bluuebunny/crossref_metadata_2025 huggingface dataset:
Stall Inception in Low Pressure Ratio Fans
Authors: Kim S. , Pullan G. , Hall C. A. , Grewe R. P. , Wilson M. J. , Gunn E.
Published: August 2018

A combined experimental and computational test programme, with two low pressure ratio aero-engine fans, has been used to identify the flow mechanisms at stall inception and the subsequent stall cell growth. The two fans have the same rotor tip clearance, annulus design and downstream stators, but different levels of tip loading. The measurement data show that both fans stall via spike-type inception, but that the growth of the stall cell, and the final cell size, is different in each fan. The computations, reproducing both the qualitative and quantitative behaviour of the steady-state and transient measurements, are used to identify the flow mechanisms at the origin of stall inception. In one fan, spillage of tip leakage flow upstream of the leading edge plane is responsible. In the other, sudden growth of casing corner separation blockage leads to stall. These two mechanisms are in accord with the findings from core compressors. However, the transonic aerodynamics and low hub-to-tip radius ratio of the fans leads to the following two findings: first, the casing corner separation is driven by shock-boundary layer interaction; second, the spanwise loading distribution of the fan determines whether the spike develops into full-span or part-span stall and both types of behaviour are represented in the present work. Finally, the axial momentum flux of the tip clearance flow is shown to be a useful indicator of the leakage jet spillage mechanism. A simple model is provided that links the tip loading, stagger and solidity with the tip clearance axial momentum flux, thereby allowing the aerodynamicist to connect, qualitatively, design parameters with the stall behaviour of the fan.
Development of a Global Mechanism for Oxy-Methane Combustion in a CO2 Environment
Authors: Pryor Owen M. , Vasu Subith , Lu Xijia , Freed David , Forrest Brock
Published: August 2018

There has been some recent work on the global kinetic modeling of flames in oxy-fuel combustion for methane. The main challenge is that none of the mechanisms were developed to understand the time-scales of ignition. Here, a 3-step mechanism was developed for methane combustion in oxy-fuel environment. The mechanisms were simulated using a closed batch homogeneous batch reactor with constant pressure and compared to baseline simulations performed using a detailed mechanism. All simulations were performed for methane used a mixture of XCH4 = 0.05, XO2 = 0.10 and XCO2 = 0.85. Mechanisms were altered using the global mechanism equilibrium approach to ensure that the steady-state values matched the reference values and were further altered using an optimization scheme to match experimental data that was taken in a shock tube. Simulation results of methane, CO time-histories, and temperature profiles from the global mechanism were compared to those from the detailed mechanism. Ignition delay times were used to represent the time-scales of combustion. This was defined for current simulations as the time required for methane concentration to reach 5% of its initial value during combustion. Using this approach, the 3-step methane combustion mechanism showed excellent improvement in the ignition timing over a range of pressures (1 to 10 bar) and initial temperatures (1500 to 2000 K) for both lean and stoichiometric mixtures but fails to predict ignition delay times at 30 bar or the ignition delay times of fuel rich mixtures. Ongoing effort focuses on extending this new global mechanism to higher pressures and to syngas mixtures.
Rig and Engine Validation of the Non-Linear Forced Response Analysis Performed by the Tool OrAgL
Authors: Hartung Andreas , Hackenberg Hans-Peter , Krack Malte , Gross Johann , Heinze Torsten , Panning-von Scheidt Lars
Published: August 2018

Since the first non-linear forced response validation of frictionally coupled bladed disks, more than 20 years have passed, and numerous incremental modeling and simulation refinements were proposed. With the present work, we intend to assess how much we have improved since then. To this end, we present findings of an exhaustive validation campaign designed to systematically validate the non-linear vibration prediction for the different friction joints at blade roots, interlocked shrouds and under-platform dampers.

An original approach for the identification of crucial contact properties is developed. By using the Dynamic Lagrangian contact formulation and a refined spatial contact discretization, it is demonstrated that the delicate identification of contact stiffness properties can be circumvented. The friction coefficient is measured in a separate test, and determined as unique function of temperature, preload, wear state.

Rotating rig and engine measurements are compared against simulations with the tool OrAgL, developed jointly by the Leibniz Universität Hannover and the University of Stuttgart, in which state of the art Component Mode Synthesis and Harmonic Balance methods are implemented.
An Integrated Simulation Tool Proposed for Modeling and Optimization of CCHP Units
Authors: Safari Amir , Berezkin Vladimir , Assadi Mohsen
Published: August 2018

