressions to apply the turbulent flame data to the actual operating conditions in the primary zone of aircraft engine combustors.

The model is developed by first representing the combustor primary zone by chemical reactor networks constructed in CHEMKIN based on a statistical PDF approach to simulate the non-uniform distribution of time-evolving local mixture fraction with a beta distribution. The reactor networks are used to estimate the concentrations of soot precursor species in the rich zone. The empirical equations are then used with the predicted concentrations to predict the soot formation rate. Finally, these results are used along with the turbulent non-premixed flame data to develop the final model through a model calibration process.
Cooling Optimisation Theory: Part 2 — Optimum Internal Heat Transfer Coefficient Distribution
Authors: Kirollos Benjamin , Povey Thomas
Published: August 2015

Gas turbine cooling system design is constrained by a maximum allowable wall temperature (dictated by the material, the life requirements of the component and a given stress distribution), the desire to minimise coolant mass flow rate (requirement to minimise cycle-efficiency cost) and the requirement to achieve as close to uniform wall temperature as possible (to reduce thermal gradients, and stress). These three design requirements form the basis of an iterative design process. The relationship between the requirements has received little discussion in the literature, despite being of interest from both a theoretical and a practical viewpoint. In the companion paper, we show analytically that the coolant mass flow rate is minimised when the wall temperature is uniform and equal to the maximum allowable wall temperature. In this paper, we show that designs optimised for uniform wall temperature have a corresponding optimum internal heat transfer coefficient (HTC) distribution. In this paper, analytical expressions for the optimum internal HTC distribution are derived for a number of cooling systems, with and without thermal barrier coating. Most cooling systems can be modelled as a combination of these representative systems. The optimum internal HTC distribution is evaluated for a number of engine-realistic systems: long plate systems (e.g., combustors, afterburners), the suction-side of a high pressure nozzle guide vane, and a radial serpentine cooling passage. For some systems, a uniform wall temperature is unachievable; the coolant penalty associated with this temperature non-uniformity is estimated. A framework for predicting the optimum internal HTC for systems with any distribution of external HTC, wall properties and film effectiveness is outlined.
Conjugate Heat Transfer Analysis of a Cooled Turbine Blade Using Frozen Rotor Approach
Authors: Ho Kuo-San , Liu Jong , Urwiller Christopher , Konan S. Murthy , Aguilar Bruno
Published: August 2015

In recent years, conjugate heat transfer (CHT) computational fluid dynamics (CFD) simulation in turbomachinery played an important role in predicting metal temperature. Most of research papers of CHT CFD simulation were emphasized on the mixing plane method. In this paper the ANSYS CFX 14.0 CHT simulation using the frozen rotor approach is employed to predict the blade temperatures. The frozen rotor included five time instances in which the stator-rotor wake influence could be captured.

In this study, the temperature predictions using the frozen rotor approach were compared to the mixing plane predictions and Silicon Carbide (SiC) chip measurements on three different radial spans. The frozen rotor results predicted the minimum and maximum temperatures that bounded the SiC chip data. Compared to the mixing plane predictions, the frozen rotor approach results were similar within 8 K at the mid-span. However, the frozen rotor approach provided more insight information and detailed guidance for model calibration. Finally several future works were suggested to continue striving for high performance gas turbines.
Optical Measurements of Interacting Lean Direct Injection Fuel Nozzles With Varying Spacing
Authors: Dolan Brian , Gomez Rodrigo Villalva , Gutmark Ephraim
Published: August 2015

