bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Highly Loaded Fan Rotor Based on Throughflow Model
Authors: Wu Hong , Li Qiushi , Zhou Sheng
Published: March 2009

This paper presents an optimization method for fan/compressor which couples throughflow model solving axisymmetric Euler equations with adaptive simulated annealing (ASA) algorithm. One of the advantages of this optimization method is that it spends much less time than 3D optimization due to the rapid solving of throughflow model. In addition, the optimization space is quite extensive because more design variables can be adjusted in throughflow phase, such as swirl distribution, hub curve and sweep. To validate this optimization method, a highly loaded fan rotor with pressure ratio of 3.06 as a baseline is optimized. During the optimization process, the objective function is total pressure ratio, moreover, mass flow and efficiency are selected as the constraint conditions. Three important design variables including swirl distribution, hub curve and sweep are parameterized using Bezier curve, and then optimized in throughflow model independently, finally the optimum designs are validated using 3D viscous CFD solver. It is shown that pressure ratio and rotor loading can be improved further through optimizing swirl distribution, however, hub and sweep curves take more effects on mass flow and efficiency respectively. The optimization results demonstrate the advantage and feasibility of this optimization method.
Feasibility Study of an Intercooled-Cycle Marine Gas Turbine
Authors: Wen Xue-You , Xiao Dong-Ming
Published: March 2009

From the perspective of an overall entity analyzed was the performance obtainable from the adoption of an intercooled-cycle gas turbine under different typical cycle parameters of a gas turbine. On this basis, a study was conducted of the conversion of a high-power simple-cycle marine gas turbine (MGT-33) into a type of intercooled-cycle marine gas turbine. The precondition of the conversion is to keep the flow path and the majority of the structure of the original engine gas-generator unchanged in order to inherit the reliability of the prototype machine. The results of the study indicate that after the adoption of an intercooled cycle under the precondition of performing minimum structure modifications and maintaining the compactness of the engine as a whole, there is still a significant enhancement of the gas turbine overall performance with its power output and efficiency being increased by about 34% and 4.6% respectively, demonstrating the merits of the engineering conversion under discussion.
Maximizing 3D Clocking Effect by the Guidance of Edge Matching
Authors: Ji LuCheng , Chen Jiang , Yan Zhao , Yi WeiLin
Published: March 2009

Clocking can produce benefit has become a common viewpoint in turbomachinery field. However, there still is a question, that is “why the benefit of two-dimensional (2D) clocking model is always larger than that of three-dimensional (3D) clocking model?”. A general way of maximizing 3D clocking benefit by edge matching (EM) is put forward. On the basis of experience and knowledge accumulated in investigations on clocking effects, a further simplified method is presented and emphasized. Aachen 1.5 stage low speed subsonic axial turbine is used as an example of maximizing 3D clocking benefits by applying EM. Results show that 3D clocking benefit can be maximized by routinely using EM with relatively low computational resource requirements, and the benefit is considerable enough to be paid more attention.
The Reduction of Over Tip Leakage Loss in Unshrouded Axial Turbines Using Winglets and Squealers
Authors: Schabowski Zbigniew , Hodson Howard
Published: March 2009

The possibilities of reducing the over tip leakage loss of unshrouded rotors have been investigated using a linear cascade of turbine blades and CFD. The large-scale blade profile is the same as that of the tip profile of a low-speed HP research turbine facility. The impact of various combinations of squealer and winglet geometries on the turbine performance has been investigated. The influence of the thickness of the squealers has also been assessed. It was found that a 22% reduction in loss slope was possible, when compared to the flat tip blade, using simple tip modifications. The results obtained with the suction side squealer and cavity tip agreed well with the work of other researchers. Three winglet-based tip geometries were tested. One was a plain winglet, the other two had squealers applied. A significant impact of the squealers and their shape on the tip gap flow pattern and loss generation was found. The physical processes occurring within the tip gap region for the tested geometries are explained using both numerical and experimental results. The impact of the flow pattern within the tip gap on the loss generation is described. Good agreement between the CFD and the experimental data was found. This shows that the CFD can be used with confidence in the design process of shroudless turbines.
Steady-Flow Analysis of Low Pressure Compression System for Turbofan Engines
Authors: Sayma Abdulnaser I.
Published: March 2009

This paper has two main objectives. It first aims at presenting a method of prescribing boundary conditions for the steady-state flow simulations of low pressure compression systems for turbofan engines. The methodology is generic and it can be applied for steady and unsteady flow simulations of numerous similar multi-component applications. The basic idea is to extend the flow domain upstream to the far field and downstream beyond the first set of stator vanes, both in the bypass and core, where variable area nozzles are used. Fixed static pressure boundary conditions are used downstream of the nozzles which are representative of downstream blockage. With such an approach, the need to prescribe accurate boundary conditions immediately upstream and downstream of the fan is eliminated. An iterative approach is then used to obtain the correct bypass ratio. The second objective of the paper is to demonstrate the use of the methodology in mapping out the loss loop for the outflow guide vanes (OGV) and examine its effects on fan performance. Wherever possible, predictions were checked against measured data and good overall agreement was obtained.
The Flow Mechanism of How Distorted Flows Deteriorate Stability of an Axial Flow Compressor
Authors: Zhang J. , Lin F. , Chen J. , Nie C.
Published: March 2009

