bluuebunny/crossref_metadata_2025 huggingface dataset:
The Stability-Limiting Flow Mechanisms in a Subsonic Axial-Flow Compressor and Its Passive Control With Casing Treatment
Authors: Lu Xingen , Zhu Junqiang , Nie Chaoqun , Huang Weiguang
Published: August 2009

The phenomenon of flow instability in the compression system such as fan and compressor has been a long-standing “bottle-neck” problem for gas turbines/aircraft engines. With a vision of providing a state-of-the-art understanding of the flow field in axial-flow compressor in the perspective of enhancing their stability using passive means. Two topics are covered in this paper. The first topic is the stability-limiting flow mechanism close to stall, which is the basic knowledge needed to manipulate end-wall flow behavior for the stability improvement. The physical process occurring when approaching stall and the role of complex tip flow mechanism on flow instability in current high subsonic axial compressor rotor has been assessed using single blade passage computations. The second topic is flow instability manipulation with casing treatment. In order to advance the understanding of the fundamental mechanisms of casing treatment and determine the change in the flow field by which casing treatment improve compressor stability, systematic studies of the coupled flow through a subsonic compressor rotor and various end-wall treatments were carried out using a state-of-the-art multi-block flow solver. The numerically obtained flow fields were interrogated to identify complicated flow phenomenon around and within the end-wall treatments and describe the interaction between the rotor tip flow and end-wall treatments. Detailed analyses of the flow visualization at the rotor tip have exposed the different tip flow topologies between the cases with treatment casing and with untreated smooth wall. It was found that the primary stall margin enhancement afforded by end-wall treatments is a result of the tip flow manipulation. Compared to the smooth wall case, the treated casing significantly dampen or absorb the blockage near the upstream part of the blade passage caused by the upstream movement of tip clearance flow and weakens the roll-up of the core vortex. These mechanisms prevent an early spillage of low momentum fluid into the adjacent blade passage and delay the onset of flow instability.
Improved Performance Model of Turbocharger Centrifugal Compressor
Authors: Yang Mingyang , Zheng Xinqian , Zhang Yangjun , Li Zhigang
Published: August 2009

This paper improves the conventional performance prediction model by correlating recirculation loss at the outlet of compressor impeller with its rotational speeds. The validation is carried out on a gasoline engine turbocharger compressor. The result shows that accuracy of the new model is greatly improved over the whole operating speeds, which brings possibility to the high accurate performance prediction in off design condition and a powerful tool for the matching between turbocharger and engine.
Degradation Effects on Industrial Gas Turbines
Authors: Kurz Rainer , Brun Klaus , Wollie Meron
Published: August 2009

This paper provides a discussion on how degradation develops and affects the performance of the gas turbine. Because the function of a gas turbine is the result of the fine tuned cooperation of many different components, the emphasis of this paper is on the gas turbine and its components as a system. Therefore, the interaction of components is studied in detail. An engine model is subjected to various types of degradation, and the effect on operating parameters is studied. The focus is on three areas: How does component degradation impact the operating points of the engine compressor, how does component degradation impact full load and part load gas turbine performance characteristics, and how does component degradation impact measurable engine operating parameters. Experimental data is provided that support the theoretical conclusion. Parameters that indicate levels of degradation are outlined, thus providing guidance for condition monitoring practice.
Numerical Simulations of Onset of Volute Stall Inside a Centrifugal Compressor
Authors: Chen Hua , Guo Strong , Zhu Xiao-Cheng , Du Zhao-Hui , Zhao Stone
Published: August 2009

In a previous publication (Guo & Chen et al., 2007), the authors solved the unsteady, 3-D Navier-Stokes equations with the k-ε turbulence model using CFX software to show that there is a volute stall coincided with the stage stall of a turbocharger centrifugal compressor operated at 423m/s tip speed and the stage stall frequency is dictated by a volute standing wave. This paper presents the flow condition at the vaneless diffuser and volute from the same simulation at various mass flow rates from stage peak efficiency to deep stage stall. Time averaged flow conditions show that (1) the influence of exducer blade passing at the volute inlet rapidly diminishes at the compressor peak pressure ratio point and the influence vanishes when the stage is in stall; (2) only at the peak pressure ratio point, circumferentially averaged, spanwise distribution of radial velocity at the volute inlet has an inflection point and the distribution meets the requirement of the Fjo̸rtoft instability theorem; (3) in the volute discharge section, the flow stalls after the stage stalls and the vortex core at the cross sectional center of the section breaks down; (4) impeller total pressure rise curve has a flat region in the middle before the stage stalls and (5) diffuser stall triggers the stage stall and drives the volute into stall.
Long-Term Microturbine Exposure of an Advanced Alloy for Microturbine Primary Surface Recuperators
Authors: Matthews Wendy J. , More Karren L. , Walker Larry R.
Published: August 2009

