bluuebunny/crossref_metadata_2025 huggingface dataset:
Dry-Friction Whip and Whirl Predictions for a Rotor-Stator Model With Rubbing Contact at Two Locations
Authors: Childs Dara W. , Kumar Dhruv
Published: May 2012

The present work investigates the phenomena of whip and whirl for a rigid rotor contacting at two bearing locations. The idea originated with a paper by Clark et al. in 2009 on an anemometer undergoing dry friction whip and whirl. The anemometer rotor was supported by two Teflon® bushings within an elastically supported housing. The dry-friction forces arose at the bushings. Prior models for dry friction whirl and whip have considered rub at one non-support location. The present analytical model consists of a rigid rotor connected to a rigid stator at two rubbing contact locations. Analytical solutions are developed for the following normal reaction forces at the contact locations: (1) In phase, and (2) 180 degrees out of phase. Analytical solutions are only possible for the same RCl (Radius to Clearance ratio) at the two rub locations and define regions where dry-friction whirl is possible plus indication possible boundaries between whirl and whip. These solutions are similar to Black’s in 1968. A flexible-rotor/flexible-stator model with nonlinear connections at the bearings was developed to more correctly establish the range of possible solutions. The nonlinear connections at the rub surface are modeled using Hunt and Crossley’s 1975 contact model with coulomb friction. Dry friction simulations are performed for the following rotor center of gravity (C.G.) configurations: (1) Centered, (2) 3/4 contact-span location and (3) Overhang location outside the contacts. Results from the in-phase analytical solutions and the nonlinear simulations agree to some extent with the rotor mass centered and at 3/4 location in that whirl-to-whip transitions occur near the pinned rotor-stator bounce frequency. For the overhung mass case, the nonlinear simulation predicts whip at different frequencies for the two contact locations. Neither analytical solution modes predicts this outcome. No out-of-phase solutions could be obtained via time-transient simulations. Dry-friction whirling is normally characterized as supersynchronous precession with a precession frequency equal to running speed times RCl. Simulation predictions for models with different RCl mimic whirling. Simulation predictions show increasing backward precessional (BP) frequency with increasing rotor speeds. However, individual contact velocities show slipping at all conditions. Slipping is greater at one location than the other, netting a “whirl-like” motion. For the overhung model with different RCl ratios, apart from whipping at different frequency the two contacts also whirl at different frequencies corresponding to the RCl at the respective contacts. Simulations predict a different running speed for the “jump up” in precession frequency associated with a transition from whirl-to-whip with increasing running speed than for the jump-down in precession frequency for whirl-to-whip in a speed-decreasing mode.
On Remaining Life Analysis of Turbine Disks Subjected to High Thermal Stresses
Authors: Iyengar Vishwas , James Stephen , Simmons Harold
Published: May 2012

Disk failures can be caused by a number of mechanisms under the turbine operating conditions of high rotational speed at elevated temperatures. It is not uncommon for highly stressed turbine blades and disks to operate at temperatures in excess of 1,000°F, where increased exposure can affect their life. In the past, it has been adequate to analyze the life of these high temperature components using methods which calculate creep life and low cycle fatigue life independently in predicting service hours. More often than not, the parameters included in the creep life model are based on empirical data. Here, a practical methodology is presented to predict the remaining life of a turbine disk that utilizes a combination of Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA) and a creep model. A full three-dimensional CFD analysis is performed on the turbine disks at design and off-design conditions, in order to accurately capture the thermal loads. A detailed FEA is performed on the turbine disk. The stress inputs for the creep life model are based on the stresses obtained from the FEA. A case study is presented that utilizes the proposed methodology. It is found that the methodology is beneficial for the remaining life analysis on highly loaded turbine disks. The accuracy of the methodology is somewhat dictated by the amount of historical operating data that is available.
CFD Simulations of Flow and Heat Transfer in a Pre-Swirl System: Influence of Rotating-Stationary Domain Interface
Authors: Karnahl Joachim , von Wolfersdorf Jens , Tham Kok-Mun , Wilson Mike , Lock Gary
Published: May 2012

