bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotor Over-Speed Analysis of a Hybrid Solar Gas Turbine
Authors: Kathirgamanathan Darsini , Axelsson Lars-Uno
Published: August 2018

As the demand for environmentally friendly power production is increasing, the Hybrid Solar Gas Turbine (HSGT) power plant has the potential to provide a reliable electricity production with low carbon foot print by combining the solar heat and the fossil fuel. Compared to the conventional gas turbine system, the HSGT system has an additional heat source and larger volume due to the solar receiver and the ducting system required for guiding the air to and from the solar receiver. The additional heat source and larger volume increase the thermal capacitance which adds complexity to the operational behavior of the gas turbine.

This paper presents an investigation of the transient behavior of a hybrid solar gas turbine. The OP16 gas turbine, rated at 1.85MWe, is integrated into a solar thermal power plant as part of an ongoing R&D project. To analyze the shaft over-speed of the system, a model is created using the commercial cycle analysis software GSP. The model is validated against the measured data for a non-solar mode operation as it is similar to the conventional gas turbine operation on pure fossil fuel.

A rotor over-speed analysis of the OP16-HSGT system during load-shed shows that the rotor over-speed exceeds the acceptable limit due to the thermal capacitance and volumetric effects. An increase in shaft inertia, or re-direction of the air flow from hybrid-solar mode to non-solar mode by using control valves, or the use of blow-off valve to vent out the solar heat can be taken as safety measures to reduce rotor over-speed. It was found that the control valve should act within 0.3s to maintain acceptable rotor over-speed. As a control valve with such characteristics is scarcely available, a concept where the OP16-HSGT system uses a blow-off valve in addition to the control valve was developed. The blow-off valve reduces the rotor over-speed from 111% to 103% by venting out the thermal capacitance from the OP16-HSGT system and by that one can achieve safe operation during a load-shed or an emergency shutdown.
Dynamic Model Development and Analysis of Multiple Rotors Coupled With Thrust Collars
Authors: Kang Kyungdae
Published: August 2018

The core model of integrally geared centrifugal compressor/expander equipped with thrust collars is developed using finite element model. Each rotor model is coupled through the equivalent stiffness due to thrust collar and the gear web. Subsynchronous vibration caused by the transmitted frequency components from other shafts is analyzed through forced vibration analysis. Unlike conventional frequency response function (FRF), directional FRF technique is adopted because rotordynamic analysis requires that forward and backward mode responses should be identified according to the rotational force direction exerted on the rotor. Previous analysis results utilizing 3D FE model of geared rotors equipped with thrust collars revealed that transmitted vibration level is mostly affected by thrust collars, rather than gear tooth. The rotordynamic model developed in this paper ensures reliability and efficiency in the multi-rotor design equipped with thrust collars providing a systematic way to analyze the multi-rotor vibration responses due to the transmitted forces from one shaft to the other.
Fleet Monitoring and Diagnostics Framework Based on Digital Twin of Aero-Engines
Authors: Zaccaria Valentina , Stenfelt Mikael , Aslanidou Ioanna , Kyprianidis Konstantinos G.
Published: August 2018

Monitoring aircraft performance in a fleet is fundamental to ensure optimal operation and promptly detect anomalies that can increase fuel consumption or compromise flight safety. Accurate failure detection and life prediction methods also result in reduced maintenance costs. The major challenges in fleet monitoring are the great amount of collected data that need to be processed and the variability between engines of the fleet, which requires adaptive models.

In this paper, a framework for monitoring, diagnostics, and health management of a fleet of aircrafts is proposed. The framework consists of a multi-level approach: starting from thresholds exceedance monitoring, problematic engines are isolated, on which a fault detection system is then applied. Different methods for fault isolation, identification, and quantification are presented and compared, and the related challenges and opportunities are discussed. This conceptual strategy is tested on fleet data generated through a performance model of a turbofan engine, considering engine-to-engine and flight-to-flight variations and uncertainties in sensor measurements. Limitations of physics-based methods and machine learning techniques are investigated and the needs for fleet diagnostics are highlighted.
Treating Uncertainties to Generate a Robust Design of Gas Turbine Disk Using L Moments and Scarce Samples Including Outliers
Authors: Jayaraman Deepan , Ramu Palaniappan , Suresh Suhas Karkada , Ramanath Vinay
Published: August 2018

