bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Flow Characteristics in a Combustor With Opposed Jets
Authors: Ji Yongbin , Ge Bing , Zang Shusheng
Published: August 2018

Jet-in-cross flow (JICF) has been investigated broadly because of its wide engineering application, for example in the gas turbine field, film cooling on the turbine vanes and blades, primary and dilution jets in the combustors and so on. In the gas turbine combustors, the main flow is generated by the swirlers to stabilize the flame, which induces complicated 3D flow characteristics. Different from uniform main flow, swirling cross flow has a strong tangential velocity component, which will deflect the jets in the circumferential direction as well as in the streamwise direction. So, the degradation behavior of the jets is more complex than that in the uniform cross flow. This paper presents PIV measurement of the flow field inside of a three-nozzle annular combustor with opposed quenching jets on the liner walls. Dry ice as a newly proposed flow tracer was proposed and tried. The momentum flux ratio and jet holes configuration are studied to evaluate their effects on the primary recirculation zone, downstream flow field. Finally, numerical simulation was also performed to reveal 3D flow characteristics as well as turbulent kinetic energy generation. The results show that momentum flux ratio has a dominant influence on flow characteristics in the combustor. Getting better understanding of jets behavior in the swirling cross flow helps optimization design of quenching or dilution holes geometry and arrangement for the gas turbine combustor, which turns to be very beneficial to the low-emission and high efficient combustor development.
Twin-Web Turbine Discs: Part 2 — Fabrication and Processing
Authors: Vasilyev Boris , Magerramova Liubov , Salnikov Anton , Tsykunov Nikolay , Isakov Vladimir , Semenov Artem
Published: August 2018

The first part of this paper shows that the implementation of twin-web (hollow) discs can lead to an 8–30% decrease in mass or to a cyclic life increase of up to 300%, depending on the size of the disc and the operating conditions. The second part of this paper describes the results of the development of approaches for the manufacturing and processing of twin-web discs, both with the help of additive and traditional manufacturing methods. Several hollow discs with a closed cavity and a slot in the hub are made from the heat-resistant nickel alloy EI698P with the help of additive manufacturing (AM) and hot isostatic pressing (HIP), respectively. Various welding methods are considered for the production of the twin-web discs.

The effect of post-processing on the characteristics of the materials is investigated in specimens that were produced with AM methods. Special attention is paid to the surface treatment methods that should be used for discs manufactured by AM methods. The “printed” discs were controlled using radiographic, ultrasonic, fluorescent penetrant, and eddy current methods, and they were examined using computed tomography.

As a result, this paper shows that different approaches can be used for the manufacturing and processing of twin-web discs.
Compliant Hybrid Gas Bearing Using Modular Hermetically-Sealed Squeeze Film Dampers
Authors: Ertas Bugra , Delgado Adolfo
Published: August 2018

The following paper presents a new gas bearing concept that targets machine applications in the megawatt (MW) power range. The concept involves combining a compliant hybrid gas bearing (CHGB) with 2 hermetically sealed squeeze film damper (HSFD) modules installed in the bearing support damper cavities. The main aim of the research was to demonstrate gas bearing-support damping levels using HSFD that rival conventional open-flow squeeze film dampers (SFD) in industry. A detailed description of the bearing design and functionality is discussed while anchoring the concept through a brief recap of past gas bearing concepts. Proof-of-concept experimental testing is presented involving parameter identification of the bearing support force coefficients along with a demonstration of speed and load capability using recessed hydrostatic pads. Lastly, a landing test was performed on the bearing at high speed and load with porous carbon pads to show capability of sustaining rubs at high speeds. The component testing revealed robust viscous damping in the bearing support, which was shown to be comparable to existing state of the art SFD concepts. The damping and stiffness of the system portrayed moderate frequency dependency, which was simulated using a 2D Reynolds based incompressible fluid flow model. Lastly, rotating tests demonstrated the ability of the gas bearing concept to sustain journal excursions and loads indicative of critical speed transitions experienced in large turbomachinery.
Effect of Combined Liners on Controlling Thermoacoustic Instability in a Rijke Tube
Authors: Zhang Guangyu , Wang Xiaoyu , Sun Dakun , Sun Xiaofeng
Published: August 2018

