bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Anemometer Measurements of the Flow Field in a 4:1 Pressure Ratio Centrifugal Impeller
Authors: Skoch G. J. , Prahst P. S. , Wernet M. P. , Wood J. R. , Strazisar A. J.
Published: December 2014

A laser-doppler anemometer was used to obtain flow-field velocity measurements in a 4:1 pressure ratio, 4.54 kg/s (10 lbm/s), centrifugal impeller, with splitter blades and backsweep, which was configured with a vaneless diffuser. Measured through-flow velocities are reported for ten quasi-orthogonal survey planes at locations ranging from 1% to 99% of main blade chord. Measured through-flow velocities are compared to those predicted by a 3-D viscous steady flow analysis (Dawes) code.

The measurements show the development and progression through the impeller and vaneless diffuser of a through-flow velocity deficit which results from the tip clearance flow and accumulation of low momentum fluid centrifuged from the blade and hub surfaces. Flow traces from the CFD analysis show the origin of this deficit which begins to grow in the inlet region of the impeller where it is first detected near the suction surface side of the passage. It then moves toward the pressure side of the channel, due to the movement of tip clearance flow across the impeller passage, where it is cut by the splitter blade leading edge. As blade loading increases toward the rear of the channel the deficit region is driven back toward the suction surface by the cross-passage pressure gradient. There is no evidence of a large wake region that might result from flow separation and the impeller efficiency is relatively high. The flow field in this impeller is quite similar to that documented previously by NASA Lewis in a large low-speed backswept impeller.
Aerodynamic Modeling of Multistage Compressor Flowfields: Part 2 — Modeling Deterministic Stresses
Authors: Hall Edward J.
Published: December 2014

The primary purpose of this study was to investigate improved numerical techniques for predicting flows through multistage compressors. The vehicle chosen for this study was the Pennsylvania State University Research Compressor (PSRC). The PSRC facility consists of a 3-1/2 stage axial flow compressor which shares design features which are consistent with embedded stages of modern gas turbine engine axial flow compressors. In Part 2 of this two part paper, time-dependent predictions of rotor/stator/rotor aerodynamic interactions were employed to quantify the levels and distribution of deterministic stresses resulting from the average-passage flowfield description. Details of the spanwise and blade-to-blade distributions of the velocity correlations are examined and compared with results based on physical deterministic flow structures such as blade wakes and clearance flows. The predicted “apparent” wake profile decay resulting from the interaction of the wake through a downstream blade row is presented and compared with test data. This “apparent” wake profile decay is employed to define a simplified model for deterministic stress correlations in a steady state flowfield prediction scheme which retains the “mixing plane” methodology. Calculations based on this proposed model are described and predicted results are compared with both time-dependent predictions and test data. The resulting prediction strategy is both computational efficient and contains sufficient physical realism to permit its use in design studies.
Operation of a Primary Surface Recuperator on a Liquid Fueled Combustion System
Authors: Stephenson Michael D. , Ward Mike E. , Holman Len
Published: December 2014

Gas turbine recuperators have been put in operation in a number of applications, although the experience on liquid fuel has been minimal. Possibilities of liquid fouling of the compact surfaces of recuperators has been a significant concern.

A extended duration fouling test of a compact recuperator was conducted using a simulated gas turbine exhaust stream from a commercial dry low NOx atmospheric combustion system. This combustion system has consistently demonstrated operation with negligible smoke and low NOx emissions. The low smoke significantly reduces the likelihood of fouling of downstream equipment. Fouling of the recuperator was virtually undetectable after 1000 hours of operation. Visual inspection of the recuperator core confirmed there was no soot buildup of any kind.
Detailed Chemical Modelling Predictions of Emissions From a Reheated Gas Turbine Engine With Application to Future Supersonic Aircraft
Authors: Foster T. J. , Wilson C. W.
Published: December 2014

The exhaust plumes of modern gas turbine engines are of great concern due to the emission of atmospheric pollutants, such as carbon monoxide, unburnt hydrocarbons and oxides of nitrogen (NOx) and visibility caused by the presence of black carbonaceous smoke and nitrogen dioxide (NO2) giving rise to a new plume visibility phenomena of “yellow smoke”. A detailed hydrocarbon oxidation and NOx scheme was used to simulate chemical reactions occurring through the gas turbine engine and near-field plume. In addition limited experimental measurements have been made directly behind a reheated gas turbine engine to measure gaseous emissions and to quantify the rate of conversion of nitric oxide to nitrogen dioxide. Two experimental methods were employed to measure emissions; the first a conventional probe technique, the second a non-intrusive method. Results show a fair agreement between experimental data and predicted emissions, showing the maximum conversion of NO to NO2 at low reheat fuel flowrates. These detailed results can be used as an input to atmospheric modelling codes.
High Temperature Braze Repair for Compressor Blades
Authors: van Esch Hans , Herren Ernst
Published: December 2014

This summary describes the repair and refurbishment process development for a set of compressor blades that suffered from heavy pitting corrosion. The objective was to restore the surface of the corroded blades and regain fatigue strength, while maintaining the proper airfoil profile.

