bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering and Generation of Acoustic Energy by a Premix Swirl Burner
Authors: Gentemann Alexander , Polifke Wolfgang
Published: March 2009

The scattering and generation of acoustic energy by a premix swirl burner is scrutinized. The analysis is formulated in terms of the scattering matrix of the burner, determined by a combination of computational fluid dynamics and system identification as well as experiment supplemented with simple analytical models for flame frequency response and burner transfer matrix. Remarkably, it is found that in a narrow range of frequencies, incoming acoustic waves are amplified strongly by the unsteady heat release, i.e. acoustic energy is generated. Although the computational and experimental data were obtained for one specific swirl burner design, further analysis suggests that such behavior should be common for many burner designs. Consequences for thermo-acoustic stability as well as burner and combustor design strategies are discussed.
Reduced-Order Model of a Bladed Rotor With Geometric Mistuning
Authors: Sinha Alok
Published: March 2009

This paper deals with the development of an accurate reduced-order model of a bladed disk with geometric mistuning. The method is based on vibratory modes of various tuned systems and proper orthogonal decomposition of coordinate measurement machine (CMM) data on blade geometries. Results for an academic rotor are presented to establish the validity of the technique.
Assessment of Surface Treatment Effectiveness and Degradation by Direct Field Measurement
Authors: Rideout Curtis A. , Ritchie Scott J.
Published: March 2009

The ability to detect and quantify beneficial surface and subsurface residual stresses, and operational damage in aerospace materials/structures in a reliable and efficient manner presents significant challenges to existing nondestructive inspection technologies. Induced Positron Analysis (IPA) has demonstrated the ability to nondestructively quantify shot peening/surface treatments and relaxation effects in single crystal superalloys, steels, titanium and aluminum with a single measurement as part of a National Science Foundation SBIR program and in projects with commercial companies. IPA measurement of surface treatment effects provides a demonstrated ability to quantitatively measure initial treatment effectiveness along with the effect of operationally induced changes over the life of the treated component. Use of IPA to nondestructively quantify surface and subsurface residual stresses in turbine engine materials and components has the potential to significantly improve the understanding at the microscale level the effects of surface coatings and treatments on the durability and fatigue life of critical components.
The Influence of Real Gas Properties on Predictions of Static and Rotordynamic Properties of Annular Seals for Injection Compressors
Authors: Shin Yoon-Shik , Childs Dara W.
Published: March 2009

Predictions are presented for an annular gas seal that is representative of the division-wall seal of a back-to-back compressor or the balance-piston seal of an in-line compressor. A 2-control-volume bulk-flow model is used including the axial and circumferential momentum equations and the continuity equations. The basic model uses a constant temperature prediction (ISOT) and an ideal gas law as an equation of state. Two variations are used: adding the energy equation with an ideal gas law (IDEAL), and adding the energy equation with real gas properties (REAL). The energy equations assume adiabatic flow. The ISOT model has been used for prior calculations. Concerning predictions of static characteristics, the calculated mass leakage rate was, respectively, 9.46, 9.55 and 7.87 kg/s for ISOT, IDEAL, and REAL. For rotordynamic coefficients, predicted effective stiffness coefficients are comparable for the models at low excitation frequencies. At running speed, REAL predictions are roughly 40% lower than ISOT, which could results in lower predicted critical speeds. Predicted effective damping coefficients are also generally comparable. REAL and IDEAL predictions for the cross-over frequency is approximately 20% lower than ISOT. REAL predictions for effective damping are modestly lower in the frequency range of 40 to 50% of running speed where higher damping values are desired.
Reduction of Tip Clearance Losses in an Axial Turbine by Shaped Design of the Blade Tip Region
Authors: Kusterer K. , Moritz N. , Bohn D. , Sugimoto T. , Tanaka R.
Published: March 2009

Secondary flows and leakage flows lead to complex vortex structures in the flow field inside the passages of the vanes and blades in turbo machines. These result in aerodynamic losses and, thus, reduced efficiency. One of the major vortex structures is the tip clearance vortex, which is generated on the airfoil’s suction side due to the leakage flow through the tip clearance, e.g. between rotating blades and casing. This leakage flow is induced by the pressure difference between pressure and suction side. The tip clearance vortex intensity strongly depends on the amount of tip clearance leakage. Thus, the reduction of this leakage mass flow increases the aerodynamic efficiency of a turbo-machine. In gas turbines, two ways are commonly used to influence the tip leakage flow: contouring of the radial gap either at blade tip or endwall, or changing the blade tip geometry by application of squealers or winglets on the blade tip. In this paper, a numerical investigation on the principle physics of a specific blade tip design is presented. On the pressure side the blades are extended in the tip region comparable to winglets (“hook-shaped”). With this change, the structures of the flow entering the gap between blade tip and casing are influenced to achieve a reduction of the mass flow in the radial gap. In this approach, the contour of the blade on the pressure side surface is shaped smoothly so that only a low increase of the local stresses should be expected and the blade is manufactured in one part. Furthermore, the height of the tip clearance is not affected. The new blade tip design is applied to 2nd and 3rd blade of the axial turbine in a test configuration of a KHI industrial gas turbine. Thus, a multi-stage numerical approach has been selected for the numerical investigation. The numerical model includes the flow path, vanes and blades of the 2nd and 3rd stage. The mixing plane technique is used to couple the blocks computed in stationary system of reference and rotating system of reference. The aerodynamic efficiency of the new designed blade tip in the two-stage arrangement is compared to the original design. It shows that a slight increase can be achieved in the static polytropic efficiency of the turbine configuration. The influence of the new design on the flow structures in the tip clearance region of the blades is analysed in detail to explain the mechanisms that cause the efficiency increase.
CFD Based Development of a Fuel-Air Premixer for a Retrofittable Catalytic Combustion System
Authors: Schmitz I. , Scherer V. , Wirtz S. , Carroni R.
Published: March 2009

