bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady IR Methodology for Leading Edge Impingement Measurements
Authors: Helmer David B. , Hoefler Florian
Published: August 2015

A steady-state IR measurement is described and demonstrated for a leading edge crossover impingement configuration. Thin-walled leading edge models are used, with a constant heat flux boundary condition generated. This approach allows for rapid and low-cost hardware manufacture while simultaneously providing improved measurement quality. Test time is heavily reduced relative to traditional liquid crystal tests, and data processing is substantially simplified from transient methodologies. The thin walls minimize the impact of lateral conduction and simplify the conduction corrections. The methodology is demonstrated on a test for a blade-relevant leading edge impingement geometry, with a detailed uncertainty analysis provided.
Large-Scale DES Analysis of Unsteady Flow Field in a Multi-Stage Axial Flow Compressor at Off-Design Condition Using K Computer
Authors: Yamada Kazutoyo , Furukawa Masato , Nakakido Satoshi , Matsuoka Akinori , Nakayama Kentaro
Published: August 2015

The paper presents the results of large-scale numerical simulations which were conducted for better understanding of unsteady flow phenomena in a multi-stage axial flow compressor at off-design condition. The compressor is a test rig compressor which was used for development of the industrial gas turbine, Kawasaki L30A. The compressor consists of 14 stages, the front two stages and the front half stages of which were investigated in the present study. The final goal of this study is to elucidate the flow mechanism of the rotating stall inception in the multi-stage axial compressor for actual gas turbines, and according to the test data it is considered that the 2nd stage and the 5th or 6th stage are suspected of leading to the stall.

In order to capture precise flow physics in the compressor, a computational mesh for the simulation was generated to have at least several million cells per passage, which amounted to 650 million cells for the front 2-stage simulation and two billion cells for the front 7-stage simulation (about three hundred million cells for each stage). Since these were still not enough for the large-eddy simulation (LES), the detached-eddy simulation (DES) was employed, which can calculate flow fields except near-wall region by LES. The required computational resources were quite large for such simulations, so the computations were conducted on the K computer (RIKEN AICS in Japan).

The simulations were well validated, showing good agreement with the measurement results obtained in the test. In the validation, the effect of the boundary condition for the casing wall was also investigated by comparing the results between the adiabatic boundary condition and the isothermal boundary condition. As for the unsteady effect, the wake/blade interaction was investigated in detail. In addition, unsteady flow phenomena in the present compressor at off-design condition were analyzed by using data mining techniques such as vortex identification and limiting streamline drawing with the LIC (line integral convolution) method. The simulation showed that they could be caused by the corner separation on the hub side.
Wet Gas Compressor Surge Stability
Authors: Ferrara Veronica , Bakken Lars E.
Published: August 2015

The new wet gas compression technology provides a big potential for improved recovery from new and depleting gas/condensate fields. The current technology is based on centrifugal and axial compressor principles, which offers both the benefits of well-known concept design and the drawbacks of erosion, fouling, surge and instabilities.

These concepts are based mainly on the design of a traditional compressor. This partly reflects performance requirements for handling pure gas and partly the lack of a fundamental understanding of wet gas behaviour through an impeller stage. Process and operating conditions may vary considerably during start-up at gas only or completely filled with addition of liquid with an inlet and/or discharge transient flow regime.

An advanced wet gas test rig has been designed to identify the fundamental mechanisms related to wet gas compressor surge and instability behaviour. The open-loop wet gas rig includes a single overhung impeller, sections of visualisation for the wet gas impeller inlet, discharge and diffuser.

The paper reviews and exposes the instabilities and surge flow behaviour at the impeller eye. Main focuses are the shift in inlet flow regime, the impact on overall compressor stage performance and the ability to handle wet transient inlet conditions. Any flow separation and/or slip across the inlet and impeller eye section will alter the established dry gas design guide lines for compressors. Visualisation of the impeller inlet during surge progression is the focal point of the present study. The investigation is supplemented by fast Fourier transform (FFT) analyses and high-speed measurements.
Dynamic Simulation of Energy Systems: Comparison of a Physics-Based Against Time Constant Based Approach Applied to a Microturbine Test Rig
Authors: Roberts Rory A. , Rossi I. , Traverso A.
Published: August 2015