Haynes Alloy HR-120 forms a protective oxide scale when exposed to the harsh operating environment of a microturbine primary surface recuperator. Primary surface recuperators manufactured from HR-120 are currently in use on the Capstone C65 MicroTurbine. Long-term microturbine tests of this alloy are currently being conducted at an elevated turbine exit temperature (∼100F° higher than normal operation) at Capstone Turbine Corporation. Alloy samples that have been tested under steady-state microturbine operating conditions are removed after pre-determined exposure intervals for characterization by Capstone Turbine Corporation in collaboration with Oak Ridge National Laboratory. Such evaluations include characterization of surface oxide scales and the associated alloy compositional changes following steady-state operation ranging from 1,800 – 14,500 hours. Results from the microstructural and compositional analyses of these long-term, steady-state engine-tested HR-120 samples are used to illustrate the progression of alloy oxidation in the microturbine operating environment.
Gas Turbine Engine Noise
Authors: Mankbadi R.
Published: August 2009

This article discusses the various noise sources associated with gas turbine engines and the computational aeroacoustics techniques used for predicting the aerodynamically-generated sound. Given a sound source, several tools are presented for predicting the corresponding radiated sound. Results for sound-generation mechanism are presented using large- or very-large eddy simulations, as well as other computational means. A brief summary of the main concepts for noise reduction are then presented.
Fast Epitaxial High Temperature Brazing of Single Crystalline Nickel Based Superalloys
Authors: Laux Britta , Piegert Sebastian , Ro¨sler Joachim
Published: August 2009

A new high temperature brazing technology for the repair of turbine components made of single crystalline nickel based superalloys has been developed. It allows the repair of single crystalline parts by producing an epitaxially grown braze gap within very short times. In contrast to commonly used brazing technologies the process is not diffusion based but works with consolute systems, particularly nickel-manganese alloys. Brazing experiments with 300 μm wide parallel braze gaps as well as V-shaped gaps with a maximum width of 250 μm were conducted. Furthermore, thermodynamic simulations with the help of ThermoCalc software, Version TCR were carried out to identify compositions with a suitable melting behavior and phase formation. With the new alloys complete epitaxial bridging of both gap shapes has been achieved within brazing times as short as ten minutes.
An Innovative Passive Tip-Leakage Control Method for Axial Turbines: Linear Cascade Wind Tunnel Results
Authors: Hamik Markus , Willinger Reinhard
Published: August 2009

Depending on the blade aspect ratio, tip-leakage losses can contribute up to one third of the total losses in an axial turbine blade row. In unshrouded turbine blade rows, the radial gaps allow working fluid to pass from the pressure to the suction sides. This tip-leakage flow does not contribute to the work output of the turbine stage. Therefore, any technique which tends to reduce tip-leakage losses has the objective to decrease the flow through the tip gaps. A frequently used method of reducing the tip-leakage flow is the modification of the blade tip geometry by so-called squealers or winglets. Since this method decreases the sensitivity of tip-leakage losses on tip gap width, it is called tip desensitization. This paper presents a new method for tip desensitization: the passive blade tip injection. A low speed cascade wind tunnel is used for experimental investigations. Geometry of the turbine cascade is the up-scale of the tip section of a gas turbine rotor row. Three different gap widths in the range from 0.85% to 2.50% chord length are used. Total pressure, static pressure and flow angles are obtained by traversing a pneumatic five-hole probe about 0.3 axial chord lengths downstream of the turbine cascade. For investigations of the tip injection effect, a single blade of the cascade is modified by an injection channel. Based on experimental results, it is shown that the passive tip injection method decreases tip-leakage losses. At small tip gaps, this reduction can be rather significant. Finally, the positive influence of blade tip injection on tip-leakage losses is described by an analytical model based on the discharge coefficient.
Data Management and Adaptive Machining Technology for Efficient Repair and Manufacture of Turbine Components
Authors: Bremer Claus
Published: August 2009

The manufacture and repair of turbine components consist of a chain of different processes. Many of these processes are carried out manually today, especially in the case of repair. Currently, the repair of blisks is a central issue whenever consideration is given to replacing bladed stages with blisks; however, the feasibility of such a step hinges on the available capabilities for automated repair. A generic data management system has been developed which will constitute the core of automated repair systems for turbine components. The web-based data management system handles the logistics of the components and the accompanying data sets. As a result, different repair processes can be carried out at different facilities without any loss of information (“virtual workshop”). Furthermore, the approach described supports efficient part flow control as well as life cycle monitoring. In addition to the data management developments, existing repair methods have been improved by employing adaptive machining technology that makes use of the geometrical information provided by dedicated scanning systems or inprocess measuring devices and compensates for the part-to-part variation and inaccurate clamping position of the turbine components to be machined.
Measurements Versus Predictions for the Rotordynamic Characteristics of a 5-Pad, Rocker-Pivot, Tilting-Pad Bearing in Load Between Pad Configuration
Authors: Carter Clint R. , Childs Dara W.
Published: August 2009

