bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Effective Viscosity in Bubbly Flow Using Free-Falling Sphere
Authors: Oiwa Hiroshi , Murai Yuichi , Ishikawa Masa-aki , Yamamoto Fujio
Published: February 2009

Effective viscosity of bubbly two-phase flow is experimentally investigated by means of the falling sphere method. The terminal falling velocity of the sphere is measured by image processing to calculate the relative viscosity of the two-phase flow to the single-phase flow. The measurement results show that the effective viscosity is reduced for a range from 0 to 2% of void fraction as the shearing Weber number increases. This fact implies that the reduction of the effective viscosity is governed by the deformation of the bubbles, and the mechanism is explained by the interruption of the shear stress transfer in the two-phase medium.
Scale-Up From Laboratory Pipe-Flow Data to Large Flows
Authors: Hoyt J. W.
Published: February 2009

By scale-up, one means the prediction of pressure drop in large industrial or commercial pipelines, or other flow situations, based on results from laboratory-scale small pipe facilities. Scale-up for the use of non-Newtonian fluids or drag-reducing solutions in long-distance oil pipelines, central-station heating or cooling schemes, or application to ship design, are important current interests. A simple analytical approach has been developed which provides excellent scaling over a wide range of pipe sizes for both water-based and oil-based polymer solutions. Examples are given which show close comparisons of scaling from small pipes to actual test data from much larger diameter industrial-scale facilities.
Stability Aspects of Gas Bubbles in Slug Flow
Authors: Lu Xiaozhen , Prosperetti Andrea
Published: February 2009

In a microgravity gas-liquid flow, the greater importance of surface tension relative to body forces considerably enlarges the region of parameter space in which slug flow is encountered. This paper describes numerical simulations which focus on two aspects of the stability of this type of flow. The first one is the stability of a periodic system of axisymmetric bubbles as their mutual distance is reduced. It is found that, below a certain minimum distance dependent on the parameters of the problem, consecutive bubbles tend to merge thus triggering a transition to annular flow. The second problem concerns the stability of axisymmetric flow with respect to non-axisymmetric disturbances. To study this problem, a linear stability analysis is carried out by means of a domain perturbation approach based on a numerically computed axisymmetric base state. The perturbation equations are solved numerically on the assumption of an exponential time dependence of the perturbation quantities. The numerical method used for both problems is based on a fixed-grid, front-tracking method in which the interface is tracked by means of Lagrangian marker points.
On Two-Way Coupling in Gas-Solid Turbulent Flows
Authors: Simonin Olivier , Squires Kyle D.
Published: February 2009

An analysis of kinetic energy transfer in particle-laden turbulent flows is presented. The present study focuses on the subset in which dispersed-phase motion is restricted to particles in translation, particle diameters are smaller than the smallest lengthscales in the turbulent carrier flow, and the dispersed phase is present at negligible volume fraction. An analysis of the separate and exact two-fluid mean and turbulent kinetic energy transport equations shows that momentum exchange between the phases results in a transfer of kinetic energy from the mean to the fluctuating motion of the two-phase mixture. The source term accounting for fluid-particle coupling in the fluid turbulent kinetic energy equation is written as the sum of three parts, the first part representing the production of velocity fluctuations in the particle wake (“pseudo turbulence”), the second and third contributions — which act primarily on the larger scales of the fluid turbulent motion — representing a damping effect due to the turbulent fluctuation of the drag force and the effect of the transport of the particles by the fluid turbulence against their mean relative motion. A schematic representation of the energy transfers in particle-laden mixtures is also presented for the simplified systems under consideration, consistent with the separation of scales between perturbations introduced at the scale of the particle and the large, energy-containing scales of fluid turbulent motion. Implications of the energy transfers for ensemble-averaged modeling approaches are discussed, along with computational techniques that account for the back-effect of the particles on the flow using the point-force approximation. It is shown that the point-force approximation as typically implemented only accounts for the modulation of the large eddies, the contribution to wake production is not included, being implicitly assumed to be in local equilibrium with the corresponding viscous dissipation.
Investigation of Drag Force on Non-Spherical Particle in Gas-Particle Two-Phase Flow
Authors: You Changfu , Qi Haiying , Xu Xuchang
Published: February 2009

Research of the effect of non-spherical particle on the drag force had been carried out using numerical method. At Re<100, the flow over three different non-spherical particle (cube, cylinder and frustum) had been calculated with N-S equations. In particular, the performance of three promising correlations for the drag coefficient of the non-spherical particle had been critically examined with the computational results. The best method appears to be that of Ganser which uses the equal volume sphere diameter and sphericity of particle. Comparing the results obtained by two different cylinder’s arrangement, the axis of cylinder perpendicular to the coming flow direction and parallel to that, the divergence between them is very obvious.
Estimation of Mach Number of Shock Wave Propagating in Pipe
Authors: Yamazaki Takanori , Endo Masaki
Published: February 2009

