bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Viscous Controlled Vortex Design of a LP Turbine Stage
Authors: Zheng Qun , Gao Jie , Li Bin
Published: January 2011

Design of a low pressure (LP) turbine stage with the viscous controlled vortex techniques is presented in this paper. 3-D numerical simulation was carried out to research the aerodynamic performance of the LP turbine stage cascades designed with viscous controlled vortex method, where local circulation near the endwalls is modified to consider the viscous effects. Inviscid controlled vortex concept has been applied in the main flow area to obtain the desired reaction. Reasonable circulation redistribution near the endwalls has a special effect to improve the local drastic reaction changes due to the viscous effects near the endwalls. Simulation results are presented and discussed for the modification of a LP turbine stage with such a technique.
Investigation of Impeller Strength for a Cryogenic Liquid Turbine
Authors: Ren Yan , Sun Jinju , Zheng Rongye , Song Peng , Wang Ke
Published: January 2011

A single stage cryogenic liquid turbine is designed for a large-scale internal compression air-separation unit to replace the Joule-Thompson valve and recover energy from the liquefied air during throttling process. It includes a 3-dimensional impeller, variable geometry nozzle, and asymmetrical volute. Strength evaluation of such a liquid turbine is both essential and complicated, which involves a proper evaluation of stress acting on the components and mechanical property of the chosen materials at low temperature. For metals under low temperatures, brittle fracture of the metal may occur prior to fatigue damage. A comprehensive consideration of low-temperature mechanical properties of materials and mechanical loads (due to hydrodynamic force and centrifugal force) acting on the components is of particular importance. Aluminum alloy 2031 is used for the turbine impeller and its mechanical properties under low temperatures are analyzed. To evaluate the stress acting on the components, numerical investigation using 3-D incompressible Navier-Stokes Equation together with k-epsilon turbulence model and mixing plane approach at rotator-stator interface are carried out at design and off-design flow with different nozzle-vane settings. The obtained pressure force is transformed into hydrodynamic load acting on the solid surface by means of fluid-solid interaction technology, and then used in the FEM (Finite Element Method) structure analysis together with the centrifugal force. Stress distribution of the component is obtained and deformation of the component analyzed. Evaluation of impeller strength is conducted for the cryogenic liquid turbine by combining the foregoing two aspects, and a use of alloy 2031 for the turbine expander is validated.
Rotor Dynamic Analysis Requirements in API Standards With Case Studies
Authors: Al-Jughaiman Bader K.
Published: January 2011

This paper briefly describes the rotor dynamic analysis requirements in the API standards for process centrifugal compressors, induction motors and gearboxes. The paper also presents an example for each equipment type where the dynamic analysis performed by the manufacturer during the design stage in accordance with these standards identified critical aspects that were concerning to the purchase. The paper also highlights the measures taken to alleviate the purchaser’s concerns, the vibration behavior of these machines after commissioning and some lessons learned from these cases. The first case is for a 4,744 kW (6,400 HP) centrifugal gas compressor running at 11,889 rpm. The dynamic analysis shows that the compressor will run above its fist critical speed estimated at 5,400 rpm and below its second critical speed estimated at 20,600 rpm that is 16% less than the second multiple of the running speed. The analysis also shows that the second mode is lightly damped with an amplification factor equal to 116. The second case is for a 2,984 kW (4000 HP) induction motor running at 3,600 rpm. The dynamic analysis shows that the motor will run at almost twice its first critical speed. The first critical speed is estimated at 1,750 rpm with high amplification factor equal to 99. Also, the second critical speed is estimated at 7,400 rpm which is less than 5% from twice the line frequency and the second multiple of the running speed. The third case is for a 4,744 kW (6,400 HP) helical gearbox. The dynamic analysis shows the existence of a critical speed for the gear wheel rotor that coincides with the pinion rotor running speed at 50%–100% load range.
Development of Ultra-Low Emission Diesel Fuel-Fired Microturbine Engines for Vehicular Heavy Duty Applications: Combustion Modifications
Authors: Chen Junhua , Mitchell Mark G. , Nourse John G.
Published: January 2011