Rotordynamic data are presented for a rocker-pivot tilting-pad bearing in a load-between-pad (LBP) configuration for unit loads over the range [345, 3101 kPa] and speeds over the range [4k to 13k rpm]. The bearing was direct lubricated through a leading-edge groove with the following specifications: 5 pads, .282 preload, 60% offset, 57.87° pad arc angle, 101.587 mm (3.9995 in) rotor diameter, .1575 mm (.0062 in) diametral clearance, 60.325 mm (2.375 in) pad length. Dynamic tests were performed over a range of frequencies to investigate frequency effects on the dynamic-stiffness coefficients. Under most test conditions, the direct real parts of the dynamic stiffnesses could be approximated as quadratic functions of the excitation frequency and accounted for with the addition of an added mass matrix to the conventional [K][C] matrix model to produce a frequency-independent [K][C][M] model. Measured added mass terms in the loaded direction approached 60 kg. At low speeds, “hardening” direct dynamic stiffness coefficients that increased with increasing frequency were obtained that produced negative added-mass terms. No frequency dependency was obtained for the direct damping coefficients. The dynamic experimental results were compared to predictions from a bulk-flow CFD analysis. The static load direction in the tests was y. The direct stiffness coefficients Kxx and Kyy were slightly over predicted. Measured direct damping coefficients Cxx and Cyy were insensitive to changes in either load or speed in contrast to predictions of marked Cyy sensitivity for changes in the load. Only at the highest test speed of 13000 rpm were the direct damping coefficients adequately predicted. Measurable cross-coupled stiffness coefficients were obtained for the bearings with Kxy and Kyx being approximately equal in magnitude but opposite in sign — clearly destabilizing. However, the whirl frequency ratio was found to be zero at all test conditions indicating infinite stability for the bearing.
Integrated Test and Evaluation Techniques as Applied to an Inlet Swirl Investigation Using the F109 Gas Turbine Engine
Authors: Davis Milt , Beale Dave , Sheoran Yogi
Published: August 2009

With increasing emphasis on streamlining the acquisition process, ground-test centers like the Arnold Engineering Development Center (AEDC) are re-evaluating their roles in the development of aerospace systems. Instead of merely providing data from ground-test facilities, the new emphasis challenges AEDC to become a team member that provides knowledge for risk management and decision making during the development and operation of an aerospace system. As a key link in the transition from a laboratory or design concept to an operational system, the capabilities of a ground-test center can provide a tremendous opportunity to reduce the time and cost involved in flight vehicle system development. AEDC has aggressively accepted the challenge and has developed an Integrated Test and Evaluation (IT&E) approach to support aerospace system development efforts. This paper focuses on an integrated test and evaluation process in a joint test and analysis effort between AEDC, the USAF Academy and Honeywell. This paper reports on the role of gas turbine engine/compressor numerical simulations in the test, analysis, and evaluation process in conjunction with an investigation to discern the effects of inlet swirl on the F109 turbofan engine performance and operability.
Numerical Simulation of Tip Clearance Flow Control in Axial Turbine Rotor: Part 1—Active Flow Control Injection From Turbine Blade Tip
Authors: Li Wei , Qiao Wei-Yang , Xu Kai-Fu , Luo Hua-Ling
Published: August 2009

Reducing loss and increasing efficiency are always pursued in the designing of the turbine, and flow control is an efficient solution to minimize the tip clearance loss. Recently it aroused much attention in the field of the turbine tip clearance flow. Part-1 of this paper aims to numerically investigate the effect of active turbine clearance flow control by injection from a turbine blade tip on the tip clearance flow. Part-2 of this paper focus on the passive turbine tip clearance flow control. A density-correction based, 3D Reynolds-averaged Navier-Stokes equations CFD code with Reynolds Stress Model, which was proved to be validated, was adopted. The variable specific heat was considered. The effects of injection on the tip clearance flow were simulated in two tip clearance heights, and each height corresponds to five injection hole locations and five injection mass flow rates. Accordingly, the mechanisms of active injection control were put in evidence; the effects of the injection on the turbine efficiency which includes the effect of the jet and the tip clearance flow were highlighted; and the tip clearance flow structure was analyzed topologically. If the tip leakage flow corresponding to the injection location is subsonic, this injection can increase the efficiency, such as the first and the second jet. The combined jet could increase the efficiency by 0.35% for the case of loose tip clearance and by 0.3% for the case of tight tip clearance. The number of saddle points was equal to that of nodes near the injection hole, which could satisfy the singularity point total number law.
Numerical Simulation of Tip Clearance Control in Axial Turbine Rotor: Part 2—Passive Control of Five Different Tip Platforms
Authors: Li Wei , Qiao Wei-Yang , Xu Kai-Fu , Luo Hua-Ling
Published: August 2009

