bluuebunny/crossref_metadata_2025 huggingface dataset:
Realizability in Turbulence Modelling for Turbomachinery CFD
Authors: Moore Joan G. , Moore John
Published: December 2014

It is obvious that the Reynolds normal stresses uu¯ should always be positive in all directions, i.e. the computed turbulence stresses should be realizable. However, the commonly used two-equation turbulence models do not incorporate realizability. They take the turbulent viscosity as cμk2/ε with cμ a constant, and frequently generate negative normal stresses far from walls in the nominally inviscid sections of turbomachinery flows. Pressure gradients due to leading edge stagnation and blade turning create an inviscid strain field. These strains cause the calculation of negative normal stresses over significant portions of the flow field. The result can be erroneous increases in turbulence kinetic energy upstream of the leading edge by a factor of ten or more. This erroneous turbulence is then convected around the blade and through the blade row, significantly affecting the computed boundary layer development and profile losses.

Frequently the problem of overproduction is avoided by using artificially high values of the dissipation, ε, at the inlet. But this incorrect procedure is not needed when realizability is incorporated in the turbulence model.

The paper reviews some methods and models which ensure realizability in two-equation turbulence models. The extent of the problem and its solution are illustrated with examples from compressor and turbine cascades.
Prediction of By-Pass Transition by Means of a Turbulence Weighting Factor: Part I — Theory and Validation
Authors: Steelant J. , Dick E.
Published: December 2014

The classical intermittency factor γ for quantifying transition is redefined and extended to enable the modelling of by-pass transition. Therefore, a new parameter, the turbulence weighting factor τ, is introduced to cover both the physics of freestream turbulence diffusion and of turbulent spots. A transport equation is presented for the τ-factor including convective, diffusive, production and sink terms. In combination with the conditioned Navier-Stokes equations, this leads to improvements in the calculation of flow characteristics in both the transitional layer and the freestream.
Film Cooling Over a Concave Surface Through a Row of Expanded Holes
Authors: Chen Ping-Hei , Ding Pei-Pei , Hung Min-Sheng , Shih Po-Chou
Published: December 2014

This paper presents heat transfer coefficient and film cooling effectiveness measurements over a constant curvature concave surface. The coolant flow is ejected into the mainstream through a row of either simple holes or forward-expanded holes maintained at a streamwise injection angle (γ) of 35°. A transient liquid crystal thermography was employed to measure both the local heat transfer coefficient and film cooling effectiveness over the film-cooled concave test piece. With a pitch-to-diameter ratio (P/d) of 3, each forward-expanded injection hole has an expanded angle of 8° at the exit plane. In current study, the effect of blowing ratio (M) on film cooling performance was also investigated by varying the blowing ratio range from 0.5 to 1.5. Measurements were performed at mainstream Reynolds number (Red) of 2000 with turbulence intensity (Tu) of 2%, and coolant-to-mainstream density ratio (ρc/ρm) of 1.05. The curvature strength (2r/d) of test piece is 86.5. Comparisons were made with baseline cases of concave surface test piece with simple hole configuration done in prior studies. For forward-expanded hole configuration, measured results showed that both the laterally averaged heat transfer coefficient and film cooling effectiveness increase with increasing blowing ratio downstream of X/d = 10. A better film protection effect can be observed at M = 0.5 since coolant flows ejected at this blowing ratio might stay closer to the concave surface than other blowing ratios in present tested range for both hole configurations. As far as the hole shape is concerned, the forward-expanded hole injection provides better surface protection than the simple hole injection.
Film Cooling Effectiveness for Short Film Cooling Holes Fed by a Narrow Plenum
Authors: Hale C. A. , Plesniak M. W. , Ramadhyani S.
Published: December 2014

The adiabatic, steady-state liquid crystal technique was used to measure surface adiabatic film cooling effectiveness values in the near-hole region (X / D < 10). A parametric study was conducted for a single row of short holes (L / D ≤ 3) fed by a narrow plenum (H / D = 1). Film cooling effectiveness values are presented and compared for various L / D ratios (0.66 to 3.0), three different blowing ratios (0.5, 1.0, and 1.5), two different plenum feed configurations (co-flow and counter flow), and two different injection angles (35° and 90°). Injection hole geometery and plenum feed direction were found to significantly affect short hole film cooling performance. Under certain conditions, comparable or improved coverage was achieved with 90° holes as with 35° holes. This result has important implications for manufacturing of thin-walled film-cooled blades or vanes.
Measurement of Eddy Diffusivity of Momentum in Film Cooling Flows With Streamwise Injection
Authors: Kaszeta Richard W. , Simon Terrence W.
Published: December 2014