Uncertainties in the input variables are inevitable in any design process. As a consequence, the output responses are also uncertain. Robust design is one of the sought after approach to treat such uncertainties for controlling the variation in the output responses, while maximizing the mean performance. Variation is modeled by a measure of data spread. Often, the details of the uncertainties in the input space are not available readily and they are usually characterized from scarce sample realizations. In addition, there could also be outliers in the realizations. These will increase the error in the measure of spread of the output response. Hence, it is desirable that an approach that is insensitive to outliers but can characterize the spread of data is developed for robust design. In this work we propose using L moments to model the spread of data. The classical robust design formulation is reformulated using the second L moment (l2). The proposed approach is demonstrated on a turbine disk design with 17 design and random variables. The details of the uncertainties are not known. A DoE of 200 samples is used and at each DoE point, we propagate the uncertainties using scarce samples, which include outliers. Robust design is performed and it is shown that the proposed approach works better than the classical robust design formulation.
LES and RANS Analysis of the End-Wall Flow in a Linear LPT Cascade With Variable Inlet Conditions: Part II — Loss Generation
Authors: Marconcini Michele , Pacciani Roberto , Arnone Andrea , Michelassi Vittorio , Pichler Richard , Zhao Yaomin , Sandberg Richard
Published: August 2018

In low-pressure-turbines (LPT) at design point around 60–70% of losses are generated in the blade boundary layers far from end-walls, while the remaining 30%–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Increasing attention is devoted to these flow regions in industrial design processes. Experimental techniques have shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving CFD have provided a detailed insight into the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 profile with parallel end-walls at realistic LPT conditions, as described in the experimental setup of Duden and Fottner (1997) “Influence of Taper, Reynolds Number and Mach Number on the Secondary Flow Field of a Highly Loaded Turbine Cascade”, P. I. Mech. Eng. A-J. Pow., 211 (4), pp.309–320. The simulations target first the same inlet conditions as documented in the experiments, and determines the impact of the incoming boundary layer thickness by running additional cases with modified incoming boundary layers. Calculations are carried out by both RANS, due to its continuing role as the design verification workhorse, and highly-resolved LES. Part II of the paper focuses on the loss generation associated with the secondary end-wall vortices. Entropy generation and the consequent stagnation pressure losses are analyzed following the aerodynamic investigation carried out in the companion paper. The ability of classical turbulence models generally used in RANS to discern the loss contributions of the different vortical structures is discussed in detail and the attainable degree of accuracy is scrutinized with the help of LES and the available test data. The purpose is to identify the flow features that require further modelling efforts in order to improve RANS/URANS approaches and make them able to support the design of the next generation of LPTs.
Transport of Entropy Waves Within a HP Turbine Stage
Authors: Gaetani Paolo , Persico Giacomo
Published: August 2018

This paper presents the results of an experimental study on the transport of entropy waves, representative of those generated by gas turbine burners, within an un-cooled high-pressure gas turbine stage. The prescribed entropy waves were injected in streamwise direction featuring a 7% over-temperature with respect to the main flow at the stage inlet, with a frequency of 30 Hz. The entropy waves are injected in four different circumferential positions with respect to the stator blade. Detailed time-resolved temperature measurements as well as aerodynamic measurements upstream and downstream of the blade rows were performed. Measurements showed a relevant attenuation of the entropy waves throughout their transport within the stator blade row. The temperature distribution resulted in a severe alteration depending on the injection position. Downstream of the rotor, the waves spread over the pitch above midspan and are more concentrated at the hub. Finally, a comparison with measurements performed with conventional steady hot streaks is also reported, remarking both differences and affinities. As a relevant conclusion, it is experimentally shown that entropy waves can be proficiently simulated by considering a number of hot streaks of different amplitude.
Comparison of DDES and URANS for Unsteady Tip Leakage Flow in an Axial Compressor Rotor
Authors: Liu Yangwei , Zhong Luyang , Lu Lipeng
Published: August 2018

Tip leakage flow (TLF) has a large impact on compressor performance and should be accurately predicted by CFD methods. New approaches to turbulence modelling, such as Delayed Detached Eddy Simulation (DDES) have been proposed which allow for greater accuracy of the numerical predictions while the mesh size as well as the central processing unit (CPU) time can be tremendously reduced. In this paper, the numerical simulation of the rotor in a low-speed large-scale axial compressor based on DDES and unsteady Reynolds-Averaged Navier-Stokes (URANS) turbulence models is performed subject to different working conditions of different tip gap sizes, to improve our understanding about the tip leakage vortex (TLV) dynamic mechanisms and discrepancy of these two methods.

