bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Operating Parameters of a Recompression sCO2 Cycle for Maximum Efficiency
Authors: Sathish Sharath , Kumar Pramod , Namburi Adi Narayana , Gopi Pramod Chandra , Carlson Matthew D. , Ho Clifford K.
Published: August 2017

Supercritical CO2 power systems offer significant power density advantages along with high efficiencies, compared to traditional Rankine or Brayton cycles. Of the several viable configurations, the recompression cycle has higher efficiency compared to the simple recuperated cycle for source temperatures above 500°C. It also provides a good trade-off between efficiency and plant complexity. This paper explores the dependence of critical operational parameters on source and sink-temperature, which is then used as a means to generate guidelines for developing recompression sCO2 power plants. The maximum source temperature in the analysis is restricted to 565°C to take advantage of the existing materials and technologies associated with industrial steam turbines. However, the methodology described herein is applicable for any other source temperature range.

An important source of thermal efficiency degradation in power plants is attributable to heat exchangers. Analysis presented in this work directly relates the optimum operational parameters of the recompression cycle to the operation of the low temperature recuperator. Thermodynamic analysis confirms that a recompression fraction of 0.25 and pressure ratio of 2.5 is as an optimum design point for the recompression cycle. The penalty in efficiency and power while operating the plant in off-design conditions for a fixed recompression fraction and pressure ratio is highlighted.
Numerical Simulation of a Particle-Laden Impinging Jet: Effect of Wall Curvature on Particle Deposition
Authors: Agati Giuliano , Borello Domenico , Rispoli Franco , Salvagni Alessandro , Venturini Paolo
Published: August 2017

Jet impingement against surfaces is uses in several industrial applications, including the internal cooling of turbine blades. Coolant used for blade cooling is air bleed from a compressor and is laden with particles.

A numerical simulation of a particle-laden impinging jet is here proposed, aiming at studying and analysing the effect of surface curvature on flow field, particle motion and deposit formation. To this aim, an impinging jet on a flat and a curved walls is considered. Flow motion is be solved using Direct Numerical Simulation, thus no additional model is needed for turbulence effect on particle motion.

Results show that the deposit patterns follow some secondary flow structures, showing a series of peaks forming according to those structures. The peaks are present in both the main orthogonal direction of the jet, but they are not symmetrical due to surface curvature.
Design of a Centrifugal Compressor Stage and a Radial-Inflow Turbine Stage for a Supercritical CO2 Recompression Brayton Cycle by Using 3D Inverse Design Method
Authors: Zhang Jiangnan , Gomes Pedro , Zangeneh Mehrdad , Choo Benjamin
Published: August 2017

It is found that the ideal gas assumption is not proper for the design of turbomachinery blades using supercritical CO2 (S-CO2) as working fluid especially near the critical point. Therefore, the inverse design method which has been successfully applied to the ideal gas is extended to applications for the real gas by using a real gas property lookup table. A fast interpolation lookup approach is implemented which can be applied both in superheated and two-phase regimes. This method is applied to the design of a centrifugal compressor blade and a radial-inflow turbine blade for a S-CO2 recompression Brayton cycle. The stage aerodynamic performance (volute included) of the compressor and turbine is validated numerically by using the commercial CFD code ANSYS CFX R162. The structural integrity of the designs is also confirmed by using ANSYS Workbench Mechanical R162.
Comparison of the Influence Coefficient Method and Travelling Wave Mode Approach for the Calculation of Aerodynamic Damping of Centrifugal Compressors and Axial Turbines
Authors: Vogel K. , Naidu A. D. , Fischer M.
Published: August 2017

The prediction of aerodynamic damping is a key step towards high fidelity forced response calculations. Without the knowledge of absolute damping values, the resulting stresses from forced response calculations are often afflicted with large uncertainties. In addition, with the knowledge of the aerodynamic damping the aeroelastic contribution to mistuning can be considered. The first section of this paper compares two methods of one-way-coupled aerodynamic damping computations on an axial turbine. Those methods are: the aerodynamic influence coefficient, and the travelling wave mode method. Excellent agreement between the two methods is found with significant differences in required computational time. The average deviation between all methods for the transonic turbine is 4%. Additionally, the use of transient blade row methods with phase lagged periodic boundaries are investigated and the influence of periodic boundaries on the aerodynamic influence coefficients are assessed. A total of 23 out of 33 passages are needed to remove all influence from the periodic boundaries for the present configuration. The second part of the paper presents the aerodynamic damping calculations for a centrifugal compressor. Simulations are predominantly performed using the aerodynamic influence coefficient approach. The influence of the periodic boundaries and the recirculation channel is investigated. All simulations are performed on a modern turbocharger turbine and centrifugal compressor using ANSYS CFX V17.0 with an inhouse pre- and post-processing procedure at ABB Turbocharging. The comparison to experimental results concludes the paper.
Experimental Investigation of Total Pressure Loss Development in a Highly Loaded Low Pressure Turbine Cascade
Authors: Bear Philip , Wolff Mitch , Gross Andreas , Marks Christopher R. , Sondergaard Rolf
Published: August 2017