Particle image velocimetry and OH planar laser induced fluorescence are used to examine the flow and flame structure resulting from two adjacent fuel/air nozzles. The distance between nozzles is varied from 1.1 to 2.72 nozzle diameters to change the degree of interaction between the nozzles. Non-reacting PIV shows a flowfield which is nearly symmetric between nozzles for all four spacings. For all but the widest spacing, there exist differences in the flow structures between the inner and outer sides of the nozzles. Less distance between the nozzles results in more rapid merging of the shear layers and higher axial velocities between the nozzles. At a spacing of 1.89 nozzle diameters, the shear layers toward the adjacent nozzle are intermittently pulled into the center of the combustor, resulting in a wider and lower velocity average flow between nozzles compared to the other cases. When a flame is added, the flowfields become much more asymmetric, both between nozzles and between the shear layers toward and away from the interacting nozzle. The outer shear layers, away from the other nozzle, are pushed to the domeplate by the expanding recirculation region. With a higher airflow, this behavior is negated. At the two further spacings, the shear layers toward the adjacent nozzle also become different between swirlers. The flow from the nozzle located on the right stays near the domeplate and joins the shear layer from the left nozzle near the nozzle lip and becomes a strong and penetrating jet at an angle to the axial coordinate. OH PLIF imaging shows that the flame fronts are generally located in the shear layer between the incoming reactants and the recirculating combustion products. This includes cases where the flow is highly asymmetric and stays close to the domeplate or penetrates deep into the combustor. So there is no evidence that the addition of an adjacent nozzle has an effect on the local flow/flame interaction. However, it is also clear that the presence of interacting swirling flows with combustion can lead to very dramatic changes to the global flow behavior relative to a single nozzle experiment.
Comparison of Numerical Methods for the Prediction of Time-Averaged Flow Quantities in a Cooled Multistage Turbine
Authors: Marpu Ritu P. , Custer Chad H. , Subramanian Venkataramanan , Weiss Jonathan M. , Hall Kenneth C.
Published: August 2015

An unsteady simulation of a two-stage, cooled, high pressure turbine cascade is achieved by applying the harmonic balance method, a mixed time domain and frequency domain computational fluid dynamic technique for efficiently solving periodic unsteady flows. A comparison of computed temperature and pressure profile predictions generated using the harmonic balance method and a conventional steady mixing plane analysis is presented. The predicted temperature and pressure profiles are also compared to experimental data at the stage exit plane. The harmonic balance solver is able to efficiently model unsteady flows caused by wake interaction and secondary flow effects due to cooling flows. It is demonstrated that modeling the unsteady effects is critical to the accurate prediction of time-averaged flow field quantities, particularly for cooled machines.
Effects of Shroud Asymmetry on the Turbine Tip Shroud Cavity Flow Field
Authors: Palmer Timothy R. , Tan Choon S. , Montgomery Matthew , Malandra Anthony , Little David , Zuniga Humberto , Zhou Kunyuan
Published: August 2015

The effects of shroud asymmetry (known as a scalloped shroud) on loss generation and stage performance are assessed by numerical computations, steady as well as unsteady, in a turbine stage with tip shroud cavity. Introducing shroud asymmetry leads to cavity mixing at higher flow velocities with larger velocity difference, hence higher loss relative to a baseline axisymmetric shroud. Shroud asymmetry alters the system of toroidal vortices which characterizes tip shroud cavity flow. Specifically, the asymmetry downstream of the tip seal prevents the formation of two large, continuous toroidal vortex cores. Instead, several small, discrete cores are formed immediately downstream of the tip seal due to the onset of mixing with the main flow. Unsteady vane-rotor-shroud interaction results in a redistribution of vorticity in the cavity inlet. Compatibility requirement between main flow and cavity flow provides quantitative limits on the existence of the cavity inlet vortex as well as explains why the cavity inlet flow field looks the way it does and not otherwise.
Building Block Experiments in Discrete Hole Film Cooling
Authors: Ryan Kevin J. , Coletti Filippo , Elkins Christopher J. , Eaton John K.
Published: August 2015

This paper reports a series of building block experiments for discrete hole film cooling. Seven different configurations, including variations in injection wall curvature, mainstream pressure gradient, and boundary layer thickness are measured for a round film cooling hole, inclined 30 degrees at injection, and operated at a blowing ratio of unity. Full three dimensional, three component velocity fields and scalar coolant concentration fields are acquired using Magnetic Resonance Imaging (MRI) techniques. The results show the effect of varying the mainstream condition on the mean coolant concentration distribution and mean velocity field, including the counter-rotating vortex pair (CVP), a dominant feature of jet in crossflow type flows. The present study focuses on an analysis of the building block configurations only possible with full three dimensional velocity and concentration fields. Several scalar parameters including normalized perimeter, jet trajectory, maximum coolant concentration, and coolant concentration spread are extracted from the collected data and compared across the different configurations. The results indicate that the pressure gradient variations have the strongest effect on the calculated quantities, the boundary layer slightly less, and the curvature very little.
Performance Evaluation of an S-Duct Diffuser of a Flight-Vehicle Inlet in High-Subsonic Flow
Authors: Asghar Asad , Stowe Robert A. , Allan William D. E. , Alexander Derrick
Published: August 2015

