bluuebunny/crossref_metadata_2025 huggingface dataset:
The Two-Flux Model Applied to Radiative Transfer and Forced Convection in the Laminar Boundary Layer on a Flat Plate
Authors: Malpica Freddy , Moreno Nathaly , Tremante Andrés
Published: August 2014

This study presents the analysis of the thermal boundary layer considering combined convection and radiation in an absorbing, emitting and scattering medium flowing over a flat plate. At high temperatures the presence of thermal radiation alters the temperature distribution in the boundary layer, which in turn affects the heat transfer at the wall. In many industrial applications, such as in the cooling of turbine and compressors blades, radiative heat transfer plays an important role.

The treatment of heat transfer by combined convection and radiation in the boundary layer leads to a set of partial differential and integrodifferential equations, which must be solved simultaneously. The exact solutions are seldom possible and the investigators resort to approximate methods. In the present analysis the two-flux model is used to describe the radiative heat flux in the energy equation. This model reduces the equations that govern the problem to a set of coupled partial differential equations. A finite difference scheme, called “method of columns”, is used to transform the resulting equations into an ordinary differential equation system which simplifies the solution.

Results for the temperature profile and heat fluxes showed close agreement with the thin and thick limits.

The method proposed proves to be useful to investigate the effect of the different radiation parameters on the thermal boundary layer, and also to be accurate enough for engineering applications.
Control of Separation Bubble on a Blade Leading Edge by a Stationary Bar Wake
Authors: Funazaki K. , Harada Y. , Takahashi E.
Published: August 2014

This paper describes an attempt to suppress a blade leading edge separation bubble by utilizing a stationary bar wake. This study aims at exploration of a possibility for reducing the aerodynamic loss due to blade boundary layer that is accompanied with the separation bubble. The test model used in this study consists of semi-circular leading edge and two parallel flat plates. It can be tilted against the inlet flow so as to change the characteristics of the separation bubble. Detailed flow measurements over the test model are conducted using a single hot-wire probe. Emphasis in this study is placed on the effect of bar shifting or bar clocking across the inlet flow in order to see how the bar-wake position with respect to the test model affects the separation bubble as well as aerodynamic loss generated within the boundary layer. The present study reveals a loss reduction through the separation bubble control using a properly clocked bar wake.
Prediction of a Laminar Separation Bubble Over a Controlled-Diffusion Compressor Blade
Authors: Hobson G. V. , Weber S.
Published: August 2014

The paper describes the comparison of the prediction of the flow through a cascade of controlled-diffusion compressor blades with two Navier-Stokes solvers. Both codes solved the thin-layer N-S equations, however; one code performed implicit time marching whereas the other performed explicit time marching. Flow predictions were accomplished with the implicit code using the algebraic turbulence model of Baldwin and Lomax and the one-equation model of Spalart and Allmaras, while predictions were made with the explicit code using the two-equation model by Wilcox.

Predictions were made of the detailed laser-anemometry measurements of the flow field taken previously in a low-speed cascade wind tunnel. Comparisons were also made with the experimentally measured blade surface pressures and flow visualization of the extent of the laminar leading edge separation bubble. The one-equation turbulence model was combined with an intermittency based transition-length model for comparisons with fully turbulent calculations. Both codes predicted the leading-edge separation bubble satisfactorily when using higher order turbulence models.
Spinning Reserve Influence in a Power Generating System Integrated by Hydro Storage Plants
Authors: Bianchi M. , Gadda E. , Peretto A.
Published: August 2014

During the weekday night hours, to satisfy the lowest load demand by a power generation system, the thermoelectric unit load following strategy may be managed with the hydro storage operation.

In this paper, a methodology, for the evaluation of fuel energy consumption of fossil fuel power generation system, with or without the hydro storage application, is presented, taking into account, particularly the spinning reserve presence.

It is shown that, when pumped storage power stations are considered, for the two homogeneous sets of fossil fuel power units (conventional and advanced) analyzed, an important role is played by the spinning reserve. Moreover, a considerable saving in daily fuel consumption is achievable in the case of advanced power units. It was also found that an increase in the thermoelectric load factor may reduce the hydro storage operation saving on the kWh variable cost.
Evaluation of Operational Performance of a Gas Turbine Cogeneration Plant With Intake Air Cooled by Ice Storage
Authors: Yokoyama Ryohei , Ito Koichi
Published: August 2014

A disadvantage of a gas turbine cogeneration plant is a decrease in maximum power output during the period with high ambient air temperature. One of the ways to avoid this disadvantage is to cool intake air by ice storage and augment maximum power output. An advantage of this system is to utilize a discounted rate for energy charge of electricity consumed to drive electric compression refrigerators for ice storage during the nighttime. The objective of this paper is to investigate the effect of intake air cooling by ice storage on the operational performance of a gas turbine cogeneration plant for district heat and power supply. An optimal operational planning model based on the mixed-integer linear programming is used to assess the effect rationally and efficiently. In a numerical study, the operational performances of gas turbine cogeneration plants with and without intake air cooled by ice storage are compared with each other, and the effect of intake air cooling on the operational strategy and cost is clarified.
Inlet Fogging of Gas Turbine Engines: Part B — Practical Considerations, Control, and O&M Aspects
Authors: Meher-Homji Cyrus B. , Mee Thomas R.
Published: August 2014

