bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of Variable Inlet Guide Vane or Speed Control to Maintain Constant Compressor Pressure Ratio in Wet Gas Flow and Their Effect on Diffuser Stability
Authors: Vigdal Levi André B. , Bakken Lars E.
Published: August 2017

Improving offshore gas production requires the process compressor to be moved closer to the wellhead. This will yield such benefits as enhanced well output, longer well life and the possibility of exploiting smaller fields. However, the harsh environment, remote location and variable two-phase characteristics of an untreated gas stream pose increased challenges for operational performance and robustness. Several methods are available to ensure that a process compressor maintains constant outlet pressure regardless of inlet stream properties and flow.

Two pressure-ratio control methods — variable inlet guide vanes (IGV) and variable speed — have been investigated. Their effect on diffuser stability has been tested and analysed in dry and wet conditions. Increased diffuser stability in wet conditions with IGV has been discussed and results are presented.
Rotordynamic Energy Expressions for General Anisotropic Finite Element Systems
Authors: Settipalli Manoj , Ganji Venkatarao , Brockett Theodore
Published: August 2017

It is often desirable to identify the critical components that are active in a particular mode shape or an operational deflected shape (ODS) in a complex rotordynamic system with multiple rotating groups and bearings. The energy distributions can help identify the critical components of a rotor bearing system that may be modified to match the design requirements. Although the energy expressions have been studied by researchers in the past under specific limited conditions, these expressions require computing the displacements and velocities of all degrees of freedom over one full cycle. They do not address the overall time-dependency of the energies and energy distributions, and their effect on the interpretation of a mode shape or an ODS. Moreover, a detailed finite element formulation of these energy expressions including the effects of anisotropy, skew-symmetric stiffness, viscous and structural damping have not been identified by the authors in the open literature. In this article, a detailed account of orbit characteristics and planarity for isotropic and anisotropic systems is presented. The effect of orbit characteristics on the energy expressions is then discussed. An elegant approach to obtaining time-dependent kinetic and strain energies of a mode shape or an ODS directly from the structural matrices and complex eigenvectors/displacement vectors is presented. The expressions for energy contributed per cycle by various types of damping and the destabilizing skew-symmetric stiffness that can be obtained in a similar way are also shown. The conditions under which the energies and energy distributions are time-invariant are discussed. An alternative set of energy expressions for isotropic systems with the degrees of freedom reduced by half is also presented.
A Flow Starvation Model for Tilting Pad Journal Bearings and Evaluation of Frequency Response Functions: A Contribution Towards Understanding the Onset of Low Frequency Shaft Motions
Authors: San Andrés Luis , Koo Bonjin , Hemmi Makoto
Published: August 2017

Direct lubrication tilting pad journal bearings (TPJBs) require of less oil flow, reduce power consumption and offer cooler pad temperatures for operation at high surface speeds. Although apparently free of a hydrodynamic instability, the literature shows that direct lubrication TPJBs exhibit unexpected shaft vibrations with a broadband low frequency range, albeit small in amplitude. Published industrial practice demonstrates the inlet lubrication type, a reduced supply flow rate causing film starvation, and the bearing discharge conditions (evacuated or end sealed) affect the onset, gravity and persistency of the sub synchronous (SSV) hash motions. The paper presents a physical model to predict the performance of TPJBs with flow conditions ranging from over flooded to extreme starvation. Lubricant starvation occurs first on an unloaded pad, thus producing a (beneficial) reduction in drag power. As the supplied flowrate decreases further, fluid starvation moves towards the loaded pads and affects the film temperature and power loss, increases the journal eccentricity, and modifies the dynamic force coefficients of each tilting pad and thus the whole bearing. For a point mass rotor supported on a TPJB, the analysis produces eigenvalues and frequency response functions (FRFs) from three physical models for lateral rotor displacements: one with frequency reduced (4×4) bearing stiffness (K) and damping (C) coefficients and another with constant K-C-M (inertia) coefficients over a frequency range. The third model keeps the degrees of freedom (tilting) of each pad and incorporates the full matrices of force coefficients including fluid inertia. Predictions of rotordynamic performance follow for two TPJBs: one bearing with load between pads (LBP) configuration, and the other with a load on a pad (LOP) configuration. For both examples, under increasingly poor lubricant flow conditions, the damping ratio for the rotor-bearing low frequency (SSV) modes decreases, thus producing an increase in the amplitude of the FRFs. For the LOP bearing, a large static load produces a significant asymmetry in the force coefficients; the rotor-bearing has a small stiffness and damping for shaft displacements in the direction orthogonal to the load. A reduction in lubricant flow only exacerbates the phenomenon; starvation reaches the loaded pad to eventually cause the onset of low frequency (SSV) instability. The bearing analyzed showed similar behavior in a test bench. The predictions thus show a direct correlation between lubricant flow starvation and the onset of SSV.
Multidisciplinary Optimization of the Working Process of Uncooled Axial Turbine According to Efficiency and Strength Criteria
Authors: Marchukov Evgeny Yu. , Egorov Igor , Popov Grigorii , Salnikov Anton , Goriachkin Evgenii , Kolmakova Daria
Published: August 2017

The results of multicriteria multidisciplinary optimization of three-stage low-pressure turbine are described in the paper. The aim of the optimization is to improve turbine operation process by three criteria: turbine outlet flow angle, value of residual swirl at the turbine outlet, and turbine efficiency. Moreover, the requirements of static and dynamic strength must be fulfilled for rotor blades.

