bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric Reduced Order Models for Bladed Disks With Mistuning and Varying Operational Speed
Authors: Kurstak Eric , Wilber Ryan , D’Souza Kiran
Published: August 2018

A considerable amount of research has been conducted to develop reduced order models of bladed disks that can be constructed using single sector calculations when there is mistuning present. A variety of methods have been developed to efficiently handle different types of mistuning ranging from small frequency mistuning, which can be modeled using a variety of methods including component mode mistuning (CMM), to large geometric mistuning, which can be modeled using multiple techniques including pristine rogue interface modal expansion (PRIME). Research has also been conducted on developing reduced order models that can accommodate the variation of specific parameters in the reduced space; these models are referred to as parametric reduced order models (PROMs). This work introduces a PROM for bladed disks that allows for the variation of rotational speed in the reduced space. These PROMs are created by extracting information from sector models at three rotational speeds, and then the appropriate reduced order model is efficiently constructed in the reduced space at any other desired speed. This work integrates these new PROMs for bladed disks with two existing mistuning methods, CMM and PRIME, to illustrate how the method can be readily applied for a variety of mistuning methods. Frequencies and forced response calculations using these new PROMs are compared to the full order finite element calculations to demonstrate the effectiveness of the method.
Numerical Method for Simulating High Pressure CO2 Flows With Nonequilibrium Condensation
Authors: Furusawa Takashi , Miyazawa Hironori , Moriguchi Shota , Yamamoto Satoru
Published: August 2018

A numerical method for compressible flows with nonequilibrium condensation is reconstructed for simulating supercritical CO2 flows with nonequilibrium condensation under high pressure conditions. Thermophysical properties are interpolated from pressure-temperature look-up tables and density-internal energy look-up tables, which are generated using the polynomial equations in REFPROP. We employ the high pressure nonequilibrium condensation model in which the critical radius of a liquid droplet is modified by considering non-ideal gas. We simulate high pressure CO2 flows through a Laval nozzle, which was experimentally investigated by Lettieri et al. High-pressure CO2 passes through the nozzle, leading to a decrease in its pressure and temperature. It reaches the supercooled condition near the throat. Nucleation and the subsequent growth of droplets lead to an increase in the condensate mass fraction in the diverging area. The proposed method for real gas reproduced the peak of pressure distribution owing to the release of latent heat, whereas the numerical result assuming ideal gas is different from the experimental result. The nucleation region obtained using the present method is earlier and narrower than that in the case of ideal gas. The early and rapid nucleation leads to the high mass condensate rate at the outlet. These results show that considering the real gas effect and nonequilibrium condensation is crucial for developing the impeller of a compressor for the supercritical CO2 Brayton cycle.
Full-Annulus URANS Study of Inlet Hot-Streak Transportation in a Four-Stage Gas Turbine
Authors: Chi Zhongran , Liu Haiqing , Zang Shusheng , Pan Chengxiong , Zhang Meibao
Published: August 2018

Nonuniformity of combustor-exit-flow temperature, also named hot-streak, could strongly increase the complexity in unsteady flow and heat transfer of gas turbine cascades. Detailed investigation into the hot-streak transportation in multi-stage gas turbine should provide a valuable reference to both fault diagnosis of combustors based on the distribution of turbine exhaust temperature.

In this study, transportation of hot-streaks inside a four-stage gas turbine was numerically investigated using three-dimensional (3D), Unsteady Reynolds Averaged Navier-Stokes equations (URANS) Computational Fluid Dynamics (CFD) study with simulation domain including eight full-annulus cascades. The two-dimensional (2D) temperature fields at the rotor-stator interfaces and turbine exit was acquired by the full-annulus URANS CFD, and then discussed through comparing the circumferential and radial distributions and also the ranges of time-dependent fluctuations. The time-average temperature distributions were analyzed by Discrete Fourier Transform (DFT) method in circumferential direction to characterize the distribution.

The URANS CFD results show that the hot-streaks could travel through the entire turbine and result in nonuniformity of turbine exhaust temperature. The rotor-stator interaction could change the 2D shape of hot-streaks and intensity the time-dependent fluctuation of flow temperature. DFT results show that the typical frequencies of circumferential temperature distribution are coinciding with the number of hot-streaks and the blade number of upstream/ downstream cascades. The DFT results also indicated that the hot-streaks migrate 35°∼45° in the circumferential direction, and the maximal relative amplitude of hot-streaks is reduced from 28% to 5%. The redistribution of hot/cold fluid in stator cascade could affect the mixing of hot-streaks depending on clocking position.
Verification and Design of High Precision Eddy Current Sensor for Tip Clearance Measurement
Authors: Zhao Ziyu , Liu Zhenxia , Lyu Yaguo , Xu Xinxin
Published: August 2018

