bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Modelling Approaches for Bump-Type Foil Thrust Bearings Operating With CO2
Authors: Qin Kan , Li Daijin , Luo Kai , Tian Zhansheng , Jahn Ingo H.
Published: August 2018

Different forms of Reynolds equation are widely used to predict the performances of foil thrust bearings for air cycle machines. When analyzing bearings operating with highly dense CO2, computational fluid dynamics yields more accurate results, particularly at the high rotational speed. In addition, the structural deformation of the top and bump foils are also considered. For some applications, the high temperature increase caused by the viscous heating effect are also modelled in literature. The multi-physics effects within foil bearings, including the fluid flow, structural deformation and viscous heating create challenges and modelling complexity to accurately predict its performances. The aim of this paper is to review and compare different modelling approaches for foil thrust bearings with CO2 at a range of operating conditions, including loads and rotational speed. For steady state performances, results from turbulent Reynolds equation and computational fluid dynamics are in close agreement for foil thrust bearings operating with low load (large rotor to top foil separations). However, considerable differences exist between turbulent Reynolds equation and computational fluid dynamics method at high loads (small rotor to top foil separation). Here the computational fluid dynamics method must be employed, as the centrifugal inertia effect becomes significant. The top foil deflection need to be considered as the corresponding deformation is significant compared to the initial separation between the rotor and the top foil. At the rotational speed larger than 30000 rpm, the results from the fully fluid-structure-thermal simulations differ from other modelling approaches. The additional deformation caused by temperature increase largely alters the separation between the rotor and top foil. For dynamic performance, the top foil deflection again must be considered as the equivalent stiffness and damping are influenced by bump foil structures. This work provides recommendations for the selection of the suitable modelling approaches for bump-type foil thrust bearings operating with supercritical CO2.
Some Aspects of Operated Blades HCF Analysis: Rejuvenation and Life Estimation
Authors: Ivanov Sergey A. , Guralnik Maxim G. , Rybnikov Alexander I.
Published: August 2018

The lifecycle of modern industrial gas turbines can reach hundred thousand hours and usually the turbine blades need to be replaced. The use of super alloys and application of advanced coatings makes the cost of turbine lifecycle rather high. The methods for blade rejuvenation and life extension are based on the analysis of the main defects which can considerably reduce blade strength. The effect of long operation and typical defects in turbine blades has been studied in correlation with HCF. The decrease of blades HCF under the effect of operation has been considered as the result of influence of mechanical and thermal factors. The influence of FOD on the blade HCF strength is studied. Some random defects in turbine blades which resulted in HCF decreasing and blade failure are considered. The rejuvenation heat treatment for the blades of ZhS6K and EI893 and its positive effect on metal properties is demonstrated. The ultrasonic shot peening for operated blades have been considered. It is demonstrated that HCF strength of blades after shot peening is about 25–30% higher. Relaxation of compressing stresses in operation is shown as not essential. The remaining life of operated blades can be estimated using the correlation of endurance limit and run time.
Evaluation of Integral Turbulence Scale Through the Fan Stage of a Turbofan Using Hot Wire Anemometry and Large Eddy Simulation
Authors: Odier Nicolas , Duchaine Florent , Gicquel Laurent , Staffelbach Gabriel , Thacker Adrien , García Rosa Nicolás , Dufour Guillaume , Muller Jens-Dominik
Published: August 2018

This paper aims at evaluating wall-modeled LES capabilities to accurately predict turbulence properties in an aero-engine turbomachinery configuration. To do so, two LES numerical setups are compared, the first one using a 2nd-order space and time numerical scheme on a user-defined mesh, the second one using a 3rd order accurate in space and 4th order time numerical scheme on an automatically adapted mesh. Numerical results are compared to hot-wire anemometry measurements. Turbulence is evaluated through a triple velocity decomposition, enabling the evaluation of stochastic velocity fluctuations. A very fair agreement is evidenced regarding the numerically predicted turbulence spectra and integral turbulence time scale. Turbulence intensity values is however over estimated downstream of the stator, underlying the need for a second mesh adaptation.
Study of the Impact of Multi-Row Interaction on Flutter Analysis for a Representative LPT Geometry
Authors: Sotillo Adrian , Gallardo Juan Manuel
Published: August 2018

Acoustic reflections and multiple blade-row effects have an impact on aeroelastic behavior, which can change the aerodynamic damping by a significant amount. However, conventional flutter analyses neglect these effects as they ignore any information about the multistage unsteady interaction. In order to capture them, the authors of this paper have developed a multistage coupling methodology for ITP’s in-house unsteady 3D frequency-domain linearized RANS solver. The current approach allows carrying out CFD simulations on a multistage environment built upon an arbitrary number of blade-rows; each one of them could also have an arbitrary number of frequencies and/or interblade phase angles. The coupling mechanism between consecutive blade-rows arises in a somewhat straightforward way after the solutions are decomposed as the sum of several spinning modes in the inter-row boundaries and the continuity of acoustic, vortical and entropic waves is enforced. This method is suitable for flutter and forced response computations, and also for tonal noise propagation.

