bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation on the Effect of Vortex Generator on Axial Compressor Performance
Authors: Agarwal Ruchika , Dhamarla Anand , Narayanan Sridharan R. , Goswami Shraman N. , Srinivasan Balamurugan
Published: September 2014

The performance of the compressor blade is considerably influenced by secondary flow effects, like the cross flow on the end wall as well as corner flow separation between the wall and the blade. The present work is focused on the studying the effects of Vortex Generator (VG) on NASA Rotor 37 test case using Computational Fluid Dynamics (CFD). VG helps in controlling the inception of the stall by generating vortices and energizes the low momentum boundary layer flow which enhances the rotor performance. Three design configuration namely, Counter-rotating, Co-rotating and Plow configuration VG are selected based on the improved aerodynamic performance discussed in reference [1]. These VG are located at 90% span and 42% chord on suction side surface of the blade. Among the three configurations, the first configuration has greater impact on the end wall cross flow and flow deflection which resulted in enhanced numerical stall margin of 5.4% from baseline. The reasons for this numerical stall margin improvement are discussed in detail.
Experimental and Numerical Analysis of a Micro Plasma Actuator for Active Flow Control in Turbomachinery
Authors: De Giorgi Maria Grazia , Pescini Elisa , Marra Fedele , Ficarella Antonio
Published: September 2014

Nowadays several active flow control systems, particularly dielectric barrier discharge plasma actuators, appear to be effective for the control of flow stream separation and to improve performance of turbomachinery. However these applications require high actuation strength, higher than the one generated by conventional macro plasma actuators. Research is actually improving the design of plasma actuator in order to enhance the flow control capability and reduce the power consumption.

In this contest, this work concerns the implementation of a micro plasma actuator for the active control in a compressor cascade. For this aim, firstly the micro actuator was developed and an experimental characterization of the flow induced by the device was done. The induced flow field was studied by means of Particle Image Velocimetry and Laser Doppler Velocimetry. The dissipated power was also evaluated. Experimental results were used to validate a multi-physics numerical model for the prediction of the body forces induced by the plasma actuator.

Finally, the obtained body force field was used for modeling the separation control by means of the micro plasma actuator in a highly-loaded subsonic compressor stator.
Aerodynamic Performance of Advanced Axial Flow Fan for Power Industry Within its Operational Range
Authors: Cyrus V. , Cyrus J. , Wurst P. , Panek P.
Published: September 2014

The investigated axial flow fan investigated in our paper consisted of an advanced axial flow stage, an inlet chamber and a diffuser. The fan stage with high aerodynamic loading and the hub/tip ratio of 0.6 had the design flow and pressure coefficients of 0.60 and 0.83, respectively. The test and computed CFD aerodynamic performance of the axial flow fan and the fan’s stage were compared, with acceptable results. Subsequently, analysis of the computed 3D flow was carried out within the wide working range at the rotor blades stagger angle variation of ±20°.Consequence of the rotor blades adjustment is that the blade elements work often at the off-design working conditions with the flow separation on the blades suction and pressure sides. The flow is strictly three-dimensional.

Velocity profile distortion and swirl due to the flow separation in the stator blade row decreases the diffuser pressure recovery and efficiency. The diffuser in the axial flow fan environment achieves a significantly higher efficiency in comparison with conical diffuser furnished with ducted-flow inlet conditions due to the increased turbulent mixing.

Inlet chamber loss coefficient slightly decreased with the increasing flow rates due to the Reynolds number effect. Core flow in the inlet chamber is without occurrence of significant vortex inducing motion with the exception of the area near the tube where the fan’s shaft is located.
A Combined CFD/MRV Study of Flow Through a Pin Bank
Authors: Siekman Mike , Helmer David , Hwang Wontae , Laskowski Gregory , Tan Ek Tsoon , Natsui Gregory
Published: September 2014

RANS and time averaged URANS simulations of a pin bank are compared quantitatively and qualitatively to full 3D mean velocity field data obtained using magnetic resonance velocimetry (MRV). The ability of the CFD to match MRV velocity profiles through the pin bank is evaluated using the SST turbulence model. Quantitative comparisons of the velocity profiles showed an overprediction of peak velocity by the CFD at the first pin rows, and a smaller oscillatory error that diminishes as it moves through the pins, resulting in better matching towards the exit.
Alstom Gas Turbine Technology Overview/Status 2013
Authors: Kappis W. , Florjancic S. , Marchmont C. , Freitag E.
Published: September 2014

Market requirements for the gas turbine business have significantly changed in the last years due to a stronger demand for lifecycle cost optimization and the increased share of renewable energy. Gas turbine technology development focus must be adapted accordingly. The need for increased efficiency throughout the operation range, particularly at part load, requires more accurate and faster design methods and prediction capabilities. At the same time, technologies must be developed and validated to increased flexibility in many areas, including unlimited operation range (without aerodynamic, mechanical or emission constraints), fuel types and composition, and faster ramp up rates (despite the increased thermal stress to gas turbine components) to stabilize the grid and to compensate for intermittent renewable power generation. Further lifecycle optimization counts on new technologies in reconditioning, lifetime monitoring and improved lifetime prediction.