Improvements in turbine design methods have resulted in the development of blade profiles with both high lift and good Reynolds lapse characteristics. An increase in aerodynamic loading of blades in the low pressure turbine section of aircraft gas turbine engines has the potential to reduce engine weight or increase power extraction. Increased blade loading means larger pressure gradients and increased secondary losses near the endwall. Prior work has emphasized the importance of reducing these losses if highly loaded blades are to be utilized. The present study analyzes the secondary flow field of the front-loaded low-pressure turbine blade designated L2F with and without blade profile contouring at the junction of the blade and endwall. The current work explores the loss production mechanisms inside the low pressure turbine cascade. Stereoscopic particle image velocimetry data and total pressure loss data are used to describe the secondary flow field. The flow is analyzed in terms of total pressure loss, vorticity, Q-Criterion, turbulent kinetic energy and turbulence production. The flow description is then expanded upon using an Implicit Large Eddy Simulation of the flow field. The RANS momentum equations contain terms with pressure derivatives. With some manipulation these equations can be rearranged to form an equation for the change in total pressure along a streamline as a function of velocity only. After simplifying for the flow field in question the equation can be interpreted as the total pressure transport along a streamline. A comparison of the total pressure transport calculated from the velocity components and the total pressure loss is presented and discussed. Peak values of total pressure transport overlap peak values of total pressure loss through and downstream of the passage suggesting that total pressure transport is a useful tool for localizing and predicting loss origins and loss development using velocity data which can be obtained non-intrusively.
Modelling of Hot Surface Ignition Within Gas Turbines Subject to Flammable Gas in the Intake
Authors: Pedersen Lea Duedahl , Nielsen Kenny Krogh , Yin Chungen , Sørensen Henrik , Fossan Ingar
Published: August 2017

Controlling risks associated with fires and explosions from leaks of flammable fluids at oil and gas facilities is paramount to ensuring safe operations. The gas turbine is a significant potential source of ignition; however, the residual risk is still not adequately understood.

A model has been successfully developed and implemented in the commercial Computational Fluid Dynamics (CFD) code ANSYS CFX. This model is based on a combination of standard models, User Defined Functions (UDFs) and the CFX Expression Language (CEL). Prediction of ignition is based on a set of criteria to be fulfilled while complex kinetics is handled computationally easy by means of a reaction progress variable.

The simulation results show a good agreement with the trends experimentally observed in other studies. It is found that the hot surface ignition temperature (HSIT) increases with increase in velocity and turbulence but decreases with increase in initial mixture temperature and pressure.

The model shows a great potential in reliable prediction of the risk of hot surface ignition within gas turbines in the oil and gas industry. In the future, a dedicated experimental study will be performed not only to improve the understanding of the risk of hot surface ignition but also to collect experimental data under well-defined conditions to further validate or refine the model.
Effect of Active Modulation of Through-Casing Coolant Injection on Turbine Efficiency
Authors: Tang Brian M. T. , Bacic Marko , Ireland Peter T.
Published: August 2017

This paper presents a computational investigation into the impact of cooling air injected through the stationary over-tip turbine casing on overall turbine efficiency. The high work axial flow turbine is representative of the high pressure turbine of a civil aviation turbofan engine. The effect of active modulation of the cooling air is assessed, as well as that of the injection locations. The influence of the through-casing coolant injection on the turbine blade over-tip leakage flow and the associated secondary flow features are examined. Transient (unsteady) sliding mesh simulations of a one turbine stage rotor-stator domain are performed using periodic boundary conditions. Cooling air configurations with a constant total pressure air supply, constant mass flow rate and actively controlled total pressure supply are assessed for a single geometric arrangement of cooling holes. The effects of both the mass flow rate of cooling air and the location of its injection relative to the turbine rotor blade are examined.

The results show that all of the assessed cooling configurations provided a benefit to turbine row efficiency of between 0.2 and 0.4 percentage points. The passive and constant mass flow rate configurations reduced the over-tip leakage flow, but did so in an inefficient manner, with decreasing efficiency observed with increasing injection mass flow rate beyond 0.6% of the mainstream flow, despite the over-tip leakage mass flow rate continuing to reduce.

