bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Dimensional Optimization of Centrifugal Compressor Impellers Using Online Quasi-3D Flow Solver and Genetic Algorithm
Authors: Ma Ying , Engeda Abraham
Published: January 2011

Modeling tools are widely used to create a performance map and decrease design cycle time in computer-aided centrifugal compressor impeller optimization procedures. However, a high-dimensional performance map is difficult to create and application of the approximate performance map brings errors into optimization procedures. This paper presents an online flow solver optimization procedure, in which a Quasi-three dimensional flow solver is directly used to evaluate impeller performances in the genetic algorithm (GA). Also, this procedure is compared with offline flow solver optimization procedure. In offline flow optimization procedure, the flow solver is employed to calculate performances in training database for creating a performance map trained by one type of artificial neural network (ANN), radial basis function network (RBFN). This performance map is further used to calculate the performances of impeller geometries. Results of these two optimization procedures under same GA parameters setting are compared and show that online flow solver optimization procedure can find better optima than offline flow solver optimization procedure. Moreover, influences of GA operators, parameters and local search algorithm on online flow solver optimization procedure are also investigated.
Investigation of Stress Assisted Grain Boundary Oxidization (SAGBO) Cracking in Mar-M002 High Pressure Turbine Blades
Authors: Selvig Austin , Huang Xiao , Hildebrand Mike , Stek David
Published: January 2011

Modern superalloys have enabled High Pressure Turbine (HPT) blades in Gas Turbine Engines (GTE) to operate at higher temperatures. Unfortunately the complexity of these materials can make it difficult to understand the failure mechanisms of these blades. HPT blades made of the nickel based superalloy Mar-M002 have been found to suffer from Stress Assisted Grain Boundary Oxidation (SAGBO) cracking. HPT blades removed from an RB211-24C aero-derivative industrial GTE were sectioned and the cracks and microstructure were studied using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). No cracks were found on the external surface of the blade which had been coated with an oxidation resistant material. Surface irregularities were found along the walls of the inner cooling channels throughout the entire blade. Larger SAGBO cracks were observed to be near the lower 25% span of the blade and had initiated from the surfaces of the cooling channels. SEM/EDS analysis showed that these cracks had large amounts of alumina and Hafnium-rich particles within them. It is evident that these cracks occurred in locations where the combination of high stress and high temperature led to higher rates of oxygen diffusion and subsequent oxidation of grain boundary carbides. Hafnium Carbide precipitates along the grain boundaries expanded as they converted into Hafnium Oxide, thus further increasing the stress. It is envisaged that this increase in stress along the grain boundary has caused the cracks to initiate and coalesce. Based on this observation, it is believed that the inner cooling channels of these HPT blades could benefit from the application of an oxidation resistant coating in order to prevent or delay the formation of these cracks.
Practical Uses of Advanced Rotor Dynamics Tools to Ensure Trouble Free Operation of an Overhung Turbo-Expander Rotor
Authors: Marin Manuel A.
Published: January 2011

The intent of this paper is to illustrate how rotor dynamics analysis can be an effective tool to improve rotor dynamic characteristics. Analytical methods, such as undamped critical speeds, unbalance response and stability (damped eigenvalues) analysis are used to evaluate the vibration characteristics of rotating machinery. Advanced rotor dynamics software is capable of generating and analyzing rotor models. By removing undesirable sources of instability and ensuring reliable separation margin, rotor-stability improvement is validated. This study presents an overhung rotor with a proven stable operating history; however, higher power requirements and changes in components resulted in a potential resonant condition of concern. Based on the rotor dynamics analysis outputs, design changes were implemented to ensure the rotor will meet API’s vibration acceptance limits. After evaluating different design alternatives using computer modeling, a change in the inboard bearing diameter proved to be the best solution for attaining smooth operation. Although this paper focuses mainly on the analysis performed on an overhung rotor, the methodology used can be applied to any rotating equipment. It is clear that rotor dynamics analysis is a powerful instrument for predicting operating behavior, thus allowing for necessary changes in analytical modeling and ensuring more stable machines.
Analysis and Validation of a Unified Slip Factor Model for Impellers at Design and Off-Design Conditions
Authors: Qiu Xuwen , Japikse David , Zhao Jinhui , Anderson Mark R.
Published: January 2011