In present paper, theoretical investigation on the effect of combined liners of a drum-like liner and a perforated liner with bias flow on controlling thermoacoustic instability in a Rijke tube is carried out by transfer element method (TEM). TEM is used to consider the interactions between the acoustic waves and the soft boundary of the drum-like liner or perforated liner with bias flow. The respective effect of the drum-like liner and perforated liner with bias flow on changing the frequency and growth rate of the first two planar modes are investigated. In addition, effects of main features of the combined liners on the growth rate and natural frequency of the thermoacoustic system are explored by calculating the complex resonance frequency in some representative configurations. It is found that the frequency decrease induced by the usage of the liners can lead to increase of the phase difference between unsteady heat release and pressure oscillation, which is helpful for controlling thermoacoustic instability. Besides, the change of frequency may result in the jump of the phase difference between heat and pressure oscillations at some fixed point in the tube, the potential positive side of which can be utilized to make the unsteady release stabilized. It is found that the damping effect of the perforated liner, which is manifested by attenuation of the sound pressure, is maximized when the perforated liner is placed close to the downstream end of the Rijke tube. At this “optimal” position for the perforated liner with bias flow, the inclusion of the drum-like liner will deteriorate control effect by decreasing the natural frequency. Nevertheless, when the perforated liner is located near the heat source, the damping effect of the perforated liner is weakened, and at this “non-ideal” position, the incorporation of the drum-like liner will help control thermoacoustic instability. It brings out an inspiration that the thermoacoustic instability can be controlled more effective when the main damping source is not at the “optimal” position with this technique without bringing in any aerodynamic loss.
Effects of Cavity Purge Flow on Intermediate Turbine Duct Flowfield
Authors: Liu Jun , Du Qiang , Liu Guang , Wang Pei , Liu Hongrui , Xu Qingzong
Published: August 2018

To increase the power output without adding additional stages, ultra-high bypass ratio engine, which has larger diameter low pressure turbine, attracts more and more attention because of its huge advantage. This tendency will lead to aggressive (high diffusion) intermediate turbine duct design. Much work has been done to investigate flow mechanisms in this kind of duct as well as its design criterion with numerical and experimental methods. Usually intermediate turbine duct simplified from real engine structure was adopted with upstream and downstream blades. However, cavity purge mass flow exists to disturb the duct flow field in real engine to change its performance. Naturally, the wall vortex pairs would develop in different ways. In addition to that, purge flow rate changes at different engine representative operating conditions. This paper deals with the influence of turbine purge flow on the aerodynamic performance of an aggressive intermediate turbine duct. The objective is to reveal the physical mechanism of purge flow ejected from the wheel-space and its effects on the duct flow field. Ten cases with and without cavity are simulated simultaneously. On one hand, the influence of cavity structure without purge flow on the flow field inside duct could be discussed. On the other hand, the effect of purge flow rate on flow field could be analyzed to investigate the mechanisms at different engine operating conditions. According to this paper, cavity structure is beneficial for pressure loss. And the influence concentrates near hub and duct inlet.
Unsteady Flow Simulation of Buoyancy-Driven Flows in High-Pressure Compressor Disk Cavities
Authors: Tateishi Atsushi , Watanabe Toshinori , Himeno Takehiro
Published: August 2018

This paper focuses on the buoyancy-induced unsteady flow phenomenon inside high-pressure compressor disk cavities. In order to understand the flow structure in a realistic configuration, a 10-stage core compressor of the NASA/GE Energy Efficient Engine is adopted as a computational target. The numerical flow simulation is conducted on a full annulus model, where the temperature distribution on the wall is modeled based on the core test results. The time-averaged flow fields are obtained by detached eddy simulation (DES) and two-dimensional axisymmetric Reynolds-averaged Navier-Stokes (RANS) simulation, and the difference is discussed in detail.

The DES result showed large-scale, vortical structures with significant radial velocity fluctuations especially in the rear part of the compressor. These fluctuations create radial arm-like structure in the temperature distribution in the cavity, and greatly enhance the mixing between the bore coolant and hot air near the cavity wall. In addition, it is observed that the hot air discharged from the cavities creates a large cell at bore region, which extends across several rear stages.

Although the present study successfully illustrates the entire structure of unsteady flow in heated compressor disk cavities including full stages, a more detailed validation will be needed to further confirm the applicability of DES for the targeted flow.
Numerical Study on Interaction of Tip Synthetic Jet With Tip Leakage Flow in Centrifugal Impeller
Authors: Huang Wenlin , Zhao Huijing , Wang Zhiheng , Xi Guang , Liu Haijun
Published: August 2018

The synthetic jet, located at the shroud and close to the blade leading edge, is used to control the flow in a typical centrifugal impeller. The effects of the synthetic jet control and the interaction with the tip leakage flow are mainly investigated at the near-stall working point of impeller using the unsteady numerical analysis. The results indicate that, the effect of the synthetic jet with a small injection angle (15deg) is better when the excitation position is located over the main blade leading edge. However, the synthetic jet with a large injection angle (90deg) obtains a better result when the excitation position is located at the downstream of main blade leading edge. The synthetic jet with a larger velocity amplitude has a more remarkable effect on deflecting the main flow/tip leakage flow interface to the downstream direction. With typical parameters, the synthetic jet increases the circumferentially averaged streamwise location of the main flow/tip leakage flow interface by 12.5% compared with the case without a synthetic jet. The interaction between the tip leakage flow and synthetic jet makes the tip leakage flow out of the tip clearance with larger streamwise momentum, which is favorable to restrain the tip leakage flow to spill out the leading edge. Besides, the periodic blade loading drop is deflected to downstream direction and the flow fluctuation near the leading edge decrease significantly with the presence of synthetic jet.
A Review of Impingement Jet Cooling in Combustor Liner
Authors: Xie Rong , Wang Hao , Xu Baopeng , Wang Wei
Published: August 2018

