bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tip Clearance Effects in a Turbine Rotor: Part II — Velocity Field and Flow Physics
Authors: McCarter Andrew A. , Xiao Xinwen , Lakshminarayana Budugar 
Published: August 2014

A comprehensive experimental investigation was undertaken to explore the flow field in the tip clearance region of a turbine rotor to understand the physics of tip leakage flow. Specifically the paper looks at its origin, nature, development, interaction with the secondary flow, and its effects on performance. The experimental study was based on data obtained using a rotating five-hole probe, laser doppler velocimeter, high-response pressure probes on the casing, and static pressure taps on the rotor blade surfaces.
The first part of the paper deals with the pressure field and losses. Part II presents and interprets the vorticity, velocity, and turbulence fields at several axial locations. The data provided here indicates that the tip leakage vortex originates in the last half chord. The leakage vortex is confined close to the suction surface corner near the blade tip by the relative motion of the blade and the casing, and by the secondary flow in the tip region. The tip leakage flow clings to the blade suction surface until midchord then lifts off of the suction surface to form a vortex in the last 20% of the blade chord. The relative motion between blades and casing leads to the development of a scraping vortex which, along with the secondary flow, reduces the propagation of the tip leakage flow into the mainflow. The rotational effects and corriolis forces modify the turbulence structure in the tip leakage flow and secondary flow as compared to cascades.
The Influence of the Clearance of Shrouded Rotor Blades on the Development of the Flowfield and Losses in the Subsequent Stator
Authors: Peters Patrick , Breisig Volker , Giboni Andre , Lerner Christian , Pfost Heiner 
Published: August 2014

Although turbines are commonly noted for their high efficiency this efficiency can be improved further. The importance of the leakage flow for the losses of turbine stages makes this flow a promising candidate to be examined for loss reduction: first it decreases the workflow through the rotor and second, the suction side incidence of the re-entering leakage flow in the subsequent stator causes additional losses.
As an essential parameter for leakage flow the clearance and its influence on the losses is investigated by experimental and numerical approach as well. The measurements of the experimental part were carried out on a 1.5 stage axial model turbine of an enlarged scale. The rotor of the turbine consists of shrouded blades with two teeth on the shroud. The clearance was varied from s/D = 0.0007 up to 0.004. Linear traverse measurements with a pneumatic 5-hole probe were taken in front of and behind the second stator. The re-entering leakage flow extremely influences the flow properties in radial direction (up to 50% of the span) at the inlet of the following stator. So the flow angle α1 deviates up to 90° of the flow angle in the mid-span, depending on the clearance. Along with mixing losses, this suction side incidence leads to an increase of the losses within the stator. In addition numerical investigations of the flow field were done with the commercial flow solver CFX-TASCflow. The interaction between the leakage flow and the secondary losses of the following stator is shown, and a comparison with available loss correlations is carried out in this paper.
Three-Dimensional Turbulent Flow Field Downstream of a Single-Stage Axial Compressor Rotor
Authors: Ma Hongwei , Jiang Haokang 
Published: August 2014

This paper reports an experimental investigation of the three-dimensional turbulent flow downstream of a single-stage axial compressor rotor. The flow fields were measured at two axial locations in the rotor-stator gap at different mass-flow conditions. Both hot-wire probe and fast-response pressure probe were employed to survey the flow structure.
At the design condition, substantial flow blockage, turbulence, loss and aerodynamic noise mainly occur in the tip mid-passage, the rotor wake and at the hub corner of the suction surface. The radial component is the highest of the three turbulence intensities at 15% axial chord downstream of the trailing edge. With the flow downstream, the radial turbulence components decay fast. Interactions of the tip leakage vorticities and the rotor wake are found at 30% axial chord downstream of the trailing edge.
With the mass-flow decrease, the turbulence intensities and shear stresses become stronger, while the radial components increase fast.
The flow separation and tangential migration of the low-energy fluids at the tip corner of the suction surface play an important role in the tip flow field at a low mass-flow condition.
An Experimental Study of Stall in Four Axial Compressor Stages
Authors: Cyrus Vaclav 
Published: August 2014