This paper presents a unified slip model for axial, radial, and mixed-flow impellers. The core assumption of the model is that the flow deviation or slip velocity at impeller exit is mainly originated from the blade loading near the discharge of an impeller and its subsequent relative eddy in the impeller passage. The blade loading is estimated and then used to derive the slip velocity using Stodola’s assumption. The final form of the slip factor model can be successfully related to Carter’s rule [1] for axial impellers and Stodola’s [2] slip model for radial impellers, making the case for this model to be applicable to axial, radial, and mixed-flow impellers. Unlike conventional slip factor models for radial impellers, the new slip model suggests that the flow coefficient at the impeller exit is an important variable for the slip factor when there is significant blade turning at the impeller discharge. This explains the interesting off-design trends for slip factor observed from experiments, such as the rise of the slip factor with flow coefficient in the Eckardt A impeller [3]. Extensive validation results for this new model are presented in this paper. Several cases are studied in detail to demonstrate how this new model can capture the slip factor variation at the off-design conditions. Furthermore, a large number of test data from more than 90 different compressors, pumps, and blowers were collected. Most cases are radial impellers, but a few axial impellers are also included. The test data and model predictions of the slip factor are compared at both design and off-design flow conditions. In total, over 1,650 different flow conditions are evaluated. The unified model shows a clear advantage over the traditional slip factor correlations, such as the Busemann-Wiesner model [4], when off-design conditions are considered.
Effects of a Realistically Rough Surface on Vane Aerodynamic Losses Including the Influence of Turbulence Condition and Reynolds Number
Authors: Erickson E. L. , Ames F. E. , Bons J. P.
Published: January 2011

Aerodynamic loss surveys are reported for a vane with a realistically rough surface. Aerodynamic losses are investigated over a range of turbulence levels {low (0.7%), grid (8.5%), aero-combustor, (13.5%)} and a range of chord Reynolds numbers {Rec = 500,000, 1,000,000, and 2,000,000}. The realistically rough surface distribution was generated by Brigham Young University’s accelerated deposition facility. The surface is intended to represent a TBC surface which has accumulated 7500 hours of operation with a particulate concentration of 0.02 ppmw. The realistically rough surface was scaled by 11 times for consistency with the vane geometry and cast using epoxy to comply with the vane geometry. The surface was applied over the vane pressure surface and about 10% of the suction surface. The 958 by 573 point roughness array generated by Brigham Young on a 9.5 by 5.7 mm region was averaged to a 320 by 191 array for fabrication. The calculated surface roughness parameters of this scaled and averaged array included the maximum roughness, Rt = 1.99 mm, the average roughness, Ra = 0.25 mm and the average forward facing angle, αf = 3.974°. The peak to valley roughness, Rz, was determined to be 0.784 mm. The sand grain roughness of the surface (ks = 0.466 mm) was estimated using a correlation offered by Bons [1]. Based on estimates of skin friction coefficient using a turbulence correlation with the vane chord Reynolds numbers, representative values for the surface’s roughness Reynolds number are 23, 43, and 80 for the three exit condition Reynolds numbers tested. Exit survey measurements for the realistically roughened vane have been compared with the base vane geometry. Total pressure loss measurements have shown an incremental increase above the original base vane which averages 0.68% for the low turbulence, 0.48% for the grid turbulence and 0.24% for the aero-combustor turbulence conditions. A portion of this increment, about 0.20%, could be attributed to the thicker trailing edge due to the average thickness of the roughened tile applied. The roughness on the near suction surface along with the abrupt end of the roughness tiles at about 0.05 m from the stagnation region causes early transition on the suction surface. This early transition influences the comparison of the low turbulence cases much more due to laminar flow on the base vane suction surface. The grid turbulence shows an incremental loss of 0.48% and this difference is likely due to both the thicker trailing edge and the suction surface roughness. The incremental loss increase for the aero-combustor is lower suggesting that the thicker trailing edge has the largest affect on incremental losses.
The Effects of Radial Inlet on the Performance of Variable Inlet Guide Vanes in a Centrifugal Compressor Stage
Authors: Tan Jiajian , Qi Datong , Wang Rui
Published: January 2011

Variable inlet guide vanes (VIGVs) can regulate pressure ratio and mass flow at constant rotational speed in centrifugal compressors as a result of inducing a controlled prewhirl in front of impellers. Radial inlets and VIGVs are typical upstream components in front of the first-stage impellers in many pipeline and multistage centrifugal compressors. However, previous investigations on VIGVs in centrifugal compressors were mostly conducted under the condition of axial inlets, and present work aims to focus on the effects of radial inlet on the VIGVs performance of a centrifugal compressor stage. The axial inlet stage model was compared with the radial inlet stage model using numerical flow simulation. The flow from the radial inlet was nonuniform in both circumferential and radial direction, thus the VIGVs, the impeller, the vaneless diffuser, and the return vane channel were modeled with fully 360-deg passages. The three-dimensional flow field was numerically simulated with FINE™/Turbo at VIGVs setting angles range from −20° to +60°. The overall stage performance parameters were obtained by integrating the field quantities. The simulation results show that the performance of VIGVs was significantly degraded by its inlet flow distortions resulting from a radial inlet. The stage performance map indicates that the overall stage polytropic efficiency decreased by an average of 2.5% and total pressure ratio decreased by an average of 1% because of the flow distortions at different VIGVs setting angles, in comparison with the axial stage model.
Flow and Heat Transfer of Air and Steam in Internal Cooling Passages of Turbine Blade
Authors: Wang Xinjun , Wang Wei , Chou Luke , Han Yumeng , Xu Liang , Shui Linqi
Published: January 2011

