bluuebunny/crossref_metadata_2025 huggingface dataset:
Endwall Heat Transfer for a Turbine Blade With an Upstream Cavity and Rim Seal Leakage
Authors: Lynch Stephen P. , Thole Karen A. , Kohli Atul , Lehane Christopher , Praisner Tom
Published: November 2013

Aerodynamic loss and endwall heat transfer for a turbine blade are influenced by complex vortical flows that are generated at the airfoil-endwall junction. In an engine, those flows interact with clearance gaps between stationary and rotating components, as well as with leakage flow that is designed to exhaust through the gaps. This paper describes experimental measurements of endwall heat transfer for a high-pressure turbine blade with an endwall overlap geometry, as well as an upstream leakage feature that supplied swirled or unswirled leakage relative to the blade. For unswirled leakage, increasing its mass flow increased the magnitude and pitchwise uniformity of the heat transfer coefficient upstream of the blades although heat transfer further into the passage was unchanged. Leakage flow with swirl shifted the horseshoe vortex in the direction of swirl and increased heat transfer on the upstream blade endwall, as compared to unswirled leakage. For a nominal leakage mass flow ratio of 0.75%, swirled leakage did not increase area-averaged heat transfer relative to unswirled leakage. At a mass flow ratio of 1.0%, however, swirled leakage increased overall heat transfer by 4% due to an increase in the strength of the vortical flows.
Characterizing Combustion of Synthetic and Conventional Fuels in a Toroidal Well Stirred Reactor
Authors: Vijlee Shazib Z. , Kramlich John C. , Mescher Ann M. , Stouffer Scott D. , O’Neil-Abels Alanna R.
Published: November 2013

The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of the performance envelopes and emissions characteristics relative to the behavior of conventional fuels. In this study, experiments in a toroidal well-stirred reactor (TWSR) are used to study lean premixed combustion temperature and extinction behavior for several fuels including simple alkanes, synthetic jet fuels, and conventional JP8. A perfectly stirred reactor (PSR) model is used to interpret the observed behavior.

The first portion of the study deals with jet fuels and synthetic jet fuels with varying concentrations of added aromatic compounds. Synthetic fuels contain little or no natural aromatic species, so aromatic compounds are added to the fuel because fuel system seals require these species to function properly. The liquid fuels are prevaporized and premixed before being burned in the TWSR. Air flow is held constant to keep the reactor loading roughly constant. Temperature is monitored inside the reactor as the fuel flow rate is slowly lowered until extinction occurs. The extinction point is defined by both its equivalence ratio and temperature. The measured blowout point is very similar for all four synthetic fuels and the baseline JP8 at aromatic concentrations of up to 20% by volume. Since blowout is essentially the same for all the base fuels at low aromatic concentrations, a single fuel was used to test the effect of aromatic concentrations from 0 to 100%. PSR models of these complex fuels show the expected result that behavior diverges from an ideal, perfectly premixed model as the combustion approaches extinction.

The second portion of this study deals with lean premixed combustion of simple gaseous alkanes (methane, ethane, and propane) in the same TWSR. These simpler fuels were tested for extinction in a similar manner to the complex fuels, and behavior was characterized similarly. Once again, PSR models show that the TWSR behaves similar to a PSR during stable combustion far from blowout, but as it approaches blowout and becomes less stable a single PSR no longer accurately describes the TWSR.

This work is a step towards developing chemical reactor networks (CRNs) based on computational fluid dynamics (CFD) of the simple gaseous fuels in the TWSR. Ultimately, CRNs are the only realistic way to accurately perform detailed chemical modeling of the combustion of complex liquid fuels.
Heat Transfer Characteristics of a Blade Trailing Edge With Pressure Side Bleed Extraction
Authors: Saxer-Felici H. , Naik S. , Gritsch M.
Published: November 2013

This paper investigates the heat transfer and pressure loss characteristic in the internal cooling system of the trailing edge of a gas turbine blade. The geometrical profile of the blade trailing edge and the operating conditions considered are representative of that normally found in a heavy-duty gas turbine. The trailing edge geometry consists of two radial passages with inclined turbulators which are connected with a bend. The trailing edge section consists of pins rows and a flow ejection cut-out slot. The impact of a cross-over hole in the web connecting the serpentine passages is also investigated.

Both numerical and experimental studies were conducted at several passage Reynolds numbers ranging from 104 to 106. Experiments were conducted in a Perspex model at atmospheric conditions. The internal heat transfer coefficients were measured via the transient liquid crystal method and the pressure drop was measured via pressure taps. The impact of blade rotation on the heat transfer and pressure drop was also assessed numerically.

