bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Investigations of HPC Blisks With a Focus on Travelling Waves
Authors: Strehlau Ulrik , Ku¨hhorn Arnold
Published: January 2011

The motivation for the usage and a further development of blade integrated disk (blisk) technology is driven by a rising demand for efficient, economical and environment-friendly aero engines. In contrast to conventional bladed disks with separated blade and disk design, blisks are either manufactured from solid or disk and blades are assembled by friction welding. Due to an optimized stress distribution, the integrated design leads to potentially higher maximum rotational speeds of the HP-shaft and thus to an improved pressure ratio. This fact offers the opportunity to reduce the number of blades or even to save whole compressor stages. In order that a significant mass-reduction is achieved, which is increased since heavy blade-disk connections of the conventional design are not necessary anymore. Apart from the advantages of the integrated design, the vibration behaviour of a real blisk is more sophisticated compared to the conventional bladed disk design. Due to the very low mechanical damping, effects like mode-localization and amplitude magnification can lead to high cycle fatigue problems of such complex structures. Extensive experimental and numerical investigations are carried out considering a real rotor-stage 1 blisk of the Rolls-Royce E3E/1 demonstrator-HPC. In order to identify “blade individual frequencies” and “blade individual damping”- values, a new patented blade by blade measurement method is used, that provides FRFs characterized by an unique resonance, as known from SDOF-systems. Based on the adjusted FE-model, numerical and experimental investigations of the vibration behaviour in the frequency range of splitted double eigenvalues are carried out. In doing so the expressions “travelling wave” and “standing waves” are commonly used to characterize the eigenmodes and forced modes of vibration respectively. The splitting of eigenvalues could be proved and a novel criterion to distinguish travelling and standing waves is introduced.
Probabilistic CFD Simulation of a High-Pressure Compressor Stage Taking Manufacturing Variability Into Account
Authors: Lange Alexander , Voigt Matthias , Vogeler Konrad , Schrapp Henner , Johann Erik , Gu¨mmer Volker
Published: January 2011

The present paper addresses a non-deterministic CFD simulation of a high-pressure compressor (HPC) stage. The investigation focuses on the determination of the influence of the manufacturing scatter of compressor blades on the aerodynamic performance of the analyzed HPC stage. A set of 150 blades was scanned using an optical 3D digitizer to obtain a three-dimensional point cloud representing the surface of the blades. Classical profile parameters were identified at several sections of constant spanwise coordinate. The radial stacking of these parameters forms a parameter vector that constructs the airfoil model of each scanned blade. Consequently these parameters were used to define the geometric variability of the entire measured blade set. A statistical analysis of the distribution of these parameters defines the input data of the probabilistic 3D CFD simulation. The Monte-Carlo method is used to identify the scatter of the performance values of the HPC stage and their sensitivity to the geometric variability of profile parameters.
Numerical Investigation of the Unsteady Flow Fields in Centrifugal Compressor Diffusers
Authors: Abdelwahab Ahmed
Published: January 2011

The performance of radial diffusers in centrifugal compressor stages is influenced by the impeller exit flow characteristics as well as the vaneless and semi-vaneless space flow characteristics. Both steady and unsteady flow interactions are present due to the propagation of pressure fields upstream and downstream between the impeller and diffuser. Furthermore, unsteady flow interactions occur when the impeller moving wakes developed due to secondary and tip clearance flows propagate through the diffuser passages. The present study aims at presenting a model that describes the unsteady wake propagation in the centrifugal compressor diffuser using vorticity principles. 3D unsteady Reynolds-Averaged Navier Stokes simulations are performed for both a vaned and a vaneless diffuser centrifugal stage. The simulations are used to examine the mechanism for the unsteady wake flow interactions in the diffuser. The unsteady streamwise vortical structures present in the impeller wakes and their propagation through the diffuser flow field is presented. The effect of the unsteady flow on loss production in the compressor stage is investigated. The velocity perturbations due to these vortical structures are presented. The present study indicates that the impeller wake propagation in the diffuser can be represented by a series of unsteady streamwise vortices superimposed on a uniform flow field. These vortices result in velocity perturbations that take the form of both positive and negative jets in the diffuser.
On the Development of Short Axial Length Turbine Stator With Outlet Mach Number 2
Authors: Neˇmec Martin , Straka Petr , Jeli´nek Toma´sˇ , Baba´k Martin
Published: January 2011