The stalling behavior in a single-stage low-speed axial compressor under inlet distortion is investigated. A blade-passage-scale flow mechanism is proposed to explain the stability deterioration caused by inlet distortion for the tested compressor exhibiting spike stall inception. In contrast to the existing understanding of inlet distortion based on system scale dynamics, the main elements of this flow mechanism are the unsteady behavior of tip leakage vortices (TLV) under inlet distortion; its effect on the initiation of spike flow disturbances, and its interaction with distorted sectors. Rotating inlet distortion (RID) is used as a tool because RID makes it possible to directly compare the flows between distorted and clean flow sectors with fixed measurement stations on the casing, and the fact that the stationary inlet distortion is only a special case of RID makes the results generic. The tests demonstrate that the blade loading in the distorted sector is heavier than that in the non-distorted sector, causing the TLV in the distorted sector move closer to the leading edge of the rotor blade and thus be the first to initiate the spike-like disturbance. The unsteady CFD simulation further confirms that such a disturbance corresponds to a vortex spinning out of the leading edge of the blades. However, the initiation of this spike-like disturbance doesn’t necessarily trigger the full stall immediately. The tracking of the disturbances indicates that most of such spike-like disturbances will be smeared by non-distorted sector and the growth of the spike-like disturbances actually relate closely to how and how often the path of the propagating disturbances come across the path of the rotating distorted sector. The proposed blade-passage-scale flow mechanism also offers an alternative explanation to the “resonance” phenomenon in rotating inlet distortion research, which was explained with excitation-and-response theory for compressors that exhibit modal stall inception.
A Novel Turbomachinery Air-Brake Concept for Quiet Aircraft
Authors: Shah P. N. , Mobed D. D. , Spakovszky Z. S.
Published: March 2009

A novel air-brake concept for next generation, low-noise civil aircraft is introduced. Deployment of such devices in clean airframe configuration reduces aircraft source noise and noise propagation to the ground. The generation of swirling outflow from a duct, such as an aircraft engine, is demonstrated to have high drag and low noise. The simplest configuration is a ram pressure driven duct with stationary swirl vanes, a so-called swirl tube. A detailed aerodynamic design is performed using first principles based modeling and high-fidelity numerical simulations. The swirl-drag-noise relationship is quantified through scale-model aerodynamic and aeroacoustic wind tunnel tests. The maximum measured stable flow drag coefficient is 0.83 at exit swirl angles close to 50 degrees. The acoustic signature, extrapolated to full-scale, is found to be well below the background noise of a well populated area. Vortex breakdown is found to be the aerodynamically and acoustically limiting physical phenomenon, generating a white-noise signature that is about 15 dB louder than a stable swirling flow.
Sprays in Cross Flow: Dependence on Weber Number
Authors: Lubarsky Eugene , Reichel Jonathan R. , Zinn Ben T. , McAmis Rob
Published: March 2009

This paper describes an experimental investigation of the spray created by Jet A fuel injection from a plate containing sharp edged orifice 0.018 inches (457 μm) in diameter and L/D ratio of 10 into the crossflow of preheated air (555 K) at elevated pressure in the test section (4 ata) and liquid to air momentum-flux ratio of 40. A 2 component Phase Doppler Particle Analyzer used for measuring the characteristics of the spray. The Weber number of the spray in crossflow was varied between 33 and 2020 and the effect of Weber number on spray properties was investigated. It was seen that shear breakup mechanism dominates at Weber number greater than about 100. Droplets’ diameters were found to be in the range of 15-30 microns for higher values of Weber numbers, while larger droplets (100-200 microns) were observed at Weber number of 33. Larger droplets were observed at the periphery of the spray. The droplet velocities and diameters were measured in a plane 30mm downstream of the orifice along the centerline of the spray at an incoming air flow Mach number of 0.2 and liquid to air momentum-flux ratio of 40. The droplets reach a maximum of 90% of the flow velocity at this location. The velocity of droplets in the directions perpendicular to the air flow direction is higher at the periphery of the spray possibly due to the presence of larger droplets. The RMS values of the droplet velocities are highest slightly off center of the centerline of the spray showing the presence of strong vortices formed due to the liquid jet in crossflow. The data presented here could serve as benchmark data for CFD code validation.
Design, Performance Evaluation and Endwall Flow Structure Investigation of an S-Shaped Intermediate Turbine Duct
Authors: Axelsson Lars-Uno , Osso Carlos Arroyo , Cadrecha David , Johansson T. Gunnar
Published: March 2009