Fourteen low-speed axial compressor stages have been tested in the SVÚSS and AHT laboratories. In four cases a detailed analysis of stall development was carried out while the stage working point moved from the design condition to the stability limit. In majority of cases the primary flow mechanism for stall was found. In most stages stalled flow arose in the upper half of the rotor blade row, thereby, tip clearance flow contributed to the growth of low-energy fluid near the casing. An alternative flow mechanism occurred only in one stage with very high aerodynamic loading. Near the stability limit, stalled flow appeared in the rotor blade row in the hub corner. The spanwise distribution of the diffusion factor helped us in the description of stalled flow in stage blade rows.
It follows from these experimental results that the conditions in the rotor blade row play the main role in the rotating stall onset. The extent of stall in the inlet guide vanes and stator vanes did not have a large affect on this phenomenon. The extent of stalled flow in stator row near the stability limit changed with the turning of vanes. At higher values of the IGV turning nonsteady flow patterns can appear.
The conditioning of the stage inlet flow field by means of a specially designed grid affects the stall development in the stage and the onset of rotating stall. A higher value of flow turbulence intensity (Tu = 6–7 %) caused the shift of the stage stability limit to lower flow rates. The stage stall margin was not sensitive to peripheral flow non-uniformities.
Effect of Turbulence Modeling on Particle Dispersion and Deposition on Compressor and Turbine Blade Surfaces
Authors: El-Batsh Hesham , Haselbacher Hermann 
Published: August 2014

One of the main mechanisms that control particle movement is the turbulent diffusion by which the particles in the turbulent boundary layer migrate to the surface under the influence of random flow fluctuations. Theoretical approaches to particle dispersion use random walk models to represent the effect of turbulent fluctuation velocity on particle movement. As a consequence, the turbulence model has a significant effect on the particle trajectory. Particle sticking probability, on the other hand depends upon the particle impact velocity. Moreover, the wall shear stress that is calculated from the turbulence model is the main cause of particle detachment from the surface.
In this work, the effect of turbulence models on particle dispersion, deposition on turbine blade surfaces and detachment from the surfaces is studied. Two turbulence models have been tested: the Renormalization Group (RNG) k-ε model and the standard k-ε model. The near-wall region is solved by two different models: the standard wall function and the two-layer zonal model.
It is found that the RNG k-ε model with the two-layer zonal near-wall model is the more appropriate turbulence model for particle deposition. It is also concluded that the standard wall function should not be used when solving the flow field near the wall for particle deposition. The reason is that this method does not give the detailed solution of the flow near the wall that is very important for deposition models.
The Combined Use of Navier-Stokes Solvers and Optimization Methods for Decelerating Cascade Design
Authors: Manna Marcello , Tuccillo Raffaele 
Published: August 2014

The authors present an optimization strategy applied to decelerating cascades, with the combined use of a Navier-Stokes flow solver, correlation functions and a gradient based optimization method. In the initial stages of the searching the configurations proposed by the optimizer are mainly investigated with a semi-empirical analysis tool so to provide the flow solver with an improved initial guess. In the later stages the optimizer directly controls the flow solver. The objective of the optimization is two fold: determining the geometrical characteristics of the cascade yielding the best aerodynamic performances, and defining an appropriate cost function accounting for optimality conditions in a more general sense.
The method is applied to blade profiles of the C4 type, whose geometrical characteristics are determined as a function of a few parameters (typically the camber angle, the maximum thickness to chord ratio, and the chord). By doing so the number of design parameters is substantially reduced, and the validity of the present methodology is correctly demonstrated, without loss of generality, with a limited computational effort.
The examples deal with the design of decelerating cascades realizing considerable flow turning both in subsonic and transonic regimes and demonstrate the potential of the method.
The Calculation of the Forced Response of Shrouded Blades With Friction Contacts and its Experimental Verification
Authors: Sextro Walter 
Published: August 2014

Shrouds with a frictional interface are used to reduce the dynamic stresses in turbine blades. Due to dry friction energy is dissipated, which can be used to decrease vibration amplitudes and, hence, to increase the life time of turbine blades.
The spatial motion of the blades results in a spatial motion of the contact planes. Due to the non-linearity of the problem, the contact planes are discretized. For each contact area, the developed contact model is used to calculate the corresponding tangential and normal contact forces. This contact model includes the roughness of the contact surfaces, the normal pressure distribution due to roughness, the stiffnesses in normal and tangential direction and dry friction. Due to the roughness of the contact planes the normal contact forces and the contact stiffnesses in normal and tangential direction are nonlinear dependent on the relative displacements in the normal direction. This effect is verified by experiments.
An experiment with one shrouded blade and two non-Hertzian contacts is used to verify the developed contact model and the calculation method. The comparison between measured and calculated frequency response functions for bending and torsional vibrations of the blade show a very good agreement.
A bladed disk assembly with shrouds is investigated and optimized with respect to the vibration amplitudes and alternating stresses. Varying the normal contact force best damping effects are obtained. Separation of the contacts leads to an increase of the alternating stresses and, thus, has to be avoided.
A Prototype for the First Commercial Pressurized Fuel Cell System
Authors: Ali Sy A. , Moritz Robert 
Published: August 2014