A novel framework for operation optimization of a combined cooling, heating, and power (CCHP) system has been proposed. The goal of the study was to develop an automatic optimization tool based on the integration of IPSEpro simulation software and the MATLAB programming environment to strategically manage the operation of a hybrid energy system of micro gas turbine (MGT), auxiliary boiler, and absorption chiller. Data exchange between the tools was organized via a COM interface. An experimentally validated model of the commercial AE-T100 CCHP unit was utilized, the objective being to minimize a cost function of operational and capital investments costs, subject to a set of constraints. The micro CCHP plant was considered to be a part of a grid. Electricity trading was therefore taken into account. The performance of the developed framework was investigated through the optimization task, case study data for a 24-hour period in July and December, different electricity and gas price profiles and ambient conditions being used. The operation strategy could be heat-led or power-led. The optimum number and load of the CCHP units and the boilers and the amount of electricity which should be bought from and/or sold to the grid were therefore determined by the optimization strategies. Lastly, the results were analyzed and show that the integrated optimization tool developed provides a valuable contribution to the enhanced management of such a CCHP system, specifically when a large number of distributed units are considered. In other words, the proposed framework was flexible enough and has the potential to be extended and further developed to handle more complicated energy systems and operational conditions.
Shape Optimization of Partly Removed Straight Ribs in Turbine Internal Rectangular Cooling Channel With 45 Degree Ribs
Authors: Zhu Jiangnan , Wang Xiying , Zhang Changxian , Miao Hui
Published: August 2018

Angled ribs have been widely used in the rectangular internal cooling channel of gas turbine to enhance heat convection strength and the optimal rib parameters have been shown in the former investigations. However, the heat transfer strength of the wall near the terminal of angled ribs is less enhanced by the rib and the local Nusselt number ratio may be lower than 1, which means that the local heat transfer strength of the ribbed wall is lower than that of smooth wall. At the same time, the ribs also generate large friction loss. As a result, a part of ribs which provides little heat transfer enhancement effect are removed in order to both reduce friction loss and maintain or enhance local heat transfer strength. In order to find out the optimal geometry parameters of the removed part of the rib, the optimization study are conducted in this paper based on the ANSYS Workbench software. The channel width to height ratio is 1 and 4. The rib attack angle is 45 degrees. The length of removed part, the transverse location of the removed part and the angle between the flow direction and the incision edge are chosen as the design variables. The area-averaged Nusselt number ratio and temperature on the ribbed wall, the friction factor ratio of the channel and the thermal performance factor are chosen as the objectives. The samples are generated by Latin Hypercube Sampling method and the CFD calculation is conducted by ANSYS CFX module using SST turbulence model. The response surface is obtained by Kriging model based on the CFD results and the Pareto optimal solution of this multi-objective problem is conducted by Multi-Objective Genetic Algorithm (MOGA) in the Response Surface Optimization module of ANSYS Workbench. The results show that the removed part of rib could both maintain or slightly enhance the overall Nusselt number ratio and obviously reduce the friction factor at the same time. Furthermore, the Nusselt number ratio in the terminal region of original ribs is also largely enhanced.
Influence of Oscillating Boundary Layer Suction on Aerodynamic Performance in Highly-Loaded Compressor Cascades
Authors: Hao Xu , Bao Liu , Le Cai , Xun Zhou , Songtao Wang , Zhongqi Wang
Published: August 2018

Vortex structures of the separation flow fields in compressor cascades controlled by the boundary layer oscillating suction (BLOS) are numerically investigated. The proper orthogonal decomposition (POD) method is adopted to present the variation of characteristics owned by large-scale vortices. It is found that unsteady perturbation re-organizes the aspirated flow fields and, if in a proper situation, reduces the loss furthermore. Through POD analysis, variations of vortical structures are described. The results turn out that the periodic perturbation leads to a vortex shedding process with the same frequency as the excitation. The reason of loss reduction could be summarized by actuated vortices enhancing the momentum of the stagnated fluid in the reverse flow region as well as decreasing the frequencies of vortex shedding. Finally, 3-D numerical results turn out that the oscillation can transform the stable corner separation bubble to vortex rings shedding downstream and hence improve cascade performance.
A Reduced Order Model for Nonlinear Dynamics of Mistuned Bladed Disks With Shroud Friction Contacts
Authors: Pourkiaee S. Mehrdad , Zucca Stefano
Published: August 2018

A new reduced order modeling technique for nonlinear vibration analysis of mistuned bladed disks with shrouds is presented. It has been shown in the literature that the loss of cyclic symmetry properties which is known as mistuning could considerably increase the response level, localize the vibration around few number of blades and finally bring high cyclic fatigue. The developed reduction technique employs two component mode synthesis methods, namely, the Craig-Bampton (CB) method followed by a modal synthesis based on loaded interface modeshapes (Benfield and Hruda). In the new formulation the fundamental sector is divided into blade and disk components. The CB method is applied to the blade, where nodes lying on shroud contact surfaces and blade-disk interfaces are retained as master nodes, while modal reductions is performed on the disk sector with loaded interfaces. The use of loaded interface component modes allows removing the blade-disk interface nodes from the set of master nodes retained in the reduced model. The result is a much more reduced order model with no need to apply any secondary reduction. In the paper it is shown that the reduced order model of the mistuned bladed disk can be obtained with only single-sector calculation, so that the full finite element model of the entire bladed disk is not necessary. Furthermore, with the described approach it is possible to introduce the blade frequency mistuning directly into the reduced model. In this way, reduction is performed only once in case of multiple analyses, necessary for statistical characterization of the nonlinear response of the system. The nonlinear forced response is computed using the harmonic balance method (HBM) and alternating frequency/time domain (AFT) approach. Friction contacts are introduced into the FE model using a 3D contact element. Numerical simulations revealed the accuracy, efficiency and reliability of the new developed technique for nonlinear vibration analysis of mistuned bladed disks with shroud friction contacts.
Robust Design Optimization of a Steam Turbine Labyrinth Seal Based on Surrogate Models
Authors: Cremanns Kevin , Roos Dirk , Hecker Simon , Penkner Andreas , Musch Christian
Published: August 2018