Annular S-shaped intermediate turbine ducts are used in modern multi-spool jet engines to connect the high pressure turbine with the low-pressure turbine. The trend towards engines with larger by-pass ratios requires the future intermediate turbine ducts to be shorter and have larger radial off-set. This paper deals with the design and performance evaluation of a state-of-the-art annular S-shaped intermediate turbine duct. The details of the design of the intermediate turbine duct are presented together with static pressure measurements and oil film flow visualization along the endwalls, and area traverses at the inlet and outlet planes using a 5-hole probe. The measurements were done for three operating points of the turbine. From the flow visualization no separation could be detected at design point conditions, but for off-design conditions regions of separation were detected on the guide vanes located within the inter-turbine duct. The pressure loss coefficient was shown to be comparable for the two cases with lowest swirl angle, but the design point showed a slightly lower pressure loss. For the case with the largest flow angle the pressure loss coefficient was clearly larger than for the other two cases, which can be associated with the separation found on the guide vanes.
Expectations and Recent Experience for Gas Turbine Reliability, Availability, and Maintainability (RAM)
Authors: Steele Robert F. , Paul Dale C. , Rui Torgeir
Published: March 2009

Since the early 1990’s there have been significant changes in the gas turbine, and power generation market place. The ‘F-Class’ Gas Turbines, with higher firing temperatures, single crystal materials, increased compressor pressure ratios and low emission combustion systems that were introduced in the early 1990’s have gained significant field experience. Many of the issues experienced by these new product introductions have been addressed. The actual reliability growth and current performance of these advanced technology machines will be examined. Additionally, the operating profiles anticipated for many of the units installed during this period has been impacted by both changes in the anticipated demand and increases in fuel costs, especially the cost of natural gas. This paper will review how these changes have impacted the Reliability, Availability, and Maintainability performance of gas turbines. Data from the ORAP® System, maintained by Strategic Power Systems, Inc, will be utilized to examine the actual RAM performance over the past 10 to 15 years in relation to goals and expectations. Specifically, this paper will examine the reliability growth of the F-Class turbines since the 1990’s and examine the reliability impact of duty cycle on RAM performance.
Performance Assessment of Cogeneration Systems for Industrial District Applications
Authors: Campanari Stefano , Chiesa Paolo , Silva Paolo
Published: March 2009

This paper discusses the development and testing of an optimization tool for the energy and economic analysis of cogeneration systems and its application to industrial districts composed by different factories (with electrical, heating and in some cases cooling demand), with time-variable loads and several day-types profiles. The discussion compares three cogeneration systems, respectively based on: (i) a simple cycle gas turbine or (ii) a recuperative cycle gas turbine, both with heat recovery and an absorption chiller, and (iii) an internal combustion engine with electrical chiller units. Test case specifications also include tariff, regulatory and weather conditions, provided that performance of the main components are corrected as a function of load and ambient conditions. The model demonstrates to be really effective in defining the best operating strategy for each cogeneration system; detailed results are presented, in terms of annual energy balances, energy savings compared to separate generation systems (grid losses as well as heat distribution losses are taken into account) and economic analysis. A final parametric analysis is carried out to show the influence on the final results of different assumptions on the combination of fuel prices and electricity tariffs.
Experimental Studies on Aerodynamic Performance and Unsteady Flow Behaviors of a Single Turbine Stage With Variable Rotor-Stator Axial Gap: Comparisons With Time-Accurate Numerical Simulation
Authors: Funazaki Ken-Ichi , Yamada Kazutoyo , Kikuchi Mamoru , Sato Hideaki
Published: March 2009

This paper describes experimental results from detailed measurements of aerodynamic performance of a single stage in the turbine test rig of Iwate University, focusing on effects of the rotor-stator axial gap in the turbine stage. The measurements using a 5-hole Pitot tube provide time-averaged flow information such as stagnation pressure distributions and velocity vectors behind the stator as well as the rotor. Time-accurate three-dimensional flow analyses are also made in this study using an in-house N-S code. Realistic flow analyses are achieved in terms of blade-count ratio only by adding one stator vane, resulting in 3:4 blade-count ratio for the present simulation. Aerodynamic characteristics at the exits of the stator as well as the rotor for three axial gap cases are examined in detail through the experimental data and the numerical results. It follows that the increase in the axial gap gives rise to small increment in exit flow angle from the stator, seemingly affecting the flow structure near the hub as well as tip regions around the rotor blades. Furthermore, the turbine stage efficiency slightly decreases with the axial gap enlargement.
The Flow Field and Main Gas Ingestion in a Rotor-Stator Cavity
Authors: Roy R. P. , Zhou D. W. , Ganesan S. , Wang C.-Z. , Paolillo R. E. , Johnson B. V.
Published: March 2009