Metallurgical evaluation during the development and refurbishment indicated where improvements were needed and later on controlled the progress of the repair. Mechanical tests, such as fatigue and hardness, were performed to ensure that mechanical property criteria were met following the complete refurbishment of the blades.

The resulting repair scheme is generic and can be used on most types of gas turbine compressor blades.
Heat Transfer Coefficient Distributions for the Convective Cooling of Non-Cylindrical Geometries in Crossflow Using Extended Surfaces
Authors: Neely Andrew J. , Ireland Peter T. , Harper Les R.
Published: December 2014

An experimental investigation of the performance of extended fin surfaces for the forced convective cooling of a range of engine component geometries in crossflow is reported. The experiments were undertaken to measure the surface heat transfer coefficient distributions of external finning around non-cylindrical geometries for use in aviation gas turbines in which the cooling performance/mass ratio must be maximised. The geometries examined were a box (square with rounded corners), a flute (rectangle with circular ends) and a 30° wedge. These models were sized to have equivalent cross sectional area to allow a direct comparison of performance. Perspex models coated with thermochromic liquid crystal were tested at a range of Reynolds numbers in a heat transfer wind tunnel in which a step change in flow temperature was used to measure the transient thermal behaviour of the fins. This technique enables the full surface mapping of local heat transfer coefficients on the surface of the fins.

These measurements are compared with those for the equivalent smooth geometries and also with empirical calculations from the literature where available. A comparison with previous cylindrical measurements is also made. Knowledge of the distributions of local heat transfer coefficients enables the optimisation of the geometry through strategies such as baffling of the fins. Some examples of these strategies have been implemented and the results are reported.

The finned geometries are seen to outperform the unfinned geometries (by factors greater than 3) though by factors less than simply the increase in area. The enhancement in h results because the increased surface area of the fins more than outweighs the decrease in local h on the fin surface as compared to the smooth geometries.
Analysis of Interfacial Cracks in a TBC/Superalloy System Under Thermo-Mechanical Loading
Authors: Nusier S. Q. , Newaz G. M.
Published: December 2014

In thermal barrier coatings (TBC) residual stresses develop during cool down from processing temperature due to the thermal expansion mismatch between the different layers (substrate, bond coat, and TBC). These residual stresses can initiate micro cracks at the bond coat/TBC interface and can lead to debonding at the bond coat/TBC interface. The effect of voids or crack like flaws at the interface can be responsible for initiating debonding and accelerate the oxidation process. Effect of oxide layer growth between bond coat and ceramic layer (TBC) can be modeled as volume increase. In this work we represent this change in volume as an induced pressure across the interface. Mixed-mode fracture analysis of a thin circular delamination in an-axisymmetrically multi layer circular plate is developed. Geometrical nonlinearity is included in the analysis, since we have a large deflection case. The elastic deformation problem of a circular plate subjected to a clamped boundary condition at the edge of the delamination, an out of plane pressure load, and a compressive stress due to thermal mismatch between different layers, was solved numerically using a Rayleigh-Ritz method. The strain energy release rate was evaluated by means of the path-independent M-integral. The numerical results of this problem based on the energy method were verified using finite element method. Both methods correlate well in predicting the energy release rate for Mode I and Mode II, deflection, and postbuckling solutions. The energy release rates G, for both Mode I and Mode II using virtual crack extension method were evaluated. The specimen was cooled down from processing temperature of 1000 °C to 0 °C. The variation of the properties as a function of temperature was used for analysis. It was found that the use of temperature dependent properties in contrast to constant properties provides significantly different values of J-integral and G.
On the Design Criteria for Suppression of Secondary Flows in Centrifugal and Mixed Flow Impellers
Authors: Zangeneh M. , Goto A. , Harada H.
Published: December 2014

In this paper, for the first lime, a set of guide-lines are presented for the systematic design of mixed flow and centrifugal compressors and pumps with suppressed secondary flows and a uniform exit flow field. The paper describes the shape of the optimum pressure distribution for the suppression of secondary flows in the impeller with reference to classical secondary flow theory. The feasibility of achieving this pressure distribution is then demonstrated by deriving guide-lines for the design specifications of a 3D inverse design method, in which the blades are designed subject to a specified circulation distribution or 2πrV¯θ. The guide-lines will define the optimum choice of the blade loading or ∂rV¯θ/∂m and the stacking condition for the blades. These guide-lines are then used in the design of three different low specific speed centrifugal pump impellers and a high specific speed industrial centrifugal compressor impeller. The flow through all the designed impellers are computed numerically by a 3D viscous code and the resulting flow field is compared to that obtained in the corresponding conventional impeller. The results show consistent suppression of secondary flows in all cases. The design guide-lines are validated experimentally by comparing the performance of the inverse designed centrifugal compressor impeller with the corresponding conventional impeller. The overall performance of the stage with the inverse designed impeller with suppressed secondary flows was found to be 5% higher than the conventional impeller at the peak efficiency point. Exit flow traverse results at the impeller exit indicate a more uniform exit flow than that measured at the exit from the conventional impeller.
Transient Thermoelastohydrodynamic Study of Tilting-Pad Journal Bearings Under Dynamic Loading
Authors: Monmousseau Pascal , Fillon Michel , Frêne Jean
Published: December 2014