Full reprofiling of all blade rows is carried out while solving optimization problem. Reprofiling includes a change in both shape of flat blade sections (profiles) and threedimensional shape of the blades.

The study is carried out with 3D numerical models of turbines both gas-dynamic and strength.

The gas-dynamic improvement of turbine operation is performed as the first step. Then, strength improvement is carried out for the best variants in order to provide satisfactory margins of static and dynamic strength. Mutual strength and gas-dynamic optimization is done as the next step. The final variant of turbine that meets best the gas-dynamic and strength criteria is found as the result of this optimization.
High-Fidelity Multiphysics Simulation of a Confined Premixed Swirling Flame Combining Large-Eddy Simulation, Wall Heat Conduction and Radiative Energy Transfer
Authors: Koren Chai , Vicquelin Ronan , Gicquel Olivier
Published: August 2017

A multi-physics simulation combining large-eddy simulation, conjugate heat transfer and radiative heat transfer is used to predict the wall temperature field of a confined premixed swirling flame operating under atmospheric pressure. The combustion model accounts for the effect of enthalpy defect on the flame structure whose stabilization is here sensitive to the wall heat losses. The conjugate heat transfer is accounted for by solving the heat conduction within the combustor walls and with the Hybrid-Cell Neumann-Dirichlet coupling method, enabling to dynamically adapt the coupling period. The exact radiative heat transfer equation is solved with an advanced Monte Carlo method with a local control of the statistical error. The coupled simulation is carried out with or without accounting for radiation. Excellent results for the wall temperature are achieved by the fully coupled simulation which are then further analyzed in terms of radiative effects, global energy budget and fluctuations of wall heat flux and temperature.
Towards Higher Micro Gas Turbine Efficiency and Flexibility: Humidified MGTS — A Review
Authors: De Paepe Ward , Montero Carrero Marina , Bram Svend , Parente Alessandro , Contino Francesco
Published: August 2017

Micro Gas Turbines (mGTs) offer several advantages for small-scale Combined Heat and Power (CHP) production compared to their main competitors, the Internal Combustion Engines (ICEs), such as low vibration level, cleaner exhaust and less maintenance. The major drawback is their lower electrical efficiency, which makes them economically less attractive and explains their low market penetration. Next to improving the efficiency of the components of the traditional recuperated mGT, shifting towards more innovative cycles may help enhancing the performance and the flexibility of mGTs.

One interesting solution is the introduction of water in the mGT cycle — either as auto-raised steam or hot liquid —, preheated with the waste heat from the exhaust gases. The so-called humidification of the mGT cycle has the potential of increasing the electrical performance and flexibility of the mGT, resulting in a higher profitability. However, despite the proven advantages of mGT humidification, only few of these engines have been experimentally tested and up to now, no cycle is commercially available.

With this paper, we give a comprehensive review of the literature on research and development of humidified mGTs: we examine the effect of humidification both on the improvement of the cycle efficiency and flexibility and on the performance of the specific mGT components. Additionally, we will present the different possible layouts, both focusing on the numerical and experimental work. Finally, we pinpoint the technological challenges that need to be overcome for humidified mGTs to be viable. In conclusion, humidification of mGT cycles offers great potential for enhancing the cycle’s electrical efficiency and flexibility, but further research is necessary to make the technology commercially available.
Academic Blade Geometries for Baseline Comparisons of Industry-Specific Forced Response Predictions
Authors: Little James H. , Kauffman Jeffrey L. , Huels Matthias
Published: August 2017

Predicting the energy dissipation associated with contact of underplatform dampers remains a critical challenge in turbomachinery blade and friction damper design. Typical turbomachinery blade forced vibration response analyses rely on reduced order models and simplified nonlinear codes to predict blade vibration characteristics in a computationally tractable manner. Recent research has focused on both the model reduction process and simulation of the contact dynamics. This paper proposes two academic turbine blade geometries with coupled underplatform dampers as vehicles by which these model reduction and forced response simulation techniques may be compared. The blades correspond to two types of freestanding turbine blades and demonstrate the same qualitative behavior as more complex industry geometries. The blade geometries are fully described here and analyzed using the same procedure as used for an industry-specific blade. Standard results are presented in terms of resonance frequency, amplitude, and damping across a range of aerodynamic excitation. In addition, the predicted blade vibration characteristics are examined under variations in the contact interface: friction coefficient, damper / platform surface roughness, and damper mass, with relative sensitivities to each term generated. Finally, the effect of the number of modes retained in the reduced order model is studied to uncover patterns of convergence as well as to provide additional sets of standard data for comparison with other model reduction and forced response simulation methods.
Rotation Effects on the Heat Transfer Distribution in a Two-Pass Rotating Internal Cooling Channel Equipped With Triangular Ribs
Authors: Mayo Ignacio , Arts Tony , Van de Wyer Nicolas
Published: August 2017