A useful way to estimate the local Mach number of shock propagating in a pipe is proposed in this paper. The shock Mach number, or the shock strength gradually decreases or increases as the shock propagates downstream in pipe due to the shock-boundary layer interaction. In general, the shock Mach number is estimated through the measurement of the time, which it takes for the shock to propagate between any two points along the pipe. This technique is very useful if the decreasing rate of the shock strength is given and it, after all, yields the average Mach number between the two points. In this paper the measurement of the local Mach number of shock in the shock tube is examined using one pressure transducer. The pressure history after the shock reaches the pressure tap is analyzed. The method to estimate the local Mach number is discussed considering the dynamic characteristic of the pressure transducer.
Structure, Multiphase Systems and Yield Stress
Authors: De Kee D. , Zhu L.
Published: February 2009

We will discuss a new slotted-plate device to directly measure static yield stresses of complex multiphase systems. Possible wall effects associated with our earlier yield-stress plate instrument have been minimized. Our new setup avoids the disadvantages of the vane instrument. Yield stress values on a variety of systems have been obtained and have been compared with the values obtained via a variety of other methods.
Feed Forward Neural Network-Based Diagnostic Tool for Gas Turbine Power Plant
Authors: Dambrosio Lorenzo , Bomba Marco , Camporeale Sergio M. , Fortunato Bernardo
Published: February 2009

A diagnostic tool able to detect faults that may occur in a gas turbine power plant at an early stage of their emergence is of a great importance for power production. In the present paper, a diagnostic tool, based on Feed Forward Neural Networks (FFNN), has been proposed for gas turbine power plants with a condition monitoring approach. The main aim of the proposed diagnostic tool is to reliably detect not only every considered single fault, but also two or more faults that may occur contemporarily. Two different FFNNs compose the proposed diagnostic tool. The first network, that is not-fully connected, operates a fault pre-processing in order to evaluate the influence of the single fault variable on the single fault condition. The second FFNN detects the fault conditions by means of an iterative process. Such a diagnostic tool has been applied to a mathematical model of a single shaft gas turbine for power generation, resulting able to detect the 100% of single faults and the 80% of combined faults.
Identifiability in Multi-Point Gas Turbine Parameter Estimation Problems
Authors: Gro¨nstedt Tomas U. J.
Published: February 2009

A method for estimating performance parameters in jet engines with limited instrumentation has been developed. The technique is applied on a nonlinear steady state performance code by making simultaneous use of a number of off-design operating points. A hybridized optimization tool using a genetic algorithm to obtain an initial estimate of the performance parameters, and a gradient method to refine this estimate, has been implemented. The method is tested on a set of simulated data that would be available during performance testing of a PW100 engine. The simulated data is generated assuming realistic noise levels. The technique has been successfully applied to the estimation of ten performance parameters using six simulated measurement signals. The determination of identifiability (the property governing whether the performance parameters of the model can be uniquely determined from the measured data) and the selection of parameters in the performance model has been based on the analysis of the system Hessian, i.e. the multidimensional second derivative of the goal function. It is shown, theoretically as well as in practice, how the process of selecting model parameters can be approached in a systematic manner when nonlinear multi-point problems are studied.
Non-Linear Engine Component Fault Diagnosis From a Limited Number of Measurements Using a Combinatorial Approach
Authors: Aretakis N. , Mathioudakis K. , Stamatis A.
Published: February 2009

A method for diagnosing component faults of jet engines is presented. It uses non-linear gas path analysis techniques to determine the values of health parameters, with the help of a suitably formulated engine simulation model. The incentive of the method is to achieve the determination of the values of component health indices when a limited number of measured quantities is available, which do not allow the determination of all the fault indices simultaneously. A combinatorial approach is introduced, in order to circumvent the problem of the insufficient information for determining a full set of indices. After obtaining a set of possible solutions, a selection procedure is applied to isolate the ones that can give the actual fault identity. Quantification of the fault comes at a final step, when the faulty component has been identified. Different scenarios of faults on a twin spool partially mixed turbofan engine are considered in order to demonstrate the effectiveness of the method. The limitations of the method are also discussed.
Time Domain Simulation of Combustion Instabilities in Annular Combustors
Authors: Pankiewitz Christian , Sattelmayer Thomas
Published: February 2009