This paper provides an overview of the recent research and development activities, the approach to bring them into a product and the resulting trend in Alstom gas turbine technologies.
Combined Heat and Power Plants Based on Mirror Heat Exchange Brayton Cycles
Authors: Passarella Andrea , Arnulfi Gianmario L.
Published: September 2014

As gas turbine exhaust gases leave the turbine at high temperature, heat recovery is often carried out in a combined heat-and-power system or in the steam section of a combined-cycle plant. An interesting alternative is a mirror cycle, which involves coupling together a direct Brayton top cycle and an inverted Brayton bottom cycle; this results in significantly higher power output and efficiency, though at the expense of added complexity. The research illustrated in the present paper was based on two in-house codes and aimed to analyze different plant configurations, one of which was a heat recovery (regenerative) top cycle with the heat exchanger hot side located between the top and bottom cycle turbo-expanders. The authors call this configuration a distorting mirror, as the hot side may not be at atmospheric pressure. A parametric analysis was carried out in order to optimize plant performance vs. pressure levels. Simulation showed that, at the design point, very good performance is obtained: efficiency close to 0.50 with plant cost (per megawatt) about half vs. combined-cycle plants. An off-design analysis showed that the mirror plant is a little more sensitive to changes in load than a simple Brayton, single-shaft GT.
A Transonic Mixed Flow Compressor for an Extreme Duty
Authors: Hazby Hamid , Casey Michael , Numakura Ryusuke , Tamaki Hideaki
Published: September 2014

This paper describes the design of a transonic mixed flow compressor stage for an extreme duty, with an extremely high flow coefficient (Φ) of 0.25 and a high isentropic pressure rise coefficient (ψ) of 0.56. The impeller design makes use of modern aerodynamic practice from radial and transonic axial compressors, whereby the aerodynamic blade shape involved arbitrary surfaces on several spanwise sections. Some aspects of the aerodynamic optimization of the design were limited by mechanical considerations, but nevertheless the test data obtained on a prototype stage demonstrates that acceptable performance levels can be achieved at these extreme design conditions, although map width enhancement devices were needed to obtain an acceptable operating range. The test data is compared with CFD predictions to demonstrate the validity of the design methods used.
Parametrical Diagnostics of Gas Turbine Performance on Site at Gas Pumping Plants Based on Standard Measurements
Authors: Komarov Oleg V. , Sedunin Viacheslav A. , Blinov Vitaly L. , Skorochodov Alexander V.
Published: September 2014

The operation and maintenance of gas pumping units at the Gazprom transport systems are carried according to the current number of equivalent working hours of the gas turbine and the centrifugal natural gas compressor. Modern concepts of lean production requires maintenance procedures are to be done according to the current technical operating performance of units and its parametrical diagnostics. To meet these requirements an appropriate research project is ongoing at Ural Federal University. In this article a methodology for the technical performance estimation of GTU’s is proposed, verified and discussed. The method is based on processing of data gathered from standard thermodynamic measurements and therefore is applicable in the frame of most gas turbine units without major modifications.

The method includes a verified high-order mathematical model based on the Gas dynamic function for the precise analytical description of turbomachinery aerodynamics. A correction factor is introduced for adjusting the mathematical model in case of a non-traditional (not optimised) design applied in the exact turbine design.

Models are defined for different types of multi-shaft GT’s and an automated algorithm for calculation of the coefficients of technical performance of the overall unit is provided. A series of experiments showed convergence between traditional and new methods in effective power output and efficiency of units does not exceed 2%. Special software is designed for online monitoring of technical performance.
Heat Transfer Enhancement due to Coolant Extraction on the Cold Side of Effusion Cooling Plates
Authors: Da Soghe R. , Andreini A. , Facchini B. , Mazzei L.
Published: September 2014

Effusion cooling represents one the most innovative technique to limit and control the metal temperature of aero-engine combustors liner and, recently, attention has been paid by the scientific community on the characterization and the definition of design practices of such devices. Most of these studies were focused on the heat transfer on the hot side of effusion cooling plates while just few contributions deal with the effusion plates cold side convective cooling. This paper reports a numerical survey aimed at the characterization of the convective cooling at the effusion plates cold side. Several effusion holes spacing are accounted for in conjunction with representative operating conditions.