The severe dependence of gas turbine output on ambient temperature has created the need for inlet cooling technologies. This paper focuses on the practical aspects of direct evaporative cooling by fogging of the inlet air to a gas turbine compressor. This paper covers several of the practical considerations relating to the location of nozzles, water quality and operations and maintenance issues that relate to implementation of such systems. A design and implementation checklist is provided to assist users in ensuring a reliable installation.
Numerical and Experimental Study on the Suppression for the Infrared Signatures of a Marine Gas Turbine Exhaust System
Authors: Zhou Shaorong , Du Zhaohui , Chen Hanping , Zhong Fangyuan
Published: August 2014

The flow and thermal fields within the cooling air injection device which is widely used to suppress the infrared (IR) signatures of a marine gas turbine exhaust system were studied numerically and experimentally. A turbulence near-wall model based on the wall function method was adopted. The discretization equations were derived for the control volumes when conjugate heat transfer exists at their interfaces, with the radiation heat flux at the interfaces appearing as an additional source term. The solution method of entrained velocities at the entrance of secondary flow was introduced. The distributions of temperature and static pressure on the diffuser surface, and the temperature of gas at the outlet of the exhaust duct were simulated numerically. The numerical calculated results agreed well with corresponding scale model experimental data. Lastly, the measured IR radiation distributions by scale model experiments at different view angles and various engine power settings, with and without IR signature suppression (IRSS) devices were presented.
U.S. Navy Shipboard Fleet Evaluation of the Redundant Independent Mechanical Start System and Full Authority Digital Control
Authors: Hoffman Matthew G. , Kozuhowski Helen J. , Overton Leonard L.
Published: August 2014

U.S. Navy and Rolls -Royce Allison have conducted a fleet evaluation of the Redundant Independent Mechanical Start System (RIMSS) and Full Authority Digital Control (FADC) installed aboard USS Porter (DDG 78), No. 2 Ship Service Gas Turbine Generator (SSGTG). The fleet evaluation has resulted in design, production and operational improvements, which would not have been quickly realized under normal implementation programs. A critical objective of the fleet evaluation demonstrated the system configuration and operational compatibility with existing shipboard environments over the course of a one-year period. This process evaluated the usability of the RIMSS and FADC interface by ships force and the performance of functions related to operation and troubleshooting. It also provided feedback from Navy users for improvements. This paper describes RIMSS and FADC fleet evaluation elements and the benefits derived from performing a fleet evaluation. Fleet evaluation findings aboard USS Porter have resulted in system improvements that were achieved prior to production. Cost savings to the U.S. Navy and the original equipment manufacturer will be realized through out the life cycle of the ships.
Improved Processing Route for Aluminization of Gas Turbine Components
Authors: Kircher Thomas A. , Solovei David , Steck Joseph H. , Shankar Srinivasan (Shanks)
Published: August 2014

Pack aluminizing and vapor-phase aluminizing (VPA) are common methods for producing protective coatings on aero and industrial gas turbine hot section components. SermAlcote® slurry aluminization is an alternative to many industrial pack and vapor-phase aluminizing processes. SermAlcote® slurry aluminization processes are designed to meet existing commercial specifications while offering significant improvements in cost, quality and turntime over competitive aluminizing processes. Advantages of this processing route include simplified masking, shorter thermal processing cycles, improved diffusion capacity (no powder, simplified racks), and elimination of powder handling/storage concerns.

Unlike conventional slurry aluminizing methods, the SermAlcote® process produces very uniform diffused aluminide coatings over a very wide range of applied slurry amounts. This simplifies the manufacturing process and produces high degree of process repeatability and uniformity.

Data and examples are presented in order to describe the characteristics of SermAlcote® slurry aluminization processes for producing aluminide coatings, platinum-modified aluminide coatings, and over-aluminized MCrAlY coatings.
High Temperature Brazing for Cobalt-Based Gas Turbine Components
Authors: Greaves Wayne , van Esch Hans
Published: August 2014

A unique high temperature brazing process was developed for crack repair and surface restoration of cobalt superalloy components of industrial gas turbines. The repair method begins with a special cleaning operation consisting of both chemical and ultrahigh vacuum processes. A new high-temperature braze material, with a composition compatible with most of the common cobalt-based turbine alloys, was developed. The mechanical properties and weldability of the brazed material are comparable with those base alloys. Microstructural evaluation and mechanical testing confirmed the desired properties. Also, actual refurbishment applications of General Electric, Westinghouse, and ABB gas turbine components are shown.
Fluoride Ion Cleaning (FIC) at Sub-Atmospheric Pressure
Authors: Miglietti Warren , Cullen Tom
Published: August 2014