Numerical prediction of three-dimensional flow and heat transfer of air and steam are presented for serpentine cooling channels by using the commercial software CFX. The results show that SSG model is the best turbulence model for the ribbed channels. A study of Grid Generation was performed for flow and heat transfer in serpentine cooling channels, with the same turbulence model. And the results show that the space between the first node and the wall surface (Δy) is 0.0001 mm and the grid density is 1.3 or Δy of 0.001 mm and grid density of 1.2 is the appropriate choice for grid generation. Ribbed channels are not sensitive to mesh generation compared with smooth passages. With the same inlet flux, steam heat transfer efficiency is higher than that of air about 15–20%; steam superheat degree is not the key factor for heat transfer, but it had an effect on flow resistance. Compared with smooth channels, ribbed channels reduce the impact of the turn; the best heat transfer regions appear downstream of the turn. V-type ribs have better heat transfer performance than the parallel type ribs; the highest heat transfer occurs in the section between the ribs.
Evaluation of Combustion and Emissions Using Biodiesel and Blends With Kerosene in a Low NOx Gas Turbine Combustor
Authors: Li Hu , Altaher Mohamed , Andrews Gordon E.
Published: January 2011

Biofuels offer reduced CO2 emissions for both industrial and aero gas turbines. Industrial applications are more practical due to low temperature waxing problems at altitude. Any use of biofuels in industrial gas turbines must also achieve low NOx and this paper investigates the use of biofuels in a low NOx radial swirler, as used in some industrial low NOx gas turbines. A waste cooking oil derived methyl ester biodiesel (WME) has been tested on a radial swirler industrial low NOx gas turbine combustor under atmospheric pressure and 600K. The pure WME and its blends with kerosene, B20 and B50 (WME:kerosene = 20:80 and 50:50 respectively), and pure kerosene were tested for gaseous emissions and lean extinction as a function of equivalence ratio. The co-firing with natural gas (NG) was tested for kerosene/biofuel blends B20 and B50. The central fuel injection was used for liquid fuels and wall injection was used for NG. The experiments were carried out at a reference Mach number of 0.017. The inlet air to the combustor was heated to 600K. The results show that B20 produced similar NOx at an equivalence ratio of ∼0.5 and a significant low NOx when the equivalence ratio was increased comparing with kerosene. B50 and B100 produced higher NOx compared to kerosene, which indicates deteriorated mixing due to the poor volatility of the biofuel component. The biodiesel lower hydrocarbon and CO emissions than kerosene in the lean combustion range. The lean extinction limit was lower for B50 and B100 than kerosene. It is demonstrated that B20 has the lowest overall emissions. The co-firing with NG using B20 and B50 significantly reduced NOx and CO emissions.
Semi-Analytical Procedure for Prediction of Radial Clearances in Industrial Steam Turbines
Authors: Hesse Christian , Schoene Sophie , Gampe Uwe , Kober Juergen , Fogt Hannes
Published: January 2011

Industrial steam turbines cover a wide capacity range from a few MW up to about 150 MW and usually they are individually designed for their application for mechanical and generator drive according to the specific customer requirements. For both applications, the extraction of steam at various pressure and temperature levels is often required to supply external steam consumers. The resulting compact and non-rotational symmetric design of the turbine casing with significant temperature differences between the various regions of the casing has to meet both the requirement of safe operation with sufficient clearances at any operational mode and at the same time of high inner turbine efficiency by minimum clearances. The paper presents a semi-analytical procedure for the estimation of thermal casing distortions and resulting radial clearances, which allows a rapid prediction and covers a multiplicity of design variants. The method is based on an analytical calculation model and the casing is considered as a sequence of cylindrical sections with different geometry and thermal loading. After solving a system of equations the thermal bending line of the casing is found. However, the pure analytical approach doesn’t incorporate nozzles or cut outs of the casing that are necessary for steam extraction. Their influence on casing distortion is considered by systematic finite element parameter studies. In combination with the dynamic rotor deflection the radial clearances can be predicted. The authors report about the application of the procedure for the example of a turbine test run, where temperature and displacement measurements were conducted. The boundary conditions for the calculation, i.e. the temperature distribution in every section, were derived from the measurements. The predicted casing distortion is in good accordance with the results of a complete 3D FE analysis and the measurements.
Improving the Design of a High Pressure Casing With the Help of Finite Element Analysis to Ensure the Rotor Dynamic Stability of a High Pressure Centrifugal Compressor Equipped With a Hole Pattern Seal
Authors: Bidaut Yves , Baumann Urs
Published: January 2011

