bluuebunny/crossref_metadata_2025 huggingface dataset:
Conceptual Aerodynamic Design of a Tail-Cone Thruster System Under Axi-Symmetric Inlet Distortion
Authors: Lee B. J. , Liou May-Fun , Liou Meng-Sing
Published: August 2018

This paper presents a conceptual design of a tail-cone thruster system which is operating under an axisymmetric inlet distortion. An effort to realize the targeted fuel burn saving that was proposed in NASA’s STARC_ABL aircraft design is made through a CFD based design approach. This method employs three iterative steps to exploit the CFD tools until the design requirements are met: a quasi-2D through-flow model to design the fan/EGV, a 3-D RANS simulation of the single blade row to account for the inlet/fan and the EGV/nozzle interaction, and a 3-D RANS simulation of the airframe with a propulsor installed – propulsion airframe integration (PAI). The design requirements which include the thrust, and shaft power of the propulsor are matched throughout the evaluations coming from two CFD domains, i.e., the turbo-machinery and the PAI. During the switch between these different computational domains, the inlet and exit profiles are matched via the correction factors of the body-force model.

The present tail-cone thruster (TCT) aerodynamic design leverages a low-pressure ratio fan (FPR = 1.2∼1.25) of which the camber-line angles are predicted by a quasi-2D through-flow model. The quasi-2D model is derived to analyze the radially distorted flow resulting from the ingested boundary layer at the inlet. It also estimates the appropriate velocity vectors of the metal angles of the fan and EGV which is subjected to different types of vortex at the fan exit.

The baseline geometry is revisited and its internal flow-path and exhaust cone are redesigned to illustrate the strong correlation among the components of the propulsor in the PAI domain. The peak efficiency point of the fan/EGV with respect to the blade counts, a.k.a. solidity, and rotational speed is chosen for the cruise condition via parametric studies. The corresponding performance maps are presented. The resulting performance metrics of the new conceptual design of the BLI propulsor are analyzed and compared with these of the baseline in the PAI aspect. Finally, ideas of the CFD based design of a BLI propulsor are discussed based on the observations drawn from the numerical results.
Advanced Welding Materials and Technologies for Repair of Turbine Engine Components Manufactured of High Gamma Prime Nickel Based Superalloys
Authors: Gontcharov Alexandre , Tian Yuan , Lowden Paul , Tollett Robert , Brochu Mathieu
Published: August 2018

The current study reports on modification of conventional welding materials with titanium, boron and silicon to enhance weldability by reducing the solidus temperature and promoting the formation of low temperature eutectics. Melting behavior, weld microstructure, tensile and stress rupture strength are reported for several alloy compositions. Some examples of repairs of IGT and aero HPT blades using the materials and technologies are provided.
Numerical Modelling of Shock Wave Boundary Layer Interactions in Aero-Engine Intakes at Incidence
Authors: Kalsi Hardeep S. , Tucker Paul G.
Published: August 2018

During situations of high incidence, high curvature of aero-engine intake lips can locally accelerate flow to supersonic speeds, producing undesirable shock wave boundary layer interactions (SWBLIs). The present work describes simulations of a novel experimental model resembling a lower intake lip at incidence. RANS, LES and hybrid RANS-LES are carried out at two angles of attack, α = 23° and α = 25°, with α = 25° possessing a high degree of shock oscillation. Modifications to the Spalart-Allmaras (SA) RANS turbulence model are proposed to account for re-laminarisation and curvature. These provide an improvement in prediction compared standard SA model. However, RANS models fail to reproduce post shock interaction flow, giving incorrect shape of the flow distortion. LES and hybrid RANS-LES perform well here, with downstream flow distortion in very good agreement with experimental measurements. LES and hybrid RANS-LES also capture the time averaged smearing of the shock which RANS cannot. However, low frequency shock oscillations in the α = 25° case are costly for LES, requiring long simulation time to obtain time averaged flow statistics. Hybrid RANS-LES offers a significant saving in computational cost, costing approximately 20% of LES.
Turbine Nozzle Endwall Phantom Cooling With Compound Angled Pressure Side Injection
Authors: Liu Kevin , Xu Hongzhou , Fox Michael
Published: August 2018