A novel method for the simulation of combustion instabilities in annular combustors is presented. It is based on the idea to solve the equations governing the acoustics in the time domain and couple them to a model for the heat release in the flames. The linear wave equation describing the temporal and spatial evolution of the pressure fluctuations is implemented in a finite element code. Providing high flexibility, this code in principle allows both the computational domain to be of arbitrary shape and the mean flow to be included. This yields applicability to realistic technical combustors. The fluctuating heat release acting as a volume source appears as a source term in the equation to be solved. Employing a time-lag model, the heat release rate at each individual burner is related to the velocity in the corresponding burner at an earlier time. As saturation also is considered, a non-linearity is introduced into the system. Starting the simulation from a random initial perturbation with suitable values for the parameters of the heat release model, a self-excited instability is induced, leading to a finite-amplitude limit cycle oscillation. The feasiblity of the approach is demonstrated with 3D-simulations of a simple model annular combustor. The effect of the model parameters and of axial mean flow on the stability and the shape of the excited modes is shown.
Low-Order Acoustic Modelling for Annular Combustors: Validation and Inclusion of Modal Coupling
Authors: Evesque Ste´phanie , Polifke Wolfgang
Published: February 2009

A two-dimensional low-order model of a generic annular premixed combustor, comprising an annular combustion chamber connected to an annular plenum via a finite number of burners, is developed and validated. The shapes and frequencies of the eigenmodes as well as the stability of the combustor against self-excited oscillations can be predicted with such a model. The dynamical characteristics of each burner is described mathematically in terms of its transfer matrix. The case where the transfer matrices of individual burners differ from each other can be handled by the model formulation presented. This is important in situations where non-identical burners are used in an annular combustor as a means of passive control, or where nonlinear effects lead to non-identical burner behaviour. The resulting loss of axisymmetry enhances the coupling between nonplane acoustic modes of different order. This modal coupling is accounted for by the model. The eigenmode shapes and frequencies predicted by the low-order model are validated by comparison with the results of a three-dimensional finite element acoustic model of a generic annular combustor configuration.
Thermoacoustic Flame Response of Swirl Flames
Authors: Krebs Werner , Hoffmann Stefan , Prade Bernd , Lohrmann Martin , Bu¨chner Horst
Published: February 2009

The operating range of heavy duty gas turbines featuring lean premix combustion to achieve low Nox emissions may be limited by thermoacoustic oscillations. The most promising way to extend the operational envelope of the gas turbine is to modify the burner outlet conditions which itself strongly affect the flame response on acoustic perturbations. The objective of the present paper is the analysis and prediction of the flame response of premixed swirl flames which are typical for gas turbine combustion. The flame response has been determined experimentally by measuring the velocity fluctuations of a forced pulsated burner flow with hot wire probes and the resulting heat release fluctuations OH radiation. The experimentally determined flame response function for the swirl premixed flame follows almost a time lag law. Hence, reasonable agreement has been found between measurements and calculations using a time lag model.
An Annular Combustor Natural Gas Ignition Model Derived From Atmospheric Sector Experiments
Authors: Hirsch C. , Ku¨enzi T. , Kno¨pfel H. P. , Paikert B. , Steinbach C. , Geng W. , Do¨bbeling K.
Published: February 2009

Results from ignition and cross-ignition tests performed on an atmospheric 60°-sector test rig equipped with three EV-type burners are presented. Based on these results a model was developed for an annular combustor, which calculates the primary ignition and burner-burner cross-ignition limits for the combustor in terms of burner operation variables (equivalence ratio and pilot fuel ratio) using a generally applicable methodology described in the paper. Key ingredients of the model are the description of mixture flammability and a mixing model representing the ignition relevant mixing behaviour of the burners in the annular combustor. Ignition and cross-ignition are observed to occur, if the mixture equivalence ratio determined from the mixing model is above the flammability limits calculated for the particular operating conditions. Even in the case of cross iginition across an externally piloted or switched-off burner, the model reproduces the experimental cross-ignition limits, confirming that the basic physics have been captured.
Turbulence-Chemistry Interactions in Spray Combustion
Authors: Sankaran Vaidyanathan , Menon Suresh
Published: February 2009

A prediction methodology based on Large-Eddy Simulation (LES) has been used to study turbulence-chemistry interactions in spray combustion. The unsteady interactions between spray dispersion and vaporization, fuel-air mixing and heat release has been investigated using a Stochastic Separated Flow model for spray within the LES formulation. The effects of swirl intensity and heat release are investigated here. Results show that the central toroidal recirculation zone (CTRZ), which is a manifestation of the vortex breakdown process, occurs only under high swirl conditions. Under non-reacting condition, droplets tend to concentrate in regions of low vorticity and increase in swirl increases the dispersion of the droplets. Mixing efficiency is enhanced and the size of the corner recirculation zone is decreased with increase in swirl. Increase in swirl also enhances the combustion processes for cases with heat release.
Improvement of Gas Turbine Injection Systems by Combined Experimental/Numerical Approach
Authors: Riccio G. , Adami P. , Martelli F. , Cecchini D. , Carrai L.
Published: February 2009

