bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Equalization Method for Passive Flow Control of an S-Duct Intake for High Subsonic Speeds
Authors: Asghar Asad , Pym Stephen , Allan William D. E. , LaViolette Marc , Stowe Robert
Published: August 2018

High subsonic aircraft with fuselage-embedded engines often employ inlet ducts with multiple bends in order to induct ambient air into the propulsion system while also diffusing it to engine-acceptable Mach numbers. Engine performance, stability margin, and safety of the integrated aircraft-engine system can be negatively affected by separated, swirling and distorted flow that often characterizes S-ducts. This paper reports the investigation of a flow control strategy aimed at the improvement of the aerodynamic performance of S-duct diffusers. Passive pressure equalization was employed to reduce the size and intensity of the separated flow downstream of curved duct sections, utilizing naturally occurring pressure differences. Characteristic secondary flows promote instability and contribute to flow separation and losses in the inner radius region of a duct bend. In the present scheme, boundary layer flow upstream of the separation point on the inner radius of the first bend is energized by re-injecting higher momentum air, drawn from the higher pressure region at the outer radius of the same bend. The flow control effectiveness of this passive pressure equalization was evaluated by test-rig measurements of the flow in an S-duct at an inlet Mach number of 0.80. Static surface pressure was measured along the length of the S-duct and the total pressure was measured at the aerodynamic interface plane using a pressure rake with five high performance pressure transducers. It was possible to reveal pressure recovery, total pressure loss, and the general nature of flow distortion at the AIP.
Large Eddy Simulations of a Low-Pressure Turbine: Roughness Modeling and the Effects on Boundary Layer Transition and Losses
Authors: Hammer F. , Sandham Neil D. , Sandberg Richard D.
Published: August 2018

Large eddy simulations of a linear low-pressure turbine cascade with the T106A profile and different surface roughness patches were carried out. The aim was to investigate the effects on the laminar and turbulent boundary layer on the blade suction surface. Two different approaches were used to represent the roughness patches. Firstly, a forcing model, reducing the computational costs compared to fully resolved roughness surfaces, was incorporated. Secondly, an immersed boundary method representing an as-cast roughness surface was used, for a more detailed analysis of flow mechanisms over roughness.

It was found that the roughness model was able to induce boundary layer transition and alter the turbulent boundary layer, with the results in line with findings in the literature. The instantaneous flow data at different time instants of the as-cast roughness case showed the development of streaks due to distinct roughness peaks, resulting in highly uneven transition positions across the spanwise direction.
Foreign Object Damage Diagnosis of Aero-Engine Compressor Based on Damping Averaging Built-in Matrix Method
Authors: Wu Shuming , Chen Xuefeng , Russhard Pete , Wang Shibin , Zhai Zhi , Zhao Zhibin
Published: August 2018

Blade Tip Timing (BTT) methods are being implemented that have led to a non-intrusive technique being deployed in certain sectors of Industry. Data sets produced during the development cycle are now providing upfront information that is being used to develop monitoring capability supporting in-service health monitoring. Recent years have witnessed a growing interest in blade health monitoring and its potential to detect the occurrence of both transient and permanent foreign object damage (FOD) and estimate the severity of damage to blades. FOD damage detection is beneficial to both the fan and first stage compressors and the ability to detect it leads to a reduction in the number of inspection that recurrently scheduled.

The expected behaviour under transient FOD condition is a ‘ringing’ signal which is a damped exponential signal. The lack of real FOD data collected requires that a signal is simulated and used to develop and validate detection systems.

Blade tip timing is an effective implementation of non-intrusive technology by circumferentially arranged sensors to obtain the time of arrival (TOA) of blades. However, due to the high degree of undersampling inherent in the data the detection of short-lived events poses a problem.

In this paper the use of a method called ‘Damping Averaging Built-in Matrix’ (DABM), which use the combination of several revolutions data and OPR (once per revolution) data to enhance the sample rate while eliminating the damping effect. After solving the matrix we are able to obtain the frequency and damping of the blade when transient FOD occurs. The FEM (finite element model) of the blade is also built to infer the stress of blade at different levels of FOD. The method is applied to both the simulated data and experimental data to verify its effectiveness. By developing this method further we can provide a capability that could reduce the operation and maintenance cost and increase the security of the engine whilst in operation.
A Numerical Study of Dust Deposition in a Model Turbine Vane Cooling Passage
Authors: Cheng Way Lee , Lundgreen Ryan , Guo Bing
Published: August 2018