The fluoride Ion cleaning (FIC) process is used to assist in the successful braze repair of nickel-based superalloy components. This process is especially effective in removing embedded oxides in cracks typically found in aircraft parts such as in combustors and turbine blades and vanes. Where, Al and Ti are present in the base metal, the FIC process depletes these elements from the surface, thereby improving the braze flow and repair of the cracked components. The objective of this paper is to show that mechanical properties of the braze repaired region can be adequate when the FIC process at sub-atmospheric pressure is utilized, prior to brazing. To achieve this, firstly entailed designing and producing specimens suitable to study the fatigue crack behavior of braze repaired cracks/joints under mechanical and thermal loading. The cracks/joints prior to brazing were either in an unclean form i.e. had an oxide layer on, or were fluoride ion cleaned at sub-atmospheric pressure. Fatigue crack propagation tests under constant load as well as under constant stress intensity factor range were conducted in order to study fatigue crack growth characteristics in the parent and braze repaired area. In addition, the resistance to thermal cycling was investigated using single-edge wedge specimens containing braze repaired joints.

For the unclean crack specimens, abnormally high crack growth rates were obtained from the brazed repaired area as compared to parent Ni-based material; whereas for the fluoride ion cleaned crack specimens, lower crack growth rates were experienced. Similarly for the unclean crack specimens, the thermal fatigue crack initiation life was significantly shorter compared with the fluoride ion cleaned crack specimens.
CFD Predictions and Field Measurements of NOx Emissions From LM1600 Gas Turbine During Part Load Operation
Authors: Price G. R. , Botros K. K. , Goldin G. M.
Published: August 2014

CFD simulations of the combustion process and formation of emissions in an industrial GE LM1600 gas turbine have been performed over a range of unit loads. Two combustion models were considered here to characterize the combustion process, the chemical equilibrium model and the non-equilibrium laminar flamelet model. The flamelet model predictions of nitric oxide concentration demonstrated much closer agreement with field measurements of continuous emissions monitoring systems, due to accurate modeling of the oxygen radial concentration. The predictions made with this model are within 15% at maximum load and considerably better at lower loads. Field measurements also showed that nitric oxide constitutes about 95% of the total NOx measured. Unburnt hydrocarbons and carbon monoxide emissions are significantly over-predicted, however, arguably as a result of neglecting their oxidation in the high temperature, fuel-lean environment of the turbine and exhaust stack downstream of the combustor.
Contact Stresses in Dovetail Attachments: Physical Modeling
Authors: Sinclair G. B. , Cormier N. G.
Published: August 2014

Simple physical models for the stresses in dovetail attachments are developed. These models address: to slip or not to slip, nominal stresses during loading up, peak contact and shear stresses during loading up, hoop stresses during loading up, peak contact and shear stresses during unloading, and hoop stresses during unloading. Comparisons are made with a previous paper on companion finite element modeling. Generally there is good agreement between the simple physical models and the finite element analysis. Together the two identify a pinching mechanism as leading to large fluctuations in hoop stresses at the edges of contact. These fluctuating hoop stresses can be expected to be a major contributor to the fatigue of dovetail attachments.
Experimental Investigation of Shock-Induced Blade Oscillation at an Elastically Suspended Turbine Cascade in Transonic Flow
Authors: Urban Brigitte , Stetter Heinz , Vortmeyer Nicolas
Published: August 2014

Experimental investigations on shock-induced flutter in a linear transonic turbine cascade are presented. To examine the relation between trailing edge shock oscillations on adjacent blades in transonic flow and observed turbine blade vibrations, an elastic suspension system has been developed so that only aerodynamic coupling occurs in the system.

The experimental investigations have been performed on a linear test rig with superheated steam as working fluid. The test facility enables Mach and Reynolds numbers to be varied independently.

The investigated cascade consists of seven blades which are taken from the tip section of a transonic low pressure steam turbine blade. Each blade is attached by an elastic spring system which allows the respective blade to vibrate in a mode equal to the real blade’s first bending mode. By varying the individual spring stiffness it is possible to either get a tuned or mistuned cascade.

The examinations mainly deal with the oscillatory behavior of the blades with respect to a variation in the isentropic outlet Mach number. In addition, the complex shock-boundary-layer interaction on the blades’ suction sides is described.

An important result is that the maximum blade oscillation amplitude can be related to a specific outlet Mach number. At this Mach number all seven blades are vibrating with exactly the same frequency. This phenomenon is observed at both the tuned and the mistuned cascades.

Spectrum analysis shows that one of the major shock oscillation frequencies corresponds to the flutter frequency.

In addition to this frequency the spectrum analysis of the blade oscillation shows the dominant frequencies of the shock oscillation which are not natural blade frequencies.