An aerodynamic study for the premixing device of an industrial turbine gas combustor is discussed. The present work is based on a joint application of numerical CFD and experimental investigation tools in order to verify and optimize the combustor gaseous fuel injection system. The objective is the retrofit of an old generation gas turbine combustion chamber that is carried out considering new targets of NOx emission keeping the same CO and combustion stability performances. CFD has been used to compare different premixing duct configurations for improved mixing features. Experimental test has been carried out in order to assess the pollutant emissions, flame stability and pattern factor characteristics of the full combustion chamber retrofitted with the modified injection system.
Optimisation of Biomass Fuelled Gas Turbines Using Genetic Algorithms
Authors: Ferreira Sandro B. , Pilidis Pericles , Widell Henrik
Published: February 2009

The economic and design optimisation of gas turbine cycles using biomass fuel gives a clear picture of which kind of cycle is more suitable for a given application, regarding capital and fuel costs. Due to its low specific energy, raw fuel transportation plays a large role in the final cost of electricity. Other factors of influence are the availability of the biomass in each season and the power plant location. An economic and exergy destruction optimisation of a BIGGT, biomass integrated gasification/gas turbine, and EFGT, externally fired gas turbine, cycles is carried out in this paper. Then the sensitivity of the systems to fuel costs, as well as to investment life, is assessed in order to evaluate the influence of these parameters in the final optimised cost of electricity. The Genetic Algorithms, GA, technique, a well known robust technique, is used for the optimisation in this work. The GA tool, GENIAL 1.1® has been written in Fortran77 computer language and was developed by Widell, 1997. The software for the cycle design performance was developed under Fortran90. The EFGT cycle seems to be very promising in terms of cost of electricity and efficiency. The calculations also show that the BIGGT cycle still needs further improvements in the gasification process regarding costs and performance. The cycle used as reference is the well known gas natural/gas turbine cycle, NGGT.
Brayton or Brayton-Rankine Combined Cycle With Hot-Gas Recirculation and Inverse Mixing Ejector
Authors: Stankovic Branko
Published: February 2009

An open/closed gas-turbine simple Brayton cycle or Brayton-Rankine gas- and steam-turbine combined-cycle power-producing system is proposed, with the gas turbine recirculating a large portion of partly expanded high-temperature gas into an inverse mixing ejector. The inverse mixing ejector uses injected-gas velocity that is necessarily greater than jet-gas velocity to increase the hot-gas pressure up to the compressor-discharge level. This is a necessary condition for achieving very high cycle thermal efficiency. Maximum combined-cycle thermal efficiency can be expected to reach up to about 80%, up to an appropriate temperature-level Carnot-cycle efficiency. The inverse mixing ejector can operate in either subsonic or supersonic (necessary for higher cycle thermal efficiencies) regions of gas velocity. The gas turbine cycle can operate in either simple-cycle, single-intercooled-cycle or multi-intercooled-cycle mode.
Design and Economics of the HTGR-GT Power Plant by JAERI
Authors: Muto Yasushi , Ishiyama Shintaro , Shiozawa Shusaku , Tanihira Masanori , Miyoshi Yasuyuki , Ohashi Kazutaka
Published: February 2009

This paper describes the conceptual design and cost estimation of a 600MW(t) HTGR-GT power plant, which has been completed in the framework of the HTGR-GT feasibility study project in the duration of FY 1996 to FY 2000. The project is assigned to JAERI by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) (former Science and Technology Agency) in Japan. The inlet and outlet gas temperatures in the reactor are 460°C and 850°C, respectively. Helium gas pressure is 6MPa. The gas turbine system type is an intercooled recuperative direct cycle. Designs of reactor and gas turbine are presented. The main feature of the plant is a relatively large 600 MW(t) HTGR, horizontal single shaft helium turbine and divided power conversion vessel, that is, a turbomachine vessel and heat exchanger one. Their main specifications and drawings are presented. As a result of cost estimation, an economically attractive construction cost and a power generation cost have been obtained.
New Possibilities for Combined Cycles Through Advanced Steam Technology
Authors: Jordal Kristin , Fridh Jens , Hunyadi La´szlo´ , Jo¨nsson Mikael , Linder Ulf
Published: February 2009

In order to improve the performance of the combined cycle, much effort has been spent over the past decade on increasing gas turbine performance. As a contrast to this, the present work focuses on possibilities for combined cycle performance enhancement through present and expected future steam cycle and boiler technology. The use of various heat recovery steam generators, (single and dual pressure) with or without supplementary firing are studied, in combination with steam turbine admission temperatures of up till 973 K. Supplementary firing is applied either in the entire gas turbine exhaust duct or in part of it, in a so-called split-stream boiler (SSB). Furthermore, the flashing of pressurized water from an overdimensioned economiser in the SSB, to produce steam for gas turbine vane cooling is studied. Many of the supplementary fired cycles studied are found to have a thermal efficiency superior of the unfired cycles, based on the same gas turbines. Hence, available steam technology and expected future development mean that most of the cycles studied are realistic concepts that merit further attention in the quest for more efficient power production.
Effects of Tip Geometry and Tip Clearance on the Mass/Heat Transfer From a Large-Scale Gas Turbine Blade
Authors: Papa M. , Goldstein R. J. , Gori F.
Published: February 2009