Worldwide regulations currently set very stringent emissions standards for new on-road heavy-duty diesel engines (HDDE’s). For example, the United States Environmental Protection Agency (US EPA) and the California Air Resources Board (CARB) will require 2010 and subsequent HDDE to emit less than 0.2 g/bhp-hr (0.27 g/kW-hr) NOx and 5.0 g/bhp-hr (6.7 g/kW-hr) CO in addition to other strictly regulated pollutants such as formaldehyde, volatile organic compounds, and particulate matter. Diesel or biodiesel fired Microturbine engines are in use in hybrid electric vehicular (HEV) urban bus applications in part because of their low emissions. A vehicular test cycle based on practical driving data of The New York City M60 route duty cycle for an urban bus is presented and discussed. Engine only test cycles that would represent in vehicle engine usage are also discussed. In the process of developing new technologies to meet the upcoming 2010 EPA and CARB HDDE regulations, Capstone Turbine has demonstrated a significant reduction in the emissions of its C30 family engines fired with ultra low sulfur diesel (ULSD) without any post-combustion treatment. The technical approaches which yielded the emissions improvements, included enhancements to the fuel vaporization and mixing processes in an effort to reduce local primary zone temperatures. With only injector modifications the ULSD-fired engine achieved emission levels of 0.046 g/hp-hr NOx, 0.87 g/hp-hr CO, 0.003 g/hp-hr PM, 0.013 g/hp-hr NMHC and 0.006 g/hp-hr HCHO in a recent third party demonstration test. NOx levels of 5–7 ppmV at 15% O2 were achieved for a power range of 50–100% while running on diesel fuel #2. With these new injector modifications the C30 engine has the potential capability to meet the same HDDE standards while burning other opportunity liquid fuels, including biodiesel, and ethanol.
Effects of Fan Speed on Rotating Stall Inception and Recovery
Authors: Choi Minsuk , Vahdati Mehdi , Imregun Mehmet
Published: January 2011

An implicit, time-accurate 3D compressible RANS solver is used to simulate rotating stall inception and recovery, the so-called rotating stall hysteresis, in a modern fan geometry. In the first instance, rotating stall was simulated for 70%, 80% and 90% fan speeds using a whole-annulus fan model with a variable-area nozzle downstream. As the fan speed is increased, the stall cell also increases in size but the number of stall cells decreases. One large stall cell is predicted to rotate along the annulus at 80% and 90% speeds, while there are three smaller cells at 70% speed. In all cases, the reverse flow is confined to the near-tip region and the rotating stall does not develop into a full-span stall because of the fan blade’s high-aspect ratio. To simulate stall recovery, the nozzle area was increased gradually at 70% and 90% speeds and the flow was seen to recover from rotating stall to reach an unstalled operating condition. The recovery process was found to be affected by the fan speed. At 70% speed, the large disturbances decay first to form almost symmetric stall cells. Thereafter, the stall cells shrink into smaller ones as the mass flow rate decreases further. At 90% fan speed, a single stall cell rotates along the annulus, the disappearance of which results in recovery. An attempt has been made to explain the dependence of the stall inception and recovery patterns on the fan speed.
A Novel Multi-Functional Energy System (MES) for CO2 Removal With Ultra-Low Energy Penalty by Hybrid Natural Gas and Solar Radiation
Authors: Han Wei , Jin Hongguang
Published: January 2011

In this paper, a novel multi-functional energy system (MES) fueled by natural gas and solar radiation is proposed. In this MES, hydrogen and electricity are co-generated and approximately 92% of CO2 derived from natural gas is removed. The solar concentrated process provides high-temperature thermal energy to the methane/steam reforming reaction. The resulting syngas enters a pressure swing adsorption unit to separate approximately 80% of hydrogen. This process significantly increases the concentration of carbon dioxide in syngas from nearly 19% to 49%, which decreases energy consumption in CO2 removal. As a result, the overall efficiency of the new system becomes about 61.1%. Compared to a conventional natural gas-based hydrogen plant with CO2 removal and a concentrated solar power tower plant, the overall efficiency of the new system is increased by 13.3 percentage points. Based on the graphical exergy analysis, the integration of synthetic utilization of natural gas and solar radiation, combination of the hydrogen production plant and power plant, and integration of the energy utilization processes and CO2 separation were found to play significant roles for the improvement of system performance. The result obtained here provides a new approach for CO2 removal with ultra-low thermal efficiency reduction (energy penalty) and high efficient use of solar radiation.
Heat Transfer and Effectiveness on the Film Cooled Tip and Inner Rim Surfaces of a Turbine Blade
Authors: Park Jun Su , Lee Dong Hyun , Cho Hyung Hee , Rhee Dong-Ho , Kang Shin-Hyung
Published: January 2011

Detailed heat/mass transfer coefficients and film-cooling effectiveness were measured on the tip and inner rim surfaces of a rotor blade with a squealer rim. The blade was a two-dimensional version of a modern first-stage gas turbine rotor blade with a squealer rim. The experimental apparatus was equipped with a linear cascade of three blades, the axial chord length (Cx) of which was 237 mm with a turning angle of 126°. The mainstream Reynolds number based on the axial chord was 1.5×105. The turbulence intensity level at the cascade inlet was approximately 12%. Measurements were made at three different rim heights (H) of about 3%, 6%, and 9% of the axial chord length. The tip clearance (C) ranges were 1–3% of the axial chord length. Also, three different types of blade tip surfaces were equipped with a single row of film-cooling holes along the camber line, near the pressure and the suction side rim. In particular, a coolant was injected at an incline of 45° from near the suction side film cooling holes. The film cooling experiments were done with a fixed tip clearance and rim height at 1% and 6% of the axial chord length. The blowing rate was fixed at 1.5. High heat transfer rates were observed near the leading edge on the tip surface in some cases, due to the reattachment of tip leakage flow. The peak values moved toward the suction-side edge, and the magnitude and area of high heat transfer increased near the leading edge as the tip clearance increased. The heat transfer decreased on the tip surface with increases in the rim height. In the film-cooling cases, the high heat transfer and film-cooling effectiveness region appeared near the film-cooling holes.
Development of a High Speed Gas Bearing Test Rig to Measure Rotordynamic Force Coefficients
Authors: Moore J. Jeffrey , Lerche Andrew , Allison Timothy , Ransom David L. , Lubell Daniel
Published: January 2011