The study led to the development of an empirical correlation for the prediction of the cold side heat transfer coefficient enhancement factor EF: it expresses the EF related to each extraction hole as a function of the pressure ratio β and the effusion plate porosity factor.
Experimental Performance of an Open Ends, Centrally Grooved, Squeeze Film Damper Operating With Large Amplitude Orbital Motions
Authors: San Andrés Luis , Jeung Sung-Hwa , Bradley Gary
Published: September 2014

Aircraft engines customarily implement Squeeze Film Dampers (SFDs) to dissipate mechanical energy caused by rotor vibration and to isolate the rotor from its structural frame. The paper presents experimental results for the dynamic forced performance of an open ends SFD operating with large amplitude whirl motions, centered and off-centered. The test rig comprises of an elastically supported bearing with a damper section, 127 mm in diameter, having two parallel film lands separated by a central groove. Each film land is 25.4 mm long with radial clearance c = 0.251 mm. The central groove, 12.7 mm long, has a depth of 9.5 mm (38c). An ISO VG 2 lubricant flows into the groove via three 2.5 mm orifices, 120 degrees apart, and then passes through the film lands to exit at ambient condition. Two orthogonally placed shakers apply dynamic loads on the bearing to induce circular orbit motions with whirl frequency ranging from 10 Hz to 100 Hz. A static loader, 45° away from each shaker, pulls the bearing to a static eccentricity (es). Measurements of dynamic loads and the ensuing bearing displacements and accelerations, as well as the film and groove dynamic pressures, were obtained for eight orbit amplitudes (r = 0.08c to ∼0.71c) and under four static eccentricities (es = 0.0c to ∼0.76c). The experimental damping coefficients increase quickly as the bearing offset increases (es/c→0.76) while remaining impervious to the amplitude of whirl orbit (r/c→0.51). The inertia coefficients decrease rapidly as the orbit amplitude grows large, r>0.51c, but increase with the static eccentricity. A comparison with test results obtained with an identical damper but having a smaller clearance (cs = 0.141 mm) [1], show the prior damping and inertia coefficients are larger, ∼5.0 and ∼2.2 times larger than the current ones. These magnitudes agree modestly with theoretical ratios for damping and inertia coefficients scaling as (c/cs)3 = 5.7 and (c/cs) = 1.8, respectively. In spite of the large difference in depths between a groove and a film land, the magnitudes of dynamic pressures recorded at the groove are similar to those in the lands. That is, the groove profoundly affects the dynamic forced response of the test damper. A computational physics model replicates the experimental whirl motions and predicts force coefficients spanning the same range of whirl frequencies, orbit radii and static eccentricities. The model predictions reproduce with great fidelity the experimental force coefficients. The good agreement relies on the specification of an effective groove depth derived from one experiment.
Influence of Boss-Tip Radius Ratio of Impeller on Aerodynamic Performance of a Multistage Centrifugal Compressor
Authors: Nishioka Takahiro , Kobayashi Hiromi , Nakajima Shigeo , Nishida Hideo , Enomoto Hiroki
Published: September 2014

The influence of the boss-tip radius ratio of the impeller on the aerodynamic performance of a multistage centrifugal compressor were numerically and experimentally investigated. Three impellers, which boss-tip radius ratios were 0.28, 0.34, and 0.40, were developed for a design suction flow coefficient of 0.125. The inlet radius at the shroud of each impeller was designed to provide the minimum inlet relative velocity, and the exit width was also designed to keep the inlet to exit relative velocity ratio. The numerical and experimental results suggested that the impeller pressure-rise decreased as the boss-tip radius ratio increased. The decrease of the impeller efficiency due to the increase of the boss-tip radius ratio could be minimized by minimizing the inlet relative velocity at the shroud side and by keeping the inlet to exit relative velocity ratio constant in the tested cases. The ribbed diffuser seemed to be useful to improve the performance of compressor stage with the high boss-tip radius ratio impeller, although further investigations will be needed to clarify the change in the flow fields and the loss generation mechanism in the ribbed diffuser with the high boss-tip radius ratio impeller.
Future Use of Large Eddy Simulation in Aeroengines
Authors: Tyacke James , Tucker Paul
Published: September 2014

