bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deterministic Stress Modeling of Hot Gas Segregation in a Turbine
Authors: Busby Judy , Sondak Doug , Staubach Brent , Davis Roger 
Published: December 2014

Simulation of unsteady viscous turbomachinery flowfields is presently impractical as a design tool due to the long run times required. Designers rely predominantly on steady-state simulations, but these simulations do not account for some of the important unsteady flow physics. Unsteady flow effects can be modeled as source terms in the steady flow equations. These source terms, referred to as Lumped Deterministic Stresses (LDS), can be used to drive steady flow solution procedures to reproduce the time-average of an unsteady flow solution. The goal of this work is to investigate the feasibility of using inviscid lumped deterministic stresses to model unsteady combustion hot streak migretion effects on the turbine blade tip and outer air seal heat loads. The LDS model is obtained from an unsteady inviscid calculation. The inviscid LDS model is then used with a steady viscous computation to simulate the time-averaged viscous solution.
The feasibility of the inviscid LDS model is demonstrated on a single stage, three-dimensional, vane-blade turbine with a hot streak entering the vane passage at mid-pitch and mid-span. The steady viscous solution with the LDS model is compared to the time-averaged viscous, steady viscous and time-averaged inviscid computations. The LDS model reproduces the time-averaged viscous temperature distribution on the outer air seal to within 2.3%, while the steady viscous has an error of 8.4%, and the time-averaged inviscid calculation has an error of 17.2%. The solution using the LDS model is obtained at a cost in CPU time that is 26% of that required for a time-averaged viscous computation.
The NEREUS Installation — The Nuclear Part (HTR)
Authors: Crommelin Gulian A. K. 
Published: December 2014

The paper highlights on-going studies and design efforts by a team of several specialists in aspects related to a type of power generation installation, which consists of a directly coupled closed-cycle gas turbines (the Light Water Reactors have a double loupe energy transfer system coupled by a heat exchanger) to an inherently safe nuclear heat source. In particular the NEREUS installation will be discussed. NEREUS is the God for shipping in Greek mythology, but in this case it stands for: a Naturally safe, Efficient, Reactor, Easy to operate, Ultimately simple and Small. This describes very well the aims of the design team. This part will explain the inherently safe character of the nuclear heat source, the way the energy production in the heat source is controlled, the type of nuclear fuel and the treatment of the nuclear waste, the refuelling, the weight, the dimensions and the construction of the nuclear part of the NEREUS installation.
Part two will describe the non-nuclear part of the installation, the possible applications, its potential markets and the technical and financial indications from the on-going study.
This paper should be read in conjunction with the paper “The NEREUS installation — the Non-Nuclear part (GT)”.
Time-Resolved Numerical Analysis of the 2-D Aerodynamics in the First Stage of an Industrial Gas Turbine for Different Vane-Blade Spacings
Authors: von Hoyningen-Huene Martin , Hermeler Jürgen 
Published: December 2014

A numerical 2D study of the unsteady flow in the first stage of an industrial axial flow gas turbine is presented. The study focuses on the influence of the axial spacing between stator and rotor on the unsteady flow field and relevant design parameters. For six different axial spacings between 18.5 % and 60 % of rotor chord length, time-averaged and time-resolved results are presented, focusing mainly on the pressure distribution on the rotor, stage efficiency and flow angle variation.
The instantaneous pressure and entropy contours at midspan are presented for different rotor positions. The underlying physical principles are described making a clear distinction between the impact of the potential flow interaction and the wake-blade interaction. The pressure fluctuations over the stator and rotor blades and the seal air injection gap as well as the effects of axial spacing are investigated. The major focus of this paper is to examine the variation of stage efficiency and rotor incidence angle with a changing axial gap.
A simple design rule is derived in order to optimize the vane-blade spacing and it is shown that the gap chosen for the real life machine offers a good compromise between the opposing design requirements.
PIV Investigation of the Flow Characteristics in an Internal Coolant Passage With 45deg Rib Arrangement
Authors: Schabacker J. , Boelcs A. , Johnson B. V. 
Published: December 2014

Flow characteristics in a model of a stationary two-pass internal coolant passage were measured with the stereoscopic PIV technique. From the PIV measurements, the 3D mean velocity field and turbulence quantities of the flow were obtained simultaneously with high spatial resolution, which allowed for an understanding of the flow phenomena in the coolant passage.
The model of the coolant passage consists of two square legs, each having a length of 19 hydraulic diameters that are connected by a sharp 180deg bend with a rectangular outer wall. In the two legs, 45deg ribs are mounted in a staggered arrangement on the bottom and top wall, with rib heights equal to 0.1 hydraulic diameter, and rib spacing of 10 rib heights. The measurements were carried out for a Reynolds number of 45,700 with air as working medium.
The paper presents results of the flow development in the straight legs of the passage and in the bend. The oblique ribs in the straight legs contribute to the development of secondary flows that transport fluid from the leg center towards the walls. In the bend of the passage, the interaction between rib-induced and bend-induced secondary flows leads to a three-dimensional flow. Downstream of the bend, the ribs quickly dominate the flow and thus lead to a fast recovery of the flow from the bend effect.
Modeling Transfer Matrices of Premixed Flames and Comparison With Experimental Results
Authors: Schuermans Bruno B. H. , Polifke Wolfgang , Paschereit Christian Oliver 
Published: December 2014