As distributed systems arise as the dominate approach in energy production, new and time-effective methods to study global configuration of small scale generation systems have to be discovered. This work proposes a comparison between two disparate approaches to microturbine modelling. The target system is a modified Turbec T100 microturbine coupled with an external vessel, which aims to simulate the dynamic global behavior of a fuel cell gas turbine hybrid system generator. The first model is based on first principles with ordinary differential equations to capture the dynamic performance of the turbine and it is developed with Matlab/Simulink environment. The second model is based on a simplified-physics time constant approach and it is developed with Excel/Visual Basic software, thus aiming at a viable tool for distributed applications, despite any lose in accuracy. Both models have been verified against the experimental data of the microturbine test rig, and compared in terms of computational efforts, modelling flexibility, prediction accuracy.
A Novel Mixing Plane Method Using Non-Reflecting Boundary Conditions for Multi-Row Analysis in Turbomachines
Authors: Gisbert Fernando , Corral Roque
Published: August 2015

A new formulation of the mixing plane boundary condition to analyze the steady state interaction between adjacent rows of a turbomachine, used in conjunction with steady two-dimensional non-reflecting boundary conditions, is presented. Existing mixing plane formulations rely on the differences between some variables at the rows that conform the mixing plane to determine the boundary condition. These differences are driven to zero as the case is converged to the steady state. By contrast, the proposed approach determines the differences that result in the conservation of mass, momentum and energy after the boundary condition is enforced, ensuring conservation at any instant during the iterative process. The reverse flow within the mixing plane boundary is naturally treated, but both inlet and outlet boundary conditions fail when the mixing plane normal velocity tends to zero, giving rise to sharp variations of the fluid variables that must be properly limited to prevent convergence problems. Some examples will be given to demonstrate the ability of the new method to resolve those cases while preserving the boundary condition robustness.
The Dissipation Function-Based Efficiency for Turbomachinery: Part 2 — The Power of a Cooled Turbine
Authors: Cha Chong M.
Published: August 2015

Euler’s turbine equation is generalized to include cooling flow addition. Euler’s turbine equation for the uncooled case is still used for the design and analysis of today’s cooled turbines. A simple, one-dimensional control volume model is developed to illustrate the impact of cooling flow addition on the turbine power and efficiency. The efficiency measures include the familiar isentropic turbine efficiencies and the dissipation function-based measure, introduced in Part 1 [1] of this work.
Experimentally Determining the Acoustic Damping Rates of a Combustor With a Swirl Stabilized Lean Premixed Flame
Authors: Stadlmair Nicolai V. , Wagner Michael , Hirsch Christoph , Sattelmayer Thomas
Published: August 2015

In this study, we employ a method based on Bayesian statistics to determine the rate of acoustic decay from dynamic pressure measurements inside a combustor. It is common, that lean premixed flames tend to drive thermoacoustic instabilities at specific eigenfrequencies. Hence, the dissipation of acoustic energy inside the combustor, its absorption at the boundaries and its transfer over the in- and outlets must always exceed the acoustic excitation from the flame to avoid pulsations. Quantitative measures for the level of stability are of high technical relevance. In that context the occurring eigenfrequencies and their damping rates are important indicators for the stability margin of gas turbine combustors. A modular swirl burner is investigated in an atmospheric single burner test rig under lean premixed conditions. For the experimental determination of the damping rates, a siren is used to externally excite resonant frequencies of the combustion system. After interrupting the forcing abruptly, time series of the decaying signals are recorded by dynamic pressure sensors inside the combustion chamber. For the analysis of this data, an algorithm based on a Bayesian network approach, which uses a Gibbs Sampler is employed. Probability distributions of frequencies and decay rates are obtained with the Markov-Chain Monte-Carlo (MCMC) method. For the investigated configuration, the influence of the acoustic boundary conditions and the preheat temperature on eigenmodes and damping rates is evaluated. Finally, the results are compared to a network model of the test rig. With that approach, the Open-Loop Gain (OLG) is evaluated for the frequency range of interest. Eigenfrequencies as well as their corresponding damping rates are obtained from Nyquist analysis.
Effect of Rib Angle Orientation on Flow Field in a Two-Pass Parallelogram Channel With 180-Deg Sharp Turn
Authors: Liou Tong-Miin , Chang Shyy-Woei , Chan Shu-Po , Liu Yu-Shuai
Published: August 2015