This paper focuses on the casing geometry of High Pressure Compressors. It is common practice to use damper seals, typically the hole pattern type, at the balance piston to ensure the stability of the compressor when compressing fluids with high density levels. Special attention must be paid to the clearance of the hole pattern seal which must be kept convergent at all operating conditions because a clearance divergence can lead to a rotor dynamic instability of the compressor. Furthermore, the clearance must be kept as low as possible to reduce the leakage losses through the balance piston. Therefore, extensive Fine Element Analyses are performed to determine the mechanical casing deflections in operation and hence, the correct clearance behaviour of such damper seals. This paper discusses the history of the casing design during the last ten years and compares the configurations with respect to the clearance distribution along the damper seal length. To validate the analytical predictions, leakage and stability measurements (using a magnetic shaker) are performed for these high pressure compressors during the full-load, full-pressure testing. This paper presents the stability measurements carried out on two compressors (390 bar and 655 bar discharge pressure) and compares the results.
Vibration Response Characteristics of Bladed Disk With Continuous Ring Type Structure Losing Shroud and Stab
Authors: Kaneko Yasutomo , Mori Kazushi , Ohyama Hiroharu
Published: January 2011

This paper presents a simple analysis method for predicting vibration response characteristics of a bladed disk with continuous ring type structure losing a shroud or a shroud and a stab between two blades. This loss introduces a mistuning of the system and the whole bladed disk model must be used to conduct the study. However, the vibration modes change regularly from a sine and a cosine mode, if the bladed disk consists of many blades. By utilizing this phenomenon, the simple formulation of vibration response of a bladed disk can be derived. Second, the parametric study on the vibration response characteristics of a bladed disk losing a shroud or a shroud and a stab is carried out extensively, utilizing the analysis method proposed here. From the calculated results, the vibration response characteristics of a bladed disk are clarified for both of resonant vibration and random vibration. Lastly, the results calculated by the simple analysis method proposed are compared with the results obtained from FEA (Finite Element Analysis) in order to verify the validity of the analysis method.
The Influence of Different Rim Seal Geometries on Hot-Gas Ingestion and Total Pressure Loss in a Low-Pressure Turbine
Authors: Schuler P. , Kurz W. , Dullenkopf K. , Bauer H.-J.
Published: January 2011

In order to prevent hot-gas ingestion into the rotating turbo machine’s inside, rim seals are used in the cavities located between stator- and rotor-disc. The sealing flow ejected through the rim seal interacts with the boundary layer of the main gas flow, thus playing a significant role in the formation of secondary flows which are a major contributor to aerodynamic losses in turbine passages. Investigations performed in the EU project MAGPI concentrate on the interaction between the sealing flow and the main gas flow and in particular on the influence of different rim seal geometries regarding the loss-mechanism in a low-pressure turbine passage. Within the CFD work reported in this paper static simulations of one typical low-pressure turbine passage were conducted containing two different rim seal geometries, respectively. The sealing flow through the rim seal had an azimuthal velocity component and its rate has been varied between 0–1% of the main gas flow. The modular design of the computational domain provided the easy exchange of the rim seal geometry without remeshing the main gas flow. This allowed assessing the appearing effects only to the change of rim seal geometry. The results of this work agree with well-known secondary flow phenomena inside a turbine passage and reveal the impact of the different rim seal geometries on hot-gas ingestion and aerodynamic losses quantified by a total pressure loss coefficient along the turbine blade. While the simple axial gap geometry suffers considerable hot-gas ingestion upstream the blade leading edge, the compound geometry implying an axial overlapping presents a more promising prevention against hot-gas ingestion. Furthermore, the effect of rim seals on the turbine passage flow field has been identified applying adequate flow visualisation techniques. As a result of the favourable conduction of sealing flow through the compound geometry, the boundary layer is less lifted by the ejected sealing flow, thus resulting in a comparatively reduced total pressure loss coefficient over the turbine blade.
Syngas Fuel Hybrid 45 MW GTCC/ORC Power Plant Using Modular 500 TPD Coal/Biomass Modular Pyrolytic Gasification
Authors: van der Linden Septimus , Wiley Mark , Williams Gary , Swart Roel
Published: January 2011