Dust accumulation in jet engines reduces engine efficiency and even affects aviation safety. A computational fluid dynamics study was carried out to evaluate the capability of a computational fluid dynamics (CFD) wherein the Ohio State University coefficient of restitution model (OSU model) was incorporated. The model was used to determine the effects of particle size and operating conditions similar to experiments in dust deposition in the cooling passage in a turbine vane. An impingement hole array was used to model the turbine vane cooling passage, so that the flow interactions between neighboring jets could be accounted for. The Discrete Phase Model in ANSYS Fluent was used to predict the particle impact locations, after convergence of the flow field simulation. Deposition results were obtained for an inlet-to-outlet pressure ratio of 1.015 with back pressure of 1 atm and three temperatures (300 K, 700 K and 1000 K). The CFD predictions of dust deposition qualitatively agree with experimental results. However, quantitative agreements between the CFD model and experiments will be pending improvements of the model, in areas such as thermophoretic deposition, resuspension simulation and coefficient of restitution model that accounts for varying surface conditions.
Application of Fluidic Curtains to Turbine Rotor Tip Seal Geometries
Authors: MacCalman James , Hogg Simon , Ingram Grant
Published: August 2018

Fluidic curtain sealing has recently been shown to offer strong potential especially when a combination of fluidic curtain and a conventional labyrinth seal is used. A series of fundamental dimensionless ratios have been proposed and the design space created by these parameters explored and validated experimentally using a simple annular test rig. The advance described in this paper is to use these design parameters to develop a set of engine realistic designs to demonstrate how a fluidic curtain seal may be realized in a high pressure steam turbine stage. Design tools of increasing fidelity are used to support this exploration; firstly basic ratios in the geometry and their known influence on performance are used to identify candidate geometries. CFD is used to demonstrate that previous performance predictions can be transferred to a realistic tip seal, and that candidate fluidic curtain seal designs are able to provide significant leakage reduction over the baseline seal design.
NOx-Hydrocarbon Kinetics Model Validation Using Measurements of H2O in Shock-Heated CH4/C2H6 Mixtures With NO2 As Oxidant
Authors: Mathieu O. , Mulvihill C. R. , Petersen E. L. , Curran H. J.
Published: August 2018

One method frequently used to reduce NOx emissions is exhaust gas recirculation (EGR), where a portion of the exhaust gases, including NOx, is reintroduced into the combustion chamber. While a significant amount of research has been performed to understand the important fuel/NOx chemistry, more work is still necessary to improve the current understanding on this chemistry and to refine detailed kinetics models. To validate models beyond global kinetics data such as ignition delay time or flame speed, the formation of H2O was recorded using a laser absorption diagnostic during the oxidation of a mixture representing a simplistic natural gas (90% CH4 /10% C2H6 (mol.)). This mixture was studied at a fuel lean condition (equiv. ratio = 0.5) and at atmospheric pressure. Unlike in conventional fuel-air experiments, NO2 was used as the oxidant to better elucidate the important, fundamental chemical kinetics by exaggerating the interaction between NOx and hydrocarbon-based species. Results showed a peculiar water formation profile, compared to a former study performed in similar conditions with O2 as oxidant. In the presence of NO2, the formation of water occurs almost immediately before it reaches more or less rapidly (depending on the temperature) a plateau. Modern, detailed kinetics models predict the data with fair to good accuracy overall, while the GRI 3.0 mechanism is proven inadequate for reproducing CH4 / C2H6 and NO2 interactions.
Detailed Chemical Kinetics Based Simulation of Detonation-Containing Flows
Authors: Sato Takuma , Voelkel Stephen , Raman Venkat
Published: August 2018

Reliable and robust simulations of detonations in inhomogeneous and turbulent environments are of direct importance in the design of rotating detonation engines (RDEs). In particular, computational models will be especially useful in designing and optimizing discrete injectors that introduce fuel and air separately into the detonation chamber, but ensure appropriate level of mixing to sustain detonations but minimize backflow of detonation products and pressure waves into the feed plenums. Since the structure of detonations itself is non-ideal, models have to include a detailed description of this reacting flow in order to be predictive in nature. Here, a highly-scalable open source based solver has been developed for complex detonating flows such that a) the detonation processes are described using detailed chemical kinetics, b) the method is computationally efficient through the introduction of adaptive mesh refinement, and c) the solver can handle complex geometries of relevance to RDE design. Grid convergence of key metrics for detonations is evaluated using canonical flows. Further, the importance of the use of detailed chemical kinetics is illustrated by extracting the composition structure behind a two-dimensional detonation front. Finally, simulations of a practical RDE configuration are used to demonstrate the applicability of this solver to analyzing geometries. The simulation captures the general trends of the experiment well. It is found that the detonation occurs under partially-premixed conditions. Propagation of pressure waves to the injection system is observed which could influence flow behavior in the oxidizer plenum.
Investigation of Air-Oil Distribution of Low Oil-Supplied Pressure Grooved Ring Floating Ring Bearing
Authors: Yan Wang , Yuhong Li
Published: August 2018