A combined analytical/experimental investigation of the thermoacoustic properties of a gas turbine burner with a premixed, turbulent, swirl-stabilized flame is presented. In an enclosed flame, an interaction occurs between acoustic fluctuations and non-steady heat release, which may lead to thermoacoustic instabilities. This interaction may be characterized by the transfer matrix of the burner with flame. The transfer matrix describes the coupling between fluctuations of acoustic pressure and velocity on both sides of burner and flame, incorporating also the effects of heat release fluctuations on the acoustic quantities. The transfer matrix has been modeled and validated with experimental results. For the burner, an analytical model is proposed, which is based on the Bernoulli equation for instationary flow through compact elements. The model is based on the Rankine-Hugoniot relations across a thin heat source. The fundamental assumption underlying the model is that acoustic fluctuations cause modulations of fuel concentrations at the fuel injector, which result, after a certain time lag, in a fluctuating heat release rate at the flame. The oscillating heat release couples with pressure and velocity fluctuations in the combustion chamber, thereby creating a feedback loop between combustor acoustics and flame dynamics which may result in self-excited combustion instability.
The transfer matrix of the burner with flame has been determined experimentally in an atmospheric combustion test facility. The test rig was equipped with loudspeakers and microphones in order to measure the response to an acoustical excitation. Our new flame model shows to be in agreement with the measured results.
On the Development and Application of the FRAP® (Fast-Response Aerodynamic Probe) System in Turbomachines: Part 3 — Comparison of Averaging Methods Applied to Centrifugal Compressor Measurements
Authors: Köppel Pascal , Roduner Christian , Kupferschmied Peter , Gyarmathy Georg 
Published: December 2014

Typically several hundred million data points arise from a comprehensive measurement campaign carried out in a centrifugal compressor test rig with the FRAP® system (see Part 1). In order to obtain a maximum of information about the unsteady flow at any position in this turbo machine the time-resolved data processing method has to be optimized. In contrast to the standard time-averaged flow measurements with pneumatic probes, the objective of FRAP® measurements and of data processing is to extract novel information about crucial unsteady phenomena like turbulence, row-to-row interaction, modal or rotating stall, leakage flow effects etc. In such cases the simultaneous measurement of static and total pressures and flow vectors is of particular interest. Novel information means the analysis of averaged and time-resolved (wavelet) spectra, autocorrelations or time averages properly conserving physical fluxes, etc..
Different averaging methods are applied to compress the time dependent data measured by a 1-sensor-probe (see Part 2) in a centrifugal compressor. Such results could be used for comparison with pneumatic sensor measurements and CFD calculations. The comparison of averaging methods includes the averaging theories by Traupel and by Dzung which are compared to simple arithmetic time averaging. From there the specific stage work is calculated.
In analysing the time dependency several ensemble-averaging procedures for flow pressure and velocity are utilized for separating deterministic from stochastic fluctuations, extracting blade row finger prints or investigating low-frequency surge type fluctuations.
With respect to the selection and overall optimization of data processing methods an overview of generic tools is given and the modularity of the processing procedures is discussed.
A Combined Experimental and Numerical Investigation of the Flow in a Heated Rotor/Stator Cavity, With a Radial Inflow
Authors: Laroche E. , Desportes S. , Djaoui M. , Debuchy R. , Paté L. 
Published: December 2014

A combined experimental and numerical study has been conducted in order to investigate the turbulent flow in a heated rotor-stator cavity of low gap ratio, subjected to a superposed centripetal flow. In the scope of this work, the fluid can be considered as incompressible, with the consequence that the heat transfer process is dissociated from the dynamical effects. The flowfield is characterized by two separated Ekman layers and a core region.
Detailed velocity measurements have been carried out. Reynolds stresses were examined in great detail using hot wire measurements, whereas temperature-velocity correlations were obtained using combined hot wire–cold wire measurements. The temperature distribution was specified on the stator and heat fluxes were measured with fluxmeters.
Numerical simulations of the above configuration have been carried out with the following turbulence models: a two equation k-1 model, an Explicit Algebraic Reynolds Stress Model (EARSM), and an anisotropic thermal extension of the k-1 ASM model. The agreement between experimental and numerical results is generally good for the nondimensional velocities, except in the Ekman layer region. A comparison of Reynolds Stresses is also provided. The heat flux on the stator appears to be underestimated, due to the poor prediction of the Ekman layer zone.
The numerical study reveals the critical importance of the inlet conditions, and in particular of the nondimensional tangential velocity on the flow inside the cavity. A comparison with experimental data also confirms that the anisotropy is of importance mainly in the Ekman layer region.
On Instability of Overhung Centrifugal Compressors
Authors: Berot François , Dourlens Hervé 
Published: December 2014

