bluuebunny/crossref_metadata_2025 huggingface dataset:
A Practical Approach to Implementing Linear Elastic Fracture Mechanics in Gas Turbine Rotor Disk Analyses
Authors: Keller Scott
Published: August 2015

The failure of vital components is not uncommon in the gas turbine industry. In the event excessive degradation occurs within a component, e.g. extensive cracking in a turbine blade or vane, solutions exist to either repair or replace defective parts. Such parts are readily accessible and mostly exchangeable in the field, limiting the amount of outage time and assessment required for defective parts. When more critical components exhibit extreme wear or cracking, e.g. a crack in a rotor disk, repairs typically necessitate a complete rotor destack and refurbishment or have the potential to require the replacement of individual disks. In extreme cases, defects found in rotor disks can be known to retire an entire compressor or turbine rotor. The OEM solution of replacing disks puts a substantial cost on the customer, thus providing an incentive for characterization and advanced analyses to determine the residual life in critical rotating components.

Considered an advanced analysis, linear elastic fracture mechanics (LEFM) provides the theory and fundamental structure to conduct crack growth analyses in components that exhibit nominally elastic behavior. Successful implementation of LEFM requires extensive characterization of the material, engine operating boundary conditions, and high fidelity finite element models. Upon the detection of a flaw, whether an internal or external indication, the results from finite element analyses can be used to derive the crack tip stress field and subsequent crack tip driving parameters. These parameters are then utilized in a comprehensive crack propagation model, calibrated to temperature- and load-dependent material data, to determine the number of cycles to unstable propagation. As a result, the remaining life of a component with a given indication is readily obtained, enabling our engineering team to provide a thorough life assessment of critical rotating components.

An overview of the linear elastic fracture mechanics crack growth analyses conducted is presented, with a special emphasis on compressor and turbine disks.
Large Eddy Simulation and CO Prediction of Reheat Burner Switch-Off Concept
Authors: Kulkarni Rohit , Duesing Michael , Ferreira-Providakis Theodoros , Marchione Teresa
Published: August 2015

The reduction of the Minimum Environmental Load (MEL) is a key requirement for increased operational flexibility of Combined Cycle Power Plants (CCPP). In reheat combustors, the MEL is in general limited by CO emissions. The sequential combustion system used in Alstom GT24/GT26 gas turbines [1, 2] offers a unique operation concept, namely Low Part Load operation concept with switched off SEV burner (LPL). This concept is able to significantly reduce CO and thus MEL. Details of the CO formation mechanisms for this concept are analyzed via unsteady CFD calculations. These results are used to predict CO emissions for the full engine. Results are validated against experiments on full engine scale. Field implementation of the LPL concept and validation experience collected during long term commercial operation is described in a separate paper [4].
Consistent Conceptual Design and Performance Modeling of Aero Engines
Authors: Samuelsson Sebastian , Kyprianidis Konstantinos G. , Grönstedt Tomas
Published: August 2015

During the conceptual design process of an engine, a thermodynamic cycle is initially defined. This is done to ensure that all aircraft requirements, defined in a number of discrete operating points, can be met. Critical component requirements can then be screened off from these operating points underpinning the conceptual design process. As an example, this has traditionally meant that aerodynamic sizing for low specific thrust turbofan engines occurs at top-of-climb and mechanical and temperature constraints are set at take-off.

By providing additional parameters indicating the level of technology assumed, such as diffusion factors and stage loadings, a basic geometric representation of the engine can be mapped out as part of the conceptual design process. However, by choosing the parameters representing the component technology levels explicitly, the ability to trade efficiency for weight, or efficiency for cost, becomes less potent. In general, an explicit parameter choice will mean that a suboptimal solution is found.

Hence, it makes sense to develop methods that allow including these technology parameters into the conceptual design and performance modeling process in a consistent way. If, for instance, component efficiency is modeled based on turbomachinery stage loading, including the stage loading parameters into the optimization means that the efficiency must be updated based on the stage loading variation. In general, a consistent method requires that conceptual design input is collected in a number of performance operating points, transferred into the conceptual design process and that output from the conceptual design process is returned to the optimizer.

To illustrate the consistent conceptual design and performance modeling process, turbomachinery component models are included in the paper, interrelating polytropic efficiency, Reynolds number, size effects and component entry into service. These equations are solved consistently in the conceptual design and performance modeling to establish an optimum year 2020 engine. The method is then further illustrated by comparing the year 2020 engine with two year 2030 engines. The first year 2030 engine is established by an optimization assuming fixed polytropic turbomachinery efficiencies. The other case is defined by assuming the same engine architecture, i.e., the same number of turbomachinery stages as the year 2020 engine. In this case, the efficiency modeling is done using a consistent conceptual design optimization. The consistent optimization produced a more efficient engine despite the fact that the stage numbers were limited to the year 2020 configuration. The benefit is obtained by more thoroughly exploring the pressure ratio distribution between the engine components, as a result of the consistent optimization methodology.
Life Prediction of Power Turbine Components for High Exhaust Back Pressure Applications: Part I — Disks
Authors: Dua Dipankar , Vasantharao Brahmaji
Published: August 2015

Industrial and aeroderivative gas turbines when used in CHP and CCPP applications typically experience an increased exhaust back pressure due to pressure losses from the downstream balance-of-plant systems. This increased back pressure on the power turbine results not only in decreased thermodynamic performance but also changes power turbine secondary flow characteristics thus impacting lives of rotating and stationary components of the power turbine.