Comparison of the measured and predicted heat transfer coefficients and pressure drops shows a good agreement for several flow conditions. The three-dimensional flow field in the passage and in the downstream pin banks was well captured numerically, with and without coolant injection via cross-over hole.
A Simplified Model to Assess the Influence of Load Ramps on the Durability of Hot Gas Path Components in Heavy-Duty Gas Turbines
Authors: Ramaglia Alessandro D. , Bozzi Luca
Published: November 2013

According to current trends in the energy market, heavy duty gas turbines are increasingly being used to fill gaps in the power energy supply and are less frequently operated in pure steady-state base load conditions. This tendency implies more rapid load ramps and is confirmed by utilities’ requirements for more operational flexibility in order to increase their net revenues. In order to assess the effects of such load variations on temperature gradients withstood by the various components, a series of simple correlations are derived that take in account key operating parameters of gas turbines. To this end, each blade and vane has been schematized as a compound of different portions to which specific values of cooling efficiency and gas temperature were assigned. This results in a simplified model of the engine allowing for the prediction of the temperature gradients on the base material of the critical zones of blades and vanes as a function of different cooling schemes. Method results can subsequently be exploited both to improve thermal design of hot gas path components, as well as to set up material testing campaigns targeting any specific duty cycle.
Integrated HPC OGV and Pre-Diffuser Design Optimization Using Kriging Surrogate Model
Authors: Wang Hongtao , Xie Weiliang , Chen Meining
Published: November 2013

The integration of high compressor outlet guide vane (OGV) and combustor pre-diffuser requires some radial turning to be performed within the OGV passage. However, the enhanced loading of OGV leads to the increase in adverse pressure gradient within the OGV passage. Consequently, both the end-wall and blade boundary layers are thickened which could lead to boundary layers separation. In this work, an adaptive global optimization process is applied for the OGV/pre-diffuser system, which combines design of experiment (DOE), Kriging surrogate model and micro genetic algorithm. The meridional flow passage of OGV/pre-diffuser system is parameterized using Bezier curves with the combination of mean line and thickness distribution. In order to prevent the OGV corner separation, the bowed design is applied to the OGV to help delay flow separation. A composite curve combined with two straight lines and a conic Bezier curve is used to represent the OGV stacking line along circumference so that the bowed blades could be parameterized. Aerodynamic performance evaluations of the compressor are performed using a three dimensional Reynolds-averaged Navier-stokes computational fluid dynamics solver — NUMECA. In the optimization process, expected improvement sample criteria is adopted for balancing the exploration and exploitation with Kriging surrogate model. Reasonably high performance is confirmed by comparing the baseline and optimal designs. This study gives some insights into design optimization of an integrated OGV/Pre-diffuser for axial compressor.
Numerical Analysis of Effusion Plates for Combustor Liners Cooling With Varying Density Ratio
Authors: Andrei L. , Andreini A. , Bianchini C. , Facchini B. , Mazzei L.
Published: November 2013

Effusion cooling technology has been assessed in past years as one of the most efficient methods to maintain allowable working temperature of combustor liners. Despite many efforts reported in literature to characterize the cooling performances of those devices, detailed analysis of the mixing process between coolant and hot gas are difficult to perform especially in case superposition and density ratio effects become important. Furthermore, recent investigations on the acoustic properties of these perforations pointed out the challenge to maintain optimal cooling performance also with orthogonal holes which showed higher sound absorption.

This paper performs a CFD analysis of the flow and thermal field associated with adiabatic wall conditions to compute the cooling effectiveness. The geometry consists of an effusion cooling plate drilled with 18 holes and fed separately with a cold and hot gas flow. Two types of perforations equivalent in porosity and pitches are investigated to assess the influence of the drilling angle between 30 and 90 deg. The reference conditions considered in this work comprehend an effective blowing ratio ranging between 1 and 3 at isothermal conditions (reaching a maximum hole Reynolds number of 10000) and high inlet turbulence intensity (17%). This set of conditions was exploited to perform a validation of the numerical procedure against detailed experimental data presented in another paper. Inlet turbulence effects highlighted by measurements for the slanted perforation were also investigated simulating a low turbulence condition corresponding to 1.6% of intensity. Furthermore the nominal DR = 1.0 was increased up to 1.7 to expand the available data set towards typical working conditions for aero-engines.

Steady state RANS calculations were performed with the commercial code ANSYS® CFX, modeling turbulence by means of the k — ω SST. In order to include anisotropic diffusion effects due to turbulence damping in the near wall region, the turbulence model is corrected considering a tensorial definition of the eddy viscosity with an algebraic correction to dope its stream-span components. Computational grids were finely clustered close to the main plate and inside the holes to obtain y+ < 1, to maximize solver accuracy according to previous similar analysis.
The Role of Rotor Welding Design in Meeting Future Market Requirements
Authors: Kern T.-U. , Almstedt H. , Thiemann Th. , Brussk S. , Niepold K.
Published: November 2013

The demand for current and future steam turbine components is driven by higher efficiency but also by higher plant cycling needs and optimized cost balance. An increase in efficiency increases the demand for higher life steam temperatures of up to 620/630°C for today’s units and of even up to 720°C for future steam power plants. The gap between required material properties in the hot and cold running parts of a steam turbine rotor is widened by the increased live steam temperatures and the increased demand for flexibility and adaptability to current and expected future energy market conditions. Besides further material development, welding is one measure to realize such contradictory rotor characteristics. Whereas 720°C is more a future related task, solutions for 560°C / 620°C apply already welded rotors.

