bluuebunny/crossref_metadata_2025 huggingface dataset:
Compressor Performance Recovery Systems: A New Thermoeconomic Approach
Authors: Fabbri Andrea , Traverso Alberto , Cafaro Silvio
Published: May 2012

Compressor fouling in a Gas Turbine (GT) is an important issue which has to be studied to define compressor performance and GT reliability. Three main aspects have to be taken into account: the type of pollutants that could enter into the compressor, with their possible effects such as blade erosion and/or corrosion; the power and efficiency losses caused by fouling;the economic loss due to increase in fuel consumption and reduction in power output. Two main solutions can be considered for reducing the fouling effect and restoring compressor performance: compressor washing and the High Efficiency Particulate Air filter (HEPA). The choice of the most effective devices for each power plant is not trivial, because of the great number of parameters to be taken into account. The aim of this study is to provide a guide to identifying and managing the best washing or filter devices for a GT in a specific power plant site, using information from the literature and GT user data from European Turbine Network (ETN) members. Two procedures were designed in order to have a user friendly tool: “Best Cleaning Devices” was developed to help GT users in the choice of the best devices for recovering compressor performance. “Best Cleaning Time” is based on the “Best maintenance time” theory and it provides the user with an estimate about the best time to perform compressor off-line or on-line washing. The procedures are explained in detail and tested on some real cases.
Laminar Flame Speed Measurements and Modeling of Alkane Blends at Elevated Pressures With Various Diluents
Authors: Kochar Yash , Seitzman Jerry , Lieuwen Timothy , Metcalfe Wayne , Burke Sine´ad , Curran Henry , Krejci Michael , Lowry William , Petersen Eric , Bourque Gilles
Published: May 2012

Laminar flame speeds at elevated pressure for methane-based fuel blends are important for refining the chemical kinetics that are relevant at engine conditions. The present paper builds on earlier measurements and modeling by the authors by extending the validity of a chemical kinetics mechanism to laminar flame speed measurements obtained in mixtures containing significant levels of helium. Such mixtures increase the stability of the experimental flames at elevated pressures and extend the range of laminar flame speeds. Two experimental techniques were utilized, namely a Bunsen burner method and an expanding spherical flame method. Pressures up to 10 atm were studied, and the mixtures ranged from pure methane to binary blends of CH4/C2H6 and CH4/C3H8. In the Bunsen flames, the data include elevated initial temperatures up to 650 K. There is generally good agreement between model and experiment, although some discrepancies still exist with respect to equivalence ratio for certain cases. A significant result of the present study is that the effect of mixture composition on flame speed is well captured by the mechanism over the extreme ranges of initial pressure and temperature covered herein. Similarly, the mechanism does an excellent job at modeling the effect of initial temperature for methane-based mixtures up to at least 650 K.
Design Considerations for Axial Steam Turbine Rotor Inlet Cavity Volume and Length Scale
Authors: Barmpalias Konstantinos G. , Kalfas Anestis I. , Abhari Reza S. , Hirano Toshio , Shibukawa Naoki , Sasaki Takashi
Published: May 2012

In this paper we examine the interaction between the cavity and main flows of three different rotor cavities. For each of the three rotor cavities, the cavity inlets differ in their axial cavity lengths, which are modified by extending the upper casing stator platform. The three cavity volumes are comprised of a baseline case, along with a 14% and a 28% volume reduction relative to the baseline case. Measurements show that there is an increase in efficiency of 0.3% for the 14% cavity volume reduction case (relative to the baseline case), whereas a further volume reduction of 28% (relative to the baseline case) decreases the efficiency. Computational analysis highlights the break-up of a toroidal vortex within the cavity as the primary factor explaining the changes in efficiency. The dominant cavity vortex originally present in the baseline case firstly broken up into two smaller vortices for the 14% cavity volume reduction case and secondly, completely replaced with a strong radial jet for the 28% volume reduction case. From a design perspective, reducing the cavity volume by extending the upper casing stator platform yields improvements in efficiency provided that the cavity vortex is still present. The design considerations, analysis and the associated aerodynamics are discussed in detail within this paper.
Experimental and Numerical Investigation of Tip Clearance and Bleed Effects in a Centrifugal Compressor Stage With Pipe Diffuser
Authors: Kunte Robert , Schwarz Philipp , Wilkosz Benjamin , Jeschke Peter , Smythe Caitlin
Published: May 2012

The subject of this paper is the experimental and numerical investigation of a state-of-the-art high pressure centrifugal compressor stage with pipe diffuser for a jet engine application. This study shows the impact of impeller tip clearance- and bleed-variation on the centrifugal stage. The purpose of this paper is threefold. In the first place, it investigates the effects on the stage performance. Secondly, it seeks to explain local flow-phenomena, especially in the diffuser. Finally, it shows that steady CFD simulations are capable of predicting these phenomena. Experimental data were gathered using conventional pitot and three-hole-probes as well as Particle-Image-Velocimetry. Numerical simulations with the CFD solver TRACE were conducted to get fundamental insight into the flow. Thus, this study contributes greatly towards understanding the principle of the flow phenomena in the pipe diffuser of a centrifugal compressor.
Emissions Assessment of Alternative Aviation Fuel at Simulated Altitudes
Authors: Chishty Wajid A. , Davison Craig R. , Bird Jeffrey , Chan Tak , Cuddihy Kevin , McCurdy Mark , Barton Peter , Krasteva Aneliia , Poitras Pierre
Published: May 2012