Nowadays, the tilting-pad journal bearings are submitted to more and more severe operating conditions. The aim of this work is to study the thermal and mechanical behavior of the bearing during the transient period from an initial steady-state to a final steady-state (periodic). In order to study the behavior of this kind of bearing under dynamic loading (Fdyn) due to a blade loss, a nonlinear analysis, including local thermal effects, realistic boundary conditions and bearing solid deformations (TEHD analysis) is realized. After a comparison between theoretical results obtained with four models (ISO, ADI, THD and TEHD) and experimental data under steady-state operating conditions (static load Ws), the evolution of the main characteristics for three different cases of the dynamic load (Fdyn/Ws<1, Fdyn/Ws=1 and Fdyn/Ws>1) is discussed. The influence of the transient period on the minimum film thickness, the maximum pressure, the maximum temperature and the shaft orbit is presented. The final steady-state is obtained a long time after the appearance of a dynamic load.
A Shock Loss Model for Supersonic Compressor Cascades
Authors: Bloch Gregory S. , Copenhaver William W. , O’Brien Walter F.
Published: December 2014

Loss models used in compression system performance prediction codes are often developed from the study of two-dimensional cascades. In this paper, compressible fluid mechanics has been applied to the changes in shock geometry that are known to occur with back pressure for unstarted operation of supersonic compressor cascades. This physics-based engineering shock loss model is applicable to cascades with arbitrary airfoil shapes.

Predictions from the present method have been compared to measurements and Navier-Stokes analyses of the L030-4 and L030-6 cascades, and very good agreement was demonstrated for unstarted operation. A clear improvement has been demonstrated over previously published shock loss models for unstarted operation, both in the accuracy of the predictions and in the range of applicability.

The dramatic increase in overall loss with increasing inlet flow angle is shown to be primarily the result of increased shock loss, and much of this increase is caused by the detached bow shock. For a given Mach number, the viscous profile loss is nearly constant over the entire unstarted operating range of the cascade, unless a shock-induced boundary layer separation occurs near stall. Shock loss is much more sensitive to inlet Mach number than is viscous profile loss.
Effects of Non-Axisymmetric Tip Clearance on Axial Compressor Performance and Stability
Authors: Graf M. B. , Wong T. S. , Greitzer E. M. , Marble F. E. , Tan C. S. , Shin H.-W. , Wisler D. C.
Published: December 2014

The effects of circumferentially non-uniform lip clearance on axial compressor performance and stability have been investigated experimentally and analytically. A theoretical model for compressor behavior with non-axisymmetric tip clearance has been developed and used to design a series of first-of-a-kind experiments on a four-stage, low speed compressor. The experiments and computational results together show clearly the central physical features and controlling parameters of compressor response to non-axisymmetric lip clearance.

It was found that the loss in stall margin was more severe than that estimated based on average clearance. The stall point was, in fact, closer to that obtained with uniform clearance at the maximum clearance level. The circumferential length scale of the tip clearance (and accompanying flow asymmetry) was an important factor in determining the stall margin reduction. For the same average clearance, the loss in peak pressure rise was 50% higher for an asymmetry with fundamental wavelength equal to the compressor circumference than with wavelength equal to one-half the circumference. The clearance asymmetry had much less of an effect on peak efficiency; the measured maximum efficiency decrease obtained was less than 0.4 percent compared to the 8% decrease in peak pressure rise due to the asymmetric clearance. The efficiency penalty due to non-axisymmetric tip clearance was thus close to that obtained with a uniform clearance at the circumferentially-averaged level.

The theoretical model accurately captured the decreases in both steady-state pressure rise and stable operating range which are associated with clearance asymmetry. It also gave a good description of the observed trends of (i) increasing velocity asymmetry with decreasing compressor flow, and (ii) decreasing effect of clearance asymmetry with decreasing dominant wavelength of the clearance distribution. The time resolved data showed that the spatial structure of the pre-stall propagating disturbances in the compressor annulus was well represented and that the stability limiting process could be linked to the unsteady structure of these disturbance modes.

