bluuebunny/crossref_metadata_2025 huggingface dataset:
Communicating flood forecast uncertainty under operational circumstances
Authors: Cullmann J. , Krausse T. , Philipp A.
Published: October 2009

Required model input data are not always completely available and model structures are only a crude description of the underlying natural processes; therefore, model parameters need to be calibrated. Different model concepts (interflow, direct runoff), or rather the processes represented, such as infiltration, soil water movement, etc. are more or less dominating different sections of the runoff spectrum. Most models do not account for such transient characteristics inherent to the hydrograph. This falls together with uncertain input data (e.g. rainfall intensity on different scales and the rainfalls' spatial distribution, especially if rainfall is a predicted parameter). In this paper, we try to show a way towards a possible online evaluation of model uncertainty and the graphical means to communicate the uncertain forecast in a probabilistic but yet comprehensible way. This is based on the development of a flood forecasting system, which combines artificial neural networks with process models Monte‐Carlo evaluation of the forecast uncertainty. The Monte‐Carlo results are evaluated in an operationally applicable model and the uncertainty is colour coded in uncertainty plots of the forecast, which are updated at each time step. This provides operators in flood warning centres much more reliable and easy to interpret information about the probability of the forecast well in advance of the occurrence.
Multiplex 16S rRNA haplotype‐specific PCR, a rapid and convenient method for fish species identification: an application to West African Clupeiform larvae
Authors: DURAND J. D. , DIATTA M. A. , DIOP K. , TRAPE S.
Published: October 2009

A multiplex haplotype‐specific polymerase chain reaction (MHS‐PCR) method was developed, which identified seven Clupeiform species living in the tropical Eastern Atlantic region: Sardinella aurita, Sardinella maderensis, Ethmalosa fimbriata, Sardina pilchardus, Engraulis encrasicholus, Pellonula leonensis and Ilisha africana. 16S rRNA fragments were amplified using a species‐specific set of primers, yielding species‐specific size fragments, and then separated using agarose gel electrophoresis, enabling direct visual identification of targeted species. This method provides an accurate, easy and rapid tool for identifying species within large Clupeiform samples. It is suitable for investigations on early Clupeiform stages, species and identification in fishery management in the tropical Eastern Atlantic area.
Rockets and feathers: Understanding asymmetric pricing
Authors: Tappata Mariano
Published: October 2009

Prices rise like rockets but fall like feathers. This stylized fact of many markets is confirmed by many empirical studies. In this article, I develop a model with competitive firms and rational partially informed consumers where the asymmetric response to costs by firms emerges naturally. In contrast to public opinion and past work, collusion is not necessary to explain such a result.
Flow Boiling Heat Transfer in Horizontal Metal-Foam Tubes
Authors: Zhao C. Y. , Lu W. , Tassou S. A.
Published: October 2009

The two-phase flow and boiling heat transfer in horizontal metal-foam filled tubes are experimentally investigated. The results show that the heat transfer is almost doubled by reducing the cell size from 20 ppi to 40 ppi for a given porosity, thanks to more surface area and strong flow mixing for the smaller cell size. The boiling heat transfer coefficient keeps steady rising, albeit slowly, by increasing the vapor quality for high mass flow rates, while the same story does not hold for the cases of low mass flow rates. The flow pattern can be indirectly judged through monitoring the cross-sectional wall surface temperature fluctuations and wall-refrigerant temperature difference. As the operating pressure increases, the boiling heat transfer at low vapor quality (x<0.1) exhibits similar behavior with pool boiling heat transfer, namely, the heat transfer is enhanced by improving the pressure. However the flow boiling heat transfer is suppressed to some extent as the pressure increases. The heat transfer coefficient of copper foam tubes is approximately three times higher than that of plain tubes.
Experimental and Numerical Study of Single Bubble Dynamics on a Hydrophobic Surface
Authors: Nam Youngsuk , Wu Jinfeng , Warrier Gopinath , Ju Y. Sungtaek
Published: October 2009

The growth and departure of single bubbles on two smooth surfaces with very different wettabilities are studied using high-speed video microscopy and numerical simulations. Isolated artificial cavities of approximately 10 μm diameter are microfabricated on both a bare and a Teflon-coated silicon substrate to serve as nucleation sites. The bubble departure diameter is observed to be almost 3 times larger and the growth period almost 60 times longer for the hydrophobic surface than for the hydrophilic surface. The waiting period is practically zero for the hydrophobic surface because a small residual bubble nucleus is left behind on the cavity from a previous ebullition cycle. The experimental results are consistent with our numerical simulation results. Bubble nucleation occurs on nominally smooth hydrophobic regions with root mean square roughness (Rq) less than 1 nm even at superheat as small as 3°C. Liquid subcooling significantly affects bubble growth on the hydrophobic surface due to increased bubble surface area. Fundamental understanding of bubble dynamics on heated hydrophobic surfaces will facilitate the development of chemically patterned surfaces with enhanced boiling heat transfer performance and novel phase-change based micro-actuators and energy harvesters.
The Influence of Surface Roughness on Nucleate Pool Boiling Heat Transfer
Authors: Jones Benjamin J. , McHale John P. , Garimella Suresh V.
Published: October 2009

