bluuebunny/crossref_metadata_2025 huggingface dataset:
Film Flow Characteristics of Droplet Cooling in a Simplified Bearing Chamber
Authors: Kay E. D. , Power H. , Hibberd S.
Published: November 2013

Droplet-cooled oil films develop on the internal surfaces of an aero-engine bearing chamber and are a primary mechanism in removing heat from the chamber as oil is continuously collected and externally cooled and recycled. Predicting the internal oil temperature and oil temperature history is an important thermal problem which becomes more apparent with potential increases in operating temperatures of gas turbines. Studying interacting oil flow and thermal processes within a simplified bearing chamber geometry provides useful information on the trends and characteristics which can arise under different applied flow conditions (e.g. mass flow rate of oil through the system) and insight to the effect chamber design parameters may have on oil degradation and cooling of chamber walls. Thin oil films develop on the walls of a bearing chamber as oil is injected or shed from bearings and impinges on the walls under a strong airflow set in motion by rotating components. Typically the film is also subject to a heat flux from the hot chamber walls and the droplets provide an important cooling effect through “heat-to-oil” mechanisms.

We present a mathematical model for the depth-averaged flow and associated heat transfer by thin oil films on the walls of a simplified aero-engine bearing chamber. Cases corresponding to generic flow conditions relevant to an aero-engine bearing chamber are presented. Characteristics of the film and the efficacy of the flow regime to transfer heat from the chamber is explored through calculating residence times and time histories of oil particles as they make a transit of the internal system.
Probabilistic and Numerical Modelling of a Lobed Mixer at Windmilling Conditions
Authors: Lecoq Maxime , Grech Nicholas , Zachos Pavlos K. , Pachidis Vassilios
Published: November 2013

Aero-gas turbine engines with a mixed exhaust configuration offer significant benefits to the cycle efficiency relative to separate exhaust systems, such as increase in gross thrust and a reduction in fan pressure ratio required. A number of military and civil engines have a single mixed exhaust system designed to mix out the bypass and core streams. To reduce mixing losses, the two streams are designed to have similar total pressures. In design point whole engine performance solvers, a mixed exhaust is modelled using simple assumptions; momentum balance and a percentage total pressure loss. However at far off-design conditions such as windmilling and altitude relights, the bypass and core streams have very dissimilar total pressures and momentum, with the flow preferring to pass through the bypass duct, increasing drastically the bypass ratio. Mixing of highly dissimilar coaxial streams leads to complex turbulent flow fields for which the simple assumptions and models used in current performance solvers cease to be valid. The effect on simulation results is significant since the nozzle pressure affects critical aspects such as the fan operating point, and therefore the windmilling shaft speeds and air mass flow rates.

This paper presents a numerical study on the performance of a lobed mixer under windmilling conditions. An analysis of the flow field is carried out at various total mixer pressure ratios, identifying the onset and nature of recirculation, the flow field characteristics, and the total pressure loss along the mixer as a function of the operating conditions. The data generated from the numerical simulations is used together with a probabilistic approach to generate a response surface in terms of the mass averaged percentage total pressure loss across the mixer, as a function of the engine operating point. This study offers an improved understanding on the complex flows that arise from mixing of highly dissimilar coaxial flows within an aero-gas turbine mixer environment. The total pressure response surface generated using this approach can be used as look-up data for the engine performance solver to include the effects of such turbulent mixing losses.
Spark Ignition of Confined Swirled Flames: Experimental and Numerical Investigation
Authors: Cordier M. , Vandel A. , Renou B. , Cabot G. , Boukhalfa M. A. , Cazalens M.
Published: November 2013

A swirl burner was designed to experimentally study the impact of spark location on ignition efficiency and detailed ignition scenarios until flame stabilization or blow-off were established, following experimental observations. Premixed and non-premixed configurations were investigated for the same turbulent flow, in order to evaluate the fuel heterogeneities on ignition efficiency. Attention was paid to providing accurate data on cold flow velocity field statistics (obtained by stereoscopic PIV) and fuel mole fraction field statistics (obtained by PLIF on acetone). Ignition probability maps were established for all conditions by using laser-induced spark for a constant level of deposited energy. No systematic correlations were observed between local flow properties and ignition probability, which leads to the conclusion that history of the flame kernel inside the combustion chamber, must be taken into account to fully explain the ignition mechanism. From this conclusion, ignition scenarios were built using fast flame visualization and dynamic pressure record. Different steps of the ignition process were identified according to the location of the spark.