This paper presents computational fluid dynamic (CFD) predictions of flow and heat transfer for an over-swirled low-radius pre-swirl system and comparison with experimental data. The rotor-stator CFD model comprises a stationary domain with the pre-swirl nozzles and a rotating domain with the receiver holes. The fluid-dynamic conditions feature an over-swirled system with a swirl ratio at the nozzle radius βp = 1.4–1.5 and rotational Reynolds number Reφ = 0.8×106 and 1.2×106. Three different treatments for the rotating and stationary domain interface are used to evaluate the influence on the flow and heat transfer behavior: a stationary approach (including Coriolis forces in the rotating domain) with “direct connection” and fixed angle between pre-swirl nozzle and receiver holes; a stationary approach with circumferential averaging of the velocity at radial bands; and a full transient simulation with the rotating domain capturing the unsteady flow due to the rotating receiver holes. Results at different circumferential angles show high variability in pressure and velocity distributions at the pre-swirl inlet nozzle radius. Circumferential averaging of these flow parameters lead to an alignment of the pressures and velocities between the three different interface approaches. Comparison with experimental pressure and swirl-ratio data show a quantitative agreement but the CFD results feature a systematic overestimation outward of the pre-swirl nozzle radius. Heat transfer contours at the rotor surface show the effect of the different interface approaches and dependence on the flow structure (for example the impinging jet and vortex structures). The three different interface approaches result in significant differences in the computed heat transfer coefficients between pairs of receiver holes. Circumferentially averaged heat transfer coefficients inward of the receiver holes radius show good agreement between the transient and stationary direct connection interfaces, whereas those for the circumferential averaging interface differ, contrary to the flow parameters, due to smoothing of local effects from the pre-swirl jets.
Novel Approach for Loss and Flow-Turning Prediction Using Optimized Surrogate Models in Two-Dimensional Compressor Design
Authors: Schmitz Andreas , Aulich Marcel , Nicke Eberhard
Published: May 2012

Two-dimensional (2D) streamline curvature methods are still an important tool in modern compressor design. In the past most of the streamline curvature methods made use of empirical correlations to approximate the blade row losses and deviation functions on which the accuracy of streamline curvature methods mainly depend. These empirical correlations are just accurate for a small set of geometric airfoil design parameters for which they where obtained and the prediction of airfoil performance at high Mach numbers or at off-design condition is inaccurate. Nowadays, a new approach is needed to consider highly customized, modern airfoil geometries with an increased number of design parameters. A new method with the possibility to predict the performance of these highly customized airfoils also at off-design condition and high Mach numbers is presented in this paper. This method uses a large airfoil database together with optimized surrogate models to accurately predict airfoil performance. The database consists of approximately 106 randomly created airfoils with randomly created inflow conditions and the airfoil performance which results from the 2D Euler-boundary layer code MISES [16]. The airfoil geometry in this database is described by ten geometrical parameters, e.g. stagger angle, chord length etc.. The flow condition is described by four flow parameters such as the relative inflow Mach number, MVDR, relative inflow angle and Reynolds number. Airfoil performance is represented by total pressure loss and flow-turning. This database was used to train neural networks that provides the relationship between the geometrical/flow parameters and the airfoil performance. The topology of the neural networks was optimized to achieve a model which represents this highly nonlinear functionality at best. This model was integrated in the DLR’s in-house streamline curvature tool ACDC which is based on the equations of MO¨NIG et al. [12], GALLIMORE [8]. The code allows viscous throughflow calculations taking into account radial mixing by turbulent diffusion, endwall boundary layers and a model for tip clearance based on the work of DENTON [7], KRO¨GER et al. [9].
Characteristics of Bluff Body Stabilized Turbulent Premixed Flames
Authors: Briones Alejandro M. , Sekar Balu , Thornburg Hugh
Published: May 2012

Non-reacting and reacting flows past typical flameholders are modeled with URANS and LES. The continuity, momentum, energy, species, and turbulence governing equations are solved using two- and three-dimensional configurations. Either 2-step global or 44-step reduced chemical mechanism for C3H8-air combustion, accounting for turbulence-chemistry interaction, and with temperature- and species-dependent thermodynamic and transport properties is utilized. For square and rectangular bluff bodies the flow separates at the leading edges, whereas for triangular bluff body separation occurs only at the trailing edges. These bluff bodies exhibit two shear layers at the trailing edges that shed asymmetric vortices. For rectangular bluff bodies with aspect ratios (AR) less than 2.3 there is backflow from the wake. With increasing AR from unity, backflow is gradually diminished, and the von Ka´rma´n Strouhal number (StvK) decreases. For 2.0<AR<2.3, StvK jumps to a higher value and separation again occurs at the trailing edges for AR = 2.3. Further increase in AR decreases StvK again. The simulations with URANS qualitatively and quantitatively match experimental results for StvK vs. AR. Quantitative discrepancies are, however, found for AR≥2.3. In addition, two-dimensional non-reacting flows with URANS are sufficient to predict StvK. Moreover, two-dimensional simulations of reacting flow indicate that the flame promotes static and dynamic stability for AR = 1.0 and 2.3. The flame is dynamically unstable for AR = 2.0, exhibiting a von Ka´rma´n flow pattern. Stable flames anchored at the most downstream separation location (e.g., the flame anchored at AR = 1.0 is attached to the leading edge, whereas that of AR = 2.3 is attached to the trailing edge). Realizable k-ε URANS and LES simulations for the triangular cylinder closely match the experimental StvK for both non-reacting and reacting flows. Nonetheless, LES predicts a smaller recirculation length than k-ε URANS. LES predicts a flow field in which Be´rnard/von Ka´rma´n (BvK) instability is suppressed, whereas URANS predicts a competition between the Kelvin-Helmholtz (KH) instability and BvK.
Development of a PLC Based Controller for Marine Gas Turbine Generator
Authors: Godbole Amrut Dilip , Gulati Ankush , Bhagwat Alok
Published: May 2012