The rotor simulations are carried out on the same mesh based on the DDES requirements, and compared to experimental stereoscopic particle image velocimetry (SPIV) data before flow physics investigation. The simulation results capture the location of TLV and show qualitatively good agreement with experiments. DDES method brings improvements in time-averaged results over the Reynolds-Averaged Navier-Stokes (RANS) method. Firstly, the time-averaged and instantaneous results are compared to divide the TLV into three parts. Then the anisotropy of the Reynold stress of these two methods are analyzed in the tip leakage flow through Lumley triangle, to see the difference between the way to get the Reynold stress, using Boussinesq-type approximation in URANS and unsteady velocity fluctuation in DDES. The turbulent anisotropy can be derived from the nondimensional form of the anisotropy tensor. In the rotor simulation, the anisotropy varies along the TLV. The anisotropy of RANS method is weak because the eddy viscosity model is isotropic. Last, the velocity fluctuation data along the TLV core at different chord length are transformed to velocity spectra using fast Fourier transformation (FFT) method to discuss the TLV unsteadiness. The high frequency amplitude becomes obvious downstream the TLV because of losing stability. The result of URANS also has a conspicuous frequency but lower than DDES. The amplitude of URANS is much smaller. From this investigation it is determined that URANS can only predict the large-scale low-frequency dominant unsteady features. While the scale of dissipation and unsteadiness of TLV is small, the Reynolds averaging of URANS may neglect this unsteady phenomenon.
Applying Dynamic Programming Algorithms to the Energy Management of Hybrid Electric Aircraft
Authors: Donateo Teresa , Ficarella Antonio , Spedicato Luigi
Published: August 2018

To explore the application of dynamic programming (DP) to the energy management strategies of hybrid electric aircraft, a hybrid powertrain for a lightweight rotorcraft is introduced and its dynamic control model is designed. The model is conceived for the Agusta-Westland A109 helicopter, a twin-engine rotorcraft used in various roles, such as light transport, search-and-rescue and military roles. The turboshaft single spool engines are modeled with the use of performance maps that allow part load specific fuel consumption to be calculated as a function of actual power request and flight conditions. The state-of-the-art lithium polymer batteries are used for the hybridization and their behavior is evaluated by the Sheperd-Peukert model. The control problem is modeled through a graph structure where a node is obtained from the intersection between a time value, representing the starting of a phase of flight, and a splitting factor, representing the percentage of propulsive power required to the battery in such a phase. The edge connecting two nodes concerns with the state transition and the weight of the edge refers to the transition cost. The goal is to find an optimal splitting sequence to minimize the total cost over the whole mission, that is given with regard to speed and altitude. The Dijkstra algorithm, which allows the shortest energy path to be found between nodes in a graph, is used to look for the optimum. A local optimum is achieved when the cost is defined as the fuel consumption whereas the global optimum can be attained when the model is enhanced to include the effect of the battery usage into the cost.

The results are compared with the original non-hybrid case and the engine efficiency was suitable evaluated. The applicability to other mission data is suitably evaluated so as to deduce the concept of similarity of mission.
Low-Order Network Modeling for Annular Combustors Exhibiting Longitudinal and Circumferential Modes
Authors: Yang Dong , Morgans Aimee S.
Published: August 2018

Modern gas turbine combustors often have annular geometries. These are able to sustain thermoacoustic modes which vary in both the longitudinal and circumferential directions. Effects such as nonlinearity of the flame response to perturbations and differing burners around the annulus lead to the coupling of acoustic modes with different circumferential mode numbers. Such coupling renders differing spatial patterns of instability possible — for example purely longitudinal modes, circumferential standing modes, circumferential spinning modes, mixed modes and slanted modes. Accurately predicting the spatial pattern of limit cycle oscillations resulting from thermoacoustic instability remains an open challenge. This work develops a frequency domain low-order thermoacoustic network model for annular combustors which is notable in (i) accounting for both longitudinal and circumferential modes and (ii) allowing for generic acoustic boundary conditions at either end of the network. Linear acoustic waves are considered, with the different circumferential wavenumbers decoupled for sections both before and after the flames. Modal coupling occurs only at the flames, and is accounted for by summing all modal contributions prior to application of the flame models, and decomposing back into circumferential modes after application of flow conservation equations across the flames. By applying acoustic boundary conditions at either end of the network, an eigenvalue system is established which allows the thermoacoustic modes of the whole combustion system to be analysed. This low order modelling approach is applied to a simplified annular combustor set-up and is demonstrated to be able to capture limit cycles exhibiting longitudinal modes, circumferential spinning modes, circumferential standing modes and even the recently identified slanted modes.
An Experimental Setup for Idealised Studies on Transition to Turbulence on a Generic Compressor Outlet Guide Vane
Authors: Fransson Jens H. M. , Mamidala Santhosh B. , Fallenius Bengt E. G. , Mårtensson Hans , Wallin Fredrik
Published: August 2018