To address the global fuel challenges of energy security, economic sustainability and climate change the stakeholders of aviation industry are actively pursuing the development and qualification of alternative ‘drop-in’ fuels. New standards will be required to regulate the use of these new fuels, which requires not only fuel specification and rig/engine and flight testing but also an emission life cycle impact assessment of these fuels. This paper reports on emission data measured at various simulated altitudes and engine speeds from a jet engine operated on conventional and alternative aviation fuels. The work was conducted as part of on-going efforts by departments within the Government of Canada to systematically assess regulated as well as non-regulated emissions from the use of alternative aviation fuels. The measurements were performed on an instrumented 1000 N-thrust turbojet engine using a baseline conventional Jet A-1 fuel and a semi-synthetic (50/50) blend with Camelina based Hydroprocessed Renewable Jet (JP8-HRJ8) fuel. Emission results reported here include carbon dioxide, carbon monoxide, nitrogen oxides and particulate matter measured at several simulated altitudes and power settings. In order to ensure that the assessments have a common baseline, relevant engine performance and operability data were also recorded.
Passive Absorption/Emission Spectroscopy for Gas Temperature Measurements in Gas Turbine Engines
Authors: Li Hejie , Wang Guanghua , Nirmalan Nirm , Dasgupta Samhita , Furlong Edward R.
Published: May 2012

A novel technique is developed to simultaneously measure hot surface and gas temperatures based on passive absorption/emission spectroscopy (PAS). This non-intrusive, in situ technique is the extension of multi-wavelength pyrometry to also measure gas temperature. The PAS technique uses hot surface (e.g., turbine blade) as the radiation source, and measures radiation signals at multiple wavelengths. Radiation signals at wavelengths with minimum interference from gas (mostly from water vapor and CO2) can be used to determine the hot surface temperature, while signals at wavelengths with gas absorption/emission can be used to determine the gas temperature in the line-of-sight. The detection wavelengths are optimized for accuracy and sensitivity for gas temperature measurements. Simulation results also show the effect of non-uniform gas temperature profile on measurement results. High pressure/temperature tests are conducted in single nozzle combustor rig to demonstrate sensor proof-of-concept. Preliminary engine measurement results shows the potential of this measurement technique. The PAS technique only requires one optical port, e.g., existing pyrometer or borescope port, to collect the emission signal, and thus provide practical solution for gas temperature measurement in gas turbine engines.
On Occurrence of Reverse Full Annular Rub
Authors: Yu John J.
Published: May 2012

This paper discusses reverse full annular rub based on a two degree-of-freedom rotor/seal model where a rubbing location can be simulated away from the lumped rotor mass. The analytical model is much closer to the experimental setup for comparison of results, and real machines for analysis, than the previous one degree-of-freedom model. Its closed-form solution is given including reverse rub amplitudes and relative phases as well as the normal contact force. The exact frequency equation in polynomial form yields reverse full annular rub frequencies without having to neglect any parameters. Many conclusions can be drawn directly from explicit expressions without numerical calculations. The solution with non-positive normal contact force indicates a dry-friction whirl/whip-free region, usually accompanied by low friction and/or high damping. The analytical study covers both dry-friction whirl and dry-friction whip, and their relations with dry friction factor, damping, and rotor speed. Range of reverse rub frequencies, their relation with rotor and rotor/seal coupled natural frequencies, and direction of frictional force, are also revealed. Destructive dry-friction whip experimental results are given which have fully confirmed the analytical formulas.
Comparison Between Oxygen-Blown and Air-Blown IGCC Power Plants: A Gas Turbine Perspective
Authors: Parulekar Prashant S.
Published: May 2012

The gasifier in an Integrated Gasification Combined Cycle (IGCC) Power Plant gasifies coal using an oxidant gas that facilitates partial combustion and effective gasification of the coal feed. When electricity generation is the prime objective of the IGCC facility this oxidant can be ambient air, or gaseous oxygen produced from an Air Separation Unit (ASU). Gasification technology providers are presently divided in their type of offering and information in the public domain does not effectively guide End Users in the advantages and disadvantages of the two gasification methods as applicable to the particular project being developed. This paper highlights key design aspects that should guide End Users in making an effective assessment and perform detailed evaluation of the gasification technologies for the particular IGCC project in consideration.
Numerical Simulation of Surge in Turbocharger Centrifugal Compressor: Influences of Downstream Plenum
Authors: Guo Strong , Chen Hua , Zhu Xiaocheng , Du Zhaohui
Published: May 2012

