bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Performance of a High Pressure Gas Turbine Stage Using a Profiled Endwall
Authors: Miyoshi Ichiro , Higuchi Shin’ichi , Kishibe Tadaharu
Published: November 2013

A non-axisymmetric endwall contouring technology has been developed in highly loaded axial turbomachinery. This paper describes the computational and experimental evaluation of our contouring approach applied in an air turbine nozzle. The geometrical parameters and the flow conditions are consistent with a modern high pressure gas turbine. In the design of the non-axisymmetric endwall, our original design concept is applied in order to improve the aerodynamic performance. The concept, derived from the governing equation of compressible flow, is verified in comparison with the previous researches. Effectiveness of our endwall contouring technology is shown in detail through the results of a computational study for the secondary flow in the vicinity of the endwall. The flow is seen to be significantly different from that of the annular endwall. The numerical results showed that the contoured endwall controlled both generation of a horseshoe vortex near the leading edge and the growth of secondary flow in the blade passage. The effective control of the secondary flow ensures more uniform flow in the front and rear part of the passage than that in the case of the non-contoured endwall. The effect also influences the increment of Mach number in the turbine nozzle and significantly changes the distribution of the total pressure loss coefficient in the main flow region. We confirmed 35% loss reduction using an air turbine test rig. Our study demonstrates the potential of the developed non-axisymmetric endwall contouring technology for enhancing the aerodynamic performance of turbine nozzles.
A Novel Flue Gas Heat Recovery System Integrated With Air Preheating in a Utility Boiler
Authors: Xu Cheng , Xu Gang , Zhou Luyao , Yang Yongping , Li Yuanyuan , Deng Jianling
Published: November 2013

Exhaust gas temperature in coal-fired power plants can reach approximately 120 °C to 140 °C, with the thermal energy accounting for approximately 3% to 8% of the total input energy. Therefore, the heat recovery of exhaust flue gas can improve the thermal efficiency of coal-fired power plants. Currently, the waste heat of flue gas can be recovered by installing an extra heat exchanger, also called low-temperature economizer (LTE), at the end of the boiler flue to heat a part of the condensed water. Extra work can then be obtained by saving the extracted steam and using it to heat the condensed water. However, the temperature of exhaust flue gas is only about 130 °C, which causes the flue gas to heat only the condensed water in the #7 and #8 regenerative heaters. Thus, the energy savings are inconspicuous. This paper proposes a novel flue gas heat recovery system to dramatically increase the temperature of flue gas in the LTE by comprehensive optimization of the air preheater and the LTE. A low-temperature (LT) air preheater can be installed after the LTE in the novel system so that the flue gas can be divided into two parts to heat the air. Simultaneously, the LTE can be installed between the two air preheaters, causing the temperature of flue gas in the LTE to reach above 170 °C. Hence, the temperature of condensed water in the LTE can be increased significantly. In addition, the LTE can replace the high-pressure extracted steam from the turbine, resulting in better energy savings. We also conduct case studies based on a typical 1,000 MW supercritical power generation unit in China. The results indicate better performance of the novel system, with a decrease in exergy loss and improvement in heat transfer characteristics. The reduction in standard coal equivalent of the novel system can reach 3.31g/kWh, nearly 2.4 times that of the system that uses conventional waste heat recovery. Our achievements provide a promising waste heat recovery methods of the utility boiler flue gas.
The Influence of Dump Gap on Aerodynamic Performance of a Low-Emission Combustor Dump Diffuser
Authors: He Pei , Suo Jianqin , Xie Kaicheng , Chen Sutao , Shen Shanping , Zeng Qinglin
Published: November 2013

In modern civil aero-engine gas turbine combustors, lean burn technology is widely adopted to achieve low NOx emission target. As such, most of the flow issued from the compressor is expected to flow into the combustor dome, compared with a typical value of 30% in conventional combustors. To accommodate this increased mass flow rate, lean module fuel injectors should be significantly larger than their conventional counterparts. This will change the combustor external aerodynamic layout such as a deeper flame tube together with an enlarged dump gap, which is the distance between the pre-diffuser outlet and the flame tube. The modification will potentially increase the total pressure loss due to enlarged turning within the dump region. Thus it is important to investigate the influence of the dump gap on the aerodynamic performance of the diffuser. Experiments have been carried out and presented in this paper. The tested geometry comprises a pre-diffuser, followed by a sudden expansion through which the main flow is divided into three passages, i.e., the combustor dome, the outer passage, and the inner passage. Up to 60% of the airflow issued from the pre-diffuser flows into the dome. It is found that the loss coefficient of pre-diffuser decreases as dump gap increases. The overall loss coefficient is relatively high when the dump gap ratio is smaller than 1.2 or larger than 2.8, and is relatively low and insensitive to dump gap with intermediate dump gaps. It is also found that the proportion of the pre-diffuser loss to the overall loss is larger than conventional dump diffuser.
Numerical Investigation on Flow Characteristics of Low Pressure Exhaust Hood Under Off-Design Conditions for Steam Turbines
Authors: Shao Shuai , Deng Qinghua , Shi Heshuang , Feng Zhenping , Cheng Kai , Peng Zeying
Published: November 2013