By contrast, the active total pressure controlled injection provided a more efficient manner of controlling this leakage flow, as it permitted a redistribution of cooling air, allowing it to be applied in the regions close to the suction side of the blade tip which more directly reduced over-tip leakage flow rates and hence improved efficiency. Cooling air injected close to the pressure side of the rotor blade was less effective at controlling the leakage flow, and was associated with increased aerodynamic loss in the passage vortex.
State-of-the-Art Cooling Technology for a Turbine Rotor Blade
Authors: Town Jason , Straub Doug , Black James , Thole Karen , Shih Tom
Published: August 2017

Effective internal and external cooling of airfoils is key to maintaining component life for efficient gas turbines. Cooling designs have spanned the range from simple internal convective channels to more advanced double-walls with shaped film-cooling holes. This paper describes the development of an internal and external cooling concept for a state-of-the-art cooled turbine blade. These cooling concepts are based on a review of literature and patents, as well as, interactions with academic and industry turbine cooling experts. The cooling configuration selected and described in this paper is referred to as the “baseline” design, since this design will simultaneously be tested with other more advanced blade cooling designs in a rotating turbine test facility using a “rainbow turbine wheel” configuration. For the baseline design, the leading edge is cooled by internal jet impingement and showerhead film cooling. The mid-chord region of the blade contains a three-pass serpentine passage with internal discrete V-shaped trip strips to enhance the internal heat transfer coefficient. The film cooling along the mid-chord of the blade uses multiple rows of shaped diffusion holes. The trailing edge is internally cooled using jet impingement and externally film cooled through partitioned cuts on the pressure side of the blade.
Experimental Characterization of Reverse-Oriented Film Cooling
Authors: Prenter Robin , Hossain Mohammad A. , Agricola Lucas , Ameri Ali , Bons Jeffrey P.
Published: August 2017

Reverse-oriented film cooling, which consists of film cooling holes oriented to inject coolant in the opposite direction of the freestream, is experimentally investigated. Tests are conducted at various blowing ratios (M = 0.25, 0.5, and 1.0) under both low and high freestream turbulence (Tu = 0.4% and 10.1%), with a density ratio near unity. The interesting flow field that results from the reverse-jet-in-crossflow interaction is characterized using flow visualization, particle image velocimetry, and thermal field measurements. Heat transfer performance is evaluated with adiabatic film effectiveness and heat transfer coefficient measurements obtained using infrared thermography. Adiabatic effectiveness results show that reverse film cooling produces very uniform and total coverage downstream of the holes, with some reduction due to increased freestream turbulence. The reverse film cooling holes are evaluated against cylindrical holes in the conventional configuration, and were found to perform better in terms of average effectiveness and comparably in terms of net heat flux reduction, despite augmented heat transfer coefficient. Compared to shaped hole data from previous studies, the reverse film cooling holes generally had worse heat transfer performance. The aerodynamic losses associated with the film cooling are characterized using total pressure measurements down-stream of the holes. Losses from the reverse configuration were found to be higher when compared to cylindrical holes in the conventional and compound angle configurations.
Case for Exploring Compressor Water Injection for Airport Emission Reduction
Authors: Block Novelo David Alejandro , Igie Uyioghosa
Published: August 2017

The increasing world population, higher accessibility to air transportation, coupled with new low-cost airline models has resulted in an unprecedented increase in demand for civil aviation. The industry is currently experiencing a global increase of operational civil aircraft at a rate of 5–6% annually. This growth suggests a vibrant future for the industry, however, the environmental implications and the footprint is worth considerable attention given the expected scale of growth in the industry and the possible side effects to human health. The stakeholders involved, some of which include: airports and airline operators, jet engine and airframe manufacturers and various government bodies, are introducing measures in order to mitigate the increase in certain emissions and hence their impact.

This study focuses on one of the many existing approaches targeting the reduction in gaseous emissions, predominantly nitrogen oxides (NOx). This is through compressor water injection that is estimated to reduce NOx emissions by almost half under certain ambient conditions and water-to-air ratio. Apart from reviewing this technology, the study, more importantly, presents the ideas in relation to other major existing approaches/concepts.

It would be observed that compressor water injection can be more readily applied to the existing infrastructure when compared to other approaches. This technique is one of the most promising methods for reducing NOx emissions, an area of particular importance given that modern engines, though more thermally efficient, operate at higher pressure ratios and flame temperature, both of which enhance nitrogen oxides formation.

One of the main contributions of this paper is the categorisation of existing approaches focused on reducing aircraft-borne airport emissions. Different technologies and operational changes are classified according to the key pollutants that they target with respect to the landing and takeoff cycle based on 11 different engine types. These gaseous-emissions mitigating approaches are analyzed based on their individual merits, limitations and feasibilities. Compressor water injection is re-introduced here as a more readily applicable solution despite its technological challenges, many of which can be better resolved with today’s knowledge.
Variable Inlet Guide Vane Losses and Their Effect on Downstream Impeller and Diffuser in Wet Gas Flow
Authors: Vigdal Levi André B. , Bakken Lars E.
Published: August 2017

Adopting the innovative technology found in a compressor able to compress a mixture of natural gas and condensate has great potential for meeting future challenges in subsea oil and gas production. Benefits include reduced size, complexity and cost, enhanced well output, longer producing life and increased profits, which in turn offer opportunities for exploiting smaller oil and gas discoveries or extending the commercial life of existing fields.