This contribution deals with development of a small-size axial steam turbine stator with nominal outlet Mach number equal to 2. Shortening of existing stator geometry was the main goal in order to improve rotor dynamic behaviors. The stator inlet angle appreciably differs in a real machine, therefore it was very important to ensure insensitivity to the inlet angle in a wide range of it. Technological simplicity was also followed to decrease production costs. Description of the new profile geometry development is introduced and results from numerical simulations done by turbine producer Prvni´ Brneˇnska´ Stroji´rna (PBS) are summarized. Developed geometry of a linear cascade and also stator geometry was studied experimentally at the research institute Vy´zkumny´ a Zkusˇebni´ Letecky´ U´stav (VZLU) in the next step. A comparison of the numerical and the experimental results is discussed in this paper and some remarks are mentioned.
Emissions From a Gas Turbine Sector Rig Operated With Synthetic Aviation and Biodiesel Fuel
Authors: Pucher Greg , Allan William , Poitras Pierre
Published: January 2011

Differences in exhaust emissions, smoke production, exhaust pattern factor, deposit build-up and fuel nozzle spray characteristics for various blends of conventional commercial jet fuel (Jet A-1) with synthetic and biodiesel formulations were investigated. Three synthetic fuel formulations and four Fatty Acid Methyl Esters (FAME) were evaluated as such. The synthetic fuels were tested in both neat (100%) and 50% by volume blends with Jet A-1, while the FAME fuels were blended in 2% and 20% proportions. The Combustion Chamber Sector Rig (CCSR), which houses a Rolls Royce T-56-A-15 combustion section, was utilized for emissions, deposits and exhaust pattern factor evaluation. A combustion chamber exhaust plane traversing thermocouple rake was employed to generate two dimensional temperature maps during operation. Following combustion testing, several combustion system components, including the combustion chamber, fuel nozzle and igniter plug were analyzed for relative levels of deposit build-up. A Phase Doppler Anemometry (PDA) system was employed to determine differences in droplet size distributions while an optical spray pattern analyzer was used to compare the spray pattern for the various fuel blends as they emerged from the T-56 nozzle.
Evolutionary Optimization of Micro- Thrust Bearings With Periodic Partial Trapezoidal Surface Texturing
Authors: Papadopoulos C. I. , Nikolakopoulos P. G. , Kaiktsis L.
Published: January 2011

An optimization study of trapezoidal surface texturing in slider micro-bearings, via Computational Fluid Dynamics (CFD), is presented. The bearings are modeled as microchannels, consisting of a moving and a stationary wall. The moving wall (rotor) is assumed smooth, while part of the stationary wall (stator) exhibits periodic dimples of trapezoidal form. The extent of the textured part of the stator, and the dimple geometry are defined parametrically; thus, a wide range of texturing configurations is considered. Flow simulations are based on the numerical solution of the Navier-Stokes equations for incompressible isothermal flow. To optimize the bearing performance, an optimization problem is formulated, and solved by coupling the CFD code with an optimization tool based on genetic algorithms and local search methods. Here, the design variables define the bearing geometry, while load carrying capacity is the objective function to be maximized. Optimized texturing geometries are obtained for the case of parallel bearings, for several numbers of dimples, illustrating significant load carrying capacity levels. Further, these optimized texturing patterns are applied to converging bearings, for different convergence ratio values; the results demonstrate that, for small and moderate convergence ratios, substantial increase in the load carrying capacity, in comparison to smooth bearings, is obtained. Finally, an optimization study performed at a high convergence ratio shows that, in comparison to the parallel slider, the optimal texturing geometry is substantially different, and that performance improvement over smooth bearings is possible even for steep sliders.
Optimizing the Operation of the Intercooled Turbofan Engine
Authors: Gro¨nstedt Tomas , Kyprianidis Konstantinos
Published: January 2011

The performance of an intercooled turbofan engine is analysed by multidisciplinary optimization. A model for making preliminary simplified analysis of the mechanical design of the engine is coupled to an aircraft model and an engine performance model. A conventional turbofan engine with technology representative for a year 2020 entry of service engine is compared to a corresponding intercooled engine. A mission fuel burn reduction of 4.3% is observed. The results are analysed in terms of the relevant constraints such as compressor exit temperature, turbine entry temperature, turbine rotor blade temperature and compressor exit blade height. It is then shown that a separate variable exhaust nozzle mounted in conjunction with the intercooler together with a variable low pressure turbine may further improve the fuel burn benefit to 5.5%. Empirical data and a parametric CFD study is used to verify the intercooler heat transfer and pressure loss characteristics.
Approximation of Critical Speeds for Shafts With Thermal Gradients Using a Rotating Heat Rig
Authors: Mixa Michael , Gordon Ali P.
Published: January 2011