The understanding of flow phenomena in turbomachinery has come far with respect to three-dimensional flow patterns and pressure distributions. Much is due to improved measurements and a continuously evolving fidelity in computational fluid dynamics (CFD). Turbulence and transition in boundary layers are two classical areas where improvements in modeling are desired and where experimental validation is required. Apart from this, fundamental improvements in efficiency can be obtained by developing experimental resources where technologies affecting transition can be studied. The reduction in friction drag can be considerable if the transition to turbulence can be delayed. An experimental setup in an idealized configuration has been designed and built with the objective to study transition on a very large-scale guide vane profile at low speed. The purpose of the rig is to enable high quality fundamental studies of technologies to delay transition, but also to see how effects of manufacturing or other constraints may affect the boundary layer. In the present paper we report the first validation of the experimental setup, by comparing the first test results to CFD calculations performed during the rig design, i.e. no post-calculations with experimental data as input to the simulations have been done yet. The pressure distribution is in line with the design intent, which is a good indicator that the tunnel design is suitable for the intended purpose. At last we report some velocity measurements performed in the wake and we calculate the total drag based on the wake velocity deficit for various Reynolds numbers and with and without turbulence tripping tape. We illustrate that a two dimensional tripping around 7% of the chord from the leading edge can increase the total drag by 50% with respect to the reference case without tripping tape.
Experimental Analysis of a NACA 0021 Airfoil Under Dynamic Angle of Attack Variation and Low Reynolds Numbers
Authors: Holst D. , Church B. , Wegner F. , Pechlivanoglou G. , Nayeri C. N. , Paschereit C. O.
Published: August 2018

The wind industry needs reliable and accurate airfoil polars to properly predict wind turbine performance, especially during the initial design phase. Medium- and low-fidelity simulations directly depend on the accuracy of the airfoil data and even more so if e.g. dynamic effects are modeled. This becomes crucial if the blades of a turbine operate under stalled conditions for a significant part of the turbine’s lifetime. In addition, the design process of vertical axis wind turbines (VAWTs) needs data across the full range of angles of attack between 0 and 180 deg.

Lift, drag and surface pressure distributions of a NACA 0021 airfoil equipped with surface pressure taps were investigated based on time-resolved pressure measurements. The present study discusses full range static polars and several dynamic sinusoidal pitching configurations covering two Reynolds numbers Re = 140k and 180 k, and different incidence ranges: near stall, post stall and deep stall. Various bi-stable flow phenomena are discussed based on high frequency measurements revealing large lift-fluctuations in the post and deep stall regime that exceed the maximum lift of the static polars and are not captured by averaged measurements. Detailed surface pressure distributions are discussed to provide further insight into the flow conditions and pressure development during dynamic motion.

The experimental data provided within the present paper is dedicated to the scientific community for calibration and reference purposes, which in the future may lead to higher accuracy in performance predictions during the design process of wind turbines.
Analysis of Nonlinear Modal Damping due to Friction at Blade Roots Using High-Fidelity Modelling
Authors: Chen Junjie , Zang Chaoping , Zhou Biao , Petrov E. P.
Published: August 2018

In this paper, a methodology is developed for analysis of modal damping in root joints of bladed discs using large finite element models and detailed description of friction contacts at contact interfaces of the joints. The methods allows the analysis of: (i) a single blade vibration and (ii) a bladed-disc assembly for any family of modes (lower and higher modes) calculating the modal damping factors for different levels of vibrations.

Three-dimension solid finite element models are used in the calculations. The analysis is performed in time domain through the transient dynamics analysis. The methodology allows the use of widely available finite element packages and based on the direct calculation of the energy dissipated at root joints due to micro-slip over the multitude of contact elements modelling the surface-to-surface friction contact interactions.

The numerical studies of the dependency of modal damping factors on the vibration amplitudes are performed for simplified and realistic bladed disc models for different blade mode shapes, engine-order excitation numbers and nodal diameter numbers using high-fidelity models.
Flow and Heat Transfer Characteristics in Models of Turbine Blade Tip-Walls With Three Kinds of Turning Vanes
Authors: Wu Bin , Yang Xing , Ye Lv , Liu Zhao , Jiang Yu , Zhao Qiang , Feng Zhenping
Published: August 2018

In this paper, effects of three kinds of turning vanes on flow and heat transfer of turbine blade tip-walls with a U-shaped channel have been numerically studied. Numerical simulations are performed to solve three-dimensional, steady, Reynolds-averaged Navier-Stokes equations with the standard k-ω turbulence model. The aspect ratio (AR) and the hydraulic diameter of the channel are 2 and 93.13 mm, respectively. The effects of single-layer, double-layer and double-layer dome-shaped turning vanes in the turn region on the tip-wall heat transfer and overall pressure loss of rectangular U-shaped channels are analyzed. Detailed flow and heat transfer characteristics over the tip-walls, as well as the overall performance, are presented and compared with each other. Results show that the tip-wall heat transfer coefficients with double-layer dome-shaped turning vanes are the highest among the three cases. Double-layer dome-shaped turning vanes can promote the lateral spreading of secondary flow and effectively increase the uniformity of heat transfer on the tip-wall. More importantly, this structure can make the cooling air expand and accelerate at the center region of the top of the U-shaped channel, resulting in more heat to be removed from the tip-wall. Additionally, double-layer dome-shaped turning vanes can effectively reduce the pressure loss of the channel.
Implementation of the Multi-Level Multi-Integration Cluster Method to the Treatment of Vortex Particle Interactions for Fast Wind Turbine Wake Simulations
Authors: Saverin Joseph , Marten David , Pechlivanoglou George , Paschereit Christian Oliver , van Garrel Arne
Published: August 2018