In order to evaluate ignition probability according to spark location and flow conditions (velocity, turbulence and mixing), we extended the predictive model of Neophytou et al. [1], with some modifications, to examine whether it can be applied to ignition of swirling premixed flames. Flame particles are emitted by the spark and tracked in the flow with a Langevin equation by using non-reactive velocity fields obtained by PIV. Physical criteria are proposed to represent flame particles generation, expansion and extinction. Results indicate a relatively good agreement with the experimental database and the ignition scenarios are also well reproduced.
Design of Counter-Rotating Turbine to Improve the Off-Design Performance of Turbo-Compounding Systems
Authors: Zhao Rongchao , Zhuge Weilin , Zheng Xinqian , Zhang Yangjun , Yin Yong , Li Zhigang
Published: November 2013

Engine turbo-compounding (TC) is an effective technology to improve the engine efficiency and cut down CO2 emission. A power turbine downstream of the conventional turbocharger turbine is used to recover the exhaust energy and transfer it into mechanical work. However, the performance of turbo-compound system deteriorates seriously at engine off-design points. It is mainly caused by the fact that the designs of turbocharger turbine and power turbine are independent from each other, failing to consider the effects of upstream swirls on the downstream power turbine performance.

Analysis showed that the off-design conditions, off-design incidence loss, transition duct loss and non-uniformity inlet loss contributed to the deterioration performance of power turbine at off-design conditions. Among these reasons, the incidence loss played significant effect on power turbine’s performance. The current research aims to improve the turbo-compounding performance at engine off-design conditions by counter-rotating turbine (CRT) configuration. CRT consists of a radial-flow turbocharger turbine and an axial-flow power turbine with counter-rotating direction. The main purpose is to decrease the incidence loss and turning loss in the power turbine stator by CRT. Performance comparisons between the counter- and co-rotating turbines have also been conducted.

First, meanline analysis was carried out to investigate the influences of design parameters on the velocity triangles and turbine performance. Analysis shows that counter-rotating turbine requires the design of high reaction radial turbine. Then, the 1D preliminary design starts and it is followed by 3D detail design. Finally, the computational fluids dynamic (CFD) method was used to evaluate the counter-rotating turbines performance. Results show that the designed counter-rotating turbine improves the off-design performance effectively, with 3.8% increase of power turbine efficiency points at 1200rpm condition. Further analysis on the flow field was conducted and it was found that the flow angle distribution at upstream turbine exit was highly non-uniformity along the span. To weaken the non-uniformity may be a potential way to further improve the performance of turbo-compounding systems.
Three Components- and Tomographic-PIV Measurements of a Cyclone Cooling Flow in a Swirl Tube
Authors: Biegger Christoph , Weigand Bernhard , Cabitza Alice
Published: November 2013

Swirl cooling is a very efficient method for turbine blade cooling. However, the flow in such a system is quite complicated. In order to gain understanding of the flow structure, the velocity field in a leading edge swirl cooling chamber with two tangential inlet ducts is experimentally studied via Particle Image Velocimetry (PIV). The examined swirl tube is 1 m long and has a diameter of 50 mm. It represents an upscaled generic model of a leading edge swirl chamber. The Reynolds number, defined by the bulk velocity and the swirl tube diameter, ranges from 10,000 to 40,000, and the swirl number is 5.3. Velocity fields are measured in the center plane of the tube axis with stereo- and tomographic-PIV using two and four CCD cameras respectively. Tomographic-PIV is a three-dimensional PIV technique relying on the illumination, recording, reconstruction and cross correlation of a tracer particle distribution in a measurement volume opposed to a plane in stereo-PIV. For statistical analysis 2,000 vector maps are calculated and evaluations show a sample size of 1,000 ensembles is sufficient. Our experiment showed, that the flow field is characterized by a vortex system around the tube axis. Near the tube wall we observed an axial flow towards the outlet with a circumferential velocity component in the same order of magnitude. In contrast the vortex core consists of an axial backflow (vortex breakdown). The gained understanding of the flow field allows to predict regions of enhanced heat transfer in swirl chambers.
Assessment of a Noise Reduction Concept for a Hot Supersonic Jet Using Large Eddy Simulation
Authors: Erwin James P. , Sinha Neeraj
Published: November 2013

