bluuebunny/crossref_metadata_2025 huggingface dataset:
A Development of EMAS (Easy Maintenance Assistance Solution) for Industrial Gas Turbine Engine
Authors: Lee Myungkuk , Kang Myoung-Cheol , Roh Hongsuk , Ki Jayoung
Published: September 2014

The solution was developed for the maintenance decision support of combined cycle power plant gas turbine. The developed solution provides the calculated result of optimal overhaul interval through the following modules: Overhaul Interval Prediction, Real Time Performance Monitoring, Model-Based Diagnostics, Performance Trend Analysis, Compressor Washing Period Management, and Blade Path Temperature Analysis. Model-Based Diagnostics module analyzed the differences between the data of MHI501G gas turbine performance model and the online measurement. Gas turbine performance model can be modified by the type of gas turbine of each combined cycle power plant. Compressor washing management module suggests the optimal point of balancing between the compressor performance and the maintenance cost. The predicted results of compressor washing period and overhaul period are able to support the operators in combined cycle power plant to make a proper decision of maintenance task. The developed solution was applied to MHI501G gas turbine and is, in present, on the process of field test at GUNSAN combined cycle power plant, South Korea.
The Experimental Investigations of Centripetal Air Bleed With Tubed Vortex Reducer for Secondary Air System in Gas Turbine
Authors: Chen Xiao , Feng Ye , Wu Lijun
Published: September 2014

In a modern gas turbine, the air bled through High Pressure Compressor (HPC) rotor drums from the main flow is transported radially inwards and then transferred to cool the High Pressure Turbine (HPT). The centripetal air flow creates a strong vortex, which results in huge pressure losses. This not only restricts the mass flow rate, but also reduces the cooling air pressure for down-stream hot components. Adding vortex reducer tubes to the centripetal air bleed can reduce the pressure loss and ensure the pressure and mass flow rate of the supply air. Design optimization of the tubed vortex reducer is essential in minimizing the pressure losses.

This paper describes experimental investigations of different configurations of tubed vortex reducers at different rotational speeds and mass flow rates. Particular attention is paid to the shape of the drum hole, the length of the tubed vortex reducers at the same installation location, and the angles of the nozzle guide vane outlets. The core section of test rig is comprised of two steel disks, one drum rotor and stationary cases with nozzle guide vanes. It operates at representative engine parameters, such as the turbulent flow parameter, λT(0.2–1.8) and the Rossby number Ro(0.05–0.08). Three conclusions can be drawn based on the experimental results. 1) The shape of the drum hole is a key factor of the bleed system pressure loss. An oval hole configuration has less flow resistance and results in lower pressure losses compared with a circular hole design. 2) The tests prove that tubed vortex reducers are instrumental in minimizing centripetal air flow. These components effectively restrain the free vortex development and decrease the pressure losses in the cavity. 3) Basically, the flow field consists of a free vortex and a forced vortex. The length of the tube influences the flow field and the pressure losses at the inlet and outlet of the tubed vortex reducer. However, the tube length is less important when compared with the shape of drum hole.
Hot-Film Measurements on a LPT Linear Cascade With By-Pass Transition
Authors: Gomes Reinaldo A. , Stotz Stephan , Blaim Franz , Niehuis Reinhard
Published: September 2014

Transition of the state of the boundary layer from laminar to turbulent plays an important role in the aerodynamic loss generation on turbine airfoils. An accurate simulation of the transition process and of the state of the boundary layer is therefore crucial for prediction of the aerodynamic efficiency of components in rotating machines. A lot of the research in the past years dealt with the transition over laminar separation bubbles, especially concerning flows in low pressure turbines (LPT) of air jet engines. Nevertheless, by-pass transition is also frequent in turbomachines at higher Reynolds numbers as well as for properly designed profiles. Compared with transition over a laminar separation bubble, a by-pass transition is experimentally much more difficult to detect with standard measurement techniques. In such cases it becomes necessary to use more sophisticated techniques, such as hot film anemometry, hot wires or Preston probes in order to obtain accurate information on the state of the boundary layer.

The study presented is carried out using a linear cascade with a LPT blade profile with strong front loading and gentle flow deceleration at the rear suction side of the blade. Measurements were performed at the High-Speed Cascade Wind Tunnel of the Institute of Jet Propulsion at engine relevant Mach and Reynolds numbers. Emphasis is put on the evaluation of the different transition processes at mid-span and its influence on profile losses. The data post processing was adapted for compressible flows, which allows a more accurate determination of the transition area as well as qualitatively better distributions of the wall shear stress. Finally, comparisons with simulations, using computational fluid dynamics (CFD) tools, are performed and fields for improvement of the turbulence and transition models are identified.
3D Multi-Disciplinary Inverse Design Based Optimization of a Centrifugal Compressor Impeller
Authors: Zangeneh Mehrdad , Mendonça Fred , Hahn Youngwon , Cofer Jack
Published: September 2014