The advent of processor based controllers including the PLC has provided a low cost alternative for up gradation of control systems when faced with the challenges of maintenance and obsolescence. A project was undertaken at the Centre of Marine Engineering Technology of the Indian Navy to design, develop and test a PLC based controller for a Gas Turbine Generator as an alternative to the legacy relay logic based control system. The paper explains the methodology adopted towards the various stages of the development of the PLC based controller using Commercially-Off-The-Shelf (COTS) items. It also brings out the salient advantages offered as a result of this transformation.
Conditional Moment Closure LES Modelling of an Aero-Engine Combustor at Relight Conditions
Authors: Stow Simon R. , Zedda Marco , Triantafyllidis Antonios , Garmory Andrew , Mastorakos Epaminondas , Mosbach Thomas
Published: May 2012

A Conditional Moment Closure (CMC) approach embedded in an LES CFD framework is presented for simulation of the reactive flow field of an aero-engine combustor operating at altitude relight conditions. Before application to the combustor geometry, the CMC model was validated on the standard lab-scale Sandia flame D. For the combustor simulation, a global mechanism for n-heptane was used along with a Lagrangian approach for the spray, to which a secondary break-up model was applied. The simulation modelled a multi-sector sub-atmospheric rig that was used to verify the altitude relight capability of the combustor. A comprehensive suite of diagnostics was applied to the rig test, including high-speed OH and kerosene PLIF as well as high speed OH* chemiluminescence. The CMC-based CFD simulation was able to predict well the position of the flame front and fuel distribution at the low pressure, low temperature conditions typical of altitude relight. Furthermore, the simulation of the ignition showed strong similarities with OH* chemiluminescence measurements of the event. An EBU-based LES was run too and showed to be unable to capture the flame front as well as the CMC model could. This work demonstrates that CMC LES can be an effective tool to support assessment of the relight capability of aero-engine combustors.
Validation of an Ignition and Flame Propagation Model for Multiphase Flows
Authors: Boyde J. M. , Le Clercq P. , Di Domenico M. , Rachner M. , Gebel G. C. , Mosbach T. , Aigner M.
Published: May 2012

This paper presents a numerical investigation of a generic lab scale combustor with focus on the ignition characteristics. The test case has been examined thoroughly in a comprehensive measurement campaign to provide a detailed set of boundary conditions and a profound data base of results. The experimental setup comprises five parallel-aligned mono-disperse droplet chains which are ignited, using a focused laser beam. One aspect of the experimental study is the ignitability with respect to the imposed boundary conditions. The second covers the growth and the propagation of the flame after the establishment of an initial kernel. The outcome of the numerical simulations is compared to the experimental results which allows an in-depth assessment of the employed numerical models. The chemistry and, thus, the flame propagation behavior is captured by a turbulent flame speed closure approach with an adaptation to render the model suitable to multiphase flows. For the dispersed phase a Lagrangian particle tracking scheme is employed in combination with a continuous thermodynamics fuel model for the evaporation. The overall good agreement demonstrates the capability of a multiphase flow CFD solver in the field of ignition modeling.
Criteria for Boundary Layer Transition
Authors: Becker Stefan , McEligot Donald M. , Walsh Edmond , Laurien Eckart
Published: May 2012

New results are deduced to assess the validity of proposed transition indicators when applied to situations other than boundary layers on smooth surfaces. The geometry employed utilizes a two-dimensional square rib to disrupt the boundary layer flow. The objective is to determine whether some available criteria are consistent with the present measurements of laminar recovery and transition for the flow downstream of this rib. For the present data — the proposed values of thresholds for transition in existing literature that are based on the freestream turbulence level at the leading edge are not reached in the recovering laminar run but they are not exceeded in the transitioning run either. Of the pointwise proposals examined, values of the suggested quantity were consistent for three of the criteria; that is, they were less than the threshold in laminar recovery and greater than it in the transitioning case.
Experimental Analysis of Confined Jet Flames by Laser Measurement Techniques
Authors: Lammel Oliver , Sto¨hr Michael , Kutne Peter , Dem Claudiu , Meier Wolfgang , Aigner Manfred
Published: May 2012