Surge is an important instability seriously affecting compression systems. This paper presents a numerical simulation of surge flow phenomenon inside a turbocharger centrifugal compressor with a vaneless diffuser. The compressor was discharged into a plenum and the effect of the plenum on surge behavior of the compressor system was investigated. The entire geometry of the compressor, including the impeller, vaneless diffuser, volute housing and downstream plenum, were included in the simulation. Three-dimensional Reynolds averaged compressible Navier–Stokes equations were solved with the k–ε turbulence model using commercial software CFX and two different sizes of plenum were studied. A new plenum model is proposed which allows temporal variation of temperature inside the plenum. The numerical technique employed to set up CFD (computational fluid dynamics) with such an unstable flow system are described. The results show that when the plenum volume was nearly doubled, the dominating frequency of the system suddenly dropped from 72Hz to 23Hz. During the surge cycle, the compressor characteristic (pressure ratio ν mass flow curve) showed distinct differences. With the smaller plenum, the characteristic showed random traces with little global backflow at the compressor inlet, while with the larger plenum, clear surge cycles are displayed with strong global backflow at the inlet. The flow fields of the two systems are presented as functions of time and show distinct differences. In the case of the smaller plenum, the circumferential flow field inside the impeller is non uniform, showing influences of rotating stall, while in the case of the large plenum, the circumferential uniformity returns and the flow field behaves quasi-steadily during the surge cycle. With the larger plenum, the volute flow synchronises with the inlet mass flow oscillation in time and a completed vortex break down occurs at every volute cross section, but with the smaller plenum the synchronisation disappears and vortex break down only occurs partially at the centers of some volute cross sections.
Investigation of the Tip Clearance Flow in a Compressor Cascade Using a Novel Laser Measurement Technique With High Temporal Resolution
Authors: Fischer Andreas , Bu¨ttner Lars , Czarske Ju¨rgen , Gottschall Marcel , Mailach Ronald , Vogeler Konrad
Published: May 2012

The understanding of the tip clearance flow in axial compressors is a key issue for developing new compressors with enhanced efficiency and reduced noise for instance. However, necessary flow measurements in the blade tip region and within the tip clearance are challenging due to the small gap width. The application of a novel optical measurement technique named Doppler global velocimetry with laser frequency modulation is presented, which provides velocity field measurements of all three velocity components non-intrusively in the tip clearance flow of a linear cascade at near stall conditions. These array measurements have a high temporal resolution enabling turbulence analysis such as the evaluation of velocity standard deviations and turbulence spectra up to several kilohertz. Conventional pneumatic and hot-wire measurements in planes at the inlet and the outlet as well as on the blade surface were taken to complete the flow pattern and validate the data of the Doppler global velocimetry. Wake measurements identified a strong flow separation in the rear suction side dominating the transient character of the cascade flow. Towards the endwall this high loss region is reduced by the clearance flow and the resulting vortex, which is obviously not affected by the profile separation and the pulsating blockage frequency. Inside the blade passage and the tip clearance the Doppler global velocimetry measurements allowed a spatial assignment of the origin of the tip leakage flow and the downstream developing vortex. In addition, the tip clearance vortex could be resolved and identified successfully as the most dominant turbulence generating effect in the near endwall region at this high loading operating point of the blading.
Influence of Abradable Coating Wear Mechanical Properties on Rotor Stator Interaction
Authors: Batailly Alain , Legrand Mathias , Pierre Christophe
Published: May 2012

In the field of turbomachines, better engine performances are achieved by reducing possible parasitic leakage flows through the closure of the clearance distance between blade tips and surrounding casings. Accordingly, direct contact is now commonly accepted as part of aircraft engines everyday life. In order to avoid possibly catastrophic scenarii due to high contact forces between the rotating and static components, implementation of abradable coatings has been widely recognized as a robust solution offering several advantages: reducing potential damage to the incurring blade as well as adjusting operating clearances, in-situ, to accept physical contact events. In the present work, macroscopic behavior of the abradable coating is numerically approximated through a piecewise linear plastic constitutive law which allows for real time access to the current abradable layer profile. Contact simulations are carried out considering a three-dimensional industrial finite element model of a blade from a compressor stage and its surrounding casing, assumed perfectly rigid. Due to the large number of degrees of freedom, component mode synthesis methods are used. Simulations are repetitively carried-out over a wide rotational velocity range, and a large number of distinct values for two mechanical parameters of the abradable material are considered. Results show that the amplitude of vibration is highly sensitive to the Young modulus and the plastic modulus of the abradable and that a local maximum is detected. Also, a more realistic description of the contact forces allowing for a contribution in the tangential direction is suggested.
Experimental and Computational Approach for Jet Noise Mitigation by Mixing Control Devices
Authors: Tanaka Nozomi , Oishi Tsutomu , Ooba Yoshinori , Enomoto Shunji , Yamamoto Kazuomi , Ishii Tatsuya
Published: May 2012