This Paper discusses the Impact to Fatigue and Creep life of free power turbine disks subjected to high back pressure applications using Siemens Energy approach.

Steady State and Transient stress fields have been calculated using finite element method. New Lifing Correlation [1] Criteria has been used to estimate Predicted Safe Cyclic Life (PSCL) of the disks. Walker Strain Initiation model [1] is utilized to predict cycles to crack initiation and a fracture mechanics based approach is used to estimate propagation life. Hyperbolic Tangent Model [2] has been used to estimate creep damage of the disks.

Steady state and transient temperature fields in the disks are highly dependent on the secondary air flows and cavity dynamics thus directly impacting the Predicted Safe Cyclic Life and Overall Creep Damage. A System-level power turbine secondary flow analyses was carried out with and without high back pressure. In addition, numerical simulations were performed to understand the cavity flow dynamics. These results have been used to perform a sensitivity study on disk temperature distribution and understand the impact of various back pressure levels on turbine disk lives.

The Steady Sate and Transient Thermal predictions were validated using full-scale engine test and have been found to correlate well with the test results. The Life Prediction Study shows that the impact on PSCL and Overall Creep damage for high back pressure applications meets the product design standards.
Experimental Investigation and Numerical Analysis on Influence of Foundation Excitation on the Dynamics of the Rotor System
Authors: Yan Wenzhong , Shaposhnikov Konstantin , Yu Pingchao , Ma Yanhong , Hong Jie
Published: August 2015

Rotor system of modern aero-engine together with the case mounted on the wing represents a uniform system that is supposed to be considered as a rotor-bearings-foundation structure. Nowadays rotating machinery such as modern aircraft engines usually designed, marketed and sold for the most part based on analytical and numerical predictions. In such a way methods to incorporate the foundation effect in rotordynamic calculations are very important. For investigation purposes a rotor-foundation test rig, which can simulate the aero-engine’s typical operating condition such as wing vibration and hard landing, was built to study the influence of foundation behavior on the dynamic characteristics of rotor system. To predict natural frequencies for the full system simplified models based on FEM approach were created. Moreover, simple numerical model was created to study influence of foundation kinematic excitation on behavior of rotor disk orbit. Furthermore simulation results were compared with experimental to understand influence of main parameters which define foundation vibration on rotor deviation from normal operation condition. Obtained numerical and experimental results can help to understand principles of rotating structure-foundation interaction when the later one subjected to excitation and could be further used for improving of more complicated models for design and enhancement of aircraft engines.
Dynamic Spur Geared Rotor Analysis of a Multi-Shaft Turbine With Gear Parameters
Authors: Shiau T. N. , Wang C. R. , Liu D. S. , Wang W. C. , Hsu W. C.
Published: August 2015

The dynamic analysis of the multi-shaft turbine rotor equipped with a spur gear pair for the various gear parameters is studied. Main components of the multi-shaft turbine rotor system include the outer shaft, the inner shaft, the impeller shaft, the oil shaft and the ball bearings. The global assumed mode method (GAMM) is applied to model the rotor motion and the system equation of motion is formulated using Lagrange’s approach. The dynamic behavior of the geared multi-shaft turbine rotor system includes the natural frequency, mode shape and unbalanced response. Numerical results show that large vibration amplitude is observed in steady state at self-excited rotating speed adjacent to the natural frequency. There is no influence of the various pressure angle, modulus, and modification coefficients on unbalance response. Contrary to above cases, the variation of the system unbalance response is dominated by the tooth types rather than the other gear parameters.
Loss Audit of a Turbine Stage
Authors: Yoon Sungho , Vandeputte Thomas , Mistry Hiteshkumar , Ong Jonathan , Stein Alexander
Published: August 2015

In order to achieve high aerodynamic efficiency of a turbine stage, it is crucial to identify the source of aerodynamic losses and understand the associated loss generation mechanisms. This helps a turbine designer to maximize the performance of the turbine stage.

It is well known that aerodynamic losses include profile, endwall, cooling/mixing loss, leakage, and trailing edge loss components. However, it is not a trivial task to separate one from the others because different loss sources occur concurrently and they interact with each other in a machine. Consequently, designers tend to rely on various empirical correlations to get an approximate estimate of each aerodynamic loss contribution.

