bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Axisymmetric Endwall Profiling of a Stator Row in the Presence of the Rotor in a High Pressure Turbine
Authors: Rehman Abdul , Liu Bo , Na Zhenzhe , Cheng Hao
Published: August 2018

In an axial flow turbine, almost one-third of the total losses are caused by secondary flows, and the non-axisymmetric endwall profiling has been a major tool for years to reduce the secondary flow loss. This paper presents the non-axisymmetric endwall profile construction and optimization both for the stator hub and shroud of a high pressure turbine in the presence of an axisymmetric rotor. The flow simulation in the turbine was conducted by using steady RANS. The perturbation law of non-axisymmetric endwall was based on Bezier curves, and the commercially available optimization software NUMECA Fine/Design 3D was used to design the non-axisymmetric endwall. A genetic algorithm based on the artificial neural network was used as the optimization method. The objective function was aimed at maximizing the stage isentropic efficiency. The change in mass flow rate was kept less than 0.5% (relative) so that efficiency might not be influenced by the mass flow through the variation of the throat area. From the design point of view, the stator hub endwall was optimized at design conditions firstly, but the shroud endwall was kept constant, which resulted in an increase of stage efficiency because flow angles at stator exit were changed. The flow structures in the passage of stator were compared pre and post optimization by using 3-D streamlines in the vicinity of the endwall. Subsequently, the shroud endwall was optimized using the optimized non-axisymmetric hub as initial design. Due to hub and shroud endwall perturbation, the cross passage gradient and entropy were reduced, and the turbine stage efficiency at design conditions was calculated and the improvement in the efficiency was noticed. In addition, the improved hub and shroud contour were considered for off-design conditions as well, and efficiency was even more increased over a considerable off-design regime than at the design point condition.
Investigations on the Fatigue Load Reduction Potential of Advanced Control Strategies for Multi-MW Wind Turbines Using a Free Vortex Wake Model
Authors: Perez-Becker Sebastian , Saverin Joseph , Marten David , Alber Jörg , Pechlivanoglou George , Paschereit C. O.
Published: August 2018

This paper presents the results of a fatigue load evaluation from aeroelastic simulations of a multi-megawatt wind turbine. Both the Blade Element Momentum (BEM) and the Lifting Line Free Vortex Wake (LLFVW) methods were used to compute the aerodynamic forces. The loads in selected turbine components, calculated from NREL’s FAST v8 using the aerodynamic solver AeroDyn, are compared to the loads obtained using the LLFVW aerodynamics formulation in QBlade.

The DTU 10 MW Reference Wind Turbine is simulated in power production load cases at several wind speeds under idealized conditions. The aerodynamic forces and turbine loads are evaluated in detail, showing very good agreement between both codes. Additionally, the turbine is simulated under realistic conditions according to the current design standards. Fatigue loads derived from load calculations using both codes are compared when the turbine is controlled with a basic pitch and torque controller. It is found that the simulations performed with the BEM method generally predict higher fatigue loading in the turbine components. A higher pitch activity is also predicted with the BEM simulations. The differences are larger for wind speeds around rated wind speed. Furthermore, the fatigue reduction potential of the individual pitch control (IPC) strategy is examined and compared when using the two different codes. The IPC strategy shows a higher load reduction of the out-of-plane blade root bending moments when simulated with the LLFVW method. This is accompanied with higher pitch activity at the actuation frequency of the IPC strategy.
Fault Diagnosis Method for Inter-Shaft Bearings Based on Information Exergy and Random Forest
Authors: Tian Jing , Ai Yanting , Zhao Ming , Fei Chengwei , Zhang Fengling
Published: August 2018

To reasonably process the complex signals and improve the diagnosis accuracy of inter-shaft bearing incipient faults, this paper develops wavelet energy spectrum exergy (WESE) and random forest (RF) (short for WESE-RF) method with respect to acoustic emission (AE) signals. Inter-shaft bearing faults, which contain inner race fault, outer race fault, rolling element faults and normal status under different measuring points and different rotational speeds, are simulated based on the test rig of inter-shaft bearings, to collect the AE signals of these faults. Regarding the AE signals of inter-shaft bearing faults, the WESE values, one signal feature, are extracted from an information exergy perspective, and are applied to structure feature vectors. The WESE values of these AE signals are regarded as the sample set which include the training samples subset used to establish the WESE-RF model of fault diagnosis and the test samples subset applied to test the effectiveness of the developed WESE-RF model. The investigation on the fault diagnosis of inter-shaft bearing demonstrates the fault diagnosis method with the WESE-RF has good generalization ability and high diagnostic accuracy of over 0.9 for inter-shaft bearing fault. The efforts of this paper provide a useful approach-based information exergy and wavelet energy spectrum for inter-shaft bearing fault diagnosis.
Evaluation Method of Uncertainty of Reliability Calculation for Turbine Disk Life
Authors: Fan Jiang , Chen Gaoxiang , Shen Xiuli , Fan Tianyi
Published: August 2018