Design of centrifugal compressors in different applications from industrial to turbochargers to aeroengine is subject to difficult multi-disciplinary ( aerodynamics and mechanical) and multipoint/multi-objective requirements. These multi-disciplinary and multi-point requirements have to be met by iterations between aerodynamics and mechanical design, leading to long development times and bottlenecks in the design process. In this paper, for the first time, a commercially available solution, compatible with industrial development times, is presented for 3D multi-disciplinary and multi-point design optimisation of turbomachinery blades. The methodology combines 3D inverse design method, automatic optimizers, 3D CFD and 3D FEA codes. The key aspect of the approach is to parameterise the 3D geometry through the blade loading distribution used in 3D inverse design code TURBOdesign1, which results in ability to access large part of design space with very few design parameters. The Design of Experiments method is used to generate a number of geometries which are then analysed by 3D CFD code STAR-CCM+ and 3D FEA code Abaqus. Different performance parameters related to aerodynamics (efficiency, stable operating range etc) and structural integrity (maximum principal stress, etc) are then evaluated. The data is then used to create a response surface. The validity and accuracy of the response surface is evaluated by CFD and FEA and then once confirmed a Multi-objective Genetic Algorithm is run on the response surface to explore the trade-offs between different design parameters, such as peak efficiency, stable operating range and mechanical stress. In this paper the methodology is applied to the redesign of the well-known Eckardt centrifugal compressor impeller.
Endoscopic Chemiluminescence Measurements as a Robust Experimental Tool in High-Pressure Gas Turbine Combustion Tests
Authors: Goers Simon , Witzel Benjamin , Heinze Johannes , Stockhausen Guido , van Kampen Jaap , Schulz Christof , Willert Chris , Fleing Christian
Published: September 2014

The development process for gas turbine combustion systems includes single-burner high-pressure combustion tests as an important validation step. In these tests the performance of a combustor is investigated at realistic gas turbine conditions. Measurement techniques that are typically used in these tests include mass flow meters, thermocouples, pressure transducers, and probes for exhaust-gas composition measurements. These measurement techniques, however, do not provide direct information of the flame behavior.

Chemiluminescence measurements have proven to being a valuable and robust technique to close this gap [1,2]. This paper summarizes the results of chemiluminescence measurements performed at Siemens full-scale high-pressure single-burner combustion test rigs at the German Aerospace Center (DLR) in Cologne, Germany. To minimize the impact of the measurement system on the experiment, the optical access to the test rigs was provided by a water-cooled endoscopic probe. The probe was located in a side-wall downstream of the burner, viewing upstream towards the burner outlet. The probe was successfully operated up to full engine pressure and flame temperatures of approximately 1900 K.

For the detection of the chemiluminescence signal different approaches were applied:

• Spectral analyses of the chemiluminescence signal were done by using an USB spectrometer.

• For flame imaging up to two intensified CCD cameras were applied. In front of the cameras various combinations of optical filters were installed to selectively record the respective chemiluminescent species (OH*, CH*, CO2*).

• For studies with special focus on combustion dynamics an intensified high-speed CMOS camera was used. High-repetition-rate measurements were used for identifying the shapes of flame modes.

• Acoustic pressure oscillations inside the combustion chamber were recorded by pressure transducers simultaneously to the camera images. This allows the pressure oscillations to be correlated with flame fluctuations during post-processing [3,4].

Generally, the robustness of endoscopic chemiluminescence measurements was successfully demonstrated in numerous tests at realistic gas turbine conditions. The applied imaging setups provided new information about the connection between the flame position and NOx emissions as well as the correlation of flame fluctuations and pressure oscillations. Hence, they have become a valuable experimental tool to improve the evaluation and understanding of the combustor performance. Future work will focus on further improvement of quantitative evaluations by compensation of line-of-sight image integration, reabsorption of OH* by OH, and beam steering.
Numerical Analysis of the Unsteady Loads on a Steam Turbine Double Seat Control Valve
Authors: Bianchini Cosimo , Da Soghe Riccardo , Cosi Lorenzo , Imparato Enzo
Published: September 2014

The continuously growing request for high operational flexibility also for large scale steam turbine creates new challenges for control valve design. Such components, subjected to large static loads, may also experience strong vibrations due to unsteady turbulent fluctuations downstream the throttling section, which need to be confined sufficiently far from structural natural frequencies in the entire range of operating conditions.

This work is focused on a computational analysis of the unsteady steam flow developing within a realistic double-seat control valve employed in industrial steam turbine. Actual operating conditions are considered both in terms of steam inflow pressure and temperature, flow rates and plug height. Three plug heights were considered: two corresponding to almost closed plug thus subjected to choked flow, and the third verified at 4 different steam rates.