The model was also utilized for parametric studies to define how compressor performance and stability is affected by the circumferential distribution of clearance, steady-state compressor pressure-rise characteristic, and system dynamic parameters. Sensitivity to clearance asymmetry was found to fall off strongly with the (asymmetry-related) reduced frequency and to increase with peak pressure rise and increasing curvature of the characteristic near the peak.
Industrial Gas Turbine Uprates: Tips, Tricks and Traps
Authors: Ragland T. L.
Published: December 2014

After industrial gas turbines have been in production for some amount of time, there is often an opportunity to improve or “uprate” the engine’s output power or cycle efficiency or both. In most cases, the manufacturer would like to provide these uprates without compromising the proven reliability and durability of the product. Further, the manufacturer would like the development of this “Uprate” to be low cost, low risk and result in an improvement in “customer value” over that of the original design. This paper describes several options available for enhancing the performance of an existing industrial gas turbine engine and discusses the implications for each option. Advantages and disadvantages of each option are given along with considerations that should be taken into account in selecting one option over another.

Specific options discussed include dimensional scaling, improving component efficiencies, increasing massflow, compressor zero staging, increasing firing temperature (thermal uprate), adding a recuperator, increasing cycle pressure ratio, and converting to a single shaft design. The implications on output power, cycle efficiency, off-design performance engine life or time between overhaul (TBO), engine cost, development time and cost, auxiliary requirements and product support issues are discussed. Several examples are provided where these options have been successfully implemented in industrial gas turbine engines.
Design of a High Efficiency Industrial Turbine Blade Utilizing Third Generation Single Crystal Alloy CMSX®-10
Authors: Fitzpatrick Michael D. , Brentnall William D. , Meier Andrew , Erickson Gary L. , DeBoer Gary
Published: December 2014

Future advancements in the efficiency and reliability of Industrial Gas Turbines (IGT) will be closely tied to the application of advanced materials, together with increasingly sophisticated turbine hot section designs. An example of this trend is illustrated by the recent design of a first stage blade component for an advanced IGT concept utilizing the third generation single crystal superalloy CMSX-10. It is anticipated that alloy CMSX-10 will permit the use of increased turbine firing temperatures with reduced cooling flows compared to previous recuperated turbine designs, while maintaining acceptable blade durability and life-cycle cost.

This paper discusses some of the design/materials analyses and cost studies performed on the blade, which ultimately led to the consideration of alloy CMSX-10 for the IGT application. The solid modeling and finite element blade design methods which allowed the incorporation of state-of-the-art cooling technology and aerodynamics are described. Alloy CMSX-10 characteristics, particularly mechanical properties and microstructural stability considerations, are discussed. Additionally, the results of a recent casting demonstration in an IGT blade configuration are presented. Finally, future tasks supporting the application of the alloy are outlined, such as coatings development efforts and the DOE/ORNL sponsored Land Based Turbine Casting Initiative; activities sponsored through a cooperative agreement with the United States Department of Energy within the Advanced Turbine System (ATS) Program.
Numerical Prediction of Heat Transfer in a Channel With Ribs and Bleed
Authors: Rigby David L. , Steinthorsson E. , Ameri A. A.
Published: December 2014

In the present work numerical simulations for flow in a straight channel with square cross section is presented. While three of the walls of the channel are smooth the remaining wall was simulated to possess a combination of ribs and bleed holes. To allow for a comparative evaluation of the said heat transfer promoters that same wall was also simulated with holes only; ribs only; or simply smooth. Reynolds numbers from 10,000 to 38,000 based on the hydraulic diameter were considered. Very general multi-block structured grids were used to allow good grid quality around ribs and into the holes, and also to minimize the number of cells required. Turbulence was accounted for by a k-ω turbulence model which does not require reference to distance to a wall. Good agreement with experimental results demonstrate that the structured multi-block approach with the k-ω turbulence model is efficient and viable even for very complicated geometries.
Analysis of Efficiency and Water Recovery in Steam Injected Gas Turbines
Authors: De Paepe M. , Dick E.
Published: December 2014

The study presented in this paper has two objectives. The first objective is to analyse the efficiency of the steam injected gas turbine by modelling the thermodynamic cycle. This is done by adapting a calculation model for turbine blade cooling proposed by El Masri (1986). The expansion path is divided into small subintervals, to take into account the changing gas properties during the expansion. This model is then verified for four different industrial machines.

The basic cycle as well as cycles with thermodynamic improvements as intercooling, heat recuperation by heat exchanger and blade cooling using steam are studied. The calculations are done for a range of pressure ratios (PR) and turbine inlet temperatures (TIT), with methane (CH4) as fuel being representative of natural gas. A comparison is made with a simple cycle gas turbine and with a combined cycle system. The maximum efficiency of the basic cycle is found to be around 49 % with current gas turbine technology. Steam blade cooling is extremely simple to implement in a steam injected gas turbine and is found to be thermodynamically very attractive, bringing the maximum efficiency to about 52 %.