An experimental investigation has been performed to measure average and local mass transfer coefficients on the tip of a gas turbine blade using the naphthalene sublimation technique. The heat/mass transfer analogy can be applied to obtain heat transfer coefficients from the measured mass transfer data. Flow visualization on the tip surface is provided using an oil dot technique. Two different tip geometries are considered: a squealer tip and a winglet-squealer tip having a winglet on the pressure side and a squealer on the suction side of the blade. Measurements have been taken at tip clearance levels ranging from 0.6% to 3.6% of actual chord. The exit Reynolds number based on actual chord is approximately 7.2 × 105 for all measurements. Flow visualization shows impingement and recirculation regions on the blade tip surface, providing an interpretation of the mass transfer distributions and offering insight into the fluid dynamics within the gap. For both tip geometries the tip clearance level has a significant effect on the mass transfer distribution. The squealer tip has a higher average mass transfer that sensibly decreases with gap level, whereas a more limited variation with gap level is observed for the average mass transfer from the winglet-squealer tip.
Determination of Non-Uniform Heat Transfer Coefficients Around a Solid Aluminum Alloy Complex Shape During Quenching by Using an Inverse Method
Authors: Chen Pen-Chung , Kaminski Deborah A. , Messler Robert W.
Published: February 2009

Gas turbine systems include complex heat transfer problems. Especially, the cooling efficiency is critical to the operation of gas turbine. In order to achieve the desired cooling condition, one needs to know the distribution of heat transfer on the components; however, the cost to implement a full-scale gas turbine test is tremendous. Therefore, many researchers used simplified models to acquire the test data; certain experiments can provide heat flux measurement, whereas other techniques can measure heat transfer coefficients. The direct measurement of heat transfer coefficients on the surface of components is extremely difficult. In such situations, the inverse method using transient temperature measurements taken within the part can be used to determine heat transfer coefficients. By combining experiments and numerical modeling, this presentation attempts to provide an effective and robust method to determine heat transfer coefficients on the part’s surface during cooling. Though the setting of the present paper is the quenching of a part, the technique presented is proposed for in-service heat load. To characterize the present situation, i.e., non-uniform heat transfer coefficients occurring during quenching, a unique methodology for employing inverse heat conduction was developed to obtain heat transfer coefficients from temperature responses. In conventional inverse approaches, the heat transfer coefficient is assumed to be uniform around the periphery, but this approach sometimes is unrealistic, especially for complex shaped parts. In this study, experimental data were used to find parameters in a heat transfer correlation, rather than to determine the coefficients directly. The resulting analysis provided an improved fit to measurements compared to conventional inverse approaches. The method developed was robust and is extendable to parts of arbitrary shape.
Predictions of External Heat Transfer for Turbine Vanes and Blades With Secondary Flowfields
Authors: Hermanson K. , Kern S. , Picker G. , Parneix S.
Published: February 2009

Detailed heat transfer distributions on the endwall and along the vane/blade surface are essential for component mechanical integrity and life predictions. Due to secondary flows, high gradients in heat transfer are present at the endwall and at the vane or blade surface itself where the passage vortex influences the mainstream flow. This paper documents the benchmarking of three turbulence models; (1) k-ε realizable with wall functions (2) k-ε realizable with two layer model, and (3) the V2F model for endwall and surface heat transfer and flowfield predictions. Benchmark experimental data from a scaled-up low speed rig for both a stator and rotor geometry are used for comparisons of heat transfer and flowfield. While the k-e realizable turbulence models give a good prediction of the secondary flow pattern, the heat transfer at the endwall and at the surface is not well predicted due to the inadequate modeling of near wall turbulence. The V2F model gives better agreement with the experiments on the endwall and vane midspan heat transfer is also well predicted, although transition occurs too far upstream on the suction surface. The results from this study represent the feasibility of CFD utilization as a predictive tool for local heat transfer distributions on a vane/blade endwall.
Combined 3D Flow and Heat Transfer Measurements in a 2-Pass Internal Coolant Passage of Gas Turbne Airfoils
Authors: Chanteloup D. , Juaneda Y. , Bo¨lcs A.
Published: February 2009

A study of the flow and heat transfer in a stationary model of a two-pass internal coolant passage is presented, which focuses on the flow characteristic effects on the wall heat transfer distribution. Results are given in the upstream fully developed region. Heat transfer measurements were made with a transient technique using thermochromic liquid crystal technique to measure a surface temperature. The technique allows full surface heat transfer coefficient measurements on all the walls. Flow measurements were made with a stereoscopic digital PIV system, which measures all three-velocity components simultaneously. The coolant passage model consists of two square ducts, each having a 20 hydraulic diameter length. The ducts are connected by a sharp 180° bend with a rectangular outer wall. 45° ribs are mounted in a staggered arrangement on the bottom and top walls of both legs. The height of the ribs is equal to 0.1 hydraulic diameters. They are spaced 10 rib heights apart. The flow and heat transfer measurements were obtained at one flow condition with an inlet flow Reynolds number, based on the hydraulic diameter, of 50,000. The paper presents detailed measurement results of the flow characteristics and of the heat transfer distribution in the upstream straight leg of the passage and describes how the main and secondary flows influence the heat transfer distribution in the fully developed regions of the channel.
Numerical Analysis of Turbomachinery Flows With Transitional Boundary Layers
Authors: De Palma P.
Published: February 2009