An experimental analysis of confined premixed turbulent methane/air and hydrogen/air jet flames is presented. A generic lab scale burner for high-velocity preheated jets equipped with an optical combustion chamber was designed and set up. The size and operating conditions were configured to enable flame stabilization by recirculation of hot combustion products. The geometry of the rectangular confinement and an off-center positioning of the jet nozzle were chosen to resemble one burner nozzle of a FLOX®-based combustor. The off-center jet arrangement caused the formation of a pronounced lateral recirculation zone similar to the one in previously investigated FLOX®-combustors [1, 2]. The analysis was accomplished by different laser measurement techniques. Flame structures were visualized by OH* chemiluminescence imaging and planar laser-induced fluorescence of the OH radical. Laser Raman scattering was used to determine concentrations of the major species and the temperature. Velocity fields were measured with particle image velocimetry. Results of measurements in two confined jet flames are shown. The mixing of fresh gas with recirculating combustion products and the stabilization of the methane flame are discussed in detail. The presented findings deliver important information for the understanding of confined jet flames operated with different fuels. The obtained data sets can be used for the validation of numerical simulations as well.
Combustor and Augmentor Combustion Modeling for LES Based on Stochastic Model Parameterization
Authors: Calhoon William H. , Zambon Andrea C. , Sekar Balu , Kiel Barry
Published: May 2012

A new modeling formulation for turbulent chemistry interactions in large eddy simulation (LES) is presented that is based on a unique application of the linear-eddy model (LEM) that includes large scale strain effects. This novel application of the LEM may be used to predict turbulent flame extinction limits due to both small and large scale strain effects. Statistics from this modeling formulation may be used to generate an inexpensive run-time model for LES predictions. This paper presents the LEM modeling formulation and demonstrates the capabilities of the approach for augmentor conditions. A methodology is also presented to formulate a LES subgrid model based on the simulation data.
Altitude Performance of a Turbojet With Alternate Fuels
Authors: Davison Craig R. , Chishty Wajid A.
Published: May 2012

To enhance energy security and reduce the environmental impact of aviation, alternate fuels derived from various non-petroleum based sources are being developed. Currently alternate fuels are produced to match the properties of existing jet fuels allowing the new fuels to be used in current fleets concurrently with traditional jet fuel. The alternate fuels must, therefore, perform as well as the traditional fuels through the entire operating envelope. This paper provides the results of performance testing in an altitude chamber up to 11,300 m (35,000 feet) with a simulated forward speed up to Mach 0.75. The test engine was an instrumented 1.15 kN thrust turbojet burning conventional Jet A-1 as a baseline; a semi-synthetic blend of camelina based hydro processed renewable jet and JP8; a blend of 50% Fischer-Tropsch synthetic paraffinic kerosene and 50% JP8; and a 100% Fischer-Tropsch synthetic paraffinic kerosene. Both steady state and transient performance are presented. The theoretical effect of the alternate fuels for a simple idealized Brayton cycle is also presented. The work was conducted as part of on-going efforts by departments within the Government of Canada to systematically assess alternative aviation fuels.
Magnetic Resonance Imaging Studies of Flow and Mixing for Single-Hole Film Cooling
Authors: Issakhanian Emin , Elkins Chris J. , Eaton John K.
Published: May 2012

Magnetic resonance imaging (MRI) measurement techniques are used to reveal the coupled 3D velocity and coolant concentration fields for a single film cooling hole with L/D of 4, ejection angle of 60°, and blowing ratios of 0.5 and 1. The jet exits into a boundary layer with momentum thickness of 0.1D. Magnetic resonance velocimetry (MRV) measures 3 component mean velocity everywhere within the channel, cooling hole, and feed plenum. Magnetic resonance concentration (MRC) provides the coolant concentration distribution which is directly analogous to film cooling effectiveness. The coupled velocity and concentration show that high velocity ratios lead to a detached jet which lowers effectiveness. Vorticity from the feed hole creates a streamwise oriented counter rotating vortex pair which lifts the coolant stream from the surface and sweeps in main channel flow inducing a kidney-shape to the coolant jet cross-section. Without the need for optical access, MRV allows study of the flow inside the feed hole including the entrance separation and secondary flows. Cross-stream feeding of the cooling hole shows added spanwise asymmetry at the hole entrance, but this asymmetry is significantly reduced moving up the hole.
First Generation Graz Cycle Power Plant for Near-Term Deployment
Authors: Sanz W. , Hustad Carl-W. , Jericha H.
Published: May 2012

Carbon Capture and Storage (CCS) is a recognized technology pathway to curb the increasing emissions of carbon dioxide (CO2) from the power generation sector. But most available technologies are still on the study or laboratory-scale level, so that considerable R&D efforts are needed to achieve commercialization level. The Graz Cycle originally presented in 1995 by Jericha [1] is an oxyfuel technology and promises highest efficiency using state-of-the-art turbine materials and improved thermodynamic developments in a comparatively complex interaction of rotating machinery, condensers and heat exchanger components. But although detailed conceptual design for all main components has been presented, there is still a large step towards a Graz Cycle pilot demonstration plant. In order to facilitate construction of a demonstration plant we consider the performance of a near-term Graz Cycle process design based on modest cycle data and available turbomachinery components using a simplified flow scheme. The work is supported by on-going development work for a first generation oxyfuel turbine that has already been undertaken by Clean Energy Systems, Inc. [2]. Their further work on a second generation oxyfuel turbine received $30 million funding support from the U.S. Department of Energy in September 2010 [3]. Two near-term Graz Cycle plants are presented based on basic and advanced operating conditions of the proposed commercially available turbine. Besides the turbine the additional equipment for a first-generation cycle is discussed. The predicted optimum net efficiency is 23.2% (HHV). A near-term zero-emission power plant can only be commercially attractive if it will be deployed in a niche market. Therefore an economic analysis commensurate with an early pre-FEED conceptual study is carried out for the U.S. Gulf Coast where revenue from multiple product streams that could include power, steam, CO2 and water, as well as argon and (potentially) nitrogen from the ASU is provided. The economic analysis suggests that a capital investment of $94 million can secure construction of a 13.2 MWe zero emission oxyfuel power plant and yield a 14.5% (unlevered) return on capital invested.
Statistical and Theoretical Models of Ingestion Through Turbine Rim Seals
Authors: Zhou Kunyuan , Wood Simon N. , Owen J. Michael
Published: May 2012