The tip leakage flow has significant effects on turbine in loss production, aerodynamic efficiency, etc. Then it’s important to minimize these effects for a better performance by adopting corresponding flow control. The active turbine tip clearance flow control with injection from the tip platform is given in Part-1 of this paper. This paper is Part-2 of the two-part papers focusing on the effect of five different passive turbine tip clearance flow control methods on the tip clearance flow physics, which consists of a partial suction side squealer tip (Partial SS Squealer), a double squealer tip (Double Side Squealer), a pressure side tip shelf with inclined squealer tip on a double squealer tip (Improved PS Squealer), a tip platform extension edge in pressure side (PS Extension) and in suction side (SS Extension) respectively. Combined with the turbine rotor and the numerical method mentioned in Part 1, the effects of passive turbine tip clearance flow controls on the tip clearance flow were sequentially simulated. The detailed tip clearance flow fields with different squealer rims were described with the streamline and the velocity vector in various planes parallel to the tip platform or normal to the tip leakage vortex core. Accordingly, the mechanisms of five passive controls were put in evidence; the effects of the passive controls on the turbine efficiency and the tip clearance flow field were highlighted. The results show that the secondary flow loss near the outer casing including the tip leakage flow and the casing boundary layer can be reduced in all the five passive control methods. Comparing the active control with the passive control, the effect brought by the active injection control on the tip leakage flow is evident. The turbine rotor efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine rotor efficiency, and it increased by 0.215%.
Siemens SGT-800 Industrial Gas Turbine Enhanced to 47MW: Design Modifications and Operation Experience
Authors: Shukin Sergey , Annerfeldt Mats , Bjorkman Mats
Published: August 2009

Mid year of 2007 Siemens Oil & Gas and Industrial Applications introduced an enhanced SGT-800 gas turbine. The new power rating is 47MW at a 37.5% electrical efficiency in open cycle (ISO). Four components in the gas turbine are modified and are fully interchangeable between the existing 45MW and the 47MW rating. Improved cooling designs were introduced in the turbine stages #1 and #2 requiring no change to the casting design. The only modification is to the machining of the parts and to the guide vane cooling inserts and impingement screens. A re-stagger of the stage #1 compressor blade was made to give a slightly increase in the airflow. The combustor outlet temperature (COT) remains the same. The first SGT-800 with 47MW rating was successfully tested during the autumn of 2006 and the expected performance figures were confirmed. This unit has, up to November 2007, accumulated 8 000 hours and a planned follow up inspection made after 4 000 hours by borescope of the hot section showed that the parts were in excellent condition. This article presents some details of the design work carried out during the development of the enhancement from 45MW to the mature rating of 47MW and the operation experience from the first units.
A Study of Thermohydrodynamic Features of Multi Wound Foil Bearing Using Lobatto Point Quadrature
Authors: Feng Kai , Kaneko Shigehiko
Published: August 2009

The applications of foil air bearings, which are recognized to be the best choice for oil free applications, have been extended for use in a wide range of turbo-miachineries with high speed and high temperature. Lubricant temperature becomes an important factor in the performance of foil air bearings, especially at high rotational speeds and high loads or at high ambient temperature. However, most of the published foil air bearing models were based on the isothermal assumption. This study presents a thermohydrodynamic analysis (THD) of Multi Wound Foil Bearing (MWFB), in which the Reynolds’ equation is solved with the gas viscosity as a function of temperature that is obtained from the energy equation. Lobatto point quadrature, which was proposed by Elrod and Brewe and introduced into compressible calculation by Moraru and Keith, is utilized to accelerate the iteration process with a sparse mesh across film thickness. A finite element model of the foil is used to describe the foil elasticity. An iterative procedure is performed between the Reynolds’ equation, the foil elastic deformation equation and the energy equation, until the convergence is achieved. A three-dimensional temperature prediction of air film is presented and a comparison of THD to isothermal results is made to emphasize the importance of thermal effects. Finally, published experimental data are used to validate this numerical solution.
Flame Transfer Matrices of a Premixed Flame and a Global Check With Modelling and Experiments
Authors: Alemela Panduranga Reddy , Fanaca Dan , Ettner Florian , Hirsch Christoph , Sattelmayer Thomas , Schuermans Bruno
Published: August 2009

In this paper alternative ways to obtain the thermo-acoustical characteristics of perfectly premixed flames given by their flame transfer matrix (FTM) is investigated. In particular a model based data reduction procedure which greatly reduces the experimental effort and therefore enables to provide this flame data for many more operation points than previously possible is proposed and validated. It is shown how the acoustic pressure field measured from two forcing states using the multi microphone method leads to the determination of the direct experimental FTM. The next relatively simpler method shown is the hybrid method which is based on Rankine-Hugoniot relations and the experimental flame transfer function (FTF) from OH*-chemiluminescence measurements for heat release fluctuations. Later to obtain the FTM using a network model based on Rankine-Hugoniot relations and an n-τ-σ FTF model representing the flame by regression analysis of the acoustical measurements is presented. Experimental results for the direct experimental FTM and the hybrid FTM are compared with the model based result. The results indicate very good consistency between the direct, hybrid and model based techniques providing a global check of the methods/tools used for analysing the thermoacoustic mechanisms of flames.
Casing Treatment and Blade Tip Configuration Effects on Controlled Gas Turbine Blade Tip/Shroud Rubs at Engine Conditions
Authors: Padova Corso , Dunn Michael G. , Barton Jeffery , Turner Kevin , Turner Alan , DiTommaso Darin
Published: August 2009

