bluuebunny/crossref_metadata_2025 huggingface dataset:
Demonstration of a Transient Total Pressure Distortion Generator for Simulating Aircraft Inlet Distortion in Turbine Engine Ground Tests
Authors: Beale Dave , Wieland Scott , Reed Jim , Wilhite Larry
Published: March 2009

The development of high-performance aircraft demands the successful integration of the airframe, engine, and control systems. Advancements in aircraft technologies bring with them the need to improve the computational and experimental tools applied to the airframe-engine compatibility evaluations. This paper focuses on the need to improve one of these tools, the direct-connect turbine engine test method. In the absence of the airframe, the direct-connect test must use devices that simulate the effects of the external airframe and the inlet system on the engine inflow. To meet the challenges presented by advanced aircraft, the Arnold Engineering Development Center (AEDC) embarked on the development of a distortion generator to simulate, in real time, the total-pressure distortion the engine experiences in the flight environment. The AEDC distortion generator development progressed through a five-step process that started with the definition of the distortion characteristics that must be simulated and culminated with the testing of a fully functional transient total pressure distortion generator prototype. Prototype validation tests conducted in an AEDC turbine engine test facility entailed the measurement of steady-state and transient total pressure patterns as well as the high-frequency pressure fluctuations produced. The tests demonstrated the ability to remotely set distortion patterns and the ability to sweep through sequences of patterns at rates commensurate with aircraft maneuvers. The paper focuses on the testing of the prototype. First, the paper provides background information on the motivation for the work and summaries of results from the earlier development steps. Next, the paper provides descriptions of the prototype configuration and the validation tests. It then provides initial test results with examples of remotely set distortion patterns. The paper concludes with a summary of future plans for the prototype as well as for other distortion generators in development.
Aeroelastic Analysis of Rotors With Flexible Disks and Alternate Blade Mistuning
Authors: Bleeg James M. , Yang Ming-Ta , Eley James A.
Published: March 2009

A new reduced order Aeroelastic Model using the Principal Shapes of modes (AMPS) is presented. Rotors with flexible disks and alternate blade mistuning can challenge the fidelity of flutter prediction techniques that assume uniform blade-to-blade geometry and mode shape invariance with nodal diameter pattern. The AMPS method, however, accounts for alternating blade geometry as well as varying blade mode shapes, providing accurate flutter predictions for a large number of modes from a small number of CFD (computational fluid dynamics) simulations. AMPS calculations on rotors with alternate blade mistuning are presented and compared to other prediction techniques. The results provide insight into how alternate blade mistuning affects aerodynamic coupling and the flutter characteristics of a rotor.
Testing and Performance Verification of a High Bypass Ratio Turbofan Rotor in an Internal Flow Component Test Facility
Authors: Van Zante Dale E. , Podboy Gary G. , Miller Christopher J. , Thorp Scott A.
Published: March 2009

A 1/5 scale model rotor representative of a current technology, high bypass ratio, turbofan engine was installed and tested in the W8 single-stage, high-speed, compressor test facility at NASA Glenn Research Center (GRC). The same fan rotor was tested previously in the GRC 9×15 Low Speed Wind Tunnel as a fan module consisting of the rotor and outlet guide vanes mounted in a flight-like nacelle. The W8 test verified that the aerodynamic performance and detailed flow field of the rotor as installed in W8 were representative of the wind tunnel fan module installation. Modifications to W8 were necessary to ensure that this internal flow facility would have a flow field at the test package that is representative of flow conditions in the wind tunnel installation. Inlet flow conditioning was designed and installed in W8 to lower the fan face turbulence intensity to less than 1.0% in order to better match the wind tunnel operating environment. Also, inlet bleed was added to thin the casing boundary layer to be more representative of a flight nacelle boundary layer. On the 100% speed operating line the fan pressure rise and mass flow rate agreed with the wind tunnel data to within 1%. Detailed hot film surveys of the inlet flow, inlet boundary layer and fan exit flow were compared to results from the wind tunnel. The effect of inlet casing boundary layer thickness on fan performance was quantified. Challenges and ‘lessons learned’ from testing this high flow, low static pressure rise fan in an internal flow facility are discussed.
Active Control of Fuel Splits in Gas Turbine DLE Combustion Systems
Authors: Bulat Ghenadie , Skipper Dorian , McMillan Robin , Syed Khawar
Published: March 2009