In recent papers, orifice models have been developed to calculate the amount of ingestion, or ingress, that occurs through gas-turbine rim seals. These theoretical models can be used for externally-induced (EI) ingress, where the pressure differences in the main gas path are dominant, and for rotationally-induced (RI) ingress, where the effects of rotation in the wheel-space are dominant. Explicit ‘effectiveness equations’, derived from the orifice models, are used to express the flow rate of sealing air in terms of the sealing effectiveness. These equations contain two unknown terms: Φmin, a sealing flow parameter, and Γc, the ratio of the discharge coefficients for ingress and egress. The two unknowns can be determined from concentration measurements in experimental rigs. In this paper, maximum likelihood estimation is used to fit the effectiveness equations to experimental data and to determine the optimum values of Φmin and Γc. The statistical model is validated numerically using noisy data generated from the effectiveness equations, and the simulated tests show the dangers of drawing conclusions from sparse data points. Using the statistical model, good agreement between the theoretical curves and several sets of previously-published effectiveness data is achieved for both EI and RI ingress. The statistical and theoretical models have also been used to analyse previously-unpublished experimental data, the results of which are included in separate papers. It is the ultimate aim of this research to apply the effectiveness data obtained at rig conditions to engine-operating conditions.
Combustion Emission Measurements With Preheated Jet Fuel
Authors: Zheng Qing-ping , Yun Sangsig , Titirica Dan , Sampath Sam , Yimer Ibrahim
Published: May 2012

Jet fuel thermal stability at high temperature is receiving increased attention recently as advanced aero engines are being pushed to high power, high pressure and temperature regimes for improved engine cycle performance and low emissions. This paper describes the rig experimental tests to assess the high fuel temperature effect on combustor emissions. A special test rig facility has been designed and set up for emission measurements with preheated fuel. The purpose of the tests is to evaluate the combustor emission characteristics under nominal and elevated fuel temperatures. The scope of the project is two fold: (1) to design, procure and establish a dedicated hot fuel deoxygenation, fuel preheat facility that can reach temperature up to 600 °F (589 K); (2) to measure combustion emissions, mainly NOx, CO and UHC, at normal and elevated fuel temperature under representative engine operating conditions. The test rig has run for extended duration and proved reliable over the whole test campaign. Measured emission results show that fuel temperature effect on NOx, CO, UHC emissions are marginal, possibly due to the low emission capability of the sector combustor that is less sensitive to fuel inlet condition changes than other combustor designs. These results indicate a manageable risk for engine development with elevated fuel temperature from the emission viewpoint.
Heat Transfer, Hydrodynamics and Pressure Drop in the Model of a Blade Leading Edge Cyclone Cooling
Authors: Khalatov Artem A. , Borisov Igor I. , Severin Sergey D. , Romanov Vyacheslav V. , Spitsyn Vladimir Y. , Dashevskyy Yuriy Y.
Published: May 2012

The heat transfer, hydrodynamics and pressure drop have been studied experimentally at the air swirling flow in the round tube with 90° exit bend, simulating the blade cyclone cooling. The flow was supplied into the test section from the closed circular plenum through one or two tangential slots (swirl generators) made on the round tube surface. The flow angle to the first swirl generator was 60° (β = 0° is the “classic” tangential inlet). The following three configurations, reflecting the actual blade design, were studied, namely: (i) the tube with one swirl generator and open exit, (ii) the tube with one swirl generator and 90° exit bend, (iii) the tube with two swirl generators and 90° exit bend. The Reynolds number, based on the average axial velocity and tube internal diameter was ranged from 40000 to 105000. The surface streamline swirl flow angle, static and total pressure excess, heat transfer and pressure losses in the round tube, swirl generator area and exit bend were measured. In terms of the heat transfer rate the best results has demonstrated the configuration with one swirl generator and 90° exit bend.
Probabilistic High-Cycle Fatigue Risk Assessment of an Integrally Bladed Rotor
Authors: Hall Benjamin D. , Gray Lauren
Published: May 2012