The focus of this paper is on the study of multiple blade-row effects on flutter stability margin. A brief analysis of results for a couple of simple test cases is presented to demonstrate the correctness of the method. Then, a detailed flutter analysis for a representative LPT geometry is performed and the results are compared with a single row conventional analysis. The impact of neighboring and further blade-rows, as well as spinning modes scattered from the fundamental circumferential mode, are accounted for in the unsteady aerodynamic loading of the excited blade.
HRSG Duct Firing Revisited
Authors: Gülen S. Can
Published: August 2018

Duct firing in the heat recovery steam generator (HRSG) of a gas turbine combined cycle power plant is a commonly used method to increase output on hot summer days when gas turbine airflow and power output lapse significantly. The aim is to generate maximum possible power output when it is most needed (and, thus, more profitable) at the expense of power plant heat rate.

In this paper, using fundamental thermodynamic arguments and detailed heat and mass balance simulations, it will be shown that, under certain boundary conditions, duct firing in the HRSG can be a facilitator of efficiency improvement as well. When combined with highly-efficient aeroderivative gas turbines with high cycle pressure ratios and concomitantly low exhaust temperatures, duct firing can be utilized for small but efficient combined cycle power plant designs as well as more efficient hot-day power augmentation. This opens the door to efficient and agile fossil fuel-fired power generation opportunities to support variable renewable generation.
Combined Aerodynamic and Phased Array Microphone Studies on Basic Models of Low-Speed Axial Fan Blade Sections
Authors: Balla Esztella , Vad János
Published: August 2018

The paper presents comparative aerodynamic and aeroacoustic studies on basic models of blade sections of low-speed, low-Reynolds-number axial fans. The wind tunnel experiments incorporated representative cambered plate and airfoil blade profiles. The aerodynamic measurements revealed that, for low Reynolds numbers, cambered plate blade sections may perform aerodynamically better than airfoil sections. A phased array microphone system, combined with a dipole beamforming and spatial filtering technique, offered a potential for localizing the noise sources in both streamwise and transversal direction. The acoustic studies focused on the profile vortex shedding noise. The results were qualitatively evaluated and compared with the semi-empirical noise prediction model developed by Brooks, Pope, and Marcolini. The measurements are considered as preparation of a dataset contributing to the background for designing high-efficiency, low-noise axial fans operating at low Reynolds number.
Emulsion Jet in Crossflow Atomization Characteristics and Dynamics
Authors: Leask Scott B. , McDonell Vincent G. , Samuelsen Scott
Published: August 2018

This work presents the atomization characteristics and dynamics of water-in-heptane (W/H) emulsions injected into a gaseous crossflow. W/H mixtures were tested while varying momentum flux ratios and aerodynamic Weber numbers. Different injector orifice diameters and orifice length-to-diameter ratios were used to test the generality of the results.

The atomization properties of W/H mixtures were compared with properties of neat water and neat heptane to evaluate the effect of an emulsion on droplet sizing, cross-sectional stability and dispersion, and jet penetration depth. Liquid dynamics were extracted through analyzing instantaneous spray measurements and dynamic mode decomposition (DMD) on high-speed video recordings of the atomization processes. Correlations were proposed to establish preliminary relationships between fundamental spray processes and test conditions. These correlations allowed for emulsion behavior to be compared with neat liquid behavior.

The use of emulsions induces greater spray instability than through using neat liquids, likely due to the difficulty in injecting a stable emulsion. Neat liquid correlations were produced and successfully predicted various spray measurements. These correlations, however, indicate that injector geometry has an effect on spray properties which need to be addressed independently. The emulsions are unable to adhere to the neat liquid correlations suggesting that an increased number of correlation terms are required to adequately predict emulsion behavior.
Linear Grey-Box Modeling of Gas Turbine Engines for MIMO Control Design
Authors: Moroto Robert H. , Bitmead Robert R. , Pandey Amit
Published: August 2018

High-fidelity models are an increasingly indispensable tool for evaluating high-performance control and optimization algorithms of gas turbine (GT) engines. However, GT high-fidelity models (HFM’s) are often too complex for synthesizing model-based control and optimization algorithms, which are much more amenable to low-order linear dynamic models. Obtaining models suitable for control synthesis can be arduous and costly. White-box (first-principles) methods may produce models that lose fidelity in off-nominal conditions, while black-box (data-driven) methods yield model parameters without physical significance, preventing generalization of the model across product configurations. This paper presents a grey-box method for obtaining low-order linear dynamic models for a 5.5 MW GT engine that retain fidelity at off-nominal conditions and generalize to multiple product configurations. The approach exploits the structure of an available HFM by grouping its constituent component-level models according to their suitability to white-box or black-box modeling. Specifically, the rotor model is linearized, yielding a first-order linear model with adjustable physical parameters, e.g. inertia. A second-order open-loop linear model is obtained from remaining component-level models via system identification using closed-loop data generated by the HFM. The linear models are combined to form a third-order open-loop linear GT engine model, which retains fidelity with the HFM in transient validation experiments, and multiple rotor inertia values.
Heat Generation in a Main-Shaft Turbine Aero-Engine Bearing Considering Metal and Ceramic Rolling Elements
Authors: Nicholson Brian D. , Nickell Jeremy T.
Published: August 2018