Secondly the water recuperation in the condenser is analysed. Due to the combustion of the fuel, water is formed. As a result, the dew point temperature of the combustion gas without steam injection can be rather high, i.e. around 45 °C. As a consequence, the amount of water corresponding to the injected steam can be recuperated by cooling the gas mixture to the original dew point temperature. Closing the cycle for water is in this case thermodynamically possible. The practical recuperation of water in the condenser is studied on a test rig with a simulated gas turbine augmented with a condenser and steam injection. This proves that complete recuperation of the injected water is technically possible.

The conclusion of the study is that a steam injected gas turbine with complete water recuperation is possible and has a high efficiency.
Concavity Enhanced Heat Transfer in an Internal Cooling Passage
Authors: Chyu M. K. , Yu Y. , Ding H. , Downs J. P. , Soechting F. O.
Published: December 2014

The present study evaluates an innovative approach for enhancement of surface heat transfer in a channel using concavities, rather than protruding elements. Serving as a vortex generator, a concavity is expected to promote turbulent mixing in the flow bulk and enhance the heat transfer. Using a transient liquid crystal imaging system, local heat transfer distribution on the surface roughened by an staggered array based on two different shapes of concavities, i.e. hemispheric and tear-drop shaped, have been obtained, analyzed and compared. The results reveal that both concavity configurations induce a heat transfer enhancement similar to that of continuous rib turbulators, about 2.5 times their smooth counterparts 10,000 ≤ Re ≤ 50,000. In addition, both concavity arrays reveal remarkably low pressure losses that are nearly one-half the magnitudes incurred with protruding elements. In turbine cooling applications, the concavity approach is particularly attractive in reducing system weight and ease of manufacturing.
Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part II — Opposed Rows of Orifices in Rectangular Ducts
Authors: Holdeman James D. , Liscinsky David S. , Bain Daniel B.
Published: December 2014

This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex 3-D flowfield in the combustion chambers in gas turbine engines.

The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio >1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5 respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.
Physics of Airfoil Clocking in Axial Compressors
Authors: Gundy-Burlet Karen L. , Dorney Daniel J.
Published: December 2014

Axial compressors have inherently unsteady flow fields because of relative motion between rotor and statnr airfnils. This relative motion leads to viscous and inviscid (potential) interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead in progressively more complex wake/wake and wake/airfnil interactions. Variations in the relative circumferential positions of stators or rotors can change these interactions, leading to different unsteady forcing functions on airfoils and different compressor efficiencies. The current study uses an unsteady, two-dimensional thin-layer Navier-Stokes zonal approach to investigate the unsteady aerodynamics of stator clocking in a low-speed 2 ½-stage compressor. Relative motion between rotors and stators is made possible by the use of systems of patched and overlaid grids. Results include surface pressures instantaneous forces and efficiencies for a 2 ½-stage compressor configuration.
Identification of the Modal Parameters of a Flexibly Supported Casing
Authors: Feng N. S. , Hahn Eric J.
Published: December 2014

Satisfactory means for evaluating the vibration behaviour of gas turbine installations where it is impractical to obtain a satisfactory model of the support structure and where it has natural frequencies in the operating range are not yet available. This paper investigates the feasibility of identifying the modal parameters of a flexibly supported rigid casing to predict the unbalance response of the contained rotor. Assumed known are the location of the principal axes of inertia of the casing. Numerical experiments demonstrate that the identification procedure works well even with a measurement accuracy of only two significant digits. Thus, the procedure is expected to be practically feasible, though no sensitivity studies have yet been carried out to determine the limitations imposed by the assumed location of the principal axes.
Entropy Generation Measurement in a Laminar Turbine Blade Boundary-Layer
Authors: Wallace John D. , Davies Mark R. D.
Published: December 2014

This paper demonstrates a method of calculating the entropy generation rate in an incompressible laminar turbine blade boundary-layer from measurements of surface heat transfer rate. It is shown that the entropy generated by fluid friction in an incompressible blade boundary-layer is significantly less than that generated by heat transfer at engine representative temperature ratios. The centre blade in a low-speed linear cascade is electrically heated and isolated from the airflow with a bypass valve. Upon opening the valve the blade is transiently cooled and thin film heat transfer gauges, painted on machinable glass ceramic inserts mounted into the surface of the blade, are used to record blade surface temperature and surface heat transfer rate signals; local Nusselt numbers are then calculated. Non-dimensional temperature distributions are derived across the boundary-layer using the blade surface heat transfer rate and a similarity condition. The equation describing the local entropy generation per unit volume is then integrated through the boundary-layer at each chordwise measurement point on the blade surface.
Comparisons Between Measured and Calculated Stall Development in Four High-Speed Multi-Stage Compressors
Authors: Demargne A. A. J. , Longley J. P.
Published: December 2014