For the deviation of replacing the actual physical model with the surrogate model in the probability analysis of the turbine disk life, an uncertainty evaluation method of reliability calculation of turbine disk life considering the geometric parameter dispersion and surrogate model error is developed. The main approach of this method is to quantify the maximum fluctuation range of the prediction life of the surrogate model and the maximum fluctuation range of the prediction life deviation between the surrogate model and the life model. The safety margin of turbine disc life is calculated and evaluated. Finally, the quantitative evaluation of uncertainty of the low cycle fatigue life of the engine GH720Li turbine disk is completed by this method.
Detailed Flow Analyses Through Crossover Holes Between Two Adjacent Rib-Roughened Cooling Channels and the Resulting Impingement Heat Transfer
Authors: Xue Fei , Taslim Mohammad E.
Published: August 2018

Impingement cooling in airfoils cooling cavities, solely or combined with film and convective cooling, is a common practice in gas turbines. Depending on the cooling cavity design, the mass flow rate through individual crossover holes could vary significantly in the flow direction thus creating jets of different strengths in the target cavity. This jet flow variation, in turn, creates an impingement heat transfer coefficient variation along the channel. A test section, simulating two adjacent cooling cavities on the trailing side of an airfoil, is made up of two channels with trapezoidal cross-sectional areas. On the partition wall between the two channels, eleven crossover holes create the jets. Two distinct exit flow arrangements are investigated — a) jets, after interaction with the target surface, are turned towards the target channel exit axially and b) jets are exited from a row of racetrack-shaped slots along the target channel. Flow measurements are reported for individual holes and heat transfer coefficients on the eleven target walls downstream the jets are measured using the steady-state liquid crystal thermography technique. Smooth as well as rib-roughened target surfaces with four rib geometries (0°,45°, 90° and 135° rib angles) are tested. Correlations are developed for mass flow rate through each crossover hole for cases with different number of crossover holes, based on the pressure drop across the holes. Heat transfer coefficient variations along the target channel for all rib geometries and flow conditions are reported for a range of 5000 to 50000 local jet Reynolds numbers. Major conclusions of this study are: 1) A correlation is developed to successfully predict the mass flow rates through individual crossover holes for geometries with six to eleven crossover holes, based on the pressure drop across the holes, 2) impingement heat transfer coefficient correlates well with the local jet Reynolds number for both exit flow arrangements, and 3) the case of axial flow in the target channel exiting from the channel end, at higher jet Reynolds numbers, produced higher heat transfer coefficients than those in the case of flow exiting through a row of slots along the target channel opposite to the crossover holes.
An Adaptive Harmonic Method for Unsteady Quasi-One-Dimensional Periodic Flow
Authors: Zhu Yalu , Luo Jiaqi , Liu Feng
Published: August 2018

A uniform formulation of linear harmonic method, nonlinear harmonic method and harmonic balance method, referred to as the uniform harmonic method, is first proposed for the quasi-one-dimensional Euler equations; and a modified adaptive technique is employed, by which the harmonic contents at each cell can be automatically augmented or diminished to efficiently capture the local flow details. Then the unsteady flows in a convergent-divergent nozzle are computed and analyzed for a test case with an oscillating shock wave in it. The harmonic contents, computational time and error in pressure are presented and compared for different harmonic interaction options, segment widths and thresholds, from which the adaption setups with excellent computational performance and high-level accuracy are determined. Finally, the adaptive harmonic method is extended to the multiple-perturbation case, which is verified by an example with pressure perturbations of two different fundamental frequencies. Compared to the non-adaptive harmonic balance method, the adaptive harmonic method produces accurate enough solutions with a 75.4% reduction in computational time and a 71.8% save in memory consumption for the single-perturbation case, while the drop rates are 42.0% and 62.8% respectively for the multiple-perturbation case.
The Influence of Different Endwall Contouring Locations on the Secondary Flow Losses in a Highly Loaded Low Pressure Turbine
Authors: Duan Wenhua , Qiao Weiyang , Wei Zuojun , Liu Jian , Cheng Haoyi
Published: August 2018