This paper presents a system for the active control of the fuel split within a two-stream Dry Low Emissions (DLE) gas turbine. The system adjusts the fuel split based upon the amplitude of combustor pressure fluctuations and burner metal temperature. The active control system, its implementation and its performance during engine tests on Siemens SGT-200 is described. The paper describes the active fuel split control algorithm. Engine test results are then presented for steady and transient loads with different rates of change of the engine operation temperature, including rapid load acceptance and load shedding. Additionally, cycling operating conditions were tested to evaluate the performance of the algorithm in typical island mode and mechanical drive applications. The active control algorithm was successful in providing stable and reliable control of the turbine allowing very low emissions levels to be attained without manual intervention. In fact it allows areas to be reached that until now were excluded. The impact of operational parameter changes (e.g. load change, ambient temperature, fuel composition etc.) on the engine operability proved the active control software’s ability to respond seamlessly. In addition, it prevented flameout and/or high pressure fluctuation while keeping burner temperatures within limits. Recorded emissions showed a reduction in NOx was achieved when the fuel split was controlled by the algorithm compared to standard operation. This was a direct result of the algorithm successfully identifying the lean stability limit and operating close to it.
Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine: Experimental Investigation
Authors: Behr Thomas , Kalfas Anestis I. , Abhari Reza S.
Published: March 2009

This paper presents an experimental investigation of a novel approach for controlling the rotor tip secondary flow by injecting cooling air from the stationary casing onto the rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the rotor tip region and its impact on the rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly-loaded, high-pressure gas turbine stage. Measurements conducted with a two-sensor fast response pressure probe (FRAP) have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the rotor. Cooling air has been injected in circumferential direction at a 30° angle from the casing tangent, opposing the rotor turning direction through a circumferential array of 10 equidistant holes per rotor pitch. Different cooling air injection configurations have been tested. Injection parameters such as massflow, axial position and size of the holes have been varied to see the effect on the rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the rotor tip leakage vortex and the rotor tip passage vortex reduce. Both vortices move towards the tip suction side corner of the rotor passage. With an appropriate combination of injection massflow rate and axial injection position the isentropic efficiency of the stage was improved by 0.55 percent points.
A Gas Path Diagnostic and Prognostic Approach for Gas Turbine Applications
Authors: Li Y. G. , Nilkitsaranont P.
Published: March 2009

Gas turbine engines experience degradation over time that cause great concern to gas turbine users on engine reliability, availability and operating costs. It has been realized in recent years that gas turbine diagnostics and prognostics is one of the key technologies to enable the move from time-scheduled maintenance to condition-based maintenance in order to improve engine reliability and availability and reduce life cycle costs. The objective of this paper is to introduce a systematic diagnostic and prognostic approach to assess the health condition and estimate the remaining useful life of gas turbine engines before their next major overhaul. A non-linear Gas Path Analysis (GPA) approach is used to assess engine performance degradation with the confidence measured by a GPA Index. A combined regression techniques, including both linear and quadratic models, is proposed to predict the remaining useful life of gas turbine engines. A statistic “Compatibility Check” is used to determine the switch point from linear regression to quadratic regression. The developed diagnostic and prognostic approach has been applied to a model gas turbine engine similar to Rolls-Royce Industrial AVON 1535 implemented with compressor degradation over time. The analysis shows that the developed diagnostic and prognostic approach has great potential to provide an estimation of engine remaining useful life before next major overhaul for gas turbine engines experiencing a typical slow degradation.
Reduced-Order Model of a Mistuned Multi-Stage Bladed Rotor
Authors: Sinha Alok
Published: March 2009

This paper deals with a reduced-order model of a multi-stage rotor in which each stage has a different number of blades. In particular, it is shown that a reduced-order model can be developed on the basis of tuned modes of certain bladed disks. The validity of this algorithm is shown for a spring-mass model with three degrees of freedom per sector. In addition, the statistical distributions of the peak maximum amplitude are generated via Monte Carlo simulations, and the impact of mistuning is examined for a two-stage rotor.
Response of Spray and Heat Release to Forced Air Flow Fluctuations in a Gas Turbine Combustor at Elevated Pressure
Authors: Meier U. , Heinze J. , Hassa C.
Published: March 2009

The objective of this work was to investigate the response of the heat release and liquid fuel distribution to forced periodic modulations of the primary air flow through diffusion type burners with different exit geometries. The spatial distribution of spray density and heat release at different modulation frequencies was studied using phase-resolved OH chemiluminescence for heat release visualization, and planar Mie scattering of kerosene. Experiments were performed for a variety of operating conditions. It was observed that the exit geometry of the nozzle has a considerable effect on the flame shape and fuel distribution, but also on the amplitude of the response to forcing of the air flow. The expanding and contracting fuel spray cone drives the region of the heat release during a period of the air flow modulation, by establishing favourable flammability conditions at varying locations during the oscillation. The temporal shape of the response of the fuel mass in the combustor, as well as the large modulation depth at low frequencies compared to the changes of air flow velocity, suggest that the fuel feed rate into the combustor is affected by a storage mechanism.
Spiral Vibration of a Turbogenerator Set: Case History, Stability Analysis, Measurements and Operational Experience
Authors: Eckert Lothar , Schmied Joachim
Published: March 2009