Measurements of mean velocity and turbulent shear stress are presented for the mixing region of a film cooling situation in which the coolant is streamwise injected with an injection angle of 35°. Measurements are performed using triple-sensor anemometry so that all three instantaneous velocity components are documented. The freestream turbulence intensity level is 12%, the ratio of the integral length scale to injection hole diameter is 4.0, the coolant-to-mainstream momentum flux ratio is 1.0, and the density ratio is unity. From these measurements, values for the eddy diffusivities of momentum in the lateral and wall-normal directions are calculated. Additionally, calculated values of the ratio of eddy diffusivity in the spanwise direction to eddy diffusivity in the wall-normal direction are presented, which provide documentation of the anisotropy of turbulent transport in this film cooling flow.
Prediction of Transitional Heat Transfer Characteristics of Wake-Affected Boundary Layers
Authors: Kim Kyoungjin , Crawford Michael E.
Published: December 2014

The presence of wake-passing in the gas turbine environment significantly modifies the heat transfer characteristics on the downstream blade surface by causing wake-induced transition. In this study, time-dependent boundary layer calculations were carried out using a model for wake-induced transition based on a prescribed time-dependent intermittent function. The model is determined from the well-known turbulent spot propagation theory in a time-space diagram and from experimental evidence in the ensemble-averaged sense. Time-averaged heat transfer distributions are evaluated and compared with experimental results for different flow and wake-generating conditions over a flat plate. Comparison showed that the present time-dependent calculations yield more accurate results than existing steady superposition models.
Film Cooling Effectiveness in the Showerhead Region of a Gas Turbine Vane: Part I — Stagnation Region and Near-Pressure Side
Authors: Polanka Marc D. , Witteveld Virginia C. , Bogard David G.
Published: December 2014

An experimental program to study film cooling adiabatic effectiveness in the showerhead region of a turbine vane was completed. A typical first stage turbine stator vane was modeled in a nine-times scale, low speed test facility. The leading edge showerhead consisted of a row of holes at the stagnation point of the vane as well as two rows on the pressure surface and three rows on the suction surface. Film cooling performance on the pressure side of the showerhead is described in this paper. Experiments were conducted for a number of blowing ratios, from 0.3 to 2.9, and at a density ratio of nominally 1.8. The impact of high mainstream turbulence was studied by comparing performance at turbulence levels of 0.5% and 22%. The sensitivity to the stagnation line position was also investigated. The approaching stagnation line was positioned either directly on the stagnation row of holes or just to the suction side of that row. With the stagnation line directly on the stagnation row of holes at low turbulence, the direction of the coolant jets was observed to vary along the span of the airfoil. At high turbulence, this same effect did not occur. Moreover, at the high mainstream turbulence level, the coolant from the entire stagnation row of holes seemed to be spread more evenly throughout the stagnation region. At high blowing ratios, this resulted in higher effectiveness values in the stagnation region. Farther downstream, the high mainstream turbulence reduced the effectiveness at all blowing ratios.
Passive Control of Combustion Instability in Lean Premixed Combustors
Authors: Steele Robert C. , Cowell Luke H. , Cannon Steven M. , Smith Clifford E.
Published: December 2014

A Solar fuel injector that provides lean premixed combustion conditions has been studied in a combined experimental and numerical investigation. Lean premixed conditions can be accompanied by excessive combustion driven pressure oscillations which must be eliminated before the release of a final combustor design. In order to eliminate the pressure oscillations the location of fuel injection was parametrically evaluated to determine a stable configuration. It was observed that small axial changes in the position of the fuel spokes within the premix duct of the fuel injector had a significant positive effect on decoupling the excitation of the natural acoustic modes of the combustion system.

In order to further understand the phenomenon, a time-accurate 2D CFD analysis was performed. 2D analysis was first calibrated using 3D steady-state CFD computations of the premixer in order to model the radial distribution of velocities in the pre mixer caused by non-uniform inlet conditions and swirling flow. 2D time-accurate calculations were then performed on the baseline configuration. The calculations captured the coupling of heat release with the combustor acoustics, which resulted in excessive pressure oscillations. When the axial location of the fuel injection was moved, the CFD analysis accurately captured the fuel time lag to the flame-front, and qualitatively matched the experimental findings.
Extended Liquid-Phase Oxidation of Aviation Fuels
Authors: Balster Lori M. , Balster Walter J. , Jones E. Grant
Published: December 2014

Liquid-phase oxidation of two jet fuels classified as hydro-treated and straight-run (without dissolved metals) is studied at 185°C by measuring the depletion of dissolved oxygen in an isothermal, high-pressure flowing system. The goal is to simulate some of the effects of fuel recirculation by studying changes in oxidation that occur during the course of reaction. Recirculation of fuel is used in modem aircraft to optimize the ability of the fuel to dissipate heat from component systems. Following extended oxidation (prestressing), hydrotreated fuel oxidizes more rapidly than in its neat form resulting, in part, from formation of catalytic oxidation products such as hydroperoxides and depletion of synthetic primary antioxidants. In contrast, the straight-run fuel oxidizes more slowly following prestressing; this effect is ascribed to the formation of efficient secondary antioxidants and to depletion of radical initiators. Results are discussed in terms of changes in the distribution of primary and secondary antioxidants and their effect on subsequent oxidation and the thermal stability of recirculated fuel.
Hydrogen Donors: Thermal Stabilizers for JP-8+100 at High Temperatures
Authors: Corporan Edwin , Minus Donald K.
Published: December 2014