This paper provides a numerical study of the flow through two turbomachinery cascades with transitional boundary layers. The aim of the present work is to validate some state-of-the-art turbulence and transition models in complex flow configurations. Therefore, the compressible Reynolds-averaged Navier–Stokes equations, with an Explicit Algebraic Stress Model (EASM) and k − ω turbulence closure, are considered. Such a turbulence model is combined with the transition model of Mayle for separated flow. The space discretization is based on a finite volume method with Roe’s approximate Riemann solver and formally second-order-accurate MUSCL extrapolation with minmod limiter. Time integration is performed employing an explicit Runge–Kutta scheme with multigrid acceleration. Firstly, the computations of the two- and three-dimensional subsonic flow through the T106 low-pressure turbine cascade are briefly discussed. Then, a more severe test case, involving shock-induced boundary-layer separation and corner stall is considered, namely, the three-dimensional transonic flow through a linear compressor cascade. In the present paper, calculations of such a transonic flow are presented, employing the standard k − ω model and the EASM, without transition model, and a comparison with the experimental data available in the literature is provided.
The Development of High Performance Leaf Seals
Authors: Nakane H. , Maekawa A. , Akita E. , Akagi K. , Shinohara T. , Uehara H.
Published: February 2009

Recently, from the environmental point of view, demand for combined cycle plant is increasing, and superior gas turbine performance is being rapidly promoted at the same time. As one of the key technologies for superior performance, reduction of secondary air leakage which is necessary for blade cooling and bearing sealing is required. Especially, reduction of air leakage through rotating parts and stationary parts clearance is critical problem. Hitherto, a non-contact type labyrinth seal has been widely used as a seal between rotating parts and stationary parts. However, this seal requires a large clearance to avoid contact, and this causes reduction of performance due to large amount of air leakage. Currently, application of brush seal is rapidly increasing as an improvement, however, a brush seal maintains contact not only at shut down, but also during operation, thereby wear of wire is accelerated during prolong operation, and reducing the sealing performance. In addition, since stiffness of the wire itself is low, differential sealing pressure is also low. In order to overcome these short comings, so-called “Leaf seal” which is MHI’s patent has been developed over the years. Leaf seal has a structure in which multi layered flexible leaves are arranged in the circumferential direction. In this seal, tip of the leaf is lifted up from the rotor surface by the hydrodynamic effect as the rotating speed is accelerated. As a result of this mechanism, wear of the seal is reduced during operation. The clearance generated by the leaf tip lifting up is negligibly small and, therefore, sealing performance is better. Moreover, because the leaf has an axial width, it can endure seal differential pressure several times that of the brush seal. The effect of the leaf lifting up and the leakage air amount were verified by rig tests. After these verification tests, this leaf seal is now being used for M501G gas turbine, installed at *T-point, in order to confirm sealing performance and durability. The leaf seal can sustain high differential pressure even if it is used in single stage, and has very good durability. To conclude it can be said that the leaf seal is the next generation seal replacing the brush seal. * MHI constructed the long-term in-house verification plant known as T-point for verifying new gas turbine technology prior to commercialization. The facility at T-Point consists of a M501G gas turbine, steam turbine, HRSG and associated controls. The output of the M501G gas turbine at T-Point is 225MW.
Upgrades of Steam Turbine Generator Units in Watson Cogeneration Combined Cycle Plant
Authors: Ingistov Steve
Published: February 2009

This paper describes efforts that were implemented in modifying two Steam Turbine Generators (STG) that are presently operating in Watson Cogeneration Company (WCC) Plant. WCC Plant is comprised of four identical GE made Gas Turbine Generators (GTG) and four Heat Recovery Steam Generators (HRSG) designed and fabricated by Vogt. Portion of high pressure steam is expanded inside two Dresser-Rand-made Steam Turbine Generators (STG). The modifications presented in this paper include replacement of six original stages of expansion, introduction of shaft retractable labyrinths/packing and installation of the spill strips around shrouded blades. The modifications of high pressure steam path (except 1st stage blading) were completed in 1992 and modification of rotor steam sealing elements such as shaft labyrinths were completed in April and May 2001. The steam path modification uprated STG from original 34.50MW to present 40MW each. The upgrades of the rotor sealing elements resulted in 2.80% Heat Rate (HR) reduction.
Development of the Advanced Cycle Low-Power Gas Turbine Alternator (ACL GTA)
Authors: English C. R. , Fielder J.
Published: February 2009