Cooling of the turbine nozzle endwall is challenging due to its complex flow field involving strong secondary flows. Increasingly-effective cooling schemes are required to meet the higher turbine inlet temperatures required by today’s gas turbine applications. Therefore, in order to cool the endwall surface near the pressure side of the airfoil and the trailing edge extended area, the spent cooling air from the airfoil film cooling and pressure side discharge slots, referred to as “phantom cooling” is utilized. This paper studies the effect of compound angled pressure side injection on nozzle endwall surface. The measurements were conducted in a high speed linear cascade, which consists of three nozzle vanes and four flow passages. Two nozzle test models with a similar film cooling design were investigated, one with an axial pressure side film cooling row and trailing edge slots; the other with the same cooling features but with compound angled injection, aiming at the test endwall. Phantom cooling effectiveness on the endwall was measured using a Pressure Sensitive Paint (PSP) technique through the mass transfer analogy. Two-dimensional phantom cooling effectiveness distributions on the endwall surface are presented for four MFR (Mass Flow Ratio) values in each test case. Then the phantom cooling effectiveness distributions are pitchwise-averaged along the axial direction and comparisons were made to show the effect of the compound angled injection. The results indicated that the endwall phantom cooling effectiveness increases with the MFR significantly. A compound angle of the pressure side slots also enhanced the endwall phantom cooling significantly. For combined injections, the phantom cooling effectiveness is much higher than the pressure side slots injection only in the endwall downstream extended area.
Numerical Investigation for Characteristics and Oil-Air Distributions of Oil Film in a Tilting-Pad Journal Bearing
Authors: Ding Aoshuang , Xiao Yaobing
Published: August 2018

This paper analyzes the effects of air in the oil film of a tilting-pad journal bearing on oil-air distributions and characteristics. With a gaseous cavitation model and shear stress transport (SST) model with low-Re correction included, the air backflow from the outlet boundary is analyzed in numerical simulations of a titling-pad journal bearing at 3000 rpm rotation speed and under 180 kN load. The simulated bearing load, pressure and mechanical loss are in good accordance with the experimental data, indicating that the simulation results of the air backflow from the outlet boundary can catch the hydrodynamic characteristics accurately. Based on the analyses of simulated air volume fraction and shear stress, the shear stress of the high-pressure loaded area is mainly influenced by the velocity gradient in the normal direction to the rotor-side wall, not the air backflow and gaseous cavitation. In the unloaded area, the gaseous cavitation occurs around the center part, following the gaseous cavitation mechanisms. The backflow air flows into the low-pressure unloaded area from the outlet boundary and has a clear interval with the air from the gaseous cavitation. The air volume fraction increases with these two air sources and affects the mixture viscosity significantly, eventually influencing the shear stress on the rotor-side wall and bearing mechanical loss.
Impact of Blade Flexibility on Wind Turbine Loads and Pitch Settings
Authors: Chen Jinge , Shen Xin , Zhu Xiaocheng , Du Zhaohui
Published: August 2018

Along with the upscaling tendency, lighter and so more flexible wind turbine blades are introduced for reducing cost of manufacture and materials. The flexible blade deforms under aerodynamic loads and in turn affects the flow field, arising the aero-elastic problems. In this paper, the impact of blade flexibility on the wind turbine loads, power production, and pitch actions is discussed. An aeroelastic model is developed for the study. A free wake vortex lattice model is used to calculate the aerodynamic loads, and a geometrically exact beam theory is adopted to compute the structural dynamics of the blade. The flap, lead-lag bending and torsion DOFs are all included and nonlinear effects due to large deflections are considered. The NREL 5MW reference wind turbine is analyzed. Influences of pure-bending and bending-torsion deformations of the blade on aerodynamic loads are compared. The aerodynamic force distributions under various wind speeds for rigid and flexible blades are also compared. The steady state deformations across the operational conditions are calculated, along with the rotor power production. Significant reduction of power is seen especially under large wind speeds, due to the blade twist deformations under torsion moments. Lower pitch angle settings should be applied to maintain the constant power.
Investigation of Engine Waste Heat Recovery Using Supercritical CO2(S-CO2) Cycle System
Authors: Song Jian , Ren Xiao-dong , Gu Chun-wei
Published: August 2018

Primary energy consumption of diesel engines is increasing rapidly and strict emission standards are introduced by the government. Interests in engine waste heat recovery have been renewed to alleviate the energy shortage and emission issues. Supercritical CO2 (S-CO2) cycle has emerged as a promising method considering its compact structure and system safety level in addition to the environmental friendly characteristics. This paper explores the potential of using S-CO2 cycle system for engine waste heat recovery. Both heat load from the low temperature jacket cooling water and the high temperature engine exhaust gas are intended to be recovered. In the original system, the jacket cooling water is used to preheat the S-CO2 working fluid and the engine exhaust gas is utilized in the preheater. As an optimized scheme, system with two preheaters is presented. The engine exhaust gas is further cooled in a high temperature preheater after the jacket cooling water in the low temperature preheater. The available heat load from these two heat sources can be entirely recovered. However, the increasing preheating temperature suppresses the regeneration effect. A regeneration branch is then added in the system. Part of the S-CO2 working fluid from the compressor goes into a low temperature regenerator and then converges with the other part from the two preheats. A deeper utilization of the regeneration heat load is achieved and performance enhancement of the S-CO2 cycle system is expected. The maximum net power output of the system with regeneration branch reaches 82.8 kW, which results in an 8.5% increment on the engine power output.
Numerical Study of Blade Tip Cooling at High Speed With Tip and Pressure-Side Coolant Injections
Authors: Zhou Zhihua , Wang Songtao , Chen Shaowen
Published: August 2018