The effect of surface roughness on pool boiling heat transfer is experimentally explored over a wide range of roughness values in water and Fluorinert™ FC-77, two fluids with different thermal properties and wetting characteristics. The test surfaces ranged from a polished surface (Ra between 0.027 μm and 0.038 μm) to electrical discharge machined (EDM) surfaces with a roughness (Ra) ranging from 1.08 μm to 10.0 μm. Different trends were observed in the heat transfer coefficient with respect to the surface roughness between the two fluids on the same set of surfaces. For FC-77, the heat transfer coefficient was found to continually increase with increasing roughness. For water, on the other hand, EDM surfaces of intermediate roughness displayed similar heat transfer coefficients that were higher than for the polished surface, while the roughest surface showed the highest heat transfer coefficients. The heat transfer coefficients were more strongly influenced by surface roughness with FC-77 than with water. For FC-77, the roughest surface produced 210% higher heat transfer coefficients than the polished surface while for water, a more modest 100% enhancement was measured between the same set of surfaces. Although the results highlight the inadequacy of characterizing nucleate pool boiling data using Ra, the observed effect of roughness was correlated using h∝Ram as has been done in several prior studies. The experimental results were compared with predictions from several widely used correlations in the literature.
Length to Diameter Ratio and Row Number Effects in Short Pin Fin Heat Transfer
Authors: Brigham B. A. , VanFossen G. J.
Published: October 2009

Recently, several experiments concerning heat transfer from short pin fins have been conducted with the results indicating lower heat transfer from short pin fins than from longer pin fins found in tube banks and other similar configurations. Assessments of the effect of the number of pin rows and row geometry have also been made. It was felt that there was a need to determine the relative contribution of pin length to diameter ratio and pin row geometry on the heat transfer. Array-averaged heat transfer coefficients on pin and endwall surfaces were measured for two configurations of staggered arrays of short pin fins (length to diameter ratio of 4). One configuration contained eight streamwise rows of pins, while the other contained only four rows. Results showed that both the eight-row and the four-row configurations for an Lp/D of 4 exhibit higher heat transfer than in similar tests on shorter pin fins (Lp/D of 1/2 and 2). It was also found that for this Lp/D ratio the array-averaged heat transfer was slightly higher with eight rows of staggered pins than with only four rows.
Effects of Pin Shape and Array Orientation on Heat Transfer and Pressure Loss in Pin Fin Arrays
Authors: Metzger D. E. , Fan C. S. , Haley S. W.
Published: October 2009

Modern high-performance gas turbine engines operate at high turbine inlet temperatures and require internal convection cooling of many of the components exposed to the hot gas flow. Cooling air is supplied from the engine compressor at a cost to cycle performance and a design goal is to provide necessary cooling with the minimum required cooling air flow. In conjunction with this objective, two families of pin fin array geometries which have potential for improving airfoil internal cooling performance were studied experimentally. One family utilizes pins of a circular cross section with various orientations of the array with respect to the mean flow direction. The second family utilizes pins with an oblong cross section with various pin orientations with respect to the mean flow direction. Both heat transfer and pressure loss characteristics are presented. The results indicate that the use of circular pins with array orientation between staggered and inline can in some cases increase heat transfer while decreasing pressure loss. The use of elongated pins increases heat transfer, but at a high cost of increased pressure loss. In conjunction with the present measurements, previously published results were reexamined in order to estimate the magnitude of heat transfer coefficients on the pin surfaces relative to those of the endwall surfaces. The estimate indicates that the pin surface coefficients are approximately double the endwall values.
The Rolls-Royce Annular Vaporizer Combustor
Authors: Sotheran A.
Published: October 2009

The term “vaporizer” continues to be used to describe the well-known Rolls-Royce fuel injector, although its most important action is probably that it fires the fuel upstream towards the combustor head. This and the annular configuration are the distinguishing combustor features which have been retained through a long series of engines which include the Royal Aircraft Establishment/Metropolitan Vickers F-series engines and the Sapphire/J65 which used the first annular vaporizer. It is represented today in the engines of Concorde, Tornado, and Harrier/AV-8. With the wealth of experience obtained from these many applications, the operating characteristics of the combustor are very firmly established and new combustors can be designed with confidence that project requirements will be met with minimum development. For the future, the system is well set to accommodate anticipated operating environments and duties and is competitive enough to have been specified for the Rolls-Royce RB211-CE3 advanced technology engine.
A Summary of Developments of the Mean-Streamline Method in China
Authors: Cai R.
Published: October 2009

The mean-streamline method (MSLM) proposed by Wu more than 30 years ago has been further developed in many ways in China since the fifties. Major progress in this method is summarized here. This progress includes: a completely analytical solution of the inverse problem which is extremely quick and more accurate than the original solution, the extension of MSLM to the axisymmetrical flow channels, the extension of the calculation range to transonic flow and nonisentropic flow, the estimation of applicable limits of MSLM, the improvement of MSLM with higher order derivatives, and the development of practical computer programs. The comparison of the calculation results with the experimental data is good, and the method has been widely applied in China with good success.
A Theory of Rotating Stall of Multistage Axial Compressors: Part I—Small Disturbances
Authors: Moore F. K.
Published: October 2009