A hydrogen-cooled turbogenerator operating at 3600 rpm showed the phenomenon of spiral vibration with a forward rotating unbalance vector. The relative shaft vibration measured at the NDE-bearing was close to the trip level. Spiral vibration is observed at various types of rotating machinery with both rotation directions of the unbalance vector, forward and backward. Spiral vibration is caused by a vibration-induced hot spot on the shaft surface generated by friction. The turbogenerator has three bearings: two main bearings and the brush gear bearing. The carbon brushes sliding on the slip rings were identified as the hot spot location. Potential modifications were studied using hot spot stability analyses with a rotor dynamic model of the generator rotor on three journal bearings. The applied method, introduced by J. Schmied [1], allows the handling of general systems. The hot spot model is based on the theory of W. Kellenberger [2, 3] using a thermal equation between the shaft’s thermal deflection and the shaft displacement at the hot spot location. Three different relations between the heat input and the shaft vibration were modeled: heat input proportional to the shaft displacement, to the shaft velocity and to the shaft acceleration. The model in which the heat input is proportional to the velocity is the most suitable variant for slip rings. This was confirmed by comparison with the measured vibration behavior. A modification of the shaft line was selected based on the calculation results and successfully implemented. This generator and other generators with the same modified brush gear unit are in operation since more than four years.
A Method for Enclosed Rotating System Multiple-Plane Equivalent Imbalance Detection
Authors: Luo Huageng , Hallman Darren , Wang Shixiao
Published: March 2009

In this paper, we present an approximation procedure for identifying lumped mass imbalances at multiple locations without accessing to the shaft 1/rev signal. As a first step, an experimental or analytical procedure is applied to optimize the sensor locations, such that a transmissibility matrix with minor off-diagonal terms can be established. Transfer functions between the mass imbalance correction planes and the vibration sensor locations are established by rotordynamics analytical modeling, finite element methods, or experimental testing through a specially designed unit with access to the 1/rev signal. Then, the synchronous responses of the system are obtained by peak-hold average spectrum or waterfall measurement and post-processing to get the synchronous vibration amplitudes as a function of the running speed. For multiple-plane imbalance detection without access to the rotor 1/rev signal, it is mathematically underdetermined to obtain both the amplitude and the phase of the imbalance. A unique estimation method is developed to extract the lumped mass imbalances from the recorded data. Numerical simulations results are reported in the end.
FLOX® Combustion at High Pressure With Different Fuel Compositions
Authors: Lu¨ckerath Rainer , Meier Wolfgang , Aigner Manfred
Published: March 2009

In Flameless Oxidation (FLOX®) the combustion is distributed over a large volume by a high internal flue gas recirculation. This technology has been successfully used for many years in technical furnaces under atmospheric conditions with very low NOx emissions. In the work presented here, FLOX® combustion was for the first time investigated at high pressure in order to assess its applicability for gas turbine combustors. A FLOX® burner was equipped with a combustion chamber with quartz windows and installed into a high pressure test rig with optical access. The burner was operated under typical gas turbine conditions at pressure of 20 bar with thermal powers up to 475 kW. Natural gas as well as mixtures of natural gas and H2 were used as fuel. The NOx and CO emissions were recorded for the different operating conditions. OH* chemiluminescence imaging and planar laser-induced fluorescence of OH were applied in order to characterize the flame zone and the relative temperature distributions. The combustion behaviour was investigated as a function of equivalence ratio and fuel composition, and the influence of the gas inlet velocity on mixing and emissions was studied. For various operating conditions the lean extinction limits were determined.
Remote Monitoring and Failure Diagnosis for a Microturbine Cogeneration System
Authors: Kataoka Tadashi , Kishikawa Tadahiko , Sakata Shigeru , Nakagawa Takahiro , Ishiguro Jun
Published: March 2009

This paper presents the implementation of failure detection and diagnosis, and predictive maintenance for a microturbine cogeneration system. It also introduces a remote monitoring system with capabilities for high-capacity high-speed data acquisition and storage, as well as data sharing via the Internet. Additionally, this paper provides failure diagnosis that uses high-speed transient data in order to determine the root cause of microturbine emergency shutdown or start failure, as well as failure prediction that uses long-range trend data in order to carry out the appropriate maintenance with some examples.
Thermodynamic Analysis of Buoyancy-Induced Flow in Rotating Cavities
Authors: Owen J. Michael
Published: March 2009