The tip clearance between turbine blade and stationary casing leads to the exposure of blade tip to high temperature gas and contributes to a high thermal load in this region. Then it is necessary to perform cooling on the blade tip. Moreover, the tip leakage flow in a high speed brings complex aerothermal conditions to the blade tip. The blade tip film cooling on the transonic squealer tip is investigated in this research. The effects of tip and pressure-side coolant injections on the blade tip heat transfer are discussed. And the influences of total pressure ratio of coolant to main flow and endwall moving on the film cooling are considered. Firstly, the reliability of a commercial CFD code with different turbulence models was first validated by contrasting with the experimental results. The heat flux and isentropic Ma number predicted with the BSL k-ω model shows a better agreement with the test data. Then the mesh independency study was performed. The mesh with tip and pressure-side injection hole is generated by in-house code. For the tip without film cooling at outlet Mach number of 0.96, the squealer tip shows a high heat transfer at front of the tip cavity floor caused by the impingement of tip leakage flow, besides the suction-side rim has high heat transfer coefficient. With the tip coolant injection, the tip coolant is pushed towards the cavity pressure-side and provides better coverage in this region. At the front of cavity floor near suction-side, there is almost no coolant coverage then it shows little cooling effects. The coolant discharges from the tip over the suction-side rim thereby the heat transfer near the trailing edge is less affected by the tip coolant injection. With the pressure-side near tip film cooling, the coolant injection shows high film-cooling effectiveness at low coolant stagnation pressure and lift off blade surface at high coolant stagnation pressure. The endwall motion increases the total heat load of the blade tip by increase heat load at cavity floor and suction-side near tip region and the reduces film-cooling effectiveness.
Using Turbulence Intensity and Reynolds Number to Predict Flow Separation on a Highly Loaded, Low-Pressure Gas Turbine Blade at Low Reynolds Numbers
Authors: Van Treuren Kenneth , Pharris Tyler , Hirst Olivia
Published: August 2018

The low-pressure turbine has become more important in the last few decades because of the increased emphasis on higher overall pressure and bypass ratios. The desire is to increase blade loading to reduce blade counts and stages in the low-pressure turbine of a gas turbine engine. Increased turbine inlet temperatures for newer cycles results in higher temperatures in the low-pressure turbine, especially the latter stages, where cooling technologies are not used. These higher temperatures lead to higher work from the turbine and this, combined with the high loadings, can lead to flow separation. Separation is more likely in engines operating at high altitudes and reduced throttle setting.

At the high Reynolds numbers found at takeoff, the flow over a low-pressure turbine blade tends to stay attached. At lower blade Reynolds numbers (25,000 to 200,000), found during cruise at high altitudes, the flow on the suction surface of the low-pressure turbine blades is inclined to separate. This paper is a study on the flow characteristics of the L1A turbine blade at three low Reynolds numbers (60,000, 108,000, and 165,000) and 15 turbulence intensities (1.89% to 19.87%) in a steady flow cascade wind tunnel. With this data, it is possible to examine the impact of Reynolds number and turbulence intensity on the location of the initiation of flow separation, the flow separation zone, and the reattachment location. Quantifying the change in separated flow as a result of varying Reynolds numbers and turbulence intensities will help to characterize the low momentum flow environments in which the low-pressure turbine must operate and how this might impact the operation of the engine. Based on the data presented, it is possible to predict the location and size of the separation as a function of both the Reynolds number and upstream freestream turbulence intensity (FSTI). Being able to predict this flow behavior can lead to more effective blade designs using either passive or active flow control to reduce or eliminate flow separation.
Effect of Circumferential Location of Radial Injection on Rotordynamic Performance of Hybrid Air Foil Bearings
Authors: Zamanian Yazdi Behzad , Kim Daejong
Published: August 2018

Air foil bearings (AFBs) are introduced as promising bearings for oil-free turbomachinery applications. AFBs provide reliable operation at high speed and high temperature with negligible power loss. Hybrid Air Foil Bearing (HAFB) technology utilizes the radial injection of externally pressurized air into the traditional hydrodynamic AFB’s film thickness through orifices attached to the top foil. Previous studies have reported enhancement in the rotordynamic stability of HAFBs compared to traditional hydrodynamic AFBs. HAFBs have several orifices distributed in the circumferential direction. In this study, the effect of the circumferential location of radial injection on the rotordynamic performance of the rotor-HAFB is studied. Analytical and experimental evaluations of the rotordynamic performance of a rotor supported by two single-pad HAFBs are presented. Parametric studies are conducted using three sets of single-pad HAFBs. The circumferential locations of orifices are different for each set. The presented simulation analyses consist of time-domain orbit simulation and frequency-domain modal analysis. Imbalance responses of rotor-HAFB were measured with various orifice locations and the results agree well with predictions. Comparison of the rotordynamic performance of HAFBs with different orifice configurations demonstrate substantial improvement in rotordynamic stability as well as enhancement in the stiffness and damping coefficients of HAFBs by choosing the best circumferential location for radial injection to control rotor eccentricity and attitude angle.
Performance Impact of Manufacturing Tolerances for a Turbine Blade Using Second Order Sensitivities
Authors: Luo Jiaqi , Liu Feng
Published: August 2018