The paper discusses from a perspective of a steam turbine manufacturer the technical features to enable flexible high efficient rotor components with a focus on advanced welding technologies suitable for different large steam turbine components and what further steps for new welding technologies are under way.
Foreign Object Damage (FOD) of Ceramic Thermal Barrier Coatings (TBCs) in Gas Turbine Airfoils
Authors: Wright Jennifer M. , Faucett D. Calvin , Ayre Matthew , Choi Sung R.
Published: November 2013

Ceramic thermal barrier coatings (TBCs), attributed to their inherent brittle nature, are highly susceptible to damage by impacting foreign particles when the impacting kinetic energy exceeds certain limits. The damage is termed foreign object damage (FOD) in related turbine components and results in various issues/problems to coatings as well as to substrates from delamination to spallation to cracking to catastrophic failure depending on the severity of impact. The FOD testing was performed using a ballistic impact gun for turbine airfoil components coated with 7% yittria stabilized zirconia (7YSZ) by electron beam physical vapor deposit (EB-PVD). A range of impact velocities up to Mach 1 was applied with three different projectile materials of steel, silicon nitride, and glass balls. The damage was assessed and characterized in terms of impact velocity, projectile material, and remaining life of turbine components. An energy-balance approach was made to develop a model to predict delamination of the TBCs upon impact.
The Effect of Film Cooling on Nozzle Guide Vane Deposition
Authors: Bonilla C. , Clum C. , Lawrence M. , Casaday B. , Bons J. P.
Published: November 2013

An accelerated deposition test facility was used to study the relationship between film cooling, surface temperature, and particle temperature on deposit formation. Tests were run at gas turbine representative inlet Mach numbers (0.1) and temperatures (1090°C). Deposits were created from lignite coal fly ash with mass median diameters of 1.3 and 8.8μm. Two CFM56-5B nozzle guide vane doublets, comprising three full passages and two half passages of flow, were utilized as the test articles. Tests were run with different levels of film cooling back flow margin and coolant temperature. Particle temperature upon impact with the vane surface was shown to be the leading factor in deposition. Since the particle must traverse the boundary layer of the cooled vane before impact, deposition is directly affected by the film and metal surface temperature as well. Film coolant jet strength showed only minor effect on deposit patterns on the leading edge. However, larger Stokes number (resulting in higher particle impact temperature) corresponded with increased deposit coverage area on the showerhead region. Additionally, infrared measurements showed a strong correlation between regions of greater deposits and elevated surface temperature on the pressure surface. Thickness distribution measurements also highlighted the effect of film cooling by showing reduced deposition immediately downstream of cooling holes. Implications for engine operation in particulate-laden environments are discussed.
Dynamics of a Transversely Excited Swirling, Lifted Flame: Part II — Flame Response Modeling and Comparison With Experiments
Authors: Acharya Vishal , Malanoski Michael , Aguilar Michael , Lieuwen Timothy
Published: November 2013

This paper is the second of a two-part series, describing work to model the response of a swirling, lifted flame to transverse flow excitation. The problem is motivated by combustion instabilities associated with transverse acoustic modes of combustors. This paper develops a formulation that relates the unsteady flame response characteristics to both the spatially filtered disturbance field and mean flow field characteristics. The flow and flame features from Part I [1] of this paper are used as model inputs in order to compare the global heat release fluctuations with those measured from the experiment, showing quite good agreement. As such, this paper shows that, given a nearly axisymmetric configuration and sufficient flow field information, the dynamic flame response can be reasonably predicted. However, we also show that the strongly helical disturbances present in the flow have minimal impact on the global response of axisymmetric flames, as the local heat release fluctuations that they induce cancel each other azimuthally. An important needed next step is a similar exercise on a more strongly non-axisymmetric configuration (such as a multi-nozzle configuration), where the helical nature of the flow disturbances manifest themself in the global unsteady heat release more significantly.
Film Cooling From Circular and Elliptical Exit Shaped Holes With Sister Hole Influence
Authors: Khajehhasani Siavash , Jubran B. A.
Published: November 2013

In traditional film cooling configuration, coolant is injected through a cylindrical pipe with an inclined angle (0<α<90), which results in an elliptical exit shaped hole (EESH) at the blade surface. The present study makes use of an elliptical injection coolant pipe that leads to a circular exit shaped hole (CESH). The film cooling effectiveness and the associated flow for both cases of circular and elliptical shaped holes are numerically investigated. A comparison between the predicted results and the available experimental results from the literature for blowing ratios of M = 0.5 and 1, clearly indicated a better agreement with the experimental results when the realizable k-ε model was used. Further, the results indicate that the circular exit shaped hole improves the centerline and laterally averaged adiabatic effectiveness, particularly, at a higher bowing ratio of 1. The analysis of the vortex generation downstream of the jet for both exit shaped holes, shows a considerable decrease in the jet lift-off where the coolant flow tends to adhere more to the surface and hence, provides a better film cooling protection for the circular exit shaped hole, in comparison with the common elliptical exit shaped hole. The influence of sister holes on film cooling performance tends to be more effective with circular exit shaped hole than that with elliptical exit shaped hole.
Comparison of Pin Surface Heat Transfer in Arrays of Oblong and Cylindrical Pin Fins
Authors: Kirsch Kathryn L. , Ostanek Jason K. , Thole Karen A.
Published: November 2013