Detailed flow patterns and turbulence parameters, including secondary-flow mean velocity vector, turbulent intensity, Reynolds stress and turbulent kinetic energy, are compared between three different rib orientations (45-deg, −45-deg, and 90-deg) in a two-pass ribbed-wall parallelogram channel with a 180-deg sharp turn. Velocity measurements were performed with Particle Image Velocimetry (PIV). The channel has a cross-sectional equal length, 45.5 mm, of adjacent sides and two pairs of opposite angles are 45-deg and 135-deg. The rib height-to-hydraulic diameter ratio and pitch-to-height ratio were 0.1 and 10, respectively. All the measurements were performed at a fixed Reynolds number, characterized by channel hydraulic diameter of 32.17 mm, cross-sectional bulk mean velocity, and fluid property of air at room temperature, of 10,000 and a null rotating number. A correlation between pitchwise variations of the reattachment lengths and rib-edge normal mean velocities is found. In addition, a comparison of the spanwise reattachment loci in the present parallelogram channel with those reported previously in the square channels is made. Overall, the 45-deg ribs and −45-deg or 90-deg ribs augment the secondary flow motion most in the first and second pass, respectively. Among the rib orientations investigated, the 45-deg and −45-deg ribs induce a pair of counter-rotating longitudinal vortices that strengthens the inlet-generated secondary flow in the first pass and the 180-deg sharp turn generated secondary flow in the second pass, respectively. One interesting finding is the noticeable difference in the flow characteristics near the top and bottom walls of the parallelogram channel for all three rib angles examined. On the contrary, previous studies with the square channels revealed almost the same heat transfer distributions on the ±45-deg ribbed top and bottom walls.
Assessment of Partial-Admission Characteristics in Twin-Entry Turbine Pulse Performance Modelling
Authors: Chiong Meng Soon , Rajoo Srithar , Romagnoli Alessandro , Costall Aaron W. , Martinez-Botas Ricardo F.
Published: August 2015

One-dimensional modelling of a twin-entry turbine usually considers only the full-admission characteristic in their analysis. However, due to out-of-phase exhaust flow, the actual operating environment is constantly under the intermittent combination of full, unequal and partial-admission conditions. This leads to unsatisfactory on-engine performance prediction, even though some present models have already accounted the finite twin-entry volute and interaction between the volute entries. This paper explores the potential improvement in twin-entry pulse flow model by including the partial-admission characteristics through the established one-dimensional model domain. The predicted results are validated against the experimental data obtained from the Imperial College pulse-flow testing facility. In addition, influences of the quality of partial-admission performance map are also analysed. The mathematical prediction methodology, which was revised from literature works, derived the twin-entry turbine partial-admission characteristics from the known full-admission performance. This study is intended to outline the importance of twin-entry turbine partial-admission characteristics in pulse performance modelling. In comparison to the literature findings, current model has satisfactorily resolved the twin-entry out-of-phase pulse flow performance, particularly the instantaneous actual power. The model prediction shows a twin-entry turbine unsteady swallowing capacity is mostly encapsulated within the quasi-steady full and partial-admission characteristic lines. On the other hand, the unsteady actual power hysteresis curve is found beyond quasi-steady characteristic lines at most instant throughout the pulse cycle.
A Shape Memory Alloy-Based Morphing Axial Fan Blade: Part I — Blade Structure Design and Functional Characterization
Authors: Fortini Annalisa , Suman Alessio , Aldi Nicola , Merlin Mattia , Pinelli Michele
Published: August 2015

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of Shape Memory Alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called Shape Memory Effect (SME) takes place.

This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the non-stationary operating condition. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures were experimentally evaluated by imposing the actual operating thermal gradient.

The SMA strips were then thermo-mechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered.

According to these results, the best coupling of SMA strips and polymeric structure is assessed and its time-wise behavior is compared to the traditional time-wise behavior of a viscous fan clutch.
Analysis and Comparison of Clean vs Inlet Distortion Flow Physics at Design Operating Condition Using Proper Orthogonal Decomposition
Authors: Spencer Ronald A. , Gorrell Steven E. , Jones Matthew R. , Duque Earl P. N.
Published: August 2015

Assessing the impact of inlet flow distortion in turbomachinery is critical to the safe and efficient operation of many engineered systems. This paper introduces and validates the use of methods based on the Proper Orthogonal Decomposition (POD) to analyze clean and 1/rev static pressure distortion simulation results at design operating condition. The value of POD comes in its ability to efficiently extract both quantitative and qualitative information about dominant spatial flow structures as well as information about temporal fluctuations in flow properties. The analysis was used to quantify circumferential varying stage performance in terms of shock location and strength. Since the result of 1/rev total pressure distortion is circumferential varying stage performance, POD is a useful means to analyze and quantify such variation. Observation of the modes allowed qualitative identification of shockwaves as well as quantification of their location and range of motion. Modal coefficients revealed the location of the passage shock at a given angular location. Distortion amplification and attenuation between rotors was also identified.
Ansaldo Energia AE64.3A Gas Turbine Upgrade
Authors: Torbidoni Leonardo , Abba Luca
Published: August 2015