Buoyancy-induced flow occurs in the rotating cavities between the adjacent discs of a gas-turbine compressor rotor. In some cases, the cavity is sealed, creating a closed system; in others, there is an axial through-flow of cooling air at the centre of the cavity, creating an open system. For the closed system, Rayleigh-Be´nard (R-B) flow can occur in which a series of counter-rotating vortices, with cyclonic and anti-cyclonic circulation, form in the r-φ plane of the cavity. For the open system, R-B flow can occur in the outer part of the cavity, and the core of fluid containing the vortices rotates at a slower speed than the discs: that is, the rotating core ‘slips’ relative to the discs. These flows are examples of self-organizing systems, which are found in the world of far-from-equilibrium thermodynamics and which are associated with the maximum entropy production (MEP) principle. In this paper, these thermodynamic concepts are used to explain the phenomena that have been observed in rotating cavities, and expressions for the entropy production have been derived for both open and closed systems. For the closed system, MEP corresponds to the maximisation of the heat transfer to the cavity; for the open system, it corresponds to the maximisation of the sum of the rates of heat and work transfer. Some suggestions, as yet untested, are made to show how the MEP principle could be used to simplify the computation of buoyancy-induced flows.
Noise Control of an 11,000 Horsepower Single Stage Pipeline Centrifugal Compressor
Authors: Liu Zheji , Kuzdzal Mark J.
Published: March 2009

Centrifugal compressors installed for natural gas transmission produce significant noise. Many of these compressors have a single impeller with high power input. Large diameter pipes are typically connected to the inlet and discharge of the compressors. As a result, a single stage pipeline compressor not only has a strong noise source but also has a large structure to radiate noise to the ambient. As pipeline compressors are installed close to residential areas, community noise complaints become a concern to pipeline companies and compressor manufacturers. To make compressors more environmentally friendly, duct resonator acoustic arrays have been developed to lower the acoustic energy emanating to the environment. This paper focuses on acoustic technology applied to a single stage pipeline direct-inlet compressor with a 28-inch diameter impeller. The effectiveness of the duct resonator acoustic array is described in this paper with field noise data from three different tests — one test before the compressor was retrofitted with the resonator arrays and two tests afterwards. A baseline noise test was first conducted in January 2002 to obtain the compressor noise signature and to establish the baseline noise data. Using the baseline noise data, duct resonator arrays were designed, manufactured, and retrofitted into the compressor to reduce noise. A second test was performed in October 2002, just after the upgrade, to check the effectiveness of the resonator arrays. The compressor was tested under six different operating points (two speed lines at three points per speed line) from overload to surge during both the first and the second tests. In February 2004, fifteen months after the second test, a third noise test of the same unit was performed to assess the effectiveness of the resonator array over time. The purpose of this third test was to identify if there was any degradation of noise attenuation due to fouling. A comparison of the data taken on the third noise survey with those measured on the second noise survey indicated there was no change in noise levels. After the third test, the unit was disassembled for an aerodynamic retrofit. At this point, the array was inspected and found to be clean. This indicates that the duct resonator array has been performing well since its installation. Fouling has not been detected and the array performance did not degrade over time. This paper provides acoustic data for all three field tests conducted with a focus on the technology applied to reduce the acoustic energy of this centrifugal compressor.
Mitigation of Fretting Fatigue Damage in Blade and Disk Pressure Faces With Low Plasticity Burnishing
Authors: Preve´y Paul S. , Jayaraman N. , Ravindranath Ravi A. , Shepard Michael
Published: March 2009

Low Plasticity Burnishing (LPB) is now established as a surface enhancement technology capable of introducing through-thickness compressive residual stresses in the edges of gas turbine engine blades and vanes to mitigate foreign object damage (FOD). The “Fatigue Design Diagram” (FDD) method has been described and demonstrated to determine the depth and magnitude of compression required to achieve the optimum high cycle fatigue (HCF) strength, and to mitigate a given depth of damage characterized by the fatigue stress concentration factor, kf. LPB surface treatment technology and the FDD method have been combined to successfully mitigate a wide variety of surface damage ranging from FOD to corrosion pits in titanium and steel gas turbine engine compressor and fan components. LPB mitigation of fretting induced damage in Ti-6AL-4V in laboratory samples has now been extended to fan and compressor components. LPB tooling technology recently developed to allow the processing of the pressure faces of fan and compressor blade dovetails and mating disk slots is described. Fretting induced micro-cracks that form at the pressure face edge of bedding on both the blade dovetail and the dovetail disk slots in Ti-6-4 compressor components can now be arrested by the introduction of deep stable compression in conventional CNC machine tools during manufacture or overhaul. The compressive residual stress field design method employing the FDD approach developed at Lambda Technologies is described in application to mitigate fretting damage. The depth and magnitude of compression and the fatigue and damage tolerance achieved are presented. It was found that microcracks as deep as 0.030 in., (0.75 mm) large enough to be readily detected by current NDI technology, can be fully arrested by LPB. The depth of compression achieved could allow NDI screening followed by LPB processing of critical components to reliably restore fatigue performance and extend component life.
Computational Analysis of Surface Curvature Effect on Mist Film Cooling Performance
Authors: Li Xianchang , Wang Ting
Published: March 2009