Introducing liquid into a centrifugal compressor creates several thermodynamic and fluid-mechanical challenges. The paper reviews some of the drive mechanisms involved in wet gas compression and views them in the context of the test results presented. An inlet guide vane (IGV) assembly has been installed in a test facility for wet gas compressors and the effect of wet gas on IGV performance documented. The impact of changes in IGV performance on impeller and diffuser has also been documented. The results have been discussed and correction methods compared.
An Introduction to the Ansaldo GT36 Constant Pressure Sequential Combustor
Authors: Pennell Douglas A. , Bothien Mirko R. , Ciani Andrea , Granet Victor , Singla Ghislain , Thorpe Steven , Wickstroem Anders , Oumejjoud Khalid , Yaquinto Matthew
Published: August 2017

This paper introduces and presents validation of the Constant Pressure Sequential Combustion system (denoted CPSC), a second generation concept developed for and applied to the new Ansaldo GT36 H-class gas turbine combustors. It has evolved from the well-established sequential burner technology applied to all current GT26 and GT24 gas turbines, and contains all architectural improvements implemented since original inception of this engine frame in 1994, with beneficial effects on the operation turndown, fuel flexibility, on the overall system robustness, and featuring the required aspects to stay competitive in the present day energy market. The applied air and fuel management therefore facilitate emission and dynamics control at both the extremely high and low firing temperature ranges required for existing and future Ansaldo gas turbine engine classes.
Transient Analysis of an Innovative Cycle Integrating a SOFC and a Turbogenerator for Electric Propulsion
Authors: Chakravarthula Venkata Adithya , Roberts Rory A.
Published: August 2017

Gas turbine technology for aerospace applications is approaching limits in efficiency gains as efficiency gains today occur in very small increments. One limitation in conventional gas turbine technology is the combustion process, which destroys most of the exergy in the cycle. To address this limitation in a traditional Brayton power cycle, a hybrid system which is integrating a Solid Oxide Fuel Cell (SOFC) and gas turbine is developed. Hybrid systems involving fuel cells have better efficiencies than conventional power generation systems. The combination of a SOFC with a gas turbine has shown higher efficiencies than conventional gas turbine systems due to the reduction of exergy destruction in the heat addition process. A one-dimensional dynamic model of a SOFC is integrated in a SOFC-Combustor configuration with a gas turbine to develop efficient electrical power generation for aviation applications. The SOFC–Combustor configuration is an unique concept for reducing system weight, volume, complexity, and response time, which are important attributes for aerospace systems. SOFC-Combustor model was developed based on first principles with detailed modeling of the internal steam reformer, electrochemical and thermodynamics of the SOFC included. The overall purpose of this paper is to analyze the performance of the hybrid SOFC system for high altitude operation for both on-design and off-design operating conditions. Steady-state analysis for cruise condition performed to calculate the respective mission efficiencies. By determining the operating efficiencies of the system, gravimetric comparisons including fuel are performed for alternative power cycles for given flight durations. Transient analysis is performed to understand the behavior in the SOFC temperatures and hybrid system with sudden perturbations to the system (rapid throttle changes, environment changes).
Limit Cycles of Spinning Thermoacoustic Modes in Annular Combustors: A Bloch-Wave and Adjoint-Perturbation Approach
Authors: Mensah Georg A. , Moeck Jonas P.
Published: August 2017

The most straightforward way to assess the thermoacoustic stability of a combustion system is based on modal approaches. The modes are typically computed from linearized equations in the frequency domain, such as the Helmholtz equation. Due to the linear character, nonlinear saturation effects cannot be computed with such models. Flame describing functions have been suggested to fill this gap. They describe the flame response in an amplitude-dependent manner and have been successfully used in recent work for the prediction of limit-cycle amplitudes in single-burner systems and annular combustors.

This paper presents a more efficient approach of computing limit-cycle amplitudes of spinning thermoacoustic modes in an annular combustion chamber. As one important feature, adjoint perturbation theory is utilized for the solution of the thermoacoustic Helmholtz equation associated with a flame describing function. This avoids iterations over different amplitude levels to find the limit cycle amplitude, i.e., the amplitude level at which the modal growth rate is zero, as required in previous approaches. Moreover, based on the discrete rotational symmetry of the system, the computation is also accelerated by means of Bloch-wave theory, which reduces computations for annular combustors to a single burner/flame segment.

Results for a generic model and a laboratory-scale annular combustion system are presented and discussed.
Impact of Equation of State Model and CO2 Diluent on Combustion Characteristics of a Directly Heated Supercritical Oxy-Fuel Combustor
Authors: Chowdhury A. S. M. Arifur , Choudhuri Ahsan , Love Norman , Kim Hwanho , Ma Jiefu , Tsiava Remi
Published: August 2017

Directly heated supercritical oxy-fuel power cycles have potential to offer a higher thermal efficiency and lower pollutant emissions compared to existing power cycles. Due to the fact that combustion occurs at the supercritical phase, usually at or above 30MPa, conventional gas turbine combustors cannot be used to produce electricity using this concept. Besides, oxy-fuel combustion produces relatively higher temperatures than the air-fuel combustion process, which introduces material limitations particularly at the high pressures. Motivated by the advantages of the directly heated supercritical phase combustion technique, the authors present a design of an injector inside a combustion chamber. The combustor presented in this paper is designed to operate at a 30MPa pressure. The current study incorporates methane as the fuel and oxygen as the oxidizer. The design process of such a combustor incorporates an immense amount of challenges since the fluid properties as well as combustion behavior at the supercritical phase are still largely unknown. However, in order to design this type of system a reasonable understanding of fluid behavior in the combustion environment is essential.