Experimental results obtained for an Inconel compressor blade rubbing bare-steel and treated casings at engine speed are described. Since 2002 a number of experiments were conducted to generate a broad database for tip rubs, the Rotor-Blade Rub Database (RBR database) obtained using the unique experimental facility at the OSU Gas Turbine Laboratory. As of 2007, there are seven completed groups of measurements in the database. Among them a number of blade-tip geometries and casing surface treatments have been investigated. The purpose of this paper is to provide a detailed interpretation of this database. Load cell, strain, temperature and accelerometer measurements are discussed and then applied to analyze the interactions resulting from progressive and sudden incursions of varying severity, defined by incursion depths ranging from 13 μm to 762 μm (0.0005 in to 0.030 in). The influence of blade-tip speed on these measurements is described. The results presented describe the dynamics of rotor and casing vibro-impact response at representative operational speeds similar to those experienced in flight. Force components at the blade tip in the axial and circumferential directions are presented for rub incursions ranging in depth from very light (13 μm) to severe (406 μm). Trends of variation are observed during metal-to-metal and metal-to-abradable contacts for two airfoil tip shapes and tip speed 390 m/s (1280 ft/s) and 180 m/s (590 ft/s). The non-linear nature of the rub phenomena reported in earlier work is confirmed. In progressing from light rubs to higher incursion, the maximum incurred circumferential load increases significantly while the maximum incurred axial load increases much less. The manner in which casing surface treatment affects the loads is presented. Concurrently, the stress magnification on the rubbing blade at root mid-chord, at tip leading edge, and at tip trailing edge is discussed. Computational models to analyze the non-linear dynamic response of a rotating beam with periodic pulse loading at the free-end are currently under development and are noted. A companion paper on a method to determine blade tip forces is presented separately in this Turbo Expo conference.
Combustion Characteristics of a Can Combustor With a Rotating Casing for an Innovative Micro Gas Turbine
Authors: Shih Hsin-Yi , Liu Chih-Zong
Published: August 2009

A can type combustor with rotating casing for the innovative micro gas turbine has been modeled, and the combustion characteristics were investigated. The simulations were performed using commercial code STAR-CD, in which three-dimensional compressible k-ε turbulent flow model and one-step overall chemical reaction between methane/air were used. The results include the detailed flame structure at different rotation speed of outside casing, ranging from stationary to the maximum speed of 58000 rpm of the design point. The airflows are baffled when entering the combustor through the linear holes due to the centrifugal force caused by the rotating casing and the inlet flow angle is inclined. When the rotation is in the opposite direction of the swirling flows driven by the designed swirler, a shorter but broader recirculation zone and a concave shape flame are found at higher rotating speed. At maximum rotating speed, the swirling flows are dominated by the rotating flows caused by the casing, especially downstream of the combustor. The combustor performance were also analyzed, indicating higher combustion efficiency and higher exit temperature when casing rotates, which benefits the performance of gas turbine, but the cooling and possible hot spots for turbines are the primary concerns.
Large-Eddy Simulation of Film Cooling Flow Ejected in a Shallow Cavity
Authors: Renze Peter , Schro¨der Wolfgang , Meinke Matthias
Published: August 2009

In the present paper the flow field of a film cooling configuration with cylindrical holes embedded in a shallow cavity is investigated using large-eddy simulation (LES). The cooling jet is injected through a single row of inclined holes from a transverse cavity into a turbulent flat plate boundary layer at a temperature ratio of TR = 0.44. The mixing of the cooling fluid and the crossflow within the cavity is a highly unsteady process generating complex vortical structures. The impact of the boundary layer separation at the upstream cavity edge on the jet-crossflow interaction is studied in detail. The driving mechanisms of the momentum and heat exchange between the jet and the crossflow are identified and discussed. The flow field and the adiabatic cooling efficiency is compared to a standard cylindrical film cooling configuration without a cavity. The development of the counter-rotating vortex pair (CVP) downstream of the jet injection is investigated. An analysis of the vortex dynamics shows an impinging behavior of the jet fluid in this area. The Reynolds stress shows a more two-dimensional distribution compared to the anisotropic nature of the jet-in-a-crossflow (JICF) at standard cylindrical holes. Since the heat exchange is closely connected to the transport of momentum in the mixed boundary layer, this observation explains the enhanced lateral spreading of the cooling fluid.
The Effects of Manufacturing Tolerances on Gas Turbine Cooling
Authors: Bunker Ronald S.
Published: August 2009