The effectiveness of hydrogen donor compounds as additives to reduce pyrolytic deposition in JP-8+100 at high temperatures was assessed. Decalin and 1,2,3,4 tetrahydroquinoline (THQ) were added to JP-8+100 at 0.5% (decalin only), 1.0 and 2.5% w/w concentrations and tested in a flow reactor at a fuel exit temperature of 600°C at 5.2 MPa. Measurements of carbon deposits along the tube and gas chromatography/mass spectrometry (GC/MS) analysis of the stressed and unstressed liquid fuel were used to assess effectiveness of the additive, and the degree of fuel decomposition. Additionally, liquid-to-gas conversion was determined, and the composition of the gas was determined via GC. Experimental results show significant reductions in pyrolytic deposition in JP-8+100 with the additives relative to the baseline fuel. Tests with decalin showed negligible effects on thermal oxidative deposits, while THQ produced significant increases in thermal oxidative deposits. The effects of the additives on fuel thermal decomposition and conversion rates are also discussed.
Validation of the Booster Bleed Valve Control Logic in the New BR715 Jet Engine
Authors: Peitsch Dieter , Fiola Roland , Brodmuehler Rene , Nielsen Annette
Published: December 2014

The subject of this paper is the validation of the newly developed booster bleed valve control logic, which has been implemented into the new BR715 turbo fan jet engine.

The booster compressor is protected from surges in the low power regime as well as during transient operation by opening a booster bleed valve. This bleed valve is situated just after the booster compressor and passes bleed air into the bypass duct, hence unloading the booster compressor in critical operational conditions. The BR715 jet engine takes advantage of a newly developed logic driving this valve. Monitoring input parameters such as spool and flight speeds as well as altitude, the combined steady state and transient logic provides the capability of appropriately positioning the valve. This ensures maintaining an optimum performance of the engine throughout the whole operating range. Furthermore the logic allows for reaction on special requirements such as surge events.

During testing for certification of this engine, extensive handling tests have been performed. The performance of the logic was investigated in detail and the results are documented within this paper. They prove the logic to be working very successfully. The booster compressor is totally protected from surge in the low power regime during steady state conditions. For transient operation, especially during rapid decelerations as well as during bodie manoeuvres of the engine, the core logic for the transient modulation showed extremely effective behaviour.

The various schedules inside the logic were partially varied for testing. This paper comprises this development process and each table’s contribution to the booster compressor’s behaviour is explained in detail.
Emergence of Recuperated Gas Turbines for Power Generation
Authors: McDonald Colin F.
Published: December 2014

In the emerging deployment of microturbines (25–75Kw), a recuperator is mandatory to achieve thermal efficiencies of 30 percent and higher, this being important if they are to successfully penentrate the market currently dominated by Diesel generator sets. This will be the first application of gas turbines for electrical power generation, where recuperators will be used in significant quantities. The experience gained with these machines will give users’ confidence that recuperated engines will meet performance and reliability goals. The latter point is particularly important, since recuperated gas turbines have not been widely deployed for power generation, and early variants were a disappointment. Recuperator technology transfer to larger engines will see the introduction of advanced heat exchanged industrial gas turbines for power generation in the 3–15 Mw range.

After many decades of development, existing recuperators of both primary surface and plate-fin types, have demonstrated acceptable thermal performance and integrity in the cyclic gas turbine environment, but their capital costs are high.

A near-term challenge to recuperator design and manufacturing engineers is to establish lower cost metallic heat exchangers that can be manufactured using high volume production methods. A longer term goal will be the development and utilization of a ceramic recuperator, since this is the key component to realize the full performance potential of very small and medium size gas turbines.
Maximizing Multistage Turbine Efficiency by Optimizing Hub and Shroud Shapes and Inlet and Exit Conditions of Each Blade Row
Authors: Petrovic Milan V. , Dulikravich George S. , Martin Thomas J.
Published: December 2014

By matching a well established fast through-flow analysis code and an efficient optimization algorithm, a new design system has been developed which optimizes hub and shroud geometry and inlet and exit flow-field parameters for each blade row of a multistage axial flow turbine. The compressible steady state inviscid through-flow code with high fidelity loss and mixing models, based on stream function method and finite element solution procedure, is suitable for fast and accurate flow calculation and performance prediction of multistage axial flow turbines at design and significant off-design conditions. A general-purpose hybrid constrained optimization package has been developed that includes the following modules: genetic algorithm, simulated annealing, modified Nelder-Mead method, sequential quadratic programming, and Davidon-Fletcher-Powell gradient search algorithm. The optimizer performs automatic switching among the modules each time when the local minimum is detected thus offering a robust and versatile tool for constrained multidisciplinary optimization. An analysis of the loss correlations was made to find parameters that have influence on the turbine performance. By varying seventeen variables per each turbine stage it is possible to find an optimal radial distribution of flow parameters at the inlet and outlet of every blade row. Simultaneously, an optimized meridional flow path is found that is defined by the optimized shape of the hub and shroud. The design system has been demonstrated using an example of a single stage transonic axial gas turbine, although the method is directly applicable to multistage turbine optimization. The comparison of computed performance of initial and optimized design shows significant improvement in the turbine efficiency at design and off-design conditions. The entire design optimization process is feasible on a typical single-processor workstation.
Feedstock Blending in Indirectly Heated Gasifier/Liquifiers
Authors: Green Alex E. S. , Schaefer Greg P.
Published: December 2014