In this paper the development of rotating stall in four different high-speed multi-stage compressors is investigated using a numerical simulation. Below 90 per cent of design speed the model calculates well the two-dimensional moderate to long lengthscale development of rotating stall, irrespective of the lengthscale and form of the stall inception mechanism. At higher operating speeds the model is less reliable, providing better comparisons for those compressors which exhibited modal rather than spike stall inception. The model is also used to investigate the feasibility of actively controlling the stall development process in a compressor. The conclusions reached are that mass injection and removal is far more effective than varying the blade stagger angles and that sensors must be upstream of actuators.
Influence of Turbulence Intensity on Intermittency Model in By-Pass Transition
Authors: Hogendoorn C. J. , de Lange H. C. , van Steenhoven A. A. , van Dongen M. E. H.
Published: December 2014

The influence of free stream turbulence intensity on boundary layer transition was studied for a weakly compressible flow along a flat plate. The test facility consisted of a Ludwieg tube in which values of Mach number, Reynolds number and free stream turbulence could be varied over the following ranges: 0.09 < M < 0.6, 5.105 < Reu/m < 1.107, 1.2% < Tu < 9%. In this paper the turbulence intensity was varied up to 4.0 %. Unsteady heat flux to the flat plate was measured using cold thin film gauges. From these measurements, the intermittency was computed using an integral technique. For turbulence intensities of 1.2 %, the intermittency distribution is somewhat below the Narasimha and Johnson model, whereas a good agreement is obtained for a free stream turbulence intensity of 4.0 %. The calculated dimensionless spot production rates is proved to agree very well with existing data sets from other experiments. For a Mach number equal to 0.36 the production rates seems a bit higher when compared to the incompressible data. However, the differences are small.
Effects of Stator Indexing on Performance in a Low Speed Multistage Axial Compressor
Authors: Barankiewicz Wendy S. , Hathaway Michael D.
Published: December 2014

The results of an experimental investigation to determine the impact of stator row indexing or clocking on multistage axial compressor performance are presented. Testing was conducted in the NASA Lewis Research Center’s Four-Stage Axial Compressor Facility. The impact of stator row indexing on both the overall and stator 3 blade element performance is presented for both the peak efficiency and peak pressure operating conditions. The change in overall performance due to stator indexing is 0.2% for both operating conditions. Indexing resulted in a 5% change in stator 3 mass averaged loss coefficient at the peak efficiency condition and a 10% change at the peak pressure condition. Since the mass-averaged stator 3 loss coefficient is on the order of 7%, the changes in loss coefficient due to indexing are on the order of 0.35–0.7%. These changes are considered to be small and are of the same order of magnitude as the passage-to-passage differences in loss coefficient due to manufacturing and assembly tolerances in the test compressor. The effects of stator-stator wake interactions are also shown and indicate that for rows with unequal blade counts it may be necessary to survey across more than one blade row pitch for accurate blade row performance measurements.
An Experimental Investigation of Vibration Localization in Bladed Disks: Part I — Free Response
Authors: Kruse Marlin J. , Pierre Christophe
Published: December 2014

The results of an experimental investigation of the effects of random blade mistuning on the free dynamic response of bladed disks are reported. Two experimental specimens are considered: a nominally periodic twelve-bladed disk with equal blade lengths, and the corresponding mistuned bladed disk, which features slightly different, random blade lengths. In the experiment, both the spatially extended modes of the tuned system and the localized modes of the mistuned system are identified. Particular emphasis is placed on the transition to localized mode shapes as the modal density in various frequency regions increases. Excellent qualitative and quantitative agreement is obtained between experimental measurements and results obtained by finite element analysis. Experimental results are additionally used to validate a component mode-based, reduced-order modeling technique for bladed disks. This work reports the first systematic experiment carried out to demonstrate the occurrence of vibration localization in bladed disks.
WR-21 Recuperator Core Test
Authors: Stossier Walt , Stauffer Matt , Perkins Glenn E.
Published: December 2014

WR-21 is the designation for the Intercooled, Recuperated (ICR) Gas Turbine Engine System currently under development for the U.S. Navy (USN), with the Royal Navy (RN) and French Navy as major participants. The purpose of the program is to design, develop and qualify a fuel efficient engine system for surface ships. A key enabling technology for the ICR Engine System is the recuperator used to recover exhaust gas heat for reinsertion into the engine cycle thereby reducing specific fuel consumption. A test of a full scale, reduced capacity WR-21 recuperator core was conducted at the Naval Surface Warfare Center, Carderock Division, Ship Systems Engineering Station (NSWCCD-SSES) to determine system response to transient maneuvers typical to ship gas turbine engines. Existing Navy gas turbines located at the site were used to provide the air and gas media for the test apparatus. The test program was directed by Northrop Grumman Marine Systems, the ICR prime contractor, and Allied Signal Aerospace, the recuperator manufacturer. This paper provides a description of the core test premise, test facility, test instrumentation, test experiments and resultant test data.
Investigation of Cooling-Air Injection on the Flow Field Within a Linear Turbine Cascade
Authors: Hong Yang , Fu Chen , Cunzhong Gong , Zhongqi Wang
Published: December 2014