Performance changes due to manufacturing variations for a turbine blade are evaluated in the paper using the first order (FO) and second order (SO) sensitivities, which are calculated by a continuous adjoint method. In the case of newly manufactured blades, the geometric variation at each scanning point is assumed to meet a standard normal distribution. In the study, a modelling method taking into account the spatial correlations is employed to quantify the geometric uncertainty, where the contour of manufacturing tolerance is produced by imposing a series of shape functions on the blade. The basis modes of the geometric variations are extracted by principle component analysis. Firstly, the calculations of both FO and SO Sensitivities by solving the Euler adjoint equations are introduced. By regarding a finite number of primary basis modes of the geometric variations as the geometric parameters, the SO sensitivities can be obtained with significantly reduced computation cost. Sensitivity validations and performance evaluations based on sensitivities for each basis mode are then presented, illustrating the dramatic improvements on performance evaluations using the SO sensitivities. Finally, the statistics of performance changes for the turbine blade are evaluated by using the Monte Carlo simulations with respect to two different probability density functions for the input random variables. The results further demonstrate that the nonlinear dependence of the aerodynamic performance on the geometric variations can be captured by using the SO sensitivities.
A Numerical Model for Simulating Liquid Particles Deposition on Surface
Authors: Liu Zhenxia , Zhang Fei , Liu Zhengang
Published: August 2018

The deposition of liquid particles, which may be converted from solid particles due to high temperature gas heating, makes much more harm on turbine vane blades compared to solid particles, since it may block film-cooling holes, worsen the cooling efficiency and aerodynamic performance of the turbine vane blades. Due to the similarity between the deposition of liquid particles on a surface and the icing on a surface, a numerical model for simulating particles deposition was developed based on the Myers icing model, an extension of the Messinger model, which has been applied in predicting aircraft icing or aero-engine icing. Compared to the conventional liquid particle deposition model, the numerical model in this paper considers the heat transfer and the flow of liquid particles during the particles phase transition from liquid state to solid state. In this model, the change of the surface profile due to the particles deposition was also considered, which was implemented with dynamic mesh technique. To test this model, deposition distribution and thickness obtained from the numerical simulations were compared to the experimental results. Additionally, a numerical simulation was conducted for liquid particle deposition on a flat plate. The result showed that the deposition thickness at the leading edge was much larger than that on the upper surface where the deposition appeared mainly at the middle and rear of the plate. The deposition mass and thickness increased with the increasing in the particle size. The effect of the particle size on the deposition thickness was more notable on the upper surface compared to that at the leading edge.
A Comparison of Two Microslip Contact Models for Studying the Mechanics of Underplatform Dampers
Authors: Xu Chao , Li Dongwu , Gola Muzio M. , Gastaldi Chiara
Published: August 2018

In turbine blade systems, under-platform dampers are widely used to attenuate excessive resonant vibrations. Subjected to vibration excitation, the components with frictionally constrained interfaces can involve very complex contact kinematics induced by tangential and normal relative motions. To effectively calculate the dynamics of a blade-damper system, contact models which can accurately reproduce the interface normal and tangential motions are required. The large majority of works have been developed using macroslip friction models to model the friction damping at the contact interface. However, for those cases with small tangential displacement where high normal loads are applied, macroslip models are not enough to give accurate results. In this paper two recently published microslip models are compared, between them and against the simple macroslip spring-slider model. The aim is to find to which extent these models can accurately predict damper mechanics. One model is the so called GG array, where an array of macroslip elements is used. Each macroslip element of the GG array is assigned its own contact parameters and for each of them four parameters are needed: normal stiffness, tangential stiffness, normal gap and friction coefficient. The other one is a novel continuous microslip friction model. The model is based on a modification of the original classic IWAN model to couple normal and tangential contact loads. Like the GG array the model needs normal and tangential stiffness, and friction coefficient. Unlike the GG array the model is continuous and, instead of the normal gap required by the GG array, the Modified IWAN model needs a preload value. The two models are here applied to the study of the mechanics of a laboratory under-platform damper test rig. The results from the two models are compared and allow their difference, both for damper mechanics and for the complex-spring coefficients, to be assessed.
Improvement of Low Frequency Vibration Isolation Capability of AMB Using a Cascade PID Controller
Authors: Su Yixin , Ma Yanhui , Gu Yongpeng , Yu Suyuan , Ren Gexue
Published: August 2018