A detailed experimental and numerical investigation of the effect of endwall contouring on the secondary flow was performed in a highly loaded low pressure linear cascade. A comparison between a planar and three contoured configurations has been performed, and the three-dimensional endwall secondary flow structures and the secondary flow losses are here analyzed and discussed. For the contoured endwall, three locations of the same contouring were investigated, first one with the contouring starting upstream the airfoil and ending just before the leading edge of the airfoil, secondary one with the contouring starting upstream the airfoil and ending in the middle of the airfoil passage, the last one with the contouring starting just from the leading edge of the airfoil and continuing through the airfoil passage just ending at the trailing edge. The results suggest that the numerical results offer a reliable prediction for the endwall secondary flow structure together with suction surface separation bubble. It was found that all the three locations of contouring could reduce the secondary flow losses effectively. The location through the airfoil passage got the most benefit in the reduction of secondary flow losses whereas the all contouring upstream the airfoil location got the least. It was also found that the profile losses was affected by the contoured endwall.
A New Index to Evaluate the Potential Damage of a Surge Event: The Surge Severity Coefficient
Authors: Munari Enrico , Morini Mirko , Pinelli Michele , Brun Klaus , Simons Sarah , Kurz Rainer
Published: August 2018

Industrial compressors suffer from strong aerodynamic instability that arises when low ranges of flow rate are achieved; this instability is called surge. This phenomenon creates strong vibrations and forces acting on the compressor and system components due to the fact that it produces variable time averaged mass flow and pressure. Therefore, surge is dangerous not only for aerodynamic structures but also for mechanical parts. Surge is usually prevented in industrial plants by means of anti-surge systems which act as soon as surge occurs, however some rapid transients or system upsets can lead the compressor to surge anyway. Despite the fact that surge can be classified as mild, classic or deep, depending on the amplitudes and frequency of the fluctuations, operators are used to simply referring to surge, without making a distinction between the three main classes. This is one of the reasons why, when surge occurs in industrial plants, it is common practice to stop the machine to perform inspections and check if any damage occurred. Obviously, this implies maintenance costs and time, during which the machine does not operate. On the other hand, not all surge events are dangerous in terms of damage, and they can be tolerated by the mechanical structures of the compressor; thus, in these cases, inspections would not be required. Unfortunately, a method for establishing the potential damage of a surge event is not available in literature. In order to fill this gap, this paper proposes a final formulation of a surge severity index, which was only preliminarily formulated by the authors in a previous work. The preliminary form of this coefficient demonstrated some limitations which are overcome in this paper. The surge severity index derives from an energy-force based analysis. The coefficient demonstration is carried out in this paper by means of i) the application of the Buckingham’s Pi-theorem, and ii) a careful analysis of the causative and restorative factors of surge. Finally, some simple practical evaluations are shown by means of a sensitivity analysis, using simulation results of an existing model, to effectively further highlight the consistency of this coefficient for industry.
Throughflow Method for a Combustion Chamber With Effusion Cooling Modelling
Authors: Liu Xiaoheng , Jin Donghai , Gui Xingmin
Published: August 2018

The most progressive liner cooling technology for modern combustion chambers is represented by effusion cooling (or full-coverage film cooling), which is based on the use of several inclined small diameter cylindrical holes. However, as to simulation of the gas turbine combustion chamber, meshing of these discrete holes needs too much computer resource and demanding calculation time. The homogeneous boundary condition was attempted to apply in the throughflow method for the simulation of the full-scale combustion chamber. The verification of this uniform condition was performed through the model of two straight channels. Obtained results were compared with detailed LES simulations, highlighting well accordance and accurate flow structure around the plate. Furthermore, the modelling was used in the simulation of a loop combustion chamber with throughflow method on isothermal state. Performance characteristic and flow fields from this method were then contrasted with the details from the FLUENT simulation upon high geometric fidelity, and prove that the homogeneous boundary condition exerts a good prediction of the performance characteristics and flow field in the combustion chamber.
A New Experimental Database for the Investigation of Soot in a Model Scale Swirled Combustor Under Perfectly Premixed Rich Conditions
Authors: Roussillo M. , Scouflaire P. , Darabiha N. , Candel S. , Franzelli B.
Published: August 2018