Pin fin arrays are most commonly used to promote convective cooling within the internal passages of gas turbine airfoils. Contributing to the heat transfer are the surfaces of the channel walls as well as the pin itself. Generally the pin fin cross-section is circular; however, certain applications benefit from using other shapes such as oblong pin fins. The current study focuses on characterizing the heat transfer distribution on the surface of oblong pin fins with a particular focus on pin spacing effects. Comparisons were made with circular cylindrical pin fins, where both oblong and circular cylindrical pins had a height-to-diameter ratio of unity, with both streamwise and spanwise spacing varying between two and three diameters. To determine the effect of relative pin placement, measurements were taken in the first of a single row and in the third row of a multi-row array. Results showed that area-averaged heat transfer on the pin surface was between 30 and 35 percent lower for oblong pins in comparison to cylindrical. While heat transfer on the circular cylindrical pin experienced one minimum prior to boundary layer separation, heat transfer on the oblong pin-fins experienced two minimums, where one is located before the boundary layer transitions to a turbulent boundary layer and the other prior to separation at the trailing edge.
Derivation of 2-D Empirical Correlations for Film-Cooling Effectiveness and Heat Transfer Augmentation From Spanwise Averaged Data and Correlations
Authors: Ingram Peter T. , Yavuzkurt Savas
Published: November 2013

In existing gas turbine heat transfer literature, there are several correlations developed for the spanwise-averaged film-cooling effectiveness and heat transfer augmentation for inline injection on flat plates. More accurate and detailed predictions of film-cooling performance, particularly 3-D solid temperatures are needed for design purposes. 2-D correlations where effectiveness and heat transfer augmentation are functions of streamwise and spanwise directions are necessary to satisfy this need. Previously developed 2-D correlations for single row of cylindrical holes with inline injection have been improved to include the effects of shaped holes such as hole breakthrough width (t/D) and area ratio (AR). The correlations are improved to better match spanwise effectiveness of a single row of shaped cooling holes using data and spanwise-averaged correlations. Modifications to the correlations to improve application to compound injection (β) have been implemented. The blowing ratio is modified to account for the compound angle effect. The spanwise location of maximum film-cooling effectiveness and heat transfer augmentation are obtained as functions of the streamwise coordinate. Iterative Conjugate Heat Transfer Reduced Order Film Model (ICHT-ROFM) was used to obtain 3-D conjugate temperature distribution in film cooled solids.

The developed correlations predicted a relative cooling effect in the near hole region for shaped holes (24 K) and for compound angle injection (20K) compared to cylindrical holes. Spanwise variations in the solid temperature in the near hole region are between 40–50K for a temperature difference of 250K between the surface and the main stream and are quite significant, showing the need for 3-D simulations. Shaped and compound angle holes increase this temperature difference due to the increased cooling. The comparisons of solid temperatures for conjugate and non-conjugate heat transfer cases show about 13–18K or 8–10% of the local temperature difference of 180K. Therefore it can be concluded that the calculations of 3-D temperature distributions using conjugate heat transfer are very important for design purposes.
Numerical Study on the Effect of Real Syngas Compositions on Ignition Delay Times and Laminar Flame Speeds at Gas Turbine Conditions
Authors: Mathieu Olivier , Petersen Eric L. , Heufer Alexander , Donohoe Nicola , Metcalfe Wayne , Curran Henry J. , Güthe Felix , Bourque Gilles
Published: November 2013

Depending on the feedstock and the production method, the composition of syngas can include (in addition to H2 and CO) small hydrocarbons, diluents (CO2, water, and N2), and impurities (H2S, NH3, NOx, etc.). Despite this fact, most of the studies on syngas combustion do not include hydrocarbons or impurities and in some cases not even diluents in the fuel mixture composition. Hence, studies with realistic syngas composition are necessary to help designing gas turbines. The aim of this work was to investigate numerically the effect of the variation in the syngas composition on some fundamental combustion properties of premixed systems such as laminar flame speed and ignition delay time at realistic engine operating conditions. Several pressures, temperatures, and equivalence ratios were investigated. To perform this parametric study, a state-of-the-art C0-C5 detailed kinetics mechanism was used. Results of this study showed that the addition of hydrocarbons generally reduces the reactivity of the mixture (longer ignition delay time, slower flame speed) due to chemical kinetic effects. The amplitude of this effect is however dependent on the nature and concentration of the hydrocarbon as well as the initial condition (pressure, temperature, and equivalence ratio).
Progress of the 40MW-Class Advanced Humid Air Turbine Tests
Authors: Yagi Manabu , Araki Hidefumi , Tagawa Hisato , Koganezawa Tomomi , Myoren Chihiro , Takeda Takuya
Published: November 2013

A 40MW-class test facility has been constructed to verify practicability of applying the advanced humid air turbine (AHAT) system to a heavy-duty gas turbine. Verification tests have been carried out from January 2012, and interaction effects between the key components were established.