Ansaldo Energia AE64.3A gas turbine is especially effective in small to medium size applications such as grid support, co-generation and district heating applications due its F-class efficiency coupled with proven affordability, optimal size and low life cycle costs. This paper describes the latest AE64.3A gas turbine configuration that is now available. Technical features are presented in detail: the compressor and the hot-section turbine fourth stage have been directly derived from the AE94.3A F-class 310 MW size gas turbine design; the exhaust gas duct improved with profiled struts; the journal and axial-thrust bearing enhanced in performance; a two-steps secondary air optimization strategy for engine performance increase has led the upgrades of the air-cooled turbine stages, of the combustion chamber equipped with ceramic-tiles and of the high-temperature low-NOx burners. The specific burners which are capable of burning low-BTU gas with LHV down to 19 MJ/kg are also described. Finally the technical features of the turbine blades and vanes with maintenance intervals extended to 33’000 Equivalent Operating Hours are presented.
Effect of Porosity on Flow Behavior and Heat Transfer Characteristics of Sintered Woven Wire Mesh Structures
Authors: Yangpeng Liu , Guoqiang Xu , Luo Xiang , Jiandong Ma , Haiwang Li
Published: August 2015

The structure of sintered woven wire mesh is one of classical porous medium. The porosity is one of the major parameters for the porous media. This paper presents the experimental results of the effect of porosity on internal flow behavior and heat transfer characteristics of sintered metal wire mesh structures. All the three test pieces made of stainless steel wires with the same wire diameter (d = 0.14mm) were sintered after woven. One of them was sintered using two sintered metal wire mesh structures with different porosities (55% and 26%) so that the porosity changed along the flow direction. The porosities of the other two test pieces are 55% and 26%, respectively. The experiments were completed with the Reynolds number in the range of 10 to 42. The permeability and inertia coefficient of each test piece were obtained as well as the friction factor. Infrared camera was used to measure the wall temperature of the test pieces to get the Nusselt numbers. The results show that for all test pieces permeability increases as porosity increases, while inertia coefficient shows the opposite trend. Pressure drop of all pieces increases with respect to the mass flow rate. Friction factor decreases as the Reynolds number increases. The curves for test piece #3 fall between those for test piece #1 and #2 and are more close to that for test #2. Nusselt number increases when the Reynolds number keeps arising. However, The Nusselt numbers of the test piece with changed porosity are influenced by the flow direction. There are no significant correlations of the flow behavior and heat transfer characteristics between the test piece with changed porosity and the other two test pieces with constant porosities.
Modeling Thermal Effects on Performance of Small Gas Turbines
Authors: Visser W. P. J. , Dountchev I. D.
Published: August 2015

Gas turbines are applied at increasingly smaller scales for both aircraft propulsion and power generation. Recuperated turboshaft micro turbines below 30 kW are being developed at efficiencies competitive with other heat engines. The rapidly increasing number of unmanned aircraft applications requires the development of small efficient aircraft propulsion gas turbines.

Thermal effects such as steady-state heat losses and transient heat soakage on large engine performance are relatively small and therefore often neglected in performance simulations. At small scales however, these become very significant due to the much higher heat transfer area-to-volume ratios in the gas path components. Recuperators often have high heat capacity and therefore affect transient performance significantly, also with large engine scales. As a result, for accurate steady-state and transient performance prediction of micro and recuperated gas turbines, thermal effects need to be included with sufficient fidelity.

In the paper, a thermal network model functionality is presented that can be integrated in a gas turbine system simulation environment such as the Gas turbine Simulation Program GSP [1]. In addition, a 1-dimensional thermal effects model for recuperators is described. With these two elements, thermal effects in small recuperated gas turbines can be accurately predicted. Application examples are added demonstrating and validating the methods with models of a recuperated micro turbine. Simulation results are given predicting effects of heat transfer and heat loss on steady-state and transient performance.
Desensitization of Axial Compressor Performance and Stability to Tip Clearance Size
Authors: Erler Engin , Vo Huu Duc , Yu Hong
Published: August 2015

This paper presents a computational and analytical study to identify and elucidate fundamental flow features associated with the desensitization of performance and aerodynamic stability of an axial compressor rotor to tip clearance change. Parametric studies of various design change on a baseline double circular arc axial rotor led to the identification of two flow features associated with reducing sensitivity to tip clearance, namely high incoming meridional momentum in the tip region and reduction/elimination of double tip leakage. Numerical experiments were subsequently performed on the baseline rotor geometry to validate these two flow features and explain the associated flow physics by variations in incoming meridional momentum and pitch size. Finally, two designs were proposed, namely full forward chordwise sweep and partially low stagger angle, to exploit these flow features. The results indicated that both designs produce the intended flow effects and exhibit lower performance and aerodynamic stability sensitivity to tip clearance.
Post-Surge Load Prediction for Multi-Stage Compressors via CFD Simulations
Authors: Dumas Martial , Vo Huu Duc , Yu Hong
Published: August 2015