This work presents a robust multi-objective optimization of a labyrinth seal used in power plants steam turbines. The conflicting objectives of this optimization are to minimize the mass flow and to minimize the total enthalpy increase in order to increase the performance and to reduce the temperature, which results in elevated component utilization. The focus should be the robustness aspect to be involved into the optimization. So that the final design is not only optimized for its deterministic values but also robust under its uncertainties. To achieve a robust and optimized design, surrogate models are trained and used to replace the computational fluid dynamic solver (CFD), so as to speed up the calculations. In contrast to most techniques used in literature, the robustness criteria are directly involved in the multi-objective optimization. This leads to a more robust Pareto front compared to a purely deterministic one. This method needs many design evaluations, which would be not effective, if a CFD solver were used.
Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows: Part I — Design Concept and Typical Performance of a Swirl Breaker
Authors: Shibata Takanori , Fukushima Hisataka , Segawa Kiyoshi
Published: August 2018

In high and intermediate pressure (HIP) steam turbines with shrouded blades, it is well known that shroud leakage losses contribute significantly to overall losses. Shroud leakage flow with a large tangential velocity creates a significant aerodynamic loss due to mixing with the mainstream flow. In order to reduce this mixing loss, two distinct ideas for rotor shroud exit cavity geometries were investigated using computational fluid dynamics (CFD) analyses and experimental tests. One idea was an axial fin placed from the shroud downstream casing to reduce the axial cavity gap, and the other was a swirl breaker placed in the rotor shroud exit cavity to reduce the tangential velocity of the leakage flow. In addition to the conventional cavity geometry, three types of shroud exit cavity geometries were designed, manufactured and tested using a 1.5-stage air model turbine with medium aspect ratio blading. Test results showed that the axial fin and the swirl breaker raised turbine stage efficiency by 0.2% and 0.7%, respectively. The proposed swirl breaker was judged to be an effective way to achieve highly efficient steam turbines because it not only reduces the mixing losses but also improves the incidence angle distribution onto the downstream blade row. This study is presented in two papers. The basic design concept and typical performance of the proposed swirl breaker are presented in the first paper Part I, Design Concept and Typical Performance of a Swirl Breaker, and the efficiency improvement effect of the swirl breaker when applied to a real steam turbine is discussed in Part II – Effect of Axial Distance between a Swirl Breaker and Rotor Shroud on Efficiency Improvement.
Influence of Rotating Directions on Hydro-Thermal Characteristics of a Two-Pass Parallelogram Channel With Detached Transverse Ribs
Authors: Liou T. M. , Huang C. Y. , Lan I. A. , Chan S. P. , Chang S. W.
Published: August 2018

Two pairs of detailed Nusselt number (Nu) distributions on leading (LE) and trailing (TE) endwalls together with the Fanning friction factors (f) of a rotating two-pass parallelogram channel enhanced by the detached transverse ribs are simultaneously measured under forward and backward rotations. The tested Reynolds number, rotating number, density ratio, and buoyancy number are respectively in the ranges of 5,000 ≤ Re ≤ 15,000, 0 ≤ Ro ≤ 0.3, 0.044 ≤ Δρ/ρ ≤ 0.2, and 0 ≤ Bu ≤ 0.142. Due to the accelerating flows through the gaps between the detached ribs and channel endwalls, the transverse high Nu stripe emerges along the projection area of each detached rib on both static and rotating smooth endwalls. The disparities in the relative directions between Coriolis forces and channel periphery that restrains Coriolis flows at forward and backward rotations cause different heat transfer properties on the two pairs of rotating LE and TE. The area-averaged leading and trailing Nusselt numbers at forward rotations are 0.69–1.77 and 0.85–1.98 relative to the static-channel Nusselt number references (Nu0) respectively. With backward rotations, the ratios of regionally averaged Nusselt numbers between rotating and static channels for leading and trailing walls fall in the respective change to 0.86–2 and 0.91–1.76. At both forward and backward rotations, all the f factors over LE and TE are elevated from the static-channel levels (f0) and increased by increasing Ro. Channel averaged f/f0 ratios are respectively raised to 1.21–2.21 and 1.21–2.1 at forward and backward rotations. As the heat transfer enhancements attributed to the presence of detached transverse ribs taking precedence of the accompanying f augmentations, all the thermal performance factors (TPF) are above unity in the range of 1.26–2.94. Relative to the similar rotating two-pass parallelogram channel with attached 90° ribs, the detached ribs generate the higher degrees of heat transfer enhancements with the larger extents of f augmentations.
Post-Stall Behaviour of a Multi-Stage High Speed Compressor at Off-Design Conditions
Authors: Zhao Fanzhou , Dodds John , Vahdati Mehdi
Published: August 2018