Co-utilization of solid fuels with combustion turbines (CTs) can be accomplished by blending feedstocks in indirectly heated gasifier/liquifiers (IHG/L), Blending could improve the quality and yields of gaseous and liquid fuel outputs and, with gas clean-up (GCU) or liquid distillation, serve valuable societal functions. Gas yields vs. temperature, time and other variables have been obtained using batch fed and continuous fed laboratory scale IHG/Ls using particle sizes suitable for commercial systems. The rates of solids to gas/liquid conversion are mainly dependent upon the heat transfer and diffusion coefficients of the biomass rather than the rate constants for chemical decomposition. Phenomenological engineering formulas are developed for use with biomass that can be treated as a blend of hemicellulose, cellulose and lignin. The main immediate goals are to develop: 1) laboratory scale process development units (PDUs) that can help anticipate results with commercial IHG/L systems, 2) predictive models for estimating gaseous, liquid and char yields when various blends of biomass and other domestic fuels are processed in IHG/Ls and 3) applications of IHG-GCU-CT systems that could drive technology development during periods of low oil and natural gas prices.
Operating Experience of the GT13E2 at Kawasaki Gas Turbine Research Center
Authors: Fujii Tatsuo , Uenaka Takakazu , Masuo Hitoshi
Published: December 2014

The first Kawasaki-ABB GT13E2 gas turbine began operating at Kawasaki Gas Turbine Research Center (KGRC) in Sodegaura city, Japan in January 1994. This facility is a simple-cycle power station and is operated in DSS (Daily Start and Stop) operation mode as a peaking unit, and its output electricity is delivered to Tokyo Electric Power Company (TEPCO).

The GT13E2 gas turbine at KGRC was manufactured jointly by Kawasaki Heavy Industries (KHI) and Asea Brown Boveri (ABB). KHI and ABB have a joint test program with this facility to research for high reliability, high performance and low emission for the GT13E2 and future gas turbines.

The performance of the KGRC GT13E2 has been monitored continuously. It was found from these monitored data that the thermal efficiency has been maintained at a high level and could be recovered by compressor washing when the compressor was fouled.

Several factors which influence NOx emissions were studied on the gas turbine, and it was found that atmospheric humidity has a major influence on NOx emissions. Also other factor such as the position of the variable inlet guide vanes (VIGV) and fuel gas flow through each burner of the combustor were adjusted to reduce NOx emission. As a result, NOx emission from the KGRC GT13E2 has been maintained at a very low level.

Reliability, availability and maintainability (RAM) has been evaluated by Operational Reliability Analysis Program (ORAP®) of Strategic Power Systems, Inc. (SPS) in order to identify and improve RAM performance of the GT13E2 at KGRC. These analyses made it clear what kind of outage had an impact on the reliability, availability and starting reliability of the KGRC GT13E2 and appropriate actions have increased the starting reliability.

This paper describes operating experiences of the KGRC GT13E2 including performance, emissions and RAM performance.
Seawater Contamination of a Gas Turbine Lube Oil System in the U.S. Navy
Authors: Russom Dennis M.
Published: December 2014

The Ship Service Gas Turbine Generator sets (SSGTGs) on the U.S. Navy’s DDG-51 Class ships have experienced several gas turbine engine failures resulting from seawater contamination of the lube oil. The seawater enters the turbine lube oil system after a corrosion related failure of the lube oil cooler. This paper examines the system design, failure mechanism, and consequence of the failure. It also discusses maintenance actions intended to minimize the possibility of cooler failures, methods that have been used to clean up contaminated systems and alternate cooler designs that are being considered for backfit.
Characterization of Deterministic Correlations for a Turbine Stage: Part 1 — Time-Averaged Flow Analysis
Authors: Bardoux Fabien , Leboeuf Francis , Dano Cédric , Toussaint Clément
Published: December 2014

This paper analyses the flow in a transonic turbine stage, using time-dependent numerical results.

Unsteady blade-row interaction has repercussions on the time-averaged flow, which are represented by the so-called “deterministic correlations”. These correlations appear in the system of equations governing the time-averaged flow; they can be divided into four types with different physical meanings.

Time-dependent results enable direct computation of these correlations in both rotor and stator frames of reference. The computed deterministic correlations are analysed in the paper, in order to bind them to physical phenomena and to evaluate their influence on the time-averaged flow field.

