bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Optimization of Industrial Centrifugal Compressor Stations Employing Data-Driven Methods
Authors: Xenos Dionysios P. , Cicciotti Matteo , Bouaswaig Ala E. F. , Thornhill Nina F. , Martinez-Botas Ricardo
Published: September 2014

This paper addresses optimal operation of centrifugal compressors operating in a parallel configuration. A group of compressors operates in parallel to increase the supply of a gas. One current practice is to distribute the load equally without considering the fact that the individual compressors have different characteristics and they are in a different health condition due to past hours of operation and non-uniform maintenance plan. Data from past operation is used for generating data-driven models of the compressors. These models and operational constraints of the compressor station are used in an optimization model. The optimization model computes the distribution of both the load and cooling water of each compressor which reduces the operational cost, i.e. power consumption of the motors and purchase of cooling water. The suggested optimization model is applied on a real process case study. The results from optimal operation from optimization show a reduction in the power consumption of the compressor station compared to the actual power consumed in past operation. The magnitude of this benefit ranges between 0.67 up to 2.16 %.
Analytical and Numerical Evaluation of the Axial Stress Distribution of Two Soft-Packed Stuffing-Box Configurations
Authors: Kazeminia Mehdi , Bouzid Abdel-Hakim
Published: September 2014

Stuffing-box packed valves which confine high-pressure fluids are often subjected to leakage failure. The lack of a design procedure and the vulnerability of packing ring sealing materials to withstand different operating conditions are the root cause of the problem. The sealing performance of valves with packed stuffing-box depends on the ability of the assembly to maintain a minimum threshold contact pressure between the packing and the stem and the packing and the housing throughout service operation. The distribution of the contact stresses in the packing materials is a key parameter to efficient sealing performance.

This study presents a contact stress modeling study of two different design configurations that are helpful to produce a uniform distribution of the contact stress. The first model is based on the introduction of a variable gap between the packing and the side walls. The second model is based on a multistage loading of the packing rings. The two developed analytical models are validated by comparison with the numerical simulation using FE method and the results show a good agreement. The two design configurations can be used to improve valve sealing performance.
Identification of Mistuning for Casted Turbine Wheels of Small Size
Authors: Hemberger David , Filsinger Dietmar , Bauer Hans-Jörg
Published: September 2014

The production of bladed structures, e.g. turbine and compressor wheels, is a subject of statistical scatter. The blades are designed to be identical but differ due to small manufacturing tolerances. The manufacturing tolerances may lead to difference in shape, mass and stiffness distribution of the turbine blades. But it can also take effect on in-homogeneities in the material, which are caused by the casting process and can, for example, reflect in residual stresses and grain size differences. These properties can lead to so called mistuning that increases vibration amplitudes compared to the ideal tuned case, which can end in critical vibration conditions.

The object of this study is to determine the main source of mistuning for casted turbine wheels in automotive turbocharger applications. The authors have shown in context of a study on mistuning modeling for turbine wheels in automotive turbochargers, that the mistuning due to the geometrical deviation of the shape is not necessarily solely the main mistuning source.

To examine this, various numerical models were evaluated, but also measurements during operation and standstill condition were carried out. Casted turbine wheels with different grain structures and also milled turbine wheels from forged round blanks were analyzed. Besides these, FE-models from casting simulations were used to analyze residual stress and material property effects on mistuning.

For the milled turbine wheels the source of the mistuning could be assigned to the deviation of the blade shape. The source of mistuning for the casted turbine wheels, however, could be attributed to the material in-homogeneity.
Efficient Rotating Frame Simulation in Turbomachinery
Authors: Remaki L. , Ramezani A. , Blanco J. M. , Antolin J. I.
Published: September 2014

This paper deals with the simulation of steady flows in turbomachinery. Two approaches are proposed, the first one is the classical multiple-rotating frame method (MRF) by multi-zone approach where the different zones are separated by non-overlapping interfaces and solved independently. Since each zone is loaded separately, a transferring system should be properly implemented at the interface boundaries. Two techniques are considered, in the first one the conservative variables are interpolated between zones while in the second one the fluxes are transferred through the interfaces.

The other proposed approach is a new version of the MRF using a virtual interface (VMRF). This is a simplified of the previous one where the interfaces are created virtually at the solver level, rendering the method easy to implement especially for edge-based numerical schemes, and avoiding any re-meshing in case one needs to change interface position, shape or simply remove or add new one. Finally, numerical tests are performed to demonstrate the efficiency of the proposed methods by comparison with commercial codes (ANSYS FLUENT).
Application of an Analytical Method to Locate a Mixing Plane in a Supersonic Compressor
Authors: Benichou E. , Trébinjac I.
Published: September 2014

In order to achieve greater pressure ratios, compressor designers have the opportunity to use transonic configurations. In the supersonic part of the incoming flow, shock waves appear in the front part of the blades and propagate in the upstream direction.