Impingement jet cooling is a promising cooling method in modern dry low emission combustor because of its high local heat transfer coefficient. This paper investigates the recent research progress on impingement jet cooling in combustor liner. Firstly, the different flow characteristics in the different impingement jet flow regions are described. Then, the factors influencing impingement jet cooling are discussed, including flow factor and geometry factor. The researches in a large range of flow parameters, including Reynolds number, Mach number and temperature ratio, are reported. The researches in different geometry parameters, such as nozzle geometry, nozzle-to-nozzle spacing, nozzle-to-target distance and inclined angle, are presented. Next, the crossflow effect in array impingement jet is considered. Due to the crossflow decreases the heat transfer performance, varieties of structures which can restrict the crossflow and improve the channel flow are introduced. Finally, the methods to enhance the impingement jet cooling are presented. These methods focus on retrofitting the nozzle and target surface. The combination of impingement jet cooling with other methods, such as effusion cooling, rib roughened surface, is important development direction in combustor liner in the future.
The Physical Mechanism of Tip Leakage Loss Reduction by Means of Passive Injection in Low Mach Number Flows
Authors: Passmann Maximilian , aus der Wiesche Stefan , Joos Franz , Willinger Reinhard
Published: August 2018

Tip clearance losses represent a major source of efficiency losses in turbomachinery. A novel method based on passive injection for reducing tip leakage losses in axial turbine cascades has been proposed in 2007 by Willinger and co-workers, and first experimental demonstrations of the potential of this approach were reported recently. However, these experimental tests were limited to linear cascade experiments w6ith stationary endwalls, and they were not able to explain the underlying physical mechanism of the observed loss reduction. In the present contribution, results of detailed experimental and numerical analyses of the tip gap flow, the interaction of the passive tip injection jet with the gap and the main flow, and the effect of the moving endwall are presented. Both numerical and experimental results indicated that the beneficial effect of the passive injection mainly results from a weaker tip gap vortex and not so much from a simple blockage of the tip gap flow itself.
The Impact of Manufacturing Variations on Performance of a Transonic Axial Compressor Rotor
Authors: Lejon Marcus , Andersson Niklas , Ellbrant Lars , Mårtensson Hans
Published: August 2018

In this paper, the impact of manufacturing variations on performance of an axial compressor rotor are evaluated at design rotational speed. The geometric variations from the design intent were obtained from an optical coordinate measuring machine and used to evaluate the impact of manufacturing variations on performance and the flow field in the rotor. The complete blisk is simulated using 3D CFD calculations, allowing for a detailed analysis of the impact of geometric variations on the flow. It is shown that the mean shift of the geometry from the design intent is responsible for the majority of the change in performance in terms of mass flow and total pressure ratio for this specific blisk. In terms of polytropic efficiency, the measured geometric scatter is shown to have a higher influence than the geometric mean deviation. The geometric scatter around the mean is shown to impact the pressure distribution along the leading edge and the shock position. Furthermore, a blisk is analyzed with one blade deviating substantially from the design intent, denoted as blade 0. It is shown that the impact of blade 0 on the flow is largely limited to the blade passages that it is directly a part of. The results presented in this paper also show that the impact of this blade on the flow field can be represented by a simulation including 3 blade passages. In terms of loss, using 5 blade passages is shown to give a close estimate for the relative change in loss for blade 0 and neighboring blades.
Efficient Generation of Engine Representative Tip Timing Data Based on a Reduced Order Model for Bladed Rotors
Authors: Figaschewsky Felix , Hanschke Benjamin , Kühhorn Arnold
Published: August 2018

In modern compressors the assessment of blade vibration levels as well as health monitoring of the components are fundamental tasks. Traditionally, this assessment is done by the application of strain gauges to some blades of the assembly. In contrast to strain gauges, blade tip timing (BTT) offers a contactless monitoring of all blades of a rotor and there is no need of a telemetry system. A major issue in the interpretation of BTT data is the heavily undersampled nature of the signal. Usually, newly developed BTT algorithms are tested with sample data created by simplified structural models neglecting many of the uncertainties and disturbing influences of real applications. This work focuses on the creation of simulated BTT datasets as close as possible to real case measurements. For this purpose a subset of nominal system modes (SNM) representation of a compressor rotor is utilized. This model is able to include a large number of features present in real measurements, such as mistuning, static blade deflections due to centrifugal loads, aerodynamic damping and multiple mode resonances. Additionally, manufacturing deviations of the blade geometry, probe positioning errors in the BTT system and noise in the time of arrivals (TOAs) are captured by the BTT simulation environment. The main advantage of the created data is the possibility to steadily increase the signal complexity. Starting with a “perfect” signal the simulation environment is able to add different uncertainties one after the other. This allows the assessment of the influence of different features occurring in real measurements on the performance and accuracy of the analysis algorithms. Finally, a comparison of simulated BTT data and real data acquired from a rig test is shown to validate the presented approach of BTT data generation.
Flame Describing Functions of a Confined Premixed Swirled Combustor With Upstream and Downstream Forcing
Authors: Gaudron R. , Gatti M. , Mirat C. , Schuller T.
Published: August 2018