Oil lubricated floating ring bearings (FRBs) are popular among the passenger vehicle turbochargers. Air entrainment occurs in the inner film of the FRB under low oil-supplied pressure. Air entrainment has great impact on the bearing performance. Experiments reported that FRB with a circumferential groove on the ring shows lower ring-to-shaft speed and improved stabilizing capacity at high shaft speed. This study aims to construct the numerical simulation method to predict the multiphase flow in the grooved ring (GR) FRB. Computational fluid dynamic (CFD) method is adopted to obtain the bearing performance considering air entrainment. CFD calculation can obtain detailed air entrainment results that experiment cannot provide. Calculation results are compared with the experimental results to validate the proposed CFD method. Analysis shows the great influence of grooved ring on the air entrainment. Air entrainment contributes to the decrease of the ring-to-shaft speed ratio in the GR FRB. The proposed CFD calculation considering air entrainment can give good prediction of the ring rotation speed under different shaft speed. Besides, detailed analysis of the effective viscosity indicates that outer film is mainly affected by thermal effect. Inner film is affected by both thermal effect and air entrainment effect, where latter is more predominant.
Performance Improvement of a Micro Gas Turbine Adopting Exhaust Gas Recirculation for CO2 Capture by Integration With Liquid Air Energy Storage
Authors: Kim Min Jae , Won Dong Hyeok , Kim Tong Seop
Published: August 2018

Exhaust gas recirculation (EGR) can be applied to a micro gas turbine (MGT) for the efficient removal of CO2 using post-combustion capture. The EGR increases the CO2 concentration of the exhaust gas for the capture process, which augments the capture rate. However, the performance penalty of the MGTs caused by the rise in the compressor inlet temperature due to the EGR is a drawback. In this research, we investigated the integration of an MGT, adopting EGR with liquid air energy storage (LAES), an emerging energy storage technology. LAES stores electric energy from renewables or the power grid in the form of cryogenic liquid air. The liquefied air is pressurized and regasified to generate electricity during peak demand hours. In our proposed system, a portion of the cryogenic air is injected into the MGT’s compressor inlet. The purpose of the injection is twofold. Firstly, it decreases the compressor inlet air temperature, which enhances the MGT performance, especially the power output. Secondly, it increases the carbon dioxide composition of the exhaust gas, which enhances the carbon capture performance. An MGT system, equipped with a post-combustion capture and integrated with the cryogenic air injection, was analyzed. The analysis shows that the system power, system efficiency, and CO2 capture rate were improved, with the heat duty of the carbon capture process reduced in accordance with the increase in cryogenic flow rate, as expected. Moreover, the heat duty of the carbon capture process decreased significantly due to the increase in temperature and O2 concentration in the cryogenic air.
The Use of Additive Technologies to Create Lightweight Parts for Gas Turbine Engine Compressors
Authors: Magerramova Liubov , Volkov Michail , Svinareva Maria , Siversky Alex
Published: August 2018

One of the most urgent questions in aviation engine development is how to reduce the mass of composition details, while meeting the demands for strength and reliability. The production of complex, critical aircraft engine details is constrained by the limited capabilities of traditional fabrication methods. However, complex-shaped parts can now be created using emerging additive technologies that will avoid many of the traditional manufacturing methods’ limitations and reduce material and time costs. In addition, using additive technologies facilitates the manufacturing of details such as cellular and lattice structures, the production of which is impossible with traditional methods. The use of cellular structures is one way to reduce the weight of parts. Lattice structures are used to provide rigidity and strength in industries where parts are exposed to compression, bending and impact loads. The cell structures can withstand significant deformation without fracture and have a high resistance to fatigue. Since the weight of such structures is much less than the original prototypes, using them creates new opportunities for future aircraft applications. This article discusses the issue of creating lightweight structures for compressor components containing different cellular structures and their manufacturing using additive technology methods. We have examined several simple models of cellular structures and studied their geometrical, mass and stiffness characteristics. Analysis of the stress states of the cellular structures was conducted on the samples, with testing intended for three-point bending and cantilever beams. The influence of the geometrical parameters of the cells on the mass and strength characteristics of the structures was determined. The method for determining the density and elastic modulus of the equivalent homogenous material using these parameters in the calculations was complex. A few models containing the cellular region were proposed and the designs of several fan blades containing the cellular region were discussed. Samples to determine the strength of the developed structural elements were made from titanium alloy powder using Powder Bed Fusion (PBF). Continuous model samples and samples with different cellular structures were manufactured to test.
The Behavior of the Casing Boundary Layer With the Presence of Tip Leakage Vortex
Authors: Nan Xi , Lin Feng , Himeno Takehiro , Watanabe Toshinori
Published: August 2018

Casing boundary layer effectively places a limit on the pressure rise capability achievable by the compressor. The separation of the casing boundary layer not only produce flow loss but also closely related to the compressor rotating stall. The motivation of this paper is to present a viewpoint that the casing boundary layer should be paid attention to in parallel with other flow factors on rotating stall trigger. This paper illustrates the casing boundary layer behavior by displaying its separation phenomena with the presence of tip leakage vortex at different flow conditions. Skin friction lines and the corresponding absolute streamlines are used to demonstrate the three-dimensional flow patterns on and near the casing. The results depict a Saddle, a Node and several tufts of skin friction lines dividing the passage into four zones. The tip leakage vortex is enfolded within one of the zones by the separated flows. All the flows in each blade passage are confined within the passage as long as the compressor is stable. The casing boundary layer of a transonic compressor is also examined in the same way, which results in qualitatively similar zonal flows that enfolds the tip leakage vortex. This research develops a new way to study the casing boundary layer in rotating compressors. The results may provide a first-principle based explanation to stalling mechanisms for compressors that are casing sensitive.
Enhanced Heat Transfer and Thermal Performance of a Blade With Tree-Shaped Film Cooling Channels
Authors: Zhang Guohua , Xie Gongnan , Sundén Bengt
Published: August 2018