The notched nozzle as a new concept has been investigated for conventional nozzle design together with the Chevron nozzle and Micro-jets, through feasibility studies. The notched nozzle has a plurality of triangular pyramid-shaped dent positioned in a circumferential direction along the nozzle exit. These studies include acoustic experiments that utilize a lab-scale simple model in an anechoic chamber and numerical approaches. The results of the Large Eddy Simulation are compared with the results of either acoustic or aerodynamic experiments. The objective of these investigations is to verify the effects of noise mitigation and to gain understanding of the physics of fluid dynamics around the nozzle exit, especially within the shear layer between high velocity jet flow and external flow/or ambient air. One concept of conventional noise mitigation devices involves mixing enhancements in the shear layer, but this sometimes produces high frequency self noise. Moreover it will result in a penalty in terms of thrust loss, additional weight and extra manufacturing cost due to the complicated shapes around the nozzle exit. It is difficult to produce a nozzle design without affecting high frequency self-noise and decreasing low-frequency noise towards to down stream of the jet engines even though there is no thrust loss. Most of this study, the experimental data were physically validated by three kinds of nozzle concepts designed to be equal to the conventional model in terms of size of nozzle exit diameter and Mach number. Essentially far-fields noise measurements and pressure measurements are conducted by polar angle microphones and arch-shaped pitot tubes are located downstream of the jet. The noise benefit which is produced by the notched nozzle as a lab-scale in far-fields noise measurements is up to 1.3dB at the side of the jet and 0.5dB at downstream, in terms of size of small-engine. Furthermore this provided an advantage over the chevron nozzle due to the decreasing self-noise production when the Mach number of the jet was lower than 0.9. Moreover, numerical predictions which are provided by the Large Eddy Simulation were used to estimate the noise mitigation by performing turbulence statistical analysis. Numerical results which refer to the turbulent statistics are discussed in order to define how they can be affected to the acoustic results at the side of the jet. This shows how each device can deform the shear layer without producing additional streamwise and small scale vortices.
Effects of Rotating Stall on an Axial Fan Design
Authors: Wilt K. R. , Story D. , Scarton Henry A. , Hunter A. I. C. , Salamah S. A. , Ramtahal J.
Published: May 2012

This paper presents the physical measurements and analysis of data pertaining to rotating stall observed during testing at the GE fan test facility located at Rensselaer Polytechnic Institute. Although never detected in actual GE applications, the rotating stall was encountered while testing fan cooling blade prototypes used in electrical generators. The effects of this phenomenon on the flow rate and pressure rise across the fan are considered, along with the frequency content of the adjacent flows on either side of the fan. Further, the effects of the addition of flow constrictions before and after the fan on the behavior of the rotating stall are investigated.
Case Study of Morton Effect Shaft Differential Heating in a Variable-Speed Rotating Electric Machine
Authors: Lorenz Joshua A. , Murphy Brian T.
Published: May 2012

Hydrodynamic journal bearings can exhibit a particular form of Shaft Differential Heating (SDH) sometimes known as the Morton Effect. This paper presents test data of the Morton Effect in the form of synchronous spiral vibration observed in a 4200 rpm rotating electric machine. With its original partial arc bearings, divergent spiral vibration prevented stable operation above 4000 rpm. Subsequent analytical SDH studies of different bearing types are described which led to a switch to 4 lobe sleeve bearings. The 4 lobe bearing retrofit eliminated the unstable spiral vibration behavior. To the authors’ knowledge, this is the first published instance of a verified case of the Morton Effect to be solved exclusively by a change in bearing hardware with no accompanying changes to the rotor, shaft or journal.
Experimental Investigations of Corner Stall in a Linear Compressor Cascade
Authors: Ma Wei , Ottavy Xavier , Lu Lipeng , Leboeuf Francis , Gao Feng
Published: May 2012

In order to gain a better knowledge of the mechanisms of corner stall and to calibrate computational-fluid-dynamics (CFD) tools including both Reynolds-averaged Navier-stokes and large eddy simulation, a detailed and accurate experiment of three-dimensional flow field through a linear compressor cascade has been set up. Experimental data were acquired for a Reynolds number of 3.82 × 105 based on blade chord and inlet flow conditions. First, inlet flow conditions were surveyed by hot-wire anemometry in boundary layers. Second, in order to investigate the effects of incidence, measurements then were acquired at five incidences from −2° to 6°. The results included the outlet flow variables of the cascade, measured by a five-hole pressure probe, and static pressures on both blade and endwall surfaces, measured by pressure taps. Third, the flow field details were measured at an incidence angle of 4°. In this configuration the corner stall region was large enough to be investigated, and without two-dimensional (2D) separation at mid-span on the blade suction side near the trailing edge. The velocity field was then measured by 2D Particle Image Velocimetry in cross-sections parallel to the endwall. And the velocity field in the vicinity of the blade suction side was measured with 2D Laser Dropper Anemometry. In order to test the performance of CFD and also to validate the experimental results, a series of numerical simulations were carried out and compared with the experimental results. We thus obtained a set of detailed measurements which constitute an original and complete data base and in good agreement with the published experimental results in literature. These data were also compared with CFD results and showed that the improvements needed in turbulence modeling in order to accurately simulate the three-dimensional separation configuration of corner stall.
Blade Loading and its Application in the Mean-Line Design of Low Pressure Turbines
Authors: Coull John D. , Hodson Howard P.
Published: May 2012