The frequency response of a confined premixed swirled flame is explored experimentally through the use of describing functions that depend on both the forcing frequency and forcing level. In these experiments, the flame is forced by a loudspeaker connected to the bottom of the burner in the fresh gas region or by a set of loudspeakers connected to the combustion chamber exhaust tube in the burnt gas region. The experimental setup is equipped with a hot-wire probe and a microphone, both of which located in front of each other below the swirler. The forcing level is varied between |v′0|/v̄0 = 0.10 and 0.72 RMS where v̄0 and v′0 are respectively the mean and fluctuating velocity at the hot-wire probe. An additional microphone is placed on a water-cooled waveguide connected to the combustion chamber backplate. A photomultiplier equipped with an OH* filter is used to measure the heat release rate fluctuations. The describing functions between the photomultiplier signal and the different pressure and velocity reference signals are then analyzed in the case of upstream and downstream forcing. The describing function measured for a given reference signal is shown to vary depending on the type of forcing. The impedance of the injector at the hot-wire location is also measured using the hot-wire and microphone signals for both upstream and downstream forcing. For all describing functions investigated, it is found that their phase lags do not depend on the forcing level whereas their gains strongly depend on |v′0|/v̄0 for certain frequency ranges. It is furthermore shown that the Flame Describing Function measured with respect to the hot-wire signal can be retrieved from the specific impedance at the hot-wire location and the describing function determined with respect to the signal of the microphone located in front of the hot-wire. This relationship is not valid when the signal from the microphone located at the combustion chamber backplate is considered. It is then shown that a ID acoustic model allows to reproduce the describing function computed with respect to the microphone signal inside the injector from the microphone signal located at the combustion chamber backplate in the case of downstream forcing. This relation does not hold for upstream forcing because of the acoustic dissipation across the swirler which is much larger compared to downstream forcing for a given forcing level set at the hot-wire location. This study sheds light on the differences between upstream and downstream acoustic forcing when measuring describing functions. It is also shown that the upstream and downstream forcing techniques are equivalent only if the reference signal used to determine the flame describing function is the acoustic velocity in the fresh gases just before the flame.
Research on Accuracy of Flowing Field Based on Numerical Simulation for Tonal Noise Prediction in Axial Compressor
Authors: Song M. R. , Yang B. , Dong G. M. , Liu X. L. , Wang J. Q. , Xie H. , Lu Z. H.
Published: August 2018

For the predicting of compressor noise, Lighthill analogy method based on numerical simulation has usually been adopted. Therefore, accuracy of the numerical simulation of the flowing filed is very important to the noise estimation. In this paper, nonlinear harmonic (NLH) method, which is one of promising numerical simulation methods used for the noise prediction, is compared with dual time step (DTS) method based on the calculating of the flowing field of one and a half stage compressor. It is found that the time consumption of NLH is actually decreased by about 70% compared with DTS. All the same, pressure fluctuation in the results obtained from NLH is more obvious than that of DTS in the upstream channel and downstream channel. Meanwhile, the two series of numerical simulation results are compared respectively with experiment data measured by dynamic pressure sensors. It is observed that the results from DTS is much closer to experimental data in both time domain and frequency domain. It is believed that the overmuch fluctuation found in NLH method is mainly caused by the contradiction between actual flowing pattern and periodical assumption made by NLH method initially. In addition, the pressure distribution around rotor blade surface, which is one of important tonal noise sources, is studied in detail as well.
Representation and Analysis of Geometric Uncertainties in Rotor Blades
Authors: Carassale Luigi , Bruzzone Silvia , Cavicchi Andrea , Marrè Brunenghi Michela
Published: August 2018

Geometric uncertainties involved in the rotor blade manufacturing process are a major concern for designers. The deviation of the produced components from their nominal geometry have an impact on the Natural Frequencies (NF) that, under certain circumstances, may have negative effects on the dynamic forced response in operative conditions.

Geometric defects are usually limited by imposing dimensional tolerances based on empirical considerations, simplified approach that may lead to costly manufacturing requirements that still may not guarantee safe results.

This paper proposes a probabilistic representation of the geometric uncertainties for rotor blades and defines a procedure to evaluate their effects on the blade NFs. The deviation from nominal geometry is represented through the Principal Component Analysis (PCA) where it is expressed as a sum of characteristic geometric shapes (GUMs) modulated by mutually uncorrelated random variables (Principal Components, PC). The effect of each GUM is then linearly propagated on the blade NFs and a sensitivity matrix is finally defined.