A method for the treatment of the evolution of the wake of aerodynamic bodies has been implemented. A vortex particle method approach has been used whereby the flow field is discretized into numerical volumes which possess a given circulation. A lifting line formulation is used to determine the circulation of the trailing and shed vortex elements. Upon their release vortex particles are allowed to freely convect under the action of the blade, the freestream and other particles. Induced velocities are calculated with a regularized form of the Biot-Savart kernel, adapted for vortex particles. Vortex trajectories are integrated in a Lagrangian sense. Provision is made in the model for the rate of change of the circulation vector and for viscous particle interaction; however these features are not exploited in this work. The validity of the model is tested by comparing results of the numerical simulation to the experimental measurements of the Mexico rotor. A range of tip speed ratios are investigated and the blade loading and induced wake velocities are compared to experiment and finite-volume numerical models.

The computational expense of this method scales quadratically with the number of released wake particles N. This results in an unacceptable computational expense after a limited simulation time. A recently developed multilevel algorithm has been implemented to overcome this computational expense. This method approximates the Biot-Savart kernel in the far field by using polynomial interpolation onto a structured grid node system. The error of this approximation is seen to be arbitrarily controlled by the polynomial order of the interpolation. It is demonstrated that by using this method the computational expense scales linearly. The model’s ability to quickly produce results of comparable accuracy to finite volume simulations is illustrated and emphasizes the opportunity for industry to move from low fidelity, less accurate blade-element-momentum methods towards higher fidelity free vortex wake models while keeping the advantage of short problem turnaround times.
Numerical Investigation of the Influence of Hood Height Variation on Performance of Low Pressure Steam Turbine Exhaust Hoods
Authors: Munyoki Dickson , Schatz Markus , Vogt Damian M.
Published: August 2018

Performance optimization of low pressure steam turbine exhaust hood has been a subject of a number of both numerical and experimental studies. This is driven by the understanding that improving the diffuser and exhaust hood outer casing performance results in a lower turbine back pressure and hence an increased plant overall output.

The performance of the exhaust hood is greatly influenced by many structural factors such as the size of its outer casing, design of the diffuser parts and the arrangement of the internal supports.

A number of studies have shown that a decrease of the hood height is detrimental to the exhaust hood performance [1, 2], however, up to now the impact of increased hood height has not been researched. In the present study, a scaled axial-radial diffuser test rig operated by ITSM is used as reference configuration for a parameter study. A total of fourteen different configurations with both increased and reduced hood height are investigated numerically. Design load at three different tip jet Mach numbers (no tip jet, tip jet Mach number of 0.4 and 1.2) is chosen as operating condition. Numerical and experimental data is available for the reference configuration and the numerical results have already been validated in a previous paper by the authors [3].

While a decrease of hood height shows the expected deterioration of efficiency, an increase of the hood height only initially results in an improved performance. After reaching a maximum efficiency, which is dependent on the tip leakage, the exhaust hood performance decreases noticeably again. Apart from the variation of pressure recovery, the results allow a better understanding of the loss mechanisms and flow phenomena in exhaust hoods, showing that the deflection of the flow coming out of the diffuser in the top part of the hood has a major impact on exhaust hood pressure recovery.
Experimental and Numerical Investigation of Optimized Blade Tip Shapes: Part I — Turbine Rainbow Rotor Testing and CFD Methods
Authors: Cernat Bogdan , Pátý Marek , De Maesschalck Cis , Lavagnoli Sergio
Published: August 2018

Blade tip design and tip leakage flows are crucial aspects for the development of modern aero-engines. The inevitable clearance between stationary and rotating parts in turbine stages generates high-enthalpy unsteady leakage flows that strongly reduce the engine efficiency and can cause thermally induced blade failures. An improved understanding of the tip flow physics is essential to refine the current design strategies and achieve increased turbine aerothermal performance. However, while past studies have mainly focused on conventional tip shapes (flat tip or squealer geometries), the open literature suffers from a shortage of experimental and numerical data on advanced blade tip configurations of unshrouded rotors.