The Royal Navy is pursuing the ‘All Electric’ ship under its Marine Engineering Development Strategy. This strategy envisages the use of long life, fuel efficient, advanced cycle marine gas turbine alternator sets in an Integrated Full Electric Propulsion (IFEP) system which includes the wide scale electrification of auxiliary systems. The IFEP system favoured by the Royal Navy requires just four prime movers for a typical European sided Frigate or Destroyer; two high power units (2 × 20–25MW), one medium power (1 × 4–8MW), one low power unit (1 × 1–2MW), and employs single engine operation at sea. The high power unit, the WR21, has already completed development. In December 2000 the Royal Navy placed a contract on Turbomeca Limited of France to develop a 1.8 MW advanced cycle gas turbine alternator. The paper provides details of the development of this 1.8MW gas turbine alternator know as the Advanced Cycle Low-power Gas Turbine Alternator (ACL GTA). It describes the basic engine design including recuperator, outlines the predicted performance, and gives details of the directly coupled high speed alternator and associated power electronic to provide the 800V DC output. The overall programme is discussed, along with the outstanding issues. Reference is made to the GTA’s ability to compete in a highly competitive market dominated by diesel driven alternators.
Gas Turbine Performance Prediction by Using Generalized Performance Curves of Compressor and Turbine Stages
Authors: Spina P. R.
Published: February 2009

The paper presents a method for gas turbine performance prediction which uses compressor and turbine performance maps obtained by using generalized stage performance curves matched by means of the “stage–stacking” procedure. In particular, the overall multistage compressor performance is predicted using generalized relationships between stage efficiency, pressure coefficient and flow coefficient, while the multistage turbine performance is predicted by modeling each turbine stage by a series of two nozzles, a fixed one (stator) and a moving one (rotor). The characteristic of the proposed method is that the unknown parameters defining the generalized stage performance curves are determined by combining a Cycle Program with the compressor and turbine performance maps obtained using the “stage–stacking” procedure, and by searching for the values of the unknown parameters which better reproduce, by means of the Cycle Program, the overall performance and thermodynamic data measured on a gas turbine.
On Reducing Piping Vibration Levels: Attacking the Source
Authors: Liu Zheji , Hill D. Lee , Motriuk Roman
Published: February 2009

Centrifugal compressors used in the pipeline market generate very strong noise, which is typically dominated by the blade passing frequency and its higher harmonics. The high level noise is not only very disturbing to the people living nearby the installation site but also causes expensive structural failures in the downstream piping. A novel design of Helmholtz array has been developed to address this type of noise problem. Computational studies show that the installation of the Helmholtz array acoustic liner on the compressor diffuser walls is very effective in reducing noise level of the compressor, especially the dominant blade passing frequency noise. The acoustic liner design has been built and tested at an installation site by the customer. The data clearly shows that the use of acoustic liners is indeed very effective in the reduction of both the noise and the vibration levels of the machine.
Predicting Bladerow Interactions Using a Multistage Time-Linearized Navier-Stokes Solver
Authors: Ning W. , Li Y. S. , Wells R. G.
Published: February 2009

A multistage frequency domain (time-linearized/nonlinear harmonic) Navier-Stokes unsteady flow solver has been developed for predicting unsteady flows induced by bladerow interactions. In this paper, the time-linearized option of the solver has been used to analyze unsteady flows in a subsonic turbine test stage and the DLR transonic counter-rotating shrouded propfan. The numerical accuracy and computational efficiency of the time-linearized viscous methods have been demonstrated by comparing predictions with test data and nonlinear time-marching solutions for these two test cases. It is concluded that the development of efficient frequency domain approaches enables unsteady flow predictions to be used in the design cycles to tackle aeromechanics problems.
Dynamic Response of a Hydrodynamic Thrust Bearing-Mounted Rotor
Authors: Shiau T. N. , Hsu K. S. , Chang J. R.
Published: February 2009

For investigating the dynamic response of a hydrodynamic thrust bearing-mounted flexible rotor, the dynamic characteristic data of thrust bearings for high surface velocities are applied for constructing the equation of motion for the rotor system, which is modeled with the finite element method (FEM). Based on the short bearing approximation and the π film cavitation model of the nonlinear oil-film forces, the dynamic responses are investigated using direct numerical integration with a variable order solver based on the numerical differentiation formulas (NDFs). Harmonic, quasi-periodic and chaotic motions are predicted for a range of spin speeds of the rotor. Poincare´ maps of predicted rotor trajectories are also examined. It shows that spin speeds of the rotor and the oil film force coefficient might promote undesirable non-synchronous vibrations.
An Experimental and Computational Study of the Formation of a Streamwise Shed Vortex in a Turbine Stage
Authors: Pullan Graham , Denton John , Dunkley Michael
Published: February 2009