In this study, a systematic loss audit of an uncooled turbine stage has been undertaken by conducting a series of numerical experiments. By comparing entropy growth across the turbine stage, aerodynamic losses are broken down within the stator, rotor, and inter-bladerow gap. Furthermore, losses across each blade row are broken down into profile, leakage, endwall and trailing edge losses. The effect of unsteady interaction due to the relative motion of the stator and the rotor was also identified.

For the examined turbine stage, trailing edge losses of the rotor dominated, contributing to more than a third of the total aerodynamic loss. The profile loss across the stator and the rotor, unsteady loss between the stator and the rotor, and the stator endwall loss were also identified to be significant loss sources for this turbine stage. The design implications of the findings are discussed.
Numerical Investigation of the Flow Field and Mixing in a Swirl-Stabilized Burner With a Non-Swirling Axial Jet
Authors: Tanneberger Tom , Reichel Thoralf G. , Krüger Oliver , Terhaar Steffen , Paschereit Christian Oliver
Published: August 2015

In the present study numerical results of simulations, using RANS and LES, of the non-reacting flow in a swirl-stabilized burner are presented. The burner was developed for lean premixed combustion with high fuel flexibility at low emissions. An important challenge for a fuel-flexible, low emission combustor is the prevention of flashback for fuels of high reactivity, such as hydrogen, without compromising on lean blow out safety and mixing quality. Flashback safety can be increased by a sufficiently high and uniform axial velocity at the end of the mixing tube. In the investigated combustor the velocity deficit in the center of the mixing tube, which results from the swirl, is prevented by a non-swirling axial jet. In a parametric study the effect of different amounts of axial injection on the flow field is investigated. The results are validated with experimental data, gained from PIV measurements in a vertical water tunnel. It is shown that the mean flow field can be well captured by steady-state RANS simulations using a realizable k-ε turbulence model. The most suitable geometry is identified and, subsequently, transient LES simulations are conducted. The dynamic flow field characteristics are investigated. It was found that in spite of the high swirl, the flow field is quite stable and no dominating frequency is detected. The flow field of the swirling flow in the combustion chamber can be captured well using LES. Furthermore, the mixing quality is compared to the experiments, which are performed in a water tunnel. In contrast to the RANS simulation, the LES can qualitatively capture the spatial unmixedness observed from experimental data. All simulations were conducted using water as fluid.
Waste Heat Recovery in a Cruise Vessel in the Baltic Sea by Using an Organic Rankine Cycle: A Case Study
Authors: Ahlgren Fredrik , Mondejar Maria E. , Genrup Magnus , Thern Marcus
Published: August 2015

Maritime transportation is a significant contributor to SOx, NOx and particle matter emissions, even though it has a quite low CO2 impact. New regulations are being enforced in special areas that limit the amount of emissions from the ships. This fact, together with the high fuel prices, is driving the marine industry towards the improvement of the energy efficiency of current ship engines and the reduction of their energy demand. Although more sophisticated and complex engine designs can improve significantly the efficiency of the energy systems in ships, waste heat recovery arises as the most influent technique for the reduction of the energy consumption. In this sense, it is estimated that around 50% of the total energy from the fuel consumed in a ship is wasted and rejected in fluid and exhaust gas streams. The primary heat sources for waste heat recovery are the engine exhaust and the engine coolant. In this work, we present a study on the integration of an organic Rankine cycle (ORC) in an existing ship, for the recovery of the main and auxiliary engines exhaust heat. Experimental data from the operating conditions of the engines on the M/S Birka Stockholm cruise ship were logged during a port-to-port cruise from Stockholm to Mariehamn over a period of time close to one month. The ship has four main engines Wärtsilä 5850 kW for propulsion, and four auxiliary engines 2760 kW used for electrical consumers. A number of six load conditions were identified depending on the vessel speed. The speed range from 12–14 knots was considered as the design condition, as it was present during more than 34% of the time. In this study, the average values of the engines exhaust temperatures and mass flow rates, for each load case, were used as inputs for a model of an ORC. The main parameters of the ORC, including working fluid and turbine configuration, were optimized based on the criteria of maximum net power output and compactness of the installation components. Results from the study showed that an ORC with internal regeneration using benzene would yield the greatest average net power output over the operating time. For this situation, the power production of the ORC would represent about 22% of the total electricity consumption on board. These data confirmed the ORC as a feasible and promising technology for the reduction of fuel consumption and CO2 emissions of existing ships.
Controlling Corner Stall Separation With Plasma Actuators in a Compressor Cascade
Authors: Akcayoz Eray , Vo Huu Duc , Mahallati Ali
Published: August 2015