In this paper, numerical investigations on the aerodynamic characteristics of the last three stages and the exhaust hood for a large power steam turbine were conducted under a series of mass flow conditions (100% ∼ 10% of the design condition) using the commercial CFD software ANSYS-CFX. The single passages of the last three stages and the whole exhaust hood are combined together as the computational domain. The main objective of this present work is to analyze the aerodynamic performance and the flow behavior of the exhaust hood. The variations of the static pressure recovery coefficient and the total pressure loss coefficient while the mass flow rate decreasing were analyzed. The static pressure distributions along the diffuser surface under different flow conditions were illustrated. The development of the vortex near the outlet of the diffuser was demonstrated through the velocity vector distribution at the meridional plane of the exhaust hood. The windage conditions were analyzed under 20% and 10% mass flow rate of the design condition. In addition, the back flow phenomenon was observed when the mass flow rate was below 50% of the design condition, and it starts from the hub region of the last stage rotor and grows up along the radial direction. The back flow also induces a sharp turning on the span-wise distribution of the angle θ (defined in Fig. 9) at the outlet of the last stage rotor. The three-dimensional streamlines inside the exhaust hood under different mass flow conditions were also compared.
Turbojet Engine Noise Prediction Utilizing Empirical Methods
Authors: Barbosa João Roberto , Dezan Daniel Jonas
Published: November 2013

This work deals with the prediction of noise generated by gas turbines, which includes engines being designed. One has in mind the fulfillment of the ever-increasing concerns with environment, in particular noise. Analytical and empirical methods have been focused by researchers and industry, although only empirical prediction methods are utilized in this work, for the calculation of the one-third octave band sound pressure levels associated to the main engine noise sources. The methodology for the calculation of the engine noise has been combined with performance and design computational programs to evaluate the noise emitted by each engine component and, by proper combination, the engine total noise. A newly designed and manufactured 5 kN/1.2 MW turbojet engine serves as the basis for the noise prediction. For the study, the main noise sources are: compressor, combustor, turbine and propelling nozzle. In terms of the overall sound pressure level, OASPL, are compatible with the noise produced by similar engines. The noise predictions are performed at engine design speeds in the range of 100% down to 70% of the design speed (28,150 rpm). The engine has not run yet, but it is expected that measured noise will be available in the near future. However, it is important to emphasize that all prediction models used to evaluate the radiated noise from the engine were validated. The engine operating conditions were calculated using a high fidelity engine simulator developed to provide the data used in this study. The methods to estimate the one-third octave band sound pressure levels are reported in NASA TM-195480, SAE ARP-876D, NASA-ANOPP and ESDU Item 98019. No atmospheric attenuation and ground reflection were considered in this work.
Crystallographic Orientation Evolution in NbSS-Nb5Si3 Eutectic Alloys by EBSD Analyses
Authors: Li Y. L. , Ma C. L. , Zhang H.
Published: November 2013

The progresses in high temperature materials encourage the development of turbine engine in terms of thrust and efficiency. Ni-based superalloys, which are predominant in elevated temperature application, have limited potential to raise serving temperature. In-situ composites, such as Cr-Cr3Si, NiAl-Cr and Nb-Nb5Si3 eutectic alloys, consisting of a ductile metallic phase and a hard intermetallic phase, are attractive candidates to replace Ni-based superalloys. The microstructure and mechanical properties of these in-situ composites are widely investigated. However, little work is focused on crystallography of in-situ composites, except for preferred growth direction and crystallographic orientation relationship.

In this paper, Nb-Si-Mo-based alloys were fabricated by non-consumable arc melting, and then were directionally solidified in an optical floating zone (OFZ) melting furnace. The crystallographic orientation evolutions in Nb-Nb5Si3 eutectic alloy are studied by electron back-scattered diffraction (EBSD) analyses. First, the effect of solidification condition on crystallographic orientation is examined. The as-cast alloy displays cellular microstructure. The Nb phase shows different crystallographic orientations in different cells, while the Nb5Si3 phase shows similar crystallographic orientation in a number of cells. In directionally solidified alloys, when growth rate is 5mm/h without seed rod rotation, the grain sizes of Nb and Nb5Si3 are both several millimeter. As growth rate rises or seed rod rotates, the grain size of Nb decreases much more drastically than that of Nb5Si3. Thus, solidification condition is supposed to influence nucleation of the Nb phase rather than the Nb5Si3 phase. Second, the effect of annealing on crystallographic orientation is studied. The Nb5Si3 has three allotropic phases. The allotropic phase transformations occur through annealing, during which the Nb5Si3 grain size decreases.
Investigation of Turbine Cascade Blades With Part-Span Sweep With an Open End
Authors: Trehan Rachel , Roy Bhaskar
Published: November 2013