This work details an analytical assessment of heat generation in a turbine aero-engine main-shaft bearing and the development of a model to predict that heat generation. The new model is based on an empirical model, previously developed by the Air Force Research Laboratory (AFRL), which features physics based terms multiplied by empirical regression coefficients. That model proved to be limited in that portions of the terms were essentially an extension of the regression coefficients due to the fact that the experimental data was limited to that of one bearing. Additionally, there were separate models for each rolling element material. To develop the new model, the validated bearing analysis code ADORE was used to generate power loss data for angular contact ball bearings of various sizes. The effects of speed, thrust load, pitch diameter, element diameter, number of rolling elements, lubricant inlet temperature, lubricant flow rate, and rolling element material (AISI M50 bearing steel and silicon nitride) are examined. Speed and thrust load are addressed at four levels each. Number of elements, bore diameter, and element diameter as well as lubricant temperature and flow rate are each addressed at three levels. These effects are captured in the model through traction (friction), churning (drag), and shearing (viscous) terms and their respective regression coefficients. The material effect is address through the use of an effective elastic modulus within an estimate of raceway to rolling element contact area. The performance of the model was then compared with experimental data collected in the AFRL High Mach Engine (HME) Bearing Rig. The model created in this work provides designers with an effective tool to examine bearing heat generation during the early engine design phases, avoiding the significant computational and front end expense of other, more detailed methods.
Application and Experience of the SSS (Synchro-Self-Shifting) Clutch for High Speed Gas Turbine Marine Propulsion Systems
Authors: Hendry Morgan L.
Published: August 2018

Synchro-Self-Shifting (SSS) Overrunning Clutches are used in a myriad of propulsion system configurations for naval and commercial vessels powered by gas turbines and/or combined gas turbine and cruise engines worldwide. Of these, much has been written about high power gas turbine propulsion clutches for large naval vessels (frigates, destroyers, cruisers, etc.), whereas less has been published about the application and experience of the propulsion machinery with Synchro-Self-Shifting Clutches for hydrofoils, hovercraft, fast patrol boats, fast ferries, yachts, etc. Space, weight, and high-speed constraints can be different for high speed gas turbine propulsion systems used in these smaller types of vessels, and can therefore provide gearing challenges, including system design challenges for these clutches.

A comparison between Synchro-Self-Shifting overrunning clutches and other types of freewheels will be given discussing the advantages and disadvantages of each, particularly as they relate to high speed gas turbine marine propulsion applications. Lastly, this paper will give some history of a number of high speed gas turbine driven marine propulsion applications with clutches from the early 1960’s until the present, describe various gearing arrangements that were used in particular vessels, articulate where these clutches are incorporated, and discuss the application experience of these clutch installations.
Effect of Coolant Injection Angle on Nozzle Endwall Film Cooling: Experimental and Numerical Analysis in Linear Cascade
Authors: El-Gabry Lamyaa , Xu Hongzhou , Liu Kevin , Chang James , Fox Michael
Published: August 2018

Gas turbine components can withstand gas temperatures exceeding the melting point of the alloys they’re made of due to increasingly effective cooling methods. Increasing the operating temperature of a gas turbine is key to improving its power density and exhaust heat for steam or combined-cycle efficiency. In the turbine, the component that experiences the highest gas temperature is the vane directly downstream of the combustor; the most complex flow field in a vane occurs near the endwall. In this study, an experimental investigation is carried out to determine the effect of coolant injection angle and mass flow ratio on film effectiveness on the endwall using the pressure sensitive paint technique for various configurations of jump cooling hole configurations. Two rows of angled holes are upstream of an uncooled vane in a three-vane linear cascade. Injection angle including compound angle is varied from 20 to 60 and coolant to mainstream massflux ratio is varied from 0.5% to 3%. Contours of endwall surface film effectiveness are presented along with span-averaged film effectiveness. CFD models of the cascade are developed using a commercial solver to predict film effectiveness for some of the test conditions and comparisons are made between the experimental and numerical results. The CFD models provide further insight into the flow field and explain trends observed in the experiment by understanding the interaction of jump coolant flow with the 3D endwall mainstream flows.
Measurements of the Leakage and Rotordynamic Performance of Interlocking Labyrinth Seals
Authors: Gary Keith , Childs Dara W. , Ramirez Mauricio A.
Published: August 2018