First, water atomization cooling (WAC) was confirmed to contribute to both increased mass flow rate and pressure ratio for the axial flow compressor. The good agreement between measured and calculated temperatures at the compressor discharge was also confirmed. These results demonstrated the accuracy of the developed prediction model for the WAC.

Second, a control method which realized both flame stability and low NOx emissions was verified. Although the power output and air humidity were lower than the rated values, NOx concentration was about 10 ppm.

Finally, a hybrid nozzle cooling system, which utilized both compressor discharged air and humid air, was developed and tested. The metal surface temperatures of the first stage nozzles were measured, and they were kept under the permissible metal temperature. The measured temperatures on the metal surface reasonably corresponded with calculation results.
Suppression of Supersonic Jet Noise From Rectangular Nozzle by Microjet Injection: Influence of Main Jet Condition
Authors: Okada Ryuichi , Watanabe Toshinori , Uzawa Seiji , Himeno Takehiro , Oishi Tsutomu
Published: November 2013

Jet noise reduction is essential for next-generation environmentally-friendly supersonic transport. In the present study, experimental and numerical investigations were performed to clarify the effect of microjet injection on supersonic jet noise and flow field. The experiments were focused on supersonic jet with Mach number up to 1.39, issuing from a rectangular nozzle with high aspect ratio.

The experiments varied several parameters including main nozzle pressure ratio, total pressure of microjet, number of microjets and microjet injection angle. Far-field sound pressure measurement was performed, and the characteristics of noise reduction, including its directivity, were investigated. On the other hand, the flow field was visualized with a Schlieren technique in order to understand the mechanism of noise reduction. The unsteady behavior of the shock structure and the shear layer were investigated based on the visualization results. To investigate the effect of microjets on the 3-dimensional flow field, steady RANS analysis of the flow field was performed under various conditions of the main jet and the microjets.
On the Selection of an Optimal Pattern Recognition Technique for Gas Turbine Diagnosis
Authors: Loboda Igor , Yepifanov Sergiy
Published: November 2013

Efficiency of gas turbine monitoring systems primarily depends on the accuracy of employed algorithms, in particular, pattern recognition techniques to diagnose gas path faults. In investigations many techniques were applied to recognize gas path faults, but recommendations on selecting the best technique for real monitoring systems are still insufficient and often contradictory.

In our previous works, three recognition techniques were compared under different conditions of gas turbine diagnosis. The comparative analysis has shown that all these techniques yield practically the same accuracy for each comparison case.

The present contribution considers a new recognition technique, Probabilistic Neural Network (PNN), comparing it with the techniques previously examined. The results for all comparison cases show that the PNN is not practically inferior to the other techniques. With this inference, the recommendation is to choose the PNN for real monitoring systems because it has an important advantage of providing confidence estimation for every diagnostic decision made.
Single-Stream Jet Noise Prediction Using Empirical Methodology for a Newly Designed Turbojet Engine
Authors: Barbosa João Roberto , Dezan Daniel Jonas
Published: November 2013

The Center for Reference on Gas Turbines (CRTG), at the Technological Institute of Aeronautics, carries out research in relevant areas of gas turbines, to provide the support for teaching and the ability to design high performance gas turbines. Noise prediction, by means of theoretical and empirical methods, is among such areas. Emphasis is given to the prediction of noise from new engines, to anticipate problems at very early design stage and to take the necessary actions to guarantee that the engine noise is below the recommended limits. Noise prediction is part of a high fidelity gas turbine performance prediction computer program, which provides the designer, at any time during the design phases, with information on the noise levels generated by each component and by the engine. This paper presents results obtained with such methodology incorporated to the high fidelity engine performance prediction computer code, and in the format usually used in the literature. The SPL — far-field one-third octave band sound pressure level — and the OASPL — overall sound pressure level — for single-stream jet were calculated for several engine rotational speeds and observer positions. Two methods have been for the single-stream jet noise prediction, namely: ESDU item 98019 and SAE ARP 876D. Nozzle details were taken from a 5 kN turbojet engine, designed at the CRTG, and which is being installed in the test rig for the preliminary evaluation. In this paper the influence of the observer position on the calculated SPL is presented, and the corresponding OASPL for steady engine operation, combined with the effect of the engine rotational speeds on exhaust jet noise. It is shown that they are in agreement with the noise of similar operating conditions. Ground reflection and atmospheric attenuation were not considered in this work. The results indicate that the noise prediction is adequate for use during the design phase and that the model derived in the SAE ARP 876D paper provides better single-stream jet noise prediction than ones predicted using the ESDU Item 98019.
Heat Transfer Measurements Using the Hybrid Heat Transfer Technique With Thermally Adiabatic and Participating Ribs
Authors: Tran Lucky V. , Kapat Jayanta S. , Pham Anne L. , Little Zachary D. , Tran Patrick K.
Published: November 2013