The present paper addresses the detailed heat transfer pattern in a two-pass rotating internal cooling channel model, with a square cross section and equipped with triangular ribs on one of its walls. The turn region consists of a smooth high curvature U-bend that generates a complex flow field and wall heat transfer. The investigation is based on Liquid Crystal Thermography (LCT) measurements in a rotating facility at Reynolds numbers varying from 20,000 to 60,000, and a maximum rotation number equal to 0.20. For these experimental conditions, the centripetal buoyancy effects are negligible. The channel is rotated around an axis perpendicular to the main flow direction in clockwise and counter-clockwise senses, in order to observe the impact of cyclonic and anti-cyclonic behavior on the heat transfer in both legs. The objective of the present study is two-fold: firstly, it aims to understand the flow physics and heat transfer phenomena at different regimes. Secondly, the detailed heat transfer measurements are intended to be a reference set for Computational Fluid Dynamics (CFD) validation. The measurements obtained in the first leg have been compared with previous experimental data in channels with square ribs and radially outward flow, showing a similar behavior in terms of heat transfer distribution and overall dependency on the rotation number. In the second leg, the heat transfer distribution is more complex. The heat transfer distribution is not symmetric, and high gradients are present in the span-wise direction. Nevertheless, the dependency of the heat transfer to increasing rotation shows a trend similar to the one observed in the first pass. The combined effects of rib-induced secondary flows stabilization/destabilization by rotation, Coriolis-induced stream-wise vortices and high streamline curvature on the heat transfer distribution are analyzed in the paper.
Cyber-Physical Observer for Fluidized Bed-Chemical Looping Control Applications
Authors: Shadle Lawrence , Tucker David , Breault Ronald , Bayham Samuel , Weber Justin , Pezzini Paolo , Bryden Kenneth M. , Monazam Esmail , Panday Rupendranath
Published: August 2017

A cyber-physical fluidized bed-chemical looping reactor (FB-CLR) is proposed to observe and control the multiphase flow behavior and improve process operations, stability, and performance. The cyber-physical observer (CPO) provides an opportunity to probe a duplicate, or mirrored, non-reacting, multiphase flow system in real-time and provide response data not available from the hot reacting system in order to control the hot unit. A control strategy was developed to share and integrate this information between to the two systems. During test operations the data from the shifting inventory of granular particles in the cold flow unit will be used to control some of the valves controlling the gas flow paths in the hot unit. Taken in conjunction with the inlet flows, temperatures, and pressures in the hot unit a control system is proposed to balance the exhaust flow through the various gas outlets of the different vessels. System identification studies are needed to characterize the process delays, time constants, and interactions between control parameters.
Experimental and Computational Investigation of Rayleigh-Bénard Flow in the Rotating Cavities of a Core Compressor
Authors: Puttock-Brown M. R. , Rose M. G. , Long C. A.
Published: August 2017

This paper presents new experimental measurements, at conditions representative of an aero engine, of heat transfer from the inner peripheral surface (shroud) of a rotating cavity. The results are taken from the University of Sussex Multiple Cavity Rig, which is designed to be similar to a gas turbine high pressure compressor internal air system. The shroud Nusselt numbers are shown to be dependent on the shroud Grashof number and insensitive to throughflow axial Reynolds number. The magnitude of the shroud Nusselt numbers are consistent with accepted correlations for turbulent free convection from a horizontal plate, yet show a trend (gradient of Nusselt to Grashof numbers) that is similar to laminar free convection.

A supporting high-resolution 3D unsteady RANS simulation was conducted to investigate the cavity flow structure with particular attention paid to the near shroud region. This demonstrated flow structures that are consistent with published work but also show the existence of a type of Rayleigh-Bénard flow that manifests as a series of streaks that propagate along the periphery of the cavity. These structures can be found in the literature albeit in different circumstances. Whilst these streaks have been shown in the simulation their existence cannot be ratified without experimental confirmation.
Development of the New Ansaldo Energia Gas Turbine Technology Generation
Authors: Ruedel U. , Stefanis V. , Ramaglia A. D. , Florjancic S.
Published: August 2017

This paper provides an overview of the ongoing development activities for the Ansaldo Energia gas turbines AE64.3A, AE94.2, AE94.2K, AE94.3A, GT26 (2006), GT26 (2011), GT36-S6 and GT36-S5. The improvements significantly reduce the energy consumption in gas turbine combined cycle (GTCC) power plants and are directed towards improved operational and fuel flexibility, increased GT power output, GT efficiency and improved component lifetime.