Stall followed by surge in a high speed compressor can lead to violent disruption of flow, damage to the blade structures and, eventually, engine shutdown. A knowledge of unsteady blade loading during such events is crucial in determining the aeroelastic stability of blade structures, experimental test of such events is however significantly limited by the potential risk and cost associated. Numerical modelling, such as unsteady CFD simulations, can provide a more informative understanding of the flow field and blade forcing during post-stall events, however very limited publications, particularly concerning multi-stage high speed compressors, can be found.

The aim of this paper is to demonstrate the possibility of using CFD for modelling full-span rotating stall and surge in a multi-stage high speed compressor, and, where possible, validate the results against experimental measurements. The paper presents an investigation into the onset and transient behaviour of rotating stall and surge in an 8-stage high speed axial compressor at off-design conditions, based on 3D URANS computations, with the ultimate future goal being aeroelastic modelling of blade forcing and response during such events. By assembling the compressor with a small and a large exit plenum volume respectively, a full-span rotating stall and a deep surge were modelled. Transient flow solutions obtained from numerical simulations showed trends matching with experimental measurements. Some insights are gained as to the onset, propagation and merging of stall cells during the development of compressor stall and surge. It is shown that surge is initiated as a result of an increase in the size of the rotating stall disturbance, which grows circumferentially to occupy the full circumference resulting in an axisymmetric flow reversal.
Fuel Injection Control for a Valve Array in a Shockless Explosion Combustor
Authors: Schäpel Jan-Simon , King Rudibert , Yücel Fatma , Völzke Fabian , Paschereit Christian Oliver , Klein Rupert
Published: August 2018

Approximate constant volume combustion (aCVC) is a promising way to optimize the combustion process in a gas turbine, which would exceed the gain in efficiency resulting from optimizing other components significantly. This work deals with a recently proposed approach: shockless explosion combustion (SEC). Compared to already known concepts, such as pulsed detonation combustion (PDC), it overcomes several disadvantages, e.g., sharp pressure transitions and entropy generation due to shock waves. For an SEC, accurate fuel stratification is required to achieve a quasi-homogeneous auto-ignition. In an atmospheric test rig quasi-homogeneous ignitions were achieved previously in non-resonant operation. To achieve a resonant operation, which goes along with a higher firing frequency, lower ignition and injection times are required. For this purpose, an array of solenoid valves was designed to allow for highly dynamic operation within short filling time spans. Using a novel mixed-integer control approach, these solenoid valves were actuated such that a desired fuel profile was generated. In this paper, the mentioned test rig was used for non-reacting fuel measurements to compare the quality of the axial fuel stratification achieved by using the valve array with the one achieved by using a slower proportional valve. In the experimental investigation the actuation with the valve array proved to adjust the required fuel stratification with the same quality as the actuation with the proportional valve, which was already successfully applied to the reactive set-up. Hence, the mixed-integer controlled valve array is considered a useful concept for upcoming resonant reactive SEC investigations.
Design of a Closed-Loop Optical-Access Supersonic Test Facility for Organic Vapours
Authors: White Martin T. , Sayma Abdulnaser I.
Published: August 2018

Despite significant research activities into organic Rankine cycles for the conversion of low-temperature heat into power, there remain uncertainties with regards to non-ideal gas effects and their role in turbine performance. Moreover, existing performance models and numerical solvers have yet to be validated for turbines operating with organic fluids. This paper documents the design of a closed-loop supersonic test facility intended for experimental characterisation of the flow of organic fluids under typical operating conditions experienced within an ORC turbine. The test section forms part of a wider test facility, developed for the study of ORC expanders, which includes a screw compressor, the supersonic test section, a heat exchanger and an expander test section. The working fluid is R1233zd, and the test facility is sized to deliver test conditions up to 20 bar and 125 °C with a mass-flow rate of 1 kg/s. After an overview of the test facility, the detailed design of the upstream diffuser, settling chamber, contraction zone and converging-diverging nozzle to deliver a flow with a Mach number of 2 to the test section is discussed. The performance of the test section is confirmed by CFD simulations. Finally, the intended flow visualisation using particle-image velocimetry is discussed. This includes the identification of a suitable seeding method considering both liquid and solid tracer particles. The assessment is completed considering constraints such as the operating conditions, the required particle size to accurately trace the fluid flow, maintenance issues, and compatibility with the working fluid. In particular, the possibility of using the compressor lubricating oil as the seeding particle is evaluated.
Numerical Assessment of Reduced Order Modeling Techniques for Dynamic Analysis of Jointed Structures With Contact Nonlinearities
Authors: Yuan Jie , El-Haddad Fadi , Salles Loic , Wong Chian
Published: August 2018