The development of a novel, hybrid catalytic combustor compatible with current and future gas turbine requirements is the goal of the EU project CATHLEAN. One main prerequisite for the operability of this catalytic combustor is the provision of a homogenous mixture of fuel and air at the entrance of the catalyst. A novel mixer unit consisting of a fuel injection, a large scale turbulence generator and a fine scale mixer should fulfil this requirement. Furthermore, a specific flow-correcting geometry promotes a near-uniform velocity distribution at the catalyst inlet. The present paper describes the computational development process of the fuel injection and the large scale turbulence generator. Detailed 3-D CFD studies using RANS models were carried out. The following optimisation steps have been performed: • fuel injection optimisation; • basic large scale turbulence generator development and optimisation; • detailed analysis of the final mixing section design (combination of fuel injection and large scale turbulence generator in a common mixing section). The results will be presented in light of the main design parameters: optimum mixing quality, minimized pressure loss and avoiding ignition of the fuel within the mixing device.
Verification of Low-Flow Conditions in a Multistage Turbine
Authors: Herzog N. , Binner M. , Seume J. R. , Rothe K.
Published: March 2009

Modern power plants face increasing problems with windage effects in high pressure steam turbines, due to the bigger size of the rotor blades and a more flexible demand of the electricity market, which may lead to more frequent operation at low-flow conditions. So far, no theoretical model exists to fully describe these flow phenomena which would help to prevent an overheating of the turbine blades and minimize the risk of damage. The main goal of this research project therefore is to predict the part-load behavior. Measurements of the flow field of a four-stage research air turbine were carried out at low Mach numbers to better understand the aerodynamic characteristics and the flow mechanisms at part-load. The experimental data such as temperature, pressure, velocity, and flow angles, measured in 6 different planes along the turbine annulus for different rotational speeds and different relative mass flows, have been compared with the numerical results of the CFDsolver TRACE. To obtain more realistic results than in computations published earlier, a newly generated finer grid and an extension of the computational domain at the outlet were used. It is shown that with the right initialization, the CFD-Solver is capable of providing converged calculation results even for low mass flows and high rotational speeds. The results are verified with experimental data e.g. by the temperature distribution within the four-stage turbine and the pressure and temperature profiles in the measurement planes. As a general result, the highest temperatures in the turbine do not occur behind the last stage, but in the downstream third of the machine, which agrees with experiences of damage observed in real turbines.
Three-Dimensional Calculations of Evaporative Flow in Compressor Blade Rows
Authors: Payne R. C. , White A. J.
Published: March 2009

The present paper describes a three-dimensional computational method developed to solve the flow of a two-phase airwater mixture, including the effects of evaporation for a monodispersion of liquid droplets. The calculations employ a fully Eulerian method for the conservation of droplet number and liquid mass and are applicable to multiple blade rows, both stationary and rotating. The method is first tested to ensure that it computes the correct droplet evaporation rate and the correct physical behaviour for evaporation within a 1-D duct. Results are then presented for flow within a single compressor stage — i.e., a rotor-stator combination.
Active Control of Combustion Instability Using Symmetric and Asymmetric Premix Fuel Modulation
Authors: Guyot Daniel , Paschereit Christian Oliver
Published: March 2009