Computational fluid dynamics (CFD) has become a critical tool in the design of aeroengines. Increasing demand for higher efficiency, performance and reduced emissions of noise and pollutants has focused attention on secondary flows, small scale internal flows and flow interactions. In conjunction with low order correlations and experimental data, RANS (Reynolds-Averaged Navier-Stokes) modelling has been used effectively for some time, particularly at high Reynolds numbers and at design conditions. However, the range of flows throughout an engine is vast, with most, in reality being inherently unsteady. There are many cases where RANS can perform poorly, particularly in zones characterised by strong streamline curvature, separation, transition, relaminarisation and heat transfer. The reliable use of RANS has also been limited by its strong dependence on turbulence model choice and related ad-hoc corrections. For complex flows, Large-Eddy Simulation (LES) methods provide reliable solutions, largely independent of turbulence model choice and at a relatively low cost for particular flows. LES can now be used to provide in depth knowledge of flow physics, for example in areas such as transition and real wall roughness effects. This can be used to inform RANS and lower order modelling. For some flows, LES can now even be used for design. Existing literature is used to show the potential of LES for a range of flows in different zones of the engine. Based on flow taxonomy, best practices including meshing requirements and turbulent inflow conditions are introduced, leading to the proposal of a tentative expert system for industrial use. In this way, LES becomes a well controlled tool, suitable for design use and reduces the burden on the end user. Further attention is also given to how LES can be used currently and in the future.
On the Prediction and Theory of the Temperature Increase of Low Pressure Last Stage Moving Blades During Low Volume Flow Conditions, and Limiting it Through Steam Extraction Methods
Authors: Beevers Adam , Havakechian Said , Megerle Benjamin
Published: September 2014

During extreme low volume flow conditions, the last stages of a low pressure steam turbine operate in ventilation conditions that can cause a significant temperature increase of critical regions of the last stage moving blade. Under some conditions, the blade temperature may rise above a safe operating temperature, requiring the machine to be shut down. Limiting the heating effect on the last stage moving blade increases the allowable operating range of the low pressure turbine. One common method is to spray water droplets into the low pressure exhaust. As the length of last stage moving blades continues to increase, this method reaches its limit of practical operating effectiveness due to the amount of water required and its impact on the erosion of the LSB.

An investigation into complimentary solutions to limit the temperature increase was conducted using CFD. An appropriate CFD setup was chosen from a sensitivity study on the effect of geometry, mesh density, turbulence model and time dependency. The CFD results were verified against steam turbine data from a test facility. The proposed complimentary solutions to limit the temperature increase include low temperature steam extraction, targeted for critical regions of the moving blade. From the test turbine and CFD results, the drivers of the temperature increase during ventilation conditions are identified and described.
Numerical Investigation on the Heat Transfer Enhancement due to Coolant Extraction on the Cold Side of Film Cooling Holes
Authors: Andreini A. , Caciolli G. , Da Soghe R. , Facchini B. , Mazzei L.
Published: September 2014

Film cooling represents one the most widely-used cooling techniques for hot gas path components. In particular, effusion cooling has recently become an important focus of attention in the context of aero-engine design due to its high cooling performance. Notwithstanding the huge amount of work dedicated to the heat transfer on the hot side of effusion cooling plates, it has been demonstrated that up to 30 % of the total cooling effectiveness of a typical effusion cooling configuration can be ascribed to cold side convective cooling. Nevertheless, in open literature it is possible to notice a lack of knowledge as far as this topic is concerned.

This paper describes a numerical activity aimed at investigating the phenomenology of the heat transfer at the entrance of film cooling holes. First of all the accuracy of the numerical approach has been validated through a comparison of enhancement factor measurements on a test case available in literature. Steady state RANS simulations have been performed, modeling turbulence by means of the k–ω SST model. The use of a transition model has been taken into account, since in these configurations the transitional behavior of the boundary layer has been highlighted in literature. Subsequently, the attention has been turned to the comprehension of the phenomena involved in the heat transfer augmentation, focusing the attention to the influence of fluid dynamic parameters such as suction ratio and Reynolds number. A good agreement has been highlighted with experimental data, therefore this work provides a starting point for future investigations on more representative configurations.
Experimental Study of Ingestion in the Rotor-Stator Disk Cavity of a Subscale Axial Turbine Stage
Authors: Balasubramanian J. , Pathak P. S. , Thiagarajan J. K. , Singh P. , Roy R. P. , Mirzamoghadam A. V.
Published: September 2014