This work presents a complete numerical and experimental investigation on the unsteady flow field of a high-pressure turbine, adopting three different blade tip profiles. The aerothermal characteristics of two novel high-performance tip geometries, one with a fully contoured shape and the other presenting a multi-cavity squealer-like tip with partially open external rims, are compared against the baseline performance of a regular squealer geometry. The turbine stage is tested at engine-representative conditions in the high-speed turbine facility of the von Karman Institute. A rainbow rotor is mounted for simultaneous aerothermal testing of multiple blade tip geometries. On the rotor disk, the blades are arranged in sectors operating at two different clearance levels. A numerical campaign of full-stage simulations was also conducted on all the investigated tip designs to model the secondary flows development and identify the tip loss and heat transfer mechanisms.

In the first part of this work, we describe the experimental setup, instrumentation and data processing techniques used to measure the unsteady aerothermal field of multiple blade tip geometries using the rainbow rotor approach. We report the time-average and time-resolved static pressure and heat transfer measured on the shroud of the turbine rotor. The experimental data are compared against CFD predictions. These numerical results are then used in the second part of the paper to analyze the tip flow physics, model the tip loss mechanisms and quantify the aero-thermal performance of each tip geometry.
Damping Behavior of Acoustic Dominant Modes in an Aeroacoustic Test Rig Representing a Simplified Geometry of a High Pressure Radial Compressor
Authors: Barabas Botond , Brillert Dieter , Dohmen Hans Josef , Benra Friedrich-Karl
Published: August 2018

Pressure ratios of modern high pressure radial compressors tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the impeller structure play an important role in designing a machine for reliable operation. However, they are not yet fully understood. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at a higher pressure level. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood.

To understand the interaction, especially regarding the damping behavior, of coupled structure and acoustic modes, a comprehension of the behavior of the uncoupled or weakly coupled modes is required. The structural damping ratio is very small and it has been analyzed in existing literature extensively. The damping behavior of uncoupled acoustic modes, however, is not yet well investigated.

This paper focuses on the damping behavior of acoustic modes that are weakly coupled to structure modes. Measurement results gathered at the aeroacoustic test rig at the University of Duisburg-Essen are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the Peak-to-Peak method. In general, the damping decreases with increasing fluid pressure. Furthermore, a relationship of the damping ratio, the kinematic viscosity, and the natural frequency of the acoustic modes has been detected.
Numerical Investigation Into the Energy Extraction Characteristics of Parallel Dual-Foil Turbine
Authors: Jiang Wei , Wang Yulu , Xie Yonghui , Zhang Di
Published: August 2018

A new concept of power generator using two oscillating foils in parallel configuration to extract energy from fluid is proposed and numerically tested in the present study. The theoretical performance of the turbine in this form is investigated through unsteady two-dimensional laminar-flow Navier-Stokes simulations. The effect of the interaction between the two foils is studied at different pitching amplitudes and phase differences between the two foils. The energy extraction performance, instantaneous force coefficients and flow details are compared between single foil and dual foils, and thus the mechanism of performance improvement by wing-in-ground effect is revealed. Two different kinds of asymmetric sinusoidal motions are utilized to further improve the performance of the turbine. Numerical results indicate that anti-phase mode can achieve higher power coefficient than the in-phase mode. The contracted passage under anti-phase mode helps produce larger lift force and power coefficient. The maximum power coefficient per foil for anti-phase dual foils is 1.4% higher than that of single foil. The asymmetric sinusoidal pitching motion in phase can improve the synchronization between plunging velocity and lift force and thus further enhance the energy extraction performance by 1.3%. Besides, the pitching motion with asymmetric amplitude also can increase the power coefficient somehow, but the improvement is very limited.
Experimental and Numerical Investigations of Novel Natural Gas Low NOx Burners for Heavy Duty Gas Turbine
Authors: Cerutti Matteo , Riccio Giovanni , Andreini Antonio , Becchi Riccardo , Facchini Bruno , Picchi Alessio
Published: August 2018

A novel dry low-NOx gas turbine technology requires well balanced assessments since the early development phases. The weak knowledge of often conflicting aspects, such as operability and manufacturability, make any roadmap difficult to be drawn. The introduction of innovative manufacturing technologies such as the Direct Metal Laser Sintering (DMLS) process allows rapid manufacturing of components and test them in dedicated facilities to support real-time development of new products. The use of such a manufacturing process allows the adoption of designed experiments based development strategies, which are still uncommon at industrial level, due to the reduced time from drawings to test.

The paper describes a reactive test campaign performed by BHGE in cooperation with University of Florence, aimed at the exploration of capabilities of different innovative burners in terms of pollutant emissions containment and blow-out margin. In particular, the test campaign has been conceived to provide a robust estimate of the effects of key geometrical parameters on principal burner performances. The flame stabilization mechanism of the investigated burners is based on the swirling flow generated by different setup of two internal channels: co-rotating and counter-rotating radial and axial swirlers. The effect of both the shape and the size of the internal air passages, as well as of the swirler characteristics, has been matter of investigation.