Noise emissions of a hot, supersonic jet at laboratory scale are predicted with and without a noise reduction concept. The hot jet is representative of an over-expanded, low bypass ratio military gas turbine engine exhaust. The reduction device consists of twelve non-penetrating chevrons that are equilateral triangles, extending tangentially from the inner nozzle wall and to the flow at the nozzle exit. The chevrons are idealized and not a result of any design or testing procedures. Hybrid Reynolds Averaged Navier Stokes and Large Eddy Simulation (HRLES) is performed at both 5.5 million and 128 million cell grid resolutions. A novel structured topology is used to perform the HRLES with and without the chevrons using the same grid, and the chevrons are turned on and off through a boundary condition switch. The noise emissions are then predicted on a circular array one hundred jet exit diameters from the nozzle exit with the permeable Ffowcs Williams and Hawkings equation method. The chevrons modify the entrained flow at the over-expanded power setting, impacting the shear layer and associated far-field noise. The chevrons stabilize the jet shock cell structure, and also reduce turbulent fluctuations throughout the length of the shear layer. An overall sound pressure level reduction of between one and four decibels is predicted at all angles to the jet, including the elimination of jet screech relative to the baseline jet with no chevrons. A significant reduction in broadband noise is also predicted downstream. The jet with chevrons is also predicted with the higher resolution grid and noise levels are compared with the low resolution grid. Upstream noise level predictions are increased due to enhanced resolution of fine scale turbulence.
Numerical Analysis of the Primary Breakup Under High-Altitude Relight Conditions Applying the Embedded DNS Approach to a Generic Prefilming Airblast Atomizer
Authors: Sauer Benjamin , Spyrou Nikolaos , Sadiki Amsini , Janicka Johannes
Published: November 2013

The primary breakup under high-altitude relight conditions is investigated in this study where ambient pressure is as low as 0.4 bar and air, fuel and engine parts are as cold as 265 K. The primary breakup is crucial for the fuel atomization. As of today, the phenomena dictating the primary breakup are not fully understood. Direct Numerical Simulations (DNS) of liquid breakup under realistic conditions and geometries are hardly possible. The embedded DNS (eDNS) approach represents a reliable numerical tool to fill this gap.

The concept consists of three steps: a geometry simplification, the generation of realistic boundary conditions for the DNS and the DNS of the breakup region. The realistic annular airblast atomizer geometry is simplified to a Y-shaped channel representing a planar geometry. Inside this domain the eDNS is located. The eDNS domain requires the generation of boundary conditions. A Large Eddy Simulation (LES) of the entire Y-shaped channel and a Reynolds-Averaged Navier-Stokes Simulation (RANS) of the liquid wall film are performed prior to the DNS. All parameters are stored transiently on all virtual DNS planes. These variables are then mapped to the DNS. Thus, high-quality boundary conditions are generated. The Volume-of-Fluid (VOF) method is used to solve for the two-phase flow.

The results provide a qualitative insight into the primary breakup under realistic high-altitude relight conditions. Instantaneous snapshots in time illustrate the behavior of the liquid wall film along the prefilmer lip and illustrate the breakup process. It is seen that a slight variation of the surface tension force has a strong impact on the appearance of the primary breakup. Case 1 with the surface tension corresponding to kerosene at 293 K indicates large flow structures that are separated from the liquid sheet. By lowering the surface tension related to kerosene at 363 K, the breakup is dominated by numerous small structures and droplets.

This study proves the applicability of the eDNS concept for investigating breakup processes as the transient nature of the phase interface behavior can be captured. At this time, the authors only present a qualitative insight which can be explained by the lack of quantitative data. The approach offers the potential of simulating realistic annular highly-swirled airblast atomizer geometries under realistic conditions.
An Experimental Study of Mist/Air Film Cooling on a Flat Plate With Application to Gas Turbine Airfoils: Part 1 — Heat Transfer
Authors: Zhao Lei , Wang Ting
Published: November 2013

Film cooling is a cooling technique widely used in high-performance gas turbines to protect the turbine airfoils from being damaged by hot flue gases. Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments in this study. A small amount of tiny water droplets (7% wt.) with an average diameter about 5 μm (mist) is injected into the cooling air to enhance the cooling performance. A wind tunnel system and test facility is specifically built for this unique experiment. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part 1 is focused on the heat transfer result on the wall and Part 2 is focused on the two-phase droplet multiphase flow behavior.

Mist film cooling performance is evaluated and compared against air-only film cooling in terms of adiabatic film cooling effectiveness and film coverage. A row of five circular cylinder holes is used, injecting at an inclination angle of 30° into the main flow.

For the 0.6 blowing ratio cases, it is found that adding mist performs as wonderfully as we mindfully sought: the net enhancement reaches a maximum 190% locally and 128% overall at the centerline, the cooling coverage increases by 83%, and more uniform surface temperature is achieved. The latter is critical for reducing wall thermal stresses.

When the blowing ratio increases from 0.6 to 1.4, both the cooling coverage and net enhancement are reduced to below 60%. Therefore, it is more beneficial to choose a relatively low blowing ratio to keep the coolant film attached to the surface when applying the mist cooling.