The simulation of internal airflow within turbine blade cooling channels can be useful in understanding the interactions between the operating temperatures, the coolant flow and its effectiveness, and the angular velocity of the blade. A rotating heat rig was designed as a meso-scale testing device to help understand these relationships within the confines of a lab. The first phase of the device was the use of a tubular shaft specimen which was mounted in series with the axis of rotation of the rig. The pipe was externally heated with the use of NiCr resistive wire to simulate the operating temperatures of a turbine blade. The heating element and the rotation of the sample were controlled digitally. Important design considerations were made such as accurate temperature control, modal changes as a function of varying temperature, and accurate bearing life estimates. As a part of carrying out this research, it was determined that none of the analytical models from literature were capable of predicting the critical speed of a shaft with non-uniform temperature distribution. Models based on Rayleigh’s method, Dunkerley’s method, and finite element analysis were created to estimate the critical speeds of the device. The analytical model that was developed makes up for the short comings of existing approaches.
Measurement of Near-Field and Far-Field Noise From Full Scale High Performance Jet Engines
Authors: McKinley Richard , McKinley Robert , Gee Kent , Pilan Tony , Mobley Frank , Gilespie Mitchell , Downing Micah
Published: January 2011

Accurate measurement of the noise fields emitted by a full scale high performance jet engine and jet plume (with supersonic jet flow) requires detailed planning and careful execution. The apparent acoustic source can be very large, more than 50 feet long and 20 feet high and wide. The jet plume contains many noise generating sources, the main two being shock (broad band and shock cells) and turbulent mixing. This paper is an initial description of a detailed method to accurately measure and describe the near-field noise while simultaneously measuring the far-field noise. For a large high performance jet engine, the acoustic far-field may not be formed until more than 1000 ft away from the plume. The paper also describes proposed methods to measure the non-linear propagation of the noise from the near-field to the far-field. The proposed methodology described with vetting will be considered as an US military standard (MILSTD) with possible later consideration as American standard measurement technique to describe noise fields for personnel noise exposure and for measuring the performance of jet engine noise reduction technologies.
A Creep Rupture Time Model for Anisotropic Creep-Damage of Transversely-Isotropic Materials
Authors: Stewart Calvin M. , Gordon Ali P.
Published: January 2011

Anisotropic creep-damage modeling has become an increasingly important prediction technique in both the aerospace and industrial gas turbine industries. The introduction of tensorial damage mechanics formulations in modeling tertiary creep behavior has lead to improved predictions of the creep strain that develops due to anisotropic grain structures and the induced anisotropy that occurs with intergranular damage. A number of isotropic creep-damage rupture time prediction models have been developed in literature; however, few rupture time prediction models for tensorial anisotropic creep-damage are available. In this paper, a rupture time model for anisotropic creep-damage of transversely isotropic materials is derived. Comparison with the Larson-Miller parameter, Monkman-Grant relation, and Kachanov-Rabotnov continuum damage mechanics (CDM) approach shows improved creep rupture time predictions for multiaxial conditions and material rotations. A parametric study of the rupture time predicted under various states of equivalent stress and material orientations is performed to demonstrate the robustness of the new formulation.
Study on a GUI Type Fault Diagnostic Program for a Turboshaft Engine Using Fuzzy and Neural Networks
Authors: Kong Changduk , Koo Youngju , Kho Seonghee , Ryu Hyeok
Published: January 2011

The helicopter to be operated in a severe flight environmental condition must have a very reliable propulsion system. On-line condition monitoring and fault detection of the engine can promote reliability and availability of the helicopter propulsion system. A hybrid health monitoring program using Fuzzy Logic and Neural Network Algorithms is can proposed. In this hybrid method, the Fuzzy Logic identify easily the faulted components from engine measuring parameter changes, and the Neural Networks can quantify accurately its identified faults. In order to use effectively the fault diagnostic system, a GUI (Graphical User Interface) type program is newly proposed. This program is composed of the real time monitoring part, the engine condition monitoring part and the fault diagnostic part. The real time monitoring part can display measuring parameters of the study turboshaft engine such as power turbine inlet temperature, exhaust gas temperature, fuel flow, torque and gas generator speed. The engine condition monitoring part can evaluate the engine condition through comparison between monitoring performance parameters the base performance parameters analyzed by the base performance analysis program using look-up tables. The fault diagnostic part can identify and quantify the single faults the multiple faults from the monitoring parameters using hybrid method.
Optimal Performance of a Modified Three-Blade Savonius Turbine Using Frontal Guiding Plates
Authors: Mohamed Mohamed H. , Janiga Ga´bor , Pap Eleme´r , The´venin Dominique
Published: January 2011

Wind energy is one of the most promising sources of renewable energy. It is pollution-free, available locally, and can help in reducing the dependency on fossil fuels. Although a considerable progress has already been achieved, the available technical design is not yet adequate to develop reliable wind energy converters for conditions corresponding to low wind speeds and urban areas. The Savonius turbine appears to be particularly promising for such conditions, but suffers from a poor efficiency. The present study considers an improved design in order to increase the output power and the static torque of the classical three-blade Savonius turbine, thus obtaining a higher efficiency and better self-starting capability. To achieve this objective three geometrical properties are optimized simultaneously: 1) the position of an obstacle shielding the returning blade; 2) the position of a deflector guiding the wind toward the advancing blade; and 3) the blade skeleton line. As a whole, fifteen free parameters are taken into account during the automatic optimization process, carried out by coupling an in-house library (OPAL) relying on Evolutionary Algorithms with an industrial flow simulation code (ANSYS-Fluent). The output power coefficient is the single target function and must be maximized. The relative performance improvement amounts to more than 50% at the design point compared with the classical configuration.
Some Limitations of Turbomachinery CFD
Authors: Denton John D.
Published: January 2011