Air film cooling has been widely employed to cool gas turbine hot components such as combustor liners, combustor transition pieces, turbine vanes and blades. Enhancing air film cooling by injecting mist with tiny water droplets with diameters of 5–10μm has been studied in the past on flat surfaces. This paper focuses on computationally investigating the curvature effect on mist/air film cooling enhancement, specifically for film cooling near the leading edge and on the curved surfaces. Numerical simulations are conducted for both 2-D and 3-D settings at low and high operating conditions. The results show, with a nominal blowing ratio of 1.33, air-only adiabatic film cooling effectiveness on the curved surface is less than on a flat surface. The concave (pressure) surface has a better cooling effectiveness than the convex (suction) surface, and the leading edge film cooling has the lowest performance due to main flow impinging against the coolant injection. By adding 2% (weight) mist, film cooling effectiveness can be enhanced approximately 40% at the leading edge, 60% on the concave surface, and 30% on the convex surface. The leading edge film cooling can be significantly affected by changing of the incident angle due to startup or part-load operation. The film cooling coverage could switch from the suction side to the pressure side and leave the surface of the other part unprotected by the cooling film. Under real gas turbine operating conditions at high temperature, pressure, and velocity, mist cooling enhancement could achieve 20% and provides a wall cooling of approximately 180K.
A Real-World Application of Fuzzy Logic and Influence Coefficients for Gas Turbine Performance Diagnostics
Authors: Eustace Richard W.
Published: March 2009

This paper presents an example of the use of fuzzy logic combined with influence coefficients applied to engine test-cell data to diagnose gas-path related performance faults. The approach utilizes influence coefficients which describe the changes in measurable parameters due to changes in component condition such as compressor efficiency. Such approaches usually have the disadvantages of attributing measurement noise or sensor errors to changes in engine condition, and do not have the ability to diagnose more faults than the number of measurement parameters that exist. These disadvantages usually make such methods impractical for anything but simulated data without measurement noise or errors. However, in this example, the influence coefficients are used in an iterative approach, in combination with fuzzy logic, to overcome these obstacles. The method is demonstrated using eight examples from real-world test-cell data.
Parametric Analysis of Thermal Energy Storage for Gas Turbine Inlet Air Cooling
Authors: Arnulfi Gianmario L. , Croce Giulio , Marini Martino
Published: March 2009

Gas turbine efficiency and power output are strongly dependent on the inlet air condition. Thus, several authors proposed the use of different inlet air cooling systems. Such systems include, as examples, spraying water in the inflow air stream or air cooling through a chiller during GT operation. In the latter case, it is possible to operate the chiller at night time, taking advantage of the remarkable price gap between peak and off-peak hours. A parametric analysis of such a system is presented, focusing on the effect of price gap, chiller and storage design parameters and climatic conditions on the optimal sizing of the plant. Both the gas turbine performance changes, due to the different inlet conditions, and thermal losses related to the storage system are taken into account. The economic return of the system is evaluated through the year-round integral of gas turbine fuel consumption and chiller electricity requirements, for given scenarios of electricity price tag, ambient temperature and humidity profile. For different boundary conditions (market constraints and climate) the optimal configurations are identified and discussed.
Aerodynamic Workings of Blade Tip End-Plates Designed for Low-Noise Operation in Axial Flow Fans
Authors: Corsini Alessandro , Perugini Bruno , Rispoli Franco , Sheard A. G. , Kinghorn Iain R.
Published: March 2009

The use of improved blade tip geometries is addressed as an effective design concept for passive noise control in industrial fans. These concepts, based on geometrical implementations of datum blade by means of end-plates at the tip, are shown to influence effectively the fan rotor-only aero acoustic signature because of the modifications of tip leakage flow behaviour. The aerodynamic merits of the proposed blade tip concepts are investigated by experimental and computational studies in fully-ducted configuration. The nature of the flow mechanisms in the blade tip region is correlated to the specific end-plate design features, and their role in creation of overall stage acoustic emissions clarified. By means of such tools, the tip leakage flow structures of the fans are analysed in terms of vortical structure detection, chordwise leakage flow evaluation, and loading distribution. Rotor losses are also investigated within the passage and invoking classical tip loss model. It was found that the tip geometrical modification markedly affects the multiple vortex behaviour of leakage flow, by altering the near-wall fluid flow paths on both blade surfaces. The improvement of rotor efficiency curves were assessed and correlated to the control of tip leakage flows exploited by the tip end-plates.
Characterisation of Static Strip Seal Flow
Authors: Farahani Arash , Childs Peter
Published: March 2009