The use of gas bearings has increased over the last several decades to include microturbines, air cycle machines, and hermetically sealed compressors and turbines. Gas bearings have many advantages over traditional bearings, such as rolling element or oil lubricated fluid film bearings, including longer life, ability to use the process fluid, no contamination of the process with lubricants, accommodating high shaft speeds, and operation over a wide range of temperatures. Unlike fluid film bearings that utilize oil, gas lubricated bearings generate very little damping from the gas itself. Therefore, successful bearing designs such as foil bearings utilize damping features on the bearing to improve the damping generated. Similar to oil bearings, gas bearing designers strive to develop gas bearings with good rotordynamic stability. Gas bearings are challenging to design requiring a fully coupled thermo-elastic, hydrodynamic analysis including complex non-linear mechanisms such as Coulomb friction. There is a surprisingly low amount of rotordynamic force coefficient measurement in the literature despite the need to verify the model predictions and the stability of the bearing. This paper describes the development and testing of a 60,000 rpm gas bearing test rig and presents measured stiffness and damping coefficients for a 57 mm foil type bearing. The design of the rig overcomes many challenges in making this measurement by developing a patented, high-frequency, high-amplitude shaker system resulting in excitation over most of the subsynchronous range.
A 150 kW Radial Inflow Steam Turbine System for the Bottoming Cycle of Reciprocating Engines
Authors: Nakano Susumu , Tsubouchi Kuniyoshi , Shiraiwa Hiroyuki , Hayashi Kazutaka , Yamada Hiroyuki
Published: January 2011

A design study for a 150 kW class radial inflow steam turbine system for the bottoming cycle in 2.4 MW class gas engine systems has been completed. The total electrical efficiency of the gas engine can be increased from 41.6% to 44.2%. A two-stage condensing turbine system is applied to increase output power under the supplied steam conditions from the exhaust heat of the gas engines. The pressure ratio of a high-pressure turbine is 3.5, and that of a low-pressure turbine is 4.6. The blade profiles of both turbines are also designed to make sure the thrust does not exceed 300 N at the rated rotational speed of 51,000 rpm. To simplify the rotor system and to reduce mechanical losses, a permanent magnet generator rotor is applied that is composed of turbine rotors in a common shaft supported by two water-lubricated bearings. The oil supply system is completely eliminated in the turbine system. Design specifications of the turbines are shown, as are operating pressure ratio ranges of upper and lower limits from the start to the rated rotational speed for a stable starting operation.
Development of Key Technologies for the Next Generation Gas Turbine
Authors: Ito Eisaku , Okada Ikuo , Tsukagoshi Keizo , Muyama Akimasa , Masada Junichiro
Published: January 2011

In order to prevent global warming, the amount of CO2 produced by fossil fuel power plants needed to be reduced. For that reason, improvement of the gas turbine thermal efficiency for GTCC is essential. Mitsubishi Heavy Industries, Ltd. is a participant in a national project aimed at developing 1700°C gas turbine technology. As part of this national project, selected component technologies are investigated in detail. Some technologies which have been verified through component tests have been applied to the design of the newly developed 1600 °C gas turbine.
OEM’s Approach to Maintain High Reliability of Hot Gas Path Parts
Authors: Usune Yoshie , Onda Masahiko , Tomita Yasuoki , Jayaraj Balaji
Published: January 2011

The reliability of gas turbine (GT) Hot Gas Path components requires both design and metallurgical expertise. There are numerous repair facilities around the world with general metallurgical expertise. However, the maintenance process can be noticeably improved through a feedback approach that incorporates the original part design know-how and the fleet wide experience gathered from operational data. A lot of users apply daily start-stop cycles so these peaking operations will impose more severe duties on the hot gas path parts (HGPPs). For this reason, we have achieved high GT reliability, low fall out rate, and improved repair processes utilizing our in-house verification plant (combined power plant of G class GT). For service units, the Remote Monitoring concept [1] was developed to provide an extra level of protection and diagnostics for power generation equipment and it has also facilitated correlation between HGPPs distress and operational profiles. The use of historical operating data, including number of cycles, trips, and rapid load changes can reveal valuable information on the HGPPs distress and assist repair process improvement. Fleet database can give lots of feedback on the reliability and durability of the repaired components. This paper describes our own process of improving HGPP design and feedback to the maintenance. This process includes analysis of thermal barrier coating (TBC) degradation, careful application of life assessment techniques on substrate metallurgy, and analysis of operational data to improve design and repair techniques for increasing fleet availability.
A New Micro Turbo-Machinery Test Facility
Authors: Xia Chen , Huang Guoping , Chen Jie
Published: January 2011