This work is focused on the application of a number of improvements to the traditional transient thermochromic liquid crystals technique, in particular the hybrid heat transfer experiment, in order to provide more detailed and accurate measurements of the surface heat transfer coefficient in internal cooling passages. More accurate measurements of heat transfer coefficient are necessary to provide a clearer understanding of the performance of the cooling channels and to not misrepresent the channel performance so that more optimal designs and progress can be achieved. Detailed Nusselt number measurements were performed for a square channel with ribs on one wall in the Reynolds number range of 50 000 to 150 000, based on channel hydraulic diameter, using the transient thermochromic liquid crystals technique. The rib aspect ratio is 1:1, the rib height-to-hydraulic diameter ratio is 0.10, the rib-pitch–to–rib-height ratio is 10, and the ribs are oriented orthogonal to the streamwise direction. Heat transfer measurements were taken on all four walls so that the bulk temperature variation throughout the channel during the experiment can also be taken into account. Adiabatic and aluminum ribs were used simultaneously. The recently developed Coupled 0D-1D model is used to resolve the average heat transfer of the metallic rib features. A comparison of the data obtained using adiabatic and metallic rib features is made to quantify experimentally the influence of the rib-induced contamination. Friction augmentation, overall heat transfer augmentation, and overall thermal performance are also reported.
Influence of Non-Uniform OGV on High Pressure Compressor Performance
Authors: Yang Ping , Xie Weiliang , Xu Feng , Feng Jinzhang
Published: November 2013

Generally, the outlet guide vanes (OGV) of a high pressure compressor (HPC) have a single vane profile and are placed uniformly circumferentially. However, in some situations, portions of the OGV are thickened to be accommodated to some special requirements which may result in negative influences on the HPC performance.

This paper describes the design of a non-uniform OGV row of a multi-stage HPC. The OGV is periodically composed of one thick vane and two thin vanes. A series of vanes are selected by changing vane geometry parameters including vane stagger and camber, location of maximum thickness, thickness distribution, chord length and vane circumference position. Numerical simulations of these different non-uniform OGV rows along with the same rotor upstream are carried out to evaluate the impact of these parameters on the non-uniform OGV performance. Through this “manual-iteration” process, the best configuration is selected as the final “optimized” design.

The results show that, firstly, it is beneficial to set the suction surface incidence angle of the thick airfoils the same with that of the thin airfoils for uniform incoming flow field; secondly, the divergence rate of passage should be carefully controlled to reduce the loss coefficient; thirdly, the vane circumference position should be adjusted to keep the mass flow of each passage being equal to ensure uniformity of the outlet flow field. Finally, it is demonstrated that after optimization, the adverse effects of the non-uniform OGV on the whole HPC performance can be nearly eliminated.
The Application of Non-Axisymmetric Profiled End-Walls for Axial Flow Turbines in the Embedded Stage Environment
Authors: Lintz Andreas , Xu Liping , Karakasis Marios
Published: November 2013

In this paper, an assessment of the effectiveness of non-axisymmetric profiled end-walls in the embedded stage environment at varying inlet conditions is presented. Both numerical and experimental results were obtained in a three-stage model turbine which offers flow conditions representative of embedded blade rows in a typical high pressure steam turbine. The end-wall profile design was carried out using automatic optimization in conjunction with 3D RANS CFD. The design target is to reduce the end-wall losses by reducing the loading in the front part of the passage, which resulted in a single trough close to the blade suction surface in the leading edge region. 5-hole probe traverses and surface flow visualization show that the intensity of the secondary flows is reduced by about 10%, but overall loss is only reduced slightly. Experimental results have been obtained for the cylindrical end-wall and three different trough depths. With increasing depth, transitional effects at the end-walls might come into play, increasing the total pressure loss in the boundary layer region. The effects of the end-wall design is similar at positive and negative incidence, despite the reduced loading in the front part of the passage at negative incidence. At very high negative incidence angles, such as those occurring at the stator tip with rotor shroud leakage flows, the mechanism of secondary flow generation changes, so that a design under nominal inlet flow conditions shows no effect on the exit flow field.
Film Cooling Flow by Double Rows of Compound Angle and Compound Angle Shaped Holes
Authors: Bazdidi-Tehrani Farzad , Pezeshkpour Pegah
Published: November 2013