Strip seals are used in gas turbine engines between two static elements or between components which do not move relative to each other, such as Nozzle Guide Vanes (NGVs). The key role of a strip seal between NGV segments is sealing between the flow through the main stream annulus and the internal air system, a further purpose is to limit the inter-segmental movements. In general the shape of the strip seal is a rectangular strip that fits into two slots in adjacent components. The minimum clearance required for static strip seals must be found by accounting for thermal expansion, misalignment, and application, to allow correct fitment of the strip seals. Any increase in leakage raises the cost due to an increase in the cooling air use, which is linked to specific fuel consumption, and it can also alter gas flow paths and performance. The narrow path within the seal assembly, especially the height has the most significant affect on leakage. The height range of the narrow path studied in this paper is 0.01–0.06 mm. The behaviour of the flow passing through the narrow path has been studied using CFD modelling and measurements in a bespoke rig. The CFD and experimental results show that normalized leakage flow increases with pressure ratio before reaching a maximum. The main aim of this paper is to provide new experimental data to verify the CFD modelling for static strip seals. The typical flow characteristics validated by CFD modelling and experiments can be used to predict the flow behaviour for future static strip seal designs.
Measurements of Low Reynolds Number Flow in Rotating Channels
Authors: Di Sante Alberto , Van den Braembussche Rene´
Published: March 2009

The impact of Coriolis forces on low Reynolds number decelerating flows is studied by means of time resolved Particle Image Velocimetry in a 6° diverging channel. Measurements are made with a high speed camera and a continuous light source rotating at the same speed as the rotating channel. This allows a direct and accurate recording of the time varying relative velocity. The Reynolds number can be varied from 3 000 to 30 000 in combination with a change of rotation number between 0.0 and 0.33. These values are characteristic for the flow in the blade passage of centrifugal impellers used in micro gasturbines. Increasing rotation stabilizes the flow on the suction side. The peak turbulence intensity shifts away from the wall with a small increase of its amplitude. The turbulence intensity on the pressure side increases its peak value and concentrates closer to the wall when increasing rotation. Instantaneous flow field analyses indicate that elongated vortical structures characterize the boundary layer in the stationary case and on the pressure side of the rotating channel. Isotropic vortices develop relatively distant from the wall on the suction side. Their position and size are tracked in time by means of a wavelet analysis.
New Steps to Improve Rotordynamic Stability Predictions of Centrifugal Compressors
Authors: Gupta Manoj K. , Soulas Thomas A. , Childs Dara W.
Published: March 2009

Improved rotordynamic stability is desired by end users, and centrifugal compressor manufacturers are expected to meet, if not exceed, this expectation. Compressor manufacturers are required to design and build machines that are rotordynamically stable on the test stand and in the field. Confidence has been established in predicting the excitation forces from seals and bearings, but impeller aerodynamic excitation forces continue to be a challenge. While much attention is paid to impellers from an aerodynamic performance point of view, more efforts are needed from a rotordynamic standpoint. A high-pressure, re-injection centrifugal compressor is analyzed in order to predict rotordynamic stability using the best available resources for seals and bearings. Impeller shroud forces are predicted using the bulk-flow model developed by Gupta and Childs [1]. Each impeller stage is analyzed and an attempt is made to improve the estimation of impeller aerodynamic excitation forces. Logarithmic decrement (log dec) predictions for the full rotor model consisting of all the stages and seals are compared to the full-load full-pressure test measured values using a magnetic bearing exciter. A good correlation is obtained between the measured test results and analytical predictions.
Development and Qualification of the Marine Trent MT30 for Next Generation Naval Platforms
Authors: Branch David , Wainwright John
Published: March 2009

Rolls-Royce has recently developed a new aero-derivative gas turbine for Naval Warship Applications; - the Trent based MT30 has been delivered for both US Navy DD(X) Integrated Power System (IPS) Engineering Development Model (EDM) generator set and Littoral Combat Ship (LCS) mechanical drive applications. The MT30 generator set for the DD(X) EDM land based demonstrator has run successfully in the US Navy’s facility in Philadelphia. The MT30 mechanical drive gas turbine module (GTM) will begin testing in the first Lockheed Martin LCS vessel, USS Freedom, in early 2007. This paper will describe the MT30 powerplant architecture, heritage and design features and will describe some of the major technical challenges overcome during the development and qualification programs. Initial experiences of the engine in its two applications will be described, together with future plans.
Synchronizing Separation Flow Control With Unsteady Wakes in a Low-Pressure Turbine Cascade
Authors: Bloxham M. , Reimann D. , Crapo K. , Pluim J. , Bons J. P.
Published: March 2009