The design and construction of a new test facility of micro turbo-machinery are presented for micro centrifugal compressors and radial turbines. The bed can be used for the full speed compressor test and the long duration hot turbine test. In order to adjust the testing condition rapidly, all the regulations of operating state are completed automatically by the control system. The test bed can be used for testing impeller performance with a series of diameter from 55 to 180 mm as a result of the modular design. A thermal protection system is designed to avoid the heat distortion caused by the high inlet temperature of turbine which may exceeds 1100K and provide a proper experimental environment for the electronic components. A photoelectric torque transducer with an accuracy of 1% is designed to measure the torque of a rigid shaft at a high speed over 120000rpm, and the maximum shaft torque is 7.7 N·m. The pressure and temperature are measured by pressure probes and thermocouples. The dynamic pressure signal of the centrifugal compressor is monitored by dynamic pressure sensors. The V-cone pressure-difference mass-flow meters are used for measuring mass-flow. The maximum rotating speed is 125000rpm, and the mass flow adjusted by the electric control valves varies from 0.1 to 1.0 kg/sec. The maximum inlet total temperature of the turbine is 1180K.
CFD Modelling and LDA Measurements for the Air-Flow in an Aero-Engine Front Bearing Chamber
Authors: Aidarinis J. , Missirlis D. , Yakinthos K. , Goulas A.
Published: January 2011

The constant development of aero engines towards lighter but yet more compact designs, without decreasing their efficiency, has led to gradually increased demands of the lubrication systems, such as the bearing chambers of the aero engine. For this reason, it is of particular importance to increase our level of understanding of the flow field inside the bearing chambers in order to optimize its design and performance. The flow field in such cases is of a complicated nature since there is a strong interaction between air-flow and lubricant oil together with the geometrical configurations and the shaft rotational speed inside the bearing chamber. The behavior of this interaction must be investigated in order to understand the flow field development inside the aero engine bearing and, at a next step, optimize its performance in relation to the lubrication and heat transfer capabilities. Such an effort is presented in this work where an investigation of the air-flow field development inside the front bearing chamber of an aero engine is attempted. The front bearing chamber is divided in two separate smaller sections where the flow passes from the first section partially through the bearing and the holding structure, to the second one where the vent and the scavenge are placed. The investigation was performed with the combined use of experimental measurements and Computational Fluid Dynamics (CFD) modeling. The experimental measurements were carried out with the use of a Laser Doppler Anemometry (LDA) system in an experimental rig modeling the front bearing chamber of an aero engine for real operating conditions taking into account both air-flow and lubricant oil-flow and for a varying number of shaft rotating speeds. The CFD modeling was performed with the use of a commercial CFD package. The air-flow inside the bearing was modeled with the adoption of a porous medium assumption. The experimental measurements and the CFD computations presented similar flow patterns and satisfactory quantitative agreement. At the same time the effect of the important parameters such as the air and oil mass flow together with the shaft rotation speed and the effect of the chamber inside geometry were identified. These conclusions can be exploited in future attempts in combination with the developed CFD model, in order to optimize the efficiency of the lubricant and cooling system. The latter forms the main target of this work which is the development of a useful engineering tool capable of predicting the flow field inside the aero engine bearing so as to be used for optimization efforts.
URANS Predictions of the Effects of Synthetic Jets on the Separated, Transitional Flow Over a Low-Pressure-Turbine-Like Flat Plate
Authors: Marconcini Michele , Pacciani Roberto , Arnone Andrea
Published: January 2011

A URANS solver has been applied to study the effects of a synthetic jet actuator on the laminar boundary layer separation over a flat plate with adverse pressure gradient. The pressure distribution over the flat plate is representative of the suction side of a ultra-high-lift, LP-turbine airfoil. Measurements for several Reynolds numbers, are provided via experimental tests carried out in the framework of the European project TATMo (Turbulence and Transition Modelling for Special Turbomachinery Applications). The actuator device, in the form of a two-dimensional slot, has been conceived in order to obtain jet aerodynamic characteristics suitable for separation control. The study has been carried out using a novel, transition-sensitive, non-linear eddy-viscosity model. It is based on the coupling of an additional transport equation for the so-called laminar kinetic energy (LKE) to a realizable, quadratic eddy-viscosity model that provides an explicit algebraic formulation for the Reynolds stresses. The analysis covers steady as well as unsteady cases characterized by different actuator frequencies. Comparisons between measurements and computations are presented. The suitability of the proposed approach to simulate the time- and phase-averaged effects of a synthetic jet for boundary layer control at typical operating conditions of high-lift LP-turbine blades will be discussed in detail.
Reduction of Forced Response Levels for Bladed Discs by Mistuning: Overview of the Phenomenon
Authors: Petrov E. P.
Published: January 2011