An analysis is made of rotating stall in compressors of many stages, finding conditions under which a flow distortion can occur which is steady in a traveling reference frame, even though upstream total and downstream static pressure are constant. In the compressor, a pressure-rise hysteresis is assumed. Flow in entrance and exit ducts yield additional lags. These lags balance to give a formula for stall propagation speed. For small disturbances, it is required that the compressor characteristics be flat in the neighborhood of average flow coefficient. Results are compared with the experiments of Day and Cumpsty. If a compressor lag of about twice that due only to fluid inertia is used, predicted propagation speeds agree almost exactly with experimental values, taking into account changes of number of stages, stagger angle, row spacing, and number of stall zones. The agreement obtained gives encouragement for the extension of the theory to account for large amplitudes.
Boundary Layer and Loss Measurements on the Rotor of an Axial-Flow Turbine
Authors: Hodson H. P.
Published: October 2009

The aerodynamic efficiency of an axial-flow turbine is significantly less than that predicted by measurements made on equivalent cascades which operate with steady inflow. This difference in efficiencies is strongly dependent upon the rotor-stator axial spacing. An experimental investigation of the rotor-stator interaction has therefore been conducted using a large-scale, low-speed turbine. The blade profile loss and surface shear stresses are presented for the midspan of the rotor and for a rectilinear cascade of identical geometry. Both wind tunnels were operated at a Reynolds number of 3.15 × 105. The turbine rotor midspan profile loss was approximately 50 percent higher than that of the rectilinear cascade. The shear stress measurements indicate that as a stator wake is connected through a rotor passage, the laminar boundary layers undergo transition in the vicinity of the wake. The 50 percent increase in loss is due to the time-dependent transitional nature of the boundary layers.
Matrix Solution of Compressible Flow on S1 Surface Through a Turbomachine Blade Row With Splitter Vanes or Tandem Blades
Authors: Wu Chung-Hua , Wang Baoguo
Published: October 2009

The basic aerothermodynamic equations of turbomachine flow expressed with respect to nonorthogonal curvilinear coordinates and corresponding nonorthogonal velocity components are used to solve the compressible flow S1 surface in a turbomachine blade row with splitter vanes or tandem blades. The equation of stream function is solved by matrix technique, and the mass flow ratio and outlet flow angle are determined by applying the Kutta-Joukowsky condition to the trailing edges of the main blade and the splitter vane. Typical examples are given to illustrate the effectiveness of the present method.
Experimental Study of Centrifugal Impeller Discharge Flow in Vaneless and Vaned Diffusers
Authors: Inoue M. , Cumpsty N. A.
Published: October 2009

The flow discharged from centrifugal impellers is highly distorted and its behavior in the diffuser could be expected to have a determining effect on the performance of the compressor. The present work sets out to investigate this. The experimental work reported in this paper was designed to investigate the interaction between the vaned diffuser and the impeller. Unsteady measurements of velocity and wall static pressure were made at numerous positions in a vaned diffuser using an on-line data logging system. Experiments were carried out at a range of flow coefficients for three diffusers with 10, 20, and 30 vanes set at each of three different radius ratios, 1.04, 1.1, and 1.2. A limited number of experiments were also carried out with restaggered diffuser vanes and as a reference case extensive measurements were made in a vaneless diffuser build. The impeller, which was designed for a pressure ratio of 4.6, was run at low speed (3000 rpm) after modification to make its overall diffusion equivalent to that at the high speed for which it was designed. The circumferential distortion from the impeller was attenuated very rapidly in the entrance region of the diffuser vanes and suprisingly had only minor effects on the flow inside the vaned diffuser passage. The effect of the diffuser vanes on the flow discharged from the impeller was evident and reversal of flow back into the impeller was detected when the diffuser vanes were close to the impeller and the flow rate was not very high. The time-mean total and static pressure at impeller outlet were found to vary over the pitch of a diffuser vane, and a variation in the strength of the impeller wake was also observed.
An Investigation of the Flow Characteristics and of Losses in Radial Nozzle Cascades
Authors: Hashemi S. G. R. , Lemak R. J. , Owczarek J. A.
Published: October 2009

A study was made of the flow in radial nozzle cascades using an air test rig and a water test rig. In the air test rig, three cobra probes were used in circumferential and spanwise traverses to determine the total pressure variations in the flow field at three radii downstream of the nozzles at which static pressure was also measured. The tests were made on two sets of nozzle blades having heights of 0.148 in. (0.376 cm) and 0.200 in. (0.508 cm), at trailing edge angles (measured from circumferential direction) of 15, 20, and 25 deg, and at two flow Mach numbers of approximately 0.2 and 0.35. The test results presented in this paper, in the form of loss coefficients and flow angles, were flow-weighted and averaged. Flow visualization in the air test rig was made on the walls bounding the nozzle blades using the graphite power-oil mixture technique. Additional tests were made on the water test rig using dye injection technique. Photographs were obtained showing clearly formation of secondary flow around each nozzle blade in the form of the leading edge vortex. The test results confirm the existence of the leading edge vortices reported peviously, and extend their study to the radial nozzle cascades.
Experimental Study of a High-Throughflow Transonic Axial Compressor Stage
Authors: Wennerstrom A. J.
Published: October 2009