In contrast with traditional mechanical bearing, Active magnetic bearing (AMB) has no friction and lubrication, and its dynamic performance can be adjusted by active control. To isolate low frequency vibration of the rotating machinery under 50Hz, a novel design of cascade PID controller (CPC) with two control loops for AMB is proposed. The main loop is a position loop and the secondary loop is a transmission force loop. According to the theoretical derivations in this study, the CPC controls both the rotor position and the transmission force. Even when the control parameters maintain constant, the dynamic characteristic parameters, equivalent stiffness and equivalent damping, vary with frequency continuously and smoothly. Therefore, they can be adjusted in a wide range to achieve isolation of low frequency vibration when using proper control parameters. A simulation example shows that the transmission force with a CPC is lower in the 8–50Hz when the rotor displacement is almost same as with a single stage PID controller (SSPC). Experimental verification was carried out in an experimental bench of AMB under unbalanced rotor condition. Results show that a CPC can reduce the vibration acceleration at 15–50Hz especially near the peaks. Simulation and experimental results well demonstrate the effectiveness and guaranteed stability of the CPC in the present study.
Simulation Study on the Work Characteristics of Combined Diesel-Electric and Gas Turbine (CODLAG)
Authors: Wang Zhitao , Li Jian , Li Tielei , Wang Weitian , Li Shuying
Published: August 2018

The combined diesel-electric and gas turbine (CODLAG) plant is a new type of ship power plant combining the advantages of electric propulsion system and mechanical propulsion system. The requires about ship power grid is lower than full electric propulsion mode, at the same time it can gain the quiet of electric propulsion in the low working conditions and increase the mobility of the ship in the high working conditions. Unlike traditional mechanical propulsion methods and forward-looking all-electric propulsion methods, the CODLAG plant has a coupling between mechanical propulsion and electric propulsion mode. The cooperative working characteristics of two different nature systems is still need further research.

For the in-depth research of CODLAG device’s characters, this study built a simulation model of CODLAG device based on Matlab/Simulink and C/C++ platform. A kind of torque-shaft speed double closed-loop control strategy based on PID was used on the CODLAG device. And the typical work condition of CODLAG, including merging, merging off and variable work condition, was simulated in this study.

Through the simulation, the dynamic response of main parameters at typical condition have been got. Then, characters of CODLAG device with CPP was simulated at variable condition. And the thrust response was compared with FPP’s. Through comparative analysis, the effectiveness of integrated simulation method specifying to CODLAG device was verified, and some useful conference was provided for the future research.
The Mechanism of the Flow in the Hub Corner and the Control by Tailing Edge Gaps
Authors: Zhao Wenfeng , Jiang Bin , Duan Yu , Tian Zhitao , Zheng Qun
Published: August 2018

High-pressure ratio is one of the important characteristics of the sustainable development of the modern aero-engine compressor components. When the fluid flows through the compressor cascade row, it will be influenced by both the streamwise pressure gradient and the transverse pressure gradient, which will cause hub-corner separation or stall. In this paper, different diffusion factors are chosen for the cascades. Each diffusion factor has different turning angles. The formation mechanism of hub-corner separation is studied under the condition of zero angle of attack. Numerical simulation is used to study the influence of pressure gradient on the flow field in the corner. The scale of the concentrated shed vortex forms in the suction surface increases with the increasing of the transverse pressure gradient during the hub-corner separation. When the streamwise pressure gradient increases, the suction surface vortex forms the corner stall. By reasonable design, the two vortexes can cancel out each other. At this time, the loss of cascades is the minimum.

Based on the flow mechanism of the corner separation/stall, the trailing gaps are set on three typical turn angle cascades. The results show that the trailing gaps can control the radial development of the suction surface vortex during the stall and improve flow field. The jet cannot blow the suction side boundary layer away during the corner separation, because the gap does not change the static pressure distribution at the root of the cascade. In a word, the trailing edge gaps can not only inhibit the separation in the hub corner but also have the minimum leakage loss at design point. It can be used as an effective and practical compressor design method.
Design Optimization of Heat Exchangers for Aero Engines With the Use of a Surrogate Model Incorporating Performance Characteristics and Geometrical Constraints
Authors: Salpingidou Christina , Misirlis Dimitrios , Vlahostergios Zinon , Flouros Michael , Donus Fabian , Yakinthos Kyros
Published: August 2018

The present work is focused on the optimization of the performance characteristics of a recuperator specifically designed for aero engine applications, targeting the reduction of specific fuel consumption and taking into consideration aero engine geometrical constraints and limitations. The recuperator design was based on the elliptically profiled tubular heat exchanger which was developed and invented by MTU Aero Engines AG. For the specific fuel consumption investigations the Intercooled Recuperated Aero engine cycle, combining both intercooling and recuperation, was considered.