In order to capture the unsteady nature of the flow and verify the fluid-dynamic forcing frequency, the Scale Adaptive Simulation principle, as implemented in Ansys® CFX 14.5 code, has been employed. Computations were run with a computational time step of 10−4 s and an effective simulation window of 0.2 s for time averaged values and pressure time signals. The unsteady response is monitored analyzing the frequency spectra of both integral variables (i.e. forces and moment on plug) and punctual pressure oscillations.

Analysis of results showed that it is possible to correlate the principal frequency and amplitude with the operating conditions. Strouhal number based on plug diameter and bulk flow velocity remains in fact constant independently on operating conditions.
Influence of Unsteadiness on the Control of a Hub-Corner Separation Within a Radial Vaned Diffuser
Authors: Marsan Aurélien , Trébinjac Isabelle , Coste Sylvain , Leroy Gilles
Published: September 2014

The present work aims at evaluating the effect of the impeller-diffuser interaction on the control of a hub corner separation, which develops in the radial vaned diffuser of a centrifugal compressor designed and built by Turbomeca, Safran group. Unsteady numerical simulations of the flow in the aspirated centrifugal compressor are then performed. Numerical results are validated by comparison with the available experimental results. The analysis of the numerical flow field shows that the hub-corner separation is not completely removed by the suction, on the contrary to the steady-state results that were obtained in previous work. The boundary layer separation is only translated downstream. Its location is explained by the scrolling of the pressure waves generated by the impeller-diffuser interaction, which strengthen when crossing the diffuser throat. This result highlights the major role played by the impeller-diffuser interaction, which should be taken into account for developing control strategies in radial vaned diffusers, and stresses the shortcoming of the steady-state numerical model when suction is applied.
Streamwise and Crossflow Vortical Structures on Turbine Blades and Swept Cylinders
Authors: Rona A. , Gostelow J. P.
Published: September 2014

Flow visualization on a lengthy time-average basis on the suction surface of turbine blades showed robust and consistent streamwise streaks at subsonic and transonic speeds. The normal flow past a circular cylinder is a more canonical case and testing was undertaken at high speeds on a 37.23 mm diameter cylinder and at low speeds on a 152 mm diameter cylinder. The lateral spacing between streaks on cylinders had been predicted by Kestin and Wood and the present tests gave excellent agreement with their theory. Their work on unswept circular cylinders provides a good baseline model for understanding and predicting sweep effects on cylinders and turbomachinery blading. Experiments on a circular cylinder were performed over a range of sweep angles from zero to 61°, giving results for lateral spacing and angular orientation of the streaks. At high sweep angles, the results are consistent with those of Poll. Hot wire measurements away from the surface indicate a variable flow structure in the spanwise direction with a wavelength matching that of the surface traces. The streamwise disturbance was predominantly stationary in nature and resilient, often persisting from leading edge to trailing edge. Crossflow instability becomes more significant at high sweep angles. It grows aggressively and rapidly, being predominantly of a traveling nature. The observed streaks could be of particular concern for the thermal design of turbine blades.
Design of Experiments to Investigate Geometric Effects on Fluid Leakage Rate in a Balance Drum Seal
Authors: Morgan Neal R. , Untaroiu Alexandrina , Migliorini Patrick J. , Wood Houston G.
Published: September 2014

Annular labyrinth seals are designed as tortuous paths that force a working fluid to expand and contract repeatedly through small clearances between high and low pressure stages of turbomachinery. The resulting expansion and recirculation reduces kinetic energy of the flow and minimizes leakage rate between regions of high and low pressure through the seal. Most current seal geometries are selected based on what has worked in the past, or by incremental improvements on existing designs. In the present research, a balance drum used in a multi-stage centrifugal pump was chosen as a starting point. A design of experiments study was performed to investigate the influence of groove scale on leakage rate across the seal for a fixed pressure differential.

The CFD model of the selected labyrinth seal has an upstream region leading to 20 evenly spaced semicircular grooves along a 267 mm seal length, with a clearance region of 0.305 mm. The seal geometry was specified by a set of five variables. The variables allow for variation in scale of the semicircular grooves within a pattern of five independently scaled grooves repeated four times along the seal length.

The seal was constructed with a parameterized CFD model in ANSYS CFX as a five degree sector of the full 3D seal. A non-central composite designed experiment was performed to investigate the effects of five parameters on leakage rate in the system. This study demonstrates a practical approach for investigating the effects of various geometric factors on leakage rate for balance drum seals. The empirical 10-parameter linear regression model fitted to the results of the experimental design yields suggested groove radii that could be applied to improve performance of future seals.
Development of a Suite of Hybrid Electric Propulsion Modeling Elements Using NPSS
Authors: Perullo Christopher A. , Trawick David , Clifton William , Tai Jimmy C. M. , Mavris Dimitri N.
Published: September 2014

NASA is actively funding research into advanced, unconventional aircraft and engine architectures to achieve drastic reductions in vehicle fuel burn, noise, and emissions. One such concept is being explored by Boeing, General Electric, Virginia Tech, and Georgia Tech under the Subsonic Ultra Green Aircraft Research (SUGAR) project [1]. A major cornerstone of this research is evaluating the potential performance benefits that can be attributed to using hybrid electric propulsion. Hybrid electric propulsion in this context involves a non-Brayton power generation or storage source, such as a battery or a fuel cell, which can be used to provide additional propulsive energy to a conventional Brayton cycle powered turbofan engine. Employing additional power sources for thrust production increases the number of degrees of freedom both from a design and configuration standpoint and from an operational one. In order to assess and understand the myriad number of potential new configurations a modeling and simulation tool is needed; however, current state of the art propulsion modeling tools such as the Numerical Propulsion System Simulation (NPSS) are not natively capable of assessing novel hybrid electric configurations.