This paper describes the synchronous vibration instability problem that occurred on a series of large overhung centrifugal compressors. The first part of this paper deals with the identification and display of the instability phenomenon: cyclic vibration amplitude variations and phase angle rotation occuring during testing of overhung centrifugal compressors. After numerical simulations and analysis of the test results, the bearing design has been identified as the cause of the problem. The second part describes the numerical study of the instability of the compressor. This problem is related to the eccentricity of the shaft in the bearing and to the shape of its orbit. We have investigated and propose different solutions to avoid this unstable dynamic behavior. These solutions have been tested on different compressors and have confirmed the results of the numerical analysis. The third part reminds a link between the thermal effect occurring in the bearings, the numerical results and the tested dynamic behavior of the compressor.
Recently, some authors such as Keogh et al. (1994) and Liebich et al. (1994) have noticed and studied this unstable behavior. Althougth the nature of the phenomenon seems to be known (de Jongh et al., 1984) (Faulkner et al., 1997a, 1997b), no universal technical solution to this important problem has been found. The contribution of this work is to present another case of the influence of the thermal effect on the dynamic behavior of an overhung compressor. We present the typical symptoms of the phenomenon, explain it, and propose the solutions we have used to avoid the problem.
Sliding Mode Control of Magnetic Bearings: a Hardware Perspective
Authors: Maslen Eric , Montie Dominick 
Published: December 2014

The physical hardware of magnetic bearing systems has a very strong impact on the application of sliding mode control to this technology. Finite current slew rates affect the character of achievable reaching conditions; flexible rotors demand the use of state observers which then affect achievable robustness; finite controller throughput and use of switching power amplifiers has substantial impact on how chatter should be addressed.
This paper formulates the sliding mode control problem for realistic rotor/magnetic actuator systems considering rotor flexibility and finite amplifier voltages. The structure of the resulting class of controllers is examined for both rigid and for flexible rotors. It is demonstrated that, fundamentally, these controllers are conventional linear state observer based controllers acting through high speed switching amplifiers as in conventional magnetic bearing technology.
Complementary Use of CFD and Experimental Measurements to Assess the Impact of Shrouded and Cantilevered Stators in Axial Compressors
Authors: Campobasso M. S. , Mattheiss A. , Wenger U. , Amone A. , Boncinelli P. 
Published: December 2014

The performance of an axial compressor with either shrouded or cantilevered stators has been analyzed. The two configurations have been compared both at design and near stall operating conditions, with the aid of CFD and experimental measurements.
Results show that shrouded or cantilevered stators impact differently on the overall performance of the tested compressor. A higher stall margin occurs with the cantilevered build, while the work coefficient and the efficiency of the shrouded build at design conditions are higher.
An overall comparison of the shrouded and cantilevered design concepts has been carried out, not only in aerodynamic but also in economic terms.
In-Service Damage Assessment and Life Prediction of Stage 1 Buckets in a Frame 9E CCGT
Authors: Kallianpur V. , Yoshioka Y. , Claeys J. , Beltran A. , Kashiwaya H. , Fujiyama K. , Tezuka H. , Sakurai T. , Aoki M. 
Published: December 2014

In-service degradation of hot gas path components were evaluated for life extension purpose in a combined cycle power plant. In this paper only results for stage 1 bucket evaluation are discussed. The study included a detailed thermal and structural analysis of the hardware simulating typical operation of the TEPCO power plant, together with nondestructive and destructive examination of the parts condition at various hot gas path inspections. The analytic predictions of critical locations compared well versus actual, and the damage trends were tracked to quantify the damage evolution in the hardware. The destructive tests also verified temperature gradients based on γ microstructure measurements at near-surface, and internal locations.
Microstructure and mechanical properties of the base metal and coating for the service exposed conditions were compared versus new buckets for baseline referencing. Also, the material properties for the service exposed condition were compared versus the original material assumptions used in the design of the original part, which also included approx. 60,000 hrs of uninterrupted creep testing. Knock down factors were established for the original materials design data in order to establish the life extension capability, and design margin beyond its specified original design life.
Life extension capability was determined using cumulative damage considerations along with the thermal-mechanical stress and strain predictions and adjusted materials properties, both of which were unique for TEPCO’s operating profile.
The Methodology of Stochastic Optimization of Parameters and Control Laws for the Aircraft Gas-Turbine Engines Flow Passage Components
Authors: Egorov I. N. , Kretinin G. V. , Kostiuk S. S. , Leshchenko I. A. , Babi U. I. 
Published: December 2014