The ingestion of mainstream gas into turbine rotor-stator disk cavities and simultaneously, the egress of cavity gas into the main gas path are consequences of the prevailing unsteady, three-dimensional flow field. To understand these processes, we are carrying out a study that combines experiments in a model single-stage axial turbine with computational fluid dynamic (CFD) simulations. The turbine stage features vanes, blades, and axially overlapping radial clearance rim seal. In this paper, we present time-resolved velocity maps, obtained by particle image velocimetry, of the flow in the disk cavity at four experimental conditions as defined by the main air flow rate, rotor speed, and purge air flow rate. Time-averaged but spatially local measurement of main air ingestion is also presented. Significant ingestion occurred at two of the four experimental conditions where the purge air flow rate was low — it is found that high tangential (swirl) velocity fluid intersperses with lower tangential velocity fluid in the rim region of the cavity. It is argued that the high tangential velocity fluid is comprised of the ingested main air, while the lower tangential velocity fluid is the indigenous cavity air. This interpretation is corroborated by the results of the unsteady, three-dimensional CFD simulation. When the purge flow rate was high, no ingestion occurred as expected; also, large-scale structures that were unsteady appeared in the cavity flow giving rise to large velocity fluctuations. It is necessary to obtain time-resolved information from experiments and computation in such a flow because even when the vane-blade relative position is matched during a particular experiment, the instantaneous flow field does not necessarily remain the same. As such, some of the flow patterns will be smeared out if the interrogation time scale is large.
Engine Health Assessment and Prediction Using the Group Method of Data Handling and the Method of Match Matrix: Autoregressive Moving Average
Authors: Wang Haixia , Lee Jay , Ueda Takahiro , Adjallah Kondo H. , Ghaffari Masoud
Published: March 2009

This paper presents a methodology for engine health assessment and prediction, which includes the following two steps: (1) engine health assessment and anomaly detection is conducted based on an inductive learning technique called Group Method of Data Handling (GMDH), and (2) engine health prediction is conducted based on the method of Match Matrix - Autoregressive Moving Average. Results from an industry case study illustrate the effectiveness of the presented methodology in engine health assessment and prediction.
Suppression of Short Length-Scale Rotating Stall Inception With Glow Discharge Actuation
Authors: Vo Huu Duc
Published: March 2009

This paper proposes and investigates the pioneering use of glow discharge (plasma) actuation to suppress short length-scale (spike) rotating stall inception. A single dielectric barrier discharge plasma actuator basically consists of two parallel offset thin electrodes separated by a dielectric material. The application of a high frequency AC voltage across the electrodes results in an induced body force on the flow adjacent to the surface. This simple, robust actuator may provide a practical low-power mean to positively alter the tip clearance flow dynamics responsible for spike stall inception. A computational study is carried out on a low-speed compressor rotor with the implementation of a published plasma actuation model in an established turbomachinery CFD code. The objective is to provide a preliminary assessment of the effectiveness of a casing circumferential plasma actuator, with varying actuator location, input voltage and frequency, in suppressing the two flow criteria associated with the formation of spike disturbances leading to stall. Results show that plasma actuation most effectively suppresses both of these flow criteria when placed near the rotor leading edge and delays the predicted stall point to a lower flow coefficient with minimal power input. The simulations also indicate that the effectiveness of the actuation decreases non-linearly with input voltage and frequency. In addition, results indicate that this technology could perhaps be used for suppression of both short and long-length scale stall inception in axial compressors.
An FE Transient Response Analysis Model of a Flexible Rotor-Bearing System With Mount System to Base Shock Excitation
Authors: Lee An Sung , Kim Byung Ok
Published: March 2009

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems such as warships, submarines and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect turbomachinery from excessive shock forces, it may be needed to accurately analyze transient responses of rotors, considering the dynamics of mount designs to be applied with. In this study a generalized FE transient response analysis model, introducing relative displacements, is firstly proposed to accurately predict transient responses of a flexible rotor-bearing system with mount systems to base-transferred shock forces. In the transient analyses the state-space Newmark method of a direct time integration scheme is utilized, which is based on the average velocity concept. Results show that for the identical mount systems considered, the proposed FE-based detailed flexible rotor model yields more reduced transient vibration responses to the same shocks than a conventional simple model or a Jeffcott rotor. Hence, in order to design a rotor-bearing system with a more compact light-weighted mount system, preparing against any potential excessive shock, the proposed FE transient response analysis model herein is recommended.
Micro Gas Turbine Combustor Emissions Evaluation Using the Chemical Reactor Modelling Approach
Authors: Russo Carmine , Mori Giulio , Anisimov Vyacheslav V. , Parente Joa˜o
Published: March 2009