Design information and experimental results are presented for a transonic axial compressor stage passing 40 lbs/s-ft2 frontal area (195 Kg/s-m2) with a pressure ratio of 1.95 at 1500 ft/s (457 m/s) tip speed. The design incorporates several unusual features that helped it achieve a peak isentropic efficiency over 88 percent at design speed. The compressor was evaluated at three rotor tip clearances and an optimum was found. Vortex generators placed upstream on the casing proved relatively ineffective in influencing stall margin. Vortex generators installed on the rotor did improve stall margin and also increased efficiency at speeds of 90 percent and below.
Three-Dimensional Structure and Decay of Vortices Behind an Axial Flow Rotating Blade Row
Authors: Inoue M. , Kuroumaru M.
Published: October 2009

Detailed measurements were made of the three-dimensional turbulent flow field behind an axial-flow rotating blade row. The flow was surveyed at 15 radial locations and 70 circumferential sampling points in five measuring planes parallel to the trailing edge of the rotor. Statistically accurate mean velocities as well as turbulence stresses were obtained from numerous hot-wire signals, more than 12,000 for each sampling point. Vorticities were derived by the numerical differentiation of these data. The three-dimensional structure of various kinds of vortices generated through the rotor, such as a leakage vortex, trailing vortices, scraping vortices, a horseshoe vortex, etc. were elucidated quantitatively by use of the local streamwise, lateral and normal components of vorticity. The decay characteristics of these vortices were investigated in relation to the distribution of the turbulent stresses.
On the Nature of Jets Issuing From a Row of Holes Into a Low Reynolds Number Mainstream Flow
Authors: Yoshida T. , Goldstein R. J.
Published: October 2009

Measurements are reported of the temperature and velocity fields above an adiabatic flat plate through which air is injected via a row of circular injection holes inclined at an angle of 35 deg to the surface. A mainstream flow of air over the plate is present, with Reynolds number based on stream velocity and injection tube diameter of 3.4 × 103 throughout the experiments. The boundary layer approaching the row of holes is either laminar or turbulent and either fully developed laminar or turbulent pipe flow is present in the injection hole (in the absence of the mainstream). The jets emanate from the holes at a mass flux rate from 0.2 to 2.0 times that of the mainstream flow. Key findings are: (i) a laminar jet can penetrate into the main flow with a smaller mass flux than a turbulent jet; and (ii) a turbulent-approaching boundary layer generates a wider domain of interaction between the jets and the mainstream than a laminar-approaching boundary layer for the same blowing rate.
Pressure Loss Through Sharp 180 Deg Turns in Smooth Rectangular Channels
Authors: Metzger D. E. , Plevich C. W. , Fan C. S.
Published: October 2009

Measured pressure distributions, pressure loss coefficients, and surface streamline visualizations are presented for 180 deg turns in smooth, rectangular cross-section channels. The flow geometry models situations that exist in multipass internal cooling of gas turbine engine airfoils. The turn geometry is characterized by parameters W*, the ratio of upstream and downstream channel widths; D*, the nondimensional channel depth; H*, the nondimensional clearance height at the tip of the turn; and R*, the nondimensional corner fillet radius. The present results cover a range of combinations of geometry parameters and Reynolds numbers to aid in prediction of coolant flow rates in present and future cooled airfoil designs.
Turbofan Mixer Nozzle Flow Field—A Benchmark Experimental Study
Authors: Paterson R. W.
Published: October 2009

An experimental investigation of the three-dimensional flow field within a multilobed model turbofan forced-mixer nozzle was conducted. The objective of the study was to provide detailed velocity and thermodynamic state variable data for use in assessing the accuracy and assisting the further development of computational procedures for predicting the flow field within mixer nozzles. Velocity and temperature data suggested that the nozzle mixing process was dominated by large-scale secondary circulations that were associated with strong radial velocities observed near the lobe exit plane. Flow field similarity for variable inlet temperature conditions was also observed, although unanticipated.
Cheng-Cycle Implementation on a Small Gas Turbine Engine
Authors: Digumarthi R. , Chang Chung-Nan
Published: October 2009

The Cheng-Cycle turbine engine is a superheated steam injected gas turbine cycle system. This work is based on the Garrett 831 gas turbine. The development effort involved the design and manufacture of an experimental heat recovery steam generator, a steam injection system, and system controls. Measured performance data indicate the 26 percent efficiency improvement has been obtained compared to that of the basic turbine engine at its continuous power rating.
A New Generation of Allison Model 250 Engines
Authors: Byrd J. A.
Published: October 2009

Allison is actively developing two new additions to the Model 250 product line, the C34 and C24 engines, targeted for mid-1980s production. The C34 engine is a growth version of the Model 250-C30 and will provide a 10 percent power increase throughout the flight envelope. The C24 engine features decreased fuel consumption, one-engine-inoperative (OEI) ratings, and substantial increases in hot day performance compared to its predecessor, the highly successful C20B. Both engines incorporate single-stage turbines, digital electronic control units, and new shafting arrangements and are designed for increased reliability and durability, reduced complexity and part count, less maintenance, and decreased operating costs.
Gas Turbine Cogeneration—Principles and Practice
Authors: Allen R. P. , Kovacik J. M.
Published: October 2009