This study presents a summary of the effects of manufacturing methods and processing steps upon the resulting thermal boundary conditions for typical highly cooled turbine airfoils. Specific emphasis is placed on the conservatism that must be “designed into” the component for survival due to realistic manufacturing tolerances. Using the features of a typical blade design, the main geometric factors that can influence the blade heat transfer capability through manufacturing variability are enumerated. The tolerances on those geometric factors are provided and the approximate quantitative impact on thermal boundary conditions is summarized. A simple example of airfoil cooling for a representative wall section is used to tabulate the variations with the resulting changes in the most affected thermal boundary conditions. Each of the main geometric factors is then evaluated in terms of its possible effect on maximum metal temperature. Paretos of the effects of manufacturing factors exhibit which factors are key and where tighter tolerances may help. Monte Carlo analysis results show the probability distributions associated with overall cooling changes tied to the tolerances.
Trapped Vortex Combustor Performance for Heavy-Duty Gas Turbines
Authors: Haynes Joel M. , Micka Daniel , Hojnacki Ben , Russell Craig , Lipinski John , Shome Biswadip , Huffman Marcus
Published: August 2009

The application of the trapped vortex combustor (TVC) concept to heavy-duty gas turbine conditions has been explored. Combustor stability, lean blow out, and emission performance requirements limit design options for conventional lean premixed combustors. The TVC concept has demonstrated reduced emissions and high turndown with liquid fuels and could overcome existing lean premixed performance constraints as well. The present study examines premixed injection of natural gas into the TVC at heavy-duty gas turbine conditions. The emission performance is measured over a range of operating conditions. The combustor turndown and dynamics performance are also presented. To forecast the performance potential of the TVC combustor a chemical reactor network model was developed. The model was anchored with experimental data and implemented in the prediction of TVC combustor emissions and turndown performance. The reactor model confirms that NOx reduction greater than 60% is possible using a trapped vortex combustor (TVC).
The Demonstration and Efficacy of the 1 Meter Sound Level Criteria for Gas Turbines in Offshore Installations
Authors: Lotton Jeff
Published: August 2009

Is the 1meter, (1m) sound level criteria really benefitting the industry? Are there alternatives that would simplify and lower the cost of gas turbine packages? This paper will show the results of a dedicated factory noise test on a gas turbine package that was used to demonstrate compliance with a sound level guarantee. In addition there will be observations, discussion and alternatives to the 1m criteria which will hopefully lead to some discussion about this criteria and if it is truly serving the industry as well as its benchmark status would indicate.
Film-Cooling Flowfields With Trenched Holes on an Endwall
Authors: Sundaram N. , Thole K. A.
Published: August 2009

The leading edge region along the endwall of a stator vane experiences high heat transfer rates resulting from the formation of horseshoe vortices. Typical gas turbine endwall designs include a leakage slot at the combustor-turbine interface as well as film-cooling holes. Past studies have documented the formation of a horseshoe vortex at the leading edge of a vane, but few studies have documented the flowfield in the presence of an interface slot and film-cooling jets. In this paper, a series of flowfield measurements are evaluated at the leading edge with configurations including: a baseline with neither film-cooling holes nor an upstream slot, a row of film-cooling holes and an interface slot, and a row of film-cooling holes in a trench and an interface slot. The results indicated the formation of a second vortex present for the case with film-cooling holes and a slot relative to the baseline study. In addition, turbulence intensity levels as high as 50% were measured at the leading edge with film-cooling holes and a slot compared to the 30% measured for the baseline study. A trench was shown to provide improved overall cooling relative to the no trench configuration as more of the coolant stayed attached to the endwall surface with the trench.
Thermodynamic Analysis of Part-Flow Cycle Supercritical CO2 Gas Turbines
Authors: Utamura Motoaki
Published: August 2009

Cycle characteristics of closed gas turbines using super critical carbon dioxide as a working fluid are investigated. It is found an anomalous behavior of physical properties of CO2 at pseudo-critical point may limit heat exchange rate of a regenerative heat exchanger due to the presence of pinch point inside the regenerative heat exchanger. Taking such pinch problem into consideration, the cycle efficiency of Brayton cycle is assessed. Its value is found limited to 39% degraded by 8% compared with the case without the pinch present inside. As an alternative a part flow cycle is investigated and its operable range has been identified. It is revealed that the part flow cycle is effective to recover heat transfer capability and may achieve the cycle thermal efficiency of 45% under maximum operating conditions of 20MPa and 800K. Optimal combination of turbine expansion ratio and a part flow ratio is 2.5 and 0.68 respectively. Parametric study is carried out. In neither compressor nor turbine, deteriorated adiabatic efficiency may affect cycle efficiency significantly. However, pressure drop characteristics of heat exchangers govern the cycle efficiency.
Effect of Computational Grid on Performance of Two-Equation Models of Turbulence for Film Cooling Applications
Authors: Yavuzkurt Savas , Habte Melaku
Published: August 2009