This analysis is also intended to help assess the shortcomings of simple mixing-plane methods and more complex approaches using deterministic correlation models. While the first part focuses on one particular type of deterministic correlation, the so-called “spatial correlation”, the second part attempts a more detailed analysis of time-dependent results and gives some clues to the orders of magnitude of the four types of deterministic correlation. The conclusions should be taken with caution; they may partly depend on the present turbine configuration with a specified structure of unsteadiness and on the present turbulence model.
Characterization of Deterministic Correlations for a Turbine Stage: Part 2 — Unsteady Flow Analysis
Authors: Bardoux Fabien , Leboeuf Francis , Dano Cédric , Toussaint Clément
Published: December 2014

The first part of this paper analysed the time-averaged flow in a transonic single stage turbine. In this second part, we analyse the three-dimensional unsteady flow and temporal correlations in the rotor frame of reference. Two main conclusions are deduced from the comparison of each correlation. First, all correlations have the same order of magnitude. This is an important conclusion for models that handle the interaction between blade rows, because the temporal correlations are usually neglected. Second, these correlations occur in complementary localizations. In particular, the largest values of spatial deterministic correlations is located between the nozzle trailing edge and the rotor leading edge, as a consequence of nozzle wakes. Conversely, temporal deterministic correlations are located within the rotor blade row.

We also establish that entropy accumulations in the stator wake near the end-wall regions generate high fluctuations of the rotor passage vortices. Such a phenomenon may have great repercussions on the radial loss distribution in the stage.
Development of the Ceramic Gas Turbine Engine System (CGT301)
Authors: Sakida Takeshi , Tanaka Shinya , Mikami Takao , Tatsuzawa Masashi , Taoka Tomoki
Published: December 2014

The CGT301 ceramic gas turbine has been developed under a contract from NEDO as a part of the New Sunshine Program of MITI since 1988 to 1998.

The CGT301 is a recuperated, single-shaft ceramic gas turbine. Ceramic parts are used in the hot section of the engine, such as turbine blades, nozzle vanes, combustion liners and so on. As a primary feature of this turbine, the rotors are composed of ceramic blades inserted into metallic disks (“hybrid rotor”) for the future applicability to the large gas turbine.

The R & D program consists of three phases, the model metal gas turbine, the primary type ceramic gas turbine and the pilot ceramic gas turbine. The pilot ceramic gas turbine showed etable operation at TIT of 1,350°C.

This paper presents the progress in the development of the pilot ceramic gas turbine of CGT301.
A Comparative Exergy Analysis of Advanced Power Cycles Using Biomass Fuel
Authors: Codeceira Neto Alcides , Pilidis Pericles
Published: December 2014

This paper describes a design point study of different power generation systems using the gasification of sugar cane bagasse, which produces a low calorific value fuel.

The biomass gasification is viewed as a process of drying the solid fuel and heating it up before the gasification reactions take place. The process is represented by equilibrium conditions. Varying pressure, temperature and feed composition in the gasifier controls the fuel gas composition.

Five alternative arrangements of an integrated gasification combined cycle (IGCC) power plant have been analysed using the exergy method. These alternatives comprise a combined gas / steam cycle using a simple gas turbine and also a reheat gas turbine, a combined gas / air cycle using a simple gas turbine and also a reheat gas turbine, and a combined gas / air / freon cycle using a reheat gas turbine.

The combined gas / steam cycles are more efficient rather than the combined gas / air cycles. Using a reheat gas turbine at the topping cycle of the combined cycles analysed contribute to increase the overall plant exergetic efficiency.

The exergy analysis has been carried out along with the performance assessment of power plants and takes into account the irreversibility of their components and the exhaust losses. The gasifier is the component of the power plant that destroys maximum exergy.

Three computer codes have been developed. One of them has the ability of simulating the thermodynamic properties of the low calorific value fuel in the gasification process and the other two are related to the performance analysis of the different power cycles using the exergy method.

The production of energy from the gasification of sugar cane bagasse has been of increasing importance to the Brazilian energetic matrix. This paper has been focused on the GEOPHILES - αlfa Programme, a project to train Latin America engineers on biomass gasification for power generation. The Commission of Energy of the European Community has supported this project.
Local Heat/Mass Transfer Measurements in a Rectangular Duct With Discrete Ribs
Authors: Cho H. H. , Wu S. J. , Kwon H. J.
Published: December 2014

The influence of the arrangement and the length of discrete ribs on heat/mass transfer and friction loss is investigated. The mass transfer experiments are conducted to obtain detailed local heat/mass transfer coefficients on the duct wall. The aspect ratio (width/height) of the duct is 2.04 and the rib height is one tenth of the duct height, such that the ratio of rib height to hydraulic diameter is 0.0743. The ratio of rib-to-rib distance to rib height is 10. The discrete ribs are made by dividing continuous ribs into 2, 3 and 5 pieces and attached periodically to the top and bottom surfaces of the duct with a parallel orientation. After examining the effects of rib angle of attack (α) for continuous ribs, the combined effects of the rib angle and the length of discrete ribs on heat/mass transfer on the duct wall are investigated for α = 90° and 45°. As the number of broken pieces of a rib increases, the more disturbed flows affect greatly heat/mass transfer and increase the uniformity of heat/mass transfer distributions. For α = 90°, the heat/mass transfer enhancement with the discrete ribs is remarkable, so that the discrete ribs augment up to 27% of the average heat/mass transfer coefficients compared with the transverse continuous rib. However, the heat/mass transfer performances of the discrete ribs are slightly higher than that of the transverse continuous rib due to the accompanied high friction loss penalty. For α = 45°, the average heat/mass transfer coefficients are decreased slightly with the discrete ribs, and the heat/mass transfer performances of the angled discrete ribs are also decreased even though the friction losses are lower.
Blade Heat Transfer Measurements and Predictions in a Transonic Turbine Cascade
Authors: Giel P. W. , Van Fossen G. J. , Boyle R. J. , Thurman D. R. , Civinskas K. C.
Published: December 2014