Modern film cooling is an essential method to protect the turbine blade from the hot gas, and the issue about how to improve the film cooling performance has attracted much attention. In this study, a tree-shaped film cooling structure is carried out to improve the overall effectiveness and better decrease the metal temperature of the blade at the same time. To validate the superiority of the proposed structure, a series of numerical simulation cases are conducted under a typical blowing ratio of M = 0.764. The first case is a film cooling channel with a single film hole which with a diameter of 5 mm and is inclined by α = 45° relative to the mainstream direction. The other three cases are tree-shaped structures with one level, two levels and three levels of bifurcations. For all cases, the same boundary conditions and turbulence model (Realizable k-ε) are adopted, and three-dimensional numerical simulations are used as well to test the thermal performance of the models. It is found from the computing results that the overall effectiveness of the tree-shaped structure is improved more than 50% compared to the case with a single film hole, and the results also demonstrate that the more levels of the structure the lower the metal temperatures. Therefore, it is indicated that this research will make a contribution to a higher performance gas turbine.
Experimental and Numerical Study on Emission Characteristics of the Double Annular Swirler Under Different Pilot Fuel Ratios
Authors: Zong Chao , Lyu Yaya , Guo Desan , Li Chengqin , Zhu Tong
Published: August 2018

Micro gas turbine is one of the ideal prime movers for small-distributed energy systems. It can effectively reduce the emission of greenhouse gases and nitrogen oxides. Moreover, the use of micro gas turbines will contribute to burning fossil fuels in a much cleaner way. The staged combustion technology is the favorite way for low pollution combustion chamber such like. Therefore, the influence of the proportion of pilot fuel in the combustion chamber on pollutant emission deserves further study.

The object of this research is the Double annular swirler (Das), which was applied to a 100 kW micro gas turbine combustion chamber. The combustion performance and emission characteristics under different Pilot Fuel Ratios (PFR) were obtained in prototype experimental system.

Under the experimental conditions, Computational fluid dynamics (CFD) method was applied to research the reacting flow field and the formation of NOx in the combustion chamber and then analyze the influences of PFRs on combustion process. Experimental results show that the NOx emission of Das decreased at first and then increased with the augment of PFR. When PFR was near to 11%, the per unit NOx emission concentration reached its minimum. The numerical simulation agreed well with the experimental data. Further analysis of the simulation results indicate that there is a strong correlation between Φlocal and NOx concentration. When it is lower than a certain value, the number of nitrogen oxides will be significantly reduced. The value has a lot to do with the inlet air temperature and the pressure of the combustion chamber under the design condition, and it needs to be confirmed by calculating the adiabatic temperature. Simultaneously, we also find that although the percentage of total air flowing into the combustor remains unchanged, the increase of PFR would reduce the airflow ratio in inner swirler. This implies that for some particular combustion chambers, special attention should be paid to the changes in air allocation caused by PFR.
Influence of Reactor Pressure on the Primary Jet Breakup of High-Viscosity Fuels: Basic Research for Simulation-Assisted Design of Low-Grade Fuel Burner
Authors: Müller Thomas , Kadel Kathrin , Habisreuther Peter , Trimis Dimosthenis , Zarzalis Nikolaos , Sänger Alexander , Jakobs Tobias , Kolb Thomas
Published: August 2018

Detail investigations on the primary breakup of high-viscosity liquids using external-mixing twin-fluid nozzles at increased system pressure are scarce. Therefore, the research work of the present study is focused on the investigation of pressure influence (1 - 11 bar (abs)) on the primary breakup by numerical simulation based on a previously studied nozzle [Müller et al., ASME Turbo Expo 2016, GT2016-56371]. The pressure influence was investigated for two liquids applying a wide range of viscosities (100 mPa s; 400 mPa s) and two atomizing air velocities (58 m/s; 74 m/s). To describe the disintegration process of the fluids, characteristic features like liquid jet morphology, breakup length and breakup frequency were evaluated.

The primary breakup was investigated using the open source CFD software OpenFOAM. To gather the morphology of the primary breakup and the flow field characteristics compressible large eddy simulations (LES) were performed and the movement of the gas-liquid interface was captured by means of the Volume of Fluid-Method (VOF).