In order to minimize the number of iterations to a turbine design, reasonable choices of the key parameters must be made at the earliest possible opportunity. The choice of blade loading is of particular concern in the low pressure (LP) turbine of civil aero engines, where the use of high-lift blades is widespread. This paper presents an analytical mean-line design study for a repeating-stage, axial-flow Low Pressure (LP) turbine. The problem of how to measure blade loading is first addressed. The analysis demonstrates that the Zweifel coefficient [1] is not a reasonable gauge of blade loading because it inherently depends on the flow angles. A more appropriate coefficient based on blade circulation is proposed. Without a large set of turbine test data it is not possible to directly evaluate the accuracy of a particular loss correlation. The analysis therefore focuses on the efficiency trends with respect to flow coefficient, stage loading, lift coefficient and Reynolds number. Of the various loss correlations examined, those based on Ainley and Mathieson ([2], [3], [4]) do not produce realistic trends. The profile loss model of Coull and Hodson [5] and the secondary loss models of Craig and Cox [6] and Traupel [7] gave the most reasonable results. The analysis suggests that designs with the highest flow turning are the least sensitive to increases in blade loading. The increase in Reynolds number lapse with loading is also captured, achieving reasonable agreement with experiments.
An Aerodynamic Design Methodology for Low Pressure Axial Fans With Integrated Airfoil Polar Prediction
Authors: Carolus Thomas H. , Starzmann Ralf
Published: May 2012

A common blade design methodology for low solidity fan rotors is based on blade element theory combined with empirical airfoil lift and drag data. Often the required airfoil characteristics have to be estimated from existing wind tunnel data, roughly estimating the effects of Reynolds number and airfoil modifications such as trailing edge thickening. This contribution presents an extension of that methodology: Polar curves are computed during the fan design procedure and applied to each blade element. Reynolds and even Mach number as well as all geometrical features of the airfoil are fully taken into account. For that the public domain code XFOIL for analysis of subsonic isolated airfoils by Drela and Youngren has been integrated in an existing blade design code. The paper summarizes blade element theory and points out the interface where XFOIL data enter. A case study demonstrates how the airfoil specification affects the fan blade design. Two fan rotors for the same duty point but with NACA 4512 and FX60-126 airfoil blades are compared. Moreover, the effect of trailing edge bluntness on the blade shape is investigated.
Prediction of the Blade Trailing-Edge Noise of an Axial Flow Fan
Authors: Guedel Alain , Robitu Mirela , Descharmes Nicolas , Amor Didier , Guillard Je´rome
Published: May 2012

The objective of this work is to predict the trailing-edge noise of axial fans with an analytical model deduced from an extension of Amiet’s formulation. The input data of the acoustic model are the frequency spectra and the spanwise correlation length scales of the wall-pressure fluctuations on the blade suction side close to the trailing edge. This model was successfully validated in former studies on single steady airfoils in anechoic wind tunnels and, to a lesser extent, on an axial fan equipped with small unsteady pressure transducers flush mounted on the blade suction side. The present research is carried out on a 6-blade axial fan no longer equipped with embedded pressure transducers. The input data of the prediction are then deduced from non-dimensional spectra and correlation lengths of the pressure fluctuations measured in the previous study and RANS simulations performed on the test fan. A validation of the prediction method is made by comparing the predicted and measured sound power spectra of the fan for two blade pitch angles and different operating points.
Numerical Study of Non-Reacting and Reacting Flow Characteristics in a Lean Direct Injection Combustor
Authors: Dewanji Dipanjay , Rao Arvind G. , Pourquie Mathieu , van Buijtenen Jos P.
Published: May 2012

The Lean Direct Injection (LDI) combustion concept has been of active interest due to its potential for low emissions under a wide range of operational conditions. This might allow the LDI concept to become the next generation gas-turbine combustion scheme for aviation engines. Nevertheless, the underlying unsteady phenomena, which are responsible for low emissions, have not been widely investigated. This paper reports a numerical study on the characteristics of the non-reacting and reacting flow field in a single-element LDI combustor. The solution for the non-reacting flow captures the essential aerodynamic flow characteristics of the LDI combustor, such as the reverse flow regions and the complex swirling flow structures inside the swirlers and in the neighborhood of the combustion chamber inlet, with reasonable accuracy. A spray model is introduced to simulate the reacting flow field. The reaction of the spray greatly influences the gas-phase velocity distribution. The heat release effect due to combustion results in a significantly stronger and compact reverse flow zone as compared to that of the non-reacting case. The inflow spray is specified by the Kelvin-Helmholtz breakup model, which is implemented in the Reynolds-Averaged Navier Stokes (RANS) code. The results show a strong influence of the high swirling flow field on liquid droplet breakup and flow mixing process, which in turn could explain the low-emission behavior of the LDI combustion concept.
A New, Iterative, Synchronous-Response Algorithm for Analyzing the Morton Effect
Authors: Childs Dara W. , Saha Rohit
Published: May 2012