This paper presents a solution for developing economies where power shortages require power plants in the range of 30/50 MW or larger to support industrial facilities such as mining or industrial parks where natural gas is not available and where diesel fuel is expensive, but where coal is readily available. Recent developments with Pyrolytic gasification systems by Wiley Consulting, capable of modular 500tpd of coal or biomass, were investigated for power starved sub-Saharan African countries. This Gasifier does not require an oxygen plant and produces a Syngas that can be combusted in modified FR6B gas turbines. The Syngas needs to be compressed and the parasitic load is accommodated with steam injection for NOx control and power enhancement to power the fuel gas compressor. To simplify the exhaust heat power recovery, the Cascading Closed Loop Cycle (CCLC) Organic Rankine Cycle (ORC) system was integrated into this system, resulting in a nominal 45 MW coal or biomass power plant at altitudes over 1000m achieving 40%+ efficiency. Coal fired steam plant Rankine cycle was considered expensive and inefficient due to the requirements of low emissions as well as more than 70% of the fuel energy rejected in the condensing system. Using the Gas Turbine Brayton cycle to combust Synthesis Gas (produced by an innovative Pyrolytic and modular gasification process that did not need an oxygen plant) was considered a practical alternative, especially as the Gas Turbine is air cooled. To fully capture the value of the Syngas fuel, the Gas Turbine exhaust energy would be recovered in an ORC which avoided the use of water and provided excellent load following characteristics as well as the capability to turndown to 40% or lower loads. The criteria established for the power plant was to build and commission the plant in 24 months or less. This necessitated looking at available used and refurbished generating equipment. The modular Gasifier, already demonstrated as a 250 tpd system, could readily be scaled to 500 tpd coal or biomass with about the same footprint and dispatched in modules for fast installation. The availability of a used 38 MW class GT for refurbishment and modification to Syngas fuel combustion system allowed site installation within one year and the provision of emergency power using available diesel fuel. This paper will fully describe the 45 MWe Hybrid GT/ORC Combined Cycle power plant utilizing the innovative Pyrolytic coal gasification process as the fuel source for an efficient low emissions power supply.
Friction Factor Behavior From Flat-Plate Tests of Smooth and Hole-Pattern Roughened Surfaces With Supply Pressures up to 84 Bars
Authors: Childs Dara W. , Kheireddin Bassem , Phillips Stephen
Published: January 2011

A flat-plate tester was used to measure the friction-factor behavior for a hole-pattern-roughened surface apposed to a smooth surface. The tests were executed to characterize the friction-factor behavior of annular seals that use a roughened-surface stator and a smooth rotor. Friction factors were obtained from measurements of the mass flow rate and static pressure measurements along the smooth and roughened surfaces. In addition, dynamic pressure measurements were made at four axial locations at the bottom of individual holes and at facing locations in the smooth plate. The test facility is described, and a procedure for determining the friction factor is reviewed. Three clearances were investigated: 0.635, 0.381, and 0.254 mm. Tests were conducted with air at three different inlet pressures (84, 70, and 55 bars), producing a Reynolds numbers range from 50,000 to 700,000. Three surface configurations were tested including smooth-on-smooth, smooth-on-hole, and hole-on-hole. The hole-pattern plates are identical with the exception of the hole depth. For the smooth-on-smooth and smooth-on-hole configurations, the friction factor remains largely constant or increases slightly with increasing Reynolds numbers. The friction factor increases as the clearance between the plates increases. The test program was initiated to investigate a “friction-factor jump” phenomenon cited by Ha et al. in 1992 in test results from a flat-plate tester where, at elevated values of Reynolds numbers, the friction-factor began to increase steadily with increasing Reynolds numbers. They tested apposed honeycomb surfaces. For the present tests, the phenomenon was also observed for tests of apposed roughened surfaces but was not observed for smooth-on-smooth or smooth-on-rough configurations. When the phenomenon was observed, dynamic pressure measurements showed a peak-pressure oscillation at the calculated Helmholtz frequency of the holes.
Blade Geometry Optimization for Axial Flow Compressor
Authors: Zheng Rongye , Xiang Jianhua , Sun Jinju
Published: January 2011

Blade geometry design is crucial for turbomachinery performance and stability. A blade optimization method is developed and presented in this paper. The method consists of several elements: geometry parameterization, numerical simulation of flow and performance, optimization algorithm. Sweep and lean are defined by centroid coordinates of sectional blades while the blade geometry is represented by B-Splines approach, through which deformation of blade shape in terms of sweep and lean can then be readily realized. Flow simulation is carried out with a commercial CFD package-NUMECA. In addition, response surface is incorporated to approximate the objective function during the optimization process for the purpose of time-saving, and two different models (polynomial model and basic-function model) are applied respectively to construct the response surface and their differences highlighted. Genetic Algorithms is incorporated to achieve a global optimal geometry of blade. For case study, the developed method was used to optimize the transonic NASA Rotor67 blading. It is demonstrated that an optimal tuning of blade sweep and lean results in evident improvement of both isentropic efficiency and pressure ratio at design and off-design flow.
Development in Gas Turbine Repairs
Authors: Thomson Allan , Anderton David A.
Published: January 2011

The need for repair rather than replace of gas turbine components is becoming increasingly important to operators in today’s economic climate. The use of commercially available numerical analysis software, computational fluid dynamics (CFD) and finite element (FE) have become well established within Wood Group Light Industrial Turbines Ltd. They have allowed the business to be extremely competitive by being able to rapidly respond to a customers request for a repair which may involve a fluid structure interaction and/or conjugate heat transfer analysis. The software has also been used to study critical design limitations and to rapidly enhance reverse engineered parts. Two such cases are presented here: the repair of a compressor rotor blade airfoil and the changes made to an existing design of a cooling passage in a high pressure turbine rotor blade. Each analysis was completed in a very competitive time span.
“Online Throughflow”: Automatic Simultaneous Simulation of an Axial Flow Turbine
Authors: Schinko Norbert , Marx Martin , Rose Martin G. , Staudacher Stephan , Gier Jochen , Hu¨bner Norbert
Published: January 2011