High temperature fuel cell stacks of commercially significant power (>100 kW) have emerged during the last 10 years. Five US programs, two Molten Carbonate and three Solid Oxide were recently awarded feasibility study funding from US Department of Energy (DOE) to define products which could achieve at least 70% efficiency to electricity.
The Department of Energy believes that these pressurized fuel cell systems will become an important part of the future power generation soruces. In support of these views, Rolls-Royce has joined fuel cell manufacturers to develop pressurized fuel cell plants which can be marketed successfully to end users.
In selecting technology which should be supported, RR-Allison considered the following critical issues: technology with US business focus; technology with potential for near term commercialization; and technology which would lead into second generation fuel cell system development over long term.
The Rolls-Royce plan is to join the DOE initiative through the pressurized Molten Carbonate program which has been funded as “Molten Carbonate Fuel Cell (MCFC) Product Design and Improvement.”
The paper outlines the functional and commercial issues to be evaluated during the proof of concept tests of the first pressurized MCFC power generation package. The key factors to be evaluated during the test program in current order of priority are:
• operational stability
• power output and system availability
• cost reduction potential
• system simplification for commercial power generation application
• enhanced reliability
• power quality
• grid interconnection
Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part II — Analysis
Authors: Ehrich F. F. , Spakovszky Z. S. , Martinez-Sanchez M. , Song S. J. , Wisler D. C. , Storace A. F. , Shin H.-W. , Beacher B. F. 
Published: August 2014

An experimental and theoretical investigation was conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor becomes displaced from the centerline of the static structure of the engine, thus creating circumferentially non-uniform, rotor-tip clearances. This displacement produces unsteady flow and creates a system of destabilizing forces, which contribute significantly to rotor whirl instability in turbomachinery. These forces were first identified by Thomas (1958) for turbines and by Alford (1965) for jet engines. In Part I, the results from an experimental investigation of these phenomena were presented.
In this Part II, three analytic models were used to predict both the magnitude and direction of the Thomas/Alford force in its normalized form, known as the β coefficient, and the unsteady effects for the compressors tested in Part I. In addition, the effects of a whirling shaft were simulated to evaluate differences between a rotor with static off-set and an actual whirling eccentric rotor. The models were also used to assess the influence of the non-axisymmetric static pressure distribution on the rotor spool, which was not measured in the experiment. The models evaluated were: (1) the Two-Sector Parallel Compressor (2SPC) model (Ehrich, 1993), (2) the Infinite-Segment-Parallel-Compressor (ISPC) model (Spakovszky, 2000), and (3) the Two-Coupled Actuator Disc (2CAD) model (Song and Cho, 2000). The results of these analyses were found to be in agreement with the experimental data in both sign and trend. Thus, the validated models provide the general means to predict the aerodynamic destabilizing forces for axial flow compressors in turbine engines. These tools have the potential to improve the design of rotordynamically stable turbomachinery.
Influence of High Pressure Water Injection on Sound Emission of Steam Valves
Authors: Bohn Dieter E. , Balkowski Ingo , Nordheim Dierk von , Saß Jochen 
Published: August 2014

In addition to the pressure reduction, a temperature reduction is often obtained in steam valves by injection of cooling water. In such cases, water is injected into the high turbulent flow immediately behind the first stage of the valve, where a major part of the whole throttle noise is generated. Additionally, the density of the steam flow is increased behind the first stage. This causes lower velocities and less sound production in the following stages.
These effects of high pressure water injection on noise production of steam valves are experimentally investigated in a real five-stage steam control valve with a steam mass flow of up to 2 kg/s at an inlet temperature of 463 K and a pressure of 900 kPa. The high pressure water injection mass flow behind the first stage is varied between 0 % and 10% of the mean steam flow. In spite of a high pressure ratio of 45 and sonic expansion behind the first stages, a significant noise reduction of up to 8 dB is observed. During the investigations, the geometry of the injection holes and the throttle geometry of the valve are varied systematically to separate the causes for this effect. The results of the experiments lead to new knowledge about the physical phenomena of sound production in steam control valves.
GEOPHILES: GEneration Of Power with HIgh Levels of Environmental Friendliness — A Technology Transfer Project Between Europe and South America
Authors: Barbosa Joao Roberto , Pilidis Pericles 
Published: August 2014