The collaborative development, validation and application of the constant pressure sequential combustion system (‘CPSC’) for the GT36 engine will be introduced. Based on the well-established sequential burner technology as installed since 1994 on all legacy GT26 gas turbines, the operation turndown, fuel flexibility and the overall system robustness is described. The development and engine validation of the first stage burner for Improved Durability and Turndown as well as the design of a Combustor Sequential Liner within a can combustion system is shown. The reconstruction and analysis of the acoustic transfer matrix of the flame in the sequential burner together with the applied air and fuel management facilitate emission and dynamics control at both, the extremely high and low firing temperature ranges.

The axial flow turbine of the GT36 heavy duty gas turbine, which has evolved from the existing and proven GT26 design, consists of an optimized annulus flow path, higher lift airfoil profiles, optimized aerodynamic matching between the turbine stages and a new and improved cooling systems of the turbine vanes and blades. A major design feature of the turbine has been to control and reduce the aerodynamic losses, associated with the airfoil profiles, trailing edges, blade tips, end walls and coolant ejection. The advantages of these design changes to the overall gas turbine efficiency have been verified via extensive experimental testing.
Improving Turbomachinery Health Monitoring Using Advanced Shaft Telemetry System
Authors: Hesler S. H. , Suprock C. A.
Published: August 2017

Turbine-generator shaft systems used in power generation applications are exposed to degradation mechanisms that could result in high consequence failures if not discovered prior to damage accumulation. Grid-induced torsional vibration, growth of cracks in the shaft forging, and large blade vibration are some examples of degradation that remains unmonitored in most commercial plants today. In many cases, the sensing and subsequent trending of high-quality vibration data obtained directly from the shaft surface can be the basis for a decision to continue to operate versus inspect or repair. Detection of small changes in torsional and lateral vibration mode properties can be sensed at a single shaft location and trended using techniques such as Advanced Pattern Recognition to reveal the very early signs of rotor distress.

Contemporary barriers to widespread application of wireless shaft vibration measurements for health monitoring were studied and addressed in the development of the Turbine Dynamics Monitoring System (TDMS). The resulting design evolved around the industry need for low sensor maintenance, high reliability, ease of installation, and high data quality to enable early detection of critical component changes. These improvements capitalized on advances in strain gage and accelerometer technology, micro-telemetry, radio-frequency power systems, and advanced adhesives for installation. The new system has been successfully applied in the field on large steam turbine-generators to detect grid-induced torsional vibration.

The paper will describe background of turbine-generator torsional vibration as well as the technical features of this advanced telemetry application with examples of field data.
Experimental Investigation of Two Competitive High Pressure Turbine Blade Cooling Systems
Authors: Risnyk Sergiy , Artushenko Andriy , Kravchenko Igor , Borys Sergii
Published: August 2017

Aeroengine high-pressure turbine (HPT) is the key engine component.

HPT blade must withstand high inlet temperatures and mechanical loads providing the necessary level of the efficiency. To achieve these objectives effective and complex blade cooling systems (internal convective and film cooling) are used in the HPT design.

The objective of this project is to design and investigate the aeroengine HPT blade cooling system that is able to withstand the blade inlet gas temperature level of approx. 1900K but with the minimal cooling airflow amount.

HPT blade of the aeroengine with unducted fan (UDF) was taken as a baseline design, namely, the monocrystal blade with a convective multipass system and the film cooling.

Advanced HPT blade inter-wall cooling system was designed, investigated and compared with the typical baseline HPT blade. In the advanced HPT blade inter-wall cooling system special types and structure of cooling channels are used.

Both types of cooling systems were investigated experimentally in the turbine rotor of the high temperature core engine. Measurements of turbine blades temperatures were performed using crystal temperature sensors (CTS). HPT blades with two competitive cooling systems incorporated with CTS (0,2–0,3 mm size) were installed in the turbine rotor of the core engine and tested on the engine Maximal rate.

After tests and the engine disassembly CTSs were extracted and the characteristics of the CTS crystal lattice were transcribed in temperature values.

Thermal state of both two competitive cooling systems was validated by experimental data.

Numerical and experimental results obtained in the research of HPT blade cooling system are presented in the article. Aeroengine high pressure turbine blade cooling systems designs are described.
Measurement of Large Flow Angles With Non-Nulling Multi-Hole Pressure Probes
Authors: Conlon Martin J. , Wright Alexander , Abo El Ella Hamza M.
Published: August 2017

In complex flow fields, the steady-state, three-dimensional attributes can be measured intrusively using a multi-hole pressure probe. These probes are built to be as small as possible to minimize flow disturbance, but the small size makes them susceptible to both manufacturing tolerances and fouling. As such, each probe must be calibrated on a regular basis and care must be taken to ensure that the geometry is not disturbed. The probes are operated in either “nulling” or “non-nulling” modes, the latter being the simpler of the two in terms of experimental setup and mechanical fixturing. This has made non-nulling mode the preferred choice for many years; however, non-nulling mode necessitates complete three-dimensional calibration data. Sector-based calibration strategies have become nearly universal, although improvement efforts continue. This paper presents a new calibration and data analysis strategy that gives shorter calibration times and more robust data reduction.
Biomass Microturbine Based EFGT and IPRP Cycles: Environmental Impact Analysis and Comparison
Authors: Zampilli Mauro , Bidini Gianni , Laranci Paolo , D’Amico Michele , Bartocci Pietro , Fantozzi Francesco
Published: August 2017