Active instability control was applied to an atmospheric swirl-stabilized premixed combustor using open loop and closed loop control schemes. Actuation was realised by two on-off valves allowing for symmetric and asymmetric modulation of the premix fuel flow while maintaining constant time averaged overall fuel mass flow. Pressure and heat release fluctuations in the combustor as well as NOx, CO and CO2 emissions in the exhaust were recorded. In the open loop circuit the heat release response of the flame was first investigated during stable combustion. For symmetric fuel modulation the dominant frequency in the heat release response was the modulation frequency, while for asymmetric modulation it was its first harmonic. In stable open loop control a reduction of NOx emissions due to fuel modulation of up to 19% was recorded. In the closed loop mode phase-shift control was applied while triggering the valves at the dominant oscillation frequency as well as at its second subharmonic. Both, open and closed loop control schemes were able to successfully control a low-frequency combustion instability, while showing only a small increase in NOx emissions compared to, for example, secondary fuel modulation. Using premixed open loop fuel modulation, attenuation was best when modulating the fuel at frequencies different from the dominant instability frequency and its subharmonic. The performance of asymmetric fuel modulation was generally slightly better than for symmetric modulation in terms of suppression levels as well as emissions. Suppression of the instability’s pressure rms level of up to 15.7 dB was recorded.
Aerodynamics of a Low-Pressure Turbine Airfoil at Low-Reynolds Numbers: Part 2 — Blade-Wake Interaction
Authors: Mahallati Ali , Sjolander Steen A.
Published: March 2009

The relative motion of rotor and stator blade rows causes periodically unsteady flows that influence the performance of airfoils through their effects on the boundary layer development. Part 1 of this two-part paper described the influence of Reynolds number, freestream turbulence intensity and turbulence length scales on a low-pressure (LP) high-lift turbine airfoil, PakB, under steady inlet flow conditions. The aerodynamic behaviour of the same airfoil under the influence of incoming wakes is presented in Part 2. The unsteady effects of wakes from a single upstream blade-row were measured in a low-speed linear cascade facility at Reynolds numbers of 25000, 50000 and 100000 and at two freestream turbulence intensity levels of 0.4% and 4%. In addition, eight reduced frequencies between 0.53 and 3.2, at three flow coefficients of 0.5, 0.7 and 1.0 were examined. The complex wake-induced transition, flow separation and reattachment on the suction surface boundary layer was determined from an array of closely-spaced surface hot-film sensors. The wake-induced transition caused the separated boundary layer to reattach to the suction surface at all conditions examined. The time-varying profile losses were measured downstream of the trailing edge. Profile losses increase with decreasing Reynolds number and the influence of increased freestream turbulence intensity is only evident in between wake-passing events at low reduced frequencies. At higher values of reduced frequency, the losses increase slightly and for the cases examined here, losses were slightly larger at lower flow coefficients than the higher flow coefficients. An optimum wake-passing frequency was observed at which the profile losses were a minimum.
Effect of Circumferential Grooves on the Aerodynamic Performance of an Axial Single-Stage Transonic Compressor
Authors: Mu¨ller Martin W. , Schiffer Heinz-Peter , Hah Chunill
Published: March 2009

This paper reports on experimental and numerical investigations on circumferential grooves in an axial single-stage transonic compressor. Total pressure ratio and efficiency speedlines were taken at design speed and three off-design conditions. The experiments comprise four different configurations with deep and shallow grooves and variable coverage of the projected rotor axial chord. All casing treatments proved to have a beneficial effect on stall range while maintaining high levels of efficiency, even at off-design operation. Deep grooves extending almost to the trailing edge showed the biggest potential: the mass flow at stall inception for design speed could be strongly reduced, and the operating range could be enlarged by 56.1%. When three shallow grooves were applied to the compressor, the stage efficiency at design speed was shifted to slightly higher values. A possible explanation could be a favorable change in stator aerodynamics due to the reduction of corner separation. For a closer look into the physical effects of grooves on the tip leakage flow, a rotor-only CFD analysis has been carried out using a steady state calculation. A multi-block grid with approximately 1.2 million nodes was used. The numerical simulations reveal strong effects of circumferential grooves on the rotor flow field at tip. Mach-number contours, axial velocity distributions and particle traces for the smooth casing and six deep grooves are presented at stall mass flow. Compared to the smooth wall case, the treated casing significantly reduces blockage in the tip area and weakens the roll-up of the core vortex. These mechanisms prevent an early spillage of low momentum fluid into the adjacent blade passage and delay the onset of rotating stall.
Qualitative and Quantitative Comparison of Two Promising Oxy-Fuel Power Cycles for CO2 Capture
Authors: Sanz W. , Jericha H. , Bauer B. , Go¨ttlich E.
Published: March 2009