A high precision eddy current sensor for tip clearance measurement was proposed to assess the dynamic tip clearance measurement for aero-engine rotator. Based on the Lenz’s law, the eddy current sensor has high sensitivity, quick response speed and strong anti-interference capability, in addition, the simple geometry and easy installation are its main merits. The aim is to study the influence of planar coil structure parameters and excitation signal parameters on the sensor coil measurement, provide the basis for design of practical sensor in turbine tip clearance measurement. The dynamic calibration experiment verified the designed planar sensor coil, the results indicated the sensor resolution was 10μm and the measurement range was not less than 3mm. The dynamic experiment proved the measuring range, resolution, response speed of designed sensor can meet the requirement of turbine blade tip clearance measurement. The work provides experience in eddy current sensor design in different application, not only in turbine. And the future work will focus on the high temperature issues.
Experimental and Numerical Investigation on Gas Turbine Package Scale Model
Authors: Lucherini Gabriele , Minotti Stefano , Ragni Giacomo , Bologna Francesco
Published: August 2018

Gas turbine packages require a ventilation system in order to keep temperatures under acceptable limits and to dilute any hazardous accumulation of gas due to unexpected leakages. As part of the design phase, a detailed CFD (Computational Fluid Dynamics) analysis is performed on the complete system to assess the fluid dynamic behavior of the flow in terms of flow path, temperature distributions and velocity field.

In this work, as additional approach, a detailed experimental 3D assessment of an entire aero-derivative gas turbine (GT) package was performed by creating a scale model (1:8) of the real configuration. The original package can be as much as 60 m3 in volume where details from pipes to valves can create severe flow distortions and the 3D CFD study might not necessarily include all details up to such level during the design phase. The scale model, built using sintered plastic material through rapid prototyping, was used for a test campaign reproducing the operation of the ventilation system, copying the dynamic similarity of the real scale. The model was equipped with a set of instruments to acquire measurements of pressure and velocity in several locations and at different flow rates. A significant benefit of using a scale model with transparent plexiglass for the external structure of the enclosure and ventilation ducts walls, was that it allowed to carry out a smoke test. This has been done by injecting a visible gas from several locations allowing the visualization of the streak lines of the local flow field. The aim of this approach was to find a fast and reliable way to investigate in detail complex phenomena such as gas leakage dilution and local flow distribution.

A good agreement between experimental and computational data was found confirming that the CFD studies currently performed during the standard design phase are accurate and reliable enough to provide a proper prediction of the flow field inside the entire package even when a high level of details is included.
Characterizing the Influence of Cyclic Re-Priming on the Prediction of Long Term Creep Damage for Gas Turbine Components
Authors: Green Richard , Douglas Jonathan , Moffat Andrew , Bellows Richard
Published: August 2018

Industrial Gas Turbines have traditionally been designed for base load operation. However, modern applications require flexibility as well as availability. These requirements lead to components in the hot section experiencing both cyclic and hold time loading, at high temperatures. These loading profiles inevitably lead to damage from both fatigue, due to engine cycles, and creep, due to dwells at load, as well as the interaction of these two damage mechanisms over the duration of the service interval. It is these interactions which can lead to higher average creep rates and more damage than expected.

This paper presents the results of a study into the influence of cyclic loading on the average creep rate for a proprietary single crystal nickel based alloy, which is based on the chemistry of INCONEL® 792, a relatively high chromium, gamma/gamma-prime strengthened superalloy. Creep tests have been conducted isothermally with reload cycles of varying duration (or dwell) that result in an unexpected reduction in creep life and an increase in overall creep rate when compared to the continuous isothermal creep tests performed at constant stress without reloading. A hypothesis is presented which attributes the increase in overall creep rate to the influence of a recovery potential stress. The dwell period of each reload cycle is critical to calculating the recovery potential and subsequent creep rate. Results show that tests with relatively short dwell periods exhibited lower lives and higher creep rates than tests with fewer cycles and longer dwell periods. The implication of these findings are significant when considering actual operation, where variations in engine cycles and dwell periods, could influence the accumulation of creep damage. Therefore, an initial approach is presented which accounts for cycles as part of the creep damage calculation.
Life-Limiting Behavior of an Oxide/Oxide Ceramic Matrix Composite at Elevated Temperature Subject to Foreign Object Damage
Authors: Presby Michael J. , Kedir Nesredin , Sanchez Luis J. , Faucett D. Calvin , Choi Sung R. , Morscher Gregory N.
Published: August 2018

The life-limiting behavior of an N720/alumina oxide/oxide ceramic matrix composite (CMC) was assessed in tension in air at 1200°C for unimpacted and impacted specimens. CMC targets were subjected to ballistic impact at ambient temperature with an impact velocity of 250 m/s under a full support configuration. Subsequent post-impact ultimate tensile strength was determined as a function of test rate in order to determine the susceptibility to delayed failure, or slow crack growth (SCG). Unimpacted and impacted specimens exhibited a significant dependency of ultimate tensile strength on test rate such that the ultimate tensile strength decreased with decreasing test rate. Damage was characterized using x-ray computed tomography (CT), and scanning electron microscopy (SEM). A phenomenological life prediction model was developed in order to predict life from one loading condition (constant stress-rate loading) to another (constant stress loading). The model was verified in part via a theoretical preloading analysis.
RANS and LES Modeling of a Linear-Array Swirl Burner Using a Flamelet-Progress Variable Approach
Authors: Jella Sandeep , Bourque Gilles , Bergthorson Jeffrey , Kwong Wing Yin , Steinberg Adam
Published: August 2018