This research addresses the gap between hybrid electric propulsion and conventional cycle analysis tools by developing a suite of native NPSS elements suitable for hybrid electric engine cycle design and analysis. Elements have been developed for a fuel cell, battery, motor, generator, and electrical distribution system. Both room temperature and cryogenically cooled superconducting variants are developed. The elements are designed such that they can be seamlessly integrated into existing NPSS cycle models to assess any system configuration or architecture the designer can envision.
Impact of Main and Splitter Blade Leading Edge Contour on the Performance of High Pressure Ratio Centrifugal Compressors
Authors: Erdmenger Rodrigo R. , Michelassi Vittorio
Published: September 2014

The impact of leading edge sweep in an attempt to reduce shock losses and extend the stall margin on axial compressors has been extensively studied, however only a few studies have looked at understanding the impact of leading edge contouring on the performance of centrifugal compressors. The present work studies the impact of forward and aft sweep on the main and splitter blade leading edge of a generic high flow coefficient and high pressure ratio centrifugal compressor design and the impact on its overall peak efficiency, pressure ratio and operating range. The usage of aft sweep on the main blade led to an increase of the pressure ratio and efficiency, however it also led to a reduction of the stable operating range of the impeller analyzed. The forward sweep cases analyzed where the tip leading edge was displaced axially forward showed a slight increase in pressure ratio, and a significant increase on operating range. The impact of leading edge sweep on the sensitivity of the impeller performance to tip clearance was also studied. The impeller efficiency was found to be less sensitive to an increase of tip clearance for both aft and forward sweep cases studied. The forward sweep cases studied also showed a reduced sensitivity from operating range to tip clearance.

The studies conducted on the splitter leading edge profile indicate that aft sweep may help to increase the operating range of the impeller analyzed by up to 16% while maintaining similar pressure ratio and efficiency characteristics of the impeller. The improvement of operating range obtained with the leading edge forward sweep and splitter aft sweep was caused by a reduction of the interaction of the tip vortex of the main blade with the splitter tip, and a reduction of the blockage caused by this interaction.
Robust Adjoint-Based Shape Optimization of Supersonic Turbomachinery Cascades
Authors: Pini M. , Persico G. , Dossena V.
Published: September 2014

An adjoint-based shape optimization approach for supersonic turbine cascade is proposed. The algorithm is based on a discrete adjoint method, state-of-the-art parametrization techniques (NURBS) and a preconditioned steepest descent optimizer to search the optimal point. The potential of the optimization approach is verified on two different design problems. Initially the design methodology is applied to the re-design of an existing supersonic turbine cascade operating at nominal conditions, with the aim of obtaining a more uniform flow at blade outlet section. Then, an original extension of the algorithm for treating off-design conditions is envisaged. The method combines a standard multi-point optimization technique with an uncertainty quantification algorithm to assess the design points and the weights of the multi-point problem. The capability of the novel approach in providing robust designs is finally investigated by maximizing the performances of the same baseline configuration working under a relatively wide range of operating conditions. In both tests remarkable outcomes are achieved in terms of improvement of blade performances and computational efficiency.
Operational Improvements for Start-Up Time Reduction in Solar Steam Turbines
Authors: Topel Monika , Genrup Magnus , Jöcker Markus , Spelling James , Laumert Björn
Published: September 2014

Solar steam turbines are subject to high thermal stresses as a result of temperature gradients during transient operation, which occurs more frequently due to the variability of the solar resource. In order to increase the flexibility of the turbines while preserving lifing requirements, several operational modifications for maintaining turbine temperatures during offline periods are proposed and investigated. The modifications were implemented in a dynamic thermal turbine model and the potential improvements were quantified. The modifications studied included: increasing the gland steam pressure injected to the end-seals, increasing the back pressure and increasing the barring speed. These last two take advantage of the ventilation and friction work. The effects of the modifications were studied both individually as well as in different combinations. The temperatures obtained when applying the combined modifications were compared to regular turbine cool-down temperatures and showed significant improvements on the start-up times of the turbine.
Simulation of the Ignition Process in an Annular Multiple-Injector Combustor and Comparison With Experiments
Authors: Philip Maxime , Boileau Matthieu , Vicquelin Ronan , Schmitt Thomas , Durox Daniel , Bourgouin Jean-François , Candel Sébastien
Published: September 2014