Detailed heat transfer measurementa and predictions are given for a turbine rotor with 136° of turning and an axial chord of 12.7 cm. Data were obtained for inlet Reynolds numbers of 0.5 and 1.0 × 106, for isentropic exit Mach numbers of 1.0 and 1.3, and for inlet turbulence intensities of 0.25% and 7.0%. Measurements were made in a linear cascade having a highly three-dimensional flow field resulting from thick inlet boundary layers. The purpose of the work is to provide benchmark quality data for three-dimensional CFD code and model verification. Data were obtained by a steady-state technique using a heated, isothermal blade. Heat fluxes were determined from a calibrated resistance layer in conjunction with a surface temperature measured by calibrated liquid crystals. The results show the effects of strong secondary vortical flows, laminar-to-turbulent transition, shock impingement, and increased inlet turbulence on the surface heat transfer.
Engine Condition Assessment Technology
Authors: Taylor Barry , Pagotto Ivano , Stewart Jeff
Published: December 2014

The OEM, using a set of planned maintenance schedules that are based upon running hours or inspections, has traditionally formulated gas turbine maintenance practice. This maintenance concept has been reasonably successful, but it fails to take into account the introduction of new technologies than can provide the operator with a more meaningful insight into the condition of the turbine, perhaps even in a prognostic manner.

The application of computer based technology to gas turbine condition monitoring can provide a significant reduction in maintenance costs. At the same time, condition-monitoring technology can provide an improvement in reliability and availability by extending the maintenance intervals and reducing the number of unplanned outages.

This paper will discuss the introduction of an integrated approach to gas turbine control and engine condition assessment. This integrated approach enables the control to turn engine data into useful information and knowledge that assists the operator with trouble shooting and maintenance condition assessments thus lowering the overall engine maintenance costs.
Effects of Orientation Angles on Film Cooling Over a Flat Plate: Boundary Layer Temperature Distributions and Adiabatic Film Cooling Effectiveness
Authors: Jung In Sung , Lee Joon Sik
Published: December 2014

Presented are experimental results describing the effects of orientation angle of film cooling holes on boundary layer temperature distributions and film cooling effectiveness. Film flow data were obtained from a row of five film cooling holes on a flat test plate. The inclination angle of the hole was fixed at 35° and four orientation angles of 0°, 30°, 60°, and 90° were investigated. The surveyed velocity ratios were 0.5, 1.0, and 2.0. The boundary layer temperature distributions were measured at three downstream locations using turn platinum wire. Detailed adiabatic film cooling effectiveness distributions were measured using thermochromic liquid crystal.

Results show that the increased lateral momentum in the case of large orientation angle injection strongly affects boundary layer temperature distributions. Temperature distribution characteristics are, in general, explained in the context of the interactions between injectant and free-stream fluid and between injectants issued from adjacent holes. The adiabatic film cooling effectiveness distributions are discussed in connection with the boundary layer temperature distributions. Spanwise-averaged effectiveness distributions and space-averaged effectiveness distributions are also presented with respect to the velocity ratios and the orientation angles.
Mist/Steam Cooling in a Heated Horizontal Tube: Part 1 — Experimental System
Authors: Guo T. , Wang T. , Gaddis J. L.
Published: December 2014

To significantly improve the vane cooling for the future generation of Advanced Turbine Systems (ATS), a fundamental experimental program has been developed to study the heat transfer mechanisms of mist/steam cooling under highly superheated wall temperatures. The mist/steam mixture was obtained by blending fine water droplets (3–15 μm in diameter) with the saturated steam at 1.5 bars. Two mist generation systems were tested by using the pressure atomizer and the steam-assisted pneumatic atomizer, respectively. The test section, heated directly by a DC power supply, consisted of a thin-walled (−0.9 mm), circular stainless steel tube with an ID of 20 mm and 203 mm in length. Droplet size and distribution were measured by a Phase Doppler Particle Analyzer (PDPA) system through view ports grafted at the inlet and the outlet of the test section. Mist transportation and droplet dynamics were studied in addition to the heat transfer measurements. The experiment was conducted with steam Reynolds numbers ranging from 10,000 to 35,000, wall superheat up to 300°C, and droplet mass ratios ranging from 1–6%.
On the Development and Application of the FRAP® (Fast-Response Aerodynamic Probe) System for Turbomachines: Part 1 — The Measurement System
Authors: Kupferschmied Peter , Köppel Pascal , Roduner Christian , Gyarmathy George
Published: December 2014

This contribution gives an overview of the current state, performance and limitations of the fast-response aerodynamic probe measurement system (FRAP® System) developed at the Turbomachinery Lab of the ETH Zurich. In particular, the following topics are addressed:

• Probe technology: Miniature probes with tip diameter ranging from 0.84 to 1.80 mm (1-sensor and 3-sensor probes respectively) have been developed. New technologies derived from microelectronics and micromechanics have been used to achieve an adequate packaging of the microsensor chips used. Both the sensor packaging and the sensor calibration (time-independent and time-dependent) are crucial issues for the DC accuracy of any measurement.