The procedure is applied to a case-study that concerns a set of 50 nominally identical compressor blades and the ability of GUMs to represent the effects of geometric uncertainties is tested.
Measurement and Abatement of PM Emitted by Stationary Gas Turbines: Experience Gained With Different Fuels and Combustor Types
Authors: Komodromos Aristotelis , Moniatis George , Kontopoulos Frixos , Zaimis George , Vierling Matthieu , Aboujaib Maher , Sokolov Dmitry , Montagne Pierre , Catrin Sven , Karpouzas Dimitris , Vamvarapis Panagiotis , Molière Michel
Published: August 2018

Whichever the type of combustion installation, liquid fuels burned in gas turbines tend to generate particulate matter (PM) emissions, which consist in soot only or in ash plus soot, according to their ash-free or ash-forming character.

Standard diffusion flame combustion systems are known as “universal” combustors, capable to burn both ash-free (naphtha, light and heavy distillates) and ash-forming (crude and heavy) fuels. In contrast, DLN systems are designed to burn gaseous fuels and light distillates.

PMs in the range of a few parts per million represent a solid micropollutant, the measurement and abatement of which creates specific technical challenges.

In order to fully characterize soot emission and investigate their reduction, GE has undertaken a multi-year investigation program covering (i) an exploratory engineering study starting from the EN13284-1 standard and (ii) the testing of a number of inorganic oxidation catalysts used in the form of fuel additives (“soot inhibitors”).

In this framework, a joint work involving GE and Electricity Authority of Cyprus has been conducted in the first half of 2017 and a full-scale test plan has been performed at the Vasilikos power plant in Cyprus, involving a Frame 6F.03 DLN2.6 that burns light distillate oil and is equipped with a DeNOx water injection system. Four types of soot inhibitor additives: cerium (IV) and (III), iron (III) and (II) were tested. This paper reviews the results of this field test and compares them with data previously acquired at other power plants featuring different liquid fuels and combustion systems.

Its goal is to provide the gas turbine community with a better understanding of PM emissions and their abatement using various soot inhibitor candidates, in function of liquid fuel type and combustion system.
Optimization of Fuel Two-Stage Screw Centrifugal Pump of Rocket Powerful Turbopump Unit
Authors: Zubanov Vasilii , Volkov Andrei , Matveev Valeriy , Popov Grigorii , Baturin Oleg
Published: August 2018

The article describes a refining method for a fuel pump of rocket powerful turbo-pump unit by the joint usage of mathematical optimization software IOSO, meshing complex NUMECA and CFD complex ANSYS CFX. The optimization software was used for automatic change of the geometry of low-pressure impeller, transition duct and high-pressure impeller to find the optimal design. It was mandatory to keep the original variant of the remaining parts of the pump. For this reason, only geometrical parameters of the blades were varied without changing the contours of the pump meridional flow part.

The investigated pump consists of five parts: inlet duct, low-pressure screw centrifugal stage, transition duct, high-pressure screw centrifugal stage and volute outlet duct. The pump main parameters with water as the working fluid (based on experiment data) were the following: high-pressure stage rotor speed was 13300 rpm; low-pressure rotor speed was 3617 rpm by gearbox; inlet total pressure was 0.4 MPa; outlet mass flow was 132.6 kg/s at the nominal mode.

Creation of vane unit mesh (rotors and stator transition duct) was performed using NUMECA AutoGrid5. Sector models were used for the calculation simplification. The flow around only one blade or screw was considered. Setting up and solution of the task were carried out in the ANSYS CFX solver. Comparison of calculated characteristics of the basic pump with the experimental data was performed before the optimization.

The analysis of characteristics for the obtained optimized pump geometry was carried out. It was found that pump with optimized geometry has greater efficiency in comparison with the original pump variant. The obtained reserve can be used to boost the rocket engine, and/or to reduce the loading of the main turbine, which operates in aggressive oxidizing environment.
Critical Suction Peformance Test of Turbopump Assembly for a Liquid-Propellant Rocket Engine
Authors: Lee Hang Gi , Shin Ju Hyun , Yoon Suk Hwan , Kim Dae Jin , Bae Jun Hwan , Choi Chang Ho
Published: August 2018