Shear layers shed by aircraft wings roll up into vortices. A similar, though far less common, phenomenon can occur in the wake of a turbomachine blade. This paper presents experimental data from a new single stage turbine that has been commissioned at the Whittle Laboratory. Two low aspect ratio stators have been tested with the same rotor row. Surface flow visualisation illustrates the extremely strong secondary flows present in both NGV designs. These secondary flows lead to conventional passage vortices but also to an intense vortex sheet which is shed from the trailing edge of the blades. Pneumatic probe traverses show how this sheet rolls up into a concentrated vortex in the second stator design, but not in the first. A simple numerical experiment is used to model the shear layer instability and the effects of trailing edge shape and exit yaw angle distribution are investigated. It is found that the latter has a strong influence on shear layer rollup: inhibiting the formation of a vortex downstream of NGV 1 but encouraging it behind NGV 2.
Investigation of Flow Structures and Losses at the Endwall Sections of the Last Stage Blade
Authors: Granovski A. V. , Kostege M. K.
Published: February 2009

The paper presents the detailed investigation of the flow structure and losses in a hub and tip sections of the last blade of the multistage turbine. The design of the last blade has been carried out on the basis of the in-house blade generator (BLAGEN) which allows to create optimal plane sections (usually 3–5) along blade height and to stack whole blades of various 3D shapes. The viscous flow structure and the loss variation have been investigated at the endwall sections of the last blade by means of 2D and 3D Navier–Stokes codes. These investigations have been carried out for a wide range of modes and incidences. As a result the influence of the following parameters (maximum thickness-to-chord ratio, leading metal angle, Re number, exit Ma number and etc.) on the flow structure and losses has been investigated. On the basis of these investigations some recommendations for the last blades design have been developed. Numerical investigations have been validated by the comparison between numerical and test data for the outlet flow.
Improving 3D Flow Characteristics in a Multistage LP Turbine by Means of Endwall Contouring and Airfoil Design Modification: Part 2 — Numerical Simulation and Analysis
Authors: Gier Jochen , Ardey Sabine , Eymann Stefan , Reinmo¨ller Ulf , Niehuis Reinhard
Published: February 2009

Endwall losses contribute significantly to the overall losses in modern turbomachinery, especially when aerodynamic airfoil load and pressure ratios are increased. Hence, reducing the extend and intensity of the secondary flow structures helps to enhance overall efficiency. This work will focus on secondary flow reduction in typical aero engine low pressure turbines. From the large range of viable approaches, a promising combination of axis symmetric endwall contouring and 3D airfoil thickening was chosen. Aerodynamic design, experimental verification and further analysis based on numerical simulation are described in a two part paper. In the second part the implications of the 3D modifications on the flow structure are analyzed by employing a 3D Navier-Stokes simulation based on the experimental data reported in part one. For obtaining reliable flow simulations at typical LP turbine conditions, it is important to apply a 3D Navier-Stokes solver with proven turbulence and transition modeling to the three-stage LP turbine of the Institute of Aeronautical Propulsion at Stuttgart University. Numerical and experimental results exhibit regions, where the modified design leads to a change in flow pattern in accordance with the design intent, as well as regions with an actual increase in loss production. The flow changes in both regions are evaluated and discussed. It is found that a certain local loss increase phenomenon can also be found in other LP turbine rigs. The reasons for this behavior are analyzed by a comparison with data from other turbine rigs and by an additional variation of the 3D design of the first stage of the investigated turbine.
Numerical Study of the Internal Flow Field Characteristics in Mixed Flow Turbines
Authors: Palfreyman D. , Martinez-Botas R. F.
Published: February 2009

Presented is a numerical investigation of the characteristics of the internal flow field of a high-speed low-pressure ratio mixed flow turbine of 95.14 mm tip diameter. A commercial computational fluid dynamics (CFD) code has been successfully employed. This has been carefully validated to experimental data taken from a turbine test facility at this institution. A comparison to gated (in phase with the turbine rotation) Laser Doppler Velocimetry measurements at the turbine trailing edge and total to static efficiencies at various operating conditions, was made showing good agreement. Details of the internal flow field from a numerical study using a 393,872 cell density model are presented. These details have been compared to a radial turbine of similar geometry and performance characteristics, also analyzed using the same cell density and analysis and boundary conditions. The flow field was found to be highly three-dimensional with the tip leakage vortex as the dominant secondary flow feature. The tip clearance flow was found to be significantly influenced by the relative motion of the shroud wall, which suppressed the development of a vortex within the mainstream passage particularly in the inducer region. Comparison to the radial turbine has shown noticeable differences concentrated in the inducer region where the greater Coriolis acceleration in the radial turbine is more influential in the development of secondary flows. Considerable loss is observed localized at the blade leading edge tip region along the full length of the blade pitch; this is associated with the increased streamline curvature in the meridional plane.