A commercial computational fluid dynamics simulation tool, ANSYS Fluent, is used to simulate the fluid flow and combustion inside the combustor. The real gas effect is added into the code by coupling equation of state with the fluid flow computation. The Lee Kesler equation, which is found in literature and in this paper to be the most relevant equation of state for this case, is implemented via user defined function along with Plocker Knapp mixing rule. The system presented in this study is intended to operate at a 1 MW power input. Carbon dioxide is delivered axially into the combustion chamber separate from fuel and oxidizer. The study shows more than 90% carbon dioxide needs to be recirculated to keep the combustor exit temperature below material operation limit of approximately 1450K. Thus, it is presumable that the combustion occurs in a carbon dioxide filled environment. The investigation has been performed by varying the carbon dioxide mass flow rate splitting between two inlets. It is observed that the 30%–70% split displays the optimum performance among all three cases. This condition offers wall temperature reduction, uniform exhaust products and an even temperature profile at the outlet of the combustor.
Experimental Study of Superheated Kerosene Jet Fuel Sprays From a Pressure-Swirl Nozzle
Authors: Manipurath Shaji S.
Published: August 2017

The development of higher thermal stability fuels and the development of onboard fuel deoxygenation systems may permit the preheating of fuel up to about 755 K before the onset of pyrolysis. At a sufficiently high fuel temperature for a given combustion chamber pressure, the flash vaporization of liquid or supercritical state fuel can ensue upon injection into the chamber. The performance of standard aviation turbine engine fuel nozzles, designed for mechanically breaking up liquid sprays, may thus be significantly altered by the employment of severely preheated fuel.

An evaluation of heated and superheated Jet A-1 sprays from a pressure-swirl atomizer was implemented in a purpose-built test facility. Laser sheet imaging of the spray yielded simultaneous axial cross-sectional maps of Mie-scatter and fluorescence signals. In addition, particle image velocimetry was also used to measure the spray droplet velocity-field. The results indicated that increasing the fuel’s dimensionless level of superheat ΔT* from −1.8 to 0.6 yielded significant changes in the spray structure; specifically, finer droplet sizes, a more uniform dropsize distribution across the spray, increased spray cone angle till about ΔT* = −0.8 followed by a contraction thereafter, marginally increased spray penetration, and significantly higher localised near nozzle tip droplet velocities. The measurements supported the hypothesis that the initial hollow-cone spray structure evolves to a near solid-cone structure with a central vapour core as the fuel is superheated.
Experimental Investigation of Combustion Dynamics in a Turbulent Syngas Combustor
Authors: Baraiya Nikhil Ashokbhai , Nagarajan Baladandayuthapani , Chakravarthy Satynarayanan R.
Published: August 2017

In the present work, the proportion of carbon monoxide to hydrogen is widely varied to simulate different compositions of synthesis gas and the potential of the fuel mixture to excite combustion oscillations in a laboratory-scale turbulent bluff body combustor is investigated. The effect of parameters such as the bluff body location and equivalence ratio on the self-excited acoustic oscillations of the combustor is studied. The flame oscillations are mapped by means of simultaneous high-speed CH* and OH* chemiluminescence imaging along with dynamic pressure measurement. Mode shifts are observed as the bluff body location or the air flow Reynolds number/overall equivalence ratio are varied for different fuel compositions. It is observed that the fuel mixtures that are hydrogen-rich excite high amplitude pressure oscillations as compared to other fuel composition cases. Higher H2 content in the mixture is also capable of exciting significantly higher natural acoustic modes of the combustor so long as CO is present, but not without the latter. The interchangeability factor Wobbe Index is not entirely sufficient to understand the unsteady flame response to the chemical composition.
Freestream Flow Effects on Film Effectiveness and Heat Transfer Coefficient Augmentation for Compound Angle Shaped Holes
Authors: Anderson Joshua B. , McClintic John W. , Bogard David G. , Dyson Thomas E. , Webster Zachary
Published: August 2017