A new turbine rig analysis method has been developed at the Institute of Aircraft Propulsion Systems (ILA) at Stuttgart University. This technique is known as “Online Throughflow” and involves the optimized adjustment of the input parameters of a Throughflow Method. The calculation is run whilst the turbine is being tested, achieving a match to measured data in about five minutes. The match between predicted and measured data is expressed as a chi-squared value. This provides a target parameter for a linear optimization procedure. Measured parameters such as inter-row static pressures, torque, mass-flow and rotational speed are used in this context. Input parameters such as row deviation and row loss are adjusted to give an optimized turbine simulation in close to real time. Less than five minutes after taking a data scan of the experimental parameters at inlet to exit from and within the turbine, a converged simulation of the turbine is available. This simulation evaluates many other parameters within the turbine that are not directly measured, e.g. circumferential exit flow angles for all rows of aerofoils. Furthermore the single values of chi-squared from every measured variable can be used to decide if there is an error in the individual measurements. The complete optimizer is programmed in LabView® and is integrated into the data acquisition system of the two-stage “Advanced Turbine Research and Demonstration Rig” (ATRD-Rig), which has been developed in a cooperation of ILA and the MTU Aero Engines (MTU). The testbed, as well as the instrumentation of the specific specimen from which all measurement values for the optimization have been taken, will additionally be described in the paper.
CFD Prediction of Partload CO Emissions Using a Two-Timescale Combustion Model
Authors: Wegner Bernhard , Gruschka Uwe , Krebs Werner , Egorov Y. , Forkel H. , Ferreira J. , Aschmoneit Kai
Published: January 2011

Todays and future electric power generation is characterized by a large diversification using all kind of sources including renewables resulting in non coherent fluctuations of power supply and power usage. In this context, gas turbines offer a high operational flexibility and a good turn down ratio. In order to guide design and down select promising solutions for improving part load emissions a new combustion model based on the assumption of two separate time scales for the fast premixed flame stabilization and the slow post flame burnout zone has been developed within the commercial CFD code ANSYS CFX. This model enables the prediction of CO emissions generally limiting the turn down ratio of gas turbines equipped with modern low NOx combustion systems. The model will be explained and validated at lab scale conditions. Finally application of the model for a full scale analysis of a gas turbine combustion system is demonstrated.
Reconstruction of the Heat Release Response of Partially Premixed Flames
Authors: Kim Kyu Tae , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic A.
Published: January 2011

The forced response of a swirl-stabilized, partially premixed flame to inlet velocity and equivalence ratio oscillations was experimentally investigated in a model lean-premixed gas turbine combustor. Three different forcing mechanisms were studied: the response of a premixed flame to velocity oscillations, the response of a partially premixed flame to equivalence ratio oscillations, and the response of a partially premixed flame to velocity and equivalence ratio oscillations. The overall heat release response of the flame was determined from measurements of the CH* chemiluminescence emission intensity from the entire flame, while the response of the spatially distributed heat release was determined from phase-synchronized chemiluminescence images. In addition, simultaneous measurements were made of the inlet velocity and equivalence ratio oscillations using the two-microphone method and the IR absorption technique, respectively. The results show that in the linear regime, the response of a partially premixed flame to simultaneous velocity and equivalence ratio oscillations can be reconstructed from independent measurements of the flame’s response to velocity oscillations and to equivalence ratio oscillations using a vector summation method. This is the first experimental demonstration of a two-input one-output model of a swirl-stabilized partially premixed flame. It suggests that the response of a partially premixed flame is governed by four physical parameters, i.e., the oscillation frequency, the amplitude of velocity oscillation, the amplitude of equivalence ratio oscillation, and the phase difference between the two oscillations. As a result, the heat release response of a partially premixed flame can be amplified or damped, depending on the phase difference between the velocity and equivalence ratio oscillations at the combustor inlet.
An Attempt at Large Eddy Simulation for Combustor Modeling
Authors: Jiang Leiyong , Campbell Ian
Published: January 2011

Large eddy simulation (LES) is recognized as a promising method for numerical simulation in combustion systems. A LES attempt in a model combustor has been made, and a few important issues including grid size, inflow condition, wall boundary conditions, physical sub-models and data sampling, have been carefully considered. It is found that the turbulence forcing with the vortex method at the air/fuel inlets does not affect the LES results for the present configuration and the turbulence can develop naturally in the inlet section. Moreover, significant computing power is required for LES to capture both the high and low frequencies of interest in a turbulent reacting flow. In the paper, some of the numerical results are presented and compared with a comprehensive experimental database, which indicates that LES can provide reasonable predictions for the mean axial velocity and temperature distributions inside the combustion chamber. However, in order to make LES a valuable and cost-effective tool in the development of advanced combustion systems, some fundamental questions remain to be addressed and more validation efforts are required.
Ultra Low Emissions Combustion and Control Systems: Installation Into Mature Power Plant Gas Turbines
Authors: Benoit Jeffrey A. , Ellis Charles , Cook Joseph
Published: January 2011