The experimental results show that oscillating shocks in a linear cascade give high potential for aeroelastic excitation of transonic blades under certain flow conditions. Blade oscillations and shock characteristics are discussed in detail.
Numerical Investigation of Nonlinear Fluid-Structure Interaction in Vibrating Compressor Blades
Authors: Carstens Volker , Belz Joachim
Published: August 2014

The aeroelastic behaviour of vibrating blade assemblies is usually investigated in the frequency domain where the determination of aeroelastic stability boundaries is separated from the computation of linearized unsteady aerodynamic forces. However, nonlinear fluid-structure interaction caused by oscillating shocks or strong flow separation may significantly influence the aerodynamic damping and hence effect a shift of stability boundaries. In order to investigate such aeroelastic phenomena, the governing equations of structural and fluid motion have to be simultaneously integrated in time.

In this paper a technique is presented which analyzes the aeroelastic behaviour of an oscillating compressor cascade in the time domain. The structural part of the governing aeroelastic equations is time-integrated according to the algorithm of Newmark, while the unsteady airloads are computed at every time step by an Euler upwind code, The link between the two time integrations is an automatic grid generation in which the used mesh is dynamically deformed as such that it conforms with the deflected blades at every time step.

The computed time series of the aeroelastic simulation of an assembly of twenty compressor blades performing torsional vibrations in transonic flow are presented. For subsonic flow, the differences between time domain and frequency domain results are of negligible order. For transonic flow, however, where vibrating shocks and a temporarily choked flow in the blade channel dominate the unsteady flow, the energy transfer between fluid and structure is no longer comparable to that of a linear system. It is demonstrated that the application of the time domain method leads to a significantly different aeroelastic behaviour of the blade assembly including a shift of the stability boundary.
A Novel Post-Processing Platform for 2D Steady and Unsteady Flows in Turbomachines
Authors: Moyroud François , Fransson Torsten H.
Published: August 2014

The paper presents a novel post-processing platform, AERO-POST, for two-dimensional steady and unsteady flow fields around turbomachinery blade rows. AERO-POST is a data manipulation facility, with a number of associated translators to read CFD results from a library of codes and experimental/numerical databases, and with a collection of conventions and associated automatic convertions so that numerical and experimental data can be rapidly compared in a consistent way. A number of specialized and well validated post-processing and visualization tools for unsteady flows around vibrating blade rows and relatively moving blade rows (aerodynamic damping and other unsteady aerodynamic coefficients, influence coefficients, stability parameter, stability maps,…) are also implemented to scrutinize unsteady CFD results. AERO-POST currently supports a library of ten CFD codes and three experimental/numerical databases, and three graphics libraries/packages. The program internal data structure and architecture is designed to support the storage of multi-dimensional variables with data attributes grouped into multiple data sets, and an extensive range of CFD reading routines, data manipulation tools and graphics libraries. Collectively, these features provide a set of powerful and original post-processing options allowing users to compare and investigate their CFD results more efficiently than with classical plotting softwares. These original post-processing and plotting options are illustrated on a series of applications.
Capabilities of Large Foil Bearings
Authors: Swanson Erik E. , Heshmat Hooshang
Published: August 2014

An experimental program was conducted on a large compliant surface foil bearing to document its performance. This large single pad foil bearing is 100 mm in diameter, and was operated at speeds of up to 30,000 RPM. Operation at 22,000 RPM with a measured load of 4190 N was also demonstrated. During coastdown runs from 30,000 RPM, maximum amplitudes of shaft vibration did not exceed 7.6 μm while passing through the two rigid shaft modes of the system. Thermal performance of the bearing was also in accord with previously documented foil bearings. This testing also demonstrates the practicality of scaling smaller foil bearing designs to the large bearings required for larger turbomachinery. To enhance the practical application of the results, the test rig shaft was designed to simulate a small gas turbine engine rotor.
Dynamic Response of a Rotor-Integral Squeeze Film Damper to Couple Imbalances
Authors: De Santiago Oscar , San Andrés Luis
Published: August 2014

Squeeze film dampers (SFDs) are used in high speed rotating machinery to reduce rotor vibration amplitudes and to isolate transmitted loads through the bearing support structures. SFDs are also effective means to ameliorate destructive subsynchronous vibrations excited by hydrodynamic bearings, seals, impellers and other unknown sources. Modern jet engines demand lighter and flexible structures with compact components to obtain the largest power to weight ratios. This current trend makes evident rotordynamic phenomena that must be adequately addressed by dissipation elements such as SFDs.