Particle image velocimetry (PIV) measurements were made on a highly loaded low-pressure turbine blade in a linear cascade. The Pack B blade has a design Zweifel coefficient of 1.15 and a peak Cp at 63% axial chord on the suction surface. Data were taken at Rec = 20K with 3% inlet freestream turbulence and a wake passing flow coefficient of 0.8. Without unsteady wakes, a non-reattaching separation bubble exists on the suction surface of the blade beginning at 68% axial chord. The time averaged separation zone is reduced in size by approximately 35% in the presence of unsteady wakes. Phase-locked hot-wire and PIV measurements were used to document the dynamics of this separation zone when subjected to synchronized, unsteady forcing from a spanwise row of vortex generator jets (VGJs) in addition to the unsteady wakes. The phase difference between VGJ actuation and the wake passing was optimized. Both steady state Cp and phase-locked velocity measurements confirm that the optimal combination of wakes and jets yields the smallest separation.
Dynamics of an Improved Inter Shaft Squeeze Film Damper: Theory and Experiment
Authors: Gupta K. , Chatterjee S.
Published: March 2009

Intershaft rolling element bearings are commonly used in aero gas turbine rotors primarily to reduce the length of the engine as well as to avoid obstruction to gas flow path at the turbine end. In order to reduce cross-excitation between the LP and HP shafts of two spool rotor, researchers have proposed introduction of squeeze film in the inter shaft bearing. However, Inter Shaft Squeeze Film Damper (ISSFD) becomes unstable above a threshold operating speeds. In the present work, an improved ISSFD which is inherently stable, is analyzed and tested. It has two rolling element bearings, one each mounted on LP and HP rotor shafts. The two bearings are configured such that the squeeze film is formed between the two non rotating races/surfaces. A centralizing spring between the two races, and a supporting spring between the ground/frame and one of the non rotating races are provided. Two design modifications of this system are analyzed and tested experimentally. Experiments on an improvised two spool rotor setup under unbalance excitation are conducted for all the three designs of ISSFD. In theoretical simulations, various design parameters are varied over a wide range. Theoretical analysis as well as the experiments show that an optimum value of radial clearance exists for a given design to have maximum damping, and a damping ratio of the order of 10% and more is achievable in an ISSFD.
Empirical Tuning of an On-Board Gas Turbine Engine Model for Real-Time Module Performance Estimation
Authors: Volponi Al , Brotherton Tom , Luppold Rob
Published: March 2009

A practical consideration for implementing a real-time on-board engine component performance tracking system is the development of high fidelity engine models capable of providing a reference level from which performance changes can be trended. Real-time engine models made their advent as State Variable Models (SVM) in the mid-80’s which utilized a piecewise linear model that granted a reasonable representation of the engine during steady state operation and mild transients. Increased processor speeds over the next decade allowed more complex models to be considered, that were a combination of linear and non-linear physics based elements. While the latter provided greater fidelity over both transient operation and the engine operational flight envelope, these models could be further improved to provide the high level of accuracy required for long-term performance tracking, as well as address the issue of engine-to-engine variation. Over time, these models may deviate enough from the actual engine being monitored, as a result of improvements made during an engine’s life cycle such as hardware modifications, bleed and stator vane schedule alterations, cooling flow adjustments, and the like, that the module performance estimations are inaccurate and often misleading. The process described in this paper will address these shortcomings while maintaining the execution speed required for real-time implementation.
Turbine Blade Film Cooling Study: The Effects of Film Hole Location on the Pressure Side
Authors: Zhang Luzeng , Moon Hee-Koo
Published: March 2009

In efforts to optimize turbine blade film cooling, film effectiveness on the pressure side was investigated for shaped hole injections at three streamwise locations in a warm cascade that simulated realistic engine operation conditions. Local film effectiveness distribution was obtained for individual row of injections as well as the combination of two and three rows using the pressure sensitive paint (PSP) technique. Nitrogen gas was used to simulate cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Three different cooling mass flows were injected to each of the film cooling rows and also the combination of them. For comparison among the locations, the same mass flow ratios (MFR) were kept for each of the rows. The corresponding blowing ratios were also provided for comparison. Local film effectiveness distributions were measured, and spanwise averaged for comparison. The curvature and Mach number associated with the film hole exit location had a significant effect to the value of the film cooling effectiveness. Comparing three single row injection locations, the film effectiveness for the downstream location was found to be higher than that for the upstream location. For the combined injections, the film effectiveness downstream from the second row was not only much higher than that for single row injection, but it was also higher than that predicted by a superposition model using individual row injection results. This suggests that for blade pressure surface film cooling, upstream injection could improve the downstream injection significantly, resulting in much improved film effectiveness overall.
CAD to CAE Process Automation Through iSIGHT-FD
Authors: Van der Velden Alex
Published: March 2009