Morton Effect problems involve the steady increase in rotor synchronous-response amplitudes due to differential heating across a fluid-film bearing that is in turn induced by synchronous response. The present work presents a new computational algorithm for analyzing Morton Effect. Previous studies on the Morton Effect were based on Eigen or Nyquist analysis for stability studies and predicted an onset speed of instability. The algorithm starts with a steady state elliptical orbit produced by the initial imbalance distribution, which is decomposed into a forward-precessing circular orbit and a backwards-precessing circular orbit. A separate (and numerically intensive) calculation based on the Reynolds equation plus the energy equation gives predictions for the temperature distributions induced by these separate orbits for a range of orbit radius-to-clearance ratios. Temperature distributions for the forward and backward orbits are calculated and added to produce the net temperature distribution due to the initial elliptic orbit. The temperature distribution is assumed to vary linearly across the bearing and produces a bent-shaft angle across the bearing following an analytical result due to Dimoragonas. This bent shaft angle produces a synchronous rotor excitation in the form of equal and opposite moments acting at the bearing’s ends. For a rotor with an overhung section, the bend also produces a thermally induced imbalance. The response due to the initial mechanical imbalance, the bent-shaft excitation, and the thermally-induced imbalance are added to produce a new elliptic orbit, and the process is repeated until a converged orbit is produced. For the work reported, no formal stability analysis is carried out on the converged orbit. The algorithm predicts synchronous response for the speed range of concern plus the speed where the response amplitudes becomes divergent by approaching the clearance. Predictions are presented for one examples from the published literature, and elevated vibration levels are predicted well before the motion diverges. Synchronous-response amplitudes due to Morton Effect can be orders of magnitude greater than the response due only to mechanical imbalance, particularly near rotor critical speeds. For the example considered, bent-shaft-moment excitation produces significantly higher response levels than the mechanical imbalance induced by thermal bow. The impact of changes for (1) bearing length to diameter ratio, (2) reduced lubricant viscosity, (3) bearing radius-to-clearance ratio and (4) overhung mass magnitude are investigated. Reducing lubricant viscosity and/or the overhung mass are predicted to be the best remedies for Morton Effect problems.
Measurements and Analysis of Bluff-Body Flame Response to Transverse Excitation
Authors: Acharya Vishal , Emerson Benjamin , Mondragon Ulises , Brown Christopher , Shin Dong-Hyuk , McDonell Vincent , Lieuwen Tim
Published: May 2012

This paper describes the interaction of bluff body stabilized flames with 450 Hz transverse acoustic standing waves at flow velocities up to 100 m/s. Two different modes of acoustic excitation were applied, corresponding to pressure and velocity nodes along the bluff body centerline. Time resolved measurements of both the flame front and velocity field were obtained. These measurements of the spatio/temporal distribution of the flame front were compared to level set equation prediction using the measured velocity field as an input, or vice-versa. These studies show that the measured flame response characteristics are qualitatively captured in almost all cases, with quantitative differences varying from values that are quite low to a factor of two. A key implication of this work is that the important features of the unsteady flame dynamics at high velocity, vitiated flow conditions are understood, but further work is needed for quantitative prediction.
Optimization of Temperature Measurement Technique Used in High Heat Flux Environment
Authors: Romanov Dmitriy , Devoe Jason , Ginzbursky Lev
Published: May 2012

The heat transfer calculations for turbine flows are known to have a substantial degree of uncertainty [1]. Therefore experimental verification of analytical predictions is needed. Properly done, metal temperature measurements could inform a designer about the existence of under-cooled or over-cooled locations, suggesting possible opportunities to improve engine thermodynamic and durability characteristics. Operating in a difficult turbine environment, temperature sensors must be well understood to be able to perform the critical task of thermal mapping accurately. The authors analyzed the influence of factors such as heat flux, sensor positioning, and thermal characteristics of installation assembly on the accuracy of the temperature measured by Crystal Temperature Sensors (CTS) and S-type Thermocouples (TC). The investigation was performed using a numerical simulation of the heat-transfer process taking place in a thin wall with the sensors installed. The recommendations drawn from this experience should help analytical designers and instrumentation engineers optimize experimental techniques and improve the quality of engine test result interpretation.
Prediction of Axial Thrust Load Acting on a Cryogenic Liquid Turbine Impeller
Authors: Wang Ke , Sun Jinju , He Zhilong , Song Peng
Published: May 2012