A methodology is proposed and developed for the simulation of post-surge condition in a multi-stage compressor that is part of a gas generator system that also includes the combustor and turbine and ducts. Given the essentially one-dimensional nature of surge, the approach basically consists of coupling single blade passage multi-stage RANS CFD simulations of the compressor for with 1D equations modelling the behaviour of the other components applied as dynamic boundary conditions. This method allows for the simulation of the flow behaviour inside a multi-stage compressor during surge and, by extension, for the prediction at the design phase of the time variation of aerodynamic forces on the blades and of the pressure and temperature at bleed locations inside the compressor used for turbine cooling. The main advantages of this method over existing methods are its relatively modest computational time and resource requirements and the fact that it does not require any empirical data input beyond what is used in standard CFD simulations.

The method is implemented in a commercial CFD code (ANSYS CFX) and applied to three compressor geometries with distinct features. Simulations on a low-speed (incompressible) three stage axial compressor allows for a validation with experimental data, which shows that the proposed methodology captures the surge behaviour of the system very well both qualitatively and quantitatively. This comparison also highlights the strong dependence of the surge cycle frequency on the volume of the downstream plenum (combustion chamber). Subsequently, the addition of a low-speed centrifugal compressor to the previous compressor is used to demonstrate the adaptability of the approach to a multi-stage axial-centrifugal configuration, yielding qualitatively realistic surge results. Finally, application of the method to an industrial transonic compressor geometry demonstrates the tool on a mixed flow-centrifugal compressor configuration operating in a highly compressible flow regime. A comparison of predicted versus measured shaft loading amplitude during surge is highly promising.
Parametric Study for Lossless Casing Treatment on a Mixed-Flow Compressor Rotor
Authors: Djeghri Noureddine , Vo Huu Duc , Yu Hong
Published: August 2015

A systematic numerical study has been carried out to investigate the effects of casing treatment slots geometry and location on the stall margin and peak efficiency of an isolated mixed-flow rotor at high subsonic flow conditions. Based on the literature review for axial rotor, a semi-circular axial skewed slot casing treatment placed in the leading edge region was chosen as the starting configuration as it has the best potential of producing stall margin improvement with low peak efficiency loss. A computational parametric study was performed from this baseline casing treatment geometry to identify the most important geometrical design parameters and to arrive at a design with noticeable stall margin improvement and no loss in peak efficiency. The results show that the design parameters with the largest impact on stall margin improvement and peak efficiency are: open area ratio, slot skew angle, slot axial length and slot axial position. The slots depth and slot shape seem to have only limited influence on performance. While not yet optimized, a slot casing treatment design with significant stall margin improvement and no loss in peak efficiency was obtained. To the authors’ knowledge, this work is the most extensive slot casing treatments parametric study so far in term of number of design parameters considered.
Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement
Authors: Harrington John , Nayebzadeh Arash , Winn Jonathan , Wang Wenping , Kapat Jayanta , Maurer Michael , Thorpe Steven
Published: August 2015

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D=31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 50,000 to 150,000 are tested. A steady-state measurement technique utilizing Temperature Sensitive Paint is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2-f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius, the decay of heat transfer after the impingement section and to check the open literature correlations. It was found that the target wall curvature caused higher heat transfer levels, with array-average Nusselt numbers increasing by an average of 28% when compared to the similar plane case. In the post-impingement section, increases in heat transfer levels were also seen with the curved case by up to 60%. Finally, CFD results were able to show agreement in stagnation point Nusselt number levels with experimental results for the curved target plate.
Precession Effects on the Relationship Between Time-Averaged and Instantaneous Swirl Flow and Flame Characteristics
Authors: Chterev I. , Sundararajan G. , Seitzman J. M. , Lieuwen T. C.
Published: August 2015