While it is widely recognized that ingestion of hot gas from the main annulus of axial gas turbine stages into rotor-stator disk cavities depend strongly on the unsteadiness of the prevailing flow field, the large computational effort needed to simulate the flow field renders its use in the design of turbine internal air system and seals difficult. As an alternative, considerable effort has been devoted in recent years to develop simple orifice models of disk cavity rim seals based on time-averaged flow information; these models contain empirical discharge coefficients for ingestion into and egress from the cavities. The present experimental work in a subscale axial turbine stage reports a simple orifice model of an axially-overlapping radial-clearance seal at the disk cavity rim and values of the discharge coefficients over a range of purge flow rate supplied to the cavity. In the experiments, the ingestion process was dominated by the main gas annulus flow. Time-averaged static pressure distribution was measured in the main annulus and in the disk cavity; the driving force for ingestion and egress was taken to be the pressure differential between the main annulus and the rim cavity at prescribed locations. Time-averaged ingestion was measured using the tracer gas technique; the pressure and ingestion data were combined to obtain the ingestion and egress discharge coefficients at several purge flow rates. The location on the vane platform 1mm upstream of its lip represented the main gas annulus pressure in the calculation of discharge coefficients. In the rim cavity, two locations on the stator, one in the ‘seal region’ and the other slightly inward radially, were prescribed to represent the rim cavity pressure as well as the sealing effectiveness. Two corresponding sets of ingestion and egress discharge coefficients are reported for the various purge flow rates. The ingestion discharge coefficient obtained using the seal region location in the rim cavity decreased as the purge flow rate increased; the corresponding egress discharge coefficient increased with purge flow rate. For the rim cavity location slightly inward radially from the seal region, the egress discharge coefficient maintained the same trend; however, the ingestion discharge coefficient decreased only slightly as the purge flow rate increased. It is suggested that the seal region location in the rim cavity is the more appropriate location in calculating the rim seal discharge coefficients. The ratio of ingestion to egress discharge coefficients exhibited considerable variation with purge flow rate.
Numerical Investigation of the Prestall Behavior in a Transonic Axial Fan Rotor
Authors: Ju Pengfei , Ning Fangfei
Published: September 2014

In this paper we describe a kind of unsteady phenomena in a transonic axial fan rotor at stable operating points based on the observation from numerical simulation results. Single-passage and full-annulus time-accurate simulations were implemented for several different operating points, when the unsteadiness phenomena occurred. Thanks to the recently introduced GPU acceleration technology, all these time-consuming computations were executed on a desktop computer. As is shown in frequency-domain analysis results, the frequency-domain behaviors of the calculated flow field at different operating points are different in single-passage and full-annulus results, which means that the single-passage simulation may lead to incorrect conclusions when simulating unsteady flow field near stall. It can be observed from flow fields that flow parameters in different passages are at different phases at the same moment. Spillage flows periodically appear in front of the blade leading edges at the tip region and no separation is observed at the blade leading edge in this process. The spillage flow is closely linked with a vortex structure, which is shed from the tip leakage vortex at the leading edge region. The circumferential movement of the vortex delivers a mechanism of propagation for the spillage status. Although the spillage occurs at some instants, these operating conditions are still stable because the leading edge region is occupied by the incoming main flow at other instants when the flow at this region is improved.
Impact of Swirl Flow on the Penetration Behaviour and Cooling Performance of a Starter Cooling Film in Modern Lean Operating Combustion Chambers
Authors: Wurm B. , Schulz A. , Bauer H.-J. , Gerendas M.
Published: September 2014

An experimental and numerical study is presented that deals with the impact of the swirled hot gas main flow on the penetration behaviour and cooling performance of a starter cooling film.

Within modern combustion chambers designed for lean combustion the whole fuel/air mixing process is done by the fuel injectors without any additional mixing ports. Typically swirl stabilization is used within this kind of combustion chambers. The swirl flow interacts in a particular way with near wall cooling flows like starter cooling films which assure a proper wall cooling near the fuel injector. Experiments without combustion show the impact of the swirled main flow on the stability of the starter cooling film. Thermal analyses reveal a reduced cooling performance of the starter film near the stagnation area of the swirl flow. Laser optical measurement techniques reveal a significant reduced penetration of the starter cooling film close to the stagnation area. Numerical simulations show the reason for the reduced starter film performance in areas which cannot be accessed by optical measurement techniques. Based on experimental and numerical data different adaptive hole geometries where tested in combination with heat shield ribs in order to improve the starter film cooling performance. Results show that the combined application of heat shield ribs and adaptive cooling holes stabilize the starter cooling film and lead to a homogenous cooling performance.
Performance Analysis of Deteriorated High Pressure Compressor Blades
Authors: Reitz Gerald , Friedrichs Jens , Marx Jonas , Städing Jörn
Published: September 2014