Leakage and rotordynamic measurements are presented for an interlocking-labyrinth gas seal. Magnetic bearings and differential-pressure transducers are used to measure dynamic forces in the labyrinth seal following the approach of Wagner et al. in 2009. Magnetic bearings precess the rotor creating a dynamic pressure wave that is measured and integrated to find the reaction forces. The interlocking seal has 3 teeth on the stator and 2 teeth on the rotor creating 4 cavities. Each cavity has an axial length of 6 mm, and all teeth have a 5 mm height. Teeth on the rotor and stator, respectively, create a 0.2 mm radial clearance with respect to the stator and rotor. All tests are conducted at ∼ 167 Hz (10 krpm) rotor speed with, and without, swirl brakes for a range of precession frequencies from 10–50 Hz forward and backward. Inlet pressure is varied between 2.75 ∼ 4.83 bar, and pressure ratios vary between 0.5 ∼ 0.8.

Static results are presented for leakage, inlet preswirl, and cavity pressure. Dynamic results are presented for rotordynamic coefficients. Dynamic results show behavior that is unique to each cavity and are presented for the entire seal as well as for each cavity individually. Cross-coupled stiffness of the entire seal increases with increasing precession frequency, yet all other rotordynamic coefficients are frequency independent. The seal shows improved stability via increased effective damping with the use of swirl brakes when considering the entire seal. Negative direct damping values are seen in all but the third cavity.
CFD Investigation of the Flow of Trailing Edge Cooling Slots
Authors: Jiang Y. , Gurram N. , Romero E. , Ireland P. T. , di Mare L.
Published: August 2018

Slot film cooling is a popular choice for trailing edge cooling in high pressure (HP) turbine blades because it can provide more uniform film coverage compared to discrete film cooling holes. The slot geometry consists of a cut back in the blade pressure side connected through rectangular openings to the internal coolant feed passage. The numerical simulation of this kind of film cooling flows is challenging due to the presence of flow interactions like step flow separation, coolant-mainstream mixing and heat transfer.

The geometry under consideration is a cutback surface at the trailing edge of a constant cross-section aerofoil. The cutback surface is divided into three sections separated by narrow lands. The experiments are conducted in a high speed cascade in Oxford Osney Thermo-Fluids Laboratory at Reynolds and Mach number distributions representative of engine conditions. The capability of CFD methods to capture these flow phenomena is investigated in this paper. The isentropic Mach number and film effectiveness are compared between CFD and pressure sensitive paint (PSP) data. Compared to steady k–ω SST method, Scale Adaptive Simulation (SAS) can agree better with the measurement. Furthermore, the profiles of kinetic energy, production and shear stress obtained by the steady and SAS methods are compared to identify the main source of inaccuracy in RANS simulations. The SAS method is better to capture the unsteady coolant-hot gas mixing and vortex shedding at the slot lip.

The cross flow is found to affect the film significantly as it triggers flow separation near the lands and reduces the effectiveness. The film is non-symmetric with respect to the half-span plane and different flow features are present in each slot. The effect of mass flow ratio (MFR) on flow pattern and coolant distribution is also studied. The profiles of velocity, kinetic energy and production of turbulent energy are compared among the slots in detail. The MFR not only affects the magnitude but also changes the sign of production.
Numerical Investigation of the Circumferential Pressure Distortion Induced by a Centrifugal Compressor’s External Volute
Authors: Ceyrowsky Thomas , Hildebrandt Andre , Schwarze Rüdiger
Published: August 2018

It is well understood that a volute, depending on its operating point, acts either as a nozzle or diffuser. However, the resulting static pressure distortion at diffuser exit is rather considered as side effect and has rarely been investigated systematically in detail. Evidence whether this distortion is amplified or alleviated towards impeller exit is even contradictory in literature. In this work a thorough investigation of aerodynamic volute-impeller interaction is presented. First, a 1D-analysis is carried out in order to understand the fundamental relation between volute matching and pressure distortion. Then, one large external volute, coupled with different impellers, is investigated by means of CFD. These configurations feature different diffuser ratios and blade exit angles, while identical matching ensures comparable conditions. The results reveal that pressure distortion is directly related to the volute’s pressure recovery coefficient. Consequently, at diffuser exit, a local pressure recovery coefficient around circumference can be defined, which is widely independent from the impeller but rather depends on volute geometry and matching. It is this local pressure recovery factor that defines the static pressure distortion at diffuser exit, together with dynamic pressure. In a next step it is analysed, how the resulting pressure distortion evolves towards the impeller. Therefore, stand-alone CFD calculations of impellers around the entire circumference are performed, applying defined pressure distortions at diffuser exit and varying operational conditions carefully. In doing so, fundamental understanding of when distortion is amplified or alleviated towards the impeller is gained.
Impact of Predicted Combustor Outlet Conditions on the Aerothermal Performance of Film-Cooled HPT Vanes
Authors: Cubeda S. , Mazzei L. , Bacci T. , Andreini A.
Published: August 2018

Turbine inlet conditions in modern aero-engines employing lean-burn combustors are characterised by highly swirled flow and non-uniform temperature distributions. As a consequence of the lack of confidence in numerical predictions and the uncertainty of measurement campaigns, the use of wide safety margins is of common practice in the design of turbine cooling systems, thus affecting the engine performance and efficiency.