This paper presents a numerical and experimental assessment of a plasma actuation concept for controlling corner stall separation in a highly-loaded compressor cascade. CFD simulations were first carried out to assess actuator effectiveness and determine the best actuation parameters. Subsequently, experiments were performed to demonstrate the concept and confirmed the CFD tool validity at a Reynolds number of 1.5×105. Finally, the validated CFD tool was used to simulate the concept at higher velocities, beyond the experimental capability of existing plasma actuators. These results were used to obtain a preliminary scaling law that would allow approximation of the plasma actuation requirements at realistic operating conditions. Several configurations were examined, but the most effective setup was found to be when plasma actuators were mounted upstream of the separation point on both the suction surface and the endwall. Most of the improvement in total pressure loss stemmed from the suction surface actuator. Comparison with experimental data showed that the CFD simulations could capture the flow features and the effect of plasma actuation reasonably well. Simulations at higher flow velocities indicated that the required plasma actuator strength scales approximately with the square of the Reynolds number.
High-Fidelity Simulations of Low-Pressure Turbines: Effect of Flow Coefficient and Reduced Frequency on Losses
Authors: Michelassi V. , Chen L. , Pichler R. , Sandberg R. , Bhaskaran R.
Published: August 2015

Large Eddy Simulations validated with the aid of Direct Numerical Simulation are used to study the concerted action of reduced frequency and flow coefficient on the performance of the T106A low-pressure-turbine profile. The simulations are carried out by using a discretization in space and time that allows minimizing the accuracy loss with respect to Direct Numerical Simulation. The reference Reynolds number is 100,000, while reduced frequency and flow coefficient cover a range wide enough to provide valid qualitative information to designers. The various configurations reveal differences in the loss generation mechanism that blends steady and unsteady boundary layer losses with unsteady wake ingestion losses. Large values of the flow coefficient can alter the pressure side unsteadiness, and the consequent loss generation. Low values of the flow coefficient are associated with wake fogging and reduced unsteadiness around the blade. The reduced frequency further modulates these effects. The simulations also reveal a clear trend of losses with the wake path, discussed by conducting a loss-breakdown analysis that distinguishes boundary layer from wake distortion losses.
Numerical Analysis of Bladed Disk-Casing Contact With Friction and Wear
Authors: Almeida P. , Gibert C. , Thouverez F. , Ousty J.-P.
Published: August 2015

In order to increase the aerodynamic performances of their engines, aircraft engine manufacturers try to minimize the clearance between rotating and stationary parts in axial and centrifugal compressors. Consequently, the probability of contact increases, leading to undesirable phenomena caused by forced excitation of the natural modes, or by modal interaction. Due to the complexity of these phenomena, many numerical studies have been conducted to gain a better understanding of the physics associated with them, looking primarily at their respective influence on potential unstable behaviors. However, the influence of other physical phenomena, such as friction and wear, remains poorly understood. The aim of this work is to show some effects associated with friction and wear on the dynamic behavior resulting from blade-to-casing interaction.

The numerical study reported here is based on a simplified finite element model of a rotating bladed disk and a flexible casing. The contact algorithm uses an explicit time marching scheme with the Lagrange multipliers method. Friction and wear are formulated using respectively Coulomb’s and Archard’s Laws. The rotational speed is set to critical speed giving rise to modal interaction between a backward mode of the casing and a counter-rotating mode of the bladed disk with one nodal diameter. Contact is initiated by a dynamic excitation of the stator.

In the presence of friction, the system becomes unstable when a sideband of the excitation frequency coincides with a one nodal diameter mode of the bladed disk. The introduction of wear leads to a vibration reduction, while the abradable material is removed by the wear process. The number of wear lobes produced on the casing is related to the ratio between the vibration frequency of the blades and the rotating speed. The ratio obtained by means of the FE model corroborates experimental observations.
Effect of Centrifugal Force on the Performance of High-G Ultra Compact Combustor
Authors: Briones Alejandro M. , Burrus Dave L. , Erdmann Timothy J. , Shouse Dale T.
Published: August 2015