The present paper describes a three-dimensional finite volume numerical simulation of turbulent flow and heat transfer over a flat plate embedded with four different configurations of film cooling jet holes. Recently, more advanced techniques are introduced to improve the effectiveness of film cooling method such as the Compound Angle Shaped Holes (CASH). The first two studied configurations in this article comprise double rows of staggered compound angle holes. The presented final configurations encompass double rows of the CASH geometry, with inline and staggered arrangements, consecutively. The second order upwind scheme is employed for the discretization of equations and the pressure-velocity coupling is performed by using the SIMPLEC algorithm. Moreover, the k-ω shear stress transport turbulence model is applied for the flow simulation. Present results on the compound angle holes show that the span wise-averaged cooling effectiveness is higher when 6D span wise hole spacing is employed as compared with 7.8D spacing. Results have emerged that the double rows of staggered CASH geometry display higher cooling effectiveness than that of the inline arrangement. Furthermore, comparison of the present spanwise effectiveness and ratio of Stanton numbers with the available experimental data shows reasonable agreement for the first and second configurations.
Turbine Endwall Film Cooling With Pressure Side Radial Holes
Authors: Zhang Yang , Yuan Xin
Published: November 2013

A key technology of gas turbine performance improvement was the increase in the turbine inlet temperature, which brought high thermal loads to the nozzle guide vane (NGV) components. Strong pressure gradients in the NGVs and the complex secondary flow field had made thermal protection more challenging. As for the endwall surface near the side gill pressure region, the relatively higher local pressure and cross flow apparently decreased the film-cooling effectiveness. The aim of this investigation was to evaluate a new design, improving the film-cooling performance in a cooling blind area with radial cylindrical holes on the pressure side.

The test cascades model was manufactured according to the GE-E3 nozzle guide vane scaled model, with a scale ratio of 2.2. The experiment was performed under the inlet Mach number 0.1 and the Reynolds number 3.5×105 based on an axial chord length of 78 mm. Four rows of staggered radial film-cooling holes were placed at the pressure side gill region. The diameter of the cylindrical holes was 1 mm and the length was 5 d, with a hole space of 6 d. The spanwise angle of the cooling holes was 35 ° and the radial angle was 90 °. Three blowing ratios were chosen as the test conditions in the experiment, M = 0.7, M = 1.0 and M = 1.3. The film-cooling effectiveness was probed using PSP (pressure sensitive painting) technology and the post processing was performed by means of a mass and heat transfer analogy.

Through the investigation, the following results could be achieved: 1) the film-cooling effectiveness on the endwall surface near the pressure side gill region increased, with the highest parameter at X/Cax = 0.3; 2) a double-peak cooled region developed towards the suction side as the blowing ratio increased; 3) the advantage of the pressure side radial cooling holes was apparent on the endwall surface near the gill region, while the coolant film was obviously weakened along the axial chord at a low blowing ratio. The influence of the pressure film cooling could only be detected in the downstream area of the endwall at the higher blowing ratio.
Numerical Simulation on Circumferential Staging of an Aeroengine LPP Combustor
Authors: Mao Ronghai , Shang Mingtao
Published: November 2013

With the increasing stringency of the CAEP regulation on the pollutant emissions, combustors in lean burn architecture are being widely developed by aero-engine manufacturers to achieve low NOx emission performance with competitive margins to CAEP thresholds. A three-dimensional numerical simulation has been carried out in the present investigation to study an LPP combustor and circumferential staging effects on its main stage, for potential application to ACAE CJ-1000A aeroengine. A realizable k-ε turbulent model has been employed by the simulation, together with a Discrete Phase model based on Lagrangian methodology for the two-phase flow. The generic performances of the combustor, mainly in terms of flow and flame structures, fuel-air enhanced mixing performance, total pressure loss, combustion efficiency, outlet temperature distribution, and pollutant emissions have been analyzed. It was found that a large-scale central recirculation region is formed in the flame tube, which is beneficial to the stability of the combustion. The total pressure loss of the combustor is insensitive to the circumferential staging. Under approach mode the circumferential staging enhances the combustion efficiency from 73.8% without staging to 93.8% with staging; meanwhile the local turbulent flame speed increases more than two times. However the OTDF deteriorates from 0.30 without staging to 0.78 with staging, although the RTDF is found to be insensitive to the circumferential staging. The radial temperature distribution profiles are found to be pretty flat during the whole LTO cycle. The NOx emission without circumferential staging is simulated to be 68% reduction relative to CAEP 6. The circumferential staging, however, increases NOx emission to 65% reduction relative to CAEP 6. While gaining higher combustion efficiency, the major drawbacks of the circumferential staging are degradations of OTDF and NOx emission. Although the numerical results seem to be quite encouraging, the uncertainty of CFD results especially the temperature distribution and emissions might be tremendous. Experimental work has to follow up for further clarification.
The Liftoff Properties of Dimethyl Ether Jet Diffusion Flames With Preheating
Authors: Zhou Jie , Ai Yuhua , Kong Wenjun
Published: November 2013