The present paper focuses on a low-speed computational investigation into the application of backward sweep for application on a typical low-pressure turbine rotor blade. A quasi-two-dimensional linear cascade using T106 profile, was investigated using flow solver Star-CCM+®. Three backward-swept tip modifications (axial sweep, tangential sweep, and a combination of both) have been applied to the baseline profile from 90%–100% span, the rest of the 90% of the blade remained straight and orthogonal to the cascade mainstream flow. The blade stacking axis near the tip was shifted away from the mainstream flow for all three sweep configurations at 15°, 30°, and 45° from the blade axis plane. The impact on pressure losses, tip blade loading, and reduction of tip leakage flow and associated vortices has been analyzed. As the leakage vortex increases in size, causing enhanced blockage to the passage flow, rotor work extraction capability decreases. The application of backward sweep to the blade tip increases the tip cross flow rate, but reduces the turbulent kinetic energy (TKE) across the tip gap. The reduction of TKE of the leakage flow, results in a smaller and less intense tip leakage vortex even though the cross flow rate increases. Minimizing the leakage vortex size and intensity reduces total pressure losses and thereby improves rotor efficiency.
Conjugate Heat Transfer CFD Predictions of Impingement Jet Array Flat Wall Cooling Aerodynamics With Single Sided Flow Exit
Authors: El-Jummah Abubakar M. , Andrews Gordon E. , Staggs John E. J.
Published: November 2013

Conjugate heat transfer CFD studies were undertaken on impingement square jet arrays with self induced crossflow in the impingement gap with a single sided exit. The aim was to understand the aerodynamic interactions that result in the deterioration of heat transfer with axial distance, whereas the addition of duct flow heat transfer would be expected to lead to an increase in heat transfer with axial distance. A square array of impingement holes was investigated for a common geometry investigated experimentally, pitch to diameter ratio X/D of 5 and impingement gap to diameter ratio Z/D of 3.3 for 11 rows of holes in the crossflow direction. A metal duct wall was used as the impingement surface with an applied heat flux of 100kW/m2, which for a gas turbine combustor cooling application operating at steady state with a temperature difference of ∼450K corresponds to a convective heat transfer coefficient of ∼200 W/m2K. A key feature of the predicted aerodynamics was recirculation in the plane of the impingement jets normal to the cross-flow, which produced heating of the impingement jet wall. This reverse flow jet was deflected by the cross flow which had its peak velocity in the plane between the high velocity impingement jets. The cross-flow interaction with the impingement jets reduced the interaction between the jets on the surface, with lower surface turbulence as a result and this reduced the surface convective heat transfer. A significant feature of the predictions was the interaction of the cross-flow aerodynamics with the impingement jet wall and associated heat transfer to that wall. The results showed that the deterioration in heat transfer with axial distance was well predicted, together with predictions of the impingement wall surface temperature gradients.
Effect of Dome Geometry on Swirling Flow Field Characteristics of a Counter-Rotating Radial-Radial Swirler
Authors: Kao Yi-Huan , Tambe Samir B. , Jeng San-Mou
Published: November 2013

An experimental study has been conducted to study the effect of the dome geometry on the aerodynamic characteristics of a non-reacting flow field. The flow was generated by a counter-rotating radial-radial swirler consisting of an inner, primary swirler generating counter-clockwise rotation and an outer, secondary swirler generating clockwise rotation. The dome geometry was modified by introducing dome expansion angles of 60° and 45° with respect to the swirler centerline, in addition to the baseline case of sudden expansion (90°). The flow downstream of the swirler is confined by a 50.8mm × 50.8mm × 304.8mm (2″ × 2″ × 12″) plexiglass chamber. A two-component laser doppler velocimetry (LDV) system was used to measure the velocities in the flow field. The dome geometry is seen to have a clear impact on mean swirling flow structure near the swirler exit rather than the downstream flow field. For the configurations with 60° and 45° expansion, no corner recirculation zone is observed and the swirling flow structure is asymmetric due to the non-axisymmetric dome geometry. The cross-section area of central recirculation zone is larger for dome geometry with 60° expansion angle, as compared to the 90° and 45° cases. The configurations with 60° and 45° expansion have higher magnitudes of negative velocity inside the core of central recirculation zone, as compared to the configuration with 90° expansion angle.
Effect of Chamber Length With Converging Exhaust on Swirling Flow Field Characteristics of a Counter-Rotating Radial-Radial Swirler
Authors: Kao Yi-Huan , Tambe Samir B. , Jeng San-Mou
Published: November 2013