Soot production in turbulent flames represents an urgent issue for applied systems and raises a range of fundamental challenges. Most of the literature effort on this question has been carried out on non-premixed turbulent flames, where mixing plays a dominant role. It is however interesting to see if soot production can be investigated in a premixed turbulent flame configuration, thus eliminating the role of mixing in this process. It is shown in the present article that this can be accomplished by making use of rich swirled ethylene/air flames under perfectly-premixed rich conditions established in a confined combustor operating at atmospheric pressure. Quantitative measurements of the soot volume fraction (fv) are carried out by the Laser Induced Incandescence (LII) technique. Although the soot volume fraction levels are one or two orders of magnitude lower than those found in non-premixed flames, it is shown that detection is feasible and that this configuration may be used to analyze effects on soot production of operating parameters such as the equivalence ratio, the power level or the wall temperature. The observed trends are interpreted numerically by considering an idealized model of a rich premixed burner-stabilized stagnation flame. This configuration is here calculated with a detailed kinetic scheme in combination with a soot sectional model. This description is able to account for some of the trends observed experimentally and indicates in particular how an increase in the wall temperature may increase the soot volume fraction as it is effectively observed in the experiment. The model predicts that the soot volume fraction level increases for high equivalence ratios. This finding is in disagreement with the experimental observations on this swirled flame, which exhibits a maximum soot volume fraction for ϕ = 2.1 for all the considered flame powers. This indicates that complex interactions take place between soot, flame, turbulence and thermal environment and that the investigation of these processes will require a comprehensive turbulent simulation. This may be guided by the database developed in the present experimental effort.
Numerical Investigation of Film and Impingement Cooling Schemes for Gas Turbine Application
Authors: da Silva Lucilene Moraes , Tomita Jesuino Takachi , Bringhenti Cleverson , Grönstedt Tomas
Published: August 2018

In modern gas turbine engines, many sophisticated cooling schemes are used to maintain the turbine blade temperature in acceptable levels. These schemes, such as convective cooling, film cooling, impingement cooling and the use of pin fins, can be combined to increase the cooling effectiveness. Jet impingement cooling, pin fins and convective cooling are internal cooling techniques, in which the cooling is achieved based on coolant flow through internal blade channels decreasing the blade metal temperature. Film cooling is an external cooling technique, in which the cold fluid (air) is injected into the hot gas flow through discrete holes providing a coolant film at blade surface, protecting the blade metal. In this way, the present work refers to the numerical investigation of internal and external cooling strategies applied in gas turbines. The methodology developed to analyze such strategies is based on the flat-plate approach with laboratory length scales and Computational Fluid Dynamics (CFD) techniques, being the flow, in the study domain, considered viscous, turbulent and compressible. A commercial CFD program is used to solve the general equations of fluid mechanics with Reynolds Average Navier-Stokes (RANS) technique for steady state regime and Shear Stress Transport (SST) turbulence model to determine the flow eddy viscosity. The combined effects of internal and external cooling is studied through a highly sophisticated scheme, called louver, which combines the effects of impingement and film cooling. Pin fins and ribs turbulator geometries applied in the channel between the impingement and the film cooling have the purpose of evaluating the impact of these geometries on the film cooling effectiveness over the flat surface in comparison to the louver scheme without turbulator. This study concluded that, pin fins proved to be the most promise solution because they increased in 7% the film cooling effectiveness. Ribs also have a good potential to increase the effectiveness, because an increase of 4% in film cooling effectiveness was observed. In addition, the effects of the turbulator are dependent on their location, since the turbulator positioned near the film cooling hole exit showed improvements in the film cooling effectiveness in relation to the turbulator near of the impingement cooling jet.
Detailed Studies on the Flow Field and Heat Transfer Characteristics Inside a Realistic Serpentine Cooling Channel With a S-Shaped Inlet
Authors: Funazaki Ken-ichi , Odagiri Hikaru , Horiuchi Takeshi , Kazari Masahide
Published: August 2018

Accurate temperature prediction of turbine blades for gas turbine is very important to assure the life-span of the blade under a hostile hot gas environment and intense centrifugal force. Therefore, there have been a number of studies carried out to clarify the cooling performance of serpentine cooling channel inside a turbine blade for gas turbine, however, it remains to be quite difficult to make an accurate numerical prediction of the performance. Apart from the effects of disk rotation as well as large temperature gradient near the wall, such a poor predictability can be attributed to the complicated vortical motions caused by the rib-roughened cooling channel whose cross-sectional shape varies along the channel and by the existence of u-bends. Furthermore, since the cooling channel inside a real turbine blade usually has a curved or S-shaped inlet, which may induce flow separation as well as swirl developed in the inlet, it can be imagined that the flow and heat transfer inside the cooling channel is likely to become much more complicated than that with a straight inlet. Despite this situation, only few studies are made in order to examine the flow and heat transfer characteristics inside the cooling channel with s-shaped inlet. Accordingly, this study aims at detailed experimental and numerical investigations on the flow and heat transfer characteristics of a realistic serpentine rib-roughened cooling channel with an s-shaped inlet, which is modeled from an actual HP turbine blade for gas turbine. This study employs a transient TLC (Thermochromic Liquid Crystal) technique to measure the heat transfer characteristics, along with the flow visualization on the inner surface of the channel using oil mixed with titanium powder. Note that a special focus in this flow visualization is placed on the area of s-shaped inlet. As for the flow measurement, 2D-PIV (Particle Image Velocimetry) method is used to understand time-dependent vortical structures of the flow field that can have significant impacts on the heat transfer. RANS-based numerical simulation is also executed to predict the heat transfer distribution on the inner surface of the cooling channel.
Effects of Upstream Step Geometry on Axisymmetric Converging Vane Endwall Secondary Flow and Heat Transfer at Transonic Conditions
Authors: Li Zhigang , Liu Luxuan , Li Jun , Sibold Ridge A. , Ng Wing F. , Xu Hongzhou , Fox Michael
Published: August 2018