The concept of Film Decay Length (FDL) is introduced and proven to be a useful guideline to quantitatively evaluate the effective cooling coverage and cooling decay rate.
Study of an Air-Oil Pump and Separator Solution for Aero Engine Lubrication Systems
Authors: Steimes Johan , Gruselle François , Hendrick Patrick
Published: November 2013

Lubrication system of aero engines have to manage a two-phase flow of oil and air created in air-sealed bearing chambers. A part of this flow goes through scavenge pumps and a de-aerator before returning to the tank, the other part passes through a de-oiler before leaving the engine. The Aero-Thermo-Mechanics Department of Université Libre de Bruxelles is developing an original and integrated system to pump and separate a liquid-gas flow. This system helps to reduce the complexity and the oil consumption of aero-engine lubrication systems by replacing the de-oiler, the de-aerator and scavenge pumps. The prototype is composed of an axial part (blades and metallic foam) that performs the separation and a radial part that pressurize the liquid. De-oiling efficiency is measured with a radio-tracer measurement system. This paper presents the test results of four configurations (different radii, flow paths, size of the metallic foam). Droplet size measurements at the inlet and the outlet of the prototype are also presented. A physical interpretation has been developed and is presented.
Performance Calculation of a Three-Shaft Gas Turbine: Experiment Evaluation and Analysis
Authors: Ji Xingxing , Gu Chunwei , Liu Hong , Xie Weihong
Published: November 2013

Analytical and experimental researches on the characteristics of a three-shaft gas turbine are presented in the paper. The concerned gas turbine engine includes a twin-shaft gas generator and a third shaft — the free turbine for power generation. The free turbine uses a variable-angle nozzle (VAN) for fuel saving and load-adjusting flexible.

The engine performance is calculated by using the multi-dimensional Newton-Raphson method, which is based on a set of matching constraints described by the error matrix and the performance maps of the related components. It has a better accuracy and stability than those of some other methods (e.g. parameter cycle method) and is well suitable for solving the off-design problem. The suggested prediction method, presented as a computer program written in Fortran 95, is extremely flexible and can be employed to various engine configurations.

Experiments are carried out on the concerned engine by controlling the stagger angle of the VAN, then adjusting the fuel consumption for different outputs. The accuracy of the prediction method is validated by the experiment.

Detailed performance characteristic of the engine is investigated under five different stagger angles of the VAN when the T3 value was controlled from 85% to 105% of its design value, revealing how the T3 and the stagger angle of the VAN affect the gas turbine performance. The results are useful for the engine operation and components optimization.
Investigation of Film Cooled Turbine With Conjugate Heat Transfer Using Source Term Model
Authors: Yin Zhao , Fang Xiang-jun
Published: November 2013

The NASA C3X cascade with 10 radial internal cooling holes and five rows of film cooling holes in the leading edge was studied in this paper. Firstly, the conjugate heat transfer (CHT) method was employed in the non-film-cooled blade to simulate the heat transfer between the main flow and the internal coolant with the blade. The turbulence models included B-L model (zero-equation model), S-A model (one-equation model), SST model (two-equation model) and S-A model with AGS transition model. Experiment results were compared with the simulation results, and S-A model was selected for next step considering its reasonable prediction of eddy viscosity. Secondly, the source term model was used to simulate the film cooling effect by adding mass flux, momentum flux, energy flux and turbulence energy flux on the cells where the film holes were located. The method was able to save a lot of time without discretization of every single hole, which is convenient for modern film-cooled turbine design. The feasibility of the source term model was discussed through a comparison between the simulation and experiment results. The effect of the film cooling on the internally cooled vane was also discussed, and detailed mechanism of the heat transfer among the internal and external coolant, hot air, and the blade was analyzed.
Numerical Investigations of Wake and Shock Wave Effects on Film Cooling Performance in a Transonic Turbine Stage: Part 1 — Methodology Development and Qualification Over Stationary Stators and Rotors
Authors: Xu Huazhao , Wang Jianhua , Wang Ting
Published: November 2013

To understand the unsteady shock wave and wake effects on the film cooling performance over a transonic 3-D rotating stage, a series of numerical investigations have been conducted and are presented in this two-part paper. Part 1 is focused on the development of the computational model and methodology of the system setup and model qualification; Part 2 is to investigate the unsteady effects of shock waves and wakes on film cooling performance in a transonic rotating stage.