An experimental study has been conducted to examine the effect of chamber length on the aerodynamic characteristics of an enclosed, non-reacting, swirling, flow field. The swirling flow was generated by a counter-rotating radial-radial swirler consisting of an inner, primary swirler generating counter-clockwise rotation and an outer, secondary swirler generating clockwise rotation. The enclosures used were square cross-section chambers of differing lengths. The internal cross section of all chambers was 50.8 mm × 50.8 mm (2 inch × 2 inch). 3 different lengths of chamber used for the tests were 76.2 mm (3″), 101.6 mm (4″), and 152.4 mm (6″) respectively. A nozzle was used at the downstream end of the enclosure to ensure the absence of reverse flow back to test chamber and to simulate the area reduction in typical combustor. The nozzle reduced the cross-section area from 50.8 mm × 50.8 mm (2″ × 2″) to 22.2 mm × 22.2 mm (0.875″ × 0.875″) via 45° slope. A two-component laser doppler velocimetry (LDV) system was used to measure the velocities in the flow fields. The chamber length has been observed to have a clear influence on the mean and turbulent velocity profile near the exit of swirler. However, this effect is not as evident further downstream in the flow field. For the short chamber length, higher values of axial and tangential velocities were observed in the swirling jet due to the proximity of the downstream nozzle to the swirler. For this chamber length, higher turbulence intensities were observed in the swirling jet and inside center toroidal recirculation zone. The magnitudes of the swirling jet velocity and the turbulence intensities decreased with an increase in the chamber length. Two counter-rotating flows could merge more complete in the exit of swirler with the chamber length decreasing.
Experimental Investigations on Aero-Thermal Interaction of Film Cooling Air Ejected From Multiple Shallow Angle Cooling Holes: Effect of Freestream Turbulence
Authors: Abdullah Kamil , Funazaki Ken-ichi
Published: November 2013

The objective of the present study is to investigate the aero-thermal interaction of the secondary air injected from multiple shallow angled film cooling holes. The focus is on the influence of freestream turbulence on the film cooling effectiveness and secondary flow field. For the experiments, infrared thermography and Laser Doppler Velocimetry (LDV) were employed. The experiments were conducted at a Reynolds number based on the hole diameter, ReD = 6200 at blowing ratio, BR = 1.0 and 2.0. Two flat plate test models; TMA and TMG, have been considered, which involved twenty cylindrical holes constituting a matrix composed of four rows with five holes in each row. The cooling holes for both test models were inclined at 20° in the streamwise direction with the lateral pitch, Pz = 6D for TMA and 3D for TMG. Two different freestream turbulence levels have been considered for both the aerodynamic and thermal investigations. The results of LDV show two distinct dynamics for each test model which influence the flow field differently. Consequently, the thermal field produced a distinctive film cooling effectiveness distribution of each test model. Higher freestream turbulence level enhances the mixing in the vicinity of the vortical structure thus deterring the film cooling effectiveness just downstream of the cooling hole but aids to lateral spreading of the coolant further downstream of the cooling hole, providing greater film effectiveness coverage.
Research of Vortex Tube Energy Separation
Authors: Sun Wen-long , Fang Xiang-jun , Eri Qi-tai , Wang Wen-chuan
Published: November 2013

Since the vortex tube was invented, a variety of theoretical explanations were proposed to reveal the process and mechanism of energy separation in it. With simple structure but complex flows, it was hard to solve the two problems. Comparisons of the numerical simulations and experiments under different cold mass fractions (μc) in the vortex tube were made in this paper. The trend of numerical simulations was convinced by analyzing the experimental data. The radial and axial distributions of three types of gas flows and the contours of temperature and pressure were obtained from the calculation results under different μc. The key factor affecting the energy separation in the vortex tube was found and the explanation of energy separation process in the vortex tube was proposed by analyzing the results. The analysis showed that the energy separation was deeply related to the exchange of velocity. At last, the explanation was validated by the simulations with the change of throat area in the nozzles.
Waste Tire Rubber Gasification Using Air Steam for Partial Oxidation and N2 as Carrier Gas
Authors: Sánchez Daniel , Paez Miguel , Sierra Rocío , Gordillo Gerardo
Published: November 2013