CFD is now an essential tool for the design of all types of turbomachinery. However, as engineers are exposed more and more to the results of CFD and less and less to experimental data there is a danger that they may not realise the limitations of CFD and so will view its predictions as more reliable than they really are and not question them sufficiently. This is particularly dangerous when CFD is use as part of an optimisation procedure. The objective of this paper is to try to expose some of the limitations of CFD as used for routine turbomachinery design. CFD is not an exact science. Errors can arise from the following sources: • Numerical errors due to finite difference approximations. • Modeling errors, where the true physics is not known or is too complex to model — e.g. turbulence modeling. • Unknown boundary conditions, such as inlet pressure or temperature profiles. • Unknown geometry such as tip clearances or leading edge shapes. • Assumption of steady flow. Each of these sources of error is discussed and examples of the differences they can cause in the predictions are shown. Despite these limitations CFD remains an extremely valuable tool for turbomachinery design but it should be used on a comparative basis and not trusted to give quantitative predictions of performance.
The Effect of Clearance on Shrouded and Unshrouded Turbines at Two Levels of Reaction
Authors: Yoon Sungho , Curtis Eric , Denton John , Longley John
Published: January 2011

In this paper, the effect of seal clearance on the efficiency of a turbine with a shrouded rotor is compared with the effect of the tip clearance when the same turbine has an unshrouded rotor. The shrouded versus unshrouded comparison was undertaken for two turbine stage designs one having 50% reaction the other having 24% reaction. Measurements for a range of clearances, including very small clearances, showed three important phenomena. Firstly, as the clearance is reduced, there is a “break-even clearance” at which both the shrouded turbine and the unshrouded turbine have the same efficiency. If the clearance is reduced further, the unshrouded turbine performs better than the shrouded turbine, with the difference at zero clearance termed the “offset loss”. This is contrary to the traditional assumption that both shrouded and unshrouded turbines have the same efficiency at zero clearance. The physics of the break-even clearance and the offset loss are discussed. Secondly, the use of a lower reaction had the effect of reducing the tip leakage efficiency penalty for both the shrouded and the unshrouded turbines. In order to understand the effect of reaction on the tip leakage, an analytical model was used and it was found that the tip leakage efficiency penalty should be understood as the dissipated kinetic energy rather than either the tip leakage mass flow rate or the tip leakage loss coefficient. Thirdly, it was also observed that, at a fixed flow coefficient, the fractional change in the output power with clearance was approximately twice the fractional change in efficiency with clearance. This was explained by using an analytical model.
Aeroacoustics and Performance Modeling of a Counter-Rotating Propfan
Authors: Olausson Martin , Avella´n Richard , So¨rman Niklas , Rudebeck Filip , Eriksson Lars-Erik
Published: January 2011

This paper presents a method for design and analysis of counter-rotating propfans with respect to performance and aeroacoustics. The preliminary design method generates the ideal optimum propeller design corrected for losses in terms of profile and compressibility drag. The propeller design is further analyzed by computational fluid dynamics, CFD, to calculate the performance and the deterministic interaction noise. The unsteady flow around the propellers is calculated using URANS such that only one blade per propeller needs to be discretized. The unsteady pressure distribution around the blades is integrated, using a Ffowcs Williams-Hawkings method, to an observer for noise evaluation. The results of the performance analysis, the CFD computations and the aeroacoustic analysis are compared with experimental data available from the nonproprietary reports regarding the counter-rotating propellers developed in the 1980s.
Data Quality Assurance for Supersonic Jet Noise Measurements
Authors: Brown Clifford , Henderson Brenda , Bridges James
Published: January 2011

The noise created by a supersonic aircraft is a primary concern in the design of future high-speed planes. The jet noise reduction technologies required on these aircraft will be developed using scale-models mounted to experimental jet rigs designed to simulate the exhaust gases from a full-scale jet engine. The jet noise data collected in these experiments must accurately predict the noise levels produced by the full-scale hardware in order to be a useful development tool. A methodology has been adopted at the NASA Glenn Research Center’s Aero-Acoustic Propulsion Laboratory to insure the quality of the supersonic jet noise data acquired from the facility’s High Flow Jet Exit Rig so that it can be used to develop future nozzle technologies that reduce supersonic jet noise. The methodology relies on mitigating extraneous noise sources, examining the impact of measurement location on the acoustic results, and investigating the facility independence of the measurements. The methodology is documented here as a basis for validating future improvements and its limitations are noted so that they do not affect the data analysis. Maintaining a high quality jet noise laboratory is an ongoing process. By carefully examining the data produced and continually following this methodology, data quality can be maintained and improved over time.
Aerodynamic Analysis of an Innovative Low Pressure Vane Placed in a S-Shape Duct
Authors: Lavagnoli S. , Yasa T. , Paniagua G. , Duni S. , Castillon L.
Published: January 2011