This work presents an assessment of classical and state of the art reduced order modelling (ROM) techniques to enhance the computational efficiency for dynamic analysis of jointed structures with local contact nonlinearities. These ROM methods include classical free interface method (Rubin method, MacNeal method), fixed interface method (Craig-Bampton), Dual Craig-Bampton (DCB) method and also recently developed joint interface mode (JIM) and trial vector derivative (TVD) approaches. A finite element jointed beam model is considered as the test case taking into account two different setups: one with a linearized spring joint and the other with a nonlinear macro-slip contact friction joint. Using these ROM techniques, the accuracy of dynamic behaviors and their computational expense are compared separately. We also studied the effect of excitation levels, joint region size and number of modes on the performance of these ROM methods.
Kongsberg Gas Turbines Through Fifty Years: A Review of the Products and the History
Authors: Naess Tore
Published: August 2018

In 1964 Kongsberg Våpenfabrikk AS decided to develop a small gas turbine for power generation, primarily for stand-by and emergency power. The engine was called the KG2 and had a unique all radial rotor design which was to become the trade mark for the later Kongsberg designs. The onset of the oil exploration in the Norwegian sector of the North Sea in the 1970’s gave the new business an opportunity to qualify for continuous drive applications and to expand into the international oil- and gas industry. In the following years a larger engine, the KG5, was launched and a third engine program was initiated, but never completed. The gas turbine know-how that was established in Kongsberg in these years was of great significance to the overall Norwegian gas turbine competence environment and was a deciding factor when Dresser-Rand first partnered with and later, in 1987, acquired the business. Under the new ownership the company became able to offer compressor- and power generation packages based on large aero-derivative gas turbines and it was soon recognized as a significant supplier, both nationally and internationally. The present paper provides a review of some of the unique design features of the KG series of engines as well as some of the typical applications. It also describes the transformation of the company from a small industrial gas turbine supplier to the recognized supplier of large, compressor- and power generation packages for the oil and gas industry.
Static and Dynamic Coefficient Measurements for a Thrust Collar Used in an Integrally Geared Compressor
Authors: Kerr Thomas , Crandall Andrew , Childs Dara , Delgado Adolfo
Published: August 2018

This paper introduces a test facility specifically designed to measure the axial stiffness and damping coefficients of an oil-lubricated thrust collar (TC). The geometry, load, and speeds of the test facility are representative of a production integrally geared compressor (IGC). Separate electric motors spin the shafts according to an assumed gear ratio, a pneumatic air piston loader provides a non-contacting, static thrust force, a remotely-controlled impact hammer delivers a perturbation force, and eddy-current motion probes record the resulting vibration. The paper uses a one degree of freedom (1DOF) axial motion model that neglects the static and dynamic stiffness of the bull wheel and presents estimates of the TC oil-film dynamic coefficients for pinion spin speeds between 5 and 10 krpm, and static loads between 200 and 400 N, using time-domain (log-dec and damped period) and static load-deflection techniques. The measurements show that the TC oil-film develops appreciable stiffness (tens of MN/m), and the 1DOF model used here is inadequate for higher loads. Axial runout on the interfacing surfaces of the test facility TC and bull wheel complicates parameter identification, but time-domain averaging effectively attenuates the runout while preserving the transient vibration that results from the impact hammer. Measurements of the TC oil-film stiffness, damping and virtual mass coefficients are useful to machinery OEMs or end-users seeking to predict or diagnose subsynchronous vibration in their machine that might be TC-related.
A Two-Layer Multi-Model Gas Path Fault Diagnosis Method
Authors: Cao Yunpeng , He Yinghui , Yu Fang , Du Jianwei , Li Shuying , Yang Qingcai , Liu Rui
Published: August 2018

This paper presents a two-layer multi-model gas path fault diagnosis method for gas turbines that includes a fault detection layer and a fault isolation layer. A health model and a gas path fault model based on a back propagation neural network are used for the real-time estimation of the output parameters of a gas turbine in the fault detection layer and the output parameter residual in the fault isolation layer, respectively. A fault detection algorithm is proposed based on fuzzy inference, and the fuzzy membership function of the output parameters residual is realized using data statistics. A similarity distance method is used to realize fault isolation, and a fault probability algorithm based on the Mahalanobis distance is presented. Finally, the proposed method is verified by a three-shaft gas turbine simulation platform, and the simulation test results show that the two-layer multi-model gas path fault diagnosis method can detect and isolate the gas path fault accurately with a low calculation cost and good extensibility.
The Effect of Stage-Diffuser Interaction on the Aerodynamic Performance and Design of LP Steam Turbine Exhaust Systems
Authors: Ding Bowen , Xu Liping , Yang Jiandao , Yang Rui , Dai Yuejin
Published: August 2018

Modern large steam turbines for power generation are required to operate much more flexibly than ever before, due to the increasing use of intermittent renewable energy sources such as solar and wind. This has posed great challenges to the design of LP steam turbine exhaust systems, which are critical to recovering the leaving energy that is otherwise lost. In previous studies, the design had been focused on the exhaust diffuser with or without the collector. Although the interaction between the last stage and the exhaust hood has been identified for a long time, little attention has been paid to the last stage blading in the exhaust system’s design process, when the machine frequently operates at part-load conditions.