The high calorific value of rubber in waste tires (RWT) and its composition, similar to that of coal, make it a promising resource for thermal treatment. This paper assesses the potential of RWT for the production of syngas through thermal gasification using air and steam as oxidizing agents. Subsequent purification of the obtained syngas and its conversion to ammonia were also evaluated. The analysis started by grinding RWT samples and submitting them to thermogravimetric analysis (TGA), ultimate analysis (UA) and proximate analyses (PA). Through TGA data, a pyrolysis Activation Energy of 110.5 KJ mol−1 was determined using isoconversional methods. The results from UA and PA were used to estimate empirical formulae, high heating value (HHV), and formation enthalpy. These data were entered in the simulation package ASPEN Plus® where a sensitivity analysis was carried out using the following models: RGibbs (for equilibrium reactions) and Non-Random Two Liquids (NRTL) coupled with UNIFAC for phase equilibrium calculations. As a result, the effects of equivalence ratio (ER) and steam to fuel ratio (W:F) on adiabatic temperature, gas composition, and energy recovery were determined. It was shown that W:F lower than 0.6 should be used, since the additional water shifted equilibrium towards oxidation of syngas components. Additionally, an ER range from 3.0 to 5.5 should be selected due to the presence of maximum values for both concentration and syngas output molar flow. Optimal operation conditions were estimated around an ER of 4.0 and a W:F of 0.5. Further simulation considered purification of the gas stream from gasification and its conversion to pure sulfur and ammonia. The purification plant, a selexol-based SOx and COx absorption, produced two streams: gas and liquid. The gas stream (containing mainly H2, CO, traces of produced hydrocarbons, some CO2 and N2 from air) entered a Water Gas Shift (WGS) unit. The liquid stream (containing the solvent that carries H2S, CO2 and SO2) was distilled to recover selexol. The gas resulting from this distillation, was entered to a Catalytic Claus reactor to recover elemental sulfur. As a result, 16.6 kg h−1 of pure sulfur (which constitutes approximately 88% of the sulfur pollutants in RWT) was recovered. The N2-H2 mixture exiting the WGS was fed to a Haber Botch where 1552 kg h−1 of ammonia were obtained from an initial 1250 kg h−1 RWT feed. This study was concluded with a cost analysis which led to calculate a cost of 0.19 USD$/MT of ammonia produced through this innovative route that uses RWT rubber as feedstock.
Effects of Jet Diameter and Surface Roughness on Internal Cooling With Single Array of Jets
Authors: Miller Nicholas , Siw Sin Chien , Chyu Minking K. , Alvin Mary Anne
Published: November 2013

The current study focused on the effects of varying jet diameter and surface roughness on the target plate from jet impingement. A single row of five jets, plenum fed, expels air onto the flat target surface and the spent air is constrained to exit in only one direction, causing the jets to encounter maximum cross-flow. Baseline jet plates were equipped with pressure taps, one for each jet, to determine flow. The initial parameters, diameter D, height to diameter H/D, and jet spacing to diameter S/D is 9.53 mm (0.375 in), 2 and 4 respectively. Upon defining the optimum array of jet diameters, three test cases will be conducted using different surface features, 90 degree ribs, chevrons and X-shaped ribs on the target plate to further enhance the heat transfer performance of the jet impingement. The parameters, width W and height H, for the surface features will be set constant at 3.18 mm (0.125 in). The Reynolds number, Re, in this experimental study ranged from 50,000 to 80,000. A transient liquid crystal technique is employed in this study to determine the local and average heat transfer coefficient distribution on the target plate. The baseline tests revealed that the heat transfer is more predominate in the upstream jets impingement zones, however, by varying the diameters the heat transfer is more uniformly distributed downstream. The results also revealed that the rib-turbulators, especially X-shaped ribs, can further enhance heat transfer enhancement in the downstream jets where crossflow can affect impingement.
Effect of Rotation on Heat Transfer of a Concave Surface With Array Impingement Jet
Authors: Jung Eui Yeop , Park Chan Ung , Lee Dong Hyun , Park Jun Su , Park Sehjin , Cho Hyung Hee
Published: November 2013

Turbine blades are directly exposed to hot oncoming combustion gases, so their leading edges require effective cooling techniques. Here, we investigated the heat transfer characteristics in a concave duct with an array of impingement jets, including the effect of rotation. The concave duct was used to simulate the inner surface of the leading edge of a blade. The inner surface was cooled by the impingement array jet method. The jet Reynolds number (Re) based on the jet nozzle diameter was fixed at 3,000, and the ratio of the height to target surface (H/d) was set to 2.0. The injection holes (d = 5 mm) were positioned in a staggered pattern, and the rotation number was about 0.032. We focused on the effects of rotating position orientations. We investigated front, leading, and trailing orientations. Naphthalene sublimation method was used to determine the local heat/mass transfer distributions, and the flow pattern was obtained by numerical simulation. Crossflow in the jet arrays was generated by the spent air from the impingement jet. The crossflow changes the flow characteristics at the stagnation point along the streamwise direction on a concave surface. Rotation of the duct increased the flow mixing compared with the stationary case. The jet flow was deflected because of the Coriolis force in the leading and trailing orientations. However, in the front orientation, the heat transfer characteristics showed deflection in the clockwise direction in the developing flow away from the stagnation point. Overall, the averaged heat transfer values were enhanced in the rotating cases. The trailing orientation case showed the highest averaged heat transfer among all tested cases.
Validation of Flow Field and Heat Transfer in a Two-Pass Internal Cooling Channel Using Different Turbulence Models
Authors: Farisco Federica , Rochhausen Stefan , Korkmaz Metin , Schroll Michael
Published: November 2013