In this paper the aerodynamics of an innovative multisplitter LP stator downstream of a high-pressure turbine stage is presented. The stator row, located inside a swan necked diffuser, is composed of 16 large structural vanes and 48 small airfoils. The experimental characterization of the steady and unsteady flow field was carried out in a compression tube rig under engine representative conditions. The one-and-a-half turbine stage was tested at three operating regimes by varying the pressure ratio and the rotational speed. Time-averaged and time-accurate surface pressure measurements are used to investigate the aerodynamic performance of the stator and the complex interaction mechanisms with the HP turbine stage. Results show that the strut blade has a strong impact on the steady and unsteady flow field of the small vanes depending on the vane circumferential position. The time-mean pressure distributions around the airfoils show that the strut influence is significant only in the leading edge region. At off-design condition (higher rotor speed) a wide separated region is present on the strut pressure side and it affects the flow field of the adjacent vanes. A complex behavior of the unsteady surface pressures was observed. Up to four pressure peaks are identified in the time-periodic signals. The frequency analysis also shows a complex structure. The spectrum distribution depends on the vane position. The contribution of the harmonics is often larger than the fundamental frequency. The forces acting on the LP stator vanes are calculated. The results show that higher forces act on the small vanes but largest fluctuations are experienced by the strut. The load on the whole stator decreases 30% as the turbine pressure ratio is reduced by approx. 35%.
ARMA Model for Turbine and Compressor Clearance Forecasting
Authors: Luo Huageng , Ghanime George , Wang Liping
Published: January 2011

In turbo machinery, clearance (the distance between the turbine or compressor blade tip to the casing) at high-pressure stages is one of the key design parameters to measure the turbine efficiency and effectiveness. Thus, appropriate modeling and prediction of the clearance under operational conditions is very important. If the clearance can be actively controlled, the turbine manufacturers get even more competitive advantages. For turbine design purpose, detailed physics based model is usually available. However, this kind of detailed model is not suitable for on-line prediction due to heavy computational requirements. Instead, a reduced order model based on the first order physics is used. Usually, the available reduced order models are computationally efficient, but they can hardly reach the accuracy desired by control engineers. In this paper, we applied an ARMA modeling technique for the reduced order clearance modeling and prediction. Typical turbine cycle operation data were used to build the ARMA model first. The built model is then used to predict other operations of the same unit, as well as other units of the same family.
Rotor Interaction Noise in Counter-Rotating Propfan Propulsion Systems
Authors: Peters Andreas , Spakovszky Zolta´n S.
Published: January 2011

Due to their inherent noise challenge and potential for significant reductions in fuel burn, counter-rotating propfans (CRPs) are currently being investigated as potential alternatives to high-bypass turbofan engines. This paper introduces an integrated noise and performance assessment methodology for advanced propfan powered aircraft configurations. The approach is based on first principles and combines a coupled aircraft and propulsion system mission and performance analysis tool with 3-D unsteady, full wheel CRP CFD computations and aero-acoustic simulations. Special emphasis is put on computing CRP noise due to interaction tones. The method is capable of dealing with parametric studies and exploring noise reduction technologies. An aircraft performance, weight and balance and mission analysis was first conducted on a candidate CRP powered aircraft configuration. Guided by data available in the literature, a detailed aerodynamic design of a pusher CRP was carried out. Full wheel unsteady 3-D RANS simulations were then used to determine the time varying blade surface pressures and unsteady flow features necessary to define the acoustic source terms. A frequency domain approach based on Goldstein’s formulation of the acoustic analogy for moving media and Hanson’s single rotor noise method were extended to counter-rotating configurations. The far field noise predictions were compared to measured data of a similar CRP configuration and demonstrated good agreement between the computed and measured interaction tones. The underlying noise mechanisms have previously been described in the literature but, to the authors’ knowledge, this is the first time that the individual contributions of front-rotor wake interaction, aft-rotor upstream influence, hub-endwall secondary flows and front-rotor tip-vortices to interaction tone noise are dissected and quantified. Based on this investigation, the CRP was re-designed for reduced noise incorporating a clipped rear-rotor and increased rotor-rotor spacing to reduce upstream influence, tip-vortex, and wake interaction effects. Maintaining the thrust and propulsive efficiency at takeoff conditions, the noise was calculated for both designs. At the interaction tone frequencies, the re-designed CRP demonstrated an average reduction of 7.25 dB in mean SPL computed over the forward and aft polar angle arcs. On the engine/aircraft system level, the re-designed CRP demonstrated a reduction of 9.2 EPNdB and 8.6 EPNdB at the FAR 36 flyover and sideline observer locations, respectively. The results suggest that advanced open rotor designs can possibly meet Stage 4 noise requirements.
Finite Length Squeeze Film Dampers With Air Entrainment: Non-Dimensional Maps and Their Applicability
Authors: Torres Jorge E. , Di´az Sergio E.
Published: January 2011