A numerical investigation of reacting flows in an advanced high-g cavity (HGC), Ultra-Compact Combustor (UCC) concept is conducted. The high-g cavity UCC (UCC-HGC) design uses high swirl in a circumferential cavity (CC) wrapped around a main stream annular flow. The high swirl is generated through angled CC driver jets. This centrifugal force is varied by changing the CC-to-core air mass flow ratio (ṁcc/ṁcore) and jet inclination angle (αjet) relative to the cavity ring surface, while maintaining the global equivalence ratio (ϕGlobal) constant. Steady, rotational periodic, 3D simulations are performed following a multiphase, Reynolds-averaged Navier-Stokes (RANS), and non-premixed flamelet/progress variable (FPV) approach using a customized FLUENT. Results indicate that under non-reacting flow conditions the driver jets impose a very strong bulk swirl flow within the CC and the mainstream flow does not entrain into the CC. Thus, the maximum g-load is primarily sensitive to ṁcc/ṁcore and secondarily to αjet. However, the g-loads become increasingly more sensitive to the latter at greater ṁcc/ṁcore. Now, under reacting flow conditions, the flame interacts with the flow and the bulk swirl flow is diminished at low ṁcc/ṁcore, while boosted at high ṁcc/ṁcore. The former happens because the flame deflects the incoming driver jet flow, enhancing radial and axial velocity components (through thermal expansion), while diminishing the tangential flow velocity. This, in turn, weakens the g-loads within the CC to below its design g-load operation. On the other hand, at high ṁcc/ṁcore and small αjet the flame is perpendicular to the bulk swirl flow, accelerating the flow tangential velocity and enhancing g-loads above its design operation. Qualitatively, the more and hotter the flame that can be sustained within the CC the shorter the flame length. The converse is also true. Flame length does not appear to be strongly influenced by ṁcc/ṁcore and αjet. Even though g-loads appear to enhance reaction progress variable source (SC) and, consequently, turbulent flame speed, through turbulence this does not necessarily mean that the turbulent flame speed under g-loads is various factors greater than its corresponding turbulent flame speed under 0g’s. As the ṁcc/ṁcore increases the center-peaked radial temperature profile at intermediate αjet starts to deteriorate, whereas the radial temperature profile at low αjet improves. For high αjet, increasing ṁcc/ṁcore has no substantial effect on the exit radial temperature profiles.
Aerothermal Measurements and Predictions of an Intermediate Turbine Duct Turning Vane
Authors: Johansson Martin , Mårtensson Jonathan , Abrahamsson Hans , Povey Thomas , Chana Kam
Published: August 2015

Flow in a turbine duct is highly complex, influenced by the upstream turbine stage flow structures, including tip leakage flow and non-uniformities originating from the upstream HPT vane and rotor. The complexity of the flow makes the prediction using numerical methods difficult, hence there exists a need for experimental validation. This paper presents experimental data including both aerodynamic and heat transfer measurements within an intermediate turbine duct. These have been conducted in the Oxford Turbine Research Facility, a short duration high speed test facility enabling the use of an engine sized turbine, operating at the correct non-dimensional parameters relevant for aerodynamic and heat transfer measurements. The current configuration consists of a HPT stage and a downstream duct including a turning vane, for use in a counter rotating turbine configuration. With a stator-to-stator vane count of 32-to-24, instrumentation was installed on three adjacent intermediate turbine duct vanes and endwalls to investigate its influence. Flow phenomena such as trailing edge wakes and vortex structures from the upstream HPT vane travels through the rotor and forms an inlet condition to the intermediate turbine duct with tangential variations. Time-averaged experimental data show this effect to be distinguishable although varying in the spanwise direction. Comparisons with results from numerical predictions are included to further analyse the flow through the 1.5 stage.
CFD Analysis of Turbec T100 Combustor at Part Load by Varying Fuels
Authors: Calabria Raffaela , Chiariello Fabio , Massoli Patrizio , Reale Fabrizio
Published: August 2015

In recent years an increasing interest is focused on the study of micro gas turbines (MGT) behavior at part load by varying fuel, in order to determine their versatility. The interest in using MGT is related to the possibility of feeding with a wide range of fuels and to realize efficient cogenerative cycles by recovering heat from exhaust gases at higher temperatures. In this context, the studies on micro gas turbines are focused on the analysis of the machine versatility and flexibility, when operating conditions and fuels are significantly varied. In line of principle, in case of gaseous fuels with similar Wobbe Index no modifications to the combustion chamber should be required. The adoption of fuels whose properties differ greatly from those of design can require relevant modifications of the combustor, besides the proper adaptation of the feeding system. Thus, at low loads or low calorific value fuels, the combustor becomes a critical component of the entire MGT, as regards stability and emissions of the combustion process. Focus of the paper is a 3D CFD analysis of the combustor behavior of a Turbec T100P fueled at different loads and fuels. Differences between combustors designed for natural gas and liquid fuels are also highlighted. In case of natural gas, inlet combustor temperature and pressure were taken from experimental data; in case of different fuels, such data were inferred by using a thermodynamic model which takes into account rotating components behavior through operating maps of compressor and turbine. Specific aim of the work is to underline potentialities and critical issues of the combustor under study in case of adoption of fuels far from the design one and to suggest possible solutions.
A Study on Energetic and Hydraulic Interaction of Combined Journal and Thrust Bearings
Authors: Hagemann Thomas , Blumenthal Hardwig , Kraft Christian , Schwarze Hubert
Published: August 2015