Chemical Reactor Modelling approach has been applied to evaluate exhaust emissions of the newly designed ARI100 (Patent Pending) recuperated micro gas turbine combustor developed by Ansaldo Ricerche SpA. The development of the chemical reactor network has been performed based on CFD reacting flow analysis, obtained with a global 2-step reaction mechanism, applying boundary conditions concerning the combustion chamber at atmospheric pressure, with 100% of thermal load and fuelled with natural gas. The network consists of 11 ideal reactors: 6 perfectly stirred reactors, and 5 plug flow reactors, including also 13 mixers and 12 splitters. Simulations have been conducted using two detailed reaction mechanisms: GRI Mech 3.0 and Miller & Bowman reaction mechanisms. Exhaust emissions have been evaluated at several operating conditions, obtained at different pressure, and considering different fuel gases, as natural gas and a high H2 content SYNGAS fuel. Furthermore, emissions at different thermal loads have been investigated when natural gas at atmospheric pressure is fuelled. Simulation results have been compared with those obtained from combustion experimental campaign. CO and NOx emissions predicted with CRM approach closely match experimental results at representative operating conditions. Ongoing efforts to improve the proposed reactors network should allow extending the range of applicability to those operating conditions whose simulation results are not completely satisfying. Given the small computational effort required, and the accuracy in predicting combustor experimental exhaust emissions, both CO and NOx, the CRM approach turnout to be an efficient way to reasonably evaluate exhaust emissions of a micro gas turbine combustor.
Large Eddy Simulation of Leading Edge Film Cooling: Part II — Heat Transfer and Effect of Blowing Ratio
Authors: Rozati Ali , Tafti Danesh K.
Published: March 2009

Detailed investigation of film cooling for a cylindrical leading edge is carried out using Large Eddy Simulation (LES). Part-II of the paper focuses on the effect of coolant to mainstream blowing ratio on flow features and consequently on the adiabatic effectiveness and heat transfer ratio. With the advantage of obtaining unique, accurate and dynamic results from LES, the influential coherent structures in the flow are identified. Describing the mechanism of jet – mainstream interaction, it is shown that as the blowing ratio increases, a more turbulent shear layer and stronger mainstream entrainment occur. The combined effect, leads to a lower adiabatic effectiveness and higher heat transfer coefficient. Surface distribution and span-averaged profiles are shown for both adiabatic effectiveness and heat transfer (presented by Frossling number). Results are in good agreement with the experimental data of Ekkad et al. [12].
Detailed Flow Study of Mach Number 1.6 High Transonic Flow in a Pressure Ratio 11 Centrifugal Compressor Impeller: Part 2 — Effect of the Inducer Shroud Bleed and Development of a Low Energy Region Along the Shroud
Authors: Higashimori Hirotaka , Morishita Susumu , Suzuki Masayuki , Suita Tooru
Published: March 2009

Requirements for aeronautical gas turbine engines for helicopters include small size, low weight, high output, and low fuel consumption. In order to achieve these requirements, development work has been carried out on high pressure ratio compressors with high efficiency. As a result, we have developed a single stage centrifugal compressor with a pressure ratio of 11 for a 1000 shp class gas turbine. This report presents a study on the internal flow of a high pressure ratio centrifugal compressor impeller. The centrifugal compressor is a high transonic compressor with an inlet Mach number of about 1.6. In high inlet Mach number compressors, the flow in the inducer is a complex transonic flow characterized by interaction between the shockwave and boundary layer, while the flow in the middle of the impeller is a distorted flow with a low energy region. In order to ensure the reliability of aerodynamic design technology for such transonic centrifugal compressors, the complex transonic flow and formation of the low energy region predicted by CFD must be actually measured, comparison must be undertaken between the CFD results and the actual flow measurement, and the accuracy and other issues pertaining to CFD must be clarified. In a previous report [12], we elucidated the flow in the inducer of a high transonic impeller by means of LDV and unsteady pressure measurement. That report showed that, in the flow of an inducer with a Mach number of approx. 1.6, the oblique shockwave in the middle of the impeller throat interacts with the blade tip leakage flow, and that reverse flow occurs in the vicinity of the casing. Furthermore, although CFD predicted a low energy region in the splitter portion, this could not be detected in actual measurement. In the context of the current report, comparative verification of the CFD and LDV measurement results was undertaken with respect to the formation of the casing wall surface boundary layer in the transonic flow within the inducer. In this conjunction, inducer bleed was introduced to control this boundary layer, and the effect of the inducer bleed on the flow was ascertained through actual measurement. It was also sought to additionally confirm the “low energy region” in the splitter. Accordingly, the flow velocity distribution was measured at two sections, thereby clarifying the characteristics of the actual flow in the region. The impeller for which measurement was performed has the same specifications as that in the previous report (see Table 1). In the present report, so as to measure the flow under conditions encouraging the formation of a boundary layer accompanying substantial inducer deceleration, measurement was conducted at 95% of design speed and a relative Mach number at the blade tips of about 1.5.
Customer Adapted Optimized Maintenance Plan for Gas Turbines
Authors: Wa¨rja Mathias , Slottner Pontus
Published: March 2009