• Aerodynamic probe calibration: The methods used for the sensor calibration and the aerodynamic probe calibration, the pertinent automated test facilities and the processing of the output data are briefly presented. Since these miniature probes are also capable of measuring the mean flow temperature, aspects related to the recovery factor and the self-heating of the probe tip are treated and some recommendations related to sensor selection are given.

• Measurement system and data evaluation: The early measurement chain described in Gossweiler, Kupferschmied and Gyarmathy 1995 has evolved into the FRAP® System. This automatic system incorporates dedicated measurement concepts for a higher accuracy and a more efficient operation in terms of time and failures. An overview of the data evaluation process is given.

The FRAP® System has been tested in real-sized turbomachines under industrial conditions within the temperature limits of 140°C imposed by the sensor technology (axial-flow turbofan compressor, axial-flow turbine, centrifugal compressor). These applications confirmed the potential of the system and encouraged its further development. Now, the system is routinely used in the facilities of the Turbomachinery Lab and in occasional measurement campaigns in other laboratories.

Part 2 of this contribution (Roduner et al.) will focus on the application of the FRAP® System in a transonic centri fugal compressor of the ETH Turbomachinery Laboratory, while Part 3 (Köppel et al.) treats more sophisticated data analysis methods.
Effect of Two-Scale Roughness on Boundary Layer Transition Over a Heated Flat Plate: Part 1 — Surface Heat Transfer
Authors: Pinson Mark W. , Wang Ting
Published: December 2014

An experimental study was conducted to investigate surface heat transfer and boundary layer development associated with flow over a flat test surface covered with two roughness scales. Two-scale roughness was used because in-service aeroengines commonly display larger roughness concentrated at the leading edge with smaller roughness distributed downstream. The first scale, covering up to the first 5 cm of the test surface, was in the form of a sandpaper strip, an aluminum strip, or a cylinder. The second roughness scale covered the remainder of the test surface (2 m) in the form of sandpaper or a smooth surface. In part 1, the surface heat transfer results are examined. Even though the roughness scales were hydraulically smooth, they induced significantly earlier transition onset, with the two-dimensional roughness causing earlier transition than three-dimensional roughness. All of the rough/smooth cases unexpectedly triggered earlier transition than rough/rough cases. This indicated that the scale of the step-change at the joint between two roughness scales was predominant over the downstream roughness on inducing early transition. Reducing the overall height of the step change was shown to have a greater effect on transition than the specific geometry of the roughness scale.
Numerical Prediction of Mainstream Pressure Gradient Effects in Film Cooling
Authors: York William D. , Leylek James H.
Published: December 2014

A documented, systematic, computational methodology is applied to singularly investigate the effects of mainstream pressure gradients on film cooling over a flat surface for realistic gas turbine parameters. Key aspects of the study include: (1) validation of the ability of computational fluid dynamics to simulate film cooling in regions of mainstream pressure gradients, accomplished through the isolation of this parameter and the careful modeling of a published experimental study; (2) documentation of the effects of the applied pressure gradient on film cooling adiabatic effectiveness, as compared to the zero-pressure gradient case; and (3) detailed discussion of the pertinent physical mechanisms involved, with appropriate flowfield results. The imposed pressure gradient is typical of the suction surface of a gas turbine airfoil, with a strong favorable pressure gradient (the acceleration parameter was K = 1.5×10−6 at injection) transitioning to a mild adverse pressure gradient region beyond 30 diameters downstream. A single row of cylindrical film-cooling holes had an injection angle of 35°, with hole length-to-diameter ratio of 4.0 and a lateral spacing of 3.0 diameters. The simulated mass flux ratios were M = 0.6, 1.0, and 1.5, and the density ratio was held constant at 1.6. Solutions were obtained using a multi-block, multi-topology grid and a pressure-correction based, fully-implicit Navier-Stokes solver. A “realizeable” k-ε turbulence model, which eliminates the documented unrealistic turbulence production of the standard k-ε model in regions of large flow strain, was employed to obtain practical results economically. The applied pressure gradient resulted in a small advantage in center-line effectiveness, while laterally averaged effectiveness was slightly lower as compared to the zero-pressure gradient reference case. The results of this study demonstrate the ability of the applied computational methodology to accurately model film cooling in the presence of mainstream pressure gradients and resolve one of the key fundamental issues in turbine airfoil film cooling.
Self-Sensing in Fault Tolerant Magnetic Bearings
Authors: Montie Dominick , Maslen Eric
Published: December 2014

Several schemes have recently been proposed for achieving either fault tolerance or self-sensing in magnetic bearings. The present work describes the fundamental connection between ability to actuate and ability to sense in a partially failed magnetic bearing system. This relationship is then exploited to construct a self-sensing scheme which operates in the presence of detectable actuator or amplifier faults. Such an approach is advantageous in fault tolerant systems because it reduces or eliminates the need to address potential independent failure mechanisms in sensors and actuators.