The optimization was performed with the development of a recuperator surrogate model, capable to incorporate major recuperator geometrical features. A large number of recuperator design scenarios was assessed, in which additional design criteria and constraints were applied. Thus, a significantly large recuperator design space was covered resulting to the identification of feasible recuperator designs providing beneficial effect on the Intercooled Recuperated Aero engine leading to reduced specific fuel consumption and weight.
An Advanced Surge Dynamic Model for Simulating ESD Events and Comparing Different Anti-Surge Strategies
Authors: Munari Enrico , Morini Mirko , Pinelli Michele , Brun Klaus , Simons Sarah , Kurz Rainer , Moore Jeffrey
Published: August 2018

Despite advancements in research and industry, compressors still have to operate in the stable region of the characteristic curves otherwise, at low flow ranges, they enter an unstable regime. The worst instability that can arise in industrial compressors is called surge, which involves the whole system in view of the fact that it generates dangerous pressure and mass flow fluctuations. Thus, this phenomenon has to be prevented since it implies the deterioration of performance and leads to mechanical damage to the compressor and system components.

It is clear that, currently, compression system models have a crucial role in predicting the phenomena which can occur in the compressor and pipelines during operation.

In this paper, a dynamic model, developed in the Matlab/Simulink environment, is further implemented to allow the study of surge events caused by rapid transients, such as emergency shutdown events (ESD). The aim is to validate the experimental data obtained in a single stage centrifugal compressor installed in the test facility at Southwest Research Institute. The test facility consists of a closed loop system and is characterized by a recycling circuit, and thus a recycling valve, which is opened in case of surge or driver shutdown. In this work, the recycling circuit is implemented in the model as well, and comparisons between recorded data and simulations were carried out. Moreover, different actions for recovering/preventing surge are simulated by controlling different valves along the piping system and by adding a check valve immediately downstream the compressor.

The results demonstrated the fidelity of the model and its capability of simulating piping systems with different configurations and components, also showing, qualitatively, the different effects of some alternative actions which can be taken after surge onset.
Stall and Surge in Wet Compression: Test Rig Development and Experimental Results
Authors: Munari Enrico , D’Elia Gianluca , Morini Mirko , Pinelli Michele , Spina Pier Ruggero
Published: August 2018

Wet compression is a strategy adopted to increase the power output of gas turbines, with respect to dry conditions, usually also incrementing the operating range of the compressor. However, stall and surge are two aerodynamic instabilities which depend on many factors, and they are expected to occur even in wet compression at low flow rates. Despite the many studies carried out in the last 80 years, literature does not offer many works concerning these instability phenomena in wet compression. In this paper, an experimental analysis of stall and surge in wet compression conditions is carried out on an axial-centrifugal compressor installed in an existing test rig at the Engineering Department of the University of Ferrara. Some modifications of the test rig were necessary.

The intake duct was implemented with a water injection system which, by means of water spray injectors, allows the uniform mixing of air and water before the compressor inlet. The control and data acquisition system of the test bench was updated with new hardware and software to obtain faster data sampling. Transient and steady-state tests were carried out to make a comparison with the experimental results in dry conditions. The analysis was carried out using traditional thermodynamic sensors, by means of both classic post-processing techniques, and cyclostationary analysis.

The aim is to i) evaluate the influence of wet compression on the stable performance of the compressor ii) qualitatively identify the characteristics of stall and surge in wet compression by means of sensors which were shown to capture these phenomena well and iii) demonstrate the reliability of cyclostationary analysis in wet compression conditions for stall and surge analysis.
A Review of Wet Gas Flow Rate Measurements by Means of Single-Phase Meters
Authors: Munari Enrico , Pinelli Michele
Published: August 2018

Nowadays, wet gas flow rate measurement is still a challenge for experimental investigators and it is becoming an even more important issue to overcome in the turbomachinery sector as well, due to the increasing trend of wet compression applications in industry. The requirement to determine gas turbine performance when processing a wet gas leads to the need to understand certain phenomena, such as type of liquid flow re-distribution, and errors introduced when the mass flow rate measurement of a two-phase gas is attempted. Unfortunately, this measurement is often affected by the presence of liquid. Literature does not offer a unique definition of the term wet gas, although it is recognized that a wet gas can generally be defined as a two-phase gas in which the liquid percentage is lower than the gas one. This paper aims to collect and describe the main works present in literature in order to clarify i) the most used parameters that describe the types of wet gas, and ii) the types of errors and flow patterns which occur in different types of applications, in terms of pressure, percentage of liquid, Reynolds number, etc. Therefore, this literature review offers a comprehensive description of the possible effects of liquid presence in a wet gas and, and an in-depth analysis of the limitations and beneficial effects of current single-phase flow rate sensors in order to identify the best solutions, and empirical corrections available in literature to overcome this challenge.
Adaptive Preliminary-Design Workflow for Aero Engine Secondary Air System Cavities With an Application Case of Windage and Heat Transfer in a Rotor-Stator Cavity With Axial Through Flow
Authors: Wildow Toni , Dengg Hubert , Höschler Klaus , Sommerfeld Jonathan
Published: August 2018

At the preliminary design stage of the engine design process, the behaviour and efficiency of different engine designs are investigated and evaluated in order to find a best matching design for a set of engine objectives and requirements. The prediction of critical part temperatures as well as the reduction of the uncertainty of these predictions is decisive to bid a competitive technology in aerospace technology. Automated workflows and Design of Experiments (DOE) are widely used to investigate large number of designs and to find an optimized solution. Nowadays, technological progress in computational power as well as new strategies for data handling and management enables the implementation of large DOEs and multi-objective optimizations in less time, which also allows the consideration of more detailed investigations in early design stages.