In this work the flow regime within a generic turbine cooling system is investigated numerically. The main objective is to validate the performance of various turbulence models with different complexity by comparing the numerical results with experimental data. To maximize surface heat transfer rates, present-day cooling systems of high pressure turbines have highly complex shapes generating high turbulence levels and flow separations. These flow structures lead to higher requirements of CFD-techniques for sufficient prediction. To simulate complex flows in the industrial design process, Reynolds averaged Navier-Stokes (RANS) techniques are applied instead of computationally expensive LES and DNS simulations. Therefore, higher order turbulence models are necessary to predict flow field and heat transfer performance in such complex motion. The DLR standard flow solver for turbomachinery flows, TRACE, is used to solve the RANS equations. Four turbulence models have been analysed: the one equation model of Spalart and Allmaras, the two equation k – ω model of Wilcox, the two equation k – ω SST model of Menter and the anisotropy resolving Explicit Algebraic Reynolds Stress model (EARSM) of Hellsten. The investigated cooling geometry consists of a two-pass smooth channel with a 180 degree bend. At the DLR institute of propulsion technology PIV measurements in a rotating cooling channel test bed for Rotation numbers up to 0.1 have been performed. This work uses the experimental data for Re = 50,000 and Ro = 0 without rotation for comparison. For all models adiabatic and diabatic calculations have been performed. In order to accurately apply the turbulence models, a study concerning the turbulent boundary conditions has been performed prior to the calculations. The results obtained through RANS simulations are presented in comparison with the experiments along planes in the flow direction and in the orthogonal direction to study the velocity field, the shape and size of the separation bubbles and the wall shear stress. The EARSM predicts the flow field overall more accurately with improved agreement between all relevant parameters compared to the other models. The diabatic simulations reflect the adiabatic results. However, it can be noticed that higher complexity in turbulence modelling is related to increased heat transfer. Our work confirms the EARSMs ability to predict complex flow structures better than the more elementary approaches.
Multi-Disciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine
Authors: Kyprianidis Konstantinos G. , Rolt Andrew M. , Grönstedt Tomas
Published: November 2013

Reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. Thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyse the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption.

With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio just below 1.2 at hot-day top of climb conditions. At ISA mid-cruise conditions a specific thrust of 86m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 55% and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines.

The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions primarily because this design variable affects core efficiency at mid-cruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. Analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor account for losses in the bypass duct and jet pipe, whilst a relatively detailed engine performance model such as the one utilised in this study does.

Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberised-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilised to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.
Numerical Investigation of the 3D Flow Field in a Steam Turbine Axial Exhaust Diffuser: Comparison With Experimental Data and Performance Evaluation
Authors: Daccà Federico , Canelli Claudio , Cecchi Stefano
Published: November 2013

The purpose of this paper is to present a numerical analysis carried out for the performance evaluation of the axial exhaust diffuser of a LP steam turbine. A set of measured data in an actual real scale steam turbine is available for direct comparison. The three dimensional exhaust flow in a LP steam turbine provided with a 48″ LSB is numerically investigated in different real working conditions by means of 3D CFD analysis. A detailed 3D model of the actual geometry is used in order to catch the highly 3D features of the flow field, avoiding the use of numerical periodicity conditions. Boundary conditions are derived both from experimental data and from specific validated 3D simulations of the main flow of the entire LP turbine section from front stages up to the LSN. The comparison with measured data allows to validate the performed CFD simulations and to provide a reliable complete performance curve of the exhaust diffuser geometry coupled with the 48″ LSB design. An important outcome of the work consists also in a generalized method for accurate performance evaluation of axial diffusers.
Strengthening of an Al-Containing Austenitic Stainless Steel at High Temperature
Authors: Dong Xianping , Zhao Lin , Sun Feng , Zhang Lanting
Published: November 2013

Three Al-containing austenitic steels with slightly different contents of Nb, V and C in the Fe-19.95Ni-14.19Cr-2.25Al-2.46Mo-1.95Mn-0.15Si-0.01B (wt.%) system were designed to study the effect of precipitations on creep/rupture resistance. After induction melting, alloys were cast into a metal mold followed by thermo-mechanical treatment. A continuous Al-rich oxide scale was formed on the surface after exposure at 800°C for 146 hrs in air. By decreasing the C content from 0.07 to 0.04%, coarse NbC precipitates in the as-cast microstructure could be removed during annealing treatment. Thermo-mechanical treatment enabled nano-scale precipitation of NbC in the alloys containing 0.04% C. Although the yield strength of the alloy with 0.07% C was relatively high at 750°C, its creep/rupture life was 164 hrs at 700°C/150 MPa. Alloys having low carbon content formed a uniform fine MC precipitation around 10–20 nm and showed a creep/rupture life between 1002 and 1530 hrs at 700°C/150 MPa. This is comparable with that of super304H tested under the same condition. Fe2(Mo,Nb) Laves phase was found in the microstructure after creep/rupture testing. NiAl precipitated in alloys after creep/rupture testing for more than 1000 hrs. However, strengthening effect from these two phases is not obvious, indicating that nano-scale NbC precipitates are the major source of strengthening during creep/rupture at high temperature. In addition, nano-scale (Nb,V)C was found in V containing alloy corresponding to the longest creep/rupture life.
Development of an Annular Combustor Chamber
Authors: Ruedel Uwe , Trbojevic Bogdan , Benz Urs , Zajadatz Martin , Doebbeling Klaus
Published: November 2013