A theoretical algorithm for the analysis of bidirectional interaction of combined journal and thrust bearings is presented. While many theoretical and experimental investigations on the operating behavior of single journal and thrust bearings can be found only few results for combined bearings are available. However, combined bearings interact by exchanging lubricant and heat which can affect significant changes of boundary conditions compared to a single bearing application. Therefore, a novel procedure is developed to combine two separate codes for journal and thrust bearings in order to iteratively determine the coupling boundary conditions due to the special design of the entire bearing unit. The degree of interaction strongly depends on the type of lubrication. In a first step predictions are verified by measurement data for a combined bearing with a fixed-pad offset-halves journal bearing and a directed lubricated tilting-pad thrust bearing. Experiments were conducted on a high speed test rig up to sliding speeds of 107 m/s at the mean radius of the thrust bearing. As expected the interaction of the two oil films is comparably low in the investigated speed and load range for this bearing design because of the active lubrication of both bearings and the low hydraulic resistance of the thrust bearing. In order to theoretically investigate interaction of thrust and journal bearings in more details a combined bearing with fixed-pad thrust parts lubricated exclusively by the side flow of the journal bearing is studied. A variation of modeling level, pocket design of the journal part, thrust load and rotating frequency provides the following results: (i) hydraulic and energetic interaction have to be modelled in details, (ii) the axial flow resistance of the pockets strongly influences flow rates and the pressure level at the interfaces (iii) the level of interface pressure rises with increasing thrust loads and decreasing rotor speed, (iv) the axial bearing clearance is rather of minor importance for the investigated bearing. Finally, improvements in order to predict operating conditions more precisely are comprehensively discussed.
Effect of the Flare Expansion Angle on the Mean and Dynamic Behavior of Swirling Flow Generated by a Counter Rotating Radial-Radial Swirler Using a Water Test Rig
Authors: Estefanos Wessam , Tambe Samir , Jeng San-Mou
Published: August 2015

A series of experiments have been conducted to study the effect of the flare expansion angle on the mean and unsteady behavior of the non-reacting swirling flow using a water test rig. The flow was examined in water using a 3X model of a counter rotating radial-radial swirler. Three flares having expansion angles of 30.9°, 35.9° and 40.9° with respect to the swirler centerline were tested. 2D high speed Particle Image Velocimetry (PIV) measurements were employed to study the instantaneous and mean velocity fields. Tests were conducted at a Reynolds number equivalent to an air pressure drop of 4% for the corresponding 1X model of the swirler under atmospheric conditions. The flare expansion angle was found to have a clear impact on the mean, turbulent and dynamic behavior of the swirling flow. With the increase in the flare expansion angle, the width of the Center Toroidal Recirculation Zone (CTRZ) increased. The length and width of the Corner Recirculation Zone decreased with increasing the flare angle. For the 30.9° flare, the high turbulence regions extended further axially compared to the other two flares. Strong flow instability was observed on the boundaries of the reverse flow zones. A temporal FFT approach was used to obtain the dominant frequencies of flow instability based on the instantaneous velocity data. The dominant frequency of this instability was slightly lower for the 30.9° flare angle. High turbulent kinetic energy (TKE) was located in the vicinity of the unstable shear layers originating from the CTRZ and CRZ. The TKE reached its maximum near the center for the 30.9° flare and near the walls for the 35.9° and 40.9° flares. The phase angle difference between the high TKE regions was 3.14 radians, indicating a circumferential mode of instability. The obtained results give a clear explanation on the mechanisms driving the flow instability and how these mechanisms change with the change in the flare angle. These results also serve as a tool to validate CFD models.
A Multiphase Computational Study of Oil-Air Flow Within the Bearing Sector of Aeroengines
Authors: Adeniyi Akinola A. , Morvan Hervé P. , Simmons Kathy A.
Published: August 2015

The bearing chamber of an aeroengine houses roller bearings and other structural parts. The spatial limitation, high operational speeds of the HP shaft and the proximity to the combustion chamber can make the operating conditions of the bearing chamber challenging. A roller bearing consists of an inner race, an outer race and a cage constraining a number of rolling elements. In the aeroengine application, oil is introduced into the bearing chamber via the inner race regions of the bearing into the rolling elements interstices. This provides lubrication for the roller bearings. The source of heat in the bearing chamber is mainly from rolling contact friction and the high temperature of combustion. Cooling results from the oil transport within the bearing chamber and thus an efficient transport of oil is critical to maintaining the integrity of the entire structure. The bearing chamber contains the oil which is eventually scavenged and recycled for recirculation. Experiments have been conducted over the years on bearing chamber flows but often simplified to create the best emulation of the real aeroengine. The complexity of the bearing chamber structure is also challenging for experimental measurements of the oil characteristic in the roller bearing elements and the bearing chamber compartment. Previous experiments have shown that the oil continuum breaks up in the bearing chamber compartment but it is not quantitatively clear how and what parameters affect these. Previous simulation attempt of bearing chamber, also, have been limited by the boundary conditions for the oil. This work presents a computational fluid dynamics (CFD) transient simulation of flow in the bearing sector in an attempt create boundary conditions for such models. The current results show that the oil emerges in the form of droplets into the bearing chamber compartment with speed of the order of 10% of the shaft rotation.
Blade Triggered Excitation of Periodically Unsteady Impinging Jets for Efficient Turbine Liner Segment Cooling
Authors: Scherhag Christian , Geiermann Jan Paul , Wartzek Fabian , Schiffer Heinz-Peter
Published: August 2015