A fully probabilistic high-cycle fatigue (HCF) risk assessment methodology for application to turbine engine blades is described. The assessment uses the Bayesian paradigm of probability theory in which probability distributions are used to encode states of knowledge. Multi-level (or hierarchical) models are employed to capture engineering knowledge of the factors important for assessing HCF risk. This structure allows us to use standard probability distributions to adequately represent uncertainties in model parameters. The model accounts for engine-to-engine, run-to-run, and blade-to-blade variability as well as uncertainty in material capability, usage (flight conditions, time at resonance), and steady and vibratory stresses. Markov chain Monte Carlo (MCMC) simulation is used to fit observed data to the engineering models, then direct Monte Carlo simulation is used to assess the HCF risk.
Effects of Pulsating Flow Conditions on Mixed Flow Turbine Performance
Authors: Chen Li , Zhuge Weilin , Zhang Yangjun , Xie Lei , Zhang Shuyong
Published: May 2012

Turbines work under actual pulsating flow conditions due to the operating characteristics of a reciprocating internal combustion engine. The pulsating flow conditions affect the flow fields in a turbine, and lead to obvious difference between actual and steady performance. A three-dimensional numerical investigation into mixed flow turbine under different kinds of pulsating flow conditions was conducted, in order to get an inner sight of the unsteady impact. The effects of the pulsation frequency and amplitude on the turbine performance were analyzed. The results show that the period average performance of the turbine under pulsating conditions is lower than the steady performance under the mean pulsating conditions. The actual power output varies little with the pulsation frequency changing, while the phase lag increases as the pulsation frequency increases. The unsteady characteristics become more obvious when the pulsation amplitude increases. Under the pulsating flow conditions, of which amplitude is 0.8, the period average efficiency is 4.11 percent lower than the steady efficiency. The flow fields fluctuate seriously under this high pulsating flow conditions. The occurrence and vanishing of the votex are dynamic procedures, and hysteresis effect is observed in the unsteady flow.
Experimental and Analytical Study on the Operation Characteristics of the AHAT System
Authors: Araki Hidefumi , Koganezawa Tomomi , Myouren Chihiro , Higuchi Shinichi , Takahashi Toru , Eta Takashi
Published: May 2012

Operational flexibility, such as faster start-up time or faster load change rate, and higher thermal efficiency, have become more and more important for recent thermal power systems. The AHAT (advanced humid air turbine) system has been studied to improve operational flexibility and thermal efficiency of the gas turbine power generation system. AHAT is an original system which substitutes the WAC (water atomization cooling) system for the intercooler system of the HAT cycle. A 3MW pilot plant, which is composed of a gas turbine, a humidification tower, a recuperator and a water recovery system, was built in 2006 to verify feasibility of the AHAT system. In this paper, ambient temperature effects, part-load characteristics and start-up characteristics of the AHAT system were studied both experimentally and analytically. Also, change in heat transfer characteristics of the recuperator of the 3MW pilot plant was evaluated from November 2006 to February 2010. Ambient temperature effects and part-load characteristics of the 3MW pilot plant were compared with heat and material balance calculation results. Then, these characteristics of the AHAT and the CC (combined cycle) systems were compared assuming they were composed of mid-sized industrial gas turbines. The measured cold start-up time of the 3MW AHAT pilot plant was about 60min, which was dominated by the heat capacities of the plant equipment. The gas turbine was operated a total of 34 times during this period (November 2006 to February 2010), but no interannual changes were observed in pressure drops, temperature effectiveness, and the overall heat transfer coefficient of the recuperator.
Heat Transfer in an Oblique Jet Impingement Configuration With Varying Jet Geometries
Authors: Schueren Simon , Hoefler Florian , von Wolfersdorf Jens , Naik Shailendra
Published: May 2012

Experimental and numerical heat transfer results in a trapezoidal duct with two staggered rows of inclined impingement jets are presented. The influence of changes in the jet bore geometry on the wall heat transfer is examined. The goal of this project is to minimize the thermal load in an internal gas turbine blade channel and to provide sufficient cooling for local hot spots. The dimensionless pitch is varied between p/djet = 3–6. For p/djet = 3, cylindrical as well as conically narrowing bores with a cross section reduction of 25% and 50%, respectively, are investigated. The studies are conducted at 10,000 ≤ Re ≤ 75,000. Experimental results are obtained using a transient thermochromic liquid crystal technique. The numerical simulations are performed solving the RANS equations with FLUENT using the low-Re k-ω-SST turbulence model. The results show that for greater pitch, the decreasing interaction between the jets leads to diminished local wall heat transfer. The area averaged Nusselt numbers decrease by up to 15% for p/djet = 4.5, and up to 30% for p/djet = 6, respectively, if compared to the baseline pitch of p/djet = 3. The conical bore design accelerates the jets, thus increasing the area-averaged heat transfer for identical mass-flow by up to 15% and 30% for the moderately and strongly narrowing jets, respectively. A dependency of the displacement between the Nu maximum and the geometric stagnation point from the jet shear layer is shown.
Development of an Edge-Based Harmonic Balance Method for Turbomachinery Flows
Authors: Corral Roque , Crespo Javier
Published: May 2012