In case of multiple blade rows, steady simulations have to impose an azimutal averaging (mixing plane) which prevents these shock waves to extend upstream. In the present paper, several mixing plane locations are numerically tested and compared in a supersonic configuration.

An analytical method is used to describe the shock pattern. It enables to take a critical look at the CFD steady results. Based on this method, the shock losses are also evaluated. The good agreement between analytical and numerical values shows that this method can be useful to wisely forecast the mixing plane location and to evaluate the shift in performances due to the presence of the mixing plane.
Fuel Influence on Targeted Gas Turbine Combustion Properties: Part II — Detailed Results
Authors: Burger Victor , Yates Andy , Mosbach Thomas , Gunasekaran Barani
Published: September 2014

The paper presents the results from a study that formed part of a bilateral project between DLR-VT and Sasol Technology Fuels Research aimed at investigating the potential influence of physical and chemical fuel properties on ignition and extinction limits within heterogeneous gas turbine combustion. The threshold of flame extinction and re-ignition behaviour of a range of alternative fuels was investigated in a representative aero-combustor sector to determine the relative influence of physical properties and chemical reaction timescales.

A matrix of eight test fuels was selected for use during the study and included conventional crude-derived Jet A-1, synthetic paraffinic kerosene, linear paraffinic solvents, aromatic solvents and pure compounds. All test fuels were characterised through full specification analyses, distillation profiles and two-dimensional gas chromatography.

The ignition and extinction behaviour of the test fuel matrix was evaluated under simulated altitude conditions at the Rolls-Royce Strategic Research Centre’s sub-atmospheric altitude ignition facility in Derby, UK. A twin sector segment of a Rich Quench Lean (RQL) combustor was employed with fuel supplied to a single burner. Combustor air inlet conditions were controlled to 41.4 kPa and 265 K. Fuel temperature was controlled to 288 K.

In addition to the standard extinction and ignition detection systems, optical diagnostics were applied during the test programme. Simultaneous high-speed imaging of the OH* chemiluminescence, and broadband flame luminosity was employed to capture the main reaction zones, the global heat release and distribution of radiative soot particles respectively.

Lean extinction points were determined using both a photodiode as well as from the OH* chemiluminescence data. The position of extinction and overall combustor ignition and extinction timescales were determined. The diagnostic methodology that was used to obtain the results reported in this paper is discussed in greater detail in a separate complementary paper.

All eight fuels, including the fully synthetic Jet A-1 fuels that formed part of the test matrix, yielded performance that was comparable to that obtained with conventional crude-derived Jet A-1.
Analysis of the Spray and Transfer Function of Swirling Spray Flames From a Multi-Jet Steam Assisted Liquid Fuel Injector
Authors: Mirat Clément , Durox Daniel , Schuller Thierry
Published: September 2014

Characterizations of the response of swirling spray flames to flow rate modulations over the entire frequency range remain scarce. This response is addressed here by determining the transfer function of spray flames stabilized on a multi-jet steam-assisted dodecane injector in a turbulent swirling flow confined by a quartz tube. This type of burner is used in some liquid fueled industrial boilers. In the absence of combustion and air flow, a phase Doppler particle analyzer is used to determine the Sauter mean diameter (SMD) of the fuel spray as a function of the atomizing gas to fuel mass flow rate ratio (GLR) injected in the nozzle. For small values of the GLR, the SMD of the generated spray decreases rapidly as the GLR increases. For GLR values above a certain threshold, the SMD reaches a constant value that is independent of the GLR. Transfer functions are measured in this second regime for swirling air flows characterized by a swirl number S = 0.92 that is determined by laser Doppler anemometry. Transfer functions defined as the normalized ratio of OH* or CH* flame chemiluminescence intensity fluctuations divided by the velocity oscillation level measured by laser Doppler velocimetry at the burner outlet are determined as a function of the forcing frequency for a small perturbation level. The response of sooty and non sooty flames at globally lean conditions are examined. Using a set of steady experiments, it is shown that the OH* signal may safely be used to confidently estimate low frequency heat release rate disturbances for both types of flames, but the CH* signal cannot be used in the sooty flame cases. The measured transfer functions of non-sooty spray flames feature many similarities with the transfer function of perfectly premixed swirling flames indicating that their dynamics is also controlled by interference mechanisms that need to be elucidated.
A New Emergency Stop and Control Valves Design: Part 1 — Experimental Verification With Scaled Models
Authors: Brüggemann Peter , Vinnemeier Philipp , Balkowski Ingo , Büscher Carsten , Stapper Philipp , Zimmer Gerta , Wirsum Manfred
Published: September 2014