During the decade of the 1960s, industrial users recognized the gas turbine as a reliable prime mover for base load process applications. Gas turbine cogeneration systems were installed in various industries, including chemical, petroleum refining, pulp and paper, and metals. Typically, the size of the cogeneration system considered, and thus the gas turbine size, was governed by the internal heat and power demands of the specific plant. More recently, worldwide concern with regard to the cost and efficient use of energy is providing continuing opportunities for gas turbine cogeneration systems. In some locations, legislation is being enacted to encourage the development of cogeneration to the benefit of the public. This legislation can increase the number of alternative methods in which a cogeneration system can be developed. This paper will briefly review cogeneration principles applicable to the development of gas turbine energy supply systems. The wide range of conditions that can be satisfied using gas turbine cogeneration systems will be introduced. Brief discussions of recent installations are presented, illustrating the actual applications of some of these concepts.
A Comparative Study of the Influence of Different Means of Cooling on the Performance of a Combined (Gas and Steam Turbines) Cycle
Authors: Wu Chuan shao , Louis J. F.
Published: October 2009

A comparative study of the influence of different means of cooling on the thermodynamic efficiency and specific power of combined (gas and steam turbines) cycle is presented. The study extends the previously developed methodology evaluating the influence of cooling and coolant requirements on gas turbine performance. In this study, the exhaust gases of the gas turbine are used as the heat source to a steam cycle using single reheat with a specified temperature difference at the pinch point. The sensitivity of the overall cycle efficiency to each key input parameter is reported.
A Non-Newtonian Flow Model for Coal-Ash Slag
Authors: Johnson E. K.
Published: October 2009

The performance of high-temperature slagging coal-utilization systems depend on the collection of coal ash on the reactor surfaces and the flow of the slag out of the reactor through a slag-tap hole. In order to develop an analytical model for flow of the slag on a reactor wall, existing data for slag viscosity were reviewed in light of new emerging-process conditions. A Bingham model was selected for viscosity and the flow characteristics along a reactor wall are developed.
Refuse-Derived Fuel Evaluation in an Industrial Spreader-Stoker Boiler
Authors: Ragland K. W. , Madding R. P. , Ham R. K. , Vetter R. J. , Smith M. L.
Published: October 2009

Municipal refuse-derived fuel and coal were cofired in a retrofitted 125,000 lb steam/hr (55,000 kg/hr) spreader-stoker boiler. Results from 19 tests, which include fuel characteristics, boiler performance, particulate and gaseous emissions, and trace element emissions, are reported. System design and economic considerations are also discussed.
Flow in a Centrifugal Fan Impeller at Off-Design Conditions
Authors: Wright T. , Tzou K. T. S. , Madhavan S.
Published: October 2009

Predicted and measured surface velocity and pressure distributions in the internal flow channels of a centrifugal fan impeller are presented for volume flow rates between 80 and 125 percent of design flow rate. Predictions are based on a fully three-dimensional, finite element analysis of the inviscid, incompressible blade channel flow. Additional predictions using a conventional quasi-three-dimensional analysis are presented for comparison. Experimental results were developed using extensive blade and sidewall surface pressure taps installed in a scale model of an airfoil-bladed centrifugal fan impeller designed for heavy industrial and power generation applications. The results illustrate the ability of both flow analyses to predict the dominant features of the impeller flow field, including peak blade surface velocities and adverse gradients at flows far from the design point. In addition, the experimental results provide valuable insight into the limiting channel diffusion values for typical centrifugal cascade performance, and the influence of viscous effects as seen in deviations from the ideal flow predictions.
Prediction of Stiffness and Damping Coefficients for Centrifugal Compressor Labyrinth Seals
Authors: Wyssmann H. R. , Pham T. C. , Jenny R. J.
Published: October 2009

A theory is presented for the calculation of stiffness and damping coefficients of the fluid-rotor interaction in centrifugal compressor labyrinth seals based on turbulent flow calculations. The theory has been confirmed by measurements on labyrinth test stands and on a centrifugal compressor impeller shroud seal at pressures up to 140 bar. Predicted rotor stability limits based on the theory are in agreement with those observed in real compressors.
Analysis for Leakage and Rotordynamic Coefficients of Surface-Roughened Tapered Annular Gas Seals
Authors: Nelson C. C.
Published: October 2009

In order to soften the effects of rub, the smooth stators of turbine gas seals are sometimes replaced by a honeycomb surface. This deliberately roughened stator and smooth rotor combination retards the seal leakage and may lead to enhanced rotor stability. However, many factors determine the rotordynamic coefficients and little is known as to the effectiveness of these “honeycomb seals” under various changes in the independent seal parameters. This analysis develops an analytical-computational method to solve for the rotordynamic coefficients of this type of compressible-flow seal. The governing equations for surface-roughened tapered annular gas seals are based on a modified Hirs’s turbulent bulk flow model. A perturbation analysis is employed to develop zeroth and first-order perturbation equations. These equations are numerically integrated to solve for the leakage, pressure, density, and velocity for small motion of the shaft about the centered position. The resulting pressure distribution is then integrated to find the corresponding rotor-dynamic coefficients. Finally, an example case is used to demonstrate the effect of changing from a smooth to a rough stator while varying the seal length, taper, preswirl, and clearance ratio.
Operational Mode Monitoring of Gas Turbines in an Offshore Gas-Gathering Application
Authors: Toler D. F. , Yorio R. N.
Published: October 2009