Squeeze Film Dampers (SFDs) are bearings that support large motion amplitudes when traversing rotor-bearing systems critical speeds. Actual practice demands bearings with operating conditions of low oil supply pressure and high frequency. In open-ended SFDs, large amplitudes of journal motion draw air into the film gap. The air ingested and entrapped results in a bubbly mixture that affects the dynamic performance and the overall damping capability of the SFDs. Diaz and San Andre´s [11] developed a model to predict the amount of air ingested into SFDs with open-ends. They proposed an innovative non-dimensional number to estimate the amount of air entrapped in the film gap, but their analytical results are limited to short length bearings. Mendez et al. [13] extended the results of Diaz and San Andre´s to finite length bearings, devising a Finite Volume Method (FVM) scheme. Even though their research presented new and significant results, they lack wider applicability that includes different geometries or boundary conditions. The present research proposes the solution of the Reynolds equation by the finite element method. Results computed by this formulation explore non-dimensional maps for determination of the amount of entrapped air. The results show that for fixed lubricant properties the amount of entrapped air depends exclusively on three dimensionless parameters: feed-squeeze flow number, length to diameter ratio, and dimensionless orbit radius.
Use of Multiple Variable Mathematical Method for Effective Condition Monitoring of Gas Turbines
Authors: Ogbonnaya Ezenwa A. , Theophilus-Johnson Kombo
Published: January 2011

All over the globe, gas turbines (GTs) play tremendous role in energy and power generation. Condition monitoring is also being used to obtain early warning of impending equipment failure to prevent costly downtime and damage to process equipment. Several scheduled visits were thus made to AFAM IV, GT 18, TYPE 13D plant located near Port Harcourt, in Rivers State of Nigeria. Continuous and periodic monitoring of the thermodynamics/performance parameters such as temperature, pressure, air pumping capability and fuel flow were carried out. These activities lasted for over a period of one year on hourly basis to examine the state of health of the engine compared with the data taken. The diagnostic method of trend performance monitoring was jointly used with multiple variable mathematical models (MVMMs), because they relate deterioration to consequences. A software code-named “THAPCOM” written in C++ programming language was used proactively monitor the engine based on this MVMMs. The values observed on the third month revealed that ηO was 27.0% and AL was 48MW. A significant variation in the results obtained shows that there is a deviation between the monitored data taken from the console and the reference data in the manufacturer’s manual. These are indications of impending failure or health uncertainty of the engine. This allowed maintenance to be scheduled, or other actions taken to avoid catastrophy.
Hot-Wire Measurements in a High Speed Counter Rotating Turbo Fan Rig
Authors: Meyer Robert , Knobloch Karsten , Linden Johannes
Published: January 2011

The German Aerospace Center (DLR) has measured the unsteady flow field of a high speed Contra-Rotating Turbo Fan (CRTF). In order to perform the measurement, hot-wire probes were placed upstream of the first rotor, between both rotors and downstream of the second rotor. With the DLR hot-wire measuring technique, unsteady flow structures (e.g. the wake of each individual rotor blade) were measured and analyzed in detail. The averaged mean vectors as well as the fluctuation components of the velocity were determined. The calculated local turbulence distribution of the flow downstream of the rotating blades shows an increase of the turbulence intensity of 3% in the wake. With the phase-locked averaging and the spectral analysis an upstream effect of the rotor 2 was verified.
Effect of Recirculation Device on Performance of High Pressure Ratio Centrifugal Compressor
Authors: Tamaki Hideaki
Published: January 2011