For the experimental verification of a new emergency stop and control valve design extended tests on a low pressure as well as a high pressure air test rig were performed. As the required thermodynamic parameters for a full scale test cannot be met, a scaled version of the valve design was tested. The scaling was done taking into account the laws of similitude. The inherent valve characteristics as well as pressure distributions and forces were gathered by means of steady and unsteady probes. While the tests in the low pressure test rig were performed at similar Mach numbers, the high pressure tests were performed also with Reynolds numbers sufficiently similar. A transformation of the pressure pulsations to the real steam valve was done by means of the Strouhal number. In the low pressure test rig ambient conditions were used for the inlet air. A vacuum pump was delivering the airflow through the tested valve model. The valve model was equipped with approximately 50 test points. For the high pressure test rig a six-stage radial compressor with interstage cooling was used. The valve model was equipped with approximately 40 test points. Due to the limitations of the compressor and other adjacent systems the tests in the high pressure test rig were conducted with a stepped operational concept using different mass flows and inlet pressures for the tested valve model. The inherent flow characteristics as well as the pressure pulsations of both measuring campaigns were compared with one another. Matches as well as mismatches are discussed. Additionally, the results were compared with steady state and transient CFD simulations, which is described in Part 2 (GT2014-25117).
Modernization of the Equipment of a Head Compressor Station
Authors: Janßen Stefan , Pätzold Peter , Emde Axel , Kurz Rainer
Published: September 2014

The Waidhaus compressor station in Germany is a key compressor station for the supply of Natural Gas from Russia into the German and the European market. The required flexibility, together with the goal of a small environmental footprint, has led to some unique, but widely applicable solutions. Since this head compressor station of the MEGAL pipeline system is of highest importance for the European gas supply, requirements for high availability and reliability of the equipment are significant. The paper consists of two parts: In the first part it describes the challenges of installing new equipment in an existing compressor station, details the characteristics of the installed equipment, and, in particular, discusses the steps that have been taken to assure the required high availability, high reliability, and high flexibility. In the second part, the acceptance test is described, taking into account site specific limitations, and how a highly accurate site test can be executed. The tested unit was accepted based on the acceptance test described. The methodology is useful for the conduct and execution of site performance tests.

The paper thus provides insight into the decision making, installation, and acceptance process for the specific situation of a strategically important brownfield compressor station.
Study of an Optimized Trench Film Cooling Configuration Using Scale Adaptive Simulation and Infrared Thermography
Authors: Schreivogel Peter , Kröss Bernhard , Pfitzner Michael
Published: September 2014

In the present paper, a narrow, angled trench layout is proposed and numerically optimized. In the optimization process the trench width and depth as well as the edge contour were varied. For each design, the optimizer automatically created the geometry and a structured hexahedral mesh. Then, six blowing ratios from M = 1 to 6 were evaluated based on RANS computations. The spatial average and the standard deviation of the film cooling effectiveness served as objective variables for the optimizer. One novel configuration was studied in more detail and compared to a trench with a depth of 0.75 hole diameters D and a cooling hole angle of α = 30 deg. For both configurations unsteady simulations using the hybrid SAS turbulence model were carried out and validated against infrared thermography measurements of the adiabatic film cooling effectiveness. The match between SAS and experiment is improved compared to RANS computations with the realizable k-ε-model. The optimized configuration yields a significant improvement of the film cooling performance. The swept shape of the trench promotes the lateral spreading of the coolant, while the decreased trench width reduces the mixing of cooling air and hot free-stream gas in the region between the cooling holes.
New Single Crystal Superalloys, CMSX®-8 and CMSX®-7
Authors: Wahl Jacqueline B. , Harris Ken
Published: September 2014

Single crystal (SX) superalloys have wide application in the high pressure turbine section of aero and industrial gas turbine engines due to the unique combination of properties and performance. Since introduction of single crystal casting technology, SX alloy development has focused on increased temperature capability, and major improvements in alloy performance have been associated with the introduction of new alloying elements, including rhenium (Re) and ruthenium (Ru). 3% Re-containing second generation alloys, such as CMSX-4®, PWA 1484 and Rene’ N5 have seen the greatest market utilization and have become the benchmark alloys for comparing new alloy developments. However, Re and Ru are rare elements with limited production/availability and corresponding high costs. This has resulted in significant escalation of SX alloy costs, and consequently, there has been much interest in the development of improved SX superalloys with lower Re or no Re content compared to second generation alloys.

Cannon-Muskegon® has developed two new SX superalloys: 1.5% Re CMSX®−8 alloy and CMSX®−7 alloy, which contains no Re, as alternatives to first and second generation alloys for applications which require slightly less ultra high temperature capability compared to CMSX-4 alloy or the improved CMSX-4(SLS) alloy. This paper provides an overview of development and characterization of these SX alloys and alloy modifications, CMSX-8 (SLS) and CMSX-8[B/C](SLS).
Nonlinear Dynamic Analysis of a Turbocharger on Foil-Air Bearings With Focus on Stability and Self-Excited Vibration
Authors: Bonello Philip , Pham Hai
Published: September 2014