The conducted simulations showed good agreement with experimental results with respect to the characteristic features (e.g. morphology and breakup length) and revealed a decrease of the breakup length with increasing ambient pressure for a constant liquid mass flow and atomizing air velocity. Moreover, those findings will contribute to a better understanding of the physics of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.
Conceptual Flutter Analysis of Labyrinth Seals Using Analytical Models: Part I — Theoretical Support
Authors: Corral Roque , Vega Almudena
Published: August 2018

A simple non-dimensional model to describe the flutter onset of labyrinth seals is presented. The linearized equations for a control volume which represents the inter-fin seal cavity, retaining the circumferential unsteady flow perturbations created by the seal vibration, are used. Firstly, the downstream fin is assumed to be choked, whereas in a second step the model is generalized for unchocked exit conditions. An analytical expression for the non-dimensional work-per-cycle is derived. It is concluded that the stability of a two-fin seal, depends on three non-dimensional parameters, which allow explaining seal flutter behaviour in a comprehensive fashion. These parameters account for the effect of the pressure ratio, the cavity geometry, the fin clearance, the nodal diameter, the fluid swirl velocity, the vibration frequency and the torsion center location in a compact and interrelated form. A number of conclusions have been drawn by means of a thorough examination of the work-per-cycle expression, also known as the stability parameter by other authors. It was found that the physics of the problem strongly depends on the non-dimensional acoustic frequency. When the discharge time of the seal cavity is much greater than the acoustic propagation time, the damping of the system is very small and the amplitude of the response at the resonance conditions is very high. The model not only provides a unified framework for the stability criteria derived by Ehrich [1] and Abbot [2], but delivers an explicit expression for the work-per-cycle of a two-fin rotating seal. All the existing and well established engineering trends are contained in the model, despite its simplicity. Finally, the effect of swirl in the fluid is included. It is found that the swirl of the fluid in the inter-fin cavity gives rise to a correction of the resonance frequency and shifts the stability region. The non-dimensionalization of the governing equations is an essential part of the method and it groups physical effects in a very compact form. Part I of the paper details the derivation of the theoretical model and draws some preliminary conclusions. Part II of the corresponding paper analyzes in depth the implications of the model and outlines the extension to multiple cavity seals.
A Novel Method of Intake and Exhausts System Simulators for Real Marine Engine Under Lab Conditions
Authors: Luan Yigang , Yang Lianfeng , Qu Yonglei
Published: August 2018

Intake and exhaust system is one of the important parts of power systems of the ships, because the resistance performance will influence the whole performance of the main propulsion engine. Therefore, the performance of the intake and exhaust systems are always studied in advance inside laboratories before they are built as the real ship system. In this paper, both CFD and experiment methods are employed to investigate the pressure loss performance of intake and exhaust systems. The RANS simulation with k-ε turbulence model is done by the commercial code ANSYS Fluent. Firstly, sixteen different intake and exhaust models were calculated with the proper boundary conditions according to the former research experience. The resistance performance of the real ship intake and exhaust models was obtained. Then a simplified geometric model was proposed to simulate the performance of the complex real ship intake and exhaust system effectively and efficiently. This kind of novel simplified model can reproduce the geometrical structures of the real ship under lab environments, which can easily adjust the angle of the resistance simulators. Additionally, a low speed wind tunnel system with a kind of small-scale aerodynamic model has been made and its pressure loss performance was measured under laboratory conditions in the experiment. Finally, the simulation results are compared with the experimental data. The results show that the simulation method employed in this paper is suitable to do such research work with high accuracy. And the simplified model can be used to mimic the resistance performance of the real ship intake and exhaust systems.
Investigation on the Leading Edge Film Cooling of Counter-Inclined Cylindrical and Laid-Back Holes With and Without Impingement: Part I — Film Cooling Effectiveness
Authors: Guo Qi-ling , Liu Cun-liang , Zhu Hui-ren , Liu Hai-yong , Wang Rui-dong , Gao Chao
Published: August 2018

Experimental investigation has been performed to study the film cooling characteristics of counter-inclined structures on the turbine vane leading edge. In this paper, four counter-inclined models are measured including cylindrical film holes with and without impingement holes, laid-back film holes with and without impingement holes. A semi-cylinder model is used to model the turbine vane leading edge. Two rows of film holes are located at ±15° on either side of the leading edge model, inclined 90° to the flow direction and 45° to the spanwise direction. Film cooling effectiveness and heat transfer coefficient have been obtained using a transient heat transfer measurement technique with double thermochromic liquid crystals with four blowing ratios ranging from 0.5 to 2 at a 1.0 density ratio. The results show that the film cooling effectiveness decreases with the increase of blowing ratio. No matter cylindrical hole or laid-back hole, the addition of impingement enhances the film cooling effectiveness. Compared with cylindrical hole, laid-back hole produces a better film cooling performance mainly because of stronger lateral momentum. Moreover, the benefits of both adding impingement and exit shaping are more obvious under a large blowing ratio.
Analytical Heat Transfer Correlation for a Multistage Steam Turbine in Warm-Keeping Operation With Air
Authors: Toebben Dennis , Hellmig Adrian , Luczynski Piotr , Wirsum Manfred , Mohr Wolfgang F. D. , Helbig Klaus
Published: August 2018