Multiple, interacting flames in DLE systems can increase flame surface area and promote mixing of hot-products into the reactants — leading to an efficient usage of combustion volume and improved injector performance. An optically-accessible, confined, linear array of five swirl nozzles was recently built [1] to investigate flame dynamics and validate computational strategies. The present work focuses on modeling a dataset representative of lean gas turbine conditions, using a flamelet approach. A preheated (500K), premixed fuel-air mixture (ϕ = 0.55, Tflame = 1732K) at atmospheric pressure was injected through the swirlers at 40 m/s into a rectangular chamber. High-speed laser measurements of the flow (3 component velocity field from 10 kHz stereoscopic particle image velocimetry (S-PIV)) and flame (planar laser induced fluorescence of the hydroxyl radical (OH-PLIF)) were used for model validation.

The objectives of this work: (1) Evaluate a flamelet-progress variable method based on flamelet-generated manifolds (FGM) and examine its sensitivity to models for micro (scalar dissipation) and large scale mixing (anisotropic RANS vs LES) and (2) Obtain insight into the velocity field and flame stabilization in an interacting system.

Computations indicate that high-swirl nozzles produce bluff-body flames anchored to shear-layer vortices due to an arrested flow expansion. The anisotropic RANS turbulence model under-predicts the recirculation zone strength but predicts flow development and Reynolds stress profiles fairly well. While LES is more accurate overall, both models over-predict flow fluctuations in the transitional flow at the end of the recirculation bubble where flow becomes axially positive. The flamelet approach predicts the flame-shape and length correctly but over-predicts the reaction rate in-between swirlers. The effect of including a reactive SDR model is to significantly increase flame-flow interaction (higher scalar variance) but does not appear to influence the overall shape or location of the flame.
Benchmark of a Novel Aero-Elastic Simulation Code for Small Scale VAWT Analysis
Authors: Marten David , Lennie Matthew , Pechlivanoglou George , Paschereit Christian Oliver , Bianchini Alessandro , Ferrara Giovanni , Ferrari Lorenzo
Published: August 2018

After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90’s in favour of horizontal axis turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfil this gap, a structural FEA model, based on the Open Source multi-physics library PROJECT::CHRONO, was recently integrated with the Lifting Line Free Vortex Wake method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34m rotor. In this work some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small scale, fast-spinning (up to 450 rpm) VAWT. The study turbine is a helix shaped, 1kW Darrieus turbine, for which other numerical analyses were available from a previous study, including the results coming from both a 1D beam element model and a more sophisticated shell element model. The resulting data represented an excellent basis for comparison and validation of the new aero-elastic coupling in QBlade.

Based on the structural and aerodynamic data of the study turbine, an aero-elastic model was then constructed. A purely aerodynamic comparison to experimental data and a BEM simulation represented the benchmark for QBlade aerodynamic performance. Then, a purely structural analysis was carried out and compared to the numerical results from the former. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.
Probabilistic TMF Life Evaluation of a Single Crystal Turbine Blade Concerning Uncertainty Quantification
Authors: Liu Xi , Hu Dianyin , Zhang Bin , Wang Rongqiao
Published: August 2018

Probabilistic-based design can efficiently quantify the risk and improve the reliability of the turbine blade. In this context, a probabilistic framework concerning the uncertainty quantification for the turbine blade’s TMF life based on the cyclic damage accumulation (CDA) method and Bayesian inference is proposed in this study. Firstly, the damage factors in the critical plane are obtained by the finite element method using Walker constitutive model, during which the discretization error is calibrated using Richardson extrapolation method. After that, the probabilistic TMF life model is established using CDA theory, in which the uncertainty of the material parameters is quantified using Bayesian inference. Finally, TMF life prediction on a single crystal nickel superalloy turbine blade is conducted using the probabilistic framework considering uncertainty quantification. The accuracy and validity of the proposed method is revealed by the comparison between the numerical and experimental results of real turbine blades.
A Numerical Study of Heat Transfer and Flow Structure in Channels With Miniature V Rib-Dimple Hybrid Structure on One Wall
Authors: Zhang Peng , Rao Yu , Li Yanlin
Published: August 2018