In Part 1, the film cooling experimental conditions (non-rotating) and test sections of Kopper et. al. and Hunter are selected for model qualification. The numerical computation is carried out by the commercial software Ansys/Fluent using the pressure based compressible flow governing equations. The effects of four turbulence models are carefully compared with the experimental data. The Realizable k-ε turbulence model is found to match the experimental data better than the other models and is thus used for the rest of the study, including Part 2. The results show that 1) the weak shock emanating from the neighboring stator’s trailing edge results in a temperature rise and a reduction of film cooling effectiveness on the suction side near the trailing edge, 2) cooling ejection from the trailing edge reduces the shock strength in the stator passage, 3) an increase in Mach number from 0.84 to 1.50 can reduce the total pressure losses of fluid flow near the end-walls, 4) the film cooling effectiveness increases with increasing blowing ratio and becomes more even on the stator with a higher blowing ratio, and 5) an increase in Mach number from 0.84 to 1.50 gives rise to a higher cooling effectiveness in the region from the cooling holes to 80% of the chord length of the stator on the pressure side, but becomes lower after this up to the trailing edge. However, on the stator’s suction side, higher Mach number results in a lower cooling effectiveness region around the film holes from 30% to 55% of the chord length, but cooling effectiveness increases downstream.
Effect of Rib Configuration and Lateral Ejection on a High Aspect Ratio Trailing Edge Channel
Authors: Kan Rui , Yang Li , Ren Jing , Jiang Hongde
Published: November 2013

Thermal issues of gas turbine blade trailing edge are complex and challenging, due to limited space for effective cooling. The trailing edge cavities are usually large aspect ratio ducts with lateral ejection. The objective of this study is to investigate the effects of different rib configurations and lateral ejection on heat transfer characteristics inside a trailing edge channel.

The investigations were conducted on a large aspect ratio wedge-shaped channel with square ribs of e/Dh = 0.05, under Reynolds number 15,000. Twelve different configurations were tested: 1)three rib types, including a symmetry V-shaped rib configuration and two non-symmetry V-shaped rib configurations, of which the rib angles are 60 degrees, 2) two rib pitches, P/e = 10 and P/e = 5, 3) two flow directions, with an open tip outlet or with lateral ejection. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal experimental method. The configurations were also investigated numerically for the detailed flow field and for the validation of CFD codes.

Results show that with lateral ejection, the heat transfer coefficients decrease from inlet to outlet. The heat transfer near the ejection holes is enhanced while heat transfer coefficients near the wall opposite to the exit holes decrease. The curvature of the streamlines creates a large separation area near the end of the channel and thus results in low local heat transfer coefficients.

The P/e = 10 configurations have higher average heat transfer compared with P/e = 5 configurations. Average heat transfer coefficient is the highest with the center of the V-shaped rib placed at the middle of the channel, and is the lowest when the V-shaped rib center is located near the narrow part of the channel.
The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade
Authors: Mack Marion , Brachmanski Roland , Niehuis Reinhard
Published: November 2013

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range.

In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves.

The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.
N+3 and N+4 Generation Aeropropulsion Engine Combustors: Part 1 — Large Engines’ Emissions
Authors: Mongia Hukam C.
Published: November 2013

A comprehensive assessment of emissions characteristics of the 1st, N and N+1 generation rich-dome combustion products has been done to identify the lowest emissions products. Focus of this paper is on the large rich-dome engines with its potential application for the (N+3) and (N+4) mixers with inspirational target takeoff NOxEI of 5 at 55 OPR.

A total of ten engine models of the 1st generation were selected in addition to eight recently certified large engines. After evaluating several choices for conducting comparative assessment, the following three expressions were proposed for average takeoff NOxEI, idle COEI and HCEI entitlements, respectively:

NOxEI L = 0.0288 × OPR 1.991

Idle COEI L = 815.36 Takeoff NOxEI L 1.159

Idle HCEI L = 0.15 × Idle COEI L - 2.0

In regard to application of the rich-dome technology to the (N+2) cycle based (N+3) mixers, the author tentatively gives it low probability of success barring success story stemming from Lee et al. [2012].
Forced-Air Diesel Locomotive Cooling: Prediction of Noise and Energy Consumption Under Realistic Operational Conditions
Authors: Knirsch Sebastian , Mandt Dietmar , Mauch Uwe , Bamberger Konrad , Carolus Thomas
Published: November 2013

An important subsystem in most surface transport vehicles is the forced-air cooling module. Under specific operational conditions of the vehicle the cooling system is the major noise source and the component with the largest consumption of energy. A comprehensive time domain simulation model was developed for simulation of the cooling module in a Diesel locomotive under realistic operational conditions. It includes the components that produce waste heat such as the engine, the turbo transmission, the brake, etc. and the cooling module with its fans. Given the operation of the locomotive e.g. in terms of speed vs. time along a track and its load, data from experimental full scale tests agree well with predictions from the time domain model. The onset of cooling fan operation is predicted well, with it their instantaneous energy consumption and sound radiation. Three optimized cooling unit assemblies for the new locomotive Voith Gravita 15L had been developed and pre-assessed utilizing the model and eventually tested in the locomotive under realistic operational conditions. A new thermodynamically advanced cooling unit with aerodynamically and acoustically optimized fans was found superior by approx. 2 dB (A) less sound power radiation and some 30% less energy consumption as compared to the benchmark. It is anticipated that those advantages are even more distinct as the ambient temperature decreases.