Previous experiences showed how only scale-resolving approaches such as Large-eddy and Scale-adapting simulations are capable of overcoming the limitations of RANS, significantly improving the accuracy in the prediction of flow and temperature fields at the combustor outlet. However it is worth investigating the impact of such differences on the aerothermal performance of the NGVs, as to understand the limitations entailed in the current approach for their thermal design. Industrial applications in fact usually rely on 1D, circumferentially-averaged profiles of pressure, velocity and temperature at the combustor-turbine interface in conjunction with Reynolds-averaged Navier-Stokes (RANS) models.

This paper describes the investigation performed on an experimental test case consisting of a combustor simulator equipped with NGVs. Three numerical modelling strategies were compared in terms of flow field and thermal loads on the film-cooled vanes: i) RANS model of the NGVs with inlet conditions obtained from a RANS simulation of the combustor; ii) RANS model of the NGVs with inlet conditions obtained from a Scale-Adaptive Simulation (SAS) of the combustor; iii) SAS model inclusive of both combustor and NGVs.

The results of this study show that estimating the aerodynamics at the NGV exit does not demand particularly complex approaches, whereas the limitations of standard RANS models are highlighted again when the turbulent mixing is key. High-fidelity predictions of the conditions at the turbine entrance proved to be very beneficial to reduce discrepancies in the estimation of local adiabatic wall temperature of even 100 K. However, a further leap forward can be achieved with an integrated simulation, capable of reproducing the transport of the unsteady fluctuations generated in the combustor up into the turbine, which plays a key role in presence of film cooling. This work therefore points out how keeping the analysis of combustor and NGVs separate can lead to a significantly misleading estimation of the thermal loads and ultimately to a wrong thermal design of the cooling system.
Investigating Damping Performance of Laser Powder Bed Fused Components With Unique Internal Structures
Authors: Scott-Emuakpor Onome , George Tommy , Runyon Brian , Holycross Casey , Langley Bryan , Sheridan Luke , O’Hara Ryan , Johnson Phil , Beck Joseph
Published: August 2018

An additive manufacturing (AM) process has been used to fabricate beam components with unique internal geometries capable of reducing weight and inherently suppressing vibration of the structure. Using the laser powder bed fusion (LPBF) AM process, four unique designs are investigated to quantify and understand the damping effectiveness of this manufacturing concept. Forced-response tests are conducted to validate the damping capability of each internal design configuration. The effects of external geometry, thermal distribution associated with internal friction, strain amplitude, and loading rate dependence on damping performance are studied. The results of the studied beams are compared to the damping performance of a fully-fused, or solid baseline LPBF beam. With only 1–4% internal beam volume alteration, the four unique beams are capable of providing up to ten times damping into their respective systems compared to the baseline, solid beam. From the studies of different parameter effects on damping, the main mechanism for vibration suppression is identified. Validation of the vibration suppression physics allows for internal feature optimization via LPBF that can maximize damping effectiveness.
Aero Derivative Mechanical Drive Gas Turbines: The Design of Intermediate Pressure Turbines
Authors: Scotti Del Greco Alberto , Michelassi Vittorio , Francini Stefano , Di Benedetto Daniele , Manoharan Mahendran
Published: August 2018

Gas turbines engine designers are leaning towards aircraft engine architectures due to their footprint, weight, and performance advantages. Such engines need some modifications to both the combustion system, to comply with emission limits, and turbine rotational speed. Aero derivative engines maintain the same legacy aircraft engine architecture, and replace the fan and booster with higher speed compressor booster driven by a single stage intermediate turbine. A multistage free power turbine (FPT) sits on a separate shaft to drive compressors for Liquefied Natural Gas (LNG) applications or generators. The intermediate power turbine (IPT) design is important for the engine performance as it drives the booster compressor and sets the inlet boundary conditions to the downstream power turbine. This paper describes the experience of Baker Hughes, a GE company (BHGE) in the design of the intermediate turbine that sits in between a GE legacy aircraft engine core exhaust and the downstream power turbine. This paper focuses on the flow path of the TCF/intermediate turbine and the associated design, as well as on the 3D steady and unsteady CFD assisted design of the IPT stage to control secondary flows in presence of through flow curvature induced by the upstream TCF.
Experimental Investigation of the Unsteady Tip Clearance Flow in a Low-Speed Axial Contra-Rotating Compressor
Authors: Yue Shaoyuan , Wang Yangang , Wei Liguo , Wang Hao , Deng Shuanghou
Published: August 2018