The effect of the computational grid on the performance of two-equation models of turbulence in predicting film cooling effectiveness has been investigated. The four turbulence models are: the standard, RNG, and realizable k-ε, and the standard k-ω models in the CFD code FLUENT. The geometry and flow-field were taken from an experimental study on discrete-hole film-cooling on a flat plate and are simulated in FLUENT. Some of the parameters are: Pitch-to-diameter ratio of 3.04, injection tube length-to-diameter ratio of 4.6. Two blowing ratios of M = 0.5 and 1.5 were considered. In earlier studies presented in Turbo Expo 2006 and 2007, a hexahedral grid for the main flow and tetrahedral grid for the short injection tubes and plenum were used as suggested by the FLUENT users’ manual. The results of predictions both under low and high freestream turbulence and for high and low blowing ratios were not that good. It was decided that some of these differences arise from the use of “hybrid mesh” with a non-conformal interface boundary between them. Also tetrahedral mesh in the injection tube could not resolve the boundary layer there leading to incorrect injection profiles at the hole exit. In order to correct this deficiency, in the current study a single hexahedral grid is used both in the injection tube, plenum and the main flow regions eliminating the need for merging two different meshes and also leading to correct boundary layer resolution in the tube resulting in more realistic jet exit profiles. The difference between the model calculations and data for effectiveness are reduced to within 40% in the near field (∼x/D < 8) of the jets and 10% in the far field (∼x/D > 8). This shows the importance of using correct mesh which fits the problem physics and expected flow pattern for the accurate solutions and indicated the necessity of using CFD codes such as FLUENT with care and experience. There were still differences between the results for four models. It looks like k-ε and k-ω models give the best predictions and the trend of the data for the centerline effectiveness in the near field, whereas all models give good (within 5–10%) predictions of the centerline effectiveness in the far field.
Compressor Wake/Leading-Edge Interactions at Off Design Incidences
Authors: Wheeler Andrew P. S. , Miller Robert J.
Published: August 2009

In this paper, the effects of wake/leading-edge interactions were studied at off-design conditions. Measurements were performed on the stator-blade suction surface at midspan. The leading-edge flow-field was investigated using hotwire micro-traverses, hotfilm surface shear-stress sensors and pressure micro-tappings. The trailing-edge flow-field was investigated using hotwire boundary-layer traverses. Unsteady CFD calculations were also performed to aid the interpretation of the results. At low flow coefficients, the time-averaged momentum thickness of the leading-edge boundary layer was found to rise as the flow coefficient was reduced. The time-resolved momentum-thickness rose due to the interaction of the incoming rotor wake. As the flow coefficient was reduced, the incoming wakes increased in pitch-wise extent, velocity deficit and turbulence intensity. This increased both the time-resolved rise in the momentum thickness and the turbulent spot production within the wake affected boundary-layer. Close to stall, a drop in the leading-edge momentum thickness was observed in-between wake events. This was associated with the formation of a leading-edge separation bubble in-between wake events. The wake interaction with the bubble gave rise to a shedding phenomenon, which produced large length scale disturbances in the surface shear stress.
The Effect of Specific Heat Ratio on the Performance of Compressible Flow Turbo-Machines
Authors: von Backstro¨m Theodor W.
Published: August 2009

The paper presents a method of determining the pressure ratio characteristic of a compressible flow turbo-machine when the specific heat ratio of the gas flowing through it is changed. It is shown that Mach number scaling in efficient machines running at low fractional increases in total temperature could tolerate limited variations in specific heat ratio. A method of finding the scaled operating conditions for the achievement of similar density ratios in scaled and prototype machines operating with gases with different specific heat ratios is presented. The method achieved very good accuracy in scaling the performance of a centrifugal impeller working with argon to its performance with carbon dioxide. The stage polytropic efficiencies were chosen to agree with measured data, although analysis indicated that polytropic stage efficiency should be independent of specific heat ratio. Further investigation and validation may lead to a standardised method of scaling turbo-machinery performance between gases with varying properties, which includes the effect of specific heat ratio.
Gas Turbine Fault Diagnostics Using a Fusion of Least Squares Estimations and Fuzzy Logic Rules
Authors: Lipowsky Holger , Staudacher Stephan , Nagy Daniel , Bauer Michael
Published: August 2009