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5 × 106. A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88Cx (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward facing step located just before the gap at 0.88Cx (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely Nusselt number, were derived. This paper also presents a comparison with CFD predictions performed by solving the steady-state Reynolds Averaged Navier Stokes (RANS) with Reynolds Stress Model using the commercial CFD solver ANSYS Fluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25 to 0% span), and five backward-facing, upstream step geometries (step heights from 0 to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures, and explain the effects of upstream step geometry.

Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the heat transfer coefficient (by ∼10%–40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3%–1.3%) as a result of the forward-facing upstream step geometry, but is slightly reduced (by 0.1%–0.3%) by the presence of the backward upstream step geometry.
Fuel Interchangeability Effects on the Lean Blowout for a Lean Premixed Swirl Stabilized Fuel Nozzle
Authors: Gadiraju Siddhartha , Park Suhyeon , Singh Prashant , Pandit Jaideep , Ekkad Srinath V. , Liberatore Federico , Srinivasan Ram , Ho Yin-hsiang
Published: August 2018

This work is motivated by an interest in understanding the fuel interchangeability of a fuel nozzle to operate under extreme lean operating conditions. A lean premixed, swirl-stabilized fuel nozzle designed with central pilot hub was used to test various fuel blends for combustion characteristics. Current gas turbine combustion technology primarily focuses on burning natural gas for industrial systems. However, interest in utilizing additional options due to environmental regulations as well as concerns about energy security have motivated interest in using fuel gases that have blends of Methane, Propane, H2, CO, CO2, and N2. For example, fuel blends of 35%/60% to 55%/35% of CH4/CO2 are typically seen in Landfill gases. Syngas fuels are typically composed primarily of H2, CO, and N2. CH4/N2 fuel blend mixtures can be derived from biomass gasification.

Stringent emission requirements for gas turbines stipulate operating at extreme lean conditions, which can reduce NOx emissions. However, lean operating conditions pose the problem of potential blowout resulting in loss of performance and downtime. Therefore, it is important to understand the Lean Blowout (LBO) limits and involved mechanisms that lead to a blowout. While a significant amount of research has been performed to understand lean blowout limits and mechanisms for natural gas, research on LBO limits and mechanisms for fuel blends has only been concentrated on fuel blends of CH4 and H2 such as syngas. This paper studies the lean blowout limits with fuel blends CH4-C3H8, CH4-CO2, and CH4-N2 and also their effect on the stability limits as the pilot fuel percentage was varied. Experimental results demonstrate that the addition of propane, nitrogen and carbon dioxide has minimal effect on the adiabatic flame temperature when the flame becomes unstable under lean operating conditions. On the other hand, the addition of diluent gas showed a potential blowout at higher adiabatic temperatures.
A Feasibility Study of Controllable Gas Foil Bearings With Piezoelectric Materials via Rotordynamic Model Predictions
Authors: Park Jisu , Sim Kyuho
Published: August 2018

This study presents a new concept of gas bearings consisting of controllable gas foil bearings (C-GFBs) in which piezoelectric actuators are applied to the GFBs. The C-GFB consists of a laminated top foil, bump foil, and piezo stacks and can simply change the bearing shape or film thickness locally and globally by varying the thickness of the piezo stacks by adjusting the input voltage. The working method of C-GFBs is as follows. First, the bearing clearance is adjusted by changing the overall piezo stack thickness (clearance control). Second, the bearing preload (preload control) is modulated by the thickness expansion of several piezo stacks. Bearing lubrication performance is predicted for four cases of C-GFBs that controlled to have different bearing clearances and preloads. The piezo stack control generates meaningful differences in the fluid-film thickness and pressure. Clearance control has a great effect on the dynamic force coefficients, but preload control slightly increases the dynamic stiffness and damping coefficients. Furthermore, the rotordynamic prediction of a rotor supported on two journal C-GFBs is conducted. As a result, both control mode for C-GFB is found to have a positive effect on rotordynamic performance in terms of synchronous motions. Finally, the C-GFB is controlled to have a small bearing clearance and large preload at critical speeds to make it possible to stably pass through the critical speeds. Consequently, it turns out that the C-GFB can generate meaningful performance change in terms of bearing lubrication and ro-tordynamic performances by controlling only the input voltage of the piezo stacks. In addition, the C-GFB can be used to form various shapes to meet the operation conditions of an applied system.
Development of ODS Coating for High Temperature Turbine Components Using DED Additive Manufacturing
Authors: Chia Eric , Kang Bruce S. , Zheng Min , Li Yang , Chyu Minking
Published: August 2018