This paper presents a numerical study on turbulent flow and heat transfer in the channels with a novel hybrid cooling structure with miniature V-shaped ribs and dimples on one wall. The heat transfer characteristics, pressure loss and turbulent flow structures in the channels with the rib-dimples with three different rib heights of 0.6 mm, 1.0 mm and 1.5 mm are obtained for the Reynolds numbers ranging from 18,700 to 60,000 by numerical simulations, which are also compared with counterpart of a pure dimpled and pure V ribbed channel. The results show that the overall Nusselt numbers of the V rib-dimple channel with the rib height of 1.5 mm is up to 70% higher than that of the channels with pure dimples. The numerical simulations show that the arrangement of the miniature V rib upstream each dimple induces complex secondary flow near the wall and generates downwashing vortices, which intensifies the flow mixing and turbulent kinetic energy in the dimple, resulting in significant improvement in heat transfer enhancement and uniformness.
Nonsmooth Thermoelastic Simulations of Blade-Casing Contact Interactions
Authors: Thorin Anders , Guérin Nicolas , Legrand Mathias , Thouverez Fabrice , Almeida Patricio
Published: August 2018

In turbomachinery, it is well known that tighter operating clearances improve the efficiency. However, this leads to unwanted potential unilateral and frictional contact occurrences between the rotating (blades) and stationary components (casings) together with attendant thermal excitations. Unilateral contact induces discontinuities in the velocity at impact times, hence the terminology nonsmooth dynamics. Current modeling strategies of rotor-stator interactions are either based on regularizing penalty methods or on explicit time-marching methods derived from Carpenter’s forward Lagrange multiplier method. Regularization introduces an artificial time scale in the formulation corresponding to numerical stiffness which is not desirable. Carpenter’s scheme has been successfully applied to turbomachinery industrial models in the sole mechanical framework, but faces serious stability issues when dealing with the additional heat equation.

This work overcomes the above issues by using the Moreau–Jean nonsmooth integration scheme within an implicit θ-method. This numerical scheme is based on a mathematically sound description of the contact dynamics by means of measure differential inclusions and enjoys attractive features. The procedure is unconditionally stable opening doors to quick preliminary simulations with time-steps one hundred times larger than with previous algorithms. It can also deal with strongly coupled thermomechanical problems.
A Numerical Study on Reducing the Stator Blade Surface Temperature in the Ultra-High Efficiency Gas Turbine Engine by Indexing Fuel Injectors and Using Film Cooling
Authors: Ghoreyshi Seyed M. , Schobeiri Meinhard T.
Published: August 2018

The Ultra-High Efficiency Gas Turbine technology, UHEGT, has been introduced in our previous publications [1]-[4]. In UHEGT, the combustion process is no longer contained in isolation between the compressor and turbine, rather distributed and integrated within the axial gaps before each stator row. As shown in the previous publications, this technology substantially increases the thermal efficiency of the engine to 45% and above. Since the combustion process is brought into the turbine stages in UHEGT, the stator blades are exposed to high temperature gases and are prone to be overheated. To address this issue, two different approaches are investigated in this paper in order to control and reduce the temperature on the stator blade surface. The first approach is indexing (clocking) of the fuel injectors (cylindrical tubes extended from hub to shroud), in which the positions of the injectors are adjusted relative to each other and the stator blades. The second approach is using film cooling, in which cooling holes are added on the blade surface to bring down the temperature via coolant injection. Four configurations are designed and studied via computational fluid dynamics (CFD) to evaluate the effectiveness of the two approaches. The objective functions in this evaluation are stator blade surface temperature, temperature non-uniformity at rotor inlet, total pressure loss over the injectors, and total power production by rotor. The results show that the second configuration, which uses the indexing approach, presents the most promising case in controlling the stator blade surface temperature. This configuration produces the lowest temperature distribution over the stator blade surface and the least amount of total pressure loss.
Investigation of Spectral Vanishing Viscosity for Stabilizing and Accelerating Solution of Time Spectral Equation System
Authors: Wu Hangkong , Wang Dingxi , Huang Xiuquan , Yan Hong , Li Jianling
Published: August 2018

Time spectral method (TSM), as a very effective frequency domain method for analyzing temporal periodic flow field, is more popular than other frequency domain methods such as the nonlinear harmonic method (NLHM), the linear harmonic method (LHM) and the classic harmonic balance method. This is due to the fact that it is much easier to be implemented in an existing steady flow solver. But the aliasing errors caused by the nonlinear terms in the Euler/Navier-Stokes equations can have an adverse effect on the convergence rate. On the worse side, it can even lead to solution instability. This paper will present investigation of the application of the time spectral vanishing viscosity (SVV) method to stabilizing the solution of time spectral method. The spectral vanishing viscosity method has long been investigated for stabilizing spectral solution of conservation laws in space. Its application to time spectral solution of unsteady flow equations is very limited. In this investigation, the accuracy and time cost of the time spectral method with the SVV will be compared with that without the SVV and the traditional time domain dual time stepping method (DT). The stiffness of the SVV and the time spectral source terms is relieved by implicitly integrating the source terms in time using the block Jacobi method (BJ). To accelerate the convergence rate, the Lower Upper Symmetric Gauss Seidel (LU-SGS) method is used as the residual smoother for a multi-stage Runge-Kutta time integration.