Since the Kyoto conference there is a broad consensus that the human emission of greenhouse gases, mainly CO2, has to be reduced. In the power generation sector there are three main alternatives which are currently studied world wide. Among them oxy-fuel cycles with internal combustion with pure oxygen are a very promising technology. Within the European project ENCAP — ENhanced CO2 CAPture — the benchmarking of a number of novel power cycles with CO2 capture was carried out [1]. Within the category oxy-fuel cycles the Graz Cycle and the Semi-Closed Oxy-Fuel Combustion Combined Cycle (SCOC-CC) both achieved a net efficiency of nearly 50%. In a second step a qualitative comparison of the critical components was performed according to their technical maturity. In contrast to the Graz Cycle the study authors claimed that no major technical barriers would exist for the SCOC-CC. In this work the ENCAP study is repeated for the SCOC-CC and for a modified Graz Cycle variant as presented at the ASME IGTI conference 2006 [2]. Both oxy-fuel cycles are thermodynamically investigated based on common assumptions agreed with industry in previous work. The calculations showed that the high-temperature turbine of the SCOC-CC plant needs a much higher cooling flow supply due to the less favorable properties of the working fluid. A layout of the main components of both cycles is further presented which shows that both cycles rely on the new designs of the high-temperature turbine and the compressors. The SCOC-CC compressor needs more stages due to a lower rotational speed but has a more favorable operating temperature. In general, all turbomachines of both cycles show similar technical challenges and are regarded as feasible.
Analysis of Low-Pressure Turbine Flutter for Different Shroud Interfaces
Authors: Wu X. , Vahdati M. , Schipani C. , Imregun M.
Published: March 2009

This paper reports the findings of a flutter investigation on a low-pressure turbine rotor having an integrally machined tip shroud with different type of constraints. Two types of tip shroud constraints, namely fully constrained and tangentially free, were used, representing two extreme conditions: (a) a typical integrated shroud design with a tight interlocking and no wear on contact surface; and (b) an extremely smooth contact surface design or the most severe wear of a fully constrained interface, or changes in the manufacturing process that result in almost no friction across the shroud surface. The tangentially free constraint is unusual in that it seeks to explore how sensitively the contact constraint could cause blades to response. The mode shapes and corresponding frequency characteristic are presented for both shroud constraints using a standard finite element analysis. The flutter analysis was firstly undertaken by considering all vibration modes of interest in a single calculation using a whole-annulus model of the rotor. It was found that the removal of the tip constraints in the tangential direction was responsible for introducing the unstable first flap family under condition of zero mechanical damping. Of considerable interest was the fact that instability in the first flap mode occurred in forward-travelling nodal diameter modes, which is considered as somewhat different from classical low-pressure turbine flutter where instability exists in backward-travelling nodal diameter modes. The flutter mechanism was verified by undertaking a detailed investigation on the forward-travelling nodal diameter modes of the first flap family using a single-passage analysis. It was concluded that tip shroud constraints are highly sensitive for turbine blade interlock designs and unusual response could be excited under extremely severe wear condition.
Infrared Radiation From Turbojet Exhaust Plume
Authors: Levy Y. , Lev M. , Ovcharenko V.
Published: March 2009

In recent years, there was an increasing interest in aircraft IR signature as an effective passive means of detecting and locking on to an aircraft. There are two main sources of the aircraft IR emission: engine-fuselage layout and gaseous exhaust plume. The size of aircraft plume is several times more than the size of aircraft. The present work focuses on the exhaust plume. The relatively high temperature plume ejected from the nozzle is a mixture of several species that are products of hydrocarbon fuel combustion under excess air condition: CO2, H2O, CO, O2, and N2. Experimental investigation of IR radiation from exhaust gases of a small turbojet engine was conducted in a micro jet engine SR-30 by Turbine Technologies, Ltd. The compact engine features a centrifugal flow compressor, reverse flow annular combustor and an axial flow turbine stage. The SR-30 follows the fundamental Brayton gas turbine cycle. The engine is operated at different regimes with various flow rates of air and kerosene. Measurements were obtained with engine operating at global equivalence ratio of about 0.23. The IR radiation images of the exhaust flow were obtained by a thermocamera equipped with a narrow bandpass filter that falls on the CO2 fundamental band emission. Temperature profiles were measured by a thermocouple in the exhaust flow. An in-house computer program was developed to calculate the IR emission from optically thick gas object and it takes into account the self-absorption of the IR radiation along a line-of-sight. An essential feature of the calculation is the fact that the optical path is non-isothermal. The typical IR spectrum of a turbo-jet engine exhaust flow was simulated using the developed computer program. The calculations allow prediction of “apparent” plume temperatures measured by the IR camera. The calculated results were compared with the experimental measurements and a good agreement was found.
Investigations on Dynamic Behaviour of Heat Recovery Steam Generators Carried Out With a Commercial Software Program
Authors: Brandstetter Gottfried , Daublebsky Christian
Published: March 2009