Burners were tested in a single-cup test rig operated at moderate pressure conditions (up to 6bar), with two levels of preheated air temperature (300°C and 400°C). Each burner was equipped with two natural gas feeding lines representing the diffusion (pilot) and premixed (main) fuel supplies: both lines were regulated during tests to assess the effect of fuel split on emissions and to identify a stable low-NOx operating window, within which a lean blow-out test was performed. Dynamic pressure probes, were used to evaluate the onset of combustion instabilities.

The burner development was supported by CFD investigations with the purpose to have a detailed understating of the flow-field and flame structure and to perform a preliminary screening to select the most promising solutions for the testing phase.

The post process of the experimental results has allowed to correlate the main design parameters to burner performance variables discovering possible two-fold optimizations in terms of emissions and operability.
High Resolution Heat Transfer Measurements of Cylindrical Holes Embedded in a Trench With Backward Injection
Authors: Shi Bo , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2018

Recent studies have demonstrated that cylindrical hole with backward injection arrangement, of which the jets are injected reverse to the mainstream flow direction, outperforms its forward injection counterpart, of which the jets are injected along the flow direction, at high blowing ratio, since the jet starts to lift off typically for forward injection when blowing ratio is greater than 1.0. However, the backward injection configuration features a large separation and induces high heat transfer near the hole. Relative few studies have been conducted to mitigated the drawbacks of backward injection arrangements. The present study investigated several flat plate trenched hole arrangements with backward injection. Experiments were conducted in a low speed suction type wind tunnel. The trench width was varied from 2d to 4d for the backward arrangements with fixed trench depth of 0.75d. Besides, a simple backward and a trenched hole with forward injection, whose width is 2d and depth is 0.75d, were also studied as references. Transient thermal measurements were carried out for all the arrangements with IR camera. Detailed distributions of heat transfer coefficient were obtained. For each case, blowing ratio was varied from 0.25 to 4.0, while the density ratio was almost unity. Effects of injection angle, trench width and blowing ratio on the surface heat transfer distributions were obtained, and the results are presented and explained in this investigation.
Multi-Pass Serpentine Cooling Designs for Negating Coriolis Force Effect on Heat Transfer: Smooth Channels
Authors: Singh Prashant , Ji Yongbin , Ekkad Srinath V.
Published: August 2018

Gas turbine blades feature serpentine internal cooling passages connected by 180-degree bends, through which coolant bled off from the compressor is routed to cool the internal walls. Under the influence of Coriolis force and centrifugal buoyancy force induced by rotation, the heat transfer for radially outward flow enhances on the trailing side (pressure side) and reduces on the leading side (suction side). A reverse trend in heat transfer is observed for radially inward flow. Rotation induced forces result in non-uniform heat transfer coefficient distribution which results in non-uniform metal temperatures under steady state condition. Present study addresses the problem of non-uniform heat transfer distribution due to rotation effect, by experimental investigation of two configurations where Coriolis effect was negated by aligning the coolant flow vector and rotation vector such that their cross product was effectively a null vector. This paper presents a novel design for serpentine cooling passages which are arranged along the chord of the blade which has similar heat transfer coefficient distribution on both leading and trailing walls. The two configurations were four-passage and six-passage serpentine smooth channels. Detailed heat transfer coefficients were measured using transient liquid crystal thermography under stationary and rotating conditions. Heat transfer experiments were carried out for Reynolds numbers ranging from 12294 to 85000 under stationary conditions. Rotation experiments were carried out at Rotation numbers of 0.05 and 0.11. Heat transfer enhancement levels of approximately two times the Dittus-Boelter correlation (for developed flow in smooth tubes) were obtained under stationary conditions. Under rotating conditions, we found that the four-passage configuration had slightly lower heat transfer compared to stationary case, and the six-passage configuration had higher heat transfer on both leading and trailing sides compared to stationary case. The leading and trailing side heat transfer characteristics were near-similar to each other, for both the configurations and the rotating heat transfer was near-similar to the stationary condition heat transfer.
Additive Manufacturing for the Manufacture of Gas Turbine Engine Components: Literature Review and Future Perspectives
Authors: Gebisa Aboma Wagari , Lemu Hirpa G.
Published: August 2018

Additive manufacturing (AM) is an emerging rapid manufacturing technique that builds parts by tracing their cross section, layer upon layer. This technology has many unique capabilities that are not found in conventional manufacturing techniques. One of these is its ability to produce very complex part geometries without the need for any tooling. This unique potential makes it the future manufacturing technique for very complex and intricate geometries such as gas turbine components. The current review investigates the available metal additive manufacturing techniques and materials, in respect of their applicability for gas turbine engine components. From the investigation, it is clear that AM is in a promising progress for the manufacture of aircraft gas turbine components. The current limitations of AM techniques for the production of gas turbine engine components are also covered. The future perspective of this technology in this regard has also been discussed.
Stress Calibration Methodology of Stator Blades Using Experimental SAFE Diagram
Authors: Ligot Jérôme , Hoffait Sébastien , de Cazenove Jean , Vallino Frédéric , Golinval Jean-Claude
Published: August 2018

This paper introduces an improvement of the stress calibration methodology of stator blades to consider a nodal diameter of interest of the structure. The proposed calibration procedure and the search for optimal excitation set-up are detailed. To this purpose, the following points are addressed.