The newly-revealed phenomenon of reduction of forced response levels in a mistuned bladed disc to levels significantly (e.g. by a factor of two and more) lower than that of its tuned counterpart is studied in detail on an example of a realistic bladed disc. Statistical properties of the amplification factor of the mistuned forced response calculated with aero-effects included have been studied for cases of random blade mistuning and for mistuned blade rearrangements. Optimization search for the best mistuning patterns providing maximum forced response reduction effect have been performed, and the robustness of the optimum mistuning patterns has been demonstrated. The combined effect of the aerodynamic and structural damping on the response reduction is assessed. It is shown that the new phenomenon is of major practical significance and has to be taken into account in analysis of the forced response and design decisions.
Modeling Separation-Induced Transition Using a Non-Linear Three Equation Turbulence Model and a Reynolds Stress Turbulence Model
Authors: Vlahostergios Zinon , Yakinthos Kyros
Published: January 2011

This paper presents an effort to model separation-induced transition on a flat plate with a semi-circular leading edge, by using two advanced turbulence models, the three equation non-linear model k-ε-A2 of Craft et al. [16] and the Reynolds-stress model of Craft [13]. The mechanism of the transition is governed by the different inlet velocity and turbulence intensity conditions, which lead to different recirculation bubbles and different transition onset points for each case. The use of advanced turbulence models in predicting the development of transitional flows has shown, in past studies, good perspectives. The k-ε-A2 model uses an additional transport equation for the A2 Reynolds stress invariant and it is an improvement of Craft et al. [12] non-linear eddy viscosity model. The use of the third transport equation gives improved results in the prediction of the longitudinal Reynolds stress distributions and especially, in flows where transitional phenomena may occur. Although this model is a pure eddy-viscosity model, it borrows many aspects from the more complex Reynolds-stress models. On the other hand, the use of an advanced Reynolds-stress turbulence model, such as the one of Craft [13], can predict many complex flows and there are indications that it can be applied to transitional flows also, since the crucial terms of Reynolds stress generation are computed exactly and normal stress anisotropy is resolved. The model of Craft [13], overcomes the drawbacks of the common used Reynolds-stress models regarding the computation of wall-normal distances and vectors in order to account for wall proximity effects. Instead of these quantities, it employs “normalized turbulence lengthscale gradients” which give the ability to identify the presence of strong inhomogeneity in a flow development, in an easier way. The final results of both turbulence models showed acceptable agreement with the experimental data. In this work it is shown that there is a good potential to model separation-induced transitional flows, with advanced turbulence modeling without any additional use of ad-hoc modifications or additional equations, based on various transition models.
Comparative Study on Tip Clearance Flow Fields in Two Types of Transonic Centrifugal Compressor Impeller With Splitter Blades
Authors: Yamada Kazutoyo , Tamagawa Yusuke , Fukushima Hisataka , Furukawa Masato , Ibaraki Seiichi , Iwakiri Ken-ichiro
Published: January 2011

Two types of transonic centrifugal compressor impeller with splitter blades, which are different in blade count, have been investigated in this study. RANS (Reynolds-Averaged Navier-Stokes) simulations were carried out for several operating conditions to clarify differences in aerodynamic performance characteristic and tip clearance flow field between the two compressors. The simulation shows that basically similar flow events happen in both compressors. A low velocity region is generated near the tip at low flow rate conditions, which results from an expansion of the tip leakage vortex. The low velocity region expands as the flow rate is decreased, and interacts with the pressure surface of the splitter blade near the leading edge. This causes a descent of the blade loading near the tip of the leading edge, and an accumulation of high entropy fluid near the casing-suction corner. Moreover, the tip clearance flow spills ahead of the leading edge of the splitter blade at near stall condition, and eventually the spillage happens at the full blade at stall condition. However, the major difference in solidity influences tip clearance flow/blade interaction, which leads to changes in the performance characteristics. In the impeller with low solidity, the tip leakage vortex breaks down with a large blockage effect because of high blade loading at the tip, which decreases the pressure ratio. The impeller with high solidity is subject to the spillage, which results in an early and large-scale stall that decreases the efficiency.
Numerical and Experimental Analysis of the Effects of Non-Axisymmetric Contoured Stator Endwalls in an Axial Turbine
Authors: Poehler Thorsten , Gier Jochen , Jeschke Peter
Published: January 2011