Centrifugal compressors used for turbochargers need to achieve a wide operating range. A recirculation device, which consists of a bleed slot, an upstream slot and an annular cavity connecting both slots, is often applied to them. The author developed a high pressure ratio centrifugal compressor with pressure ratio 5.7 for a marine use turbocharger. In order to enhance operating range, a recirculation device was applied, the benefits of its application ensuring. This paper discusses how the recirculation device affects the flow field in the above transonic centrifugal compressor by using steady 3D calculations. It is reported that the interaction between shock and tip leakage vortex is one of the primary causes of stall inception in the impeller. Analysis of shock and tip leakage flow behavior leads to an understanding of the basic mechanism of the enhancement of operating range by the recirculation device. Hence this study focuses on the effect of the recirculation devices on the shock and tip leakage flow. Steady 3D calculations were performed and the effect of the recirculation device was clarified. The bleed slot of the recirculation device works in a similar way to circumferential grooves applied to axial compressors. It reduces the blade loading in the impeller tip region. And hence the velocity of tip leakage flow exiting the bleed slot becomes lower compared with that without the recirculation device. The flow through the bleed slot impinges on the tip leakage flow originated upstream and blocks the extension of the tip leakage flow. It also deflects the trajectory of the tip leakage vortex. In addition to these effects, the bleed slot removes the fluid near the casing. The shock moves downstream due to the reduction of the blockage. All these effects induced by the recirculation device are considered to lead to the suppression of the extension of blockage and to contribute to the enhancement of the compressor operating range.
Combustor Residence Time Measurement Using Planar Laser Induced Florescence
Authors: Spencer Adrian , Cheng Liangta
Published: January 2011

Combustor performance parameters are strongly affected by the residence time of the combustion chamber. Both the time mean velocity and the turbulence fields are important to the residence time of the gases within it. However, determining the residence time via analysis of a measured velocity field is difficult, particularly due to the inherent unsteadiness and three dimensional nature of the flow within a combustor. A more direct approach is to use a passive transported scalar and look at the dynamic response of the scalar concentration to a step change in the injection rate of it. This may be done with a high spatial and temporal resolution using modern high frame rate digital cameras. A time resolved planar laser induced florescence (PLIF) technique is described that has been used to characterize the residence time within a combustion chamber. Characteristic times evaluated from the measurements are the convection (or delay time) from the point of injection and scalar decay rate (or half life) due to turbulent mixing once the effect of the reduced scalar concentration injection has been transported to the point of interest, other measures are possible but these are the most relevant to flow fields with significant recirculation. The technique is described for a single phase isothermal aerodynamic flow field, but with further consideration the technique could be extended to reacting combustors. Not only does the data provide a useful insight to the mixing phenomena and relevant time scales, it also provides suitable validation data for time dependent CFD predictions in which it is easy to solve for a conserved scalar.
PIV Analysis on the Effect of Stator Loading on Transonic Blade-Row Interactions
Authors: Reynolds Scott B. , Gorrell Steven E. , Estevadeordal Jordi
Published: January 2011

Experiments have been performed to investigate interactions between a loaded stator and transonic rotor. The Blade Row Interaction (BRI) rig is used to simulate an embedded transonic fan stage with realistic geometry (thin trailing edge) which produces a wake through diffusion. Details of the unsteady flow field between the stator and rotor were obtained using PIV. Flow-visualization images and PIV data that facilitate analysis of vortex shedding, wake motion, and wake-shock-interaction phenomena are presented. Stator wake and rotor-bow-shock interactions are analyzed for three stator/rotor axial spacings, and two stator loadings. Specific shed vortices and wake topological features are isolated for each configuration. The data analysis focuses on measuring the vortex size, strength, and location as it forms on the stator trailing edge and propagates downstream into the rotor passage. It was observed that vortex shedding is synchronized to the passing of a rotor bow shock. Results show that the circulation of a vortex increased by 19 to 23% from far to close spacing due to the increased strength of the rotor bow shock impacting the stator trailing edge. Reduction in stator loading decreased shed vortex circulation for the same stator/rotor axial spacing by 20 to 25%. Pitchwise radius of vortices also decreased by 13 to 19% from far to close spacing. Such changes in vortex size and strength should be accounted for to predict the effect of unsteady blade-row interactions on transonic compressor performance.
Experimental Investigation of Endwall and Suction Side Blowing in a Highly Loaded Compressor Stator Cascade
Authors: Nerger Daniel , Saathoff Horst , Radespiel Rolf , Gu¨mmer Volker , Clemen Carsten
Published: January 2011

The following paper describes an experimental investigation of a highly loaded stator cascade with a pitch to chord ratio of t/l = 0.6. Experiments without as well as with active flow control by means of endwall and suction side blowing were conducted. Five-hole-probe measurements in pitchwise and spanwise direction as well as endwall oil flow visualizations were carried out in order to determine the performance of the cascade and to analyze the flow phenomena occuring. To quantify the effectivity of the active flow control method, taking the additional energy input into account, corrected losses and an efficiency, which relates the difference of flow power deficit with and without active flow control to the flow power of the blowing jet itself, were evaluated. Even though an increase of static pressure rise could be achieved, a decrease of the total pressure losses was possible for a few operating points only.
A New Test Rig for Time-Resolved Pressure Measurements in Rotating Cavities With Pulsed Inflow
Authors: Schroeder Gunar , Uffrecht Wieland
Published: January 2011