Integral squeeze film dampers (ISFDs) incorporating built in elastic supports are of reduced weight and length, offer accuracy of positioning, and a split segment construction allowing easier assembly, inspection and retrofit. Yet ISFDs require of extensive experimentation to verify their dynamic forced performance and to prove their reliability for applications on high performance turbomachinery. Measurements of the synchronous response of a test rotor supported on ISFDs and due to couple-imbalances are hereby presented. Masses inserted at two axial planes in the rotor and out of phase by 180° excite the second (conical) mode of vibration of the test rotor. Peak rotor responses at the second critical speeds, vertical and horizontal, allow the determination of amplification factors from which system damping coefficients for the rotor conical motions are extracted. The measurements verify the damping capacity of ISFDs to reduce (conical mode) rotor vibrations.
Rotor/Seal Experimental and Analytical Study on Full Annular Rub
Authors: Yu John J. , Goldman Paul , Bently Donald E.
Published: August 2014

Rotor/seal full annular rub, including synchronous (forward) and reverse (backward) precessions, has been investigated both experimentally and analytically. Of particular interest is the finding of reverse precessional full annular rub (dry whip) that occurs repeatedly in small clearance cases without any outside disturbance. The experimental results include rub triggering mechanism, mass unbalance, and rotative speed effects. A simplified mathematical model is used to interpret experimental results. Nonlinear solutions for both synchronous and reverse precessions are obtained along with instability zones. Mass unbalance effect on shifting from synchronous response to reverse rub and destabilizing factors such as dry friction, rotor damping, and seal stiffness, are discussed.
Rolling Element Bearing Non-Linearity Effects
Authors: Feng N. S. , Hahn E. J.
Published: August 2014

Non-linearity effects in rolling element bearings arise from two sources, viz. the Hertzian force deformation relationship and the presence of clearance between the rolling elements and the bearing races. Assuming that centrifugal effects may be neglected and that the presence of axial preload is appropriately reflected in a corresponding change in the radial clearance, this paper analyses a simple test rig to illustrate that non-linear phenomena such as synchronous multistable and nonsynchronous motions are possible in simple rigid and flexible rotor systems subjected to unbalance excitation. The equations of motion of the rotor bearing system were solved by transient analysis using fourth order Runge Kutta. Of particular interest is the effect of clearance, governed in practice by bearing specification and the amount of preload, on the vibration behaviour of rotors supported by ball bearings and on the bearing load. It is shown that in the presence of positive clearance, there exists an unbalance excitation range during which the bearing is momentarily not transmitting force owing to contact loss, resulting in rolling element raceway impact with potentially relatively high bearing forces; and indicating that for long bearing life, operation with positive clearance should be avoided in the presence of such unbalance loading. Once the unbalance excitation is high enough to avoid such contact loss, it is the bearings with zero or negative clearance which produce maximum bearing forces.
Orbit-Based Identification of Damping Coefficients for a Rotor Mounted on Off-Centered Squeeze Film Dampers and Including Support Flexibility
Authors: Diaz Sergio , San Andrés Luis
Published: August 2014

Squeeze film dampers (SFDs) provide structural isolation and energy dissipation in jet engines and process gas compressors. The determination of linearized damping force coefficients to allow the use of well-developed linear techniques is of importance in the design and reliability analysis of rotor-bearing systems dynamic response and stability. Two parameter identification techniques to estimate the linearized viscous damping coefficients of a rotor-bearing system based on the measurement of rotor displacements are presented. The first method applies a least-square curve fitting to the damping force, while the second determines the elliptic orbit that best approximates the actual one. The filtered orbit method is applied to identify the damping force coefficients from measurements of the synchronous response of a test rotor mounted on off-centered SFDs. The identified system damping coefficients (direct and cross-coupled) are found to be independent of the imbalance magnitude and shaft speed, in spite of the large amplitude rotor motions within the dampers’ clearances. A modification of the method to include the damper bearing support flexibility shows a dramatic improvement on the predicted rotor response and more reliable force coefficients.
Reconciliation of Rotordynamic Models With Experimental Data
Authors: Maslen Eric H. , Vázquez José A. , Sortore Christopher K.
Published: August 2014

A computationally efficient strategy is presented for adjusting analytic rotordynamic models to make them consistent with experimental data. The approach permits use of conventional rotordynamic models derived using finite element methods in conjunction with conventional plant identification models derived from impact or sine sweep testing in a transfer function or influence coefficient format. The underlying assumption is that the predominant uncertainties in engineered models occur at discrete points as effects like shrink fits, seal coefficients or foundation interactions. Further, it is assumed that these unmodeled or poorly modeled effects are essentially linear (at least within the testing and expected operating domains). Matching is accomplished by deriving a dynamic model for these uncertain effects such that the resulting composite model has a transfer function which matches that obtained experimentally. The derived augmentations are computationally compatible with the original rotor model and valid for stability or forced response predictions. Further, computation of this augmentation is accomplished using well developed and widely disseminated tools for modern control. Background theory and a complete recipe for the solution are supported by a number of examples.
Experimental and Theoretical Comparison of Two Swirl Brake Designs
Authors: Nielsen K. K. , Childs D. W. , Myllerup C. M.
Published: August 2014