Due to the growing share of volatile renewable power generation, conventional power plants with a high flexibility are required. This leads to high thermal stresses inside the heavy components which reduces the lifetime. To improve the ability for fast start-ups, information about the metal temperature inside the rotor and the casing are crucial. Thus, an efficient calculation approach is required which enables the prediction of the temperature distribution in a whole multistage steam turbine. Considerable improvements of the computing power and numerical simulation tools today allow detailed investigations of the heat transfer and the flow phenomena by Conjugate-Heat-Transfer (CHT) simulations. However, these simulations are still restricted to smaller geometries mostly by the number of elements. This leads to coarser numerical meshes for larger geometries and thus, to a reduced accuracy. A highly accurate 3D-CHT simulation of a whole multistage steam turbine can only be conducted with huge computational expense. Therefore, a simplified calculation approach is required. Heat transfer correlations are a commonly used tool for the calculation of the heat exchange between fluid and solid. Heat transfer correlations for steam turbines have been developed in a multitude of investigations. However, these investigations were based on design or to some extent on part-load operations with steam as the working fluid.

The present paper deals with the theoretical investigation of steam turbine warm-keeping operation with hot air. This operation is totally different from the conventional operation conditions, due to the different working fluid with low mass flow rates and a slow rotation. Based on quasi-steady transient multistage CHT simulations, an analytical heat transfer correlation has been developed, since, the commonly known calculation approaches from literature are not suitable for this case. The presented heat transfer correlations describe the convective heat transfer separately at vane and blade as well as the seal surfaces. The correlations are based on a CHT model of three repetitive steam turbine stages. The simulations show a similar behavior of the Nusselt-number in consecutive stages. Hence, the developed area related heat transfer correlations are independent of the position of the stage. Finally, the correlations are implemented into a solid body Finite-Element model and compared to the fluid-dynamic simulations.
Effect of Coolant Mass Flow Rate of Dirt Purge Hole on Heat Transfer and Flow Characteristics at a Turbine Blade Tip Underside
Authors: Zhao Zhiqi , Luo Lei , Zhou Xun , Wang Songtao
Published: August 2018

High thermal load on the turbine blade tip surface would lead to high temperature corrosion and severe structural damage. One method to reduce blade tip high thermal stress is to use cooler fluid from the compressor, that exists dirt purge hole mounted on the tip underside, for cooling purpose. In this study, internal serpentine cooling passage is modeled as a U bend channel with a sharp 180-deg turn with the dirt purge hole arranged at the tip-wall. The effect of the layout of dirt purge hole and varying coolant mass flow rate on flow structure, heat transfer on the tip-wall and friction factor of the U bend channel are numerically studied with Reynolds number ranging from 100,000 to 440,000. The results show that the vortex pair is forced to flow near the tip-wall while the increasing shearing effect induced by the vortex pairs increases the local heat transfer. With an increase mass flow rate of the dirt purge hole, the suction effect enhances the local heat transfer performance. However, the pressure loss is also increased accordingly at all Reynolds numbers. The augmentations with Reynold analogy performance and the thermal performance for 5.8% mass flow rate case is 12.5% and 12.7%, respectively, which reaches the highest performance augmentation compared to the smooth-tip channel.
Effect of Dimple/Protrusion Depth on Flow Structure and Heat Transfer in a Rotating Channel With Pin Fin
Authors: Du Wei , Luo Lei , Wang Songtao
Published: August 2018

In this study, numerical simulations are performed to investigate the effect of the dimple/ protrusion depth on the flow structure and heat transfer characteristics in a rotating channel with pin fins. The pin fins are arranged with staggered layout. The longitudinal and transverses pitches of the pin fin are 2.5. The dimples/protrusions are located on the endwall surface between the pin fins. The print diameter of the dimple/protrusion is same as the pin fin. Five different dimple/protrusion depth-to-diameter ratios are investigated, i.e. δ/D = 0, 0.1, 0.2, 0.3, 0.4.

Results of the flow structure, heat transfer on the endwall are included in this study. It is found that the flow structure and heat transfer are sensitive to the rotational Coriolis forces, both on the leading side and trailing side. In the dimpled channel, the area of the low-speed recirculation is increased as the dimple depth increased. The trailing side has higher pressure and TKE compared to the leading side. In addition, the Nu number is high at the trailing side due to the Coriolis forces. In protrusion channel, the pressure is increased at the front of the protrusion as the protrusion depth increases. A counter-rotating vortex is found at the top of the protrusion. The Nusselt number is also higher at the trailing side compared to the leading side.
Heat Transfer Coefficient Characterization for Large Aspect-Ratio Thin Films in Film-Riding Seals
Authors: Tallman James A. , Bidkar Rahul A.
Published: August 2018