The improvement of the overall performance and efficiency of gas turbines, especially in the internal cooling air system is of general interest. This requires the reduction of pressure losses induced by vortices and secondary flow. The steady state effects are known from literature and experiments. But also pressure fluctuations and oscillations e.g. resonances have an impact on the efficiency of the internal cooling air system. These unsteady effects are only principally discussed in the literature. Experimental investigations of pressure fluctuations and oscillations in rotating cavities, which are part of the internal air system, are very rare. One reason might be given by the fact that the investigation of these unsteady effects is a technical challenge especially for higher rotational speeds. This paper presents a new rotor test rig with a telemetric measurement system which permits time-resolved pressure measurements in the cavity. The cavity dimensions are similar to those of a real industrial gas turbine. The design of the test rig and the telemetric system allows rotational frequencies up to 10000 rpm. The current experimental investigation is focused on pressure fluctuations and oscillations in rotating cavities with through flow and their dependency on the test parameters. The aim is to find out the relevant effects for operation and design optimisation of rotating cavities in gas turbines. The rig consists of a stationary air delivery and an axial air transfer interface between the stator and the rotor. The rotor contains one cavity. The interface acts as a flow chopper. The air is blown from the stator drillings to the rotating inlet holes of the rotor which provide the connection to the cavity inside the rotor. The rotating holes pass the stator holes periodically, causing pressure fluctuations in the cavity. The frequency of the fluctuations depends on the rotational frequency of the rotor and the number of inlet and stator drillings, which can be varied. The tests are carried out for a range of the parameter Reφ, calculated with the outer radius of the cavity, up to 1·106 and for different mass flow rates. The new test rig, the setup, the instrumentation and the first measurements are the topic of this paper. The non-stationary effects found in the cavity and their dependency on the parameters rotational frequency and mass flow will be discussed and compared with known theoretical approaches.
Phased Array Noise Source Localization Measurements of an F404 Nozzle Plume at Both Full and Model Scale
Authors: Podboy Gary G. , Bridges James E. , Henderson Brenda S.
Published: January 2011

A 48-microphone planar phased array system was used to acquire jet noise source localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant noise sources in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic source localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400 series nozzle provide useful insights regarding the full-scale engine jet noise source mechanisms, and document some of the differences associated with testing at model-scale versus full-scale.
Study of Swirling Air Flow Characteristics in a Lean Direct Injection Combustor
Authors: Dewanji Dipanjay , Rao Arvind G. , Pourquie Mathieu , van Buijtenen Jos P.
Published: January 2011

This paper investigates the non-reacting aerodynamic flow characteristics in Lean Direct Injection (LDI) combustors. The RANS modeling is used to simulate the turbulent, non-reacting, and confined flow field associated with a single-element and a nine-element LDI combustor. The results obtained from the simulation are compared with some experimental data available in literature. The numerical model, which is in accordance with an experimental combustor, consists of an air swirler with 6 helical axial vanes of 60 degree vane angle and a converging-diverging duct, extending in a square flame tube. The numerical model covers the entire flow passage, including the highly swirling flow passage through the swirler vanes, and the combustion chamber. Simulation has been performed with a low Reynolds number realizable k-ε model and a Reynolds stress turbulence model. It is observed that the computational model is able to predict the central re-circulation zones (CTRZ), the corner recirculation zones, and the complex flow field associated with the adjacent swirlers with reasonable accuracy. The computed velocity components for the single-element case show that the flow field is similar to the experimental observations.
Film Cooling Effectiveness Comparison Between Shaped- and Double Jet Film Cooling Holes in a Row Arrangement
Authors: Kusterer Karsten , Elyas Anas , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo , Kazari Masahide
Published: January 2011

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the needed cooling air amount. Consequently it is required to increase the cooling efficiency of applied cooling technologies. Streamwise ejection from a cylindrical hole causes kidney vortices which transport hot gas underneath the cooling jet and leads the cooling jet to lift off from the surface. Cooling performance is highly increased by using the shaped hole technique, which weakens the kidney vortex structure. However the formation of secondary flows can not completely be avoided by using shaped holes instead of cylindrical holes. Another promising film cooling technology is the double-jet film cooling, which prevents the cooling jet from lifting off the surface and raises the lateral spreading of the cooling air by generating an anti kidney vortex. This paper presents a comparison of the film cooling effectiveness between the shaped film cooling technique and the novel double jet film cooling technique for the high blowing ratios M = 1, M = 1.5 and M = 2. Various geometries of fan-shaped holes with lateral expansion angles of 10°, 14° and 18° are used for the comparison study. It can be shown that the shaped hole row arrangement provides higher cooling values in a slight region near to the hole exits, while the double jet film cooling technique shows a obvious cooling advantage in the further downstream area for high blowing ratios. Furthermore recent results of an on-going experimental comparison study between the double jet, trench and cylindrical technique are presented, which proves the advantage capability of the double jet film cooling.