The following points can be drawn from this investigation:

1. Time spectral vanishing viscosity method can accelerate convergence rate and reduce time cost.

2. Time spectral vanishing viscosity method can improve the solution accuracy and fewer harmonics can be used to analyze the flow field with the SVV than without the SVV.
Performance Enhancement of a Molten Carbonate Fuel Cell/Micro Gas Turbine Hybrid System With Carbon Capture by Off-Gas Recirculation
Authors: Ahn Ji Ho , Jeong Ji Hun , Kim Tong Seop
Published: August 2018

The demand for clean energy continues to increase as the human society becomes more aware of environmental challenges such as global warming. Various power systems based on high-temperature fuel cells have been proposed, especially hybrid systems combining a fuel cell with a gas turbine, and research on carbon capture and storage technology to prevent the emission of greenhouse gases is already underway. This study suggests a new method to innovatively enhance the efficiency of a molten carbonate fuel cell/micro gas turbine hybrid system including carbon capture. The key technology adopted to improve the net cycle efficiency is off-gas recirculation. The hybrid system incorporating oxy-combustion capture was devised, and its performance was compared with that of a post-combustion system based on a hybrid system. A molten carbonate fuel cell system based on a commercial unit was modeled. Externally supplied water for reforming was not needed as a result of the presence of the water vapor in the recirculated anode off-gas. The analyses confirmed that the thermal efficiencies of all the systems (MCFC stand-alone, hybrid, hybrid with oxy-combustion capture, hybrid with post-combustion capture) were significantly improved by introducing the off-gas recirculation. In particular, the largest efficiency improvement was observed for the oxy-combustion hybrid system. Its efficiency is over 57% and is even higher than that of the post-combustion hybrid system.
Dynamic Modelling of Blades Based on a Novel Curved Thin Walled Beam Theory
Authors: Jauregui Juan C. , Cardenas Diego , Elizalde Hugo , Probst Oliver
Published: August 2018

There are several Thin-Walled Beam models for straight beams, but few TWB models consider beams with arbitrary curvatures. Although, a curved beam can be modelled using finite elements, the number of degrees of freedom is too large and a nonlinear dynamic solution is very cumbersome, if not impossible. In this work, a general description of arbitrary three-dimensional curves, based on the Frenet-Serret field frame, is applied to determine the dynamic stresses in wing turbines blades. The dynamic model is developed using the Isogeometric Analysis (IGA) and the in plane and out-of-plane curvature’s gradients are found in an Euler-type formulation, allowing the treatment of cases with highly-curved geometry. An Isogeometrical (IGA) formulation relies on a linear combination of Non-Uniform Rational B-Splines (NURBS) to represent not just the model’s geometry, a standard practice in most Computer-Aided Design (CAD) platforms, but also the unknown solution field of each sought variable. For the unified model hitherto described, these variables are represented by a NURBS curve.
Evaluation of Friction Models for Rotor-Rubbing Predictions
Authors: Jauregui Juan C. , Saenz Jorge A. , Gonzalez Claudia A.
Published: August 2018

Rubbing, in turbomachinery, is a phenomenon difficult to identify and predict. Rubbing is a sudden event that can cause catastrophic damage, therefore, it is necessary to have good prediction models. In order to predict this phenomenon, several models have been proposed which are based on representing rubbing as an external friction force acting on the rotor.

The work presented here includes the results of two experiments. In the first one, the accelerations of a rotor rubbing a fixed spot were recorded. In the second experiment, the accelerations and the friction force were measured. All the data were analyzed using the Continuous Wavelet Transform and the data from the second experiment were used for estimating the friction force.

It was found that modelling the stiffness of the system as a Fourier Series gives better results than other models.
Computationally Efficient Modelling of Oil Jet-Breakup and Film Formation for Bearing Chamber Applications
Authors: Hee Jee Loong , Simmons Kathy , Kakimpa Bruce , Hann David
Published: August 2018

In previously published experimental work completed at the Gas Turbine and Transmissions Research Centre (G2TRC), oil fed to an aeroengine location bearing via underrace feed was seen to shed from the cage, forming a film on static surfaces near the bearing and subsequently shedding into the bearing chamber. A high-fidelity computational model of the two-phase flow in an aeroengine bearing chamber must adequately reproduce such behaviour but there are significant challenges in modelling both the oil breakup after shedding and the subsequent film formation. It is very computationally costly to resolve an oil film interface using the Volume of Fluid (VOF) approach at regions of thin film and it is unacceptably inaccurate to resolve thick film using an explicit thin film modelling technique such as the Eulerian Thin Film Model (ETFM). A proposed solution is to couple together VOF, ETFM and discrete phase modelling (DPM). Previously published G2TRC work shows how VOF and ETFM can be successfully coupled. This paper investigates the coupling of ETFM and DPM. The evaluation of film momentum transport and air-particle momentum transfer/Lagrangian particle tracking are studied using a low Reynolds number turbulence model.