Swirling flows exhibit a variety of unsteady fluid mechanic features, including large scale vortical structures and precessing recirculation zones. This paper considers the specific influence of precession on the relationship between time-averaged and instantaneous flow and flame features. The objective of this study is to aid in developing insight into high fidelity computations or experimental results. In particular, we describe how certain topological features in the time-averaged flow, such as centerline axial jets, centerline stagnation points, and symmetry of the flow about the centerline are influenced by precession. Insight is built by presenting results from a simplified model of a two-zone flow, consisting of a precessing reverse flow region embedded in a positive axial flow. A particularly significant result of this work is in regards to aerodynamically stabilized flames, which rely on the low velocity interior stagnation points in the vortex breakdown region for flame stabilization. We show how precession causes systematic differences between the location of the stagnation point of the time-averaged velocity and the time-averaged position of the instantaneous stagnation point. Indeed, an important implication of this point is that a perfect prediction of the time-averaged flow field could still lead to a completely erroneous time-averaged flame position prediction. Finally, we discuss the influence of precession and coherent motion on convergence of estimated averaged quantities.
Design of a Small Scale Gas Turbine for a Hybrid Propulsion System
Authors: Bryner Elliott , Ransom David , Bishop John , Coogan Shane , Musgrove Grant
Published: August 2015

As part of the Great Horned Owl (GHO) program Southwest Research Institute© (SwRI©) has developed a small, lightweight gas-turbine generator to provide power for an electric or hybrid electric Unmanned Aerial Vehicle (UAV). This original design for a fuel-to-electricity component of a hybrid propulsion system was designed, built and tested at the SwRI facility in San Antonio, TX. The design is based on a patented SwRI gas-turbine configuration and went through five major design iterations leading to the final configuration. The design iterations of the gas generator were driven by aggressive targets for weight, size and performance that were part of program requirements. The design of the GHO machine evolved from the initial concept based on lessons learned from previous testing at SwRI and considerations to improve manufacturability and operability. Improvements to the design were also incorporated to meet performance goals and increase life of hot section parts.

This machine is low-cost and simple to operate and in addition to the original design intent of fuel-to-electricity use in a hybrid propulsion system can be used as a technology demonstration platform. SwRI plans to use the GHO machine in projects such as instrumentation development, as a test bed for new technologies such as ceramic or additive manufactured parts and for use as a component in a hardware-in-the-loop system.
Optimizing Amine Process Design Using Liquid Phase Turbochargers
Authors: Krish Prem , Gains-Germain Andrea , Thorp Joseph , Martin Jeremy , Shirazi Max
Published: August 2015

Acid gas removal is a critical process step in natural gas processing and syngas production for ammonia and other uses. Application of a liquid phase turbocharger to the acid gas removal unit (AGRU) results in significant energy savings and improvement to reliability, availability and maintainability (RAM) of the plant. This paper describes conventional configurations with high pressure pumps and new configurations utilizing liquid phase turbochargers. Design of the equipment, process operations and controls and reliability analysis are included. The results of a RAM study comparing conventional configurations to those incorporating liquid phase turbochargers in multiple cases are also presented. From the RAM study, it can be concluded that flow sheet configurations that include a liquid phase turbocharger consistently provide lower plant downtime and maintenance costs as compared with conventional flow sheet configurations. This is in addition to the energy savings that result from energy recovery with the application of the liquid phase turbocharger to the AGRU. For the reference plant used in the study, the maintenance cost savings are as great as $2.5M over the 20 year lifetime of the plant and average annual downtime reduction is as much as 19.8 hours.
Broadband Sound Power Determination With Modal Decomposition
Authors: Xu Kun-Bo , Qiao Wei-Yang , Tong Fan , Chen Wei-Jie , Wang Liang-Feng
Published: August 2015

For the assessment and improvement of noise reduction concepts and the validation of broadband sound power determination in flow ducts, the detailed knowledge of the in-duct acoustic mode spectrum and subsequent broadband noise sources separation is of great interest. A broadband noise mode analysis method was experimentally applied on broadband sound fields at 4 operation points, which were generated by means of a low speed fan test rig. Two axial sensor arrays were mounted wall-flush upstream of the fan. Measurements were made at operating conditions from 40% to 100% rotor design speed. On the whole, broadband mode waves transmitted in the flow direction is 2dB higher than against the flow direction. Mode amplitude results show that the mode decomposition results strongly depend on the chosen reference microphone. Sound power becomes higher as the speed increases. The deviation of results in and against flow directions calculated with different reference microphones is 4dB at all the operation points except for 40% design speed. A deviation of almost 10dB appears in broadband sound power results with different reference microphone in the frequency range, much higher than the results of previous experiment. The method is more accurate if it considers the phenomenon that mode waves in turbo-machinery are partly correlated with each other.
Analysis of Laminar-Turbulent Transition of a Low-Loss Generic Low Pressure Turbine Distribution
Authors: Brück Christian , Lyko Christoph , Peitsch Dieter , Bode Christoph , Friedrichs Jens , Kožulović Dragan , Fiala Andreas , Guendogdu Yavuz
Published: August 2015

The efficiency of modern Turbofan engines can be significantly increased by using a gearbox between compressor and turbine of the low pressure section. Rotational speed of the low pressure turbine (LPT) in a Geared Turbofan is much higher than in normal LPT’s which lead to necessary adjustments in blade design.