The use of compound-angled shaped film cooling holes in gas turbines provides a method for cooling regions of extreme curvature on turbine blades or vanes. These configurations have received surprisingly little attention in the film cooling literature. In this study, a row of laid-back fanshaped holes based on an open-literature design, were oriented at a 45-degree compound angle to the approaching freestream flow. In this study, the influence of the approach flow boundary layer thickness and character were experimentally investigated. A trip wire and turbulence generator were used to vary the boundary layer thickness and freestream conditions from a thin laminar boundary layer flow to a fully turbulent boundary layer and freestream at the hole breakout location. Steady-state adiabatic effectiveness and heat transfer coefficient augmentation were measured using high-resolution IR thermography, which allowed the use of an elevated density ratio of DR = 1.20. The results show adiabatic effectiveness was generally lower than for axially-oriented holes of the same geometry, and that boundary layer thickness was an important parameter in predicting effectiveness of the holes. Heat transfer coefficient augmentation was highly dependent on the freestream turbulence levels as well as boundary layer thickness, and significant spatial variations were observed.
Conjugate Heat Transfer Scaling for Inconel 718
Authors: Stewart William R. , Dyson Thomas E.
Published: August 2017

Over the last decade, conjugate heat transfer testing has been shown to be important because it replicates the sum of the hot gas path heat transfer coefficient, film cooling, film cooling heat transfer augmentation, bore cooling, conduction through the wall, internal cooling heat transfer coefficients, and the relative amounts of heat pick up in the cooling flow. Instead of measuring these boundary conditions in individual experiments, conjugate heat transfer testing measures the cumulative effect as well as each boundary condition’s effect on the others. Typically, matched Biot number heat transfer experiments are performed at near room temperature with a surrogate material; however, this study examines how the thermal conductivity of a nickel alloy sufficiently changes between room temperature and temperatures representative of turbine engines to allow matched Bi heat transfer tests using nickel at laboratory conditions. The ratio of the thermal conductivity of air to the thermal conductivity of Inconel 718 stays mostly constant between engine representative temperatures and room temperature. Over this range, the thermal conductivity of both air and Inconel 718 change ∼2.5X, and the change in thermal conductivity allows for conjugate heat transfer tests to match Reynolds number, Nusselt number, film effectiveness, Biot number, and Stanton number. Experimental results at two temperature conditions are shown confirming the theory. Finally, a method for scaling the thermal impact of dust accumulation at laboratory conditions to turbine conditions is proposed.
The Effect of the Geometric Modifications of the Venturi on the Non-Reactive Flow and Combustion Behavior Using a Counter-Rotating Radial-Radial Swirler
Authors: Lin Sheng-Chieh , Wang Xionghui , Estefanos Wessam , Tambe Samir , Jeng San-Mou
Published: August 2017

An experimental study was conducted to perform an analysis of the effect of the geometric modifications of the venturi on the non-reactive and reactive flow behavior using a counter-rotating radial-radial swirler. In the non-reactive flow tests, measurements were taken in a central vertical plane and horizontal (cross-sectional) plane at the exit of the swirler, using a High-Speed, Two Dimensional, Particle Image Velocimetry (2D PIV) system. The size of the swirler used in the non-reactive flow tests is a 4.76X scaled size of the swirler used in combustion. The 4.76X swirler models were tested in air flow seeded with olive oil at Re = 51,500, corresponding to the pressure drop across the 1X swirler models of 4% of atmospheric pressure at ambient conditions. Compared with the 1X swirler models, the 4.76X swirler models provide high spatial and temporal resolutions from the enhanced visibility of the flow characteristics and lower velocities at the same Re. Four swirler configurations of high swirl number (SN ≈ 1.0) were used, with no modification for the baseline configuration (configuration 1), and with the chevrons on the venturi for the straight chevrons configuration (configuration 2). The design of the inclined venturi was used for the converging venturi configuration (configuration 3), and chevrons were added on the converging venturi for the converging chevrons configuration (configuration 4). In the combustion tests, the 1X swirler models were tested using 478K preheated air at 4% pressure drop across the swirler, and different chamber lengths. Measurements were conducted using a regular camera to capture the flame image, and dynamic pressure transducers to obtain the acoustic pressure oscillations. Four configurations were studied and compared in the non-reactive and reactive flows with the objective of understanding the mechanisms responsible in reducing the extent of the combustion instabilities. Results of this study show that the converging venturi in configuration 3 appears to be the best design in eliminating the combustion instabilities in the fuel-lean region as compared to the other configurations. This indicates that the prevention of the frequencies coupling between the heat release rate and acoustic oscillations has been achieved by using the design of the converging venturi.
Application of 3D Fracture Mechanics for Improved Crack Growth Predictions of Gas Turbine Components
Authors: Bhachu Kanwardeep S. , Narasimhachary Santosh B. , Shinde Sachin R. , Gravett Phillip W.
Published: August 2017

Fracture mechanics analysis is essential for demonstrating structural integrity of gas turbine components. Usually, analyses based on simpler 2D stress intensity solutions provide reasonable approximations of crack growth. However, in some cases, simpler 2D solutions are too-conservative and does not provide realistic crack growth predictions; often due to its inability to account for actual 3D geometry, and complex thermal-mechanical stress fields. In such cases, 3D fracture mechanics analysis provides extra fidelity to crack growth predictions due to increased accuracy of the stress intensity factor calculations. Improved fidelity often leads to benefits for gas turbine components by reducing design margins, improving engine efficiency, and decreasing life cycle costs.