Validation is required to ensure that these models work together as intended. To this end a preliminary CFD study was carried out on a published case investigated experimentally and computationally in which a jet is injected into a duct via a nozzle, breaking up into droplets before forming a wall film. The droplets are produced by primary atomization due to liquid instabilities at the injection point. Secondary breakup occurs due to surface instabilities prompted by the high-velocity cross-flow. Small droplets are transported downstream whereas larger droplets deflect minimally hitting the wall and forming a thin film. In the work presented here quantitative film thickness data from experiments and prior simulations are compared to current data.

The success of the simulation is found to depend on shear-transportation, turbulent dispersion of the particles, particle grouping, mass transportation as well as accurate prediction of interfacial shear-stresses. With suitable modelling parameters it was possible to predict film thickness to within 28.9% of those seen experimentally. The present ETFM-DPM modelling showed improvements over previously published models in prediction of shear-stresses and film transportation as the ω-equation could be integrated through the viscous sublayer. The developed approach is now mature enough to be applied to the bearing chamber geometry investigated experimentally at G2TRC and this is proposed for future work.
Effect of the Gas to Wall Temperature Ratio on the Bypass Transition
Authors: Rubini Riccardo , Maffulli Roberto , Arts Tony
Published: August 2018

The study of boundary layer transition plays a fundamental role in the field of turbomachinery owing to its strong influence on skin friction and heat transfer. The understanding of the laminar to turbulent transition can help designers to improve the aerodynamic and thermodynamic performances both of the components and of the whole machine. Turbulent transition models are nowadays commonly used tools in both research and design practice. In the context of high-pressure turbines design, it is then of particular interest to understand if such models are able to predict the effect of temperature on bypass transition and, in case of positive answer, the reasons of their behaviour. This becomes even more interesting as the effect of the flow aero-thermal coupling becomes prominent in the analysis of such phenomena, as this effect is typically not accountedfor in the validation of turbulence models. Two state-of-the-art transition models are examined in the present contribution: the γ–Reθ model developed by Langtry and Menter [1] and the k–kl–ω model by Walters and Cokljat [2]. The two models have been chosen also as they use two radically different approaches to describe the transition process: an empirical, correlation-based one for the former model opposed to a phenomenological, based on local transport, for the latter. To isolate the effects of the temperature ratio on the transition, the simulations have been performed keeping the same values of Reynolds and Mach numbers and changing the value of the wall to free stream Temperature Ratio (TR). The results of the two transition models have been compared between them as well as with experimental results obtained as part of a parallel effort. The results show that both models are sensitive to TR and can have qualitative agreement with the observations from experimental data. Most importantly the present results show how a transition modelling based on local transport, rather than empirical correlations should be favoured.
Start-Up Optimization of a CCGT Power Station Using Model Based Gas Turbine Control
Authors: Nannarone Alessandro , Klein Sikke A.
Published: August 2018

The rapid growth of renewable generation and its intermittent nature has modified the role of combined cycle power stations in the energy industry, and the key feature for the operational excellence is now flexibility. Especially, the capability to start an installation quickly and efficiently after a shutdown period leads to lower operational cost and a higher capacity factor. However, most of existing thermal power stations worldwide are designed for continuous operation, with no special focus on an efficient start-up process. In most current start-up procedures, the gas turbine controls ensure maximum heat flow to the heat recovery steam generator, without feedback from the steam cycle. The steam cycle start-up controls work independently with as main control parameter the limitation of the thermal stresses in the steam turbine rotor. In this paper, a novel start-up procedure of an existing combined cycle power station is presented, and it uses a feedback loop between the steam turbine, the boiler and the gas turbine start-up controls. This feedback loop ensures that the steam turbine can be started up with a significant reduction in stresses.

To devise and assess this start-up methodology, a flexible and accurate dynamic model was implemented in the Simulink™ environment. It contains more than 100 component blocks (heat exchangers, valves, meters and sensors, turbines, controls, etc.), and the mathematical component sub-models are based on physical models and experimental correlations. This makes the model generally applicable to other power plant installations. The model was validated against process data related to the three start-up types (cold start, warm start, hot start). On this basis, the optimization model is implemented with feedback loops that control for example the exit temperature of the gas turbine based on the actual steam turbine housing temperature, resulting in a smoother heating up of the steam turbine.