Current and future designs for advanced turbine systems, such as Integrated Gasification Combined Cycle (IGCC), advanced Natural Gas Combined Cycle (NGCC), and the emerging supercritical CO2 (SCO2) systems require increasing turbine inlet temperature (TIT), which is well beyond the substrate melting temperature. The well-known approach is coating the turbine blade with thermal barrier coatings (TBC) combined with internal cooling channel in the substrate. However, due to thermally grown oxide (TGO) and thermal expansion mismatch stresses, TBC spallation failure is a major concern. Furthermore, neither the ceramic coating layer nor the metallic bond coat in current TBC system can provide structural support to house the internal cooling channels. In this research, a method to fabricate high temperature protective structural coating on top of critical gas turbine components by additive manufacturing (AM) technique using oxide dispersion strengthening (ODS) metal powder is presented. A novel combined mechanochemical bonding (MCB) plus ball milling process is utilized to produce near spherical and uniformly alloyed ODS powders. AM-processed ODS coating by direct energy deposition (DED) method on MAR-247 substrate, with laser powers from 100W to 200W were carried out. The ODS coated samples were then subjected to thermal cyclic loadings for over 2200 cycles. For comparison, in our earlier studies, under the same cyclic testing condition, typical tested TBC coupons showed spallation failure after ∼400 cycles. Correlation of the measured ODS coating Young’s modulus using a unique non-destructive micro-indentation testing method with evolution of the ODS microstructures are studied to identify optimum AM processing parameters for best performance of the ODS samples. In particular, stability of secondary γ′ phase in the ODS coating after thermal cycles is analyzed. Test results revealed a thin steady durable alpha alumina oxide layer on the best performance ODS samples. After 2,200 thermal cycles, strong bonding at ODS/substrate interface is also maintained for most of the ODS coated samples. Test results also showed stable substrate microstructure due to the protective ODS coating even after 2,200 thermal cycles. These preliminary test results showed strong potential for applications of AM-assisted ODS coating on advanced gas turbine components.
Data-Driven Pre-Design Tool for Small Scale Centrifugal Compressors in Refrigeration
Authors: Mounier Violette , Picard Cyril , Schiffmann Jürg
Published: August 2018

Domestic scale heat pumps and air conditioners are mainly driven by volumetric compressors. Yet the use of reduced scale centrifugal compressors is reconsidered due to their high efficiency and power density. Recent work has demonstrated the technical feasibility of a 20 mm centrifugal compressor on gas lubricated bearings operated with R134a by achieving isentropic efficiencies in excess of 75%. The design procedure of such centrifugal compressor starts by using pre-design tools based on the Cordier line. However, the optimality of the obtained pre-design, which is the starting point of a complex and iterative process, is not guaranteed, especially when small-scale compressors operating with organic fluids are targeted. This paper proposes an updated data-driven pre-design tool tailored for small-scale centrifugal compressors used in refrigeration applications. The pre-design model is generated using an experimentally validated 1D code which evaluates the compressor performance as a function of its detailed geometry and operating conditions. Using a symbolic regression tool, a reduced order model that predicts the performance of a given compressor geometry has been built. The proposed pre-design model offers an alternative to the tools available in literature by providing a higher level of detail and flexibility. Particularly, the model includes the effect of the pressure ratio PR and additional geometrical features such as blade height ratio b4 and the shroud to tip radius ratio r2s for addressing the inlet and exhaust areas. The analysis of the centrifugal compressor losses allows identifying the underlying phenomena that shape the new isentropic efficiency contours. As a consequence, for a specific operating condition, a compressor can have different geometries that yield the same efficiency. Low Ns compressors with high b4 are limited by blade loading and recirculation losses and operate closer to the surge limit. Compressors with low b4 and high Ns are exposed to high tip clearance and skin friction losses. Finally, the design space is limited at high Ns due to choke at the compressor inlet, while high incidence losses occur at low Ns at a constant r2s. Since incidence losses relate to the impeller inlet area, increasing r2s enables to achieve higher Ns, while decreasing r2s enables to explore lower Ns conditions. Compared to the 1D model the new pre-design model yields deviations below 4% on the isentropic efficiency, while running 1500 times faster. The new pre-design model is therefore of significant interest when the compressor is part of an integrated system design process.
Thermal Management System for the MEE and Engine Embedded Electric Machine
Authors: Morioka Noriko , Oyori Hitoshi , Seki Naoki , Fukuda Tsuyoshi , Suzuki Fuminori
Published: August 2018