Numerical and experimental investigations have been performed to determine the effects of non-axisymmetric stator endwall contouring on the efficiency of an axial turbine stage. The influences of the contoured endwalls on the secondary flows in the stator and the rotor have been analyzed by conducting steady and unsteady RANS simulations as well as measurements in the 1.5-stage axial cold air turbine test rig of the Institute of Jet Propulsion and Turbomachinery. Both numerical and experimental results show an aerodynamic improvement of efficiency and secondary kinetic energy through non-axisymmetric endwall contouring. The non-axisymmetric endwall contour induces a vortex, which separates the pressure side leg of the horseshoe vortex from the passage vortex resulting in redistributed and reduced secondary flows. The modified secondary flow pattern increases the torque of the rotor blade in the hub region as a consequence of improved inlet conditions for the rotor as well as a reduction of the time interval the secondary flows are convected through the rotor passage within. Concerning the shroud region the endwall contour had no significant impact on the efficiency as a consequence of a dominating tip clearance vortex system.
Detection of Damage in Repeating Structures
Authors: Rehman A. U. , Rongong J. A. , Worden K.
Published: January 2011

Repeating structures in the form of multiple-bladed rotors are used widely in turbomachinery. Damage to blades can have significant consequences but can be difficult to identify in normal operation. This paper introduces an approach for identifying small defects such as cracks in a repeating structure that may be applicable to the limited data obtainable from developing techniques such as blade tip-timing. In order to understand the key issues involved, this initial work involves a numerical study of a simple comb-like repeating structure rather than a bladed rotor. Changes to the system modeshapes and mode order arising from damage are related to the location and severity of damage. Damage, in the form of small, open cracks, is modelled using different techniques such as material removal, periodic reduction in modulus of elasticity of selected elements at the required location and mass modification. Damage indices based on differences in the Modal Assurance Criterion (MAC) that give a measure of the change in the modeshapes are introduced. MAC matrices are obtained using a reduced number of data points. The damage index is obtained from the Frobenius norm of MAC matrix subtracted from (1) the AutoMAC of reference model without crack and (2) the identity matrix. A clear correlation between the damage indices and crack depth / location is shown. In order to account for mistuning in real repeating structures, the performance when the assembly is subjected to inhomogeneous temperature distributions is also considered.
Shaft Shape Multi Objective Optimization Based on Bacterial Chemotaxis
Authors: Guzma´n Pardo Maria Alejandra , Nicoletti Rodrigo , de Carvalho Jonas
Published: January 2011

Chemotaxis is the biased movement developed by certain living organisms as a response to chemical gradients present in their environment. Thanks to advances in the computing field, bacterial chemotactical strategies and its excellent ability in searching can be modeled, simulated and emulated, thus developing bio-inspired optimization methods alternatively to classical methods. In this work, a multi objective optimization algorithm based on bacterial chemotaxis is proposed and applied to the shape optimization of shafts. Design variables are the diameters along shaft’s length and different constraints are tested, such as variable torques, critical velocities, and position of elements. The design results are obtained in terms of final weight and design safety factors at specific points of the shaft, thus leading to a front of optimum solutions, i.e. to the different possible design solutions that satisfy design constraints, where the engineer can find the best compromise solution for his application.
Velocity and Droplet Diameter Distributions of Reacting N-Heptane Sprays at Varied Boundary Conditions in a Generic Gas Turbine Combustor
Authors: Hage Michael , Bru¨bach Jan , Dreizler Andreas
Published: January 2011

In addition to a previous isothermal study, the present work reports on reacting swirling flow fields and droplet diameter distributions. The employed combustion chamber enabled optical access from three sides allowing the application of laser based measurement techniques. It is equipped with an airblast atomizer nozzle typical for gas turbines. The parameters of the boundary conditions were varied to such an extent that laser diagnostics were feasible. The chamber pressure and the inlet temperature were 2–3 bar and 300–350°C, respectively. The analysis of the spray droplets were performed by two velocity component phase Doppler anemometry (PDA). The measurements allowed for the investigation of axial and radial droplet velocities, Sauter mean diameter (SMD) distributions and an estimation of the volume flow rates. Comparisons of the different operating conditions and the influence of the parameters are given in the discussion.
Modeling Wall Film Formation and Breakup Using an Integrated Interface-Tracking/ Discrete-Phase Approach
Authors: Arienti M. , Wang L. , Corn M. , Li X. , Soteriou M. C. , Shedd T. A. , Herrmann M.
Published: January 2011

We propose a computationally tractable model for film formation and breakup based on data from experiments and direct numerical simulations. This work is a natural continuation of previous studies where primary atomization is modeled based on local flow information from a relatively low-resolution tracking of the liquid interface [1]. Sub-models for film formation are supported by direct numerical simulations obtained with the Refined Level Set Grid (RLSG) method [2]. The overall approach is validated by a carefully designed experiment [3], where the liquid jet is cross flow-atomized in a rectangular channel so that a film forms on the wall opposite to the injection orifice. The film eventually breaks up at the downstream exit of the channel. Comparisons with Phase Doppler Particle Analyzer (PDPA) data and with non-intrusive film thickness point measurements complete this study.
Design and Characterization of a Liquid-Fueled Micro-Combustor
Authors: Peck Jay , Jacobson Stuart A. , Waitz Ian A.
Published: January 2011