In order to make clear how air injection influence the internal flows of turbine guide vanes, flows in a lagre-scale linear cascade were surveyed with secondary air injection from the locations of the blade leading-edge, and the rear of the suction and the pressure surfaces. The experimental results show that the secondary air interacts with the vortices in the cascade, alters the pressure distribution over blade profile and increases the energy loss obviously. It has been found that the air injection from the rear of the suction surface leads to the largest effect on the loss increase while the air injection from the rear of the pressure surface exerts the least influence. All the injections pertaining to the experiment have been found to have little effect on the exit flow angle. Effects on secondary flows, vortex intensity, and some averaged parameters are also discussed in this paper.
The Influence of Film-Cooling on the Aerodynamic Performance of a Turbine Nozzle Guide Vane
Authors: Osnaghi C. , Perdichizzi A. , Savini M. , Harasgama P. , Lutum E.
Published: December 2014

The paper presents the results of an investigation on the aerodynamic performance of a full coverage film-cooled nozzle guide vane. The blading is a typical high pressure turbine vane of advanced design, working in the high subsonic regime.

Tests have been carried out for a wide range of conditions, including variations in Mach number, coolant to mainstream mass flow rate ratio and location of the coolant injection. Both air and carbon dioxide at ambient conditions have been utilized, as coolant flow. Measurements have been performed in a plane located at 0.5 axial chord downstream of the trailing edge by means of a miniaturized five-hole pressure probe.

Performances, in terms of losses, flow angles and profile pressure distributions, for different cooling mass flow rates are presented and compared to the results of the solid blade tests (i.e. with no cooling holes). The results showed a significant increase of the losses with blowing. Test with air and carbon dioxide provided almost equal losses if carried out at the same global momentum flux ratio; however the density ratio was found to influence slightly the share of the coolant fluid among the injection rows and the local momentum flux ratio as well.

In order to define the individual contributions of groups of cooling rows on the performance of the blade, three different modes of injection have been tested, namely full, trailing edge and shower head injection. The main trend observed is that trailing edge injection produces the least amount of additional losses at high blowing rates. Full-coverage film-cooling injection did not lead to marked variations in the blade pressure distribution and/or outlet flow angle.
Aspirated Compressors
Authors: Kerrebrock J. L. , Reijnen D. P. , Ziminsky W. S. , Smilg L. M.
Published: December 2014

The performance of compressors can be improved in two ways by judicious removal from the flow path of the viscous flow in the boundary layers. First, removal of the boundary layer fluid just prior to or in a region of rapid pressure rise, either at shock incidence or more generally at the point of rapid pressure rise on the suction surface of the airfoil, can enable significant increases in the diffusion, hence in the work done by a stage for any given blade speed. Second, removal of the high entropy fluid in the boundary layer minimizes the required compression work in subsequent stages of compression, thereby raising the compression efficiency. Analysis has shown that the latter effect can result in approximately one half point increase in efficiency for each percent of (high entropy) fluid removal. Design studies have been carried out for two different stages to assess the increase in pressure ratio that may be achieved. One stage that has been designed would produce a pressure ratio of 2 at a tip speed of 1000 ft/sec, and may be very attractive for the fan stage of high-bypass turbofan engines. The other stage would produce a pressure ratio of 3 at a tip speed of 1500 ft/sec, and should be attractive as the first stage of a core compressor or the fan stage of a low-bypass ratio engine. An experiment has been completed, to examine the effect of boundary layer removal just prior to shock impingement on the suction surface of blades in a transonic rotor. The suction was implemented on 5 of the 23 blades of the rotor, providing a direct comparison of the flow behavior with and without suction. Analysis of the data has shown that the blades with suction have increased mass flow and that the flow more closely followed the suction surface near the trailing edge. The differences between aspirated and normal blades were most pronounced when the rotor was very close to stall. The third and fourth of the blades in the group with suction appear to be representative of the behavior to be expected of a rotor with suction on all blades. They exhibited improved efficiency and increased mass flow. The rotor as a whole with suction showed different stall behavior than its counterpart without boundary layer control. Future plans include the fabrication and experimental evaluation in the MIT Blowdown Compressor, of one of the two stages discussed above. In this experiment suction will be applied to all the blades in both rotor and stator, so that the increased work enabled by suction can be realized.