This paper describes an approach for a preliminary-design workflow that implements adaptive modelling and evaluation methods for cavities in the secondary air system (SAS). The starting point for the workflow is a parametric geometry model defining the rotating and static components. The flow network within the SAS is automatically recognized and CFD and Thermal-FE models are automatically generated using a library of generic models. Adaptive evaluation algorithms are developed and used to predict values for structural, air system and thermal behaviour. Furthermore, these models and evaluation techniques can be implemented in a DOE to investigate the impact of design parameters on the predicted values. The findings from the automated studies can be used to enhance the boundary conditions of actual design models in later design stages.

A design investigation on a rotor-stator cavity with axial through flow has been undertaken using the proposed workflow to extract windage, flow field and heat transfer information from adiabatic CFD calculations for use in thermal modelling. A DOE has been set up to conduct a sensitivity analysis of the flow field properties and to identify the impact of the design parameters. Additionally, impacts on the distribution of the flow field parameters along the rotating surface are recognized, which offers a better prediction for local effects in the thermal FE model.
Structural Analysis of Profiled Tubes for a Turbofan Engine Supercritical-CO2 Bottoming Cycle Heat Exchanger
Authors: Rengel Jon , Jacob Florian , Rolt Andrew , Sethi Vishal
Published: August 2018

The EU Horizon 2020 ULTIMATE project aims to mitigate one of the greatest loss sources in modern turbofans: the heat in core exhaust gases. The introduction of a closed-circuit recuperated bottoming cycle, using supercritical CO2 (S-CO2) as a working fluid that is heated by the exhaust gases, has been shown to be a feasible option.

Involute spiral heat exchangers have been studied for intercoolers and cooled cooling air systems. However, placing them in the core exhaust and using S-CO2 implies significant mechanical design challenges from the elevated temperatures and high internal pressures. The studied scenario considers a heat exchanger of 60% effectiveness, with an internal fluid pressure of 32 MPa. The primary objective is to minimise the total mass of the heat exchanger tubes.

The work is focused on studying elliptical tubes and an alternative multi-arc cross-section design with internal webs that is more structurally efficient. A parametric analysis of the proposed geometry has been conducted to capture the influence of each of the geometric variables on the resulting stresses.

The alloy Ti-6Al-4V is selected as the tube material and the results show that for a 400 MPa maximum allowable stress, a chord of 10 mm, a chord to thickness ratio of eight and a mi nimum wall thickness of 0.2 mm, the minimum tube weight is 20.5 g/m.
Thermal Stability Analysis of Gevo Jet Fuel Using Ellipsometry
Authors: Nash Leigh , Klettlinger Jennifer , Vasu Subith
Published: August 2018

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine’s combustion performance. In this work, the thermal stability of Gevo fuel, an alcohol to jet fuel made from plant derived feedstock, was studied. This analysis was used to comment on the effectiveness of the current thermal stability test standard. This work was performed using a spectroscopic ellipsometer to measure the thickness of deposits left on aluminum substrates. It was observed that Gevo deposit thickness increased slowly up to 375 °C and much more rapidly after that point. Similar behavior was observed in JP-8 fuel. Comparisons were also made between color standard ratings and ellipsometric thickness measurements, and it was found that in some cases, darker colors did not indicate thicker deposits. Reference tubes were used to validate the optical models used in this work, and different optical constants were found to best model the results than what are published in the ASTM D3241 test method for thermal stability.
LES and RANS Analysis of the End-Wall Flow in a Linear LPT Cascade: Part I — Flow and Secondary Vorticity Fields Under Varying Inlet Condition
Authors: Pichler R. , Zhao Yaomin , Sandberg R. D. , Michelassi V. , Pacciani R. , Marconcini M. , Arnone A.
Published: August 2018

In low-pressure-turbines (LPT) around 60–70% of losses are generated away from end-walls, while the remaining 30–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Experimental and numerical studies have shown how the strength and penetration of the secondary flow depends on the characteristics of the incoming end-wall boundary layer. Experimental techniques did shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving CFD allowed to dive deep into the details of the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 LPT profile at Re = 120K and M = 0.59 by benchmarking with experiments and investigating the impact of the incoming boundary layer state. The simulations are carried out with proven Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulation (LES) solvers to determine if Reynolds Averaged models can capture the relevant flow details with enough accuracy to drive the design of this flow region.