This paper presents a generic technique for the transient nonlinear dynamic analysis (TNDA) and the static equilibrium stability analysis (SESA) of a turbomachine running on foil air bearings (FABs). This technique is novel in two aspects: (i) the turbomachine structural model is generic, based on uncoupled modes (rotor is flexible, non-symmetric and includes gyroscopic effects; dynamics of support structure can be accommodated); (ii) the finite-difference (FD) state equations of the air films are preserved and solved simultaneously with the state equations of the foil structures and the state equations of the turbomachine modal model, using a readily available implicit integrator (for TNDA) and a predictor-corrector approach (for SESA). An efficient analysis is possible through the extraction of the state Jacobian matrix using symbolic computing. The analysis is applied to the finite-element model of a small commercial automotive turbocharger that currently runs on floating ring bearings (FRBs) and is slightly adapted here for FABs. The results of SESA are shown to be consistent with TNDA. The case study shows that, for certain bearing parameters, it is possible to obtain a wide speed range of stable static equilibrium operation with FABs, in contrast to the present installation with FRBs.
Conjugate Heat Transfer Characteristics of a Highly Thermal-Loaded Film Cooling System in Hot and Multi-Composition Gas Condition
Authors: Li Mingfei , Ren Jing , Jiang Hongde
Published: September 2014

To reach the goal of Zero-Emission or Near-Zero-Emission, the future advanced power equipment would be using hydrogen or middle/low heat-value syngas as fuel. Radiation would be more important in turbine heat transfer due to the higher temperature and multi-composition gas. The main goal of current study is analyzing the characteristic of conjugate heat transfer considering radiation heat transfer, multi-composition gas, with and without TBC coated. To study the conjugate heat transfer mechanism including conduction/ convection/ radiation in the film cooling flow field considering the effect of the gas composition, both the experimental and the numerical studies are carried out in the present work. By comparing the experimental and the numerical data, it is concluded that the implemented thermal conduction/ convection/ radiation simulation method is valid for the cases studied. The results show that higher percentage of steam in gas composition leads to the higher temperature (lower normalized temperature) on the plate. With the total percentage of steam in hot gas increasing per 7%, the normalized temperature on the plate decrease about 0.02. The heat insulation effect of TBC is more obvious when the radiation effects are strong. TBC makes the temperature distribution more uniform to some extent.
Effect of Channel Orientation on Heat Transfer in Rotating Smooth Square U-Duct at High Rotation Number
Authors: Li Yang , Deng Hongwu , Xu Guoqiang , Qiu Lu , Tian Shuqing
Published: September 2014

The effect of channel orientation on heat transfer in a rotating, two-pass, square channel is experimentally investigated in current work. The classical copper plate technique is employed to measure the regional averaged heat transfer coefficients. The inlet Reynolds number and Rotation number range from 25000 to 35000 and 0 to 0.82, respectively. Five different channel angles (−45°, −22.5°, 0°, 22.5°, 45°) are selected to study the effect of channel orientation on heat transfer.

In the radially outward flow channel, the surface average heat transfer in β = 0° channel are higher than those in angled-channel (±22.5°, ±45°) on the trailing surface at all Rotation number ranges (0–0.82). While on the leading surface, surface average heat transfer are lower before a critical Rotation number, and turn higher after the critical point. Channel orientations show less influence on heat transfer in the radially inward flow channel.

Compared with their corresponding perpendicular channel orientation values (β = 0° channel), heat transfer in angled-channels decrease on the pressure side and increase on the suction side at a relatively lower Rotation number (Ro<0.4) for both inward and outward channels. While at higher Rotation number (Ro>0.4), heat transfer in angled-channel decrease on both the leading and trailing walls in the first pass, and increase on both the leading and trailing walls in the second pass. By considering the effect of channel orientations, the relation between critical Rotation number on the leading surface in the first pass and dimensionless location (X/D) obeys a simple rule: (Roc·X/D)·cosβ = 1.31. The trailing-to-leading heat transfer differences induced by rotation increase with the increasing of Rotation number in angled-channel, and they are larger than β = 0° channel after the critical Rotation number in both passages.
Film Cooling Modeling of Turbine Blades Using Algebraic Anisotropic Turbulence Models
Authors: Li Xueying , Ren Jing , Jiang Hongde
Published: September 2014

The complex structures in the flow field of gas turbine film cooling increase the anisotropy of turbulence making it difficult to accurately compute turbulent eddy viscosity and scalar diffusivity.

An algebraic anisotropic turbulence model is developed while aiming at a more accurate modeling of the Reynolds stress and turbulent scalar flux. In this study the algebraic anisotropic model is validated by two in-house experiments. One is a leading edge with showerhead film cooling and the other is a vane with full coverage film cooling. Adiabatic film cooling effectiveness under different blowing ratios, density ratios and film cooling arrangements were measured using PSP technique. Four different turbulence models are tested and detailed analyses of computational simulations are performed.