This work has investigated the transition behavior of a modified profile geometry for low-loss at engine cruise conditions. Typical LPT conditions have thus been chosen as baseline for the experimental work. A pressure distribution has been created on a flat plate by means of contoured walls in a low speed wind tunnel. The paper will analyze the experimental results and show additionally the numerical predictions of the test case.

The experimental part of this paper describe how the blade was Mach number scaled to obtain the geometry of the wind tunnel wall contour. The pressure distribution for the incompressible test case show a very good agreement to the compressible case. Boundary layer (BL) measurements with hot-wire-anemometry have been performed at high spatial resolution under a freestream turbulence of almost 8%. Different Reynolds numbers have been investigated and will be compared with special attention being paid to the transition on the suction side by contour plots (turbulence levels, turbulent intermittency) and integral BL parameters. It was found that the transition on the suction side is not completed for small Reynolds numbers but takes place at higher velocities.

In the numerical part studies by means of steady RANS simulations with k-ω – SST turbulence model and γ-Reθ transition model have been conducted. The aim is to validate the RANS solver for the low-loss LPT application. Hence, comparison is made to the measured data and the transitional behavior of the BL. Furthermore, additional parameter variations have been conducted (turbulence intensity and Reynolds number).

The numerical investigations show partially a good comparison for the BL development indicating the different transition modi with increasing Reynolds number and turbulence intensity.
Interaction of Secondary Flow With Developing, Turbulent Boundary Layers in a Rotating Duct
Authors: Wei Kuan , Tao Zhi , Deng HongWu , You RuQuan
Published: August 2015

Investigations of the interaction of secondary flow with developing, turbulent boundary layer in a rotating square-section straight channel have been done in a new rotating facility with normal hot wire anemometry. The measurements are performed with Re=18391 and Ro=0, 0.116, 0.232, respectively, characterized by the channel hydraulic diameter of 80 mm and the bulk mean velocity. Measurements at five stations distributed in the streamwise direction have been done to study the turbulent boundary layer streamwise development. The mean velocity profiles in both ordinary and semi-logarithm coordinates and skin shear velocities at these test stations are obtained. On the leading side, the skin shear velocity firstly decreases, and then increases in the streamwise direction. This phenomenon is analogous to the critical rotation number phenomenon revealed in previous work with heat transfer. Based on this analogy, a new possible explanation of the critical rotation number phenomenon is given here. The semi-logarithm mean velocity profile is found to not obey the traditional log-law linear rotation correction. This suggested the need of a secondary flow strength correction of the log law with system rotation.
Aerothermal Characterization of a Rotating Ribbed Channel at Engine Representative Conditions: Part I — High Resolution PIV Measurements
Authors: Mayo Ignacio , Gori Gian Luca , Lahalle Aude , Arts Tony
Published: August 2015

The present work is part of a detailed aero-thermal investigation in a model of a rotating internal cooling channel performed in a novel facility setup which allows test conditions at high Rotation numbers (Ro). The test section is mounted on a rotating frame with all the required instrumentation, resulting in a high spatial resolution and accuracy. The channel has a cross section with an aspect ratio of 0.9 and a ribbed wall with 8 ribs perpendicular to the main flow direction. The blockage of the ribs is 10% of the channel cross section, whereas the rib pitch to height ratio is 10. In this first part of the paper, the flow over the wall region between the 6th and 7th ribs in the symmetry plane is investigated by means of two-dimensional Particle Image Velocimetry (PIV). Tests were carried out at a Reynolds number (Re) of 15000 in static and rotating conditions, with a maximum Ro of 0.77. Results are in good agreement with the data present in literature at the same Reynolds number and with Rotation numbers of 0 (static conditions) and 0.38 in a channel with the same geometry as in the present work. When Ro is increased from 0.38 to 0.77, the main velocity and turbulence fields show important changes. At a Rotation number of 0.77, although the extension of the recirculation bubble after the 6th rib on the trailing side does not vary significantly, it covers the full inter-rib area on the leading side in the stream-wise direction. The turbulence intensity on the leading side shows a low value with respect to the static case but roughly at the same level as in the lower Ro case. On the trailing side, the maximum value of the turbulence intensity slightly decreases from Ro=0.38 to Ro=0.77, the wall shear layer is re-stabilized along the second half of the pitch due to the high rotation, and the secondary flows are redistributed causing span-wise vortex compression. The observed result is the rapid decay of turbulent fluctuations in the second half of the inter-rib area.
The Impact of Blade Loading and Unsteady Pressure Bifurcations on Low-Pressure Turbine Flutter Boundaries
Authors: Waite Joshua J. , Kielb Robert E.
Published: August 2015