To accommodate the customer’s expectations for operational flexibility and low power generation costs, a gas turbine has to be robust, flexible and cost effective. Since its introduction in 1993 and with its more than 7.5 million operating hours and over 54’000 starts, the GT13E2 gas turbine has already demonstrated to be a most flexible and reliable engine. It is being used in connection with many different applications, and meets a very broad range of environment and operation conditions. The GT13E2 upgrade 2012 described in this paper further improves these capabilities.

The next generation of GT13E2 combustors is improved for increased lifetime, reduced total life cycle cost and implementation of a low emission dual fuel AEV burner system. The basic design philosophy for the lifetime improvement is adapted from the well-proven GT24 and GT26 annular combustors. The liner segments represent Alstom’s proven technology of sealed TBC coated metallic combustor liners that can expand in their fixations. The application of a thermal barrier coating onto the segments is simple and cost-effective. The design is robust so that the liners have to be checked only at major inspections and are not subject to reconditioning/replacement at hot gas part inspections. The closed-loop cooling arrangement is used for the backside cooling of the hot gas liner segments and to maintain the large structural components at a constant temperature. This combustion segment improvement is combined with the AEV (Advanced EnVironmental) burner. All the mentioned features result in a marked improvement of the operating and cyclic lifetime of the GT13E2 combustor.

This paper describes the development and validation process for the implementation of the combustion liner segment technology of the GT13E2. The various design phases from concept development to validation including the generic tests and final engine implementation are described and substantiated.
Fuel Flexibility at Ignition Conditions for Industrial Gas Turbines
Authors: Larsson Anders , Berg Anton , Bonaldo Alessio
Published: November 2013

The variety of gaseous fuels that Siemens Industrial Turbomachinery (SIT) is requested to consider during sales enquiries has prompted product development projects that have allowed to continuously increase gas turbine fuel flexibility. The fuel flexibility often has to be guaranteed at all engine load conditions including ignition. The gas turbine ignition capabilities have therefore been analyzed in order to assess the engines current capabilities and identify further potentials.

The authors’ approach for ignition fuel flexibility has been to model the minimum ignition energy (MIE) required for successful ignition and to validate the model by experiments conducted under test conditions reproducing engine start up flows at a combustion test rig. The experiments were performed using two hydrocarbon gases individually mixed with two inert gases at various concentrations. The mathematical model predicting the minimum ignition energy is applicable also to hydrocarbon and inert gases mixtures that were not used during the experimental campaign. The model was studied and developed in order to produce a tool for support of gas fuel enquiries received during the sales phase.

In accordance to the predictions of the mathematical model, the experimental validation in the paper shows that the difference in MIE required to ignite the gas fuel composition depends on the inert gas used as well as the hydrocarbon used. The MIE model showed the capability of assessing if a specific gas composition can be used as a reliable start-up fuel.
Experimental and Numerical Characterization of the Methyl Decanoate Combustion in Laminar Counterflow Spray Premixed Flames
Authors: Alviso D. , Scouflaire P. , Lacoste D. , Darabiha N. , Rolon J. C.
Published: November 2013

Biodiesel is a mixture of long chain fatty acid methyl esters used mainly in compression ignition engines. In order to improve engine performance, an understanding of its fundamental properties and the combustion pathways is required. A surrogate fuel: methyl decanoate (MD) is used in order to simplify the models and experiments. This study presents new data for MD combustion in a laminar counterflow premixed flame configuration (spray MD/air against methane/air) at atmospheric pressure, for different strain rate and equivalence ratio conditions. The visible and UV chemiluminescence of the excited radicals CH* (A2Δ) and OH* (A2Σ+) as well as Planar Laser-Induced Fluorescence (PLIF) of OH are employed experimentally to analyze the flame structure. The counterflow spray flame is simulated by choosing a MD skeletal reaction mechanism, to which we add CH* and OH* reactions. The numerical predictions of the CH* concentration are very close to the experimental profiles along the central axis. The numerical and experimental results indicate differences in the OH* production routes between MD and methane flames.
Experimental Evaluation of Service-Exposed Nozzle Guide Vane Damage in a Rolls Royce A-250 Gas Turbine
Authors: Bouchard D. , Asghar A. , LaViolette M. , Allan W. D. E. , Woodason R.
Published: November 2013