The work is part of the European FP7 transport research project ECOQUEST.
Assessment of a Double Hole Film Cooling Geometry Using S-PIV and PSP
Authors: Wright Lesley M. , McClain Stephen T. , Brown Charles P. , Harmon Weston V.
Published: November 2013

A novel, double hole film cooling configuration is investigated as an alternative to traditional cylindrical and fanshaped, laidback holes. This experimental investigation utilizes a Stereo-Particle Image Velocimetry (S-PIV) to quantitatively assess the ability of the proposed, double hole geometry to weaken or mitigate the counter-rotating vortices formed within the jet structure. The three-dimensional flow field measurements are combined with surface film cooling effectiveness measurements obtained using Pressure Sensitive Paint (PSP). The double hole geometry consists of two compound angle holes. The inclination of each hole is θ = 35°, and the compound angle of the holes is β = ± 45° (with the holes angled toward one another). The simple angle cylindrical and shaped holes both have an inclination angle of θ = 35°. The blowing ratio is varied from M = 0.5 to 1.5 for all three film cooling geometries while the density ratio is maintained at DR = 1.0. Time averaged velocity distributions are obtained for both the mainstream and coolant flows at five streamwise planes across the fluid domain (x/d = −4, 0, 1, 5, and 10). These transverse velocity distributions are combined with the detailed film cooling effectiveness distributions on the surface to evaluate the proposed double hole configuration (compared to the traditional hole designs). The fanshaped, laidback geometry effectively reduces the strength of the kidney-shaped vortices within the structure of the jet (over the entire range of blowing ratios considered). The three-dimensional velocity field measurements indicate the secondary flows formed from the double hole geometry strengthen in the plane perpendicular to the mainstream flow. At the exit of the double hole geometry, the streamwise momentum of the jets is reduced (compared to the single, cylindrical hole), and the geometry offers improved film cooling coverage. However, moving downstream in the steamwise direction, the two jets form a single jet, and the counter-rotating vortices are comparable to those formed within the jet from a single, cylindrical hole. These strong secondary flows lift the coolant off the surface, and the film cooling coverage offered by the double hole geometry is reduced.
Numerical Sensitivity Study and Calibration of Non-Equilibrium Wet Steam Model
Authors: Moraga F. J. , Wang L. , Ren W.-M.
Published: November 2013

Comparisons between one- and two-dimensional experiments and non-equilibrium wet steam CFD simulations are conducted paying attention not only to pressure profiles and wetness but also to the more difficult to match droplet diameter. To achieve the objective of optimizing the match of data the heat transfer model between the droplet and its surrounding vapor proposed by Young and the corrections to classical nucleation theory proposed by Moore and popularized by Gerber are adopted. It is found that the proposed models produce a better agreement with droplet diameter, without affecting the overall quality of the predictions for other quantities.
Numerical Analysis of Heat Transfer in a Leading Edge Geometry With Racetrack Holes and Film Cooling Extraction
Authors: Andrei Luca , Andreini Antonio , Da Soghe Riccardo , Facchini Bruno , Zecchi Stefano
Published: November 2013

A numerical study of a state of the art leading edge cooling scheme was performed to analyze the heat transfer process within the leading edge cavity of a high pressure turbine airfoil. The investigated geometries account a trapezoidal supply channel with a large racetrack impingement holes. The coolant jets, confined among two consequent large fins, impact the leading edge internal surface and it is extracted from the leading edge cavity through both showerhead holes and film cooling holes. The CFD setup has been validated by means of the experimental measurements performed on a dedicated test rig developed and operated at University of Florence. The aim of this study is to investigate the combined effects of jet impingement, mass flow extraction and fins presence on the internal heat transfer of the leading edge cavity. More in details, the paper analyses the impact, in terms of blade metal temperature, of large fins presence and positioning. Jet’s Reynolds number is varied in order to cover the typical engine conditions of these cooling systems (Rej = 20000 – 40000).
Acoustic Measurements of Perforated Liners in Hot and Pressurized Flow
Authors: Lahiri Claus , Knobloch Karsten , Bake Friedrich , Enghardt Lars
Published: November 2013

Thermo-acoustic instabilities in gas turbine combustors can prevent the implementation of modern combustion concepts, which are essential for higher efficiency and lower emissions. Perforated combustor liners, especially in combination with a bias flow through the liner, are able to suppress the instabilities by increasing the acoustic losses of the system. Some insight into the parameter dependencies of the acoustic absorption has been gained by means of atmospheric testing at ambient temperature. The next step towards realistic testing conditions is taking into account high temperature and high pressure, which increases the effort of the experimental tests and the complexity of their analysis significantly. Tests in a real combustor can serve as a quality check of a given liner design, but are not appropriate for parameter studies. So far, numerical models accurate enough to enable the design of hot stream liners are simply not available, so that the experimental investigation of the liner’s dependency on temperature and pressure is essential for the transfer of laboratory scale results to a real engine application.