Maintaining high levels of availability and reliability are essential objectives for many industries, especially those that are subject to high costs due to non-payment as a result of shutdowns of critical systems, e.g. gas turbines. To utilize these systems as effectively as possible, maintenance must be optimized. Though, determining what is optimal is a tough multi-variable task requiring detailed knowledge about components building the system, such as damage mechanisms, TMF/LCF crack initiation and propagation, creep deformation, creep damage, general material deterioration, erosion, oxidation and corrosion. Also, customer specific inputs are essential, e.g. value of the produced entity, fuel prices, unplanned and planned standstill cost. To efficiently funnel this information into a customer adapted, optimized maintenance plan, a probabilistic optimization model is proposed. The model will dynamically calculate the most efficient point in time for a renewal. Further, the model can, as a function of risk willingness, adjust the maintenance plan to any customer’s specific demands. This paper describes (i) the model, (ii) how information is gathered and processed, (iii) how the risk assessment is performed and (iv) how the lifetime prediction is carried out. The optimization itself can be adjusted to aim at: minimizing cost or risk or maximizing availability, performance or reliability. Also, this paper describes how the quantitative selection of critical components included in the optimization is performed.
The Behavior of Tip Clearance Flow at Near-Stall Condition in a Transonic Axial Compressor Rotor
Authors: Yamada K. , Funazaki K. , Furukawa M.
Published: March 2009

It is known that the tip clearance flow is dominant and very important flow phenomena in axial compressor aerodynamics because the tip clearance flow has a great influence on the stability as well as aerodynamic loss of compressors. Our goal is to clarify the behavior of tip clearance flow at near-stall condition in a transonic axial compressor rotor (NASA Rotor 37). In the present work, steady and unsteady RANS simulations were performed to investigate vortical flow structures and separated flow field near the tip for several different clearance cases. Boundary layer separation on the casing wall and blade suction surface was investigated in detail for near-stall and stall condition. In order to understand such complicated flow field, vortex cores were identified using the critical point theory and a topology of the three-dimensional separated and vortical flows was analyzed. In the nominal clearance case, the breakdown of tip leakage vortex has occurred at a near-stall operating condition because of the interaction of the vortex with the shock wave, leading to a large blockage and unsteadiness in the rotor tip. On the other hand, the calculation with no clearance suggested that the separation on the suction surface was different from that with the nominal clearance. Since the shock wave induced the boundary layer separation on the blade suction surface in the transonic axial compressor rotor, focal-type critical points appeared on the suction surface near the tip at near-stall condition.
Development and Design of Alstom’s Staged Fuel Gas Injection EV Burner for NOx Reduction
Authors: Zajadatz Martin , Lachner Rudolf , Bernero Stefano , Motz Christian , Flohr Peter
Published: March 2009

Alstom’s combustion development on the EV burner concept has taken another step forward with the introduction of a staged premix system, which allows even lower NOx values also at lower part load values compared to the pilot/premix EV burner. The development target was achieved by introducing one fuel stage over the conventional EV fuel lance, while other fuel stage is realized with a gas hole injection pattern over the EV air slots, similar to the conventional EV burner system. Due to this no major design modifications for the EV burner system were required, and the new system is fully retrofittable to the existing GT26 gas turbine engines including the existing fuel distribution system. The final design is a result of a step-by-step development. In a first step, variants defined in a feasibility study by CFD calculations indicated that a staged fuel gas injection over the fuel lance could substitute a part of the conventional premix gas injection. The water tunnel tests results performed with the LIF measurement technique demonstrated the improved mixing properties of the staged EV burner in the burner flow field. With a single burner test facility under atmospheric pressure conditions the broad operating range of the staged EV burner system could be confirmed. The single burner tests allowed investigation of the low NOx operating range for the burner system also with respect to flame generated instabilities. Finally the burner system was validated with gas turbine engine tests at the Alstom GT Test Power Plant in Birr, Switzerland, which demonstrated the excellent combustion performance of the staged EV burner system derived by the development procedure.
Characteristics of End-Wall Flow at Spike and Modal Stall Inceptions in a Variable-Pitch Axial-Flow Fan
Authors: Nishioka Takahiro , Kanno Toshio , Hayami Hiroshi
Published: March 2009