A unique methodology and test rig was designed to evaluate the degradation of damaged Nozzle Guide Vanes in a transonic annular cascade in the short duration facility at the Royal Military College. A custom test section was designed which featured a novel rotating instrumentation suite. This permitted 360° multi-span traverse measurements downstream of unmodified turbine NGV rings from a Rolls-Royce/Allison A-250 turbo-shaft engine. Downstream total pressure was measured at four span-wise locations on both an undamaged reference and a damaged test article. Three performance metrics were developed in an effort to determine characteristic signatures for common operational damage such as trailing edge bends or cracked trailing edges. The highest average losses were observed in the root area, while the lowest occurred closer to the NGV tips. The results from this study indicated that multiple span-wise traverses were required to detect localized trailing edge damage. Recommendations have been made for future tests, for test rigs and for ideas to develop performance metrics.
Damage Detection and Tensile Performance of Various SiC/SiC Composites Impacted With High Speed Projectile
Authors: Morscher Gregory N. , Baker Christopher , Gyekenyesi Andrew , Faucett Calvin , Choi Sung
Published: November 2013

Implementation of ceramic matrix composites (CMCs) in jet engine applications necessitates the understanding of high velocity impact behavior. To this end, various melt-infiltrated SiC/SiC composites were impacted at room temperature at ∼350 m/s with different support systems and tensile tested to failure. Non-Destructive techniques including electrical resistance (ER) and flash thermography were used to examine the specimen pre and post impact. Some specimens were then post-tested in order to assess retained properties. For post tested specimens acoustic emission was used to monitor damage accumulation during the post test and leading up to ultimate failure. Microscopy was performed to correlate damage with impact and post-impact applied stress. The properties of the impacted specimens were assessed based on relevant damage zones. The results are also compared with similar studies performed on similar composites with stress-concentrators such as holes or notches and post-impact specimens tested in bending.
Investigation of a Radial-Inflow Bleed as a Potential for Compressor Clearance Control
Authors: Atkins N. R.
Published: November 2013

The mismatch in thermal response between a High Pressure Compressor (HPC) drum and casing is a limiting factor in the reduction of compressor clearance. An experimental test rig has been used to demonstrate the concept of radial inflow to reduce the thermal time constant of HPC discs. The testing uses a simulated idle - Maximum Take Off (MTO) - idle transient in order to measure the thermal response directly. The testing is fully scaled in the dimensionless sense to engine conditions. A simple closure model based on lumped capacitance is used to illustrate the scope of potential benefits. The proof-of-concept testing shows that HPC disc time constant reductions of the order 2 are feasible with a radial-inflow bleed of only 4% of bore flow at scaled MTO conditions. Using the experimental results, the simple closure modelling suggests that for a stage with a significant mismatch in thermal response, reductions in 2D axis-symmetric clearance of as much as 50% at MTO conditions may be possible along with significant scope for improvements at cruise conditions.
Aeroengine High Pressure Turbine Blade Cooling System Concept
Authors: Riznyk S. , Artushenko A.
Published: November 2013

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

Methodology of effective HPT blade cooling system design, numerical and experimental investigations are described in the article.

Different HPT cooling systems are considered: internal convective “serpentine” schemes with ribs in channels and wall-cooled system. Two types of film cooling channels (round and shaped) are used in HPT blade cooling systems design.

The role of thermal barrier coating is described.

Experimental test rig was designed and manufactured to define the heat transfer coefficients and hydraulic parameters for HPT blade with wall-cooled system cooling channels. The results obtained on this test rig were used to determine boundary conditions and temperature fields in advanced HPT blade with wall-cooled cooling system.

Numerical and experimental results obtained in HPT blade cooling system research are presented in the article.
Traversing Hot-Jet Ignition in a Constant-Volume Combustor
Authors: Karimi Abdullah , Rajagopal Manikanda , Nalim Razi
Published: November 2013

Hot-jet ignition of a combustible mixture has application in IC engines, detonation initiation, and wave rotor combustion. Numerical predictions are made for ignition of combustible mixtures using a traversing jet of chemically active gas at one end of a long constant-volume combustor (CVC) with aspect ratio similar to a wave rotor channel. The CVC initially contains a stoichiometric mixture of ethylene or methane at atmospheric conditions. The traversing jet issues from a rotating pre-chamber that generates gaseous combustion products, assumed at chemical equilibrium for estimating major species. Turbulent combustion uses a hybrid eddy-break-up model with detailed finite-rate kinetics and a two-equation k-ω model. The confined jet is observed to behave initially as a wall jet and later as a wall-impinging jet. The jet evolution, vortex structure and mixing behavior are significantly different for traversing jets, stationary centered jets, and near-wall jets. Pressure waves in the CVC chamber affect ignition through flame vorticity generation and compression. The jet and ignition behavior are compared with high-speed video images from a prior experiment. Production of unstable intermediate species like C2H4 and CH3 appears to depend significantly on the initial jet location while relatively stable species like OH are less sensitive.