This paper experimentally investigated the evolution of the tip clearance flow of a CRAC (Contra-Rotating Axial Compressor) test rig by means of high-response dynamic pressure measurements. The unsteady pressure field along both chordwise and circumferential directions in the tip clearance is recorded. The tip clearance vortex trajectory is captured using RMS (Root-Mean Square) method. Pressure spectrum analysis indicates that the unsteadiness of tip clearance vortex occurred when the flow coefficient approaches low enough even in the stable operating point. The unsteadiness of tip clearance vortex gets stronger as the flow coefficient drops until rotating stall occurs. According to this feature, the auto-correlation analysis and the cross-correlation analysis combined probability statistics method are used to work as pre-stall warning methods. In addition to, rotating instability which is caused by disturbances propagating along circumferential direction occurred at some flow condition.
Thermodynamic Analysis on Optimum Pressure Ratio Split of Intercooled Recuperated Turbofan Engines
Authors: Li Hualei , Tan Zhiyong
Published: August 2018

Intercooled recuperated turbofan engines with high bypass ratio are becoming a research focus in recent years due to its advantages of relatively better fuel economy, lower emission and noise characteristic. The re-heater can recover waste heat in the exhaust gas downstream of the low pressure turbine to reduce the specific fuel consumption, and the intercooler can improve compression ability of the compressors with sufficient temperature difference between the high pressure compressor and the low pressure turbine. An optimal pressure ratio split is often sought to maximize the effect of the intercooler on improving the compression ability of the compressors. To determine an optimal pressure ratio split, different combinations of pressure ratio between high and low pressure spools must be calculated, and this requires huge amount of work with the traditional method to achieve the suitable cycle selections. In this paper, theoretic thermodynamic analysis is carried out to derive an explicit solution of the optimum pressure ratio split for maximizing the efficiency of the whole compression path. The effects of different variables on the optimum pressure ratio split are investigated according to the correlated variables in the solution function. A comparison calculation is also made to validate the effectiveness and accuracy of the explicit solution. The results show that the optimum pressure ratio split can be achieved with the derived solution function, which will significantly simplify the process of the cycle parameter selection.
Numerical Investigation of Passive Flow Control Using Wavy Blades in a Highly-Loaded Compressor Cascade
Authors: Wang Bo , Wu Yanhui , Liu Kai
Published: August 2018

Driven by the need to control flow separations in highly loaded compressors, a numerical investigation is carried out to study the control effect of wavy blades in a linear compressor cascade. Two types of wavy blades are studied with wavy blade-A having a sinusoidal leading edge, while wavy blade-B having pitchwise sinusoidal variation in the stacking line. The influence of wavy blades on the cascade performance is evaluated at incidences from −1° to +9°. For the wavy blade-A with suitable waviness parameters, the cascade diffusion capacity is enhanced accompanied by the loss reduction under high incidence conditions where 2D separation is the dominant flow structure on the suction surface of the unmodified blade. For well-designed wavy blade-B, the improvement of cascade performance is achieved under low incidence conditions where 3D corner separation is the dominant flow structure on the suction surface of the baseline blade. The influence of waviness parameters on the control effect is also discussed by comparing the performance of cascades with different wavy blade configurations. Detailed analysis of the predicted flow field shows that both the wavy blade-A and wavy blade-B have capacity to control flow separation in the cascade but their control mechanism are different. For wavy blade-A, the wavy leading edge results in the formation of counter-rotating streamwise vortices downstream of trough. These streamwise vortices can not only enhance momentum exchange between the outer flow and blade boundary layer, but also act as the suction surface fence to hamper the upwash of low momentum fluid driven by cross flow. For wavy blade-B, the wavy surface on the blade leads to a reduction of the cross flow upwash by influencing the spanwise distribution of the suction surface static pressure and guiding the upwash flow.
Multi-Fidelity Kriging-Based Optimization of Engine Subsystem Models With Medial Meshes
Authors: Yong Hau Kit , Wang Leran , Toal David J. J. , Keane Andy J. , Stanley Felix
Published: August 2018