An harmonic balance method for modeling unsteady nonlinear periodic flows in turbomachinery is presented. The method solves the Reynolds Averaged Navier-Stokes equations in the time domain and may be implemented in a relatively simple way into an existing code including all the standard convergence acceleration techniques used for steady problems. The application of the method to vibrating airfoils and rotorstator interaction is discussed. It is demonstrated that the time spectral scheme may achieve the same temporal accuracy at a lower computational cost at the expense of using more memory.
Advanced Experimental and Analytical Investigations on Combined Cycle Fatigue (CCF) of Conventional Cast and Single-Crystal Gas Turbine Blades
Authors: Weser Swen , Gampe Uwe , Raddatz Mario , Parchem Roland , Lukas Petr
Published: May 2012

Rotor blades are the highest thermal-mechanical loaded components of gas turbines. Their service life is limited by interaction of creep, low cycle fatigue (LCF), high cycle fatigue (HCF) and surface attack. Because assurance of adequate HCF strength of the rotor blade is an important issue of the blade design the European project PREMECCY has been started by the European aircraft engine manufacturers and research institutes to enhance the predictive methods for combined cycle fatigue (CCF), as a superposition of HCF and LCF. Although today’s predictive methods ensure safe blade design, there are certain shortcomings of assessing fatigue life with Haigh or “modified Goodman diagrams”, such as isolated HCF assessment as well as uni-axial and off-resonant testing. HCF and LCF are considered without taking into account their interaction. PREMECCY is aimed to deliver new and improved CCF prediction methods for exploitation in the industrial design process. Beside development of predictive methods the authors are involved in the design and testing of advanced specimens representing rotor blade features. In this connection the paper presents a novel test specimen type and a unique hot gas rig for CCF feature test at mechanical and ambient representative conditions.
Detailed Characterisation of a Swirled Air/Kerosene Spray in Reactive and Non-Reactive Conditions Downstream From an Actual Turbojet Injection System
Authors: Lecourt Renaud , Linassier Guillaume , Lavergne Ge´rard
Published: May 2012

As part of the investigations of the ignition of jet-engines under altitude conditions, a detailed data base was built with the results of experiments on the two-phase flow produced by an actual swirl air/kerosene turbojet injection system. The injection system had a fairly simple geometry. It was used with liquid kerosene injected through a pressure-swirl fuel atomiser. In this case the measurements were carried out at atmospheric pressure in a windowed combustion chamber, with air at ambient temperature. The tested equivalence ratio was 0.95 which corresponds to an air mass flow rate of 0.035 kg/s. For this operating point, we obtained the velocity field of the gas phase under non-reactive conditions by LDA. The axial velocity component of the gas phase was also measured in the burning spray using an original method with a phase Doppler device. The data recorded with the PDA were also processed to obtain the kerosene droplet sizes and velocities under reactive conditions. The same phase Doppler device was used in non-reactive conditions to measure the size and velocity distributions of the kerosene droplets in a section close to the injection system exit in order to complete the data base with the boundary conditions for the liquid phase. In addition the flame was visualised qualitatively. The picture of the stabilized flame was processed with an Abel transform to compare the LDA/PDA measurements with the flame structure, obtained under the reactive conditions. Finally, unsteady pressure measurements were taken under non-reactive conditions and the LDA measurements processed, close to the injection system exit, to get the PVC (Precessing Vortex Core) frequency. The data were analysed to determine the influence of the spray combustion on the two-phase flow. The geometry of the whole experimental setup and the data base are available to other researchers for testing and validating spray combustion models and unsteady two-phase flow numerical simulations.
Effect of Turbine Airfoil Shape on Aerodynamic Losses for Turbine Airfoils Operating Under Transonic Conditions
Authors: Abraham Santosh , Panchal Kapil , Ekkad Srinath V. , Ng Wing , Brown Barry J. , Malandra Anthony
Published: May 2012