The MEE (More Electric Engine) is a concept for engine system electrification and is an evolutionary step in engine system design that contributes to the reduction of aviation CO2 emissions. Mifee (Metering and integrated fuel feeding electrification) and the E3M (Engine Embedded Electric Machine) are the key technologies of the MEE. The purpose of engine thermal management is maintaining the balance between heat generation by the engine system and heat dissipation to the outside of the engine. In recent engine system designs, thermal system design has become an issue because of increased heat generation within the system. For example, a recently developed turbo-fan engine system increases the heat generation by introduction of a fan drive gear system that produces a large amount of heat in addition to the conventional heat source, such as engine main bearings and gears. The MEE will have further heat sources within its system, like the E3M, which is a high-power electric machine. In this paper, an investigation approach and the result of a feasibility study of the MEE thermal management system is described.

In addition, the perspective of the technology trend from the MEE toward future hybrid propulsion is also discussed. The global requirements for climate protection strongly demand game-changing technology that significantly improves the aircraft’s overall efficiency. A series/parallel partial hybrid propulsion system, in which both a turbo-fan engine and electrical motor-driven fans generate propulsive power, is considered to be one of the most promising approaches for the future commercial aircraft hybrid propulsion system. The MEE and E3M technology evolves until it will be applied in hybrid propulsion system.
Effect of Wake Negative Jet Flow on the Boundary Layer Transition of Compressor Cascade
Authors: Wang Yangang , Shao Qijie , Hu Wenbing
Published: August 2018

The present paper performed a numerical study on a high-loaded and high turning compressor cascade, where the unsteady boundary layer transition behavior on the cascade blade undergoing negative jet flow is revealed. The two-equation SST turbulence model coupled with Langtry-Menter transition model is verified and applied on all the computations in present study. Reynolds number and turbulent intensity are selected as two dominate candidates which can significantly influence the transition behavior and their effect were examined. Results show that under all the tested case (i.e., varying Reynolds number and turbulence intensity), the flow structures on the suction surface of the blade are rolled up when the unsteady negative jet flow directly impacting on the blade. However, the unsteady wake from upstream has not influenced the boundary layer. For high Reynolds number (i.e., Re = 400,000) the rolling up and shed of the boundary layer only occurs at blade trailing edge. The wake is evidenced be able to bring more energy into the boundary layer and thus separation and loss can be significantly decayed and reduced. Moreover, decreasing the turbulent intensity would in practical decay the transition in the boundary layer and therefore make the boundary layer easy to separate.
Investigation of Oil Jet Impingement on a Rotating Gear Using Lattice Boltzman Method (LBM)
Authors: Ambrose Stephen , Morvan Hervé , Simmons Kathy
Published: August 2018

In the drive for greater increases in fuel efficiency and reductions in CO2 emissions from aero engines, an epicyclic reduction gearbox can be used to break the link between the turbine and fan, enabling the engine to run at a higher bypass ratio. However, even small power losses can generate significant amounts of heat, due to the high loads transmitted from the gearbox. A substantial amount of cooling is required to remove this heat and a large part of this is supplied directly to the gear face. Assessing the performance of coolants and minimising the buildup of oil in the system is therefore a critical stage in the design process. Traditionally, finite volume CFD methods have been used to compute flow and heat transfer solutions. More recently, Lagrangian methods such as Smoothed Particle Hydrodynamics (SPH) have also been applied. The Lattice Boltzman Method (LBM) is a mesoscopic particle based method which uses statistical properties of particles based at each point of a lattice to calculate flow properties. This is a fully transient method and allows for a simple and efficient derivation of LES turbulence properties. In this work the Lattice Bolztman Method is used to investigate the impingement of an oil jet on a rotating spur gear. A comparison of LBM simulations is made against published work using other methods such as SPH and CFD — utilising the Volume of Fluid method — as well as a qualitative comparison with published experimental high speed images. These all show an excellent agreement and the simulations take the same order of magnitude of computational power as 3D single phase SPH, but are fully multiphase and have LES turbulence. This method is then used to investigate how changes to the oil feed delivery rate affect the spreading of the oil jet on the gear tooth and the splashing profiles. The potential for applying this method to other scenarios, such as lubricating and cooling meshing gears, is also discussed.
Preliminary Study of Supercritical CO2 Mixed With Gases for Power Cycle in Warm Environments
Authors: Baik Seungjoon , Lee Jeong Ik
Published: August 2018