The flow mechanisms for spike and modal stall inceptions in a low-speed axial-flow fan with a relatively large tip clearance were studied. The pressure and velocity fluctuations were measured to clarify the influences of blade loading, end-wall flow, and tip-leakage flow on stall inception at two stagger-angle settings for the rotor blade, which are the design and small stagger-angle settings. A rotating instability was observed near the maximum pressure-rise point at both design and small stagger-angle settings. This instability was induced by the interaction between the incoming flow, tip-leakage flow, and end-wall backflow. The stall inception patterns were a spike type at the design stagger-angle setting and a modal type at the small stagger-angle setting. At the design stagger-angle setting, the interface between the incoming flow, tip-leakage flow, and end-wall backflow became parallel to the rotor leading edge plane and reached the pressure side of adjacent blade. The interaction between these flows generated the large end-wall blockage in the rotor blade passage, and this blockage developed leading edge separation on the overloaded rotor blade at the tip. The leading edge separation that developed then grew into a spike, which traveled upstream of the rotor. At the small stagger-angle setting, the rotating instability and modal disturbance were also induced by the interaction between the incoming flow, tip-leakage flow, and end-wall backflow. However, the interface between the tip-leakage flow and end-wall backflow surrounded the suction surface of the rotor blade at the tip and neither became parallel to the leading edge plane nor reached the pressure side of the adjacent blade even though the rotor blade at the tip had stalled. Spikes did not therefore appear. The modal disturbance periodically decreased the inlet velocity and induced a long length-scale stall cell including a spike. It is concluded from these results that the stall inception patterns, which were characterized by the interaction between the incoming flow, tip-leakage flow, and end-wall backflow, depended on the stagger-angle settings for the rotor blades.
On Inverse Problems in Turbine Engine Parameter Estimation
Authors: Henriksson M. , Borguet S. , Le´onard O. , Gro¨nstedt T.
Published: March 2009

This paper extends previous work on model order reduction based on singular value decomposition. It is shown how the decrease in estimator variance must be balanced against the bias on the estimate inevitably introduced by solving the inverse problem in a reduced order space. A proof for the decrease in estimator variance by means of multi-point analysis is provided. The proof relies on comparing the Cramer-Rao lower bound of the single point and the multi-point estimators. Model order selection is discussed in the presence of a varying degree of a priori parameter information, through the use of a regularization parameter. Simulation results on the SR-30 turbojet engine indicate that the theoretically attainable multi-point improvements are difficult to realize in practical jet engine applications.
Performance and Cost Analysis of a Novel Gas Turbine Cycle With CO2 Capture
Authors: Finkenrath Matthias , Ursin Tord Peter , Hoffmann Ste´phanie , Bartlett Michael , Evulet Andrei , Bowman Michael J. , Lynghjem Arne , Jakobsen Jon
Published: March 2009

In this paper, a new gas turbine cycle with integrated post-combustion CO2 capture is presented. The concept advantageously uses an intercooled gas turbine in combination with exhaust gas recirculation to enable CO2 separation at elevated concentration and pressure. Therefore, less energy is required for the CO2 separation process. In addition, due to the reduced volume flow entering the CO2 separation unit, the costs of the CO2 separation equipment are significantly reduced. The performance and cost of CO2 avoided of the power cycle have been analyzed. The results show that the concept is able to reach high CO2 capture rates of 80% and above. When accounting for CO2 capture and compression, nearly 50% (LHV) combined cycle net efficiency is obtained based on an existing medium scale intercooled gas turbine. Furthermore, the cycle has an even higher efficiency potential if applied to larger intercooled gas turbine combined cycles in the future. Using CO2 separation membrane technology which is currently under development, the cost of CO2 avoided is estimated at 31 $/tCO2 based on a medium scale intercooled gas turbine. A future scaled-up configuration based on a large-frame intercooled gas turbine has the potential to meet 30 $/tCO2 cost of CO2 avoided.
Development of a Fuel-Air Premixer for a Sub-ppm NOx Burner
Authors: Bru¨ckner-Kalb Jochen R. , Napravnik Christian , Hirsch Christoph , Sattelmayer Thomas
Published: March 2009

The concept of the cyclic periodical mixing combustion process, which had been presented earlier [1, 2], was implemented in a test combustor with external mixture preparation [3, 4]. As a major step towards the technical implementation of the process in gas turbines a low-pressure-drop fuel-air premixer on the basis of a vortex generator has been developed and implemented in the test rig. The premixer was optimized for preheat temperatures relevant for gas turbines, so that with high air preheat between 680 K and 780 K NOx emissions below 1 ppm(v) and CO emissions below 8 ppm(v) (15% O2, dry) were achieved in the tests for adiabatic flame temperatures between 1550 K at the blowout limit and an upper limit of 1630 K. As the measured emissions are almost identical with the data measured previously for the perfectly premixed case it can be concluded that the vortex mixer generates a spatially and temporally almost uniform mixture for properly selected fuel to air momentum flux ratios.
An Analytical Model for Over-Shroud Leakage Losses in a Shrouded Turbine Stage
Authors: El-Dosoky M. F. , Rona A. , Gostelow J. P.
Published: March 2009