Heat recovery steam generators (HRSGs) downstream of gas turbines are often used in combination with process steam applications. A HRSG trip is more severe in applications with highly important process steam than in applications producing only electricity. HRSGs in important process steam applications can be equipped with a supplementary and fresh air firing system having the capacity of replacing at least the total waste heat coming from the gas turbine. A fresh air firing system provides the capability of keeping the HRSG in operation without the gas turbine running. If the HRSG is required to stay in operation even after a gas turbine trip, a change over from waste heat firing to fresh air firing has to follow immediately. The gas turbine speed rundown after a trip occurs very rapidly, so the change over procedure has to be carried out within a few seconds to avoid a HRSG shut down. Enormous gradients of heat input and steam mass flow extracted from the HRSG occur in such cases. This will cause the HRSG parameters to deviate considerably from the steady state, thus conventional HRSG calculations cannot be used in such cases. The thermal inertia of the HRSG needs to be considered, which requires the use of special software programs. A commercial boiler software program with a dynamic calculation module for unsteady calculations was utilized and a comparison with data gathered from the operation of the HRSG was performed. The boiler performance parameters during change over procedures were investigated in detail using extensive measurements at an Austrian steel mill (VOESTALPINE). The parameters of this investigation were compared with calculation results gained from a commercial software program for validation purposes. This comparison will enable predictions to be made for future projects with sufficient accuracy, which will allow the risk to be reduced when offering guarantees in this regard.
Fast Simulation of Dynamic Behaviour of Heavy Duty Gas Turbines for Quality Improvement and Reduced Design Cycle Time
Authors: Clark Alastair S. , Jurjevic Zdenko
Published: March 2009

ALSTOM has made big improvements in simulating the dynamic behaviour of the GT (rotor, bearings and structural parts), in terms of displacements and forces by developing a 2 stage approach comprising a simplified physical model and detailed calculations using finite elements condensed into a matrix super element (substructuring). The models from each have been validated against frequency measurements. The simplified approach provides a fast overview in terms of sensitivity analysis of basic physical influences. It accurately reflects the generic dynamic behaviour of both rotor and structure. Reducing the FE-calculation time by a factor of 10 has enabled the influence of small or large modifications to individual part designs on the dynamic behaviour of the GT to be understood to the highest level of detailed design features. Calculated frequency results from modal and forced response calculations are compared to measurements within a 2% margin. In particular the focus is on the improvements in the quality of the finite element modelling with more detailed features and more accurate identification of eigenfrequencies and coupled modes. Validation work comprises the modal analysis of single parts and subassemblies as well as matching mode shapes and frequencies of complete gas turbine. Models are used to evaluate design improvements prior to engine testing or implementation in field engines in order to comply with prescribed exclusion zones, to be introduced as early as the concept stage as well as providing project teams with overviews for planning and decision making. Future developments to include Modal Assurance Criteria and rapid post-processing will further reduce design cycle time and improve quality in terms of the consistency and repeatability with regard to mode shape recognition.
Effect of Trench Width and Depth on Film Cooling From Cylindrical Holes Embedded in Trenches
Authors: Lu Yiping , Dhungel Alok , Ekkad Srinath V. , Bunker Ronald S.
Published: March 2009

The present study is an experimental investigation of film cooling from cylindrical holes embedded in transverse trenches. Different trench depths are considered with two trench widths. Trench holes can occur when blades are coated with thermal barrier coating (TBC) layers. The film hole performance and behavior will be different for the trench holes compared to standard cylindrical holes that are flush with the surface. The trench width and depth depends on the mask region and the thickness of the TBC layer. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5 and 2.0. The results show that film effectiveness is greatly enhanced by the trenching due to improved two dimensional nature of the film and lateral spreading. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet-mainstream interactions for different hole orientations. CFD simulation using Fluent was also performed to determine the jet mainstream interactions to better understand the surface heat transfer coefficient and film effectiveness distributions.
Turbine Blade Tip Clearance Measurement Instrumentation
Authors: Holmquist Eric B. , Jalbert Peter L.
Published: March 2009

New and future gas turbine engines are being required to provide greater thrust with improved efficiency, while simultaneously reducing life cycle operating costs. Improved component capabilities enable active control methods to provide better control of engine operation with reduced margin. One area of interest is a means to assess the relative position of rotating machinery in real-time, in particular hot section turbo machinery. To this end, Hamilton Sundstrand is working to develop a real-time means to monitor blade position relative to the engine static structure. This approach may yield other engine operating characteristics useful in assessing component health, specifically measuring blade tip clearance, time-of-arrival, and other parameters. UTC is leveraging its many years of experience with engine control systems to develop a microwave-based sensing device, applicable to both military and commercial engines. The presentation will discuss a hot section engine demonstration of a blade position monitoring system and the control system implications posed by a microwave-based solution. Considerations necessary to implement such a system and the challenges associated with integrating a microwave-based sensor system into an engine control system are discussed.
Gill Slot Trailing Edge Heat Transfer: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness
Authors: Ames F. E. , Fiala N. J. , Johnson J. D.
Published: March 2009