In this paper, the application of 3D fracture mechanics analysis on a gas turbine blade for predicting crack arrest is presented. A comparison of stress intensity factor values from 3D and 2D analysis is also shown. The 3D crack growth analysis was performed by using FRANC3D in conjunction with ANSYS.
Characteristics of Stable Rotating Stall Cells in an Axial Compressor
Authors: Hickman Adam R. , Morris Scott C.
Published: August 2017

Flow field measurements of a high-speed axial compressor are presented during pre-stall and post-stall conditions. The paper provides an analysis of measurements from a circumferential array of unsteady shroud static pressure sensors during stall cell development. At low-speed, the stall cell approached a stable size in approximately two rotor revolutions. At higher speeds, the stall cell developed within a short amount of time after stall inception, but then fluctuated in circumferential extent as the compressor transiently approached a stable post-stall operating point. The size of the stall cell was found to be related to the annulus average flow coefficient. A discussion of Phase-Locked Average (PLA) statistics on flow field measurements during stable operation is also included. In conditions where rotating stall is present, flow field measurements can be Double Phase-Locked Averaged (DPLA) using a once-per-revolution (1/Rev) pulse and the period of the stall cell. The DPLA method provides greater detail and understanding into the structure of the stall cell. DPLA data indicated that a stalled compressor annulus can be considered to contained three main regions: over-pressurized passages, stalled passages, and recovering passages. Within the over-pressured region, rotor passages exhibited increased blade loading and pressure ratio compared to pre-stall values.
An Experimental Investigation of the Dynamic of a Blade With Two Under-Platform Dampers
Authors: Botto Daniele , Umer Muhammad , Gastaldi Chiara , Gola Muzio M.
Published: August 2017

Several experimental apparatus have been designed in the past to evaluate the effectiveness of under-platform dampers. Most of these experimental setups allow to measure the overall damper efficiency in terms of reduction of vibration amplitude in turbine blades. The experimental data collected with these test rigs do not increase the knowledge about the damper dynamics and therefore the uncertainty on the damper behavior remains a big issue. In this paper a different approach to evaluate the damper-blade interaction has been put forward. A test rig has been purposely designed to accommodate a single blade and two under-platform dampers. One side of each damper is in contact with a ground support specifically designed to measure two independent forces on the damper. In this way both the normal and the tangential force components in the damper-blade contact can be inferred. Damper kinematics is rebuilt by using the relative displacement measured between damper and blade. This paper describes the concept behind the new approach, shows the details of the new test rig and discuss the blade frequency response from a new point of view.
Investigation of Effect of Biomass Torrefaction Temperature on Volatile Energy Recovery Through Combustion
Authors: Akinyemi O. S. , Jiang L. , Buchireddy P. R. , Barskov S. O. , Guillory J. L. , Holmes W.
Published: August 2017

Biomass has received wide attention as a substitute for fossil fuel in the generation of energy because of its renewability and carbon neutrality. However, raw biomass combustion is hindered by physical properties such as low energy density and high moisture content. Biomass torrefaction is a mild pyrolysis thermal treatment process carried out at temperature of 200 to 300°C under inert conditions to improve the fuel properties of parent biomass. This yields a higher energy per unit mass product but releases non-condensable and condensable gases which results in energy and mass losses. The condensable gases (volatiles), can result in tar formation on condensing hence, system blockage. Fortunately, the hydrocarbon composition of volatiles also represents a possible auxiliary energy source for torrefaction. The present study investigated energy recovery from volatiles through clean co-combustion with NG for feedstock drying and/or the thermal treatment process of pine wood chips. The research also studied the effect of torrefaction pretreatment temperatures on the amount of energy recovered for various combustion air flow rates. For all test conditions, blue visual flames and low CO and NOx emissions at the combustor exit consistently signified clean and complete premixed combustion. Torrefaction temperature at 283–292 °C had relatively low energy recovered from volatiles, mainly attributed to higher moisture content evolution and low molecular weight of volatiles evolved. At lowest torrefaction pretreatment temperature, smaller amount of volatiles was generated with most energy recovered from the volatiles. Energy conservation evaluation on the torrefaction reactor indicated that about 40% of total energy carried by the exiting volatiles and gases has been recovered by the co-fire of NG and volatiles at the lowest temperature while 20% and 22% of the total energy were recovered at the intermediate and highest torrefaction temperature respectively.
Efficient Rotordynamic Analysis Using the Superelement Approach for an Aircraft Engine
Authors: Kumar Devesh , Juethner Konrad , Fournier Yves
Published: August 2017