Ignition is a problem of fundamental interest with critical practical implications. While there are many studies of ignition of single injector configurations, the transient ignition of a full annular combustor has not been extensively investigated, mainly because of the added geometrical complexity. The present investigation combines simulations and experiments on a complete annular combustor. The setup, developed at EM2C laboratory, features sixteen swirl injectors and quartz walls allowing direct visualization of the flame. High speed imaging is used to record the space time flame structure and study the dynamics of the light-round process. On the numerical side, massively parallel computations are carried out in the LES framework using the Filtered Tabulated (F-TACLES) flamelet model. Comparisons are carried out at different instants during the light-round process between experimental data and results of calculations. It is found that the simulation results are in remarkable agreement with experiments provided that the thermal effects at the walls are considered. Further post-processings indicate that the flame burning velocity and flame front geometry are close to those found in the experiment. This analysis confirms that the LES framework used for these calculations and the selected combustion model are adequate for such calculations but that further work is needed to confirm that ignition prediction can be used reliably over a range of operating parameters.
Investigation of Unsteady Flow Field in a Low-Speed One and a Half Stage Axial Compressor: Effects of Tip Gap Size on the Tip Clearance Flow Structure at Near Stall Operation
Authors: Hah Chunill , Hathaway Michael , Katz Joseph
Published: September 2014

The primary focus of this paper is to investigate the effect of rotor tip gap size on how the rotor unsteady tip clearance flow structure changes in a low speed one and half stage axial compressor at near stall operation (for example, where maximum pressure rise is obtained). A Large Eddy Simulation (LES) is applied to calculate the unsteady flow field at this flow condition with both a small and a large tip gaps. The numerically obtained flow fields at the small clearance matches fairly well with the available initial measurements obtained at the Johns Hopkins University with 3-D unsteady PIV in an index-matched test facility which renders the compressor blades and casing optically transparent. With this setup, the unsteady velocity field in the entire flow domain, including the flow inside the tip gap, can be measured. The numerical results are also compared with previously published measurements in a low speed single stage compressor (Maerz et al. [2002]). The current study shows that, with the smaller rotor tip gap, the tip clearance vortex moves to the leading edge plane at near stall operating condition, creating a nearly circumferentially aligned vortex that persists around the entire rotor. On the other hand, with a large tip gap, the clearance vortex stays inside the blade passage at near stall operation.

With the large tip gap, flow instability and related large pressure fluctuation at the leading edge are observed in this one and a half stage compressor. Detailed examination of the unsteady flow structure in this compressor stage reveals that the flow instability is due to shed vortices near the leading edge, and not due to a three-dimensional separation vortex originating from the suction side of the blade, which is commonly referred to during a spike-type stall inception. The entire tip clearance flow is highly unsteady. Many vortex structures in the tip clearance flow, including the sheet vortex system near the casing, interact with each other. The core tip clearance vortex, which is formed with the rotor tip gap flows near the leading edge, is also highly unsteady or intermittent due to pressure oscillations near the leading edge and varies from passage to passage. For the current compressor stage, the evidence does not seem to support that a classical vortex breakup occurs in any organized way, even with the large tip gap. Although wakes from the IGV influence the tip clearance flow in the rotor, the major characteristics of rotor tip clearance flows in isolated or single stage rotors are observed in this one and a half stage axial compressor.
A High-Resolution, Continuous-Scan Acoustic Measurement Method for Turbofan Engine Applications
Authors: Shah Parthiv N. , Vold Håvard , Hensley Dan , Envia Edmane , Stephens David
Published: September 2014

Detailed mapping of the sound field produced by a modern turbofan engine, with its multitude of overlapping noise sources, often requires a large number of microphones to properly resolve the directivity patterns of the constituent tonal and broadband components. This is especially true at high frequencies where the acoustic wavelength is short, or when shielding, scattering, and reflection of the sound field may be present due to installation effects. This paper presents a novel method for measuring the harmonic and broadband content of complex noncompact noise sources using continuously moving (referred to here as continuous-scan) microphones in conjunction with a state-of-the-art phase-referencing technique. Because the microphones are moving through the sound field produced by the noise sources, they effectively provide infinite spatial resolution of the sound directivity over the scan path. In this method, harmonic (i.e., shaft-coherent) content at the integer multiples of the instantaneous shaft rotational frequency is first extracted from the time signal using a tachometer signal and the Vold-Kalman filter. The residual broadband signal is then filtered in the time domain in fractional octave bands. The broadband spectra of the signals from the moving microphones are then computed at arbitrary positions along their scan paths using weighted averages (based on Chebyshev polynomial zero-crossings) and the assumption of a complex envelope that varies slowly over a spatial scale whose lower bound is set by the acoustic wavenumber. A benefit of this method is that the decomposition of the total measured sound field into a stochastic superposition of components preserves a meaningful phase definition for each “partial field” associated with a given shaft order. This preservation of phase data enables the forward or backward projection of each of these partial fields using acoustical holography. The benefits of the continuous-scan method are demonstrated using acoustic data acquired for a 22-inch scale-model fan stage run at the NASA Glenn Research Center’s 9-foot by 15-foot wind tunnel. Two key outcomes of the work include (1) significant improvement in the spatial resolution of the measured sound field and (2) reduction in the overall data acquisition time. Additionally, the methods described here lead to new opportunities for noise source diagnostics and visualization.
Experimental Thermal Field Measurements of Film Cooling Above the Suction Surface of a Turbine Vane
Authors: Stewart William R. , Bogard David G.
Published: September 2014