Heat transfer and film cooling distributions have been acquired downstream from the exit of a nozzle guide vane gill slot (or cutback). Additionally, heat transfer and pressure drop data have been experimentally determined for a pin fin array within the gill slot geometry. Generally, average row pin fin heat transfer levels for the converging channel correlate quite well with archival literature. However, no generalized flow friction factor correlation was found to predict the pressure drop within the array. Experimental data for the region downstream from the gill slot have been acquired over a four to one range in vane exit condition Reynolds number, with low, grid, and aero-combustor turbulence conditions. At these conditions, both heat transfer and adiabatic film cooling distributions have been documented over a range of blowing ratios. Heat transfer distributions downstream from the gill slot ejection were found to be dependent on both ejection flow rate and external conditions. Generally, adiabatic film cooling levels are high but dissipate toward the trailing edge and provide some protection on the trailing edge. Heat transfer levels on the trailing edge are affected largely by the chord exit Reynolds number and the suction surface boundary layer condition. The present paper, together with a companion paper which documents gill slot aerodynamics, is intended to provide designers with the heat transfer and aerodynamic loss information needed to compare competing trailing edge designs.
Parametric Study of Tip Injection in an Axial Flow Compressor Stage
Authors: Cassina Gabriele , Beheshti Behnam H. , Kammerer Albert , Abhari Reza S.
Published: March 2009

Tip injection upstream of the rotor blade is a well-known technique for suppressing instabilities in axial compressors and recovering from a fully developed stall. In tip critical rotors, tip injection can effectively increase the blade loading and the stable operating margin of compressors by unloading the rotor tip. Compared to fully annular injection, discrete tip injection is better able to increase the compressor stability. This paper presents a numerical study of the effects of discrete upstream air injection on the stability of an axial flow compressor. Reynolds-averaged Navier-Stokes equations have been solved using ANSYS CFX with a k-epsilon turbulence model for three compressor blade passages. To validate the simulations, mass flow rate, pressure ratio, and efficiency at the compressor design point have been computed and compared to experimental data and results are in good agreement. For simulation of tip injection, 10 axisymmetric, but circumferentially discrete injectors, positioned at 50% of the blade axial chord upstream of the rotor blade leading edge, have been modelled. The ports are mounted on the casing and provide high-pressure jet of air at a 15° angle in the radial direction. To study the effects of injection, the compressor map at design speed has been compared for the models with and without injection. Results indicate that tip injection improves the compressor stability by unloading the rotor tip. Simulations show that by increasing the injection mass flow, the compressor stable operating margin can be improved. Simulations also predict optimum values for the injection port width-to-length ratio and the injection angle when the injection mass flow rate and area are kept constant. Further studies have been done to investigate the effect of the axial position of the injector.
Comparison of Large Eddy Simulation Methods for Flows Over Gas Turbine Blades
Authors: Karimi M. , Paraschivoiu M.
Published: March 2009

In recent years there has been a considerable effort toward applying large eddy simulation methods (LES) to real industrial problems. However, there are still several challenges to be addressed to achieve a reliable LES solution, especially in the context of compressible flows. Furthermore, complex geometries require the unstructured meshes which then interdict the use of very high order schemes. Therefore, LES models are mainly derived and tested on classical problem of simple geometry for incompressible flow and based on higher order schemes. Here, the flow over a gas turbine blade at high Reynolds and Mach numbers is investigated using a mixed finite-volume-finite-element method. Implicit LES method (ILES) as well as Smagorinsky and its dynamic version have been studied. Different variations of the Smagorinsky method have been examined too. The interaction of the numerical dissipation of the scheme with LES models has been explored. The results show the capability of the ILES to take into account the effective viscosity of the flow and the negligible difference of the different LES models in this flow condition. Fairly good agreement with experimental data is found which is superior to RANS results. It is found that there are still some challenges in industrial LES applications which have to be addressed to lead to a better agreement with experimental data.
Large Eddy Simulations of Fully Developed Flow Through a Spanwise Rotating Infinite Serpentine Passage
Authors: Felten Fre´de´ric N. , Laskowski Gregory M.
Published: March 2009

The ability to predict turbine blade heat transfer is an important problem and is strongly dependant on the ability to predict the turbulent flow-field. Turbine blade internal coolant flow is often subjected to strong curvature and possibly rotational effects, two flow characteristics that make RANS modeling efforts difficult. An assessment of Large Eddy Simulation (LES) has been conducted for a flow with strong streamline curvature and rotational effects. Simulations of fully developed turbulent flow in an isothermal, smooth-wall, serpentine passage have been performed and compared to the Direct Numerical Simulation (DNS) data of Laskowski (2004). The flow is periodic in the stream-wise and span-wise directions and simulations were conducted for span-wise rotation numbers Rob = 0.0 and Rob = 0.32. The geometry has dimensions 12πδ × 2δ × 3πδ, in the stream-wise, wall-normal and span-wise directions, respectively, where δ is half the passage height. The inner radius of the bends is δ. The Reynolds number based on the bulk velocity and H = 2δ is Reb = 5600. A kinetic-energy conserving, finite-volume, collocated-mesh scheme (Felten and Lund, 2006) is applied to treat the streamwise and wall-normal directions, while Fourier collocation is used in the spanwise direction. A third-order Runge-Kutta explicit marching scheme is used to advance the solution in time and the pressure Poisson Equation is solved using a multigrid technique. The LES results are presented and close agreement with the DNS is noted for both the stationary and rotating cases.
A New Energy-Based Uniaxial Fatigue Life Prediction Method for a Gas Turbine Engine Material
Authors: Scott-Emuakpor Onome , Shen M.-H. Herman , George Tommy , Cross Charles , Calcaterra Jeffrey
Published: March 2009