Based on a model reference parameter estimation mechanism, the self-sensing scheme is shown to provide acceptable position measurement accuracy and bandwidth under various actuator/amplifier faults which are actuator tolerable. Estimates of increase in noise floor and loss of bandwidth under fault conditions are provided. The issue of estimator convergence under fault conditions is examined in detail with comments on implementation complexity arising from scheduling convergence control on fault state.
A Three-Dimensional Coupled Internal/External Simulation of a Film-Cooled Turbine Vane
Authors: Heidmann James D. , Rigby David L. , Ameri Ali A.
Published: December 2014

A three-dimensional Navier-Stokes simulation has been performed for a realistic film-cooled turbine vane using the LeRC-HT code. The simulation includes the flow regions inside the coolant plena and film cooling holes in addition to the external flow. The vane is the subject of an upcoming NASA Lewis Research Center experiment and has both circular cross-section and shaped film cooling holes. This complex geometry is modeled using a multi-block grid which accurately discretizes the actual vane geometry including shaped holes. The simulation matches operating conditions for the planned experiment and assumes periodicity in the spanwise direction on the scale of one pitch of the film cooling hole pattern. Two computations were performed for different isothermal wall temperatures, allowing independent determination of heat transfer coefficients and film effectiveness values. The results indicate separate localized regions of high heat flux in the showerhead region due to low film effectiveness and high heat transfer coefficient values, while the shaped holes provide a reduction in heat flux through both parameters. Hole exit data indicate rather simple skewed profiles for the round holes, but complex profiles for the shaped holes with mass fluxes skewed strongly toward their leading edges.
Continuous Fiber Ceramic Matrix Composites for Gas Turbine Applications
Authors: Szweda A. , Easler T. E. , Petrak D. R. , Black V. A.
Published: December 2014

Continuous fiber ceramic composites (CFCCs) are being considered as high temperature structural materials for gas turbine applications due to their high temperature capability, toughness, and durability. Polymer impregnation and pyrolysis (PIP) derived CFCCs are one class of these materials that can be fabricated using widely available polymer composite processing methods. This paper will discuss the general PIP fabrication process and thermo-mechanical properties of these materials, and show examples of complex prototype gas turbine components that have been fabricated and evaluated.
Unsteady Boundary Layer Transition on a High Pressure Turbine Rotor Blade
Authors: Tiedemann Maik , Kost Friedrich
Published: December 2014

This investigation is aimed at the experimental determination of the location, the extent, and the modes of the laminar-to-turbulent transition processes in the boundary layers of a high pressure turbine rotor blade. The results are based on time-resolved, qualitative wall shear stress data which was derived from surface hotfilm measurements. The tests were conducted in the “Windtunnel for Rotating Cascades” of the DLR in Göttingen. For the evaluation of the influence of passing wakes and shocks on the unsteady boundary layer transition, a test with undisturbed rotor inlet flow was conducted in addition to full stage tests.

Two different transition modes led to a periodic-unsteady, multi-moded transition on the suction side. In between two wakes, transition started in the bypass mode and terminated as separated-flow transition. Underneath the wakes, plain bypass transition occurred. The weak periodic boundary layer features on the pressure side indicate that this surface was not significantly affected by passing wakes or shocks.

The acquired data reveals that the periodically disturbed suction side boundary layer is less susceptible to bubble bursting than the undisturbed flowfield. Thus, these blades may be subjected to higher aerodynamic loads. Accordingly, as in low pressure turbines, the unsteady effects in high pressure turbines may allow for a reduction of the number of rotor blades, with respect to the original design.
Turbine Nozzle Film Cooling Study Using the Pressure Sensitive Paint (PSP) Technique
Authors: Zhang Luzeng , Baltz Michael , Pudupatty Ram , Fox Michael
Published: December 2014

The use of pressure sensitive paint (PSP) to measure film cooling effectiveness on a turbine nozzle surface was demonstrated in a high speed wind tunnel. Film cooling effectiveness was measured from a single row of holes located on a turbine vane suction surface with a shaped exit. Nitrogen gas was used to simulate film cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Three blowing ratios were studied for each of the five freestream conditions: a reference condition, a reduced and an increased Reynolds number condition, and a reduced and an increased Mach number condition. The freestream turbulence intensity was kept at 12.0% for all the tests. The PSP was calibrated at various temperatures and pressures to obtain better accuracy before being applied to the airfoil surface. The film effectiveness increased with blowing ratio for all the freestream conditions. The effects of secondary flow and freestream Mach number and Reynolds number on turbine nozzle suction surface film cooling are also discussed.