Low-leakage film-riding seals are a key enabling technology for utility-scale supercritical carbon dioxide (sCO2) power cycles. Fluid film-riding rotor-stator seals (operating with sCO2 as the working fluid) are designed to track rotor movements and provide effective sealing by maintaining a tight operating clearance (of the order of several microns) from the spinning rotor. Thin film-riding seals generate viscous shear heat during high-speed operation, and the reliable operation of such thin-film seals depends critically on the designer’s ability to control the thermal deformations of the seal/rotor bearing face, which in turn are tied to the designer’s ability to understand and predict the heat transfer across the seal bearing face. In this paper, we develop a simple axisymmetric thermal-mechanical model of a typical face seal to highlight how the uncertainty in heat transfer coefficient (HTC) on the seal bearing face drives uncertainty in seal deformation predictions, especially when the HTCs are an order of magnitude lower than those predicted with duct-based Dittus-Boelter correlations. This uncertainty in seal bearing face HTCs drives the need for an experimental quantification of HTCs in high-aspect ratio thin films associated with low-leakage film-riding seals. In this paper, we describe a non-rotating experimental test rig designed for estimating the HTCs on the seal bearing face using a shim-heater technique along with IR-camera-based temperature measurements. The experimental set-up consists of a thin metal shim (representing the seal bearing face) forming one wall of a pressurized duct with geometric similarity to a typical thin film of a face seal. Pressurized airflow past the shim is used to simulate the flow field expected in a non-rotating seal. The HTC test data for a non-rotating film (as against the actual seal film with rotating fluid) are lower than the actual seal, and establish a lower bound on the HTCs. This is especially useful for bounding the seal deformation uncertainty, which is vulnerable to the HTCs in the low-HTC regime. We present representative test data that is non-dimensionalized using radial-flow-based Reynolds number and compare these HTC estimates both with the predictions of Dittus-Boelter type correlations, and with the predictions of a 3D computational fluid dynamics (CFD) model. The purpose of the CFD model is to develop a HTC prediction tool for such thin-film surfaces, and the test data are used for validating this predictive model.
Effects of Density and Blowing Ratios on the Turbulent Structure and Effectiveness of Film-Cooling
Authors: Stratton Zachary T. , Shih Tom I-P.
Published: August 2018

Large eddy simulations (LES) were performed to investigate film cooling of a flat plate, where the cooling jets issued from a plenum through one row of circular holes of diameter D and length 4.7D that are inclined at 35° relative to the plate. The focus is on understanding the turbulent structure of the film-cooling jet and the film-cooling effectiveness. Parameters studied include blowing ratio (BR = 0.5 and 1.0) and density ratio (DR = 1.1 and 1.6). Also, two different boundary layers (BL) upstream of the film-cooling hole were investigated — one in which a laminar BL was tripped to become turbulent from near the leading edge of the flat plate, and another in which a mean turbulent BL is prescribed directly. The wall-resolved LES solutions generated were validated by comparing its time-averaged values with data from PIV and thermal measurements. Results obtained show that having an upstream BL that does not have turbulent fluctuations enhances the cooling effectiveness significantly at low velocity ratios (VR) when compared to an upstream BL that resolved the turbulent fluctuations. However, these differences diminish at higher VRs. Instantaneous flow reveals a bifurcation in the jet vorticity as it exits the hole at low VRs, one branch forming the shear-layer vortex, while the other forms the counter-rotating vortex pair. At higher VRs, the shear layer vorticity is found to reverse direction, changing the nature of the turbulence and the heat transfer. Results obtained also show the strength and structure of the turbulence in the film-cooling jet to be strongly correlated to VR.
An Experimental Investigation of Adiabatic Film Cooling Effectiveness and Heat Transfer Coefficient on a Transonic Squealer Tip
Authors: Saul Andrew J. , Ireland Peter T. , Coull John D. , Wong Tsun Holt , Li Haidong , Romero Eduardo
Published: August 2018

The effect of film cooling on a high pressure turbine blade with an open squealer tip has been examined in a high speed linear cascade. The cascade operates at engine realistic Mach and Reynolds numbers, producing transonic flow conditions over the blade tip. Tests have been performed on two uncooled tip geometries with differing pressure side rim edge radii, and a cooled tip matching one of the uncooled cases.

The pressure sensitive paint technique has been used to measure adiabatic film cooling effectiveness on the blade tip at a range of tip gaps and coolant mass flow rates. Complementary tip heat transfer coefficients (HTC) have been measured using transient infrared thermography, and the effects of the coolant film on the tip heat transfer and engine heat flux examined.

The uncooled data show that the tip heat transfer coefficient distribution is governed by the nature of flow reattachments and impingements. The squealer tip can be broken down into three regions, each exhibiting a distinct response to a change in the tip gap, depending on the local behaviour of the overtip leakage flow. The edge radius of the pressure side rim causes the overtip leakage flow to change dramatically at low clearance. Complementary CFD shows that the addition of casing motion causes no further change on the pressure side rim.