This study investigates the behavior of a turbopump assembly during critical cavitation of the propellant pumps in the upper rocket engine of the Korea Space Launch Vehicle-II. Turbopumps operate under conditions involving low pressure at the pump inlet and high rotational speeds to allow for a lightweight design. This severe environment can easily cause cavitation to occur in the pump. This cavitation can then cause the pump operation to fail. As the cavitation number in the pump decreases below the critical point, the pump fails to operate. There is concern regarding the behavior of the turbopump assembly arising from pump failure due to cavitation. It is necessary to verify the problems that may occur if the turbopump assembly operates under extreme conditions, such like the critical cavitation. This study performed tests to investigate the breakdown of pumps in the turbopump assembly. Tests were conducted with liquid nitrogen, water, and high-pressure air instead of the mediums used during actual operation of liquid oxygen, kerosene, and hot gas. The turbopump was tested at the design point of 27,000 rpm, while the inlet pressure of each pump was controlled to approach the critical cavitation number. The turbine power output was maintained during the tests. The results show that the breakdown point of the oxidizer pump using liquid nitrogen, which is a cryogenic medium, occurred at a lower cavitation number than during an individual component suction performance test using water. The fuel pump using water, meanwhile, experiences breakdown at similar cavitation numbers in both tests. As the breakdown of the pump occurs, the power required by that pump decreases, and the rotational speed of the turbopump increases. Compared with individual pump suction performance tests, this breakdown test can be used to determine the limit of the propellant inlet pressure of the turbopump and to characterize the behavior of the turbopump assembly when a breakdown occurs. Vibrations were also analyzed for tests at a high cavitation number and at the critical cavitation number. The vibration increased with breakdown and notable frequencies were analyzed.
Heat Transfer in a Two-Inlet Rotating Pin-Fin Roughened Rectangular Channel With Side-Wall Fluid Extraction
Authors: Chen Yanan , Wen Jie , Xu Guoqiang , Du Zhiliang , Dai Yunqing
Published: August 2018

The heat transfer characteristics in a rotating pin-fin roughened rectangular channel with an aspect ratio of 4:1 is investigated, simulating a rotor blade trailing edge. The copper plate regional average method is used to determine the heat transfer coefficient. A second inlet is added at the inner top corner of the traditional one-inlet cooling channel to improve heat transfer in the high radius region. Coolant from these two inlets mixes in the middle of the channel, and then exits through eight sidewall slots. The channel is assembled in a rotating facility, and the symmetrical plane of the rectangular channel is orientated at an angle of 135° with respect to the rotation plane. The mass flow rate of the bottom inlet is kept at a constant (Re1 = 20,000), whereas the inlet mass flow rate ratio (MR, second inlet mass flow rate/bottom inlet mass flow rate) changes from 0 to around 0.55. Results show that the second inlet improves the heat transfer in the proximity of the second inlet extensively, but the overall averaged heat transfer is decreased a bit compared to the one inlet channel. Moreover, with the local MR, the heat transfer data at different locations converge into the same trend, indicating that the local MR should be a good parameter in describing the flow in this pin-fin cooling channel. In the rotating one-inlet channel (MR = 0), a critical Ro phenomenon is observed. After the critical point, rotation stops decreasing heat transfer and starts to elevate it. A lower critical Ro is observed at higher radius location but the corresponding local Ro is a constant at around 1.0. In rotating two-inlet channel, the overall heat transfer enhancement caused by rotation is almost in the same level with different MR, indicating that high MR cases (MR > 0.2) is not recommended because the coolant from the second inlet is not efficiently used.
Simulating Wind Turbine Ice Throw: QBlade and Statistical Analysis
Authors: Lennie Matthew , Marten David , Pechlivanoglou George , Paschereit Christian Oliver , Dominin Sean
Published: August 2018

Ice throw and fall analysis using a semi-empirical Monte Carlo approach seems to be a good trade off between empirical formulation and complex full physics simulations. This paper looks at some of the challenges of running these simulations particularly at the uncertainty of certain input data. The field testing so far has helped provide data on a few of the key properties of the ice chunks. However, the output probability fields still suffer from a relatively high level of uncertainty due to the difficulty in collecting large sample sizes. A convergence study was able to establish that 60000 particle samples appear to be enough to converge the output probability field for the number of input variables selected. In a demonstration case using the new QBlade ice module, it was possible to demonstrate that it may be possible to avoid heating the inner sections of the wind turbine blades without increasing the risk compared to a standstill wind turbine.
Method for Non-Dimensional Tip Leakage Flow Characterization in Radial Turbines
Authors: Serrano José Ramón , Navarro Roberto , García-Cuevas Luis Miguel , Inhestern Lukas Benjamin
Published: August 2018

Tip leakage loss characterization and modeling plays an important role in small size radial turbine research. The momentum of the flow passing through the tip gap is highly related with the tip leakage losses. The ratio of fluid momentum driven by the pressure gradient between suction side and pressure side and the fluid momentum caused by the shroud friction has been widely used to analyze and to compare different sized tip clearances. However, the commonly used number for building this momentum ratio lacks some variables, as the blade tip geometry data and the viscosity of the used fluid. To allow the comparison between different sized turbocharger turbine tip gaps, work has been put into finding a consistent characterization of radial tip clearance flow. Therefore, a non-dimensional number has been derived from the Navier Stokes Equation. This number can be calculated like the original ratio over the chord length. Using the results of wide range CFD data, the novel tip leakage number has been compared with the traditional and widely used ratio. Furthermore, the novel tip leakage number can be separated into three different non-dimensional factors. First, a factor dependent on the radial dimensions of the tip gap has been found. Second, a factor defined by the viscosity, the blade loading, and the tip width has been identified. Finally, a factor that defines the coupling between both flow phenomena. These factors can further be used to filter the tip gap flow, obtained by CFD, with the influence of friction driven and pressure driven momentum flow.
Unsteady Flow Effects on Steam Turbine Last Stage Blades at Very Low Load Operating Condition
Authors: Tanuma Tadashi , Ogawa Michio , Okuda Hiroshi , Hashimoto Gaku , Shibukawa Naoki , Okuno Kenichi , Tsukuda Tomohiko
Published: August 2018

Unsteady aerodynamic and structural interactive analysis method for design and development of highly efficient low pressure last stage blades and results of its main application on very low load conditions are reported in this paper.