This study focuses on the design of LP exhaust systems considering both the last stage and the exhaust diffuser, over a wide operating range. A 1/10th scale air test rig was built to validate the CFD tool for flow conditions representative of an actual machine at part-load conditions, characterised by highly swirling flows entering the diffuser. A numerical parametric study was performed to investigate the effect of both the diffuser geometry variation and restaggering the last stage rotor blades.

Restaggering the rotor blades was found to be an effective way to control the level of leaving energy, as well as the flow conditions at the diffuser inlet, which influence the diffuser’s capability to recover the leaving energy. The benefits from diffuser resizing and rotor blade restaggering were shown to be relatively independent of each other, which suggests the two components can be designed separately. Last, the potentials of performance improvement by considering both the last stage rotor restaggering and the diffuser resizing were demonstrated by an exemplary design, which predicted an increase in the last stage power output of at least 1.5% for a typical 1000MW plant that mostly operates at part-load conditions.
Experimental Study of Two-Phase Air/Water Flow in a Centrifugal Pump Working With a Closed or a Semi-Open Impeller
Authors: Mansour Michael , Wunderlich Bernd , Thévenin Dominique
Published: August 2018

The characteristics of a transparent centrifugal pump of radial type were investigated for different conditions when conveying two-phase (air/water) flows. A closed impeller and a geometrically similar semi-open impeller, both made out of acrylic glass, were employed for comparison purposes when increasing air loading. The performance of the pump was measured for either a constant gas volume fraction or a constant air flow rate at the pump inlet. Hysteresis effects were studied by considering three different experimental approaches to reach the desired operating conditions. A constant rotational speed of 650 rpm was set for all experiments. The whole system was made of transparent acrylic glass to allow high-quality flow visualization. A systematic experimental database was produced based on shadowgraphy imaging, so that the resulting two-phase regimes could be properly identified. The results show that for gas volume fractions between 1 and 3%, the deterioration of pump performance parameters is much lower in the semi-open impeller compared to that of the closed impeller. Nevertheless, in the gas volume fraction range between 4 and 6%, the trend is reversed; the semi-open impeller performance is reduced compared to the closed impeller, particularly in overload conditions. At even higher gas loading, the semi-open impeller shows again superior performance. Flow instabilities and pump surging were much stronger in the closed impeller. The main reason for that was the occurrence of alternating gas pockets on the blades of the closed impeller. Additionally, pump surging was observed only in a very limited range of flow conditions in the semi-open impeller. Comparing the different experimental procedures to set the desired flow conditions, no significant hysteresis effects could be observed in the closed impeller. However, in the semi-open impeller obvious hysteresis in the performance could be seen for gas volume fractions between 4 and 6%. All the obtained experimental results will be useful to check and validate computational models used for CFD in a comparison study.
Computational Analysis of an Additively Manufactured Cooled Ultra Compact Combustor Vane
Authors: DeMarco Kevin J. , Bohan Brian T. , Polanka Marc D. , Rutledge James L. , Akbari Pejman
Published: August 2018

The Ultra Compact Combustor (UCC) aims to increase the thrust-to-weight ratio of an aircraft gas turbine engine by decreasing the size, and thus weight, of the engine’s combustor. The configuration of the UCC as a primary combustor enables a unique cooling scheme to be employed for the Hybrid Guide Vane (HGV). A previous effort conducted a Computational Fluid Dynamics (CFD) analysis that evaluated whether it would be possible to cool this vane by drawing in freestream flow at the stagnation region of the airfoil. Based on this study, a cooling scheme was designed and modified with internal supports to make additive manufacturing possible. The vane was evaluated using CFD comparing the results with those of a solid vane and hollow vane without cooling holes as a validation and demonstration of the design. Furthermore, the effects of the internal support structure were deemed beneficial to surface cooling when evaluated through comparisons of internal pressure distribution and overall effectiveness.
Linking MRO to Prognosis Based Health Management Through Physics-of-Failures Understanding
Authors: Patnaik Prakash , Wu Xijia
Published: August 2018

Traditional engine maintenance, repair and overhaul (MRO) are geared toward fixed schedules. However, with online condition monitoring, assessments and prognosis, it is required that MRO be adaptive to the life consumption with respect to the actual usage of the engine to realize the benefit of prognosis. Shifting to this new paradigm, there are several challenges:

1. How exactly the life is consumed in components under complex usage profiles that may involve a combination of low and high cycle fatigue, thermomechanical fatigue and creep, for regular usage (aside from incidents)?