Two-dimensional thermal profiles were experimentally measured downstream of a single row of film cooling holes on both an adiabatic and a matched Biot number model turbine vane. The measurements were taken as a comparison to computational simulations of the same model and flow conditions. Previously, adiabatic and overall effectiveness comparisons have been made between experimental and computational data. To improve computational models of the evolution of a film cooling jet as it propagates downstream, the thermal field above the vane, not just the footprint on the vane surface must be analyzed. This study expands these data to include 2-D thermal fields above the vane at 0, 5 and 10 hole diameters downstream of the film cooling holes. Four blowing ratios were tested, M = 0.28, 0.65, 1.11, and 2.41. In each case the computational jets remained colder than the experimental jets because they did not diffuse into the mainstream as quickly. In addition, the computational results for the higher two blowing ratios exhibited the effects of the kidney vortex commonly studied in film cooling, but the experimental thermal fields were not dominated by this vortex. Finally, in comparing results above adiabatic and matched Biot number models, these thermal fields allow for an accurate analysis of whether or not the adiabatic wall temperature was a reasonable estimate of the driving temperature for heat transfer.
Materials Selection for Variable Geometry Turbine Nozzle for Gasoline Engine Application
Authors: Shettigar Vivek O. , Pesiridis Apostolos
Published: September 2014

Turbocharging is a key technology for reducing emissions in modern automotive internal combustion engines. The application of turbochargers has been regarded as the next step in the downsizing I.C. Engines. The technology has demonstrated its ability to increase the power of small engines by over 30%. This technology had a few drawbacks such as selection of appropriate air-fuel ratio which could either provide better transient response at low load condition or provide increased power at full load condition. In the quest to obtain the benefits of the both conditions, Variable Geometry Turbochargers (VGTs) were introduced. They account for a significant share of the market in mechanical turbocharging for diesel engines. The most common and efficient type of flow control device in use in VGT is the pivoting vane array located at the inlet of the turbocharger. The technology has been effectively applied over the past 20 years in diesel engines due to their relatively lower exhaust gas temperature (compared to gasoline engines) which has allowed inexpensive materials to be used. This isn’t the case for gasoline engines due to their high exhaust gas temperatures. In light of this technical challenge, the current paper discusses the attempts at application of VGTs in gasoline engines and evaluates further material options which can be considered as appropriate candidates for use in the movable nozzle section of a VGT. Exhaust gases temperatures of up to 1050°C with the working pressures reaching in excess of 2 bar is the working environment of a typical VGT. A CFD analysis of appropriately selected materials is presented in this paper and was applied to a generic pivoting vane mechanism, producing results for the stresses and deformations experienced by the selected materials. This paper also includes cost and manufacturability discussion of requirements which will eventually dictate the choice of any given material for mass production. The material is chosen with the help of an in-depth selection processes such as the Paul and Beitz method which includes weighing factors and performance indices. Performance indices can be considered as groups of material properties which represent few important aspect of the performance of the component.
Performance Improvement of Gas Turbine With Compressed Air Injection for Low Density Operational Conditions
Authors: Arias Quintero S. , Auerbach S. , Kraft R.
Published: September 2014

Gas Turbines are an important contributor to the world’s power generation at base and peak load conditions, and this participation is expected to last for the decades to come, even with the increasing use of renewable energies given their unique ability to supply large amounts of power in a short period of time (unlike coal or nuclear plants). On the other hand, the power produced by gas turbines is significantly reduced at higher ambient temperatures, which coincides with the peak power demand. Air density is reduced, either as consequence of high elevation above the sea level, or due to higher ambient temperatures, and the air mass flow passing into a gas turbine diminishes consequently. With this flow down, the fuel flow is reduced proportionately in order to maintain combustion temperature, reducing, in turn the power generation. This paper presents a parametric evaluation of a novel power enhancement scheme: intercooled compressed air injection, with performance simulations of a “F” class industrial gas turbine in a 1×1 combined cycle application made with Thermoflow GTPro and GTMaster ® software. Results show that compressed air injection achieves significant levels of power boost at heat rates better than those of simple cycle power plants, resulting in an attractive option for power-starved utilities during summer days.
Automatic Three Dimensional Grid Generation in Turbo Machine Blade Passages
Authors: Zagitov R. A. , Dushko A. N. , Shmotin Yu. N.
Published: September 2014

Generation of the grid for blade passages with packaging using universal grid generators usually takes much time. The paper is devoted to grid generation in turbo machine blade passages with packaging in automatic mode. The main requirement to the approach is to obtain the grid with minimum engineer participant. In the developed procedure engineer must specify only general input data: number of nodes, cell size near solid bodies and geometrical data.