During the operation of a jet engine, deterioration will constantly reduce its performance. This results in an increase in specific fuel consumption (SFC) and exhaust gas temperature (EGT); the main characteristics to describe the efficiency of a jet engine. Thereby, the high pressure compressor (HPC) is particularly affected by deterioration. Multiple effects take place and decrease the efficiency of the HPC. Erosion is one of the main effects and leads to thinner or thicker leading- and trailing edges, thinner airfoils, a reduction of chord length and an increase in tip clearance. In addition, erosion and fouling may also lead to increased surface roughness on airfoils and endwalls. An additional parameter which is also dependent on the on-wing time are changes in the stagger angle of the different blade heights. The objective is to estimate the quantitative effect of the different wear mechanisms on the stage parameters, like throttle line and efficiency. Therefore, a geometry setup process is implemented to create HPC blade models with independent values of erosion. With these blades, CFD calculations based on realistic boundary conditions were carried out with the CFD solver ANSYS CFX. It could be proven that the deterioration of leading edge thickness has the major influence on stage performance, followed by the max. profile thickness and the stagger angle. The operational blade deterioration of leading edge thickness leads to an efficiency range of about 0.173 %. Moreover, the deterioration of stagger angle leads to an offset of the throttle lines towards higher or smaller loadings, depending on the direction of change.
Bi-Stable Flame Behaviour of Heavy Duty Gas Turbine Burner
Authors: Rofi Luca , Anisimov Vyacheslav , Chiarioni Aldo , Ozzano Claudia , Daccà Federico
Published: September 2014

VeLoNOx™ (Very Low NOx) burners have been developed by Ansaldo Energia to satisfy the most restrictive emission limits of many countries. The stability field range is a key element for the design of such combustion systems; ever-deeper knowledge is therefore essential. The impact on stability of flame transition is of paramount relevance. Usually, flame transition occurs during load ramp: two different flame shapes take place in a well-defined load range. When loading up to base load condition, stability requires proper choice of flame shape. Observation of flame transition in a full-scale pressure test-rig implies a) unambiguous observation of an alteration in the flame shape b) measurement of both the burner area discharge coefficient “Alfa” (on the air side) and of a temperature drop on the walls of the combustion chamber.

The aim of the present work was to verify that RANS simulations with particular setting of the physical models can provide us with realistic description of the global flame behaviour in the full-scale, pressurised test rig even during the crucial flame transition at partial base load. This aim was achieved. CFD RANS has led to two different solutions with different shape, just like in the experiment. The main global parameters of the combustion system undergo similar changes and with similar magnitude in CFD results and in the experiment. In particular, the burner discharge coefficient “Alfa” increases with flame transition from “open” to “closed” flame, while the combustion chamber wall temperature decreases with flame transition from “open” to “closed” flame. It means that this CFD RANS simulation provides us with a reliable flow and temperature fields which can be used as meaningful input data for the more detailed analysis of both thermal load at combustion chamber wall and CO and NOx emission level, thermo-acoustic behaviour of the combustion system by means of more specific tools. Such information could be useful when designing more efficient, less polluting combustion systems.
Interaction of Flame Flashback Mechanisms in Premixed Hydrogen-Air Swirl Flames
Authors: Sattelmayer Thomas , Mayer Christoph , Sangl Janine
Published: September 2014

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen-air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed PIV/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approx. 1/3 of the typical flow velocities in gas turbine burners. In that range the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approx. 0.45 and delivers NOx-emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.
Combustion Analysis in a Micro-Gas Turbine Supplied With Bio-Fuels
Authors: Cameretti Maria Cristina , Tuccillo Raffaele
Published: September 2014

The authors examine in this paper the response of a micro gas turbine (MGT) combustor when supplied with gaseous fuels from biomass treatment or solid waste pyrolysis. Actually, a sort of off-design operation is induced by the employment of low calorific value fuels both in the combustor and in the whole micro turbine system. The objective is to optimize the combustor behaviour under the point of view of combustion efficiency and pollutant control.

To this aim, several solutions are experienced for a combustor fuelled with low LHV gaseous fuels derived from biomasses or solid waste treatment. An external EGR option is also considered as activated. The combustion development is analyzed by a combined approach based on the partially stirred reactor hypothesis and on the flamelet concept within a CFD simulation workbench.
Extension of an Unsteady Hybrid Navier-Stokes/Vortex-Panel Solver to Wind Turbine Aerodynamic Simulations at Higher Yaw Angles
Authors: Suzuki Kensuke , Schmitz Sven , Ouyang Hua , Chattot Jean-Jacques
Published: September 2014