The global microturbine market will grow at an interesting Compound Annual Growth Rate during the period 2016–2020 and a key driver will be distributed generation also with unconventional fuels. This paper compares the performances of two different microturbine based technologies for biomass micro CHP. One is the Integrated Pyrolysis Regenerated Plant (IPRP), technology developed by the authors by coupling a pyrolyzer to a mGT fuelled by biomass pyrolysis gas. Two IPRP versions are considered: one in which char is burned to provide pyrolysis energy and one in which it is used as a carbon sink. The second technology is the Externally Fired Gas Turbine (EFGT) based on biomass combustion in a dedicated burner and high temperature heat exchangers used to heat up compressed air which expands in the mGT. Hot air at the turbine exhaust is used as combustion air for biomass. The layout and operational conditions considered were optimized by the authors in previous works. The environmental performance of the two technologies when fuelled with the same biomass at the same power output, is assessed through a Life Cycle Assessment (LCA) analysis, calculating impacts on acidification, carbon footprint and Cumulative Energy Demand (CED). Two sensitivity analysis are also performed on different vegetal oils used for scrubbing and different methods of allocation, referred to CHP products.

Results show that both technologies have negative carbon footprints, however the IPRP has the worst performance because of the sunflower oil, used for syngas scrubbing, which offsets the additional carbon sink benefit of biochar. If water it used as a scrubbing medium in the IPRP plant, this configuration obtains similar results in terms of environmental impact, compared to IPRP plant using vegetable oil as a scrubbing medium. However, when the effect of a different vegetal oil is considered, namely a waste frying oil, the former introduces extraordinary benefits resulting in the IPRP outperforming the EFmGT in terms of carbon negative technology.
Simulation of Multi-Stage Compressor at Off-Design Conditions
Authors: Wang Feng , Carnevale Mauro , di Mare Luca , Gallimore Simon
Published: August 2017

Computational Fluid Dynamics (CFD) has been widely used for compressor design, yet the prediction of performance and stage matching for multi-stage, high-speed machines remain challenging. This paper presents the authors’ effort to improve the reliability of CFD in multistage compressor simulations. The endwall features (e.g. blade fillet and shape of the platform edge) are meshed with minimal approximations. Turbulence models with linear and non-linear eddy viscosity models are assessed. The non-linear eddy viscosity model predicts a higher production of turbulent kinetic energy in the passages, especially close to the endwall region. This results in a more accurate prediction of the choked mass flow and the shape of total pressure profiles close to the hub. The non-linear viscosity model generally shows an improvement on its linear counterparts based on the comparisons with the rig data. For geometrical details, truncated fillet leads to thicker boundary layer on the fillet and reduced mass flow and efficiency. Shroud cavities are found to be essential to predict the right blockage and the flow details close to the hub. At the part speed the computations without the shroud cavities fail to predict the major flow features in the passage and this leads to inaccurate predictions of massflow and shapes of the compressor characteristic. The paper demonstrates that an accurate representation of the endwall geometry and an effective turbulence model, together with a good quality and sufficiently refined grid result in a credible prediction of compressor matching and performance with steady state mixing planes.
Multiple-Model Adaptive Control of a Hybrid Solid Oxide Fuel Cell Gas Turbine Power Plant Simulator
Authors: Tsai Alex , Pezzini Paolo , Tucker David , Bryden Kenneth M.
Published: August 2017

A Multiple Model Adaptive Control (MMAC) methodology is used to control the critical parameters of a Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) cyberphysical simulator, capable of characterizing 300kW hybrid plants. The SOFC system is comprised of a hardware Balance of Plant (BoP) component, and a high fidelity FC model implemented in software. This study utilizes empirically derived Transfer Functions (TF) of the BoP facility to derive the multi model adaptive controller (MMAC) gains for the BoP system, based on an estimation algorithm which identifies current operating points. The MMAC technique is useful for systems having a wide operating envelope with nonlinear dynamics. The practical implementation of the adaptive methodology is presented through simulation in the MATLAB/SIMULINK environment.
Heat Transfer Analysis of Jet Impingement Cooling on a Simulated Ceramic Matrix Composite Surface
Authors: Krishna Karthik , Ricklick Mark
Published: August 2017