A computer-assisted monitoring system has been implemented on GT-61 Gas Turbines employed in offshore gas gathering. Operating load data are continuously recorded at the site and evaluated at the turbine manufacturer’s plant on a mainframe computer, where existing analysis and testing techniques are utilized to predict the service fatigue lives of the power turbine structural components. The data acquisition hardware, the data reduction software, and the life prediction techniques are each described. The data collected indicate that offshore gas gathering equipment will experience many more operating load cycles than comparable equipment in pipeline service. The fatigue life predictions reaffirm the suitability of the GT-61 for this more severe service.
Heat Transfer in Thermal Barrier Coated Rods With Circumferential and Radial Temperature Gradients
Authors: Chung B. T. F. , Kermani M. M. , Braun M. J. , Padovan J. , Hendricks R. C.
Published: October 2009

To study the heat transfer in ceramic coatings applied to the heated side of internally cooled hot section components of the gas turbine engine, a mathematical model is developed for the thermal response of plasma-sprayed ZrO2-Y2 O3 ceramic materials with a Ni-Cr-AL-Y bond coat on a Rene 41 rod substrate subject to thermal cycling. This multilayered cylinder with temperature dependent thermal properties is heated in a cross-flow by a high veloctiy flame and then cooled by ambient air. Due to high temperature and high velocity of the flame, both gas radiation and forced convection are taken into consideration. Furthermore, the local turbulent heat transfer coefficient is employed which varies with angular position as well as the surface temperature. The transient two-dimensional (heat transfer along axial direction is neglected) temperature distribution of the composite cylinder is determined numerically.
Fuel Effects on Gas Turbine Combustion—Ignition, Stability, and Combustion Efficiency
Authors: Lefebvre A. H.
Published: October 2009

An analytical study is made of the substantial body of experimental data acquired during recent Wright-Patterson Aero Propulsion Laboratory sponsored programs on the effects of fuel properties on the performance and reliability of several gas turbine combustors, including J79-17A, J79–17C (Smokeless), F101, TF41, TF39, J85, TF33, and F100. Quantitative relationships are derived between certain key aspects of combustion, notably combustion efficiency, lean blowout limits and lean light-off limits, and the relevant fuel properties, combustor design features, and combustor operating conditions. It is concluded that combustion efficiency, lean blowout limits, and lean lightoff limits are only slightly dependent on fuel chemistry, but are strongly influenced by the physical fuel properties that govern atomization quality and spray evaporation rates.
Turbine Heat Flux Measurements: Influence of Slot Injection on Vane Trailing Edge Heat Transfer and Influence of Rotor on Vane Heat Transfer
Authors: Dunn M. G.
Published: October 2009

This paper describes the measurement of heat flux distributions obtained for a Garrett TFE 731-2 hp turbine. Measurements were obtained for a full turbine both with and without injection and for the nozzle guide vanes with and without a rotor. A shock tube is used as a short-duration source of heated air and miniature thin-film gages are used to obtain the heat flux measurements. Results are presented for values of the blowing parameter (ρcVc/ρ∞V∞)at SLOT, in the range of 0.8–1.3. The injection gas (air) as a percentage of turbine weight flow, Wc/Wo, was in the range of 2.1–3.5 percent. A comparison is presented between results obtained with the rotor operating at 100 percent of corrected speed and those obtained with the rotor replaced by a row of flow straighteners. The results suggest that: (i) the reduction of heat flux due to injection is a function of the blowing parameter, the temperature ratio, and the physical location relative to the tip or hub endwall and (ii) the presence of the rotor has a significant affect on the vane trailing edge Stanton number, increasing it by 15 to 25 percent. The vane leading edge and midchord regions were generally unaffected.
A Quasi-Three-Dimensional Turbomachinery Blade Design System: Part I—Throughflow Analysis
Authors: Jennions I. K. , Stow P.
Published: October 2009

The purpose of this work has been to develop a quasi-three-dimensional blade design and analysis system incorporating fully linked throughflow, blade-to-blade and blade section stacking programs. In Part I of the paper, the throughflow analysis is developed. This is based on a rigorous passage averaging technique to derive throughflow equations valid inside a blade row. The advantages of this approach are that the meridional streamsurface does not have to be of a prescribed shape, and by introducing density weighted averages the continuity equation is of an exact form. Included in the equations are the effects of blade blockage, blade forces, blade-to-blade variations and loss. The solution of the equations is developed for the well-known streamline curvature method, and the contributions from these extra effects on the radial equilibrium equation are discussed. Part II of the paper incorporates the analysis into a quasi-three-dimensional computing system and demonstrates its operational feasibility.
Flutter of Swept Fan Blades
Authors: Kielb R. E. , Kaza K. R. V.
Published: October 2009