Multiblock structured grids are considered. All grid blocks have node-to-node attachment between each other; periodicity is also specified from node to node. The grid in blade passage consists of two blocks: “O” grid around blade and “H” grid in blade passage. Additional blocks are used to describe different ZR-effects such us tip clearances, leakage seals and bleed air systems.

A variational method of constructing three dimensional grids composed of hexahedral cells is applied. The combination of the energy density functional and cell size functional is used. The first functional lets us control the shapes and the second functional lets us control the sizes of grid cells. Grid untangling procedure is also developed.

Developed approach was tested using the blades of axial and centrifugal compressors and axial turbines. Results of grid generation are presented.
Actuation Studies for Active Control of Mild Combustion for Gas Turbine Application
Authors: Varea Emilien , Kruse Stephan , Pitsch Heinz , Albin Thivaharan , Abel Dirk
Published: September 2014

MILD combustion (Moderate or Intense Low Oxygen Dilution) is a well known technique that can substantially reduce high temperature regions in burners and thereby reduce thermal NOx emissions. This technology has been successfully applied to conventional furnace systems and seems to be an auspicious concept for reducing NOx and CO emissions in stationary gas turbines. To achieve a flameless combustion regime, fast mixing of recirculated burnt gases with fresh air and fuel in the combustion chamber is needed. In the present study, the combustor concept is based on the reverse flow configuration with two concentrically arranged nozzles for fuel and air injections. The present work deals with the active control of MILD combustion for gas turbine applications. For this purpose, a new concept of air flow rate pulsation is introduced. The pulsating unit offers the possibility to vary the inlet pressure conditions with a high degree of freedom: amplitude, frequency and waveform. The influence of air flow pulsation on MILD combustion is analyzed in terms of NOx and CO emissions. Results under atmospheric pressure show a drastic decrease of NOx emissions, up to 55%, when the pulsating unit is active. CO emissions are maintained at a very low level so that flame extinction is not observed. To get more insights into the effects of pulsation on combustion characteristics, velocity fields in cold flow conditions are investigated. Results show a large radial transfer of flow when pulsation is activated, hence enhancing the mixing process. The flame behavior is analyzed by using OH* chemiluminescence. Images show a larger distributed reaction region over the combustion chamber for pulsation conditions, confirming the hypothesis of a better mixing between fresh and burnt gases.
Dynamic Response of a Metal and a CMC Turbine Blade During a Controlled Rub Event Using a Segmented Shroud
Authors: Langenbrunner Nisrene , Weaver Matt , Dunn Michael G. , Padova Corso , Barton Jeffery
Published: September 2014

Ceramic Matrix Composites, CMCs, provide several benefits over metal blades including weight and increased temperature capability, and have the potential for increased engine performance by reduction of the cooling flow bled from the compressor and by allowing engines to run at higher turbine inlet temperatures. These CMC blades must be capable of surviving fatigue (high cycle and low cycle), creep, impact, and any tip rub events due to the engine missions or maneuvers that temporarily close blade tip/shroud clearances.

As part of a co-operative research program between GE Aviation and the Ohio State University Gas Turbine Laboratory, OSU GTL, the response of a CMC stage 1 low-pressure turbine blade has been compared with the response of an equivalent metal turbine blade using the OSU GTL large spin-pit facility (LSPF) as the test vehicle. Load cells mounted on the casing wall, strain gages mounted on the airfoils, and other instrumentation are used to assess blade tip rub interactions with a 120-degree sector of a representative turbine stationary casing. The intent of this paper is to present the dynamic response of both the CMC and the metal blades with the turbine disk operating at design speed and with representative incursion rates and depths. Casing wear and blade tip wear are both characterized for several types of rub conditions including a light, medium, and heavy rub at room temperature. For each condition, the rub primary dynamic modes have been evaluated, and the corresponding blade tip loads have been calculated. The preliminary results suggest that a CMC blade has similar abilities to a metal blade during a rub event.
Steady VGJ Flow Control on a Highly Loaded Transonic LPT Cascade: Effects of Compressibility and Roughness
Authors: Bernardini Chiara , Benton Stuart I. , Lee John D. , Bons Jeffrey P. , Chen Jen-Ping , Martelli Francesco
Published: September 2014