Experimental and theoretical data are presented for two interchangeable swirl brakes designed in connection with the Space Shuttle Main Engine (SSME) Alternate Turbopump Development (ATD) High-Pressure Fuel Turbopump (HPFTP) program. The experimental data includes rotordynamic data for a extensive variation of test variables. Comparison of the swirl brake performance revealed that a non-aerodynamic swirl brake design proved as efficient and at times better than an aerodynamic design. For this reason a theoretical investigation using Computational Fluid Dynamics (CFD) was recently carried out. This modeling focused on predicting the seal inlet swirl ratio which is the primary swirl brake performance parameter. The non-aerodynamic swirl brake showed superior performance for a variety of test variable conditions. Strong separation vortices within the swirl vanes are the main reason for this finding.
A New CFD-Perturbation Model for the Rotordynamics of Incompressible Flow Seals
Authors: Kim Namhyo , Rhode David L.
Published: August 2014

A new, quasi-three-dimensional perturbation model is developed for the computation of rotordynamic forces for all incompressible flow seals with an axisymmetric geometry. The model assumes a small circular whirl motion of the rotor around the stator center. By avoiding the complicated perturbation coordinate transformation, the perturbation solution directly accounts for the disturbance of the wall shear stresses that are caused by the whirl motion of the rotor. The primary advantage of the present model is that it can immediately be applied to any radial-clearance seal of axisymmetric geometry without ad hoc adjustments. It was found from computations that include the upstream chamber that the magnitude of the first-order variables at the seal inlet are much larger and abruptly changing than was previously assumed.
Elasto-Plastic and Creep Analysis of a First Stage Blade in a Land Based Gas Turbine Under Steady State Operating Conditions
Authors: Sakai Takayuki , Ogata Takashi , Nomoto Akiyoshi , Watanabe Kazunori
Published: August 2014

Because first stage rotor blades are used under severe temperature and stress conditions, damage evaluation procedure for the blades is one of key technology to reduce maintenance costs for land based gas turbine. To calculate damage of the blade, stress/strain distribution should be predicted based on temperature distribution. In this study, first stage blades were analyzed by a finite element method to discuss damage profile within the blade under steady state operating condition. At first, 2-D finite element analyses were carried out to study effect of variation of combustion gas and cooling air conditions on the stress/strain distribution of the blade mid height. As a result, change on cooling air condition did not show significant effect on creep strain distribution within the blade section, whereas increase of inlet temperature of combustion gas caused increase of thermal stress and creep strain. Then, 3-D finite element analyses were carried out to identify critical portion of the whole blade in terms of fatigue and creep damage. Consequently, it was found that the leading edge of the blade would be subjected to larger plastic strain that cause fatigue damage. On the other hand, it was suggested that one-third height of the blade at pressure side surface would be the critical portion in terms of creep damage.
The Effect of Airfoil Scaling on the Predicted Unsteady Loading on the Blade of a 1 and 1/2 Stage Transonic Turbine and a Comparison With Experimental Results
Authors: Clark J. P. , Stetson G. M. , Magge S. S. , Ni R. H. , Haldeman C. W. , Dunn M. G.
Published: August 2014

In this study, two time-accurate Navier-Stokes analyses were obtained to predict the first-vane/first-blade interaction in a 1 and 1/2-stage turbine rig for comparison with measurements. In the first computation, airfoil scaling was applied to the turbine blade to achieve periodicity in the circumferential direction while modeling 1/18 of the annulus. In the second, 1/4 of the wheel was modeled without the use of airfoil scaling. For both simulations the predicted unsteady pressures on the blade were similar in terms of time-averaged pressure distributions and peak-peak unsteady pressure envelopes. However, closer inspection of the predictions in the frequency domain revealed significant differences in the magnitudes of unsteadiness at twice vane-passing frequency (and the vane-passing frequency itself, to a lesser extent). The results of both computations were compared to measurements of the vane-blade interaction in a full-scale turbine rig representative of an early design iteration of the PW6000 engine. These measurements were made in the short-duration turbine-test facility at The Ohio State University Gas Turbine Laboratory. The experimentally determined, time-resolved pressures were in good agreement with those predicted with the 1/4-wheel simulation.
A Study of the Effects of Tip Clearance in a Supersonic Turbine
Authors: Dorney Daniel J. , Griffin Lisa W. , Huber Frank W.
Published: August 2014

Flow unsteadiness is a major factor in turbine performance and durability. This is especially true if the turbine is a high work design, compact, transonic, supersonic, counter rotating, or uses a dense drive gas. The vast majority of modern rocket turbine designs fall into these categories. In this study a parallelized unsteady three-dimensional Navier-Stokes analysis has been used to study the effects of tip clearance on the transient and time-averaged flow fields in a supersonic turbine. The predicted results indicate improved performance in the simulation including tip clearance. The sources of the performance gains were: 1) reduced endwall secondary flows due to decreased blade loading near the tip, 2) a weakened shock system in the case with tip clearance, and 3) the fact that the reduction in the shock losses were greater than the losses introduced by tip clearance.
Unsteady Flow Phenomena in a Centrifugal Compressor Channel Diffuser
Authors: Kang Jeong-Seek , Cho Sung-Kook , Kang Shin-Hyoung
Published: August 2014

The aim of this paper is to understand the time averaged pressure field and unsteady pressure patterns in a high speed centrifugal compressor channel diffuser. Pressure distributions from the impeller exit to the channel diffuser exit are measured and discussed for various flow conditions. Unsteady pressure signals from six fast-response sensors in the channel diffuser are analyzed by decomposition method and wavelet transform. Measured results are shown for various operating condition from choke to surge that the effect of operating condition is well discussed.