A new energy-based fatigue life prediction framework for calculation of axial and bending fatigue life at various stress ratios has been developed. The purpose of the life prediction framework is to account for materials used in gas turbine engines, such as Titanium 6Al-4V, which experience an endurance stress limit as the number of cycles increase towards infinity. The work conducted to develop this energy-based framework consist of the following entities: (1) A new life prediction criterion for axial and bending fatigue at various stress ratios for Aluminum 6061-T6, (2) use of the previously developed improved uniaxial energy-based method to acquire fatigue life prior to endurance limit behavior [1], (3) and the incorporation of a statistical energy-based fatigue life calculation scheme to the uniaxial life criterion (the first entity of the framework), which is capable of constructing prediction intervals based on a specified percent confidence level. The exactitude of this work was verified by comparison between theoretical approximations and experimental results from recently acquired Al 606-T6 and Ti 6Al-4V data. The comparison shows very good agreement, thus validating the capability of the framework to produce accurate fatigue life predictions.
Redesign of a Highly Loaded Transonic Turbine Nozzle Blade Using a New Viscous Inverse Design Method
Authors: Daneshkhah Kasra , Ghaly Wahid
Published: March 2009

The redesign of VKI-LS89 turbine vane, which is typical of a highly loaded transonic turbine guide vane is presented. The redesign is accomplished using a new inverse design method where the blade walls move with a virtual velocity distribution derived from the difference between the current and the target pressure distributions on the blade surfaces. This new inverse method is fully consistent with the viscous flow assumption and is implemented into the time accurate solution of the Reynolds-Averaged Navier-Stokes (RANS) equations that are expressed in an arbitrary Lagrangian-Eulerian (ALE) form to account for mesh movement. A cell-vertex finite volume method is used to discretize the equations in space; time accurate integration is obtained using dual time stepping. An algebraic Baldwin-Lomax model is used for turbulence closure. The flow analysis formulation is first assessed against the LS89 experimental data. The inverse formulation that is implemented in the same code, is also assessed for its robustness and accuracy, by inverse designing the LS89 original geometry through running the inverse method with the original LS89 pressure distributions as target distributions but starting from an arbitrary geometry. The inverse design method is then used to redesign the LS89 using an arbitrary pressure distributions at a subsonic and a transonic outflow condition and the results are interpreted in terms of the blade overall aerodynamic performance.
Microstructures and Creep Properties of Powder Metallurgy Ti-48Al-2Cr-2Nb + W
Authors: Saari H. , Bulmer S. , Seo D. Y. , Au P.
Published: March 2009

The microstructures and creep properties at 760 °C and 276 MPa of three powder metallurgy TiAl alloys (Ti-48Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb+0.5W, and Ti-48Al-2Cr-2Nb+1W (atomic percent)) are presented. The results indicate that the addition of W to the base composition, the use of a solution heat treatment combined with controlled cooling (to generate a fully lamellar microstructure), and the use of an aging heat treatment (to generate precipitate particles at the lamellar interfaces) improve creep properties dramatically. The solution heat treated and aged Ti-48Al-2Cr-2Nb+1W alloy has a time to 0.5% strain of 8.3 hours, a time to 1% strain of 46.4 hours, and a creep life of 412 hours with a rupture ductility of 16.9%.
Multi-Objective Optimisation of the Humid Air Turbine
Authors: Kavanagh Ronan M. , Parks Geoffrey T. , Obana Mitsuru
Published: March 2009

Optimisation of the Humid Air Turbine (HAT) power cycle has proven an interesting challenge in multi-variate and multi-objective optimisation. A multi-objective Tabu Search optimisation algorithm, developed in the Cambridge Engineering Design Centre, has been applied to this humid power cycle. A tradeoff surface is generated to investigate the impact of nine primary system control variables on the performance (efficiency, specific work and cost of electricity) of the system. This optimisation tool was chosen for its proven robustness and flexibility in handling highly constrained, multi-variate problems. The algorithm generates a Pareto-set of optimal candidate designs, allowing the designer to analyse the trade-off between performance measures such as efficiency and cost when selecting the ultimate system operating point. The study is primarily a global optimisation, with attention being paid to the primary system control variables: pressure ratio, turbine inlet temperature, IP/HP pressure split, water flowrate distribution and heat exchanger effectiveness.
Advanced Performance Modelling of a Single and Double Pressure Once Through Steam Generator
Authors: Mucino Marco , Ojile Joel , Li Y. G. , Newby Mike
Published: March 2009