A new high-speed linear cascade has been developed for low-pressure turbine (LPT) studies at The Ohio State University. A compressible LPT profile is tested in the facility and its baseline performance at different operating conditions is assessed by means of isentropic Mach number distribution and wake total pressure losses. Active flow control is implemented through a spanwise row of vortex-generator jets (VGJs) located at 60% chord on the suction surface. The purpose of the study is to document the effectiveness of VGJ flow control in high-speed compressible flow. The effect on shock-induced separation is assessed by Mach number distribution, wake loss surveys and shadowgraph. Pressure Sensitive Paint is applied to understand the three dimensional flow and shock pattern developing from the interaction of the skewed jets and the main flow. Data show that with increasing blowing ratio the losses are first decreased due to separation reduction, but losses connected to compressibility effects become stronger due to increased passage shock strength and jet orifice choking; therefore the optimum blowing ratio is a tradeoff between these counteracting effects. The effect of added surface roughness on the uncontrolled flow and on flow control behavior is also investigated. At lower Mach number turbulent separation develops on the rough surface and a different flow control performance is observed. Steady VGJs appear to have control authority even on a turbulent separation but higher blowing ratios are required compared to incompressible flow experiments reported elsewhere. Overall, the results show a high sensitivity of steady VGJs control performance and optimum blowing ratio to compressibility and surface roughness.
Time-Resolved PIV Measurements of Non-Reacting Flow Field in a Swirl-Stabilized Combustor Without and With Porous Inserts for Acoustic Control
Authors: Meadows Joseph , Agrawal Ajay K.
Published: September 2014

Combustion noise and thermo-acoustic instabilities are of primary importance in highly critical applications such as rocket propulsion systems, power generation, and jet propulsion engines. Mechanisms for combustion instabilities are extremely complex because they often involve interactions among several different physical phenomena such as unsteady flame propagation leading to unsteady flow field, acoustic wave propagation, natural and forced hydrodynamic instabilities, etc. In the past, we have utilized porous inert media (PIM) to mitigate combustion noise and thermo-acoustic instabilities in both lean premixed (LPM) and lean direct injection (LDI) combustion systems. While these studies demonstrated the efficacy of the PIM concept to mitigate noise and thermo-acoustic instabilities, the actual mechanisms involved have not been understood. The present study utilizes time-resolved particle image velocimetry to measure the turbulent flow field in a non-reacting swirl-stabilized combustor without and with PIM. Although the flow field inside the annulus of the PIM cannot be observed, measurements immediately downstream of the PIM provide insight into the turbulent structures. Results are analyzed using the Proper Orthogonal Decomposition (POD) method and show that the PIM alters the flow field in an advantageous manner by modifying the turbulence structures and eliminating the corner recirculation zones and precessing vortex core, which would ultimately affect the acoustic behavior in a favorable manner.
Identification of Nonlinear Instabilities in Rotors Supported on Gas Bearing
Authors: González Claudia Aide , Jáuregui Juan Carlos , de Santiago Oscar
Published: September 2014

Identifying the parameters that cause gas bearing instabilities is a big challenge. The gas properties are very sensitive to temperature and pressure changes, and, as a consequence the bearing rotor-dynamic coefficients change drastically and the rotor behaves chaotically, which means that the dynamic parameters are nonlinear. In this research a methodology to identify nonlinear instabilities of gas bearings is presented. Estimating variations of the coefficients can be done using wavelets and the phase diagram. Wavelets allow the development of time-frequency maps where the behavior of each of the system frequencies can be analyzed. The time-frequency map displays frequency variations as a function of time. In this way, any change in the rotor dynamic parameter is reflected as variations in its associated frequency. Analyzing these variations it is possible to estimate the nonlinear parameters. With the phase diagram analysis, it is possible to evaluate changes in the dynamic behavior. The phase diagram relates the potential energy and kinetic energy at any time instant. If the system is stable, the phase diagram has a well define pattern that repeats steadily; whereas, if the pattern shows sudden changes in dimensions and shape, it indicates that the system parameters have change. This change may be chaotic.
High Resolution RANS NLH Study of Stage 67 Tip Injection Physics
Authors: Grosvenor Allan D. , Rixon Gregory S. , Sailer Logan M. , Matheson Michael A. , Gutzwiller David P. , Demeulenaere Alain , Gontier Mathieu , Strazisar Anthony J.
Published: September 2014

Numerical prediction of the Stage 67 transonic fan stage employing wall jet tip injection flow control and study of the physical mechanisms leading to stall suppression and stability enhancement afforded by endwall recirculation/injection is the focus of this paper. Reynolds averaged Navier-Stokes computations were used to perform detailed analysis of the Stage 67 configuration experimentally tested at NASA’s Glenn Research Center in 2004. Time varying predictions of the stage plus recirculation and injection flowpath were executed utilizing the Nonlinear Harmonic approach. Significantly higher grid resolution per passage was achieved than what has been generally employed in prior reported numerical studies of spike stall phenomena in transonic compressors. This paper focuses on characterizing the physics of spike stall embryonic stage phenomena and the influence of tip injection, resulting in experimentally and numerically demonstrated stall suppression.