In the present study an application for efficient cooling of turbine liner segments employing pulsating impinging jets was investigated. A combined numerical and experimental study was conducted to evaluate the design of a case cavity device which utilizes the periodically unsteady pressure distribution caused by the rotor blades to excite a pulsating impinging jet. Through an opening between the main annulus and a case cavity, pressure pulses from the rotor blades propagated into this cavity and caused a strong pressure oscillation inside. The unsteady CFD results were in good qualititative agreement with the measurement data obtained using high frequency pressure transducers and hot wire anemometry. Furthermore, the numerical study revealed the formation of distinct toroidal vortex structures at the nozzle outlet as a result of the jet pulsation. Within the scope of the measurements the influence of the operating point on the pressure propagation inside the cavity was investigated. The dependence of shape and amplitude of the pressure oscillation on engine speed and stage pressure ratio was found to be in accordance with an analytical consideration.
Combined Effects of Jet Plate Thickness and Fillet Radius on Leading Edge Jet Impingement With Round and Racetrack Shaped Jets
Authors: Harmon Weston V. , Wright Lesley M. , Crites Daniel C. , Morris Mark C. , Riahi Ardeshir
Published: August 2015

The effect of jet plate thickness is considered as regionally averaged Nusselt numbers are measured on a concave surface, which models the leading edge of modern gas turbine blades. The performance of both round and racetrack shaped orifices for leading edge impingement is considered. Regionally averaged heat transfer coefficient distributions are obtained in a steady state experiment using heated aluminum plates. From this traditional heat transfer technique, the heat transfer afforded by jet plates of varying thickness is quantified. The thickness of the jet plate is varied from 1.33 to 4.0 diameters (for both the round and racetrack shaped jets). To model the modern, cast airfoil, the effect of an inlet and outlet radius on the jet orifice is also investigated. For all cases, the jet – to – target surface spacing (z/djet) is 4, the jet – to – jet spacing (s/djet) is 8, and the target surface diameter – to jet diameter (D/djet) is 5.33. Target surface Nusselt numbers are obtained for three separate Reynolds numbers. For the round orifices, jet Reynolds numbers of 14,000, 28,100, and 42,100 are used while the corresponding Reynolds numbers for the racetrack shaped jets are 11,800, 23,600, and 35,400. Although the Reynolds number is reduced for the racetrack shaped jets, the mass flow through each jet remains constant (from the round to the racetrack jets). The Nusselt numbers measured in the stagnation region of the target surface are relatively insensitive to the jet plate thickness. For all cases considered, the flow is not developed as it exits the orifice, so the flow structures of the jets ensuing from each of the plates are similar. When the inlet of the jet is rounded, the vena contracta effect within the orifice is minimized, and a more symmetrical jet develops within the orifice. For a fixed flow rate, the racetrack shaped jets provide enhanced heat transfer compared to the round jets for all geometries considered.
Experimental and Tomography-Based CFD Investigations of the Flow in Open Cell Metal Foams With Application to Aero Engine Separators
Authors: de Carvalho Thiago P. , Morvan Hervé P. , Hargreaves David , Oun Hatem , Kennedy Andrew
Published: August 2015

Oil-air separation is a key function in aero engines with closed-loop oil systems. Typically, aero engine air/oil separators employ the use of a porous medium such as open cell metal foams, as a secondary separation mechanism. Assessing its impact on overall separation is important since non-captured oil is released overboard. Computational fluid dynamics offers a possibility to evaluate the metal foam separation effectiveness.

A pore scale numerical modelling methodology is applied to determine the transport properties of fluid flow through open cell metal foams. Microcomputer tomography scans were used to generate a 3D digital representation of commercial open cell metal foams of different grades. Foam structural properties such as porosity, specific surface, pore size distribution and the minimum size of a representative elementary volume are directly extracted from the CT scans. Subsequently, conventional finite volume simulations are carried out on the realistic tomography-based foam samples. Simulations were performed for a wide range of Reynolds numbers. The feasibility of using standard Reynolds-averaged Navier-Stokes (RANS) turbulence models is investigated here. As part of the method validation, samples with varying lengths were simulated. Pressure drop values were compared on a length-normalized basis against in-house experimental data.