Among all the turbulence models investigated, the algebraic anisotropic model shows better agreement with the experimental data qualitatively and quantitatively. The algebraic anisotropic model gives a good prediction of the vortex strength and turbulence mixing of the jet, therefore improves the prediction of the scalar field.
Gas Turbine Plant With Overexpansion Turbine and Heat Regeneration in the Ship Propulsion Complex
Authors: Matviienko V. , Andriets O. , Ocheretianyi V.
Published: September 2014

Gas turbine engines (GTE) are widely applied in the ship propulsion complexes. Although GTE have many technical advantages, but for the wider application in shipbuilding it is necessary to carry out one of the most important requirements that nowadays is actual for all power-engineering objects — to increase efficiency of their operating.

This problem is solved by GTE Complex Cycle together with the utilization of the exhaust gases heat. At present a non-traditional method of GTE cycle complication is an application of overexpansion turbine, which with the exhaust compressor and gas cooler between them forms turbo-compressor utilizer (TCU). In the overexpansion turbine is used internal energy of the exhaust gases, that allows to get (after deduction of energy expenditure for pressing out of gas) an additional useful work that increases engine efficiency. The tests results on experimental co-generative gas turbine plant with TCU confirmed the trustworthiness of theoretical elaboration of the operating GTE with the overexpansion turbine.

When gas is being cooled after the overexpansion turbine the portion of taken heat can be used to heat air pressed in the GTE compressor in recuperator before the combustion chamber. Hereby the heat utilization of exhaust gases inside GTE cycle is carried out, that ensures additional increasing of the engine efficiency.

Gas cooler in TCU is used as an utility boiler for the supply of heating power to ship’s consumers and other technological consumers. In that way GTE with TCU including recuperator is the co-generative plant. The applying of GTE with TCU including recuperator on the oil-tankers provides ship’s propulsion as well as the heating of oil transported in tanks, that allows GTE to reach high energy efficiency on the whole ship power plant.
Geometrical Optimization and Experimental Validation of a Tripod Film Cooling Hole With Asymmetric Side Holes
Authors: Chi Zhongran , Han Chang , Li Xueying , Ren Jing , Jiang Hongde
Published: September 2014

A tripod cylindrical film hole with asymmetric side holes is studied numerically and experimentally on a flat plate for higher film cooling effectiveness. Firstly, the influences of geometrical parameters are studied and the optimum configurations of the asymmetric tripod hole are found in a DoE optimization study based on an improved numerical model for film cooling prediction, in which more than one hundred 3D CFD simulations are carried out. Then one optimum configuration of the asymmetric tripod hole is examined experimentally using pressure-sensitive paint (PSP) measurements, and compared against the experimental results of the simple cylindrical film hole and a well-designed shaped film hole.

The flow and heat transfer characteristics of the asymmetric tripod holes were explored from the DoE results. The side holes can form a shear vortex system or an anti-kidney vortex system when proper spanwise distances of them are adopted, which laterally transports the coolant and form a favorable coolant coverage. According to the experimental results, the cooling performance of the optimized asymmetric tripod hole is significantly better than that of the simple cylindrical hole, especially at high blowing ratios. And the optimized asymmetric tripod hole can provide almost the same or even higher film cooling effectiveness on the flat plate compared with the shaped hole in the same flow conditions.
Heat Transfer in Reacting Cooling Films: Part II — Modelling Near-Wall Effects in Non-Premixed Combustion With OpenFOAM
Authors: Frank Gabriele , Pohl Stephanie , Pfitzner Michael
Published: September 2014

To account for heat losses near cooled walls an extension of the flamelet model is proposed based on an enthalpy defect parameter. A definition of the enthalpy defect and its transport equation is introduced. The inclusion of the enthalpy defect into the flamelet generation and the integration in terms of a probability density function for this parameter is discussed. The near wall extension is implemented into the OpenFOAM architecture and compared to ANSYS Fluent finite rate data for a testcase of a reacting laminar cooling film over a cooled flat plate. The near wall extension seems to improve the predicted heat flux compared to the original flamelet model, but profound validation was not possible due to a lack of suitable experimental or DNS data so far.
Effect of Swirl Cup’s Venturi Shape on Spray Structure and Ignition Process
Authors: Wang Xiaofeng , Lin Yuzhen , Hu Haosheng , Zhang Chi , Kang Yao
Published: September 2014