Experimental modal analyses are performed using both accelerometers and strain gages. Post-processing techniques are developed to determine the nodal diameters of the identified modes. SAFE (Singh’s Advanced Frequency Evaluation) diagrams are computed from the experimental data and compared with the diagrams obtained numerically by finite elements computations.

Multiple excitations are used to appropriate the targeted modes. A comparative study of different shaker types, of the number of excitation points and of their location is performed.

Calibration is achieved by comparing strain measurements taken on one gage installed on the engine and velocities measured using laser vibrometers. It allows reducing the impact of the instrumentation on the modal content.

The calibration factors obtained by the novel proposed procedure are compared to the ones given by the currently used methodology.
An Integrated Design Approach for Turbocharger Turbines Based on the Performance Optimization in Transitory Conditions
Authors: Checcucci Matteo , Becciani Michele , Bellucci Juri , Bianchini Alessandro , Ferrara Giovanni , Arnone Andrea , Cencherle Francesco , De Luca Michele , Marmorini Luca , Montesino Stephane , Pini Nicola
Published: August 2018

Turbocharged engines are setting themselves as the present standard in case of high-performance engines for sport applications. The coupling of a turbomachine with an internal combustion engine poses, however, some serious challenges, especially regarding the time lags and the transitory flow conditions. In particular, focus is presently being paid to the acceleration phase of these sport vehicles, where the mass flow is much lower than that attended at maximum efficiency condition and the transitory response of the turbocharger becomes pivotal to provide promptly high compression ratios to the engine. In this view, the global optimization process of new turbochargers must be oriented not only at maximizing the aerodynamic efficiency at the best design point but also at providing good efficiency at low mass flow rates, combined with a reduced inertia to enable fast acceleration.

In the study, a multi-objective methodological approach is presented aimed at designing the turbine of a high-performance turbocharged engine based on the following requirements: 1) high efficiency at the design point; 2) good efficiency at low mass flow rates, typical of the acceleration phase; 3) reduced inertia; 4) overall aerodynamic design adaptable with constructive constraints. In doing so, some design considerations are also provided, pointing out the different design choices that can be made in a design strategy focused either on maximum efficiency or on the minimization of the system inertia. The aerodynamic optimization has been carried out with an in-house CFD 3D code, while the turbine coupling with the engine has been obtained by embedding the aerodynamic maps into the 1D engine model.

The analysis showed that the new focus on the transitory response modified substantially the conventional design of the turbine, leading to new geometries able to improve notably the overall performance of the turbocharger.
On the Influence of an Acoustically Optimized Turbine Exit Casing Onto the Unsteady Flow Field Downstream of a Low Pressure Turbine Rotor
Authors: Simonassi L. , Zenz M. , Zerobin S. , Heitmeir F. , Marn A. , Selic T.
Published: August 2018

Modern low pressure turbines (LPT) are designed in order to fulfil a various number of requirements such as high endurance, low noise, high efficiency, low weight and low fuel consumption. Regarding the reduction of the emitted noise, different designs of low pressure turbine exit guide vanes (aerodynamically and/or acoustically optimized) of the turbine exit casing (TEC) were tested and their noise reduction capabilities and aerodynamic performance were evaluated. In particular, measurements of TEC-losses were performed and differences in the losses were reported.

Measurements were carried out in a one and a half stage subsonic turbine test facility at the engine relevant operating point approach. This work focuses on the study of the unsteady flow field downstream of an unshrouded low pressure turbine rotor. The influence on the upstream flow field of a TEC design including acoustically optimized vanes (Inverse cut-off TEC) is investigated and compared with a second TEC configuration without vanes (Vaneless TEC), by means of fast response aerodynamic pressure probe measurements. The second configuration served as a reference concerning the influence of TEGVs onto the upstream located LPT rotor.

The interactions between the stator and rotor wakes, secondary flows and the turbine exit guide vanes potential effect are identified via modal decomposition according to the theory of Tyler and Sofrin. The main structures constituting the unsteady flow field are detected and the role of the major interaction effects in the loss generation mechanism and in the acoustic emission is analysed.

This study based on the modal analysis of the unsteady flow field offers new insight into the main interaction mechanisms and their importance in the assessment of the aerodynamic and aeroelastic performance of modern low pressure turbine exit casings.