Engine subsystem models are not commonly used in design optimization studies as it is computationally expensive to solve these models for a large number of iterations. To reduce the computational cost of such optimizations, a novel multi-fidelity Kriging-based optimization approach is proposed that uses shell FEMs to provide a low-fidelity response and solid FEMs to provide a high-fidelity response. This marks the first time that shell and solid models are used together in a multi-fidelity surrogate modelling approach. The shell FEMs are generated from medial surfaces that are extracted from solid component geometries in a semi-automatic manner. This approach is applied to a case study for optimizing the intercasing subsystem from the CRESCENDO whole engine model. The results show that the optimum design found by the multi-fidelity Kriging approach was on par with the optimum design found by a single-fidelity Kriging approach using only solid FEMs which is more than twice as expensive to run. The shell and solid FEMs were also shown to be well-correlated such that optimization studies employing only the shell FEMs by themselves could generate designs that are feasible with respect to the design constraints imposed on the solid model.
Development of a Multi-Objective Preliminary Design Optimization Approach for Axial Flow Compressors
Authors: He Youwei , Sun Jinju , Song Peng , Wang Xuesong , Xu Da
Published: August 2018

A preliminary design optimization approach of axial flow compressors is developed. Loss correlations associated with airfoil geometry are introduced to relax the stringent requirement for the designer to prescribe the stage efficiency. In face of the preliminary design complexity resulted from the large number of design variables together with their stringent variation ranges and multiple design goals, the multi-objective optimization algorithm is incorporated. With such a developed preliminary design optimization method, the design space can be then explored extensively and the optimum designs of both high level overall efficiency and wide stall margin can be readily achieved. The preliminary design optimization method is validated in two steps. Firstly, an existing 5-stage compressor is redesigned without optimization. The obtained geometries and flow parameters are compared to the existing data and a good consistency is achieved. Then, the redesigned compressor is used as initial design and optimized by the developed multi-objective preliminary design optimization method, and significant performance gains are obtained, which demonstrates the effectiveness of the developed optimization methods.
CFD Study Exploring Jet Configurations and Jet Pulsing for an Aeroengine Scoop-Based Oil Delivery System
Authors: Simmons Kathy , Harrison Luke , Korsukova Evgenia , Paleo Cageao Paloma
Published: August 2018

With reduction of gas turbine core size, clearances between internal components are reduced and directing oil jets for bearing lubrication becomes more difficult. If direct access to the bearings or scallops is impeded, the inclusion of oil scoops becomes highly desirable for lubricant supply. With a scoop-based system oil is targeted at a scooped rotor, collected and fed along axial passages and delivered at a different axial location thus enhancing design opportunities. The proportion of oil from the supply jet retained by the scoop system is an important design parameter that can be characterised by the concept of capture efficiency. Previous investigations have focussed on a proposed scoop device’s operating conditions and oil jet configurations; this study proposes new methods of utilising the jets to improve scoop capture efficiency. A parametric study of a 2D scoop geometry was conducted using the Computational Fluid Dynamics (CFD) software ANSYS Fluent. The simulation utilised the Volume of Fluids (VOF) approach for multiphase modelling and the k-ω SST model to account for turbulence.

In the configuration studied the oil was supplied via two nozzles separated by 10 degrees circumferentially. An uneven flow rate between two oil jets in tandem allowed for the identification of jet interaction effects. A transition in capture efficiency responses was also highlighted between shallow and steep jet angles. The knowledge of individual jet behaviour may immediately improve existing tandem jet configurations.

Further, the concept of pulsing the jets was investigated, the idea being initiated following observation of high speed imaging of a scoop system tested experimentally. The imaging shows that most of the uncaptured oil is deflected or splashed following interaction with the scoop. Turning the oil off for part of the cycle potentially reduces or eliminates this. By defining and implementing an optimised time scheme for the pulsation of a single jet, the capture efficiency was improved by 10%. Compensating for the associated flow rate reduction by increasing the jet velocity resulted in a further 5% increase in capture efficiency. The development of pulsed jets for practical applications has the potential to significantly improve oil scoop capture efficiency.
Coupled Fluid Structure Simulation Method in the Frequency Domain for Turbomachinery Applications
Authors: Berthold Christian , Frey Christian , Schönenborn Harald
Published: August 2018

Turbomachinery components are exposed to unsteady aerodynamic loads which must be considered during the design process to ensure the structural mechanical integrity. There are two primary mechanisms which cause structural vibrations and can lead to high-cycle fatigue due to high dynamic stresses: flutter (self-excited vibrations) and forced response (forced excitation, e.g. wakes from upstream blade rows). In this work an emerging numerical frequency-domain method which is designed to efficiently simulate coupled fluid-structure interaction (FSI) problems considering nonlinearities in the flow and structure is modified and applied to an academic and a realistic test case. Furthermore complex structural eigenmodes are considered instead of purely real modes as was demonstrated in the literature so far. This method is able to predict limit cycle oscillations and forced response amplitudes. The coupled solver uses the Harmonic Balance (HB) method with an alternating frequency time approach to model periodically unsteady flows and structure dynamics. The resulting nonlinear HB equations of the flow are solved with a pseudo-time stepping method while the nonlinear HB equations of the structure are solved with a Newton method. The dynamics of the involved structure are further simplified by considering only one relevant eigenmode of the structure. The method is applied to a 3D axial turbine configuration with a modified Young’s modulus for the material of the blisk. The standard flutter curve of the blade row shows that at least one eigenmode is aerodynamically unstable at certain nodal diameters. As a first model test case for the harmonic balance solver, the nonlinear structural damping is defined as a cubic modal damping term. The results of the frequency-domain method are compared to coupled FSI simulations in the time domain. The analysis shows that the frequency-domain method is very promising in terms of both computational efficiency and accuracy.
Investigation of H2/CH4-Air Flame Characteristics of a Micromix Model Burner at Atmosphere Pressure Condition
Authors: Liu Xunwei , Shao Weiwei , Tian Yong , Liu Yan , Yu Bin , Zhang Zhedian , Xiao Yunhan
Published: August 2018