This research was supported by AFOSR, Dr. James McMichael, and by AlliedSignal Aircraft Engines, Dr. Arun Sehra.
Flow in a Rotating Square Serpentine Coolant Passage With Skewed Trips
Authors: Tse David G. N. , Steuber Gary D.
Published: December 2014

Velocity data were obtained by laser-Doppler velocimetry in rotating coolant passages with a square cross section having skewed trips. Measurements were obtained at Reynolds and Rotation numbers of 25,000 and 0.24 to quantify the influence of Coriolis effects and to explain the heat transfer phenomena observed by Johnson, et al. (1994). With rotation, outward flow and trips skewed at −45° generates counter-clockwise swirl on the high pressure side and a corner recirculation zone at the inner corner of the low pressure side. Inward flow and trips skewed at +45° generates clockwise swirl on the high pressure side and a corner recirculation zone at the upper corner of the low pressure side. The implications on heat transfer were estimated from the velocity data by the Nu-Re0.8 correlation. Johnson, et al. (1994) show that, in a passage with skewed trips, rotation increases the heat transfer from the high pressure surface of the first passage by up to 300% (relative to smooth wall stationary reference). The estimated contributions from increases in streamwise velocity, swirl and re-attachment of cross-flow in the inter-ribbed region were, respectively, 48%, <100% and >125%.
Characterization of Mechanical Properties of Aluminized CoCrAlY Coatings in Advanced Gas Turbine Blades Using a Small Punch Testing Method
Authors: Sugita Y. , Ito A. , Sakurai S. , Bloomer T. E. , Kameda J.
Published: December 2014

This paper describes examination of the microstructure/composition and mechanical properties (22–950 °C) in over aluminized CoCrAlY coatings of advanced gas turbine blades using scanning Auger microprobe and a small punch (SP) testing method. Aluminized coatings consisted of layered structure divided into four regions; (I) Al enriched and Cr depleted region, (II) Al and Cr graded region, (III) fine grained microstructure with a mixture of Al and Cr enriched phases and (IV) Ni/Co interdifusion zone adjacent to the interface. SP specimens were prepared in order that the specimen surface would be located in the various coating regions. SP tests indicated a strong dependence of the fracture properties on the various coatings regions. Coating zones I and II with high micro hardness showed much easier formation of brittle cracks in a wide temperature range, compared to regions III and IV The coating region III had lower room temperature ductility than the zone IV. However, the ductility in the coating zone III exceeded that in the region IV above 730 °C due to a precipitous ductility increase. The integrity of aluminized coatings while in-service is discussed in light of the variation of the low cycle fatigue life as well as the ductility in the layered structure.
Assessment of the dose reduction potential of a model‐based iterative reconstruction algorithm using a task‐based performance metrology
Authors: Samei Ehsan , Richard Samuel
Published: December 2014

Purpose:

Different computed tomography (CT) reconstruction techniques offer different image quality attributes of resolution and noise, challenging the ability to compare their dose reduction potential against each other. The purpose of this study was to evaluate and compare the task‐based imaging performance of CT systems to enable the assessment of the dose performance of a model‐based iterative reconstruction (MBIR) to that of an adaptive statistical iterative reconstruction (ASIR) and a filtered back projection (FBP) technique.

Methods:

The ACR CT phantom (model 464) was imaged across a wide range of mA setting on a 64‐slice CT scanner (GE Discovery CT750 HD, Waukesha, WI). Based on previous work, the resolution was evaluated in terms of a task‐based modulation transfer function (MTF) using a circular‐edge technique and images from the contrast inserts located in the ACR phantom. Noise performance was assessed in terms of the noise‐power spectrum (NPS) measured from the uniform section of the phantom. The task‐based MTF and NPS were combined with a task function to yield a task‐based estimate of imaging performance, the detectability index (d′). The detectability index was computed as a function of dose for two imaging tasks corresponding to the detection of a relatively small and a relatively large feature (1.5 and 25 mm, respectively). The performance of MBIR in terms of the d′ was compared with that of ASIR and FBP to assess its dose reduction potential.

Results:

Results indicated that MBIR exhibits a variability spatial resolution with respect to object contrast and noise while significantly reducing image noise. The NPS measurements for MBIR indicated a noise texture with a low‐pass quality compared to the typical midpass noise found in FBP‐based CT images. At comparable dose, the d′ for MBIR was higher than those of FBP and ASIR by at least 61% and 19% for the small feature and the large feature tasks, respectively. Compared to FBP and ASIR, MBIR indicated a 46%–84% dose reduction potential, depending on task, without compromising the modeled detection performance.

Conclusions:

The presented methodology based on ACR phantom measurements extends current possibilities for the assessment of CT image quality under the complex resolution and noise characteristics exhibited with statistical and iterative reconstruction algorithms. The findings further suggest that MBIR can potentially make better use of the projections data to reduce CT dose by approximately a factor of 2. Alternatively, if the dose held unchanged, it can improve image quality by different levels for different tasks.