The characteristic aerodynamics of inlets in a fuselage-embedded propulsion system of an air-vehicle vary from one configuration to other, making it necessary to document the performance of each and every type of inlet in various flight conditions. This paper focuses on the internal performance evaluation of a baseline S-duct diffuser for a future parametric investigation of a generic S-duct inlet. The generic baseline was a rectangular-entrance, transitioning S-duct diffuser in high subsonic (Mach number > 0.8) flow. The test section was manufactured using rapid prototyping for facilitating a future parametric investigation of geometry. Streamwise static pressure and exit-plane total pressure were measured in a test-rig using surface pressure taps and a 5-probe rotating rake, respectively and was simulated through computational fluid dynamics. The investigation indicated the presence of streamwise and circumferential pressure gradients leading to three dimensional flow in the S-duct diffuser and distortion at the exit plane. Total pressure losses and circumferential and radial distortions at the exit plane were higher than that of the podded nacelle type of inlet. The work represents the beginning of the development of a database for the performance of a particular type of generic inlet. This database will be useful for predicting the performance of aero-engines and air vehicles in high subsonic flight.
Sensor Selection for Aircraft Engine Performance Estimation and Gas Path Fault Diagnostics
Authors: Simon Donald L.
Published: August 2015

This paper presents analytical techniques for aiding system designers in making aircraft engine health management sensor selection decisions. The presented techniques, which are based on linear estimation and probability theory, are tailored for gas turbine engine performance estimation and gas path fault diagnostics applications. They enable quantification of the performance estimation and diagnostic accuracy offered by different candidate sensor suites. For performance estimation, sensor selection metrics are presented for two types of estimators including a Kalman filter and a maximum a posteriori estimator. For each type of performance estimator, sensor selection is based on minimizing the theoretical sum of squared estimation errors in health parameters representing performance deterioration in the major rotating modules of the engine. For gas path fault diagnostics, the sensor selection metric is set up to maximize correct classification rate for a diagnostic strategy that performs fault classification by identifying the fault type that most closely matches the observed measurement signature in a weighted least squares sense. Results from the application of the sensor selection metrics to a linear engine model are presented and discussed. Given a baseline sensor suite and a candidate list of optional sensors, an exhaustive search is performed to determine the optimal sensor suites for performance estimation and fault diagnostics. For any given sensor suite, Monte Carlo simulation results are found to exhibit good agreement with theoretical predictions of estimation and diagnostic accuracies.
A Comprehensive Through-Flow Solver Method for Modern Turbomachinery Design
Authors: Anderson Mark R. , Bonhaus Daryl L.
Published: August 2015

Through-flow solvers have historically played a very prominent role in the design and analysis of axial turbomachinery. While three-dimensional, Full Navier-Stokes (FNS) CFD is taking an increasing larger role, quasi-3D through-flow methods are still widely used. Automated optimization techniques that search over a wide design space, involving many possible variables, are particularly suitable for the computationally efficient through-flow solver.

Pressure-based methods derived from CFD solution techniques have gradually replaced older streamline curvature methods, due to their ability to capture flow across a wide range of Mach numbers, particularly the transonic and supersonic regimes. The through-flow approach allows for the solution of the three-dimensional problem with the computational efficiency of a two-dimensional solution. Since the losses are explicitly calculated through empirically based models, the need for detailed grid resolution to capture tiny flow entities (such as wakes and boundary layers) is also greatly reduced. The combined savings can result in computational costs as much as two orders of magnitude lower than full 3D CFD methods.

A state-of-the-art through-flow solver has several features that are crucial in the design process. One of these is the ability to run in both a design and an analysis mode. Also important, is the ability to generate solutions where critical components are solved using 3D FNS, while others are run using a through-flow method. Other desirable features in a through-flow solver are: an advanced equation of state, injection and extraction ability, the handling of arbitrary (non-axial) shapes, and a link to a capable geometry generation engine.

Through-flow solvers represent a unique mix of higher order numerical methods (increasingly CFD-based) coupled with empirically derived models (generally meanline based). The combination of these two methods in one solver creates a particularly challenging programming problem. This paper details the techniques required to effectively generate through-flow solutions. Special attention is given to an improved off-design loss model for compressors, as well as a transonic loss model needed for high-speed compressor and turbine flows. Validation with recognized test data along with corresponding 3D FNS CFD results are presented.
Development of 1 MWe Supercritical CO2 Test Loop
Authors: Moore Jeff , Brun Klaus , Evans Neal , Kalra Chiranjeev
Published: August 2015