Part I of the paper focuses on the critical grid needs to ensure accurate LES, and on the analysis of the overall time averaged flow field and comparison between RANS, LES and measurements when available. In particular, the growth of secondary flow features, the trace and strength of the secondary vortex system, its impact on the blade load variation along the span and end-wall flow visualizations are analysed. The ability of LES and RANS to accurately predict the secondary flows is discussed together with the implications this has on design.
Reduction of Burner Variants for Differing Fuel Compositions by Combining Intelligent Control Methods and Experimental Data of Siemens SGT-400 Dry Low Emission Combustion System
Authors: Hubbard Phill , Liu Kexin , Sadasivuni Suresh , Bulat Ghenadie
Published: August 2018

Extension of gas fuel flexibility of a current production standard SGT-400 industrial gas turbine combustor is reported in this paper.

A successful development program has increased the capability of the standard production dry low emissions burner configuration to burn a range of fuels covering a temperature corrected wobbe index from 30 to 49 MJ/m3. A standard SGT-400 13.4 MW dry low emission double skinned combustor can was tested with a standard production gas burner for a cannular combustion system. Emissions, combustion dynamics, fuel pressure and flashback monitoring via measurement of burner metal temperatures, were the main parameters used to evaluate the impact of fuel flexibility on combustor performance. High pressure rig tests were carried out to demonstrate the capabilities of the combustion system at engine operating conditions across a wide range of ambient conditions. Variations of the fuel heating value were achieved by blending natural gas with CO2 as diluent.

The standard SGT-400 combustion system employs proven dry low emissions technology for natural gas and liquid fuels such as diesel within a specified range of fuel heating values. With the aid of novel intelligent control software, the gas fuel capability of the SGT-400 standard dry low emissions burner has been extended, with the engine, achieving stable operation and reduced emissions across the load range despite variations of the composition of the fuel supply. This, combined with previous experience from high pressure rig and engine testing of the different burner configurations that covered this range, resulted in a reduction in the number of hardware configurations from three burners to two. Testing showed that the standard production burner can reliably operate with a fuel temperature controlled wobbe index as low as 30 MJ/m3 which corresponds to 20% CO2 (by volume) in the fuel.

The performance of four different fuels with heating values in terms of temperature controlled wobbe index: 30, 33, 35 and 45 MJ/m3 (natural gas), is presented for the current production hardware. Test results show that NOx emissions decrease as the fuel heating value is reduced. Also note that a decreasing temperature controlled wobbe index leads to a requirement to increase the fuel supply pressure. The tests results obtained on the Siemens SGT-400 combustion system provide significant improvement for industrial gas turbine burner design for fuel flexibility.
Unsteady Aspects of Multi-Interacting Swirlers Using POD Analysis
Authors: Vashahi Foad , Rezaei Shahnaz , Lee Jeekeun
Published: August 2018

Twin annular premixed swirler known as TAPS by GE has provided an effective solution to generate low NOx combustion by implementing both diffusion and premixed flames. The fuel injector is less susceptible to combustion instabilities owing to its central diffusion flame and eco-friendly due to its radial premixed swirler. To this extent, 2D PIV experiment was conducted on three newly designed triple swirlers to measure their corresponding velocity fields. The swirlers were designed in a way that the inner and intermediate swirlers are axial type, counter-rotating and remained unchanged with three different radial type outer swirlers. The design characteristic swirl numbers of the outer swirlers were 0.5, 1.0 and 1.5, to impose low, medium and intense swirling motion, respectively. The main objective of the current study is to investigate the interaction of the shear layers emerging from the outer swirler with the both inner and intermediate. Air is used as working fluid and experiments were done in confined condition. The study of the mean flow field indicated that the outer swirler dominates the flow field and defines the behavior of the main features such as swirling jet angle, the resultant inner recirculation zone, and the wall stagnation points. Proper Orthogonal Decomposition (POD) analysis showed a wide range of low-frequency modes spread over the entire domain and stated the domination of the outer swirling flow. It was found that an increase in the intensity of the outer swirler contributes to an intensified interaction with the model chamber walls highlighting the significance of the confinement ratio in higher swirl numbers.
Numerical Study on Deformation of Gland Seal Housing at LP Ends on a Nuclear Steam Turbine
Authors: Guo Yanan , Xie Danmei , Huang Xiangjun , Zheng Huabing , Mei Ziyue , Zhang Hengliang
Published: August 2018

The rubbing between static and moving parts of steam turbine is one of the frequent faults and difficult to diagnose accurately. In the high-speed rotation of steam turbine, if the clearance between the static and moving parts is too small, there is a possibility of rubbing accident, especially for the ends of LP steam turbine in a nuclear power plant, which will affect the safety operation of the steam turbine.

In this paper, the gland seal housing deformation of LP casing in 1000MW nuclear steam turbine is calculated and analyzed. Based on ProE and ANSYS/Workbench software, the 3D geometry model and the finite element mathematical model of LP inner casing of nuclear steam turbine are established, and the boundary conditions are determined at first. Secondly, the deformation of the gland seal housing at the LP casing end is calculated and analyzed under different conditions. Thirdly, the influence of different components temperature rise on the deformation of gland seal housing is analyzed.