2. What are the physical failure mechanism(s) in components under the above conditions, the understanding of which may help to select the most appropriate detection, repair and replacement (including material insertion) strategy, for life renewal/extension and cost reduction?

3. Understanding the limitations of repairs for the particular failure mechanism.

To overcome these challenges, one needs physics-based material failure models that can reflect the true failure mechanisms on the component level under actual (complex) usage profiles. Conventional, empirical test-data correlations for isolated conditions fall short of this requirement because pure fatigue and pure creep are not experienced by real components in service. In addition, to ensure the repaired component’s structural integrity, the material database would have to be comprehensive enough to cover the effect of intrinsic repair defects and microstructures that are not present in the original component material. While models and data are integral parts of digital twins, it is proposed that physics-based models are needed to cover the entire application domain continuously. This paper will introduce a physics-based method of life consumption evaluation and discussion through past experience in line with the development of Digital Twin concepts for sustainment.
Volumetric Velocimetry Measurements of Film Cooling Jets
Authors: Carvalho Figueiredo Artur Joao , Jones Robin , Pountney Oliver J. , Scobie James A. , Lock Gary D. , Sangan Carl M. , Cleaver David J.
Published: August 2018

This paper presents Volumetric Velocimetry (VV) measurements for a jet in crossflow that is representative of film cooling. Volumetric velocimetry employs particle tracking to non-intrusively extract all three components of velocity in a three-dimensional volume. This is its first use in a film-cooling context. The primary research objective was to develop this novel measurement technique for turbomachinery applications, whilst collecting a high-quality data set that can improve the understanding of the flow structure of the cooling jet. A new facility was designed and manufactured for this study with emphasis on optical access and controlled boundary conditions. For a range of momentum flux ratios from 0.65 to 6.5 the measurements clearly show the penetration of the cooling jet into the freestream, the formation of kidney-shaped vortices and entrainment of main flow into the jet. The results are compared to published studies using different experimental techniques, with good agreement. Further quantitative analysis of the location of the kidney vortices demonstrates their lift off from the wall and increasing lateral separation with increasing momentum flux ratio. The lateral divergence correlates very well with the self-induced velocity created by the wall-vortex interaction. Circulation measurements quantify the initial roll up and decay of the kidney vortices and show that the point of maximum circulation moves downstream with increasing momentum flux ratio. The potential for non-intrusive volumetric velocimetry measurements in turbomachinery flow has been clearly demonstrated.
Development of Method and Computer Program for Multistage Axial Compressor Design: Part II — Two-Dimensional Design and Validation Using CFD
Authors: Banjac Milan , Petrovic Milan V.
Published: August 2018

Part I of this paper presents a method and a computer program for the mean design of multistage axial compressors. This second part describes a method and an additional computer routine that use the basic mean line design to create a fully two-dimensional flow solution and a compressor design. The two-dimensional solution according to a selected swirl vortex function is calculated using streamline curvature throughflow equations and spanwise distribution of losses. An iterative calculation procedure slightly reshapes the initial flow path in order to retain the desired input flow coefficients. Other variables such as stage loading parameters are changed in order to obtain the desired overall pressure ratio. A spanwise distribution of certain stage parameters can then be adjusted to achieve desired radial flow field variations. The basic one-dimensional input data can be varied at any moment to obtain a new one-dimensional result and the corresponding two-dimensional solution. A new output is created instantaneously and can be used for further CFD analysis, external throughflow, blade-to-blade flow computations or mechanical and vibration analysis.
Effects of Transient Heat Transfer on Compressor Stability
Authors: Kiss A. , Spakovszky Z.
Published: August 2018

The effects of heat transfer between the compressor structure and primary gas path flow on compressor stability are investigated during hot engine re-acceleration transients, or so called “Bodie” transients. A mean line analysis of an advanced, high-pressure ratio compressor is extended to include the effects of heat transfer on both stage matching and blade row flow angle deviation. A lumped capacitance model is used to compute the heat transfer of the compressor blades, hub, and casing to the primary gas path. The inputs to the compressor model with heat transfer are based on a combination of full engine data, compressor test rig measurements, and detailed heat transfer computations. Transient calculations with heat transfer show a 8.0 point reduction in stall margin from the adiabatic case, with heat transfer predominantly altering the transient stall line. 3.4 points of the total stall margin reduction are attributed to the effect of heat transfer on blade row deviation and the remainder is attributed to stage re-matching. It is found that heat transfer increases loading in the front stages and destabilizes the front block. Furthermore, the stage re-matching due to heat transfer alters the slope of the compressor characteristic and promotes modal-type stall inception. Sensitivity studies show a strong dependence of stall margin to heat transfer magnitude and flow angle deviation at low speed, due to the effects of compressibility. Computations for the same transient using current cycle models with bulk heat transfer effects, such as NPSS, only capture 1.2 points of the 8.0 point stall margin reduction. This implies that, using this new capability, opportunities exist early in the design process to address potential stability issues due to transient heat transfer.
First Demonstration of an Acousto-Optically Modulated Quantum Cascade Laser As a Broadband, Time-Resolved Combustion Diagnostic
Authors: Loparo Zachary E. , Ahmed Kareem , Vasu Subith S. , Muraviev Andrey V. , Figueiredo Pedro , Lyakh Arkadiy , Peale Robert E.
Published: August 2018