The strong non-uniformity in the pressure distribution is obtained over the diffuser shroud wall caused by the impeller-diffuser interaction. As the flow rate increases, flow separation near the throat, due to large incidence angle, increases aerodynamic blockage and reduces the aerodynamic flow area downstream. Thus the minimum pressure location occurs downstream of the geometric throat, and it is named as the aerodynamic throat. And at choke condition, normal shock occurs downstream of this aerodynamic throat. The variation in the location of the aerodynamic throat is discussed.

The pressure ratio waveforms by blade passing show regular oscillation not only for the normal but also for the surge conditions and the high frequency fluctuations are superposed on the oscillating pressure waveform as the flow rate increases. Periodic unsteadiness by blade passing does not decay in the diffuser channel. It depends on the operating point and is generally larger in the channel than in the vaneless space. Aperiodic unsteadiness rapidly decrease downstream of diffuser channel.

At surge, the spectrum becomes broad banded with peaks at the surge frequency as well as blade passage frequency and the impeller rotating frequency. The surge signal was analyzed using wavelet transform and it is found that surge signal is composed of not only surge scale and blade scale but also multi-scale aperiodic waves. The broadband spectrum in surge condition is due to this multi-scale aperiodic waves.
Radial Turbines — Blade Number and Reaction Effects
Authors: Rodgers C.
Published: August 2014

Inward flow radial and mixed flow turbines are effectively utilized in both turbochargers and small gas turbine auxiliary power units (APU’s), where moderately high levels of efficiency can be readily attained with simple cast components, less sensitive to blade endgap clearances than axial turbines. This paper first provides an overview of radial turbine performance characteristics for turbocharger and gas turbine applications as basically influenced by specific speed, reaction, velocity ratio, and rotor tip to exducer root mean square (RMS) diameter ratio. Since turbine rotor mass and inertia play important roles in structural integrity and engine acceleration characteristics, the effects of rotor blade solidity on turbine efficiency are then discussed based upon past research, and supported by analysis of a one dimensional friction model of the rotor passage. Finally the effects of rotor reaction on radial turbine flow versus pressure characteristics are examined pertinent to engine matching requirements.
CFD Analysis of Unsteady Flow Interactions in a Centrifugal Compressor Stage
Authors: Koumoutsos A. , Tourlidakis A. , Elder R. L.
Published: August 2014

This paper describes the unsteady flow analysis in a centrifugal compressor stage using a three dimensional CFD algorithm. The flow unsteadiness arising from the interaction between the impeller and the diffuser has been analysed using an algorithm suitable for equal or multiple number of rotor and diffuser blades.

The multi-block, structured grid CFD code TASCflow was used as a basis and algorithm development was undertaken to provide the required capability of modelling the unsteady interactions of the impeller and the diffuser.

The centrifugal compressor stage studied consists of an impeller with splitters and a vaned diffuser. The results presented are for off-design flow conditions where some experimental results were available for comparison. The results obtained for the steady-state model show a good agreement with the measurements.

In general the unsteady flow field obtained show a reasonable agreement with experimental data and demonstrates significant differences when compared to the steady state results especially in terms of the velocity field. A detailed analysis of the unsteady flow field is carried out using Fourier transforms of velocity and pressure at various locations of the flow field and the level of unsteadiness is determined as distributed to various frequencies. The unsteadiness in the impeller passage is much less than in the diffuser where a strong coupling is predicted in the vaneless space.
Numerical Investigation of the Flow in an Aft-Swept Transonic Compressor Rotor
Authors: Blaha Christoph , Kablitz Stephan , Hennecke Dietmar K. , Schmidt-Eisenlohr Uwe , Pirker Klaus , Haselhoff Susanne
Published: August 2014

The design of an aft-swept transonic compressor rotor and the investigation of its flow field compared to the radial baseline rotor are reported. Both rotors were designed using a 3D Euler solver with body forces. Through the choice of composite material using carbon fibres, high amounts of sweep and lean could be imparted to the blades without adding mass to the rotor assembly. No compromise between aerodynamic and structural constraints had to be made.

The swept design as well as the radial base-line rotor were investigated using the commercial RANS solver CFX-TASCflow to validate the design. Complete speed lines at design speed were computed for both rotors.