A single stage cryogenic liquid turbine is developed for replacing the Joule-Thompson valve and recovering energy from the liquefied air during throttling process in the large-scale internal compression air-separation unit, and evaluation of the impeller axial thrust at different conditions is essential for a reliable bearing design and stable operation. To predict the axial thrust load, a numerical model is established to simulate the turbine flow in a turbine stage environment, which includes the main flow domain (an asymmetrical volute, variable geometry nozzle, impeller, and diffuser), impeller front and back side gaps, and shaft seal leakage. Numerical simulation of flow is conducted by using the ANSYS-CFX. Flow characteristics in both main flow domain and impeller side gaps of the turbine stage are captured and analyzed. The axial thrust is then calculated based on the obtained pressure data in the impeller and its front and side gaps by using a direct integration approach. Flow behaviour in both main flow domain and impeller side gaps has been well exhibited by the numerical results. At the impeller back side gap inlet, the back flow is encountered even for design condition and it returns the impeller main flow stream; the impeller side gap flow has much influence on the axial thrust. To investigate influence of turbine operation condition on axial thrust, flow simulation is conducted at different mass flow rates and inlet pressure for the turbine stage, based on which the axial thrust is calculated. It is demonstrated from the obtained numerical results that the axial thrust increases as the inlet pressure increases and decreases as turbine flow rate increases. Geometry parametric study is conducted for the shaft seal clearances, which has demonstrated that the axial thrust is influenced largely by the clearance size and it decreases as the clearance grows. For the purpose of comparison, the empirical method is also used to predict the axial thrust load. The obtained results are compared to the numerical ones and evident deviation of the empirical from the numerical exists and the reason is that axial force components caused by the impeller main flow stream and its side gap flow are approximated very roughly in the empirical method.
Spray and Flame Structure of a Generic Injector at Aeroengine Conditions
Authors: Meier Ulrich , Heinze Johannes , Freitag Stefan , Hassa Christoph
Published: May 2012

In support of the development of CFD for aeroengine combustion, quantitative measurements of spray properties and temperature were made. A generic swirling air blast injector was designed and built to produce well defined inlet conditions and for ease of numerical description for the CFD development. The measurements were performed in an optically accessible single sector combustor at pressures of 4 and 10 bar and preheat temperatures of 550 and 650 K, respectively. Jet A-1 was used as fuel. The burner air to fuel ratio was 20 and the pressure loss was set to 3%. Sauter mean diameter (SMD) profiles and liquid mass flux distributions were generated from the phase Doppler anemometry (PDA) measurements of the evaporating spray drop sizes and velocities. With planar measurements of Mie scattering and kerosene-LIF, the distribution of kerosene (liquid and vapor phase) was imaged. Temperatures were measured with OH-LIF. The burner was designed with a straight outlet to exhibit lifted flames. Hence initial distributions of size, velocity and density of the spray were measured before it entered the flame. Almost complete prevaporization was seen at least for the 4 bar flame. Compared with atmospheric investigations, the smaller diameters of the droplets and the small streamline curvature of the configuration led to a more uniform behavior of the spray.
Experimental Investigations on Cooling Air Ejection at a Straight Turbine Cascade Using PIV and QLS
Authors: Freund Oliver , Rehder Hans-Juergen , Schaefer Philipp , Roehle Ingo
Published: May 2012

Due to the high turbine inlet temperatures in modern aircraft engines the adoption of several cooling techniques in the first turbine blade rows is state of the art. For this reason the influence of cooling air ejection on the main flow is in the interest of scientists. In this paper experimental and numerical investigations on the trailing edge cooling air ejection at a stator profile are presented. All measurements are performed at the Straight Cascade Wind tunnel Go¨ttingen. To verify the influence of the cooling air flow on the flow field, the velocity field is measured by Particle Image Velocimetry (PIV). The development of the cooling air concentration is analyzed by utilizing the Quantitative Light Sheet (QLS) technique. For validation purposes the QLS results are compared to CO2 concentration measurements. Both measurement techniques are in good agreement with each other. One of the most important advantages of PIV and QLS is the possibility of combining them at the same test bed due to the identical experimental setup. The experimental investigations are supported by numerical simulations based on the numerical code TRACE. Both the numerical results as well as the experimental results prove the reduction of the trailing edge shock by increasing the coolant mass flow ratio.
Analysis of Unsteady Flows Past Horizontal Axis Wind Turbine Airfoils Based on Harmonic Balance Compressible Navier-Stokes Equations With Low-Speed Preconditioning
Authors: Campobasso M. Sergio , Baba-Ahmadi Mohammad H.
Published: May 2012

This paper presents the numerical models underlying the implementation of a novel harmonic balance compressible Navier-Stokes solver with low-speed preconditioning for wind turbine unsteady aerodynamics. The numerical integration of the harmonic balance equations is based on a multigrid iteration, and, for the first time, a numerical instability associated with the use of such an explicit approach in this context is discussed and resolved. The harmonic balance solver with low-speed preconditioning is well suited for the analyses of several unsteady periodic low-speed flows, such as those encountered in horizontal axis wind turbines. The computational performance and the accuracy of the technology being developed are assessed by computing the flow field past two sections of a wind turbine blade in yawed wind with both the time- and frequency-domain solvers. Results highlight that the harmonic balance solver can compute these periodic flows more than 10 times faster than its time-domain counterpart, and with an accuracy comparable to that of the time-domain solver.
On the Parallelization of a Harmonic Balance Compressible Navier-Stokes Solver for Wind Turbine Aerodynamics
Authors: Jackson Adrian , Campobasso M. Sergio , Baba-Ahmadi Mohammad H.
Published: May 2012