The supercritical carbon dioxide (S-CO2) Brayton power cycle has been receiving worldwide attention due to the high thermal efficiency and compact system configuration. Because of the incompressible liquid like characteristic (e.g. high density, low compressibility) of the CO2 near the critical point (30.98 °C, 7.38MPa), an S-CO2 Brayton cycle can achieve high efficiency by reducing compression work. In order to utilize the S-CO2 power conversion technology in various applications, such as distributed power generation and marine propulsion, air-cooled waste heat removal system is necessary. However, the critical temperature of CO2 (30.98 °C) is an intrinsic limitation on the system minimum temperature. Because of the small difference with atmospheric temperature, a large amount of cooling air flow or a very large heat exchanger is required to reach the target minimum temperature. In this paper, to improve the system efficiency and ease the problem of air-cooled waste heat removal system, the mixture of supercritical CO2 with other fluids has been studied. Also, the preliminary performance test results of CO2 mixture with pre-existing experimental facility are evaluated.
Effect of Row Spacing on the Accuracy of Film Cooling Superposition Method
Authors: Wang Lang , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2018

Film cooling technique is widely used in a modern gas turbine. Many applications in hot sections require multiple film cooling rows to get better cooled. In most situation, the additive effect is computed using Sellers superposition method, but it is not accurate when the hole rows are close to each other. In this paper, row spacing between two rows of cooling hole was investigated by numerical method, which was validated by PSP results. The validation experiments are performed on flat test bench and the freestream is maintained at 25m/s. The inlet boundary conditions of numerical simulations were same with the experiment. Both round hole and shaped hole were investigated at blowing ratio M = 0.5, density ratios DR = 1.5 and row spacing S/D = 6, 10, 15, 20. It is found that the round hole results by Sellers method are similar to experiment results only at large row spacing, and the results of Sellers are always higher than experimental results. The boundary layer has a big effect on cooling effectiveness for round hole, but very little effect on shaped hole. When the row spacing increase, the difference between experiment and prediction become smaller. The vortex is the major factor to effect the accuracy of superposition method.
Thermodynamic Modelling Aspects of Wet Compression in Radial Compressors
Authors: Schuster Sebastian , Brillert Dieter , Hermes Viktor , Yildiz Attilla , Benra Friedrich-Karl
Published: August 2018

Wet compression or evaporative cooling is used during the compression of gases. Evaporative cooling reduces the power demand and keeps the discharge temperature in a suitable range. The cooling effect can be used before the impeller as well as within the impeller. The latter is more challenging and the focus of this research is on it. This paper looks into evaporative cooling in radial impellers from a general perspective in order not to limit the scope. Therefore, a mean line calculation program is applied. The program takes into account the entropy production due to the irreversible heat exchange between gas and liquid. This paper focuses on the thermodynamic aspects and shows how to analyse them. The paper highlights the necessity to consider the additional entropy production during the design and analysis process.
On the Influence of Fuel Stratification and its Control on the Efficiency of the Shockless Explosion Combustion Cycle
Authors: Rähse T. S. , Stathopoulos P. , Schäpel J.-S. , Arnold F. , King R.
Published: August 2018

Constant volume combustion cycles for gas turbines are considered a very promising alternative to the conventional Joule cycle and its variations. The reason is the considerably higher thermal efficiency of theses cycles, at least for their ideal versions. Shockless explosion combustion is a method to approximate constant volume combustion. It is a cyclic process that consists of four stages, namely wave propagation, fuel injection, homogeneous auto-ignition and exhaust. A pressure wave in the combustion chamber is used to realize the filling and exhaust phases. During the fuel injection stage, the equivalence ratio is controlled in such a way that the ignition delay time of the mixture matches its residence time in the chamber before self ignition. This means that the fuel injected first must have the longest ignition delay time and thus forms the leanest mixture with air. By the same token, fuel injected last must form the richest mixture with air (assuming that a rich mixture leads to a small ignition delay). The total injection time is equal to the time that the wave needs to reach the open combustor end and return as a pressure wave to the closed end. Up to date, fuel stratification has been neglected in thermodynamic simulations of the SEC cycle. The current work presents its effect on the thermal efficiency of the cycle and on the exhaust conditions (pressure, temperature and Mach number) of shockless explosion combustion chambers. This is done by integrating a fuel injection control algorithm in an existing CFD code. The capability of this algorithm to homogenize the auto-ignition process by improving the injection process has been demonstrated in past experimental studies of the SEC. The numerical code used for the simulation of the combustion process is based on the time-resolved 1D-Euler equations with source terms obtained from a detailed chemistry model.