The optimization model was used to define the optimal inlet guide vanes position and gas turbine power output curves for the three types of start-up. These curves were used during real power station start-ups, leading to, for cold and warm starts, reductions in the start-up time of respectively 32.5% and 31.8%, and reductions in the fuel consumption of respectively 47.0% and 32.4%. A reduction of the thermal stress in the steam turbines is also achieved, thanks to the new start-up strategy.
Effect of Axial Force on Rotordynamics of a Rigid Rotor Supported by Foil Bearings
Authors: Liu Wanhui , Kim Daejong , Feng Kai
Published: August 2018

This paper investigates the effect of gas foil thrust bearing (GFTB) on the rotordynamic performance of the rotor-gas foil bearing (GFB) system. A rigid rotor supported on two gas foil journal bearings (GFJB) and a pair of GFTBs is studied using a five degree of freedom (5-DOF) model. The studies were performed in both frequency domain using excitation frequency-dependent bearing coefficients (modal analyses) and non-linear analyses (time domain orbit simulations). Modal analyses were performed for both symmetrically and asymmetrically supported rotor systems. For the symmetric rotor, the modal stiffness for the conical mode increases with the axial force, while cylindrical mode is not affected. The axial force has little effects on the modal damping for both the cylindrical mode and conical mode. Thus, the natural frequency and threshold speed (stability limit) for the conical mode increases as the axial force increases, while these values for the cylindrical mode remain almost constant. For the asymmetric rotor, the modal stiffness for both the cylindrical mode and conical mode increases with the axial force, and thus both natural frequency and threshold speed increase with the axial force. Rotor lateral vibrations were also predicted using synchronous bearing coefficients (of both GFJB and GFTB) for both conical and cylindrical modes. The predicted rotor lateral responses show the critical speed increases with axial force for both cylindrical mode and conical mode. The nonlinear analysis using time-domain orbit simulation was also performed including the effect of axial force on the GFTB. The effect of axial force on the stability of the rotor system were discussed. The predicted results showed that the stability of rotor system improved as the axial force increases for Case 1 when the out of phase imbalances were added on the rotor. However, the stability of the rotor system for Case 2 not only influenced by the axial force but also influenced by how asymmetry the rotor is. For the in phase imbalances, the onset speed of subsynchronous motion decreases as axial force increases for the large asymmetric rotor bearing system and the decrement of the onset speed of subsynchronous decreases as the asymmetry of the rotor bearing system decreases. For the out of phase imbalances, the onset speed of subsynchronous motion also decreases as axial force increases for the large asymmetric rotor, but an opposite trend was shown as the asymmetry of the rotor decreases.
Tonal Noise Control of Cooling Fan Module by Using Modulation Principles on Both Rotor and Stator
Authors: Peng Zhigang , Ouyang Hua , Wu Yadong , Tian Jie
Published: August 2018

Tonal noise is one of the main sources of noise generated by cooling fan module in automobile. The methods to decrease the tonal noise become more and more important with the popularity of automobiles and the demand for comfort increasing. Finding a quick way to predict the tonal noise in the early design stage will help the designer shorten the design circle and improve the efficiency. The traditional way, uneven spacing rotor blades, to modulate tonal components in noise spectrum by controlling factor “A” show positive influence in harmonic 2 and 3 (H2 and H3) but cannot work for harmonic 1 (H1) subjects to limitation of blade overlap as shown in the test result. Further step to modulate the stator vanes by adjusting parameter “χ” can attenuate the H1 dramatically based on “Venetian blind” theory of stator vanes. At last, the new cooling fan module design method to control tonal noise in design stage by “A” in rotor blade design and “χ” in stator vanes is reviewed and implemented in two cases of 7 rotor-blades & 6 stator-vanes and 7 rotor-blades & 8 stator-vanes. The experimental results agree well with the theoretical prediction.
Measurement Uncertainty in Liquid Crystal Thermography Applied to Internal Cooling Research: Two Practical Examples
Authors: Mayo Ignacio , Virgilio Marco , Cernat Bogdan C. , Arts Tony
Published: August 2018

This paper presents two examples of temperature and heat transfer measurements performed in different setups, both being representative cases of internal cooling cavities. In this investigation, Thermochromic Liquid Crystals (TLCs) were applied on the walls to perform steady-state Liquid Crystal Thermography (LCT) in the active range of 308–328 K, allowing the determination of the Nusselt number distribution. The main goal of this work is to analyze the impact of the different error sources on the wall temperature and Nusselt number uncertainties, and to represent them according to the ASME PTC 19.1 code. The first example is a stationary cooling channel model with a single heated wall, on which ribs are placed perpendicularly to the stream-wise direction. The working fluid is air, and the flow conditions are set to match a Reynolds number value equal to 53,000. The corresponding surface temperature measurement uncertainty at a 95% Confidence Level (CL) is below 0.8 K, which is about 4% of the active temperature range of the employed TLCs. On the other hand, the relative uncertainty at a 95% CL on the Nusselt number measurement is estimated to be equal to 17% The second instance is a cylindrical smooth pipe where the heating is applied over the complete inner surface. Air is also employed as operational fluid, whereas the Reynolds number value is varied from 20,000 to 78,000 in order to compare the experimental results with well-established correlations. In this setup, the surface temperature measurement uncertainty is below 1 K at a 95% CL, which corresponds to 5% of the TLC active temperature range. The relative uncertainty in the Nusselt number measurement is estimated to be between 7 and 12% at a 95% CL, depending on the Reynolds number.
Numerical Investigation of an Inverted Brayton Cycle Micro Gas Turbine Based on Experimental Data
Authors: Agelidou Eleni , Henke Martin , Monz Thomas , Aigner Manfred
Published: August 2018