The purpose of the research presented in this paper is to study the effect of sweep on fan blade flutter by applying the analytical methods developed for aeroelastic analysis of advanced turboprops. Two methods are used. The first method utilizes an approximate structural model in which the blade is represented by a swept, nonuniform beam. The second method utilizes a finite element technique to conduct modal flutter analysis. For both methods, the unsteady aerodynamic loads are calculated using two-dimensional cascade theories that are modified to account for sweep. An advanced fan stage is analyzed with 0, 15, and 30 deg of sweep. It is shown that sweep has a beneficial effect on predominantly torsional flutter and a detrimental effect on predominantly bending flutter. This detrimental effect is shown to be significantly destabilizing for 30 deg of sweep.
Aerodynamically Excited Vibrations of a Part-Span Shrouded Fan
Authors: Srinivasan A. V. , Cutts D. G.
Published: October 2009

The structural response of a part-span shrouded fan due to an aerodynamic excitation was measured using strain gages. The excitation was provided by means of a 4-lobed distortion screen mounted upstream of the rotor. Vibration measurements made with tuned and mistuned conditions at integral order speeds have been analyzed to determine the aeromechanical response charcteristics of the assembly. The results from the experimental investigation are presented and discussed.
Some Recent Advances in the Understanding and Prediction of Turbomachine Subsonic Stall Flutter
Authors: Chi R. M. , Srinivasan A. V.
Published: October 2009

In this paper, some recent advances in the understanding and prediction of subsonic flutter of jet engine fan rotor blades are reviewed. Among the topics discussed are (i) the experimental evidence of mistuning in flutter responses, (ii) new and promising unsteady aerodynamic models for subsonic stall flutter prediction, (iii) an overview of flutter prediction methodologies, and (iv) a new research effort directed toward understanding the mistuning effect on subsonic stall flutter of shrouded fans. A particular shrouded fan of advanced design is examined in the detailed technical discussion.
Influence of a Closely Coupled Throttle on the Stalling Behavior of a Radial Compressor Stage
Authors: Railly J. W. , Ekerol H.
Published: October 2009

On the basis of the classical discussion of the stability of compressor blade rows, a treatment is given of the stability of a stage consisting of a radial impeller followed by a vaned radial diffuser with a small radial gap between them. At the exit of the diffuser a radial array of adjustable vanes serves either to throttle the flow or to offer no resistance. In the latter case, throttling takes place by means of restrictions at inlet situated well upstream. The theory demonstrates that instability in the former case can only occur at the point of static instability, i.e., when the stage pressure characteristic slope becomes so positive that the throttle pressure characteristic is tangential to it. With the conventional throttling arrangement, instability is predicted as expected, when the stage characteristic has zero slope. Experimental confirmation of these predictions was obtained from tests on a slow speed radial compressor stage employing the above arrangement at exit, dischanging to atmosphere. When the vanes were used for throttling no rotating stall appeared but with throttling situated remotely from the stage a vigorous rotating stall mode developed.
Analysis of Single-Phase Cascade Flow in Power Plant Drain
Systems
Authors: Hout S. A.
Published: October 2009

The performance of a typical drain system was checked through a pressure drop analysis and the determination of valve sizing coefficients. The operation checks that two-phase flow does not occur upstream of the control valve. Erosion checks are performed at any elbow installed downstream of the control valve where flashing may take place. The analysis does not cover the performance of the feedwater heater or moisture separator and reheater drain systems under transient conditions such as load rejection, i.e., turbine trip. It is believed that accurate valve sizing and appropriate drain cascade are vital to proper drainage.
A Mathematical Model for Ringbom Engine Operation
Authors: Senft J. R.
Published: October 2009

The Ringbom or hybrid Stirling engine, essentially dormant for some 70 years, is experiencing a vigorous rebirth following recent fundamental discoveries concerning its unique mode of operation. In this paper the author’s earlier mathematical model of Ringbom engine operation is extended to include volume variation effects due to the displacer rod. This injects a new parameter, the rod-to-displacer area ratio, into the theory improving its fidelity and increasing its predictive power. It is rigorously shown that the main theorem characterizing overdriven mode operation, the basic regime of stable running for hybrids, remains valid in the extended model and is presented here in a new form.
Heat Transfer Enhancement in Channels With Turbulence Promoters
Authors: Han J. C. , Park J. S. , Lei C. K.
Published: October 2009

Repeated rib roughness elements have been used in advanced turbine cooling designs to enhance the internal heat transfer. Often the ribs are perpendicular to the main flow direction so that they have an angle of attack of 90 deg. The objective of this investigation was to determine the effect of rib angle of attack on the pressure drop and the average heat transfer coefficients in the fully developed turbulent air flow in a square duct with two opposite rib-roughened walls for Reynolds number varied from 7000 to 90,000. The rib height-to-equivalent diameter ratio (e/D) was kept at a constant value of 0.063, the rib pitch-to-height ratio (P/e) was varied from 10 to 20, and the rib angle of attack (α) was varied from 90 to 60 to 45 to 30 deg, respectively. The thermal performance comparison indicated that the increased heat conductance for the rib with an oblique angle to the flow (α = 45–30 deg) was about 10–20 percent higher than the rib with a 90 deg angle to the flow, and the pumping power requirement for the angled rib was about 20–50 percent lower than the transverse rib. Semi-empirical correlations for friction factor and heat transfer coefficients were developed to account for rib spacing and rib angle. The correlations can be used in the design of turbine blade cooling passages.
Effect of Surface Configuration During Solid Particle Impingement Erosion
Authors: Rao P. V. , Buckley D. H.
Published: October 2009