This paper presents the main theses of stochastic approach to the multimeasure parameters and control laws optimization for the aircraft gas-turbine engines. The methodology allows us to optimize the engines taking into account the technological deflections which inevitably take place in the process of manufacturing of the engine’s components as well as engine’s control deflections. The stochastic optimization is able to find highly robust solutions, stable to inaccuracies in technological processes.
The effectiveness of the methodology is shown by example of optimization problem solution to find the control laws for the flow passage controllable elements of the 4-th generation aircraft mixed-flow turbofan engine. The use of information about the existing and advanced production technology levels during the optimization process, including some components manufacturing accuracy, allows us to considerably increase the probability of optimum solution implementation in practice. In real engine there are some components manufacturing deflections as well as control accuracy deflections. It results a certain engine’s performance deviation. An engine optimization classic deterministic approach can not take into account this circumstance, so the probability of an optimum design implementation is too low.
Combustor Liner Analysis by a Thermo-Mechanical Integrated Approach
Authors: Baldi A. , Vitale E. , Piccitto U. 
Published: December 2014

In this paper we present a mixed thermofluidodynamical and mechanical approach to the life analysis of thermally-loaded components, and apply it to a combustor liner.
When studying this class of problems, we are mostly concerned with a) the material parameter identification and b) the load history definition. While testing may alleviate the need for point a), we must put a lot of care in b), since the distribution of temperature (i.e., the thermal gradient) inside components and their load history are very difficult to measure accurately.
To face these kind of problems we take as input the results of thermofluidodynamical calculations made with the FLUENT computer code[1] at the ENEL (Italian Electric Power Company) Research Centre of Pisa to simulate the experimental behaviour of a combustor liner under different load conditions (phase 1). The output data have been processed in order to use them with the MARC Finite Element (F.E.) code transient thermal analysis (phase 2). Finally we took the MARC thermal simulation results as input to the mechanical analysis (phase 3). To interface the FLUENT and MARC codes, we developed a numerical program to map grid data (FLUENT) to the Finite Element mesh (MARC) by means of an interpolation algorithm.
This way, once we got a likely temperature distribution inside the component by means of the first step, we were able to follow the load history during the second and the third phases.
By this approach we were able to a) simulate the evolution of the combustor liner under cyclic thermal loads, b) identify the critical areas and c) make estimations of the life of the component under these loads.
Back Side-Cooled Combustor Liner for Lean-Premixed Combustion
Authors: Smith Kenneth , Fahme Anthony 
Published: December 2014

This paper describes the design and initial testing of a second generation, lean-premixed combustor for a 6100 horsepower industrial gas turbine. The full scale, prototype combustor liner employed augmented backside cooling (ABC) as a means of reducing NOx and CO emissions. A thermal barrier coating (TBC) was applied on the liner hot side to reduce thermal flux from the flame zone. The goal of the effort was to demonstrate that the avoidance of film-cooling for the combustor liner would allow emissions reductions in a lean-premixed combustion system.
Testing of the combustor was conducted in both low and high pressure environments. The testing demonstrated that the use of trip-strips for backside cooling provides an effective means of reducing CO emissions. The lower CO levels can be exploited by lowering flame temperatures to achieve lower NOx emissions. Reaction quenching associated with film cooling is indicated as the cause of the higher CO emissions in more conventional liners. Cyclic rig testing showed the TBC to have good short-term durability. Long-term field testing is getting underway.
Internal Bearing Chamber Wall Heat Transfer as a Function of Operating Conditions and Chamber Geometry
Authors: Busam Stefan , Glahn Axel , Wittig Sigmar 
Published: December 2014

Increasing efficiencies of modern aero-engines are accompanied by rising turbine inlet temperatures, pressure levels and rotational speeds. These operating conditions require a detailed knowledge of two-phase flow phenomena in secondary air and lubrication oil systems in order to predict correctly the heat transfer to the oil. It has been found in earlier investigations that especially at high rotational speeds the heat transfer rate within the bearing chambers is significantly increased with negative effects on the heat to oil management. Furthermore, operating conditions are reached where oil coking and oil fires are more likely to occur. Therefore, besides heat sources like bearing friction and churning, the heat transfer along the housing wall has to be considered in order to meet safety and reliability criteria.
Based on our recent publications as well as new measurements of local and mean heat transfer coefficients, which were obtained at our test facility for engine relevant operating conditions, an equation for the internal bearing chamber wall heat transfer is proposed. Nusselt numbers are expressed as a function of non-dimensional parameter groups covering influences of chamber geometry, flow rates and shaft speed.