This paper outlines the main details of a technology transfer educational project between the EU and South America. It was sponsored by the CEC, The British Council and GUASCOR.
An international network called GEOPHILES was set up to train ten South American individuals selected by the South American partners. The technical subject was power generation with gas fuel from biomass and low calorific value coal.
The objective was to create a team of individuals with experience on a relevant discipline, giving each grantholder a different experience. To achieve this the training took place in several European Universities and a Spanish company. The trainees and their host institutions received state of the art training and material. They were also made aware of the advanced wealth creation capabilities within the European Community.
The European membership of the consortium included three Universities with important industrial and commercial links and an industrial partner. This gave the programme a valuable practical element.
The project was in two phases, firstly the preparation and delivery of the technical material in an intensive two week course. The second phase of the project was the mobility of the grantholders to Europe to carry out a six and a half month project on a subject relevant to the engineering of suitable power systems.
In the short term the benefit to the South American community was a small team of experts with an increased awareness of advanced environment friendly power generation systems. In the long term this may result in valuable business opportunities to European industry.
Integration of the ETF40B Gas Turbine Engine and FADEC System Into the Landing Craft Air Cushion Vehicle
Authors: Harris Howard , Schneider Phil , Richards John , Dvornak Mike 
Published: August 2014

The US Navy along with Textron Marine & Land Systems (TM&LS) is qualifying and field testing the ETF40B gas turbine engine along with Full Authority Digital Engine Control (FADEC) system as possible upgrades to the current TF40B engine and analog control system currently installed on the Landing Craft Air Cushion (LCAC). The ETF40B engine and FADEC control system are of interest due to: increased power, proposed increase in Mean Time Between Overhauls (MTBO), and proposed increase in engine reliability.
The primary topics presented in this paper are:
1. The design, development, and qualification of the ETF40B engine and FADEC control system
2. Integration of the ETF40B engine and FADEC into the LCAC
3. Field test data from two LCACs, follow-up testing and implementation
Steady State Performance Simulation of Auxiliary Power Unit With Faults for Component Diagnosis
Authors: Davison Craig R. , Birk A. M. 
Published: August 2014

A computer model of an auxiliary power unit has been developed. The model determines the steady state operating condition of the engine under user specified ambient conditions and load. Once the healthy baseline condition is determined faults, such as turbine degradation or flow passage blockage, were introduced and the effect on the engine’s operating parameters noted.
Comparing the results to healthy baseline data generates fault signatures and fault maps, that can be used in engine diagnosis. By observing the changes in parameters that can be economically monitored the viability of this simple diagnosis method can be determined.
Coating Rejuvenation: New Repair Technology for High Pressure Turbine Blades
Authors: Conner Jeffrey A. , Weimer Michael J. 
Published: August 2014

With the evolution of advanced directionally solidified and single crystal nickel base superalloy turbine blades, managing life cycle costs of high pressure turbine (HPT) blades has become increasingly more difficult. Today’s advanced high pressure turbine blades in aero and aero-derivative turbines feature thin walls (<.030 inches), complex internal geometries, three dimensional (3D) aerodynamic shapes, multiple protective coatings and complex film cooling schemes. A major contributor to blade life cycle cost is the ability to perform multiple repairs without compromising the integrity of these complex components.
Repair of HPT blades has traditionally fallen into two categories: mini or partial repairs where blade tips are restored and coated, and full repairs where flowpath coatings are removed, blade tips restored and new coating(s) applied to flowpath surfaces. Historically, the number of full repairs allowed ranges from zero to two based on numerous design considerations, one of which is maintaining a minimum wall thickness. Removal of protective coatings during full repair reduces wall thickness which limits the number of times a full repair can be performed. Furthermore, blades that have sufficient design allowance to permit two full repairs typically have very low yields at the second full repair due to thinning of airfoil walls below minimum thickness limits. The life of a given HPT blade is therefore controlled to a large degree by at what shop visit a full repair is performed.
GE Engine Services has developed a new blade repair approach — Coating Rejuvenation — which significantly extends blade life by restoring protective coatings and maintaining wall thickness. Included in the Coating Rejuvenation repair are technologies that allow: removal of physical vapor deposited (PVD) thermal barrier coatings from external surfaces and cooling holes without impacting the bond coat; removal of oxidation and corrosion products from engine exposed coatings without impacting adjacent intact coating; restoration of coating composition to optimize environmental resistance; and upgrade of existing aluminide coatings to platinum aluminide coatings without removal of the existing coating. Combined together, these technologies can be used to support a comprehensive blade repair workscope plan that dramatically increases the life of HPT blades and decreases the life cycle cost for these components. Overviews of these technologies are presented in this paper along with information on how the technology was matured. Due to pending patent applications with the US Patent & Trademark Office as well as pending patent applications in other countries, significant technical detail cannot be presented at this time.