Main features of this method are the enhanced analysis scope including very low load conditions and validations using measured data of real steam turbines including very low load conditions as well. Our schemes for this project were introducing boundary conditions from measured data in real steam turbines, full annulus all blade unsteady aerodynamic analysis and large scale parallel computing for unsteady structural analysis.

The aerodynamic analysis results indicate that one root cause of the relatively large blade vibration at low load conditions seems to be a tip vortex induced by the blade windage.

A modified method that introduced accurate structural analysis boundary condition data from aerodynamic analysis results is demonstrated. The structural analysis of a six-blade group with lacing wire dumping structure was performed.
Compressor Instability Analysis Within an Hybrid System Subject to Cycle Uncertainties
Authors: Cuneo Alessandra , Traverso Alberto , Massardo Aristide F.
Published: August 2018

The transient/dynamic modeling of energy systems can be used for different purposes. Important information can be obtained and used for the design phase. The control system and strategies can be safely tested on transient/dynamic models in simulation, increasing the confidence during experimental phase. Furthermore, these models can be used to acquire useful information for safety case. The analysis of energy systems in dynamic conditions is generally performed considering fixed values for both geometrical and operational parameters such as volumes, orifices, but also initial temperatures, pressure, etc. However, such characteristics are often subject to uncertainty, either because they are not known accurately or because they may depend on the operating conditions at the beginning of the relevant transient. With focus on a micro-gas turbine fuel cell hybrid system, compressor surge may or may not occur during transients, depending on the aforementioned cycle characteristics; hence compressor surge events are affected by uncertainty.

In this paper, a stochastic analysis was performed taking into account an emergency shut-down in a fuel cell gas turbine hybrid system, modelled with TRANSEO, a deterministic tool for the transient and dynamic simulations of energy systems. The aim of the paper is to identify the main parameters that impact on compressor surge margin. The stochastic analysis was performed through the RSA (Response Sensitivity Analysis) method, a sensitivity-based approximation approach that overcomes the computational burden of sampling methods such as MCS (Monte-Carlo Simulation). The results show that the minimum surge margin occurs in two different ranges of rotational speed: a high-speed range and a low-speed range, the latter being more sensitive for surge occurrence. The temperature and geometrical characteristic of the outer pressure vessel, where the fuel cell is installed, are the two main parameters that affect the surge margin during an emergency shut down.
Assessment of Scale Adaptive Simulation of a Rotor of High Pressure Compressor
Authors: Marty J. , Gaible H. , Bézard H.
Published: August 2018

The main design objectives of a high pressure compressor are the aerodynamic efficiency and the operating range (e.g. the surge margin). Those quantities are impacted by secondary and leakage flows occurring in the blade passage such as corner separation or stall and tip leakage flows. The turbulence modeling influences strongly the prediction of the overall performances. The aims of the present study were (i) the validation of the combination of the SAS approach with the DRSM turbulence model by comparison to experimental data, especially to laser measurements in the tip of a rotor of a high pressure compressor and (ii) the discussion of the flow prediction improvements with respect to turbulence approaches classically used in CFD and industry: URANS simulations and standard SAS simulation i.e. combined with SST turbulence model. The SAS results are compared to experimental data and to URANS results (SST and DRSM). Only the simulations with IGV wakes predict the velocity fluctuations near tip gap, from the leading edge. Concerning the time-averaged performances, the stagnation pressure losses are slightly overestimated by SAS, especially with DRSM model. This is due to an amplification of the hub corner separation. Moreover, the isentropic efficiency is very sensitive to the SAS approach and to the turbulence model. The spectral analysis shows that the prediction of the amplitude and frequencies of the power spectral density of static pressure is improved using the SAS approach instead of URANS one. The SAS approach leads to PSD similar to ZDES, especially with the DRSM model. Thus, the SAS-DRSM is able to well predict the tip leakage flow with the fine mesh. Nevertheless, this approach amplifies the hub corner separation leading to a strong underestimation of overall performances.
Development of a Robust LP Blade Family for Variable Speed Applications
Authors: Schubert Martin , Tusche Johannes
Published: August 2018

Industrial steam turbine applications require a high flexibility in terms of aerodynamically as well as mechanically operating conditions. Mechanical drives run at variable rotor speeds and often face high backpressure levels, which is a particularly challenging aspect for the last-stage moving blade (LSMB) row of a low-pressure (LP) steam turbine. As speed synchronous blade resonances cannot be excluded over the entire operating speed range, the LSMB needs to be designed resonance proof from viewpoint of dynamics and mechanical strength.