We provide the first demonstration of an acousto-optically modulated quantum cascade laser (AOM QCL) system as a diagnostic for combustion by measuring nitric oxide (NO), a highly-regulated emission produced in gas turbines. The system provides time-resolved broadband spectral measurements of the present gas species via a single line of sight measurement, offering advantages over widely used narrowband absorption spectroscopy (e.g., the potential for simultaneous multi-species measurements using a single laser) and considerably faster (> 15kHz rates and potentially up to MHz) than sampling techniques which employ FTIR or GC/MS. The developed AOM QCL system yields fast tunable output covering a spectral range of 1725–1930 cm−1 with a linewidth of 10–15 cm−1. For the demonstration experiment, the AOM QCL system has been used to obtain time-resolved spectral measurements of NO formation during the shock heating of mixture of a 10% nitrous oxide (N2O) in a balance of argon over a temperature range of 1245–2517 K and a pressure range of 3.6–5.8 atm. Results were in good agreement with chemical kinetic simulations. The system shows revolutionary promise for making simultaneous time-resolved measurements of multiple species concentrations and temperature with a single line of sight measurement.
Comparison of Equivalence Ratio Transients on Combustion Instability in Single-Nozzle and Multi-Nozzle Combustors
Authors: Chen Xiaoling , Culler Wyatt , Peluso Stephen , Santavicca Domenic , O’Connor Jacqueline
Published: August 2018

Low-emissions gas turbine combustion, achieved through the use of lean, premixed fueling strategies, is susceptible to combustion instability. The driving mechanism for this instability arises from fluctuations of pressure, fuel/air flow rate, and heat release rate. If these fluctuations are relatively in-phase, the combustion system will evolve to a self-excited state. The self-excited instability frequency and amplitude depend mainly on the operating condition and the geometry of the combustor. In this study, we consider the onset and decay of self-excited instabilities, resulting from transients in fuel/air ratio, in both single-nozzle and multi-nozzle combustors. In particular, we examine the differences in the instability onset and decay processes between these two flame configurations, as most gas turbine combustors have multiple nozzles, but most gas turbine combustor experiments utilize a single-nozzle. A nonlinear logistic regression analysis is applied to study the timescales of the decay and onset transients. Variations in the equivalence ratio change the heat release rate distribution inside the combustor, which is captured using chemiluminescence imaging. The normalized Rayleigh index, which shows the spatial distribution of the instability driving, is calculated to analyze the driving strength in different regions of the flame. Comparisons between the single- and multi-nozzle flame transients, including both center and outer flames for the multi-nozzle combustor, suggest that both confinement from the wall and flame-flame interaction are crucial to determining flame dynamics as the equivalence ratio transient changes the heat release rate distribution near corner recirculation zone and flame shear layers.
On the Choice of Turbine Type for a Twin-Turbine Heavy-Duty Turbocharger Concept
Authors: Anton Nicholas , Genrup Magnus , Fredriksson Carl , Larsson Per-Inge , Christiansen-Erlandsson Anders
Published: August 2018

In this study, a fundamental approach to the choice of turbocharger turbine for a pulse-charged heavy-duty diesel engine is presented. A standard six-cylinder engine build with a production exhaust manifold and a Twin-scroll turbocharger is used as a baseline case.

The engine exhaust configuration is redesigned and evaluated in engine simulations for a pulse-charged concept consisting of a parallel twin-turbine layout. This concept will allow for pulse separation with minimized exhaust pulse interference and low exhaust manifold volume.

This turbocharger concept is uncommon, as most previous studies have considered two stage systems, various multiple entry turbine stages etc. Even more rare is the fundamental aspect regarding the choice of turbine type as most manufacturers tend to focus on radial turbines, which by far dominate the turbochargers of automotive and heavy-duty applications. By characterizing the turbine operation with regards to turbine parameters for optimum performance found in literature a better understanding of the limitations of turbine types can be achieved.

A compact and low volume exhaust manifold design is constructed for the turbocharger concept and the reference radial turbine map is scaled in engine simulations to a pre-set AFR-target at a low engine RPM.

By obtaining crank-angle-resolved data from engine simulations, key turbine parameters are studied with regard to the engine exhaust pulse-train. At the energetic exhaust pressure pulse peak, the reference radial turbine is seen to operate with suboptimum values of Blade-Speed-Ratio, Stage Loading and Flow Coefficient.

The study concludes that in order to achieve high turbine efficiency for this pulse-charged turbocharger concept, a turbine with efficiency optimum towards low Blade-Speed Ratios, high Stage Loading and high Flow Coefficient is required. An axial turbine of low degree of reaction-design could be viable in this respect.