Liftoff properties of DME laminar axisymmetric diffusion flames were investigated experimentally with emphasis on the preheating effects. At room temperature, DME presented a different liftoff phenomenon from the non-oxygenated hydrocarbon fuels. It could not be lifted off directly by increasing the jet velocity except for far field ignition at relatively low mass flow rate. When fuel and dilution were preheated, the DME flame could be lifted off directly by increasing the jet velocity. The range of the mass flow rate of stabilized DME liftoff flames became much narrower and the liftoff height became much smaller at fuel preheating than that at ambient temperature. With the increase of the jet temperature, the DME liftoff flames exhibited as one of the following three types: stationary lifted flames, stable oscillating lifted flames and unstable oscillating lifted flames. Stationary lifted flames existed when the initial temperature was relatively low (less than 350 K). Stable oscillating lifted flames were observed at relatively high preheated temperature (about 350 K ∼ 750 K), and the trajectory of the liftoff flame base was nearly sinusoidal. Both the oscillating frequency and amplitude increased with the preheating temperature. The oscillating lifted flames were caused by thermal buoyancy effect, inertia and the instability in the inner flow. When the jet temperature exceeded 750 K, the oscillating lifted flames became unstable and easily to be blown out. The flame base of the stabilized DME liftoff flame had a tribrachial structure at both ambient temperature and elevated temperature.
WebEngine: A Web-Based Gas Turbine Performance Simulation Tool
Authors: Apostolidis Asteris , Sampath Suresh , Laskaridis Panagiotis , Singh Riti
Published: November 2013

The WebEngine is a web-based gas turbine performance simulation tool. The main advantage from this approach is the ease-of-use as no local installation is required. A number of different user categories such as students, researchers, gas turbine operators etc. can immensely benefit from this tool. The WebEngine has been under development for two years and is strongly supported by various associated research work in the department. It offers a large number of simulation capabilities such as design point and off-design single runs/parametric analysis, engine library, engine model design, virtual engine sensors and power plant operating plan. The WebEngine core is a high quality and robust gas turbine performance simulation code, developed by the Department of Power and Propulsion of Cranfield University, called Turbomatch. This approach offers modular component structure and high flexibility in the model development, as any engine configuration modelling is possible. In addition, the ergonomic graphical user interface offers a suitable and relaxing environment for the user. Related case studies are provided wherein a turbojet engine model development procedure, a turbofan design point fan pressure ratio optimization and an off-design parametric analysis are enumerated. Finally, a monthly power plant operating schedule is calculated for June 2013. A number of future additions is planned for the tool, with the diagnostics capability having the principal role.
Unsteady Mechanisms of Compressor Corner Separation Over a Range of Incidences Based on Hybrid LES/RANS
Authors: Wang Zhong-Nan , Yuan Xin
Published: November 2013

The separation flow pattern in compressor corners is well known but its nature is not fully understood. In this paper, the numerical simulation based on hybrid LES/RANS was performed to improve our understanding about the unsteady separation structure and its dynamic mechanisms of compressor corner flows, subject to a range of incoming flow incidences. In the simulation, the attached boundary layer near the walls was modeled by RANS, while the large separated flows in the corner were resolved by LES. The simulation was carefully validated by the experimental data before flow physics investigation. The unsteady separation structures and its effects were then investigated step by step, from phenomena observation to mechanisms analysis. First, the overall separation behavior and its associated flow physics was visualized and analyzed. It was found that the unsteady separation structure was distinct from the steady view. Some additional vortex structures, normally smeared out in the steady averaging process, were crucial in the unsteady dynamic process. These small but critical vortices corresponded to large intermittency in the separation size and strength. As the incidences increased, the vortex structure became much more complex due to the enhanced interaction of these vortices. Second, the turbulence behavior was examined in the separated regions. Anisotropy and non-equilibrium of turbulence were found to be dominant in the separation region due to non-homogenous shear of the separated flow. It posed a big challenge for conventional RANS prediction. Finally, the unsteadiness of corner separated flows was fully analyzed over a range of incidences. It was found that the unsteadiness came from two sources: the suction side separation and the wake shedding. The unsteadiness increased with the incidences. The two unsteady sources interacted with each other at high incidences, which led to a big unsteady resonance structure near the blade trailing edge. The resonance was responsible for a large pressure variation, implying the enhanced noise generation near the blade trailing edge.
A Comparative Assessment of Dry Gas Turbine Cycles for Marine Applications
Authors: Sanchez de Leon Luis , Zachos Pavlos K. , Pachidis Vassilios
Published: November 2013

This paper presents a comparative assessment of different gas turbine open ‘dry’ cycle configurations as potential prime movers for marine commercial applications. The analyses will focus on optimising a three-spool gas turbine —featuring intercooling, reheating, and/or recuperation— for maximum thermal efficiency at design point, under the premise that targeted marine applications spend most of the time at cruising, hence part-load performance of the power plant will not play a huge role. The most promising configuration will be identified, and a whole methodology of systematic design-space exploration will be established, as the first necessary steps in the context of a much broader project, with the final aim of applying the same methodology to a wider range of candidate gas-turbine based power plants and performing multi-disciplinary optimisation of these candidates to fully assess the capabilities of the gas turbines to enter the market of the large cargo ships.