The Once Through Steam Generator (OSTG) is a heat recovery system mainly used in heat and power applications that offers an alternative to the common water-tube drum Heat Recovery Steam Generator (HRSG). The main difference relies on the fact that the OTSG has no drum. The modelling of the OTSG as part of any thermal plant used for power generation or to supply industrial process heat is of great importance. The accurate performance simulation of any power plant can provide extra information to the operations team that otherwise would involve labour intensive, long field experiments or data collection programmes. A novel, realistic performance simulation model for a single and double pressure Once Through Steam Generator is presented. The generality of the model allows the user to define any physical design of an existing or theoretical OTSG and operating requirements. The model is capable of simulating fouling effects on the overall OTSG performance. The model was tested using field data provided by Manx Electricity Authority. The results obtained show the success of the approach and the potential of such a tool in any cycle performance evaluation.
Damping Performance of Axial Turbine Stages With Loosely Assembled Friction Bolts: The Non-Linear Dynamic Assessment — Part II
Authors: Szwedowicz J. , Secall-Wimmel Th. , Du¨nck-Kerst P.
Published: March 2009

An entire family of twisted and tapered low pressure steam turbine SK-blades with pinned radial root and loosely assembled conical bolts is designed by scaling of the aerodynamic and mechanical properties of the smallest airfoil. For SK-blades operating with variable speed, the friction bolts, mounted in the upper airfoil part, provide either damping or coupling capabilities for the blades with respect to resonance conditions. The damping and coupling performance have been proved experimentally in the test rig of the real turbine. The measurements of the smallest SK-disc assembly under different operating conditions have allowed understanding the dynamic and damping behaviour of the bolts that are either friction dampers or coupling devices for the vibrating blades depending on the excitation level. In this paper, non-linear dynamic analyses of the smallest and large SK-turbine stage are performed and compared with the experimental data. The modal blade dynamics is defined by 30 complex FE mode shapes of the freestanding blades coupled by the disc whereby the bolt’s motion is described by 6 rigid body modes. The sticking contact condition between the blades and bolts is represented by the normal and tangential contact stiffness. These values are firstly estimated analytically with the Hertz’s formulas for the FE reaction forces and contact areas. More realistic contact stiffness values are obtained from the iterative process, in which the resonance frequencies are calculated with the steady-state simulations and compared to the FE nodal diameter curves for sticking contact conditions that meet the experimental frequencies very well (GT2007-27502). In non-linear simulations, in case of exceeding the sticking contact condition, the induced friction forces are linearized by the Harmonic Balance Method. In this manner, the micro-slipping and sticking contact behaviour at all contact points are calculated iteratively for the specified excitation amplitudes, friction coefficient, contact roughness and aerodamping values that are known from the experiment. The computed results of the tuned smallest SK-blades agree with the experimental resonance stresses of 12 measured blades. Differences between the computed and measured stresses are caused by mistuning, which was not quantified in the experiment. The non-linear dynamic analyses provide evidence of good damping performance for the smallest and large SK-blades with respect to wide range of excitation forces, different friction coefficients and various aerodynamic damping values. For the analyzed resonances of the 8th engine order, the scalability of damping performance is found for the SK-blades of different sizes.
Development of Probabilistic Structural Analysis Integrated With Manufacturing Processes
Authors: Pai Shantaram S. , Nagpal Vinod K.
Published: March 2009

An effort has been initiated to integrate manufacturing process simulations with probabilistic structural analyses in order to capture the important impacts of manufacturing uncertainties on component stress levels and life. Two physics-based manufacturing process models (one for powdered metal forging and the other for annular deformation resistance welding) have been linked to the NESSUS structural analysis code. This paper describes the methodology developed to perform this integration including several examples. Although this effort is still underway, particularly for full integration of a probabilistic analysis, the progress to date has been encouraging and a software interface that implements the methodology has been developed. The purpose of this paper is to report this preliminary development.
A Novel Anti-Vortex Turbine Film Cooling Hole Concept
Authors: Heidmann James D. , Ekkad Srinath
Published: March 2009

A novel turbine film cooling hole shape has been conceived and designed at NASA Glenn Research Center. This “anti-vortex” design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film cooling holes. This vorticity typically entrains hot freestream gas and is associated with jet separation from the turbine blade surface. The anti-vortex film cooling hole concept has been modeled computationally for a single row of 30 degree angled holes on a flat surface using the 3D Navier-Stokes solver Glenn-HT. A blowing ratio of 1.0 and density ratios of 1.05 and 2.0 are studied. Both film effectiveness and heat transfer coefficient values are computed and compared to standard round hole cases for the same blowing rates. A net heat flux reduction is also determined using both the film effectiveness and heat transfer coefficient values to ascertain the overall effectiveness of the concept. An improvement in film effectiveness of about 0.2 and in net heat flux reduction of about 0.2 is demonstrated for the anti-vortex concept compared to the standard round hole for both blowing ratios. Detailed flow visualization shows that as expected, the design counteracts the detrimental vorticity of the round hole flow, allowing it to remain attached to the surface.