Ceramic Matrix Composite is a woven material characterized by a significant level of surface waviness of 35–60μm and surface roughness of 5–6μm. To be implemented in a future gas turbine engine they will be cooled traditionally to increase power and efficiency. To analyze the CMC surface effects on heat transfer rate, an impinging circular jet on a simulated CMC surface is studied experimentally and the CMC surface is represented by a high resolution CNC machined surface. The test parameters are jet to plate distance of 7 jet diameters, oblique impingement angles of 45° and 90° and Reynolds numbers of 11,000 to 35,000. The test surface is broken down into constant temperature segments, and individual segment Nusselt number is determined and plotted for the various impingement cases studied. Area-Averaged results show negligible changes in average Nusselt number as compared to the hydrodynamically smooth surface. The impact of the CMC surface feature is negligible compared to the uncertainty in heat transfer coefficient, and therefore traditional design tools can be utilized.
Experimental and Numerical Investigation of Heat Transfer and Film Cooling Effectiveness of a Highly Loaded Turbine Blade Under Steady and Unsteady Wake Flow Condition
Authors: Nikparto A. , Rice T. , Schobeiri M. T.
Published: August 2017

The current study investigates the heat transfer and film-cooling effectiveness on a highly loaded turbine blade under steady and periodic unsteady wake induced flow conditions from both experimental and numerical simulation points of view. For the experimental measurements, the cascade facility in Turbomachinery Performance and Flow Research Lab (TPFL) at Texas A&M University was used to simulate the periodic unsteady flow condition inside gas turbine engines. The current paper includes steady and unsteady inlet flow conditions. Moving wakes, originated from upstream stator blades, are simulated inside the cascade facility by moving rods in front of the blades. The flow coefficient is maintained at 0.8 and the incoming wakes have a reduced frequency of 3.18. For film-cooling effectiveness study a special blade was designed and inserted into the cascade facility that has a total of 617 holes distributed along 13 different rows on the blade surfaces. 6 rows cover the suction side, 6 other rows cover the pressure side and one last row feeds the leading edge. There are six coolant cavities inside the blade. Each cavity is connected to one row on either sides of the blade, except for the closest cavity to leading edge since it is connected to the leading edge row as well. The rows that are connected to the same cavity have identical injection hole numbers, arrangement (except for leading edge) and compound angles. Coolant is injected from either sides of the blade through the 6 cavities to form a uniform distribution along the lateral extent of the blade. In order to increase the effectiveness, the coolant injection holes are shaped holes. In the regions close to the end-walls of the cascade the holes have compound angles to overcome the effects of horseshoe and passage vortices. To study the film cooling effectiveness, the blade surfaces were covered with Pressure Sensitive Paint (PSP) excited with green light. Experiments were performed for Reynolds number of 150,000 and the average blowing ratio of coolant was maintained at one for all rows throughout the experiments. For heat transfer coefficient measurements, the liquid crystal method was used. For that reason the surfaces of the blade were covered by liquid crystal sheets and it was tested at the same Reynolds number. As computational platform, a RANS based solver was selected for this study. Sliding mesh technique was incorporated into the simulations to produce moving wakes. Experimental and numerical investigations were performed to determine the effect of flow separation, and pressure gradient on film-cooling effectiveness in the absence of wakes. Moreover, the effect of impinging wakes on the overall film coverage of blade surfaces and heat transfer coefficient was studied. Comparison of numerical and experimental results reveals deficiencies of numerical simulation.
Experimental Evaluation of Thermal and Mass Transfer Techniques to Measure Adiabatic Effectiveness With Various Coolant to Freestream Property Ratios
Authors: Wiese Connor J. , Rutledge James L. , Polanka Marc D.
Published: August 2017

As gas turbine engine temperatures increase, experimentally evaluating the necessary cooling schemes becomes increasingly cost prohibitive at engine conditions. Thus, researchers conduct film cooling experiments near room temperature and attempt to scale the results to engine conditions. Although thermal measurements of film cooling adiabatic effectiveness are common, an increasingly popular method of evaluating adiabatic effectiveness employs pressure sensitive paint and the heat-mass transfer analogy. Mass transfer methods are attractive because an impermeable model can be used as an analog for a perfectly adiabatic wall; however, the mass transfer analogy is imperfect. The suitability of mass transfer methods as a substitute for thermal methods is of interest in the present work.

Much scaling work has been dedicated to the influence of the coolant-to-freestream density ratio, but other fluid properties that differ between experimental and engine conditions have only been considered in more recent work. Most notably in the context of an examination of the ability of mass transfer methods to serve as a proxy for thermal methods are the properties that directly influence thermal transport — thermal conductivity and specific heat. That is, even with an adiabatic wall there is still heat transfer between the freestream flow and the coolant plume and the mass transfer analogy would not be expected to account for the specific heat or thermal conductivity distributions within the flow field. Using various coolant gases (air, carbon dioxide, nitrogen and argon) and comparing with thermal experiments, the efficacy of the pressure sensitive paint method as a direct substitute for thermal measurements was evaluated on a simulated leading edge model with compound coolant injection. The results thus allow examination of how the two methods respond to different property variations. Overall, the pressure sensitive paint technique was found to over predict the adiabatic effectiveness of a particular coolant flow when compared to the results obtained from infrared thermography, but still reveals a great deal of valuable information regarding the coolant flow structure.
Numerical Simulation of the Multistage Ultra-High Efficiency Gas Turbine Engine, UHEGT
Authors: Ghoreyshi Seyed M. , Schobeiri Meinhard T.
Published: August 2017