In a gas turbine engine combustor, combustion performance is tied to the spatial distribution of the fuel injected into the dome. Swirl cup, as an air blast atomizer, is widely used to provide a uniform presentation of fuel droplets to the combustor dome. In this paper, two swirl cups with different venturi angle have been studied: case 1 (with narrow venturi angle) and case 2 (with wide venturi angle). Kerosene is injected to the test domain through a simplex nozzle. The spatial distribution of droplet characteristics produced by the two swirl cups were measured using dual-phase Doppler anemometry (PDA). A single cup combustor has been built in order to characterize the swirl cups’ ignition phenomena. Spark ignition test has been performed for ground condition, two swirl cups’ lean ignition limits are obtained, and ignition sequences have been recorded by a high-speed video camera. Comparing the two swirl cups’ small droplets velocity, case 1 swirl cup produces a different velocity profile from typical swirl cup. The air stream outflowing from case 1 swirl cup just ran into the side wall. The droplet size around the spark plug of case 2 is smaller than case 1. Ignition test results show that case 2 swirl cup’s lean ignition limit is wider than case 1’s. Record of the ignition process deepened the understanding of spark ignition of the swirl diffusion flame. It takes some time for the kernel to anchor in swirl cup. The results demonstrate that swirl cup’s venturi shape strongly influence the spray structure. Thereby affect the combustor ignition performance.
Experimental and Analytical Investigations of Dynamic Characteristics of Magnetorheological and Nano Magnetorheological Fluid Film Journal Bearing
Authors: Bompos Dimitrios A. , Nikolakopoulos Pantelis G.
Published: September 2014

The integrity and reliability of a rotor depends significantly on the dynamic characteristics of its bearings. Bearing design has been altered in many ways in order to achieve improvement in terms of damping and stiffness. A promising field in terms of vibrations control and overall performance improvement for the journal bearings is the use of smart lubricants. Smart lubricants are fluids with controllable properties. A suitable excitation, such as an electric or a magnetic field, is used as a means of smart fluid properties control. Magnetorheological (MR) fluids consist one category of lubricants with controllable properties thanks to magnetic particles inside the fluid volume. In this case of material, a magnetostatic field affects the apparent viscosity of the fluid by aligning the magnetic particles into chains. In this work a magnetorheological fluid is produced. A magnetorheological fluid film bearing was constructed, capable of exciting the magnetorheological fluid. These bearing performances are examined experimentally and its dynamic properties are evaluated using an impact excitation method for a SAE-10W lubricant as well as with the produced magnetorheological fluid both in its active and in its inactive state.
Experimental Analysis of Dynamic Interaction Between a Centrifugal Compressor and its Casing
Authors: Almeida P. , Gibert C. , Thouverez F. , Leblanc X. , Ousty J.-P.
Published: September 2014

In turbomachinery, one way to improve aerodynamic performance and reduce fuel consumption consists of minimizing the clearance between rotor and casing. Yet the probability of contact is increased and this may lead in some specific conditions to a large and even unstable excitation on the impeller and stator. To achieve better understanding of the dynamic behavior occurring during the blade-to-casing contact, many numerical studies have been conducted but only a few experiments have been reported in the literature thus far.

The interaction experiment reported in this paper involves a low-pressure, rotating centrifugal compressor and its casing tested in a vacuum chamber. Contact is initiated by introducing a gap near zero, and certain events with significant dynamic levels are observed during the run-up. Measurements are performed using strain gauges on both the rotating and stationary parts and a Scanning Laser Doppler Vibrometer on the stator. This research focuses on an analysis of the recorded data. Time series data are also analyzed by means of standard signal processing and a full spectrum analysis in order to identify the direction of traveling wave propagation on the two structures as well as nodal diameters and frequencies.

The dynamic response of structures is accompanied by variations in other physical parameters such as temperature, static deformed shapes, speed and torque. A wearing pattern is evaluated following the contact experiments. The spectral content of response is dominated by frequency modes excited by engine orders as well as by sidebands due to inherent system non-linearity.
Stress–Strain State Prediction of High-Temperature Turbine Single Crystal Blades Using Developed Plasticity and Creep Models
Authors: Vasilyev Boris
Published: September 2014

This paper discusses a novel approach to calculating inelastic strain that incorporates elastic anisotropy in combination with ANSYS finite element analysis (FEA) software to predict the stress–strain state kinetics of a single crystal (SX) nickel-based turbine blade. The approach is based on using “equivalent direction” and allows us to correctly define the critical load value and plastic strain field in SX details for different load types. The suggested approach is simple and generic and requires only a few standard experimental material properties. This should allow for an easy transition to actual blade design application.

Predictions of plastic field distribution obtained using the suggested approach with anisotropic specimens are compared with experimental data as well as with the results obtained using a crystallographic approach. Good correlation was achieved.

The second goal of this study is to develop a physically based, readily implementable creep model SX superalloy that accurately represents the creep phenomena of these materials under complex, thermomechanical loading conditions.
Accurate Radial Vaneless Diffuser 1D Model
Authors: De Bellis Fabio , Grimaldi Angelo , Rubino Dante Tommaso , Amirante Riccardo , Distaso Elia
Published: September 2014

A simplified one dimensional model for the performance estimation of vaneless radial diffusers is presented. The starting point of such a model is that angular momentum losses occurring in vaneless diffusers are usually neglected in the most common turbomachinery textbooks: it is assumed that the angular momentum is conserved inside a vaneless diffuser, although a non-isentropic pressure transformation is considered at the same time. This means that fluid-dynamic losses are taken into account only for what concerns pressure recovery, whereas the evaluation of the outlet tangential velocity incoherently follows an ideal behavior.