The search for power plant sustainability options continues as regulating agencies exert more stringent industrial gas turbine emission requirements on operators. Purchasing power for resale, de-comissioning current capabilities altogether and repowering by replacing or converting existing equipment to comply with emissions standards are economic-driven options contemplated by many mature gas turbine operators. One Las Vegas Nevada, USA operator, NV Energy, with four (4) natural gas fired W501B6 Combined Cycle units at their Edward W. Clark Generating Station, was in this situation in 2006. The units, originally configured with diffusion flame combustion systems, were permitted at 103 ppm NOx with regulatory mandates to significantly reduce NOx emissions to below 5ppm by the end of 2009. Studies were conducted by the operator to evaluate the economic viability of using a Selective Catalytic Reduction (SCR) system, which would have forced significant modifications to the exhaust system and heat recovery steam generator (HRSG), or convert the turbines to operate with dry low-emissions combustion systems. Based on life cycle cost and installation complexity, the ultra-low emission combustion system was selected. This technical paper focuses on a short summary of the end user considerations in downselecting options, the ultra low emissions technology and key features employed to achieve these low emissions, an overview of the conversion scope and a review and description of the control technology employed. Finally, a technical discussion of the low emissions operational flexibility will be provided including performance results of the converted units.
Dynamic Response of a Rotor-Hybrid Gas Bearing System Due to Base Induced Periodic Motions
Authors: San Andre´s Luis , Ryu Keun , Niu Yaying
Published: January 2011

Rotating machinery in transportation systems experiences intermittent excitation from road conditions. Internal combustion (IC) engines exert (multiple) periodic load excitations into passenger vehicle turbochargers, for example. Too large base motions can produce severe rotor-bearing system damage, even failure. The paper shows the reliability of a rotor-hybrid gas bearing system to withstand intermittent base foundation motions induced by a shaker. The test rig consists of a rigid rotor, 190mm in length, 0.825 kg in mass, and 28.6 mm in diameter, supported on two hybrid, flexure pivot tilting pad type, gas bearings. The whole system, weighing 48 kg, is supported on two soft coil springs and its lowest natural frequency is just ∼5 Hz. The rod connecting the shaker to the base plate is not affixed rigidly to the test rig base. The rod merely pushes on the base plate and hence the induced based motions are intermittent with multiple impacts and frequencies. The base induced motions are at a low main frequency (5–12 Hz) relative to the operating speed of the rotor-bearing system (max. 35 krpm). The recorded rotor responses, relative to the bearing housings, also contain the main excitation frequency and its super harmonics; and because of the intermittency of the base motions, it also excites the rotor-bearing system natural frequency, in particular when the gas bearings are supplied with a low feed pressure. Predicted rotor dynamic displacements induced by the base excitations show reasonable agreement with the test data.
Compressor Design for Multi-Point Operating Conditions of Turbocharged Gasoline Engines
Authors: Chen Tao , Zhang Yangjun , Zheng Xinqian , Zhuge Weilin
Published: January 2011

Turbocharger compressor design is a major challenge for performance improvement of turbocharged internal combustion engines. This paper presents a multi-point design methodology for turbocharger centrifugal compressors. In this approach, several design operating condition points of turbocharger compressor are considered according to total engine system requirements, instead of one single operating point for traditional design method. Different compressor geometric parameters are selected and investigated at multi-point operating conditions for the flow-solutions of different design objectives. The method has been applied with success to a small centrifugal compressor design of a turbocharged gasoline engine. The results show that the consideration of several operating points is essential to improve the aerodynamic behavior for the whole working range. The isentropic efficiency has been increased by more than 5% at part-load conditions while maintaining the pressure ratio and flow range at full-load conditions of the gasoline engine.
Stability Enhancement by Casing Grooves: The Importance of Stall Inception Mechanism and Solidity
Authors: Houghton Tim , Day Ivor
Published: January 2011

This paper concerns the optimisation of casing grooves and the important influence of stall inception mechanism on groove performance. Installing casing grooves is a well known technique for improving the stable operating range of a compressor, but the wide-spread use of grooves is restricted by the loss of efficiency and flow capacity. In this paper, laboratory tests are used to examine the conditions under which casing treatment can be used to greatest effect. The use of a single casing groove was investigated in a recently published companion paper. The current work extends this to multiple-groove treatments and considers their performance in relation to stall inception mechanisms. Here it is shown that the stall margin gain from multiple grooves is less than the sum of the gains if the grooves were used individually. By contrast, the loss of efficiency is additive as the number of grooves increases. It is then shown that casing grooves give the greatest stall margin improvement when used in a compressor which exhibits spike-type stall inception, while modal activity before stall can dramatically reduce the effectiveness of the grooves. This finding highlights the importance of being able to predict the stall inception mechanism which might occur in a given compressor before and after grooves are added. Some published prediction techniques are therefore examined, but found wanting. Lastly, it is shown that casing grooves can, in some cases, be used to remove rotor blades and produce a more efficient, stable and light-weight rotor.
Heat Transfer Characteristics of an Oblique Jet Impingement Configuration in a Passage With Ribbed Surfaces
Authors: Hoefler Florian , Schueren Simon , von Wolfersdorf Jens , Naik Shailendra
Published: January 2011