A new test rig has been designed to overcome these problems. The Hot Acoustic Test rig (HAT) enables the study of the influence of pressure and temperature on the damping performance in an acoustically well defined environment, although the high temperature and high pressure conditions are challenging in terms of accurate acoustic measurements.

This paper introduces the Hot Acoustic Test rig with its features and limitations and shows first examples of test results. The focus lies on the hardware, instrumentation, and analysis techniques that are necessary to obtain high quality acoustic data in hot and pressurized flow environments.
Ansaldo AE94.3A Combustion Improvement Towards Flexibility Through Extensive Field Testing
Authors: Malavasi Francesco , Pesce Paolo , Pesenti Alice Virginia , Traverso Paolo , Zito Domenico
Published: November 2013

Being the European energy market in a sort of stagnation, flexibility is nowadays particularly profitable, with increasing care of environmental minimum load, maximum load and loading/unloading rate.

For its F class model AE94.3A4, Ansaldo Energia has identified two technical keys for success:

- Combustion stability

- Combustion efficiency

Thanks to a cooperation agreement with ENEL PRODUCTION, the largest Italian electricity utility, Ansaldo Energia had the possibility to design, introduce on one GT and test several combustion system modifications addressed to improve the performance of the whole GT by a synergy between proven design burners and cooling / sealing air optimization.

During 3 months, 5 combustion system configurations have been installed and tested on the GT made available from ENEL. Taking into account that each burner is equipped with different kinds of pilot injections, the number of effective tested configurations amounts to 11.

The configurations have been chosen in a large range of premixing ability, from high premixing to high diffusion rate. Due to the optimization of secondary air system, it has been necessary to install additional instrumentation in order to monitor the impact on the hot gas path components, with the aim of maintaining temperature conditions consistent with long life requirements.

In the end, 3 combustion configurations were identified as able to cover 3 ranges of environmental requirements as:

1 – High populated residential areas (NOx emission < 30 mg/Nm3)

2 – Medium populated or light industrial (NOx emission < 40 mg/Nm3)

3 – Very low populated areas or heavy industrial (NOx emission < 50 mg/Nm3)

Premixing is generally the more effective element to defeat N2 oxidation, with the side effect of making the combustion process particularly sensitive to pressure pulsations. So the efforts of the combustion designer have been spent to carefully modulate the injection of fuel in order to allow a good compromise between stability and emission.
Application of Thermal Oxidation to a Recuperated Gas Turbine: The Path to PPB NOx Emissions
Authors: Armstrong Jeffrey , Hamrin Douglas , Lampe Steve
Published: November 2013

Dry, low NOx emissions developments in the industrial gas turbine industry have focused on lean-premixed combustion to reduce NOx to single digit parts-per-million (ppmV) emissions. The reduction of thermal NOx is limited by the lowest lean-premix combustion temperatures. To overcome this limit, a thermal oxidizer is applied which can oxidize hydrocarbon fuels at temperatures below those of lean-premixed combustion in a Brayton cycle. This oxidation technique is explained in a combustion taxonomy model. This paper presents the historical development and demonstration of technology with two different recuperated gas turbines operating on landfill gas. A unique fuel-injection strategy was used to introduce the fuel into the inlet of the gas turbine’s air compressor. The technology demonstrated an order-of-magnitude reduction in the emissions of NOx to the parts-per-billion range.
Two-Way Fluid-Structure Interaction in a Gas Turbine Combustor in Limit Cycle Oscillation
Authors: Gövert Simon , Kok Jim B. W. , Casado Juan C. Roman
Published: November 2013