As part of an effort to develop a microscale gas turbine engine, this paper presents the design and experimental characterization of a micro-combustor that catalytically burns JP8 fuel. Due to the high energy densities of hydrocarbon fuels, microscale heat engines based on them may enable compact power sources with specific energies higher than those of current battery systems. In addition, utilizing a commonly available logistics fuel would provide advantages for military applications. Thus, a microscale engine burning JP8 fuel is attractive as a portable power source. A liquid-fueled micro-combustor with a combustion chamber volume of 1.4 cm3 and an overall die size of 36.4 mm × 36.4 mm × 6.5 mm was designed, micro-fabricated, and experimentally characterized. Two configurations were tested and compared; one with the combustion chamber entirely filled with a catalyst, and the other with the combustion chamber partially filled with a catalyst. In the configuration filled with a catalyst, JP8 combustion was sustained at mass flow rates up to 0.1 g/sec, and an exit gas temperature of 780 K; an overall combustor efficiency of 19%, and a power density of 43 MW/m3 were achieved. The primary limitation on increasing the mass flow rates and temperature further was structural failure of the device due to thermal stresses. With the partially-filled configuration, a mass flow rate of 0.2 g/sec, and a corresponding power density of 54 MW/m3 were obtained. The exit gas temperature for the partially-filled configuration was as high as 720 K, and the maximum overall efficiency was over 22%. Although the reduced amount of catalyst led to incomplete combustion, smaller thermal losses resulted in an increase in the overall combustor efficiency and power density. A non-dimensional operating map was constructed based on the experiment, and it suggests that improving the thermal efficiency would be necessary to achieve higher efficiencies in the device.
Simulation Framework Development for Helicopter Mission Analysis
Authors: Goulos Ioannis , Mohseni Martina , Pachidis Vassilios , D’Ippolito Roberto , Stevens Jos
Published: January 2011

Helicopter mission performance analysis has always been an important topic for the helicopter industry. This topic is now raising even more interest as aspects related to emissions and noise gain more importance for environmental and social impact assessments. The present work illustrates the initial steps of a methodology developed in order to acquire the optimal trajectory of any specified helicopter under specific operational or environmental constraints. For this purpose, it is essential to develop an integrated tool capable of determining the resources required (e.g. fuel burnt) for a given helicopter trajectory, as well as assessing its environmental impact. This simulation framework tool is the result of a collaborative effort between Cranfield University (UK), National Aerospace Laboratory NLR (NL) and LMS International (BE). In order to simulate the characteristics of a specific trajectory, as well as to evaluate the emissions that are produced during the helicopter’s operation within the trajectory, three computational models developed at Cranfield University have been integrated into the simulation tool. These models consist of a helicopter performance model, an engine performance model and an emission indices prediction model. The models have been arranged in order to communicate linearly with each other. The linking has been performed with the deployment of the OPTIMUS process and simulation integration framework developed by LMS International. The optimization processes carried out for the purpose of this work have been based on OPTIMUS’ built-in optimizing algorithms. A comparative evaluation between the optimized and an arbitrarily defined baseline trajectory’s results has been waged for the purpose of quantifying the operational profit (in terms of fuel required) gained by the helicopter’s operation within the path of an optimized trajectory for a given constraint. The application of the aforementioned methodology to a case study for the purpose of assessing the environmental impact of a helicopter mission, as well as the associated required operational resources is performed and presented.
Dual Point Redesign of an Axial Compressor Airfoil Using a Viscous Inverse Design Method
Authors: Ramamurthy Raja , Ghaly Wahid
Published: January 2011

The midspan section of Rotor 67 is redesigned simultaneously at two different design points using a new inverse blade design method where the blade walls move with a virtual velocity distribution derived from the difference between the current and the target pressure distributions on the blade surfaces. This inverse method is fully consistent with the viscous flow assumption and is implemented into the time accurate solution of the Reynolds-Averaged Navier-Stokes equations that are expressed in an arbitrary Lagrangian-Eulerian (ALE) form to account for mesh movement. A cell-vertex finite volume method of the Jameson type is used to discretize the equations in space; time accurate integration is obtained using dual time stepping. An algebraic Baldwin-Lomax turbulence model is used for turbulence closure. The CFD analysis provides the initial blade pressure distributions at both operating points, e.g. at two different back pressures and/or blade speeds. At each operating point, a target pressure distribution that results in a performance improvement, is prescribed. The inverse design method is then used to reach the prescribed target pressure distributions at both operating points, simultaneously. This is done by using a weighted average of the difference between the target and current pressure distributions at the two operating points, to modify the airfoil profile. The results show that by carefully tailoring the target pressure loadings at the two design points, some performance improvement can be achieved over the entire range between the two operating points.
Limited Qualification Tests of an F404 Engine With Blended Fischer Tropsch SPK and NATO F-34 Fuel
Authors: Hadzic Rastko , Bird Jeffrey , Chishty Wajid A. , Little Darrin , Poitras Pierre
Published: January 2011