The three major aeroelastic issues in the turbomachinery blades of jet engines and power turbines are forced response, non-synchronous vibrations, and flutter. Flutter primarily affects high-aspect ratio blades found in the fan, fore high-pressure compressor stages, and aft low-pressure turbine (LPT) stages as low natural frequencies and high axial velocities create smaller reduced frequencies. Often with LPT flutter analyses, physical insights are lost in the exhaustive quest for determining whether the aerodynamic damping is positive or negative. This paper underlines some well known causes of low-pressure turbine flutter in addition to one novel catalyst. In particular, an emphasis is placed on revealing how local aerodynamic damping contributions change as a function of unsteady (e.g. mode shape, reduced frequency) and steady (e.g. blade torque, pressure ratio) parameters. To this end, frequency domain RANS CFD analyses are used as computational wind tunnels to investigate how aerodynamic loading variations affect flutter boundaries. Preliminary results show clear trends between the aerodynamic work influence coefficients and variations in exit Mach number and back pressure, especially for torsional mode shapes affecting the passage throat. Additionally, visualizations of qualitative bifurcations in the unsteady pressure phases around the airfoil shed light on how local damping contributions evolve with steady loading. Final results indicate a sharp drop in aeroelastic stability near specific regions of the pressure ratio indicating a strong correlation between blade loading and flutter. Passage throat shock behavior is shown to be a controlling factor near the trailing edge, and like critical reduced frequency, this phenomenon is shown to be highly dependent on the vibratory mode shape.
An Iterative Inverse Design Method of Turbomachinery Blades by Using Proper Orthogonal Decomposition
Authors: Luo Jiaqi , Tang Xiao , Duan Yanhui , Liu Feng
Published: August 2015

This paper presents an iterative inverse design methodology based on proper orthogonal decomposition (POD) and its applications to the inverse design of turbomachinery blades. In the aerodynamic system with a number of snapshots, the aerodynamic performance with the corresponding aerodynamic shape within the design space can be described as a linear combination of a series of POD basis modes. In the present paper, the description ability of Gappy POD is evaluated firstly and the influence of different parametrization methods and different snapshot approaches are studied and compared in detail. In the POD-based inverse design, the aerodynamic shape can be obtained by only one design process. However, due to the error between the predicted aerodynamic performance by Gappy POD and that obtained from computational fluid dynamics, an iterative inverse design methodology is proposed herein based on the error correction to the target aerodynamic performance. Three inverse design studies of turbomachinery blades are performed. In the first two cases, the profiles of two-dimensional turbine blades are modified to approach the target pressure distributions on the blade surface in subsonic and transonic flow, respectively. In the third case, a three-dimensional supersonic turbine blade is restaggered along span to achieve a given loading distribution in the spanwise direction at the outlet. The design results are presented and compared in detail, demonstrating the effectiveness and improved accuracy of the POD-based iterative inverse design method.
Analysis of Turbofan Performance Under Total Pressure Distortion at Various Operating Points
Authors: Weston David B. , Gorrell Steven E. , Marshall Matthew L. , Wallis Carol V.
Published: August 2015

Inlet distortion is an important consideration in fan performance. The focus of this paper is a series of high-fidelity time accurate Computational Fluid Dynamics (CFD) simulations of a multistage fan at choke, design, and near stall operating conditions. These investigate distortion transfer and generation as well as the underlying flow physics of these phenomena under different operating conditions. The simulations are performed on the full annulus of a 3 stage fan and are analyzed. The code used to carry out these simulations is a modified version of OVERFLOW 2.2. The inlet is specified as a 1/rev total pressure distortion. Analysis includes the phase and amplitude of total temperature and pressure distortion through each stage of the fan and blade loading. The total pressure distortion does not change in severity through the fan, but the peak pressure distortion rotates by as much as 45° at the near stall point. This is due to a variation in the work input around the blades of the rotor. This variation is also responsible for the generation of total temperature distortion in the fan. The rotation of the total temperature distortion becomes more pronounced as the fan approaches stall, and the total temperature distortion levels increase. The amount of work performed by a single blade can vary by as much as 25% in the first stage at near stall. The variation in work becomes more pronounced as the fan approaches stall. The passage shock in the rotor blades moves nearly 20% of the blade chord in both the peak efficiency and near stall cases.