This study presents an analytical model that uses directly measurable flow quantities to predict the effects of leakage on shrouded turbine stage performance. The model displays good predictive ability for the mass leakage fraction, for the tip leakage and for the mixing losses. The model resolves the negative incidence angle induced by mixing the leakage flow with the main stream and predicts the increment in the total mixing loss coefficient at increasing injection angles. The effects of the labyrinth seal geometry, such as the tip gap width and the number of seals, on the associated leakage losses as well as on the turbine stage performance are adequately represented. Overall, the present model exhibits a good qualitative and quantitative agreement with comparative benchmark data. It is concluded that increasing the labyrinth through-flow resistance by increasing the number of fins leads to a decrement in the leakage flow and its adverse effects but the effectiveness of this reduction decreases as the number of fins increases by more than three. The mass leakage fraction, tip leakage loss coefficient and total mixing loss coefficient increase linearly as the sealing gap ratio increases. A conventional injection angle of 90° increases the total mixing loss by about 28% compared to injecting parallel to the main passage flow.
Topology Derivative Calculations for Multidisciplinary Structural-Thermal Component Design
Authors: Nagendra Somanath
Published: March 2009

Optimal shape design (OSD) is a key element of well-designed multifunctional - multidisciplinary structures. The structural shape should satisfy the design intent and perform in an environment that would include fluid flow and heat transfer. PDM (Product Data Management) and PLM (Product Lifecycle Management) processes would need efficient methodology to be successful for product design and ensure its functionality over its life. The key is to design for functionality as well as ensure product survivability at affordable maintenance cost. The design of shapes to efficiently perform is inclined to be mathematically elegant and computationally challenging as complex multidisciplinary problems are encountered. There is a critical need to have a systematic developed system that will link the physics and mathematics of shape design with the functional intent of the component. In industry optimum design is not a once and for all solution tool because engineering design is made of compromises owning to multidisciplinary aspects of the component and necessity of doing multipoint constrained design. OSD is a branch of differentiable optimization of distributed systems where gradient and Newton methods are natural numerical tools. Existence of solutions and differentiability criteria are the key elements of domain decomposition and shape evolution strategies. As shape evolves oscillations of shapes could lead to non-physical or non-intuitive solutions of the topological optimization problem. OSD is still a numerically challenging because it is computer intensive and in practice one has to make compromises between shapes that are good with respect to more than one criterion. PDM-PLM processes when combined with OSD offers efficient work flow and design information to ensure a systematic design environment within which new products can be designed. This paper focuses on presenting a systematic methodology for design within which product topology can evolve under multidisciplinary loads.
The Effect of Leading-Edge Geometry on Wake Interactions in Compressors
Authors: Wheeler Andrew P. S. , Sofia Alessandro , Miller Robert J.
Published: March 2009

The effect of leading-edge geometry on wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and circular leading-edge were tested on a Controlled Diffusion (CDA) stator-blade. Experiments were undertaken on the stator suction-surface, these included hotwire boundary-layer traverses, surface hotfilm measurements and high resolution leading-edge pressure measurements. Steady CFD predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For the blade with the elliptic leading-edge (Blade A), the leading-edge boundary-layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary-layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary-layer indicated that the wake/leading interaction for Blade A raised the suction-surface loss by 20%. For the blade with the circular leading-edge (Blade B) the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forwards whilst inducing a turbulent reattachment upstream of the time-average reattachment position. This produced a region of very high momentum thickness at the leading-edge. The suction-surface profile loss was found to be 38% higher for Blade B compared to Blade A. The total loss (suction-surface and pressure-surface) for Blade B was measured to be 32% higher than that of Blade A.
Spray Generated by an Airblast Atomizer at High-Pressure Conditions
Authors: Batarseh Feras Z. , Roisman Ilia V. , Tropea Cam
Published: March 2009

We present an experimental investigation of a spray generated by an airblast atomizer. Experiments have been performed in a pressure chamber equipped by transparent windows allowing an optical access to the spray. Several techniques of spray investigation have been applied: spray visualization using the high-speed video system, spray visualization and instantaneous velocity measurements using the PIV technique, spray velocimetry and sizing using the IPI and phase Doppler instruments. Phase Doppler instrument has been used to characterize the droplets in the spray: their diameter, two components of the velocity vector. Also the integral parameters of the spray, such as the local volume flux density, have been characterized. We conduct a parametric study of the effect of the ambient pressure, the air flow rate and the water flow rate on an atomized spray. Measurements at different radial locations in the spray and in two planes were performed. The measurements in these two planes allow one to determine the distributions of all the three components of the average drop velocity vector: axial, radial and azimuthal. PDA measurements show that atomized spray is sensitive to any change in the studied parameters. For example, increasing air flow rate from 20 SCMH to 45 SCMH and keeping same water flow rate and pressure, leads to an increase in all velocity components and also to a change in droplets diameters. On the other hand, keeping constant pressure and air flow rate and increasing water flow rate from 0.7 to 1.4 l/hr, leads to an increase in water droplets sizes and the axial velocity component, whereas the other velocity components show a non uniform change. Moreover, increasing the ambient pressure leads to the growth of the spray velocity and drops diameters.