In this paper the mechanical interaction between pressure oscillations induced by combustion dynamics in a laboratory scale combustor and the structural vibrations of the combustor wall (the liner) is investigated. The combustor has operation conditions where the feedback loop between unsteady heat release and the acoustic field in the combustion chamber is unstable. This drives the amplitudes of the acoustic pressure oscillations to very high magnitudes. Under these circumstances, there is increased risk of failure due to fatigue. To investigate the two way feedback loop between the acoustic field and the structural vibrations of the liner in a gas turbine combustor, a laboratory-size combustor has been developed. The combustor has a rectangular cross section and operates under lean, partially-premixed conditions. The flame is stabilized using a triangular bluff body. To achieve a strong liner vibration feedback, the stiffness of the liner walls is made very low. In the framework of the COPAGT project, transient numerical simulations of the coupled fluid-structure interaction (FSI) system in the combustor are carried out and the results are validated by measurements. A partitioned approach is utilized, where the fluid and structural domain are calculated by different solvers. Coupling is achieved by a two-way data exchange between the fluid and structural domain. Investigated is an operating point in limit cycle oscillation with high amplitude. The numerical results show some agreement with the experimental data, but also show some aspects for improvement. The applied procedure is suitable to reproduce the coupling of the pressure with the structure, but the structural model performance needs to be improved. Neither for the measurements nor for the simulation any influence of the structural vibration is visible in the pressure spectrum, which can be seen as the major characteristic for a closed feedback loop between structural vibration and acoustic field.
Integration of a Turbine Cascade Facility Into an Undergraduate Thermo-Propulsion Sequence
Authors: Rouser Kurt P. , Thorn Caitlin R. , Byerley Aaron R. , Wisniewski Charles F. , Nowlin Scott R. , Van Treuren Kenneth W.
Published: November 2013

The Department of Aeronautics at the United States Air Force Academy utilizes a closed-loop, two-dimensional turbine cascade wind tunnel to reinforce a learning-focused undergraduate thermo-propulsion sequence. While previous work presented in the literature outlined the Academy thermo-propulsion sequence and the contextual framework for instruction, this current paper addresses how the Academy turbine cascade facility is integrated into the aeronautical engineering course sequence. Cadets who concentrate in propulsion are to some extent prepared for each successive course through their contact with the cascade, and ultimately they graduate with an exposure to experimental research that enhances their grasp of gas turbine engine fundamentals. Initially, the cascade is used to reinforce airfoil theory to all cadets in the Fundamentals of Aeronautics course. Aeronautical engineering majors take this course during the first semester of their sophomore year. The next semester all aeronautical engineering majors take Introduction to Aero-thermodynamics. In this course, the closed-loop aspect of the cascade facility is used to reinforce concepts of work addition to the flow. Heat transfer is also discussed, using the heat exchanger that regulates test section temperature. Exposure to the cascade also prepares cadets for the ensuing Introduction to Propulsion and Aeronautics Laboratory courses, taken in the junior and senior year, respectively. In the propulsion course, cadets connect thermodynamic principles to component analysis. In the laboratory course, cadets work in pairs on propulsion projects sponsored by the Air Force Research Laboratory, including projects in the cascade wind tunnel. Individual cadets are selected from the cascade research teams for summer internships, working at an Air Force Research Laboratory turbine cascade tunnel. Ultimately, cadet experiences with the Academy turbine cascade help lay the foundation for a two-part senior propulsion capstone sequence in which cadets design a gas turbine engine starting with the overall cycle selection leading to component-level design. The turbine cascade also serves to integrate propulsion principles and fluid mechanics through a senior elective Computational Fluid Dynamics course. In this course, cadets may select a computational project related to the cascade. Cadets who complete the thermo-propulsion sequence graduate with a thorough understanding of turbine engine fundamentals from both conceptual and applied perspectives. Their exposure to the cascade facility is an important part of the process. An assessment of cadet learning is presented to validate the effectiveness of this integrated research-classroom approach.
Optimization of an Oxyfuel Combined Cycle Regarding Performance and Complexity Level
Authors: Dahlquist Adrian , Genrup Magnus , Sjoedin Mats , Jonshagen Klas
Published: November 2013

The aim of this paper is to establish and motivate the design parameters of a 125 MW Oxyfuel Combined Cycle (OCC) also referred to as the Semi-Closed Oxyfuel-Combusted Combined Cycle (SCOC-CC). This paper proposes a compatible OCC that does not include any unconventional features, beyond what is state-of-the-art in gas turbine technology today. Such features could challenge the feasibility to bring the concept to the market in a reasonable time.

The OCC requires a higher pressure ratio compared to a conventional combined cycle in order to achieve exhaust conditions that fit the design of the bottoming cycle. However, a high gas turbine pressure ratio increases the complexity of the machine and must be weighted against the gain in efficiency. The OCC gas turbine is modeled using a cooling model which keeps the metal temperature of all cooled turbine stages constant while seeking the optimum pressure ratio.

As the cycle is semi-closed the compressor inlet temperature is a design parameter: it is shown that there is an efficiency optimum clearly in the range of what is normally achievable. As the gas properties of the OCC flue gas differ from the conventional plant, the effects of this on the HRSG design are explored.