Recent studies have demonstrated that sCO2 in a closed-loop recompression. Brayton cycle offers equivalent or higher cycle efficiency when compared with supercritical- or superheated-steam cycles at temperatures relevant for CSP applications. With funding under the SunShot initiative, the authors are developing a high-efficiency sCO2 turbo-expander for the solar power plant duty cycle profile and novel compact heat exchangers for the sCO2 Brayton cycle. However, no test loop exists to test the turbine and heat exchangers under development. Therefore, a customized test loop is being developed at Southwest Research Institute that will accommodate the full test pressures (80 to 280 bar) and temperatures (45 to 700°C) of the proposed Brayton cycle. The paper describes the design methodology to predict the pipe flow behavior and thermal growths as well as material selection. A customized natural gas fired heater is currently being designed, since no heater like it is available currently.
Reduction of Gas Turbine Exhaust Temperature Limit due to HRSG Limitations by Change on Control Curve to Optimize Plant Operation and Performance
Authors: Mendoza Eduardo , Lin TsungPo , Jiang Xiaomo
Published: August 2015

Most of the GE gas turbine fleet operates with exhaust temperature control characterized by various forms of Temperature Control Curves (TCC). The TCC which all have specific isothermal limits (maximum exhaust gas temperature) assigned. The isothermal limit is defined mainly by the materials used in the exhaust area including the exhaust frame, exhaust diffuser, struts. The isothermal limit is set to protect the turbine exhaust section from damage by excessive temperature. Although the isothermal limit is typically driven by turbine exhaust temperature limitation, there is a growing demand for isothermal limit adjustment due to HRSG operation limitation, e.g., HP steam attemperation, and also due to emission issues at part load operation.

The content of this paper presents a systematic approach for adjusting the isothermal limit to enhance the plant performance while still satisfying limitations in HRSG and DLN combustor operability. This exercise is a multi-disciplinary optimization process and it requires iterative communications among different disciplinary engineering teams. The methodology was applied to the case of 107FA Combined Cycle isothermal limit reduction for part load operation.
Prediction of Thermoacoustic Oscillations With a Linearised Euler Methodology
Authors: Quaglia C. F. , Cant R. S.
Published: August 2015

Combustion instabilities in the aviation, aerospace and power generation industries have been a matter of concern for engineers since the 1950s, but with the increase in computer processing speed and the development of CFD it is now possible to attempt to predict frequencies and stability of a combustion system by numerical means, or by combining numerical, analytical and experimental approaches.

Currently available analytical methods for the prediction of the frequency and stability of thermoacoustic oscillations make use of one-dimensional models where the frequency of oscillation is assumed to be low enough that only plane waves propagate in the burner, with higher order modes decaying quickly. While accurate and well-suited for longitudinal oscillations, these methods are unable to predict the frequency of instabilities where the unsteady heat release couples with the higher frequency transverse acoustic modes. Therefore a method is needed for applications where high frequency transverse oscillations are important.

A method in which the linearised Euler equations are employed to calculate the propagation of acoustic waves is then suitable for solving this thermoacoustic problem. When a flame model that appropriately represents the frequency-dependent dynamics of the flame front is included, this method can predict the frequency of the oscillation resulting from the coupling between acoustics and combustion in an arbitrarily complex geometry.

In this paper, a linearised Euler solver called INSTANT is introduced and validated against a well known theoretical model for the calculation of thermoacoustic oscillations in a one dimensional cylindrical duct with rigid walls and a radially uniform mean flow. The frequencies of oscillation and the modeshapes for this stable configuration match the theoretical ones well.

An example calculation of transverse acoustic resonant mode is then presented. The ability of the code to predict the production of an entropy mode as a result of the interaction between an acoustic wave and a heat source region and its ability to predict frequencies of oscillation and modeshapes in a one dimensional configuration give confidence it can serve as a predictive tool for high frequency, transverse thermoacoustic oscillations in the more complex geometries of practical combustion systems once a suitable model for the frequency dependent flame response is included. The development of such a flame model is left for future work.
Investigation of Spiral and Sweeping Holes
Authors: Thurman Douglas , Poinsatte Philip , Ameri Ali , Culley Dennis , Raghu Surya , Shyam Vikram
Published: August 2015