A study of the progression of erosion and its detrimental effects due to solid particle impingement requires a detailed understanding of the erosion process and morphology of real surfaces of ductile metals. A series of experiments was conducted to investigate the erosion characteristics of aluminum alloy surfaces during spherical glass bead and angular crushed glass particle impingement. The effects of particle shape on cylindrical surfaces and surfaces with pre-existing holes and slits were determined. An attempt was made to understand the relationship between erosion rate and pit morphology. Based on the experimental observations, an empirical relationship between erosion rate and volume loss is presented. This technique provides an improved prediction method for a wide spectrum of ductile materials.
Methanol as a Soot Reducer in a Turbulent Swirling Burner
Authors: Izquierdo A. J. , Hoult D. P.
Published: October 2009

The combined effect of using methanol as a fuel additive together with a prototype multifuel injector has been evaluated with regard to soot formation in a tubular laboratory burner with a turbulent swirl stabilized diffusion flame. Kerosene, ERBS fuel, and Blending Stock with approximately 14, 12.8, and 10.3 weight percent of hydrogen, respectively, were characterized in terms of soot loading at the axial positions Z/D = 2.5 and 4.0 and normalized radius r/R = ± 0.67. Mixtures of ERBS fuel and Blending Stock with 15 and 7.5 weight percent of methanol were also characterized in the same way. Measurements with the plain fuels showed a drastic reduction in soot formation, on the order to 150-fold decrease, due to the new injector design. Further reductions by a factor of 2 and 1.5 were accomplished with mixtures of 15 and 7.5 weight percent of methanol, respectively.
Application of Reburning for NOx Control to a Firetube Package Boiler
Authors: Mulholland J. A. , Lanier W. S.
Published: October 2009

A 730 kW (2.5 × 106 Btu/hr) firetube package boiler was used to demonstrate the application of reburning for NOx emission control. An overall reduction of 50 percent from an uncontrolled NOx emission of 200 ppm was realized by diverting 15 percent of the total boiler load to a natural-gas-fired second stage burner. Tests indicate that the overall reaction order of destruction with respect to initial NOx is greater than one; thus, larger reductions can be expected from reburning applications to systems with higher initial NOx. Rich zone stoichiometry has been identified as the dominant process variable. Primary zone stoichiometry and rich zone residence time are parameters that can be adjusted to maximize NOx reduction. Reburning applied to firetube package boilers requires minimal facility modification. Natural gas would appear to be an ideal reburning fuel as nitrogen in the reburning fuel has been shown to inhibit NOx reduction.
Multifuel Gas Turbine Propulsion for Naval Ships: Gas Turbine Cycles Implementing a Rotating Gasifier
Authors: Bander F.
Published: October 2009

The purpose of this paper is to investigate the possibilities of implementing a rotating gasifier to convert aero-derived gas turbines into multifuel ship propulsion units, thereby combining the advantages of lightweight and compact gas turbines with the multifuel characteristics of a rotating gasifier. Problems (and possible solutions) to be discussed are: (i) aerodynamic interaction between gas turbine and gasifier; (ii) attaining maximum energy productivity together with ease of control; (iii) corrosion and/or erosion of gas turbine components.
Experimental Heat Transfer Investigation Around the Film-Cooled Leading Edge of a High-Pressure Gas Turbine Rotor Blade
Authors: Camci C. , Arts T.
Published: October 2009

This paper describes an experimental heat transfer investigation around the leading edge of a high-pressure film-cooled gas turbine rotor blade. The measurements were performed in the VKI isentropic compression tube facility using platinum thin film gauges painted on a blade made of machinable glass ceramic. Free-stream to wall temperature ratio, Reynolds, and Mach numbers were selected from actual aeroengines conditions. Heat transfer data obtained without and with film cooling in a stationary frame are presented. The effects of coolant to free-stream mass weight ratio and temperature ratio were successively investigated. Heat transfer modifications due to incidence angle variations were interpreted with the aid of inviscid flow calculation methods.
Turbulence Production Due to Secondary Vortex Cutting in a Turbine Rotor
Authors: Binder A.
Published: October 2009

Measurements of the unsteady flow field near and within a turbine rotor were made by means of a Laser-2-Focus velocimeter. The testing was performed in a single-stage cold-air turbine at part-load and near-design conditions. Random unsteadiness and flow angle results indicate that the secondary vortices of the stator break down after being cut and deformed by the rotor blades. A quantitative comparison shows that some of the energy contained in these secondary vortices is thereby converted into turbulence energy in the front part of the rotor. An attempt is made to explain this turbulence energy production as caused by the vortex breakdown.