Heat transfer measurements of a confined impingement cooling configuration with ribs on the target surfaces are presented. The assembly consists of four non-perpendicular walls of which one holds two rows of staggered inclined jets, each impinging on a different adjacent wall. The ribs are aligned with the inclined jet axes, have the same pitch and are staggered to the impinging jets. The flow exhausts through two staggered rows of holes opposing the impingement wall. The passage geometry is related to a modern gas turbine blade cooling configuration. A transient liquid crystal technique was used to take spatially resolved surface heat transfer measurements for the ground area between the ribs. A comparison with the smooth baseline configuration reveals local differences and a generally reduced heat transfer for the rib-roughened case. Furthermore, lumped heat capacity measurements of the ribs yielded area averaged heat transfer information for the ribs. From the combination of ground and rib heat transfer measurements it is concluded that the overall performance of the ribbed configuration depends on the Reynolds number. Of the five investigated jet Reynolds numbers from 10,000 up to 75,000, only for the highest Re the averaged Nusselt numbers increase slightly compared to the smooth baseline configuration.
3D Numerical Friction Contact Model and Its Application to Nonlinear Blade Damping
Authors: Gu Weiwei , Xu Zili
Published: January 2011

A three dimensional numerical friction contact model is proposed to investigate the nonlinear vibration of damped blade. The model describes the discrete friction forces in the time domain. By using Discrete Fourier Transforms, the discrete friction forces can be transformed into a series of harmonic functions which are used to solve the nonlinear vibration of damped blade in the frequency domain. The difference between static friction coefficient and dynamic friction coefficient is considered in the model. To consider microslip effect, an array of spring-slider contact pairs (friction contact model) is distributed on the contact surfaces. Additionally, the effect of area of the contact surface on the vibration of damped blade can be studied by altering the number of the contact pairs. Finally, the nonlinear vibration of a real turbine blade with shrouded friction dampers is solved using the proposed friction contact model, Multi-Harmonic Balance Method and Receptance Method.
Swirling Flame Instability Analysis Based on the Flame Describing Function Methodology
Authors: Palies Paul , Durox Daniel , Schuller Thierry , Candel Se´bastien
Published: January 2011

Thermoacoustic instabilities are analyzed by making use of a nonlinear representation of flame dynamics based on the describing function. In this framework, the flame response is determined as a function of frequency and amplitude of perturbations impinging on the combustion region. This methodology is applied to confined swirling flames in a laboratory scale setup (2.5 to 4 kW) comprising an upstream manifold, an injection unit equipped with a swirler (swirl number = 0.55) and a cylindrical flame tube. The flame describing function is experimentally determined and is combined with an acoustic transfer matrix representation of the system to provide growth rates and oscillation frequencies as a function of perturbation amplitude. These data can be used to determine regions of instability, frequency shifts with respect to the acoustic eigenfrequencies and they also yield amplitude levels when self-sustained oscillations of the system have reached a limit cycle. This equilibrium is obtained when the amplitude dependent growth rate equals the damping rate in the system. This requires an independent determination of this last quantity which is here based on measurements of the resonance response curve. Results obtained are compared with observations from systematic experiments carried out by varying the test combustor geometry. The demonstration of the FDF framework in a generic configuration indicates that this can be used in more general situations of technological interest.
Improved µ-Scale Turbine Expander for Energy Recovery
Authors: Keding Marcus , Dudzinski Piotr , Reissner Alexander , Hummel Stefan , Tajmar Martin
Published: January 2011

Micro power converters for energy recovery are increasingly important for a number of future applications. The Austrian Institute of Technology (AIT) is presently developing an innovative μ-scale turbine expander for work recovery in transcritical CO2 heat pumps. The main drawback of a lower COP (coefficient of performance) of transcritical CO2 heat pumps compared to conventional heat pump systems can be compensated by utilizing the pressure difference between the high pressure and low pressure part of the pump for work recovery. Work recovery can be realized by substituting the expansion valve between the high and low pressure side by a Pelton turbine with specific two phase flow turbine blades. In order to increase the power output, the generator was integrated into the turbine to reduce the friction losses and hence increase the overall efficiency. An important aspect is that the generator is directly connected with the high pressure part of the turbine. One part of the project is the optimization of the turbine geometry via simulation tools. The paper will give an overview about our microturbine development as well as a comparison of the power output of each turbine generation. Furthermore the present paper discusses a concept that utilizes our microturbine together with a micro combustion module that enables a micro power generator with very high power-to-weight ratios based on green fuels.