iSIGHT-FD manages the computer software required to execute simulation-based design processes, including commercial CAD/CAE software, internally developed programs, and Excel spreadsheets. The software enables the rapid integration of these programs and automates their execution to accelerate the evaluation of many more design alternatives. It provides design exploration and optimization technology to help the user find better designs than those that can be found manually. Inside of this framework, a set of interoperable CAD and CAE components is used to define how changes in the geometry affect the product performance. In the past year Engineous worked with several of its partners to create a seamless and automated process. We will illustrate how to setup and drive geometric changes in CAD models using the translation technologies component in iSIGHT-FD. The user can set loads & boundary conditions on the part/assembly that move with the geometric modifications. The changed geometry with loads & boundary conditions can be automatically meshed and analyzed with FEM solvers and pre/postprocessors. The user is allowed to store and view parametric and non-parametric results for every run. These 3D CAE & CAD results can then be easily embedded into Microsoft office.
Effects of Compressor Tip Injection on Aircraft Engine Performance and Stability
Authors: Horn Wolfgang , Schmidt Klaus-Ju¨rgen , Staudacher Stephan
Published: March 2009

This analytical study discusses the system aspects of active stability enhancement using mass flow injection in front of the rotor blade tip of a high pressure compressor. Tip injection is modeled as a recirculating bleed in a performance simulation of a commercial turbofan engine. A map correction procedure accounts for the changes in compressor characteristics caused by injection. The correction factors are derived from stage stacking calculations which include a simple correlation for stability enhancement. The operational characteristic of the actively controlled engine is simulated in steady and transient states. The basic steady-state effect consists of a local change in mass flow and a local increase in gas temperature. This alters the component matching in the engine. The mechanism can be described by the compressor-to-turbine flow ratio and the injection temperature ratio. Both effects reduce the cycle efficiency resulting in increased turbine temperature and fuel consumption at constant thrust. The negative performance impact becomes negligible if compressor recirculation is only employed at transient part power and if valves remain closed at steady-state operation. Detailed calculations show that engine handling requirements and temperature limits will still be met. Tip injection increases the high pressure compressor stability margin substantially during critical maneuvers. The proposed concept in combination with an adequate control logic offers promising benefits at transient operation, leading to an improvement potential for overall engine performance.
Aero-Thermal Optimisation of a Spiral Primary Surface Recuperator: Modelling and Testing
Authors: Antoine Hubert , Prieels Luc
Published: March 2009

Recently, interest in spiral heat exchangers has grown for high temperature, high cycling applications, especially in the gas turbine industry. Air and gas flow distribution in heat exchangers is known to play a major role in their pressure drop performance and effectiveness. Modelling this distribution is needed to optimise the primary surface geometry. This optimisation has been applied to the ACTE spiral recuperator and resulted in smaller and lighter recuperators thanks to a better use of the metal. A specific CFD code was developed and used to investigate different ‘state of the art’ flow configurations and hydraulic diameters. The best of these was then adapted to ACTE’s manufacturing technology. The model has been validated by pressure drop, velocity profile and effectiveness measurements. The improved geometry consists of a primary surface cross-corrugated pattern for both air and gas flows (see fig. 4 and 5). The pattern includes a central zone with a half angle of 30° for counterflow and two lateral zones with a half angle of 45° for fluid distribution and collection. The corrugations are not strictly sinusoidal but include a flat area that allows welding the two sheets together. The sheet pair (or “doublet”) is thus made resistant to ballooning. It is also used to hoop the annular heat exchanger.
Application of a Reduced Order Modeling Technique for Mistuned Bladed Disk-Shaft Assemblies
Authors: Segui´ Bartolome´ , Casanova Euro
Published: March 2009

This paper presents a reduced-order modeling technique, based on a component mode synthesis method specifically tailored for bladed disks, that allows the resulting low-order model to be attached to a shaft. Mistuning is included in the bladed disk model and the shaft is modeled using uniaxial finite elements according to the rotordynamic approach. The proposed formulation is applied to an example finite element model of a bladed disk, for both tuned and mistuned blades. Comparisons are made between the reduced model and the full finite element solution for free and forced responses in order to assess the methodology. The forced response amplitudes of the blades are found to vary significantly with the inclusion of a flexible shaft. This work suggest that stage independent analyses might not be adequate for predicting the global dynamic response of rotating assemblies of turbomachines.
CFD (Realizable K-ε) and Cold-Flow Testing for the Design of Air-Air Ejectors With Triangular Tabbed Driving Nozzles
Authors: McBean S. F. , Birk A. M.
Published: March 2009

This paper describes an investigation in which a commercial CFD software package has been used to evaluate the performance of air-air ejectors with triangular tabbed driving nozzles. The Realizable k-ε turbulence model was employed and CFD predictions were evaluated against experimental results. Ejector performance was measured on the basis of pumping, mixing, and back-pressure. It was discovered that CFD models were generally capable of predicting trends in pumping and mixing, but were unable to account for appropriate magnitude. In addition, CFD did not accurately represent the strength of the streamwise vortices generated by the tabs. At increased tab angles, CFD predicted values of back-pressure very well. However, under the 90° tab configuration, back-pressure was severely under-predicted.