The analytical results showed similar peak efficiency and indicate that the swept rotor’s stall margin is reduced as compared to the base-line rotor. The resulting flow field of the aft-swept rotor is described in this paper and an attempt is made to discuss the fidelity of the design tools used.
Radial Inflow Into the Downstream Cavity of a Compressor Stator Well
Authors: Scott R. M. , Childs P. R. N. , Hills N. J. , Millward J. A.
Published: August 2014

The subject of the interaction between the mainstream annulus flow and seal flows is now receiving increased attention as a result of concerted attempts to further improve compressor performance. In an axial compressor the use of a shroud on a stator blade row necessitates a trench and results in two such regions of interaction at the upstream and downstream stator well cavities with flow limited by a labyrinth seal. The upstream stator well cavity, with its superposed radial outflow, has received some attention and possess similarities with the cavity downstream of nozzle guide vanes in axial turbines, which have received considerable interest. The downstream compressor stator well cavity has, however, been less extensively studied. Here the flow is dominated by inflow into the cavity. This inflow is driven by the pressure gradient across the blade row and hence the pressure gradient between the upstream and downstream cavities. This paper presents preliminary pressure measurements from a high-speed two-stage research compressor. The experimental results are compared with two and three-dimensional CFD models. In order to gain confidence with CFD for compressor stator wells, the case of inflow into a rotor-stator disc wheelspace has been revisited; validating a commercial code, Fluent, for a wide range of flow conditions. This code has then been used to predict the detailed flow structure for the conditions in the experimental research compressor.
Tip-Clearance Actuation With Magnetic Bearings for High-Speed Compressor Stall Control
Authors: Spakovszky Z. S. , Paduano J. D. , Larsonneur R. , Traxler A. , Bright M. M.
Published: August 2014

Magnetic bearings are widely used as active suspension devices in rotating machinery, mainly for active vibration control purposes. The concept of active tip clearance control suggests a new application of magnetic bearings as servo-actuators to stabilize rotating stall in axial compressors.

This paper presents a first-of-a-kind feasibility study of an active stall control experiment with a magnetic bearing servo-actuator in the NASA Glenn high-speed single-stage compressor test facility. Together with CFD and experimental data a two-dimensional, incompressible compressor stability model was used in a stochastic estimation and control analysis to determine the required magnetic bearing performance for compressor stall control. The resulting requirements introduced new challenges to the magnetic bearing actuator design. A magnetic bearing servo-actuator was designed which fulfilled the performance specifications. Control laws were then developed to stabilize the compressor shaft. In a second control loop, a constant gain controller was implemented to stabilize rotating stall. A detailed closed loop simulation at 100% corrected design speed resulted in a 2.3% reduction of stalling mass flow which is comparable to results obtained in the same compressor by Weigl et al. (1998) using unsteady air injection.

The design and simulation results presented here establish the viability of magnetic bearings for stall control in aero-engine high-speed compressors. Furthermore the paper outlines a general design procedure to develop magnetic bearing servo-actuators for high-speed turbomachinery.
Control of Secondary Flows in a Turbine Nozzle Guide Vane by Endwall Contouring
Authors: Shih T. I-P. , Lin Y.-L. , Simon T. W.
Published: August 2014

Computations were performed to study the three-dimensional flow and temperature distribution in a nozzle guide vane that has one flat and one contoured endwall with and without film cooling injected from two slots, one on each endwall located just upstream of the airfoil. For the contoured endwall, two locations of the same contouring were investigated, one with all contouring upstream of the airfoil and another with the contouring starting upstream of the airfoil and continuing through the airfoil passage.

Results obtained show that when the contouring is all upstream of the airfoil, secondary flows on both the flat and the contoured endwalls are similar in magnitude. When the contouring starts upstream of the airfoil and continues through the airfoil passage, secondary flows on the contoured endwall are markedly weaker than those on the flat endwall. With weaker secondary flows on the contoured endwall, film-cooling effectiveness there is greatly improved.

This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy. Effects of turbulence were modeled by the low Reynolds number shear-stress transport k-ω model. Solutions were generated by a cell-centered, finite-volume method that uses third-order accurate flux-difference splitting of Roe with limiters and multigrid acceleration of a diagonalized ADI scheme with local time stepping on patched/embedded structured grids.
Extending the Service Life of Gas Turbine Hardware: (I) Laboratory Investigation
Authors: Warnes Bruce M. , Hampson Leonard M.
Published: August 2014

The possibility of extending the service life of the high pressure hardware for gas turbine engines using a novel repair procedure was evaluated in a laboratory study. In the laboratory simulation, both high and low activity platinum aluminide overcoatings of a partially stripped platinum aluminide were evaluated and contrasted. The results indicate that a chemically homogenous, relatively uniform thickness, platinum modified coating can be formed by low activity aluminizing on a substrate with surface areas of both bare alloy and partially stripped platinum aluminide coating. Furthermore, the CVD low activity platinum aluminide overcoat considered had better oxidation resistance than the original coating. The experimental program is outlined, plus the results are presented and discussed.