The paper discusses the parallelization of a novel explicit harmonic balance Navier-Stokes solver for wind turbine unsteady aerodynamics. For large three-dimensional problems, the use of a standard MPI parallelization based on the geometric domain decomposition of the physical domain may require an excessive degree of partitioning with respect to that needed when the same aerodynamic analysis is performed with the time-domain solver. This occurrence may penalize the parallel efficiency of the harmonic balance solver due to excessive communication among MPI processes to transfer halo data. In the case of the harmonic balance analysis, the necessity of further grid partitioning may arise because the memory requirement of each block is higher than for the time-domain analysis: it is that of the time-domain analysis multiplied by a variable proportional to the number of complex harmonics used to represent the sought periodic flow field. A hybrid multi-level parallelization paradigm for explicit harmonic balance Navier-Stokes solvers is presented, which makes use of both distributed and shared memory parallelization technologies, and removes the need for further domain decomposition with respect to the case of the time-domain analysis. The discussed parallelization approaches are tested on the multigrid harmonic balance solver being developed by the authors, considering various computational configurations for the CFD analysis of the unsteady flow field past the airfoil of a wind tubine blade in yawed wind.
Assessment of Scavenge Efficiency for a Helicopter Particle Separation System
Authors: Jiang Leiyong , Benner Michael , Bird Jeff
Published: May 2012

The effectiveness of a typical helicopter particle separation system has been numerically assessed at practical operating conditions and sand environments for various scenarios. The particle separation mechanism and its limitation are revealed by the flow characteristics and particle trajectories in the flow-field. The separation-by-inertia concept is effective for removing large particles, but problematic for small particles of diameter (d) ≤ 36μm. The particle size, shape factor, and rebound characteristics exert substantial effects on particle scavenge efficiency. On the other hand, the effects of gravity, particle inlet velocity, inlet mass distribution, and engine operating conditions on scavenge efficiency are minor or limited for the configurations and operating conditions considered in the present study. In addition, a few suggestions for further investigation on engine particle separation systems are included.
The Influence of Crystal Orientation on the Elastic Stresses of a Single Crystal Nickel-Based Turbine Blade
Authors: Savage Michael W. R.
Published: May 2012

Single crystal nickel-based turbine blades are directionally solidified during the casting process with the crystallographic direction [001] aligned with the blade stacking axis. This alignment is usually controlled within 10°, known as the Primary angle. The rotation of the single crystal about the [001] axis is generally not controlled and this is known as the Secondary angle. The variation in Primary and Secondary angles relative to the blade geometry means that the stress response from blade to blade will be different, even for the same loading conditions. This paper investigates the influence of single crystal orientation on the elastic stresses of a CMSX-4 turbine blade root attachment using finite element analysis. The results demonstrate an appreciable variation in elastic stress when analysed over the controlled Primary angle, and are further compounded by the uncontrolled Secondary angle. The maximum stress range will have a direct impact on the fatigue resistance of the turbine blade. By optimizing the Secondary angle variation the elastic stresses can be reduced, giving the potential to enhance the fatigue resistance of the turbine blade.
Improving Rotordynamic Performance of an Axial Flow Compressor With Two-Lobe Bearings Using Nonlinear Constraint Parameter Optimization
Authors: Ressing Henning , Kukla Sebastian
Published: May 2012

Bearings are a key factor in achieving a good rotor dynamics performance for turbo machinery. Large compressors, steam and gas turbines for industrial applications are generally equipped with journal bearings either as tilting pad or multi-lobe bearing type. Here bearing parameters such as bearing geometry, bearing load or oil viscosity significantly alter bearing behavior and influence the rotor dynamics of the entire rotor-bearing system. In order to find an optimal set of bearing parameters for a given rotor-bearing system a nonlinear parameter optimization approach is employed. The rotor-bearing system is parameterized using bearing width, clearance and preload as design variables, since they represent design parameters that can be modified without significantly influencing the rotor design as a whole. The set of design variables is further constraint to stay within feasible limits of bearing design. The objective function is defined as a quantitative measure of rotor dynamic performance evaluating the distance from required separation margins with respect to rotor critical speeds based on API 617 7th Ed. In order to compute the objective function based on the design variables the bearing code ALP3T, solving Reynolds equations for the bearing fluid film, is used to compute the required stiffness and damping coefficients as input to the rotor dynamics program. The rotor dynamics performance is then evaluated using the rotor dynamics code SR3 based on the transfer matrix method. Both programs have been developed by the University of Braunschweig and are defacto industry standard within the German turbo machinery industry. The two programs are coupled and the nonlinear constraint optimization problem is solved using MATLAB’s optimization toolbox. The feasibility of this method is discussed based on an example of an axial flow compressor using two-lobe bearings. It is shown that a significant improvement in rotor dynamic performance can be achieved when compared to previous bearing selections for similar compressor designs and that the approach is suitable for a real-life engineering environment.