The subsequent paper describes a new developed LP stage group for variable speed applications, which is available as fully scaled blade family with distinct exhaust area and rotational speed limit reaching from conventional 3000rpm up to high speed utilities for special purposes. It consists of two standard stages, which can be operated at off resonance as well as resonance conditions. For that reason frictional elements were implemented in both moving blade rows. They are loosely assembled into pockets, which are placed on the pressure as well as suction side of each airfoil. Basically, this feature was already introduced for certain Siemens LP blades, see [1], [2], [3] and [4]. However, the recent development on this field utilizes several design changes for the benefit of robustness and reliability. The present paper focuses on the non-linear dynamic behavior of the friction damped, coupled blade rows and outlines the underlying design method as well as calculation process.
Incremental Modeling of Rotor Lifetime Consumption During Gas Turbine Operation
Authors: Sistaninia M. , Winge T. , Ugel D.
Published: August 2018

In order to enable customers to operate gas turbines (GT) closer to the life limits, a life monitoring tool has been developed which computes rotor life consumption based on operation history of the GT. The tool can account for both creep and fatigue life consumption. The creep module can be applied to extend GTs creep life at high operational gas temperatures, whereas the fatigue module enables more flexible operations meaning more frequent operation at varying load conditions.

For creep monitoring a new incremental modeling approach has been developed to calculate rotor radial elongation based on the actual operation history of GTs. In this method the rate of elongation during GT operation is calculated based on a correlation with the total radial elongation and gas temperature. The results of this modeling approach have been validated against the field data of several GTs. A good agreement has been obtained between the simulation and measurement results for different rotor axial positions.

For fatigue life monitoring, the temperature based monitoring approach developed in a former publication [1] by the authors has been further adapted to rotating components in particular the rotor for which metal temperature measurement is very challenging. In this method life consumption is calculated based on the gas temperature history and GT power instead of metal temperature.

By considering the real-time data, the rotor life consumption can be more precisely calculated and as a result the GT can be operated closer to its life limits. Hence, this method can be used to increase the intervals between inspections and therefore to extend the service life of the GTs.
A 3D-LDA Study of the Relation Between Coincident and Time Stepped Non-Coincident Stress Measurements in a Linear Compressor Cascade
Authors: Geist Silvio , Harbeck Janneck , Joos Franz
Published: August 2018

Especially in the turbulence research, it is necessary to record three velocity components concurrently. As a result, all six components of the Reynolds stress tensor and higher-order velocity correlations can be determined. This article assesses the three-dimensional flow field of a linear transonic compressor cascade. The velocity field within the blade passage is measured using a 3D-LDA system. This requires a coincident measurement of the velocity. However, this leads to a significant reduction in the data rate. To circumvent this problem there is the general approach of a record interval window to the subsequent generation of coincident data. In comparison to previous publications, a transonic flow is considered here. For a coincident measurement it is essential that all velocities are perpendicular to each other. Because of limited arrangement possibility of the probes the system measures three non orthogonal velocity components. Therefore, a coordinate transformation is necessary. Due to uncertainties in the exact laser alignments, the transformation matrix for this arrangement is determined experimentally. This paper deals with these two problems, for a case similar to gas turbine conditions. The influence of the time interval on the measured data is compared with coincident data. Within the cascade different measuring planes are considered and a time step study is carried out.
Digital Compressor Analytics
Authors: Bakken Martin , Lunde Erling , Bakken Lars E.
Published: August 2018

Norwegian gas export is a high value business, where small and transient disturbances may cause substantial production losses. Process experience has shown that the compressor system may suffer considerably owing to surge and rotating stall in situations where the compressor is forced to trip. One of the main challenges concerns analysis of the actual trip trajectory to validate whether the compressor has entered the unstable area of the performance characteristics. This type of analysis is paramount with regard to compressor operation and tuning of the compressor safety system. Recent advances in data analytics and digitalization capabilities give promise of new ways to handle and analyse such challenges.

The current work presents data from a real compressor trip. The investigation reveals that plant data alone may not be sufficient for analysis of the trip trajectory. Hence, the trip scenario was analysed in light of experimental data, fan law principles and utilization of a detailed dynamic model. The results reveal that utilization of a dynamic model gives fruitful insight into the compressor system dynamics during a trip. These findings form a basis for future digitalization of the plant.

This idea will be developed into the specification of a concept called a Digital Compressor. The digital compressor may run in off-line or on-line mode with the aim of providing: high resolution estimates (soft sensors) for non-measured or inaccurate process variables; or identification of process parameters and characteristics, such as gas density. Use cases include: off-line “what happened” analysis; identifying the minimal viable instrumentation; on-line advanced condition and performance monitoring.

A digital compressor laboratory setup will be introduced, containing both a dynamic simulation system as well as a complete gas compressor rig — with all necessary computational and communication infrastructure.