For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potential low NOx emission solution for gas turbine combustors, especially for advanced gas turbines with high turbine inlet temperature. Compared with conventional lean premixed flames, multiple distributed slim and micro flames could lead to a lower NOx emission performance for shortening residence time of high temperature flue gas and generally a more uniform temperature distribution.

This work aims at micromix flame characteristics of a model burner fueled with hydrogen blending with methane under atmosphere pressure conditions. The model burner assembly was designed to have six concentrically millimeter-sized premixed units around a same unit centrally. Numerical and experimental studies were conducted on mixing performance, flame stability, flame structure and CO/NOx emissions of the model burner. OH radical distribution by OH-PLIF and OH chemiluminescence (OH*) imaging were employed to analyze the turbulence-reaction interactions and characters of the reaction zone at the burner exit. Micromix flames fueled with five different hydrogen content H2-CH4 (60/40, 50/50, 40/60, 30/70, 0/100 Vol.%) were investigated, along with the effects of equivalence ratio and heat load. Results indicated that low NOx emissions of less than 10 ppm (@15% O2) below the exhaust temperature of 1920 K were obtained for all the different fuels. Combustion oscillation didn’t occur for all the conditions. It was found that at a constant flame temperature, the higher the hydrogen content of the fuel, the higher the turbulent flame speed and the weaker the flame lift effect. Combustion noise and NOx emissions also increase with increasing hydrogen content. The OH/OH* signal distribution indicated that a pure methane micromix flame showed a lifted and weaken distributed feature.
Aeroacoustic Optimization of a Pressure-Side Strut Configuration for Subsonic Axial Fans Using Statistical-Empirical Modelling
Authors: Neifach Igor , Na Gi-Don , Kameier Frank , Springer Nils , Wichers Marco
Published: August 2018

This paper deals with the reduction of aerodynamically generated noise in passenger car Cooling-Fan-Modules (CFM), caused by the interaction between the impeller and the downstream-located strut configuration of the axial fan. Even after the car engine is switched off, the fan remains active, as long as cooling is required for certain vehicle components. Especially after a car has been parked in closed parking areas, in close proximity to residential buildings or public places, the noise emission can be a problem. This issue is addressed by dampening the rotor-stator-interaction through passive construction measures. In order to ensure optimal noise reduction, 8 critical design features of the struts are identified and investigated using statistical design of experiment methods (DoE). Based on the results, dedicated insights about the effects of concrete strut features on significant regions of the acoustic fan spectrum are obtained. Furthermore, an optimized strut configuration is derived and metrologically validated using a polyoptimization method. Compared to a current serial baseline configuration, a reduction of the overall sound pressure level by 2.6 dB(A), as well as a reduction of the blade passage frequency tone by 17.6 dB(A) is achieved.
Automated Meshing Algorithm for Generating As-Manufactured Finite Element Models Directly From As-Measured Fan Blades and Integrally Bladed Disks
Authors: Kaszynski Alex A. , Beck Joseph A. , Brown Jeffrey M.
Published: August 2018

Automated tetrahedral meshing from manifold tessellated optical scan data is investigated to determine its viability as an approach for finite element analysis. This approach avoids the costs of constructing a volumetric representation of the scan data that can be meshed with conventional grid generation approaches. This paper demonstrates an auto-meshing algorithm for inserted airfoil and integrally bladed rotor hardware. These automatically generated models are compared to experimentally obtained frequencies and mode shapes for validation.

In an effort to compare the fidelity as well as the effect of mesh density on analytical convergence rate, manually generated all-hexahedral models are compared against the auto-meshed tetrahedral finite element models. CPU time, solution accuracy, and mesh convergence are evaluated to determine the viability of automatically generated tetrahedral meshes versus the standard approach of manually generating hex-dominant meshes. This paper demonstrates that given the power of modern CPUs, automatically generated all-tetrahedral meshes can serve as a viable alternative to manually generated hex-dominant finite element models, especially when these meshes can be refined for solution convergence within the auto-mesher. This new approach effectively solves both the mesh convergence problem while demonstrating that models based on as-measured geometry can be rapidly built with virtually no human interaction.