Profile and secondary loss correlations have been developed and improved over the years to include the induced incidence and leading edge geometry and to reflect recent trends in turbine design. All of these investigations have resulted in better understanding of the flow field in turbine passages. However, there is still insufficient data on the performance of turbine airfoils with high turning angles operating at varying incidence angles at transonic Mach numbers. The paper presents detailed aerodynamic measurements for three different turbine airfoils with similar turning angles but different aerodynamic shapes. Midspan total pressure loss, secondary flow field, and static pressure measurements on the airfoil surface in the cascades are presented and compared for the three different airfoil sets. The airfoils are designed for the same velocity triangles (inlet/exit gas angles and Mach number). Airfoil curvature and true chord are varied to change the loading vs. chord. The objective is to investigate the type of loading distribution and its effect on aerodynamic performance (pressure loss). Measurements are made at +10, 0 and −10 degree incidence angles for high turning turbine airfoils with ∼127 degree turning. The cascade exit Mach numbers were varied within a range from 0.6 to 1.1. In order to attain a ratio of inlet Mach number to exit Mach number that is representative to that encountered in a real engine, the exit span is increased relative to the inlet span. This results in one end wall diverging from inlet to exit at a 13 degree angle, which simulates the required leading edge loading as seen in an engine. 3D viscous compressible CFD analysis was carried out in order to compare the results with experimentally obtained values and to further investigate the flow characteristics of the airfoils under study.
A Practical Approximate Method to Predict Adjusting Performance of a Centrifugal Compressor Stage With Inlet Guide Vane
Authors: Liu Changsheng , Tan Jiajian , Qi Datong , Wang Xuejun , Qin Guoliang
Published: May 2012

This paper has proposed a method for predicting an adjusting performance curve family of a centrifugal compressor stage with the inlet guide vane (IGV). The method can be separated into two steps. In the first step, a centrifugal compressor model stage is selected as a basic model stage to build the basis of prediction. Both the ordinary performance curve of the model stage without IGV and the adjusting performance curve family of the model stage at various setting angles of the IGV are obtained by experiments. Then, using the ordinary performance curve as a criterion, a non-dimensional mathematical relationship is set up between the ordinary performance curve and each curve in the adjusting performance curve family. In the second step, based on the relationship established above, a prediction is made for the adjusting performance curve family of another centrifugal compressor stage with an IGV. For this prediction, two conditions must be satisfied: 1) The adjustment must be done using the IGV of the same type as used in the first step; 2) The ordinary performance curve of the predicted model stage must have been obtained experimentally. By applying the method, a prediction was carried out for the IGV adjusting performance curve family of a centrifugal compressor stage. Comparison between the predicted results and experimental results shows that although there is relatively great discrepancy between the basic model stage and the predicted stage under the mechanical geometric construction and operating conditions, the two results agree well in most of the areas of the adjusting performance curve family. There are only greater errors of predicted results in areas of large IGV setting angle. Although the current method has some deficiencies, it still possesses some strength featuring simplicity, convenience and reliability, thus providing a practical approximate prediction method available for the centrifugal compressor manufacturers that have the model stage database, but lack the APCF for the model stages with IGV.
Experimental and Numerical Study on Effects of Turbulence Promoters on Flat Plate Film Cooling
Authors: Sakai Eiji , Takahashi Toshihiko
Published: May 2012

Turbulence promoters such as ribs inside turbine blade coolant channels are used to improve convective cooling but at the same time could influence external film cooling performance. The effects of rib orientation and rib position on film cooling performance are experimentally and numerically studied with a flat plate configuration in which external (main) flow and internal (secondary) flow are oriented perpendicular to each other. In the experiment, temperature fields are measured by thermo-couples varying blowing ratio at constant Reynolds number of main and secondary flows. To obtain detailed information about flow fields, Reynolds Averaged Navier Stokes (RANS) simulation and Detached Eddy Simulation (DES) are also performed using a commercial code Fluent. Temperature measured shows that rib orientation has a strong influence on film effectiveness. With forward-oriented ribs, higher film effectiveness is observed compared to the reference case without ribs. On the contrary with inverse-oriented ribs, lower film effectiveness is observed. The difference comes from the flow structure in the film cooling hole. With the forward-oriented ribs, straight stream lines are observed in the cooling hole, while with the inverse-oriented ribs, helical stream lines are observed. Due to the helical stream lines in the hole, ejection angle of the secondary flow to the main stream becomes large, resulting in so called lift-off and lower film effectiveness.
Prediction of Turbine Rotor Blade Forcing due to In-Service Stator Vane Trailing Edge Damage
Authors: Meyer Marcus , Parchem Roland , Davison Peter
Published: May 2012

In the following paper we will present an overview on the results of a research project whose objective is the assessment of the influence of trailing edge material loss of high pressure turbine nozzle guide vanes onto the low engine order excitation of the downstream rotor blade. To quantify the forcing, the modal forces for the rotor eigenmodes of interest are obtained by solving the unsteady Navier-Stokes equations for a full assembly of stator and rotor ring. Since the computing resources for such a calculation are too high to be routinely employed for the assessment of in-service damage patterns, an important task of the project was to investigate quick alternatives to the costly CFD simulations. The approach chosen is to perform a sufficient number of forced response calculations with different damage patterns in advance and use the results to build a surrogate model that can be used to assess the severity of damage patterns by simple interpolation. We will first present the analysis chain employed to quantify the forcing, next describe the approach to build a surrogate model with special focus on the generation of an optimal DoE matrix, and finally discuss the prediction accuracy of the surrogate model. It is shown that an interpolating surrogate model, based on radial basis functions, can successfully be used to predict the rotor forcing for damage patterns that were not analyzed using the costly CFD calculations beforehand.