The exploration of new aero-engine configurations drives unseen and complex dynamic behavior which can only be captured accurately with enhanced modeling techniques. In an earlier publication, it was established that it is possible to analyze large engine models using high-fidelity two-dimensional (2D) axisymmetric harmonic and three-dimensional (3D) shell and solid elements. This finding stands in contrast to the relatively crude one-dimensional (1D) model simplifications that were introduced several decades ago. While motivated by limited computing power and easily obtained gyroscopic terms, these models are still common in the industry today. In spite of staggering advances in computation, however, said enhanced finite element rotor models are still considered to be quite large. When transitioning from the traditional 1D to the fully 3D rotor model, for example, one encounters an increase in model size of three orders of magnitude. This motivates the use of model reduction techniques such as the External Superelement (SE) which is obtained by component mode synthesis (CMS). The External SE represents a structural component by its physical attachment points, strategically selected interior grid points, and a linear combination of its dynamic modes. Its advantages are reduced computational cost, the ability to solve very large problems, the protection of intellectual property, and the enablement of a modular model description that promotes parallel processing as well as the utilization of high performance computing (HPC). In this paper, the analysis of a realistic aircraft engine is presented in which its rotating structures are modeled with high-fidelity 3D solid/shell elements. The dynamics of the engine assembly are solved using modal analysis and External SE technology with the goals to reduce wall time and improve efficiency. A detailed comparison of wall time is presented to quantify the associated performance gain.
Innovative Design of Attachment for Turbine Blade Rotating at High Speed
Authors: Botto D. , Alinejad F.
Published: August 2017

There is evidence of a lack of knowledge in the design of the blade/disk attachment so that the strength of the materials is not fully exploited and the load capability of the attachment is underestimated. The aim of this work is to improve the engineers’ capability in designing the attachment so that higher loads can be carried with the same material. To this end, an optimization method has been applied to the attachment design. A dovetail blade root was chosen as case study and the objective function was the static equivalent stress in the blade and the disc. The dovetail was described by variable parameters under geometrical and physical constraints. Optimization was performed with a Genetic Algorithm (GA). The result of the optimization procedure is the optimal set of parameter values that minimizes the equivalent stress on the critical areas. Moreover, a surrogate function was utilized as a booster to the GA to save computational time. Stress analysis was performed with a commercial Finite Element (FE) software to provide the exact fitness value. An in-house code was developed to manage both the optimization process and the input/output interface with the FE software. The same code provides a decision-making core. This core checks for feasibility of the geometry of the current set of parameters. The expected result is an optimized profile in terms of Von-Misses equivalent stress.
Validation of a Gas Turbine Thermodynamic Model Without Accurate Component Maps
Authors: Jarrett Anthony , Chen Ying
Published: August 2017

The authors have developed an engine performance model for use within a physics-based analysis tool to predict gas turbine engine life. The model employs a multivariate optimization method to solve the gas turbine thermodynamic equations, and incorporates a calibration phase to capture the behavior of individual engines without requiring accurate component maps.

To validate this approach, a database of test cell data for a turboprop engine has been used. The data consists of approximately 80 engine tests; each one with five operating points. Using a cross-validation method, each engine was uniquely calibrated using four of the operating points, and then validated using parameters from the fifth operating point. To benchmark the calibration process, these analyses were repeated without the calibration stage.

The un-calibrated outputs showed a lack of both precision and accuracy, due to imprecision in the component maps, and variation from engine to engine. In contrast, the calibrated outputs of compressor discharge temperature (CDT), compressor discharge pressure (CDP), and turbine inlet temperature (TIT) were predicted within 1% error for more than 95% of all cases.

Although most of the key thermodynamic parameters were predicted accurately, we have found that the shaft power calculation demonstrates some significant deviations from the test cell data. This has been attributed to the formulation of the turboprop thermodynamic model, and ongoing work is attempting to mitigate this issue. This understanding of the characteristic engine algorithms will provide valuable guidance in selecting suitable engine parameters as inputs and references.
CAD-Based Adjoint Optimization of the Stresses in a Radial Turbine
Authors: Verstraete Tom , Müller Lasse , Müller Jens-Dominik
Published: August 2017

The design optimization of turbomachinery components has witnessed an increased attention in last decade, and is currently used in many companies in the daily design cycle. The adjoint method proves to have the highest potential in this field, however, has still two major shortcomings before its full potential can be used: 1) the shape is mainly parameterized by its grid and the connection to the CAD model is lost, and 2) the optimization process includes only aerodynamic performance and neglects stress and vibration requirements. Within this paper a methodology is developed to include stress calculations into a gradient-based framework, which requires the differentiation of a stress analysis tool. To allow combining the sensitivities from the structural model with those from the aero performance, the CAD model is used for parameterizing the shape, effectively defining a parametrization that controls both the fluid and solid domain that remain linked to each other without creating voids between both models.

The method is tested on a radial turbine test case in which the meridional layout is optimized to reduce the maximum von Mises stresses in the material. The results demonstrate a significant reduction in stress concentrations with a limited computational cost.