A new analysis tool, an unsteady Hybrid Navier-Stokes/Vortex model, for a horizontal axis wind turbine (HAWT) has been developed for yawed flow by coupling a prescribed wake Vortex Line Method (VLM) with an unsteady Navier-Stokes solver, and its convergence and computational cost have been studied for 10 and 20 degrees of yaw. In this study, a steady viscous solution of a hybrid method is compared in detail with a full-scale Navier-Stokes simulation as a validation. Furthermore, the unsteady hybrid solver is applied to the NREL Unsteady Aerodynamics Experiment (UAE) Phase VI rotor. A test case under 10 degrees of yaw shows that the global power output agrees well with the NREL experiment, and 10 cycles of computation require less than three days using a work station under a serial CPU simulation. The same simulation performed using a super computer is used as reference, and it is estimated that the equivalent case can be obtained about 8 times faster using the work station with the present method, while keeping the same level of accuracy, than a full-domain Navier-Stokes simulation. To treat high yaw cases, new distorted prescribed vortex sheets are modeled with the VLM code. To see the difference between the base helix and the distorted helicoidal wake, unsteady hybrid VLM/Navier-Stokes solutions are examined for selected azimuth angles, and results are contrasted to a free wake BEM and NREL experimental data. For low yaw angles, the base helix approximation agrees well with the distorted helix, and yield better prediction than a free wake model, whereas for high yaw angles of more than 30 degrees, the present distorted wake gave a lower estimation of rotor torque than the free wake solver.
Experimental Investigation of Nozzle Vane Clocking in a 2-Stage Low Pressure Turbine
Authors: Kang Jeong-Seek
Published: September 2014

This study presents an experimental investigation on the effects of nozzle clocking in a 2-stage low pressure turbine. The objective was to incorporate the clocking test results into a new turboshaft engine. The test turbine was manufactured with the same aero geometries between the transition duct of the turbine inlet and the exit expansion duct as that of the development engine and it was tested under the same engine representative conditions. Two miniature Cobra probes were used to measure the turbine inlet and exit flow, both circumferentially for 30° and radially over the range of 2% ∼ 98% span. Furthermore, six arc-type rakes with 54 Kiel heads were used to measure the total temperature and total pressure at the exit of the second stage. The measurements were performed for four different nozzle clocking positions. The overall efficiency was evaluated in three different ways, including mechanical and thermodynamic methods. All three methods produced identical clocking positions, in order from the best position to the worst. The overall change in the mechanical and thermodynamic efficiency as measured by probe traverse, as well as the thermodynamic efficiency measured by the rakes, were 0.69%, 0.77%, and 0.42%, respectively. The distribution of efficiency across the span showed that clocking affects the efficiency differently in radial positions and a phase shift of the best clocking position to the next adjacent clocking position was observed. The efficiency change due to clocking was found to be related to the deviations in both the time-averaged velocity and in the total pressure at the exit of the second rotor. This deviation is a result of the relative location of the wake package originating from the first nozzle with respect to the leading edge of the second nozzle.
A Combined Experimental and Numerical Study of the Turbine Blade Tip Film Cooling Effectiveness Under Rotation Condition
Authors: Rezasoltani M. , Lu K. , Schobeiri M. T. , Han J. C.
Published: September 2014

Detailed numerical and experimental investigations of film cooling effectiveness were conducted on the blade tips of the first rotor row pertaining to a three-stage research turbine. Four different blade tip ejection configurations were utilized to determine the impact of the hole arrangements on the film cooling effectiveness. plane tip with tip hole cooling, squealer tip with tip hole cooling, plane tip with pressure-side-edge compound angle hole cooling and squealer tip with pressure-side-edge compound angle hole cooling. To avoid rotor imbalance, every pair is installed radially. Film cooling effectiveness measurements were performed for three blowing ratios (M) of 0.75, 1.25 and 1.75. Film cooling data was also obtained for three rotational speeds; 3000 rpm (reference condition), 2550 rpm and 2000 rpm. Film cooling measurements were performed using pressure sensitive paint (PSP) technique. In a parallel effort, extensive numerical investigations of the above configurations were performed to give a better view of flow behavior using a commercially available code. The experimental investigations were performed in the three-stage multi-purpose turbine research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University.
Performance of a Finned Turbine Rim Seal
Authors: Sangan Carl M. , Scobie James A. , Owen J. Michael , Lock Gary D. , Tham Kok Mun , Laurello Vincent P.
Published: September 2014

In gas turbines, rim seals are fitted at the periphery of the wheel-space between the turbine disc and its adjacent casing; their purpose is to reduce the ingress of hot mainstream gases. A superposed sealant flow, bled from the compressor, is used to purge the wheel-space or at least dilute the ingress to an acceptable level. The ingress is caused by the circumferential variation of pressure in the turbine annulus radially outward of the seal. Engine designers often use double rim seals where the variation in pressure is attenuated in the outer wheel-space between the two seals.

This paper describes experimental results from a research facility which models an axial turbine stage with engine-representative rim seals. The radial variation of CO2 gas concentration, swirl and pressure, in both the inner and outer wheel-space, are presented over a range of purge flow rates. The data are used to assess the performance of two seals: a datum double-rim seal and a derivative with a series of radial fins.