The Ultra-High Efficiency Gas Turbine Engine (UHEGT) was introduced in our previous studies [1]–[3]. In UHEGT, the combustion process is no longer contained in isolation between the compressor and turbine, rather distributed in multiple stages and integrated within the high-pressure turbine stator rows. Compared to the current most advanced conventional gas turbines, UHEGT considerably improves the efficiency and output power of the engine while reducing its emissions and size. In the present study, a complete six-stage turbine with three stator internal combustors is designed for UHEGT. The turbine is designed for a single spool turboshaft system used for power generation. A thermodynamic cycle that has a base thermal efficiency of above 45% is designed based on an ideal mixture of methane and air. Preliminary flow path for each turbine stage is designed by 1D/2D approach (meanline calculation). The combustors, designed based on our previous [1] and parallel studies, consist of cylindrical tubes extended from hub to shroud with thin slots on top and bottom for gaseous fuel injection. CFD calculation (via ANSYS CFX) is used to simulate the high pressure turbine stages (stage 1 to 3). The simulations are unsteady, they are performed for ten total components and include a multi-species combustion process along with the rotor motion. The flow path is modified based on the CFD results in order to reduce separation and losses while enabling maximum mixing of fuel and air and reducing temperature non-uniformities. Flow patterns, secondary flow losses, temperature distribution, and pollutant emissions are presented and analyzed in the results. The results show that a relatively uniform temperature distribution is achieved at the inlet of each rotor and the system performs very well regarding the output power and flow patterns.
Fourier Descriptors for Improved Analysis of Distortion Transfer and Generation
Authors: Peterson Marshall W. , Gorrell Steven E. , List Michael G.
Published: August 2017

For fan/compressor design, quantifying distortion transfer and generation bladerow by bladerow through a fan/compressor is important to understand the flow physics and predict performance. What is needed are descriptors capable of describing distortion profiles with both high and low distortion content and account for the reshaping of distortion profiles. Four key parameters were identified as desirable to quantitatively capture distortion transfer, generation and effects on performance: distortion magnitude, shape, severity and phase. A set of distortion descriptors based on Fourier analysis are shown to quantitatively capture distortion magnitude, shape and phase change across bladerows. These Fourier descriptors are modal amplitude, total amplitude, and phase shift. When used together, these Fourier descriptors can be used to qualitatively describe any conceivable profile shape for any parameter.
Enhancement of Film Effectiveness of Cooling Holes With Fan-Shaped Exit Geometry by the Application of Double Flow-Control Devices: Optimization in Consideration of Device Offset
Authors: Funazaki Ken-ichi
Published: August 2017

This study deals with CFD-based optimization of Double Flow Control Devices (DFCDs); a patented technology for enhancing film effectiveness using Taguchi method as a robust optimizing technique. This study adopts offset of the devices with respect to the centerline of the hole, which may happen in the manufacturing process, as a noise factor in the optimizing process. The aim of this study is to explore a possibility of DFCDs to improve the cooling performance of a sophisticated fan-shaped cooling hole called 7-7-7 shaped hole developed by Penn State University [9]. Aerodynamic and thermal performances of the optimized DFCD model were evaluated through the detailed experiments using IR camera and temperature rake.
Subsynchronous Vibration Patterns Under Reduced Oil Supply Flow Rates
Authors: Nichols B. R. , Fittro R. L. , Goyne C. P.
Published: August 2017

Many high-speed, rotating machines across a wide range of industrial applications depend on fluid film bearings to provide both static support of the rotor and to introduce stabilizing damping forces into the system through a developed hydrodynamic film wedge. Reduced oil supply flow rate to the bearings can cause cavitation, or a lack of a fully developed film layer, at the leading edge of the bearing pads. Reducing oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses due to shear forces. While machine efficiency may be improved with reduced lubricant flow, little experimental data on its effects on system stability and performance can be found in the literature. This study looks at overall system performance of a test rig operating under reduced oil supply flow rates by observing steady-state bearing performance indicators and baseline vibrational response of the shaft. The test rig used in this study was designed to be dynamically similar to a high-speed industrial compressor. It consists of a 1.55 m long, flexible rotor supported by two tilting pad bearings with a nominal diameter of 70 mm and a span of 1.2 m. The first bending mode is located at approximately 5,000 rpm. The tiling-pad bearings consist of five pads in a vintage, flooded bearing housing with a length to diameter ratio of 0.75, preload of 0.3, and a load-between-pad configuration. Tests were conducted over a number of operating speeds, ranging from 8,000 to 12,000 rpm, and bearing loads, while systematically reducing the oil supply flow rates provided to the bearings under each condition. For nearly all operating conditions, a low amplitude, broadband subsynchronous vibration pattern was observed in the frequency domain from approximately 0–75 Hz. When the test rig was operated at running speeds above its first bending mode, a distinctive subsynchronous peak emerged from the broadband pattern at approximately half of the running speed and at the first bending mode of the shaft. This vibration signature is often considered a classic sign of rotordynamic instability attributed to oil whip and shaft whirl phenomena. For low and moderate load conditions, the amplitude of this 0.5x subsynchronous peak increased with decreasing oil supply flow rate at all operating speeds. Under the high load condition, the subsynchronous peak was largely attenuated. A discussion on the possible sources of this subsynchronous vibration including self-excited instability and pad flutter forced vibration is provided with supporting evidence from thermoelastohydrodynamic (TEHD) bearing modeling results. Implications of reduced oil supply flow rate on system stability and operational limits are also discussed.
Estimation of Forcing Functions on a Mistuned Bladed Rotor From Harmonic Response
Authors: Sinha Alok
Published: August 2017