Surface infrared thermography, hotwire anemometry, and thermocouple surveys were performed on two new film cooling hole geometries: spiral/rifled holes and fluidic sweeping holes. The spiral holes attempt to induce large-scale vorticity to the film cooling jet as it exits the hole to prevent the formation of the kidney shaped vortices commonly associated with film cooling jets. The fluidic sweeping hole uses a passive in-hole geometry to induce jet sweeping at frequencies that scale with blowing ratios. The spiral hole performance is compared to that of round holes with and without compound angles. The fluidic hole is of the diffusion class of holes and is therefore compared to a 777 hole and Square holes. A patent-pending spiral hole design showed the highest potential of the non-diffusion type hole configurations. Velocity contours and flow temperature were acquired at discreet cross-sections of the downstream flow field. The passive fluidic sweeping hole shows the most uniform cooling distribution but suffers from low span-averaged effectiveness levels due to enhanced mixing. The data was taken at a Reynolds number of 11,000 based on hole diameter and freestream velocity. Infrared thermography was taken for blowing ratios of 1.0, 1.5, 2.0, and 2.5 at a density ratio of 1.05. The flow inside the fluidic sweeping hole was studied using 3D unsteady RANS.
Preliminary Design Assessments of Pusher Geared Counter-Rotating Open Rotors: Part II — Impact of Low Pressure System Design on Mission Fuel Burn, Certification Noise and Emissions
Authors: Bellocq Pablo , Garmendia Inaki , Sethi Vishal
Published: August 2015

In this 2-part publication, the impact of the main low pressure system parameters of a counter rotating Geared Open Rotor (GOR) on mission fuel burn, certification noise and emissions is presented for a 160 PAX medium haul class aircraft.

Due to their high propulsive efficiency, GORs have the potential to significantly reduce fuel consumption and emissions relative to conventional high bypass ratio turbofans. However, this novel engine architecture presents many design and operational challenges both at engine and aircraft level.

The assessment of the impact of the main low pressure preliminary design parameters of GORs on mission fuel burn, certification noise and emissions is necessary at preliminary design stages in order to identify optimum design regions. These assessments may also aid the development process when compromises need to be performed as a consequence of design, operational or regulatory constraints.

Part I of this two-part publication describes the main low pressure (LP) system design choices for a GOR as well as the preliminary design philosophy and simulation framework developed for the assessments. Part II presents the assessment studies. A fixed reference aircraft and mission were used to evaluate the different GOR engine designs. The results are presented in the form of 1-D or 2-D plots in which one or two design parameters are varied at the same time. The changes in mission fuel burn, certification noise and emissions are expressed as differences relative to a baseline design, due to the fact that preliminary design tools were used for the assessments. The main conclusions of the study are:

• Increasing spacing between the propellers (from 0.65 to 1.3m) reduces noise significantly (∼6 EPNdB for each certification point) with a relatively small fuel burn penalty (∼0.3–0.5%)

• Relative to unclipped designs, 20% clipped CRPs reduce flyover noise by at least 2.5 EPNdB and approach noise by at least 4.5 EPNdB. The corresponding fuel burn penalty is ∼2%.

• Sideline and flyover noise can be reduced by increasing the diameter of the CRP and appropriately controlling CRP rotational speeds. Approach noise can be reduced by either reducing the diameters or the rotational speeds of the propellers.

• Regardless of clipping, reducing the rotational speed of the rear propeller relative to the forward propeller reduces noise and, to a certain limit, also mission fuel burn. Further reductions in rotational speed would have an adverse effect on fuel burn.

• For given rotational speeds of the propellers, the torque ratio of the gearbox is fixed within ±3%.
Failure Criteria of Diffusion-Bonded Seam Under Complex Stress State
Authors: Xianghai Chai , Zhiqiang Wang , Zhongbin Tang
Published: August 2015

Diffusion-bonded titanium hollow warren structures have been successfully used on aircraft engine components, such as fan blade, etc., for which failure behavior under impact load is one of the major considerations during design. Studies show that the welding seam de-bonding is the major failure mechanisms under the impact loads. To effectively simulate the de-bonding, phenomenological effective bond strength needs to be properly defined for both the girder region and the edges. In this paper, the bond strength at the hollow region is calibrated through quasi-static tensile tests, in which the specimens are properly designed to represent the cross-section of the hollow region of a typical warren structure. Then, the strength of the edge region is estimated through an inverse method based on the analysis-test correlation of a hollow panel impact test. Such multi-factor coupled seam failure criteria can provide reasonable accordance with test result in the simulation of impact failure of the hollow structure. This means the model with such failure criteria incorporated can provide a useful reference to the aircraft engine hollow warren structure components design.