The concept behind the finned seal is that the radial fins increase the swirl in the outer wheel-space; measurements of swirl show the captive fluid between the fins rotate with near solid body rotation. The improved attenuation of the pressure asymmetry, which governs the ingress, results in an improved performance of the inner geometry of the seal. The fins also increased the pressure in the outer wheel-space and reduced the ingress though the outer geometry of the seal.
Numerical Investigation on the Time-Variant Flow Field and Dynamic Forces Acting in Steam Turbine Inlet Valves
Authors: Domnick Clemens Bernhard , Benra Friedrich-Karl , Dohmen Hans Josef , Musch Christian
Published: September 2014

In this paper the unsteady flow in inlet valves for large steam turbines used in power stations is investigated using the method of computational fluid dynamics. As the topology of the flow depends on the stroke and the pressure ratio of the valve, it is investigated at several positions. Different turbulence models are applied to the valve in order to capture the unsteady flow field. The RANS, the SAS and the SAS-F (ZFLES) model are evaluated. In order to clarify the cause of flow induced valve vibrations the investigation is focused on the pressure field acting on the valve plug. It could be shown, that acoustic modes are excited by the flow field. These modes cause unsteady forces acting on the valve plug. The influence of valve geometry on the acoustic eigenmodes is investigated in order to lower the dynamic forces. Three major flow topologies are found which crate different dynamic forces.
Experimental Investigation of the Flow Field and the Heat Transfer on a Scaled Cooled Combustor Liner With Realistic Swirling Flow Generated by a Lean-Burn Injection System
Authors: Andreini Antonio , Caciolli Gianluca , Facchini Bruno , Picchi Alessio , Turrini Fabio
Published: September 2014

Lean burn swirl stabilized combustors represent the key technology to reduce NOx emissions in modern aircraft engines. The high amount of air admitted through a lean-burn injection system is characterized by very complex flow structures such as recirculations, vortex breakdown and processing vortex core, that may deeply interact in the near wall region of the combustor liner. This interaction and its effects on the local cooling performance make the design of the cooling systems very challenging, accounting for the design and commission of new test rigs for detailed analysis. The main purpose of the present work is the characterization of the flow field and the wall heat transfer due to the interaction of a swirling flow coming out from real geometry injectors and a slot cooling system which generates film cooling in the first part of the combustor liner. The experimental setup consists of a non-reactive three sector planar rig in an open loop wind tunnel; the rig, developed within the EU project LEMCOTEC, includes three swirlers, whose scaled geometry reproduces the real geometry of an Avio Aero PERM (Partially Evaporated and Rapid Mixing) injector technology, and a simple cooling scheme made up of a slot injection, reproducing the exhaust dome cooling mass flow. Test were carried out imposing realistic combustor operating conditions, especially in terms of reduced mass flow rate and pressure drop across the swirlers. The flow field is investigated by means of PIV, while the measurement of the heat transfer coefficient is performed through Thermochromic Liquid Crystals steady state technique. PIV results show the behavior of flow field generated by the injectors, their mutual interaction and the impact of the swirled main flow on the stability of the slot film cooling. TLC measurements, reported in terms of detailed 2D heat transfer coefficient maps, highlight the impact of the swirled flow and slot film cooling on wall heat transfer.
Numerical Investigation of Ignition Performance of a Lean Burn Combustor at Sub-Atmospheric Conditions
Authors: Soworka T. , Gerendas M. , Eggels R. L. G. M. , Mastorakos Epaminondas
Published: September 2014

Stringent environmental requirements are pushing the current development of aero gas turbine combustors towards lean combustion concepts with relatively small combustor volume. This approach has a detrimental effect on the high altitude relight capability of an aeronautical engine. But the ability to light up at a specific altitude is one of the certification requirements that an engine has to fulfil. To ensure the relight capability, extensive testing for new combustor developments is needed. These test set-ups are expensive as they have to be conducted at sub-atmospheric conditions. Thus, the use of a simple tool to evaluate the ignition tendency of a combustor at an early development stage is advantageous. The code SPINTHIR, developed by Cambridge University, is capable of calculating the ignition performance in turbulent spray flames in a simplified approach. It has been previously validated for different types of flames and applications. In order to adjust the code for lean burn combustors, a new function for a better resemblance of the turbulent spray dispersion has been introduced and the high sensitivity towards cell sizes has been balanced by modifying the ignition criteria. Finally, the results of the code have been compared in this work with recently obtained ignition test performed by Rolls-Royce. Thereby, the influence of varying combustor geometries on the lean ignition limit has been tested. In comparison with these tests, the code’s results show very good matches which verify the conducted changes and give further credence to the model.