Several attempts were presented in the past in order to consider the loss of angular momentum, mainly solving a full set of differential equations based on the various developments of the initial work by Stanitz. However, such formulations are significantly more complex and are based on two empirical or calibration coefficients (skin friction coefficient and dissipation or turbulent mixing loss coefficient) which need to be properly assessed.

In the present paper, a 1D model for diffuser losses computation is derived considering a single loss coefficient and without the need of solving a set of differential equations. The model has been validated against massive industrial experimental campaigns, in which several diffuser geometries and operating conditions have been considered. The obtained results confirm the reliability of the proposed approach, able to predict the diffuser performance with negligible drop of accuracy in comparison with more sophisticated techniques. Both preliminary industrial designs and experimental evaluations of the diffusers may benefit from the proposed model.
Pressurized SOFC Hybrid Systems: Control System Study and Experimental Verification
Authors: Larosa Luca , Traverso Alberto , Ferrari Mario L. , Zaccaria Valentina
Published: September 2014

In this paper two different advanced control approaches for a pressurized SOFC hybrid system are investigated and compared against traditional proportional–integral–derivative (PID). Both advanced control methods use model predictive control (MPC): in the first case, the MPC has direct access to the plant manipulated variables, in the second case the MPC operates on the setpoints of PIDs which control the plant. In the second approach the idea is to use MPC at the highest level of the plant control system to optimize the performance of bottoming PIDs, retaining system stability and operator confidence. Two MIMO (multi-input multi-output) controllers were obtained: fuel cell power and cathode inlet temperature are the controlled variables; fuel cell by-pass flow, current and fuel mass flow rate (the utilization factor kept constant) are the manipulated variables.

The two advanced control methods were tested and compared against the conventional PID approach using a SOFC hybrid system model. Then, the MPC controller was implemented in the hybrid system emulator test rig developed by the Thermochemical Power Group (TPG) at the University of Genoa.

Experimental tests were carried out to compare MPC against classic PID method: load following tests were carried out. Ramping the fuel cell load from 100% to 80% and back, keeping constant the target of the cathode inlet temperature, the MPC controller was able to reduce the mismatch between the actual and the target values of the cathode inlet temperature from 7 K maximum of the PID controller to 3 K maximum, showing more stable behavior in general.
Analysis of the Effect of a Slotted Flap Mechanism on the Performance of an H-Darrieus Turbine Using CFD
Authors: Daróczy László , Mohamed Mohamed H. , Janiga Gábor , Thévenin Dominique
Published: September 2014

Wind energy represents nowadays a very important source of energy for many countries. It provides an efficient and effective solution to reduce fuel consumption as well as pollutant emissions. VAWTs (vertical axis wind turbines) were originally considered as very promising, before being superseded by the present, horizontal axis turbines. There is now a resurgence of interests for VAWTs, in particular Darrieus turbines. VAWTs like the H-rotor Darrieus turbine appear to be particularly promising for low wind speed conditions, but suffer from a low efficiency compared to horizontal axis turbines. Additionally, Darrieus turbines are not self-starting, which is a major drawback. The present paper introduces a new idea to improve the global performance of Darrieus rotors, relying on a slotted flap. Due to its low manufacturing costs and size, a two-bladed H-rotor with a radius of 2 meters was retained as a first application example. The blade airfoil relies on the S1046 profile, which was shown in previous studies to be superior under relevant operating conditions [1]. The solidity (Nc/R) of the rotor is kept at 0.25 for all the computations. In the first step a parametric geometry is created, where the end of the blade is converted into a slotted flap (with appropriate rounding). The main parameters are the distance between the main part of the blade and the flap (width of gap), the angle of the slot and the angle of the flap. In the second step a systematic analysis of the effect of those variables on the force and power coefficient is carried out using three-dimensional full factorial Design-of-Experiment with an in-house parameterization and optimization software. For each configuration, force and power coefficients are calculated for four different tip-speed ratios (including the value, where the S1046 profile without flap shows its maximal power coefficient). The evaluation of each configuration is performed using a commercial CFD software. The flow is assumed in this first study to be two-dimensional and unsteady. Turbulence intensities follow the relevant norms (DIN EN 61400). Finally the results are compared to each other and to the reference design (S1046 without flap) and conclusions are given regarding power coefficient and flap load.
Comparison of Non-Linear and Linearized CFD Analysis of the Stator-Rotor Interaction of a Compressor Stage
Authors: Schoenenborn Harald , Ashcroft Graham
Published: September 2014

The prediction of resonance amplitudes due to stator-rotor interactions is still an important task within the design process of turbomachinery bladings.

In this paper the stator-rotor interaction of a compressor stage which consists of an inlet guide vane and a rotor blade is studied with a non-linear and a linearized CFD code. First, a quasi-3D-study of a section close to the tip region is considered. The passing of the wake of the inlet guide vane over the rotor is studied for six different vibration mode shapes of increasing complexity (first bending mode up to 4th chordwise bending mode).