This paper deals with the estimation of forcing functions on a mistuned bladed rotor from measurements of harmonic response via Kalman Filter in time domain. An unique feature of this approach is that the number of estimated variables can be far greater than the number of measurements. The robustness of this method to measurement errors is shown. It is also shown that direct prediction of amplitude and phase of sinusoidal force vector from input/output frequency response function has a large amount of errors in the presence of unavoidable measurement noise. Numerical examples contain both frequency mistuning and geometric mistuning.
Heat Transfer and Pressure Drop Measurements in a High Solidity Pin Fin Array With Variable Hole Size Incremental Impingement
Authors: Sheikhmohamed A. A. , Soma L. W. , Ames F. E. , Acharya S.
Published: August 2017

Leading edge heat loads on turbine vanes diminish relative to fully turbulent heat loads with increasing Reynolds number. Leading edge regions of turbine nozzles are often cooled using showerhead arrays while the near pressure surface is often protected with rows of shaped holes. However, in environments with impurities in the fuel or air cooling holes are susceptible to clogging and constitute sites where deposition can begin. Showerhead film cooling can be disruptive to downstream boundary layer development and film cooling. Also, high turbulence levels which normally exist in these regions quickly mix away film cooling protection. Consequently, internal cooling has many advantages over showerhead cooling and pressure surface film protection. Internal cooling produces higher levels of internal effectiveness and spent cooling air can be subsequently directed to near optimum discharge geometries for film protection.

Conventional cooling methods have disadvantages when trying to cool leading edge regions and near pressure surfaces. Cooling air in pin fin arrays quickly heats up developing a lower cooling potential. Impingement arrays have issues due to increasing crossflows which deflect impingement jets and insulate the surfaces needing cooling. Incremental impingement overcomes these disadvantages by incrementally adding cooling air where needed and overcoming crossflows by hiding impingement jets behind high solidity pedestals.

This paper presents heat transfer and pressure drop results for an incremental impingement array with variable hole size. The experimental measurements were acquired using a bench scale test rig. The array Reynolds numbers tested ranged from 5000 to 60,000 based on the average velocity of the accumulated flow through the minimum array flow area. The array consisted of an initial impingement row between a row of elongated pedestals followed by 7 additional high solidity round pedestal rows in a staggered arrangement. Impingement holes of variable sizes were placed behind even rows. Generally, the array consisted of rows of round pins spaced at 1.625 diameters in the spanwise direction, 1.074 diameters in the streamwise direction with a channel height to diameter ratio of 0.5. Impingement hole to pin diameter ratios used included d/D of 0.295, 0.351, and 0.417. Hole configurations were limited to arrays where the hole area upstream from the last row of holes was no more than 109% of the minimum array flow area. Heat transfer measurements were acquired at a constant temperature within the array and are reported on a row averaged basis in terms of the local internal effectiveness and the cooling parameter.
An Emerging Technique for Low-Concentration Measurement of Particulate Emissions From Gas-Fired Gas Turbines
Authors: Crosby Kevin J. , England Glenn C.
Published: August 2017

Concentrations of particulate matter (PM, PM10, PM2.5) from gas-fired gas turbines typically are near or below the overall method detection and quantitation limits of traditional hot filter/cooled impinger methods used for PM/PM10/PM2.5 emissions measurements (e.g., USEPA reference methods 5, 201A, 202). The test results can be highly variable, and may significantly overstate emissions even with application of best practices optimized to minimize bias and variability.

An emerging test protocol for modifying USEPA Conditional Test Method 39 (CTM 39), a dilution sampling method for determining PM10/PM2.5 emissions from stationary sources, was used to accurately measure much lower PM concentrations. The lower concentrations are believed to be more representative of actual PM emissions from gas turbines. The modifications include adding ambient air sample collection and analysis methods for improved method sensitivity. Data from several testing programs are presented to illustrate the limitations of traditional methods for determining PM emissions, including measurement challenges associated with post-combustion emission controls such as SCR. Results from the modified method are presented to demonstrate the potential improvement compared with traditional hot filter/cooled impinger methods.