The purpose of this project was to compare the performance and operability of 50% Fischer-Tropsch Synthetic Paraffinic Kerosene (SPK) and 50% NATO F-34 (JP-8) blend and 100% Jet A-1 in a General Electric F404-400 augmented turbofan engine in the configuration currently in use with the Canadian Forces (CF). The paper describes the main test elements to simulate several aspects of CF use of the engine like acceptance testing, post-overhaul tests, performance (steady state and transient), operability, and durability. An abbreviated endurance test is described as is the special condition monitoring instrumentation. In addition, limited combustor and augmentor combustion stability tests were conducted and some results are described. Fuel properties are documented for reference. The linkage with and support of members of The Technical Cooperation Program (TTCP) is highlighted in terms of joint development of the test plans and sharing the results. Discussions of needs for future limited alternative fuel qualification tests are also presented.
The Effect of an Upstream Compressor on a Non-Axisymmetric S-Duct
Authors: Karakasis Marios K. , Naylor Edward M. J. , Miller Robert J. , Hodson Howard P.
Published: January 2011

This paper considers the effect of an upstream compressor stage on a compressor inter-spool duct. The duct geometry must be fixed early in the engine design process, well before the design of the upstream stages. It is therefore important that the designer has a good physical insight into how engine representative inlet conditions affect the limits of the duct design space. An experimental and computational investigation of two strutted inter-spool S-ducts was undertaken. Both were tested with and without an upstream stage present. The first duct is of a conventional axisymmetric design with a radius change to length ratio ΔR/L = 0.50. This duct is characteristic of the most extreme ducts considered in modern engine design. The second duct is of a non-axisymmetric design and is 20% shorter, ΔR/L = 0.625. This is well beyond the design limit of axi-symmetric strutted ducts. The paper shows that the presence of the upstream stage increases the duct loss by 54%. The rise in loss occurs on the hub wall and is the result of the incoming stator wakes pooling onto the hub wall, forming a row of contra-rotating streamwise vortex pairs adjacent to the hub wall. These vortices pump boundary layer fluid into the free stream, thus raising the mixing loss. In the non-axisymmetric duct an extra mechanism was observed. The streamwise vortex pairs act to ‘re-energise’ the boundary layer. This reduces strut secondary losses caused by the endwall contouring. The net result is that on the non-axisymmetric duct the presence of an upstream stage only increases the duct loss by 28%. Comparing the two ducts, it is shown that with engine representative inlet conditions, the conventional symmetric duct and 20% shorter non-axisymmetric duct have identical performance. This shows that low loss ducts can be designed which are significantly more extreme than current design limits.
Compressive Creep Testing of Thermal Barrier Coated Nickel-Based Superalloys
Authors: Karaivanov Ventzislav G. , Slaughter William S. , Siw Sean , Chyu Minking K. , Alvin Mary Anne
Published: January 2011

Turbine airfoils have complex geometries and during service operation are subjected to complex loadings. In most publications, results are typically reported for either uniaxial, isothermal tensile creep or for thermal cyclic tests. The former generally provide data for creep of the superalloy and the overall performance, and the later provide data for thermal barrier coating (TBC) spallation as a function of thermally-grown oxide (TGO) thickness, surface roughness, temperature, and thermal mismatch between the layers. Both tests provide valuable data, but little is known about the effect of compressive creep strain on the performance of the superalloy/protective system at elevated temperatures. In conjunction with computational model development, laboratory-scale experimental validation was undertaken to verify the viability of the underlying damage mechanics concepts for the evolution of TBC damage. Nickel-based single-crystal Rene´ N5 coupons that were coated with a ∼150–200 μm MCrAlY bond coat and a ∼200–240 μm 7-YSZ APS topcoat were used in this effort. The coupons were exposed to 900, 1000, and 1100°C, for periods of 100, 300, 1000 and 3000 hours in slotted silicon carbide fixtures. The difference in the coefficients of thermal expansion of the Rene´ N5 substrate and the test fixture introduces thermally induced compressive stress in the coupon samples. Exposed samples were cross-sectioned and evaluated using scanning electron microscopy (SEM). Performance data was collected based on image analysis. Energy-dispersive x-ray (EDX) was employed to study the elemental distribution in the TBC system after exposure. To better understand the loading and failure mechanisms of the coating system under loading conditions, nanoindentation was used to study the mechanical properties (Young’s modulus and hardness) of the components in the TBC system and their evolution with temperature and time. The effect of uniaxial in-plane compressive creep strain on the rate of growth of the thermally grown oxide layer, the time to coating failure in TBC systems, and the evolution in the mechanical properties are presented.