The oil phase was modelled using a Lagrangian particle tracking approach. Boundary conditions for the oil phase were extracted from a previous CFD simulation of a full breather device in the ground idle regime (worst separation effectiveness). Steady state particle tracking simulations were run for droplet diameters ranging from 0.5–15 μm, and for flow inlet velocities ranging from 10–60 m/s. Stochastic tracking was taken into account in order to model the effects of turbulence on the particle trajectories. Simulations were run on different types of foam and the results are compared qualitatively. The procedure has shown that pore scale modelling is a valid tool to capture the flow field and model oil separation inside open cell metal foams. However, at the moment there is no experimental data available for validation of the oil phase modelling.
Design Improvement Survey for NOx Emissions Reduction of a Heavy-Duty Gas Turbine Partially Premixed Fuel Nozzle Operating With Natural Gas: Experimental Campaign
Authors: Cerutti Matteo , Modi Roberto , Kalitan Danielle , Singh Kapil K.
Published: August 2015

As government regulations become increasingly strict with regards to combustion pollutant emissions, new gas turbine combustor designs must produce lower NOx while also maintaining acceptable combustor operability. The design and implementation of an efficient fuel/air premixer is paramount to achieving low emissions.

Options for improving the design of a natural gas fired heavy-duty gas turbine partially premixed fuel nozzle have been considered in the current study. In particular, the study focused on fuel injection and pilot/main interaction at high pressure and high inlet temperature.

NOx emissions results have been reported and analyzed for a baseline nozzle first. Available experience is shared in this paper in the form of a NOx correlative model, giving evidence of the consistency of current results with past campaigns.

Subsequently, new fuel nozzle premixer designs have been investigated and compared, mainly in terms of NOx emissions performance. The operating range of investigation has been preliminarily checked by means of a flame stability assessment. Adequate margin to lean blow out and thermo-acoustic instabilities onset has been found while also maintaining acceptable CO emissions.

NOx emission data were collected over a variety of fuel/air ratios and pilot/main splits for all the fuel nozzle configurations. Results clearly indicated the most effective design option in reducing NOx. In addition, the impact of each design modification has been quantified and the baseline correlative NOx emissions model calibrated to describe the new fuel nozzles behavior.

Effect of inlet air pressure has been evaluated and included in the models, allowing the extensive use of less costly reduced pressure test campaigns hereafter. Although the observed effect of combustor pressure drop on NOx is not dominant for this particular fuel nozzle, sensitivity has been performed to consolidate gathered experience and to make the model able to evaluate even small design changes affecting pressure drop.
A New Algorithm for Scheduling Condition-Based Maintenance of Gas Turbines
Authors: Yılmaz Yavuz , Kurz Rainer , Özmen Ayşe , Weber Gerhard-Wilhelm
Published: August 2015

In developed electricity markets, the deregulation boosted competition among companies participating in the electricity market. Therefore, the enhanced reliability and availability of gas turbine systems is an industry obligation. Not only providing the available power with minimum operation and maintenance costs, but also guaranteeing high efficiency are additional requisites and efficiency loss of the power plants leads to a loss of money for the electricity generation companies. Multivariate Adaptive Regression Spline (MARS) is a modern methodology of statistical learning, data mining and estimation theory that is significant in both regression and classification is a form of flexible non-parametric regression analysis capable of modeling complex data. In this study, single shaft, 6MW class industrial gas turbines located at various sites have been monitored. The performance monitoring of a gas turbine consisted of hourly measurements of various input variables over an extended period of time. Using such measurements, predictive models for gas turbine heat rate and the gas turbine axial compressor discharge pressure values have been generated. The measured values have been compared with the values obtained as a result of the MARS models. The MARS-based models are obtained with the combination of gas turbine performance input and target variables and the complementary meteorological data. The results are presented, discussed, and conclusions are drawn for modern energy and cost efficient gas turbine and power plant maintenance management as the outcomes of this study.
Asymptotic Numerical Method and Polynomial Chaos Expansion for the Study of Stochastic Non-Linear Normal Modes
Authors: Panunzio Alfonso M. , Salles Loïc , Schwingshackl Christoph , Gola Muzio
Published: August 2015

Nonlinear normal mode (NNM) analysis is one emerging technique to analyse the nonlinear vibration of bladed-disk. It links the resonance frequency to the energy present in the system, and allows a simple identification of internal resonances in the structure. Non-linear vibration analysis is traditionally carried out under the assumption that the mechanical properties and forcing function are deterministic. Since every mechanical system is by nature uncertain a truly accurate nonlinear dynamic analysis requires the inclusion of random variables in the response predictions. The propagation of random input uncertainties in a NNM analysis is the main aim of the presented work. The Asymptotic Numerical Method (ANM) will be used to calculate the NNMs for a contact problem in a computationally efficient way. The stochastic NNM permits to quantify the effect of uncertainties on the resonance frequency and the change in mode shape due to non-linearities, leading to the calculation of uncertain internal resonances. The proposed method is initially applied to a simple spring-mass system to demonstrate the effects of uncertainty on the NNM predictions. In a second step a blade-casing interaction with localized contact non-linearity is investigated with a real geometry. The resulting NNMs show the presence of internal resonance for both cases.