Injected coolant interacts with the overtip leakage flow, which can locally enhance the tip heat transfer coefficient compared to the uncooled tip. The film effectiveness is dependent on both the coolant mass flow rate and tip clearance. At increased coolant mass flow, areas of high film effectiveness on the pressure side rim coincide strongly with a net heat flux reduction and in the subsonic tip region with low heat transfer coefficient.
Simulation of Gas Turbine Ignition Using Large Eddy Simulation Approach
Authors: Tang Yihao , Hassanaly Malik , Raman Venkat , Sforzo Brandon A. , Wei Sheng , Seitzman Jerry M.
Published: August 2018

This study simulates spark ignition of a modular stratified flow facility using realistic aviation fuel. The combustion model uses a look-up table approach, where the data of the look-up table are collected from lower dimension flamelet/homogeneous ignition calculations. The combustion model is incorporated into a previously developed low-Mach solver, based on which a module is further introduced that uses field patching strategies to represent the ignitor impulse. Simulated results of both ignition successful and failure can be achieved under different initial spark energy input, and the physical effects behind the different ignition behavior is related to the dynamics of the spark kernel impulse. It is further shown that the simulated ignition process exhibits similar features compared to associated experimental results and allows for detailed analysis of the transition to ignited or extinguished states.
Towards an Improved Lifing Methodology for Thermocouple Probes Used in Gas Turbines
Authors: Scervini Michele , Rae Catherine , Page Richard , Rudkin Mark , Loveless Daniel , O’Dell Stephen
Published: August 2018

The reliability of temperature probes in gas turbines is dependent on their capability to withstand the harsh environment they experience when installed in an engine. The severe conditions sensors experience during operation requires the use of appropriate methodologies to assess their life. During the ALPHET project the University of Cambridge and Esterline Advanced Sensors have been working on developing an advanced lifing methodology: in order to predict the life of thermocouple probes used in gas turbines, this combines accelerated laboratory tests based on the salt deposition method, combustor rig tests, metallurgical analysis of probes returned after engine service and information extracted from their associated temperature data acquired during their long term operation in aero gas turbines.

The work included analysis of materials used in current temperature probes and investigation of advanced materials for future thermocouple sensors that will work at temperatures higher than today’s probes.

This paper will summarise the main features of the improved lifing methodology and the challenges associated with the use of complex engineering data obtained from engines.
Numerical Investigation of Non-Isothermal Cavitating Flows on Hydrofoils by Means of an Extended Schnerr-Sauer Model Coupled With a Nucleation Model
Authors: De Giorgi Maria Grazia , Ficarella Antonio , Fontanarosa Donato
Published: August 2018

The present work aims to investigate cavitating flows of water, liquid hydrogen and nitrogen on hydrofoils numerically, using the open source code OpenFOAM. The Eulerian homogeneous mixture approach has been used, consisting in a mass transfer model which is based on the combination of a two-phase incompressible unsteady solver with a Volume of Fluid (VOF) interface tracking method. Thermal effects have been introduced by means of the activation of energy equation and latent heat source terms plus convective heat source term. The dependency of the saturation conditions to the temperature has been defined using Antoine-like equations. An extended Schnerr-Sauer model based on the Classical Nucleation Theory (CNT) has been implemented for the computation of the interfacial mass transfer rates.

In order to investigate the nucleation effects, an extension of the Classical Nucleation Theory has been considered by coupling the Population Balance Equation/Extended Quadrature-Based Method of Moments (PBE-EQBMM) with the CFD model, which has been defined in combination with a transport equation for the nuclei density. Results showed that nucleation determined a non-uniform field of nuclei density so as to produce a reduction of the temperature drop inside the vapor bubbles, as well as a warmed wake downstream the vapor cavity. Unsteady computations also revealed an influence of the nucleation on the dynamics of the vapor cavity and the bubble detachment.
Characterization and Impact of Secondary Flows in a Discrete Passage Centrifugal Compressor Diffuser
Authors: Erickson David W. , Tan Choon S. , Macrorie Michael
Published: August 2018

Truncating the exit of a discrete passage centrifugal compressor diffuser is observed to enhance a research compressor’s stall line. By interrogating the experimental data along with a set of well-designed Reynolds-Averaged Navier Stokes computations, this improvement is traced to reduced impact of secondary flows on the truncated diffuser’s boundary layer growth. The secondary flow system is characterized by counter-rotating streamwise vortex pairs that persist throughout the diffuser passage. The vortices are traced to two sources: background vortices resulting from impeller exit flow non-uniformity, and incidence vortices resulting from flow separation off the leading edge cusps unique to a discrete passage diffuser. The incidence vortices detrimentally impact the diffuser pressure rise capability by accumulating high loss flow along the diffuser wall near the plane of symmetry between the vortices. This contributes to a large passage separation in the baseline diffuser. Using reduced order flow modeling, the impact of the vortices on the boundary layer growth is shown to scale inversely with diffuser aspect ratio, and thus the separation extent is reduced for the higher aspect ratio truncated diffuser. Because the diffuser incidence angle influences the strength and location of the vortices, this mechanism can affect the slope of the compressor’s pressure rise characteristic and impact its stall line. Stall onset for the baseline diffuser configuration is initiated by the transition of the vortex location and corresponding passage separation between diffuser pressure and suction sides with increased cusp incidence. Conversely, because the extent of the passage separation in the truncated diffuser is diminished, the switch in separation from pressure to suction side does not immediately initiate instability.