Residential buildings account for approximately one fifth of the total energy consumption and 12 % of the overall CO2 emissions in the OECD countries. Replacing conventional boilers by a co-generation of heat and power in decentralized plants on site promises a great benefit. Especially, micro gas turbine (MGT) based combined heat and power systems are particularly suitable due to their low pollutant emissions without exhaust gas treatment. Hence, the overall aim of this work is the development of a recuperated inverted MGT as heat and power supply for a single family house with 1 kWel. First, an inverted MGT on a Brayton cycle MGT was developed and experimentally characterized, in previous work by the authors. This approach allows exploiting the potential of using the same components for both cycles. As a next step, the applicability of the Brayton cycle components operated in inverted mode needs to be evaluated and the requirements for a component optimization need to be defined, both, by pursuing thermodynamic cycle simulations. This paper presents a parametrization and validation of in-house 1D steady state simulation tool for an inverted MGT, based on experimental data from the inverted Brayton cycle test rig. Moreover, a sensitivity analysis is conducted to estimate the influence of every major component on the overall system and to identify the necessary optimizations. Finally, the component requirements for an optimized inverted MGT with 1 kWel and 16 % of electrical efficiency are defined. This work demonstrates the high potential of an inverted MGT for a decentralized heat and power generation when optimizing the system components.
Design of an Air-Cooled Radial Turbine: Part 2 — Experimental Measurements of Heat Transfer
Authors: Zhang Yang , Duda Tomasz , Scobie James A. , Sangan Carl M. , Copeland Colin D. , Redwood Alex
Published: August 2018

The paper focuses on manufacture and testing of an additively manufactured, cooled radial turbine. To the authors knowledge, this is the first published work that provides experimental temperature data for a small, internally cooled radial wheel constructed using Selective Laser Melting. This work is highly relevant observing the close correlation between turbine inlet temperature and system efficiency.

An internally cooled radial turbine was tested on the hot gas turbocharger rig at the University of Bath and compared with a baseline uncooled rotor. Thermal history paint was applied to the turbine rotor surfaces to determine the distribution of maximum exposed metal temperature. Both the uncooled and internally cooled turbine rotors were manufactured using Selective Laser Melting (SLM) technology. The resolution and strength of the printed prototype was tested prior to the high speed and high temperature experiment. The highest temperature at turbine leading edge and overall average thermal loading were compared quantitatively between the baseline uncooled rotor and the cooled rotor with internal secondary air plenums. The coolant was supplied from the compressor to the turbine through the centerline of the rotor shaft. The aerodynamic performance and component efficiency were also measured during the experiments. The test results indicate that the internally cooled turbine has a pronounced temperature drop at the blade leading edge and, indeed, throughout the blade passage. This increases the potential for increased turbine inlet temperature in order to achieve improved cycle efficiency. This experimental work has established a foundation for radial turbine internal cooling technology in the turbocharger and micro gas turbine industry.
Influence of Top Coat and Bond Coat Pre-Oxidation on the Corrosion Resistance of Thermal Barrier Coatings in the Presence of SO2
Authors: Jonnalagadda Krishna Praveen , Yuan Kang , Li Xin-Hai , Ji Xiaojuan , Yu Yueguang , Peng Ru Lin
Published: August 2018

Thermal barrier coatings (TBCs) degradation due to corrosion is one of the commonly observed failure types in land-based gas turbines due to the usage of low grade fuels. Sulfur in its gaseous form, as SO2, can attack the TBC system and result in the degradation of both the coating and the turbine component. The present study aims to understand the difference in the corrosion induced damage caused by SO2 gas mixture in different coating architectures. Corrosion tests were conducted at 780 °C in a tube furnace for a period of 168h. The inlet test gas had a composition of 1SO2-0.1CO-20CO2-N2 (bal.) in vol. %. The coating architectures consisted of 1) an overlay coating, 2) a single-side bond coat TBC, 3) an all-side bond coat TBC, 4) an all-side bond coat TBC subjected to pre-oxidation prior to the corrosion tests.

The results from the corrosion tests showed that the damage was the most severe for the overlay followed by single-side bond coat TBC. Between the other two systems, the TBC subjected to pre-oxidation had relatively lower corrosion damage. The corrosion damage started from the edges for the overlay and single-side bond coat TBC and as well as through the penetration of the gas through the coating. For the coatings with bond coat on all sides, the edge damage appeared to be considerably reduced and the damage is predominantly through the gas infiltration.