Whereas for low rotor speeds the comparison between linearized and non-linear calculations is quite good, large differences are found for high rotor speeds. It is shown that an acoustic interaction between the two stages with a cut-on mode is the cause for the large differences, leading to much higher unsteady pressure amplitudes on the rotor blade. This in turn leads to different aerodynamic work on the rotor blade for the different mode shapes.

The extension of the investigations to 3D shows essentially the same effects.
Conjugate Heat Transfer Predictions of Effusion Cooling With Shaped Trench Outlet
Authors: Oguntade H. I. , Andrews G. E. , Burns A. D. , Ingham D. B. , Pourkashanian M.
Published: September 2014

The influence of the application of a filleted shape trench hole outlet on the overall cooling effectiveness of a flat hot effusion Nimonic 75 metal wall with a 770K hot gas crossflow was investigated using conjugate heat transfer (CHT) CFD and the Ansys Fluent code. The baseline effusion wall had ten rows of holes with an X/D of 4.65 and a wall thickness of 6.35mm with normal injection holes. This was modelled and showed good agreement with the experimental results for overall cooling effectiveness. The aim of the work was to use these validated CHT CFD procedures to investigate improved hole outlet designs with 30° inclined effusion of X/D = 4.65 with improved hole outlet designs using various trench designs. The predictions involved the use of a gas tracer in the cooling air to simultaneously separate the predicted adiabatic film cooling effectiveness from the overall cooling effectiveness. The shaped trench outlet effusion wall designs were predicted to have a superior performance compared with the 90° effusion wall cooling design. This was due to the improved adiabatic film cooling. An increase in the trailing edge vertical wall depth of the trenched effusion wall design from 0.5D to 0.75D increased the overall and adiabatic cooling effectiveness. The filleted shaped trench outlet effusion wall only required a small amount of cooling air to achieve a satisfactory cooling performance. It was predicted that this new effusion wall design could enable a significant reduction in the coolant mass flow for cooled metal surfaces in in future high performance gas turbines.
Aerothermal Analysis of a Turbine With Rim Seal Cavity
Authors: Liu Huoxing , An Yuge , Zou Zhengping
Published: September 2014

This study presents the results of the aerothermal analysis of an axial turbine with rim seal cavity using conjugate heat transfer computation (CHT). The CHT computations were performed for a two-stage turbine with stator well cavity at the sealing flow rates between 0–2% of the main annulus flow utilizing the commercial solver ANSYS CFX. The results were compared with that of conventional uncoupled approaches in which a heat transfer coefficient is first derived from CFD solutions and then taken as boundary condition for a thermal conduction analysis of the solid domains. As it turns out, for the thermal load prediction, the global results obtained by CHT and uncoupled computations were similar, while with the increase of sealing flow rate remarkable differences emerged. In addition, the sealing flow significantly affects the thermal loading of the blade and disk as well as the strength of the secondary vortex. A negative incidence at the downstream rotor leading edge was observed along with the changing of blade loading due to the low tangential momentum cavity egress flow.
Aerodynamic Optimization Design of Exhaust Hood Diffuser for Steam Turbine With Three-Dimensional Reynolds-Averaged Navier-Stokes Solutions
Authors: Yang Jiandao , Chen Taowen , Li Jun , Feng Zhenping
Published: September 2014

Combined with three-dimensional parameterization method of exhaust diffuser profile, aerodynamic performance evaluation method, response surface approximation evaluation model and Hooke-Jeeves direct search approach, aerodynamic optimization design of exhaust hood diffuser for steam turbine is presented. The aerodynamic performance of exhaust hood design candidate is evaluated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions. Aerodynamic optimization design of exhaust hood is conducted for the maximum of the static pressure recovery coefficient of exhaust hood. The design variables are specified by the exhaust diffuser profile parameterization method. The aerodynamic performance of the optimized exhaust hood and referenced design is numerically calibrated with consideration of the full last stage and rotor tip clearance. The static pressure recovery coefficient of the optimized exhaust hood is higher than that of the referenced design with consideration of the upstream last stage influence. Furthermore, the detailed flow pattern of the optimized exhaust hood and referenced design is also analyzed and compared.
Modification of the Rolls-Royce Model MT5S Gas Turbine Engine Fuel Nozzle for Extended Fuel Flow Rates
Authors: Halsey Jack , Overton Leonard , Buelow Philip , Bretz David
Published: September 2014

The Rolls-Royce Model MT5S gas turbine engine was selected for use in the auxiliary turbine genset (ATG) of the DDG1000. This engine initially used the same fuel nozzle as the Model 501-K34 engine used in the DDG51 class ships. The Model MT5S can operate at higher powers levels and fuel flows. The fuel nozzle for the Model MT5S gas turbine engine experienced coking problems at the higher fuel flows. This paper discusses the investigation and solution to the problem to extend the operating range of the fuel nozzle for other applications.