This paper presents a method to improve the process of gas turbine diagnosis in case of a single fault event by calculating both deviations of performance parameters from their nominal values and fault probabilities. The approach is based on a thermodynamic model of the monitored gas turbine that is used to generate an Influence-Coefficient-Matrix (ICM) describing the gas turbine’s behaviour at the desired operating point in a linearised form. The ICM is used to calculate deviations of performance parameters by least squares estimation. As it is not known a priori how many components are affected by a fault, the ICM is evaluated with respect to all possible fault numbers and combinations leading to sets of analyses. The nature of least squares estimation method limits the number of detectable faults (and thus the number of analyses sets) to the number of available measurements. In a second step a fuzzy logic system is applied to calculate the probability of each performance parameter to be actually affected by the fault. This is done by applying fuzzy logic rules taking into account the frequency and the mean deviation of every performance parameter within every set of analyses. The third and last step is to sum the probabilities over all sets in order to obtain a global probability for every performance parameter. The proposed technique has been applied to several simulated test cases with encouraging results. The main benefit of the technique is that the diagnostic result contains both magnitude and probability of the deviations of performance parameters. Furthermore, robustness in terms of measurement noise is achieved by using a statistical evaluation method.
Dynamic Characteristics of Composite Helicopter Blade Solved by Using the Differential Quadrature Method
Authors: Kuang J. H. , Hsu M. H. , Hung T. P.
Published: August 2009

The dynamic characteristics of nonlinear composite helicoper blades are solved by using the differential quadrature method (DQM). The bending-torsion coupled beam model is proposed to characterize the composite blade. The Kelvin-Voigt internal and linear external damping coefficients are also employed. The DQM is used to transform the partial differential equations of a composite rotor blade into a discrete eigenvalue problem. The Chebyshev-Gauss-Lobatto sample point equation is used to select the sample points. Numerical results indicate that even nine sample points can provide the convergent results by employing this DQM for the blade analysis. The difference between the responses derived from the linear and the nonlinear models have been compared to illustrate the significance of the nonlinear effect in this case. The transitional dynamic responses of the derived systems are calculated by using Newmark method. In this study, the effects of the fiber orientation, internal damping, external damping, pre-twisted angle and the rotation speed on the dynamic behavior for a composite beam are studied. The effect of the number of sample points on the accuracy of the calculated natural frequencies is also discussed. The integrity and computational efficiency of the DQM in this problem will be demonstrated through a number of case studies. Numerical results indicated that the DQM is valid and efficient for a composite blade formulation.
The Development of Centrifugal Compressor Impeller
Authors: Xu C. , Amano R. S.
Published: August 2009

Impeller is one of the key components of industrial centrifugal compressors and turbochargers. Aerodynamic and structure designs of the impeller are critical to the success of the whole compressor stages. The requirements for efficiency and operating range of industrial centrifugal compressors and turbochargers have been increased dramatically compared with the situation in the past. The efficiency of newly developed low-pressure ratio centrifugal compressor has reached the possible level of the machine. However, the efficiency level of intermediate and high-pressure ratio machine still have gap between the current state-of-the-art and possible level. The challenge for centrifugal compressor design is to keep the efficiency level at state-of-the-art and increase the compressor operating range. Increase of the compressor operating range without sacrificing compressor peak efficiency is difficult to achieve. The product globalization requires one product design, which can be used in all locations. In some counties, due to the technology differences, electricity frequencies variations could be 10%. Turbocharger compressors work at different rotational speeds for majority of the time. The compressor impeller rotating speeds change in certain range. The impeller rotating speed variation makes the impeller structure design more challenging. In this study, a full-3D impeller was designed to optimize impeller aerodynamic performance and structure characteristics.
Extensive Studies on Internal and External Heat Transfer Characteristics of Integrated Impingement Cooling Structures for HP Turbines
Authors: Funazaki Ken-Ichi , Bin Salleh Hamidon
Published: August 2009

This paper deals with experimental and computational studies on internal and external heat transfer characteristics of advanced impingement cooling units combined with pin-fin cooling as well as film cooling, which is called integrated impingement cooling structure. This integrated cooling structure can be employed in the not too distant future as a simple model of quasi-transpiration cooling system for ultra high TIT (Turbine Inlet Temperature) aeroengines or gas turbines. The present study is motivated by the study of Nakamata et al. (2005) who carried out a series of studies on the integrated impingement cooling system. They found that several arrangements of impingement holes and film cooling holes mutually staggered with respect to pins yielded better cooling performance than other non-staggered configurations, although there was no evidence-based explanations shown in their study on the flow physics happening in the cooling models. Therefore, two large-scaled acrylic-resin test models with different arrangements of the impingement and film cooling holes around the pins are made in the present study, emulating the specimens used by Nakamata et al., to evaluate internal and external heat transfer coefficients as well as film effectiveness of the test models. This study accordingly aims at clarification of the reason for the clear distinction in cooling efficiency observed by Nakamata et al. between those two different cooling configurations. The measurement technique employed is a transient method using thermochromic liquid crystal to determine not only heat transfer coefficient but also film effectiveness at the same time. Steady RANS simulation is also executed using ANSYS CFX-10 to acquire detailed information on the flow behaviors and heat transfer characteristics inside and outside the cooling systems. The experimental data, along with the numerical information, reveal that the observed difference in cooling efficiency is can be explained mainly by the difference in internal heat transfer coefficient over the target plate, indicating that the pin arrangement around the impingement jet is an important factor in order to attain higher cooling performance of the proposed integrated impingement cooling system.