bluuebunny/crossref_metadata_2025 huggingface dataset:
High Momentum Jet Flames at Elevated Pressure: A — Experimental and Numerical Investigation for Different Fuels
Authors: Lammel Oliver , Severin Michael , Ax Holger , Lückerath Rainer , Tomasello Andrea , Emmi Yeshawini , Noll Berthold , Aigner Manfred , Panek Lukasz
Published: August 2017

In this work, results of comprehensive high-pressure tests and numerical simulations of high momentum jet flames in an optically accessible combustion chamber are presented. A generic single nozzle burner was designed as a full-scale representation of one duct of a high temperature FLOX® gas turbine combustor with a model pilot burner supporting the main nozzle. As an advanced step of the FLOX® gas turbine combustor development process, tests and simulations of the entire burner system (consisting of a multi nozzle main stage plus a pilot stage) are complemented with this work on an unscaled single nozzle combustor, thus supporting the development and testing of sub concepts and components like the mixing section and dual-fuel injectors. These injectors incorporate a gaseous fuel stage and a spray atomizer for liquid fuels, both separately exchangeable for testing of different fuel placement concepts.

The combustor was successfully operated at gas turbine relevant conditions with natural gas including a variation of the Wobbe index, and with light heating oil with and without water admixture. The presented work is the first of two contributions and covers the description of the experimental setup, an overview of the numerical methods, high-pressure test results for different fuels and variations of the operating conditions including exhaust gas measurements and basic optical diagnostic methods, together with CFD results for several cases. The other part will present detailed and focused investigations of few conditions by complex and extensive optical and laser combustion diagnostics.
Re-Ingestion of Upstream Egress in a 1.5-Stage Gas Turbine Rig
Authors: Scobie James A. , Hualca Fabian P. , Patinios Marios , Sangan Carl M. , Owen J. Michael , Lock Gary D.
Published: August 2017

In gas turbines, rim seals are fitted at the periphery of stator and rotor discs to minimise the purge flow required to seal the wheel-space between the discs. Ingestion (or ingress) of hot mainstream gases through rim seals is a threat to the operating life and integrity of highly-stressed components, particularly in the first-stage turbine. Egress of sealing flow from the first-stage can be re-ingested in downstream stages.

This paper presents experimental results using a 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disc. Re-ingestion was quantified using measurements of CO2 concentration, with seeding injected into the upstream and downstream sealing flows. Here a theoretical mixing model has been developed from first principles and validated by the experimental measurements. For the first time, a method to quantify the mass fraction of the fluid carried over from upstream egress into downstream ingress has been presented and measured; it was shown that this fraction increased as the downstream sealing flow rate increased. The upstream purge was shown to not significantly disturb the fluid dynamics but only partially mixes with the annulus flow near the downstream seal, with the ingested fluid emanating from the boundary layer on the blade platform. From the analogy between heat and mass transfer, the measured mass-concentration flux is equivalent to an enthalpy flux and this re-ingestion could significantly reduce the adverse effect of ingress in the downstream wheel-space. Radial traverses using a concentration probe in and around the rim seal clearances provide insight into the complex interaction between the egress, ingress and mainstream flows.
Comparison of Heterogeneous and Homogeneous Coolant Injection Models for Large Eddy Simulation of Multiperforated Liners Present in a Combustion Simulator
Authors: Thomas Martin , Dauptain Antoine , Duchaine Florent , Gicquel Laurent , Koupper Charlie , Nicoud Franck
Published: August 2017

With the goal of increasing the thermodynamic efficiency of aircraft engines, the temperature in the combustion chamber has risen to the point where the gas temperature is above the melting point of materials used in the chamber and cooling systems are mandatory. Today, most of the existing lean burn combustors rely on multiperforated liners to keep hot gases away from the walls. However, resolving all holes of the combustor in the CFD design phase remains beyond currently available computational resources, so the effusion cooling system is often modeled by homogeneously injecting air on the whole surface of the liner, especially in the context of Large Eddy Simulation (LES) based CFD. This paper investigates a novel approach to simulate the effect of jets emitted from discrete holes on the flow inside a combustion chamber. In this new modeling approach, jet diameters are treated to be resolvable by the grid while conserving the correct mass and momentum flow rate. LES are performed on the combustion simulator of the engine representative FACTOR test rig at two different operating points and compared to measurement data as well as previous simulations obtained using a homogeneous air injection modeling on liners. The new approach shows globally similar results as the well validated homogeneous injection model and is applicable on realistic industrial geometries at a negligible level of additional cost (+0.3%).
Experimental and Numerical Investigations of Turbocharger Rotors on Full-Floating Ring Bearings With Circumferential Oil-Groove
Authors: Chatzisavvas Ioannis , Nowald Gerrit , Schweizer Bernhard , Koutsovasilis Panagiotis
Published: August 2017

This work presents experimental and numerical investigations into the vibrations of turbocharger rotors on full-floating ring bearings with a circumferential oil-groove. The pressure distribution in the fluid-film bearings is calculated through the Reynolds equation using a highly efficient global Galerkin approach with suitable trial and test functions. The numerical efficiency of the method is markedly increased as the resultant linear system is solved symbolically, establishing a semi-analytical solution. The temperature in the oil-film may increase due to the mechanical power dissipation, affecting the pressure distribution and the load capacity of the bearing. Therefore, a reduced thermal energy model is implemented together with the Reynolds equation to account for the variable oil-viscosity and for the thermal expansion of the surrounding solids. The thermal energy balance equations are implemented in a transient form, i.e. including the time dependent temperature term. The corresponding system of nonlinear differential equations is efficiently solved, leading to a further significant reduction in simulation times. The hydrodynamic bearing model including the thermal effects is finally coupled with the equations of motion of a turbocharger rotor and numerical run-up simulations are compared with experimental results. The comparisons show that the numerical model captures adequately the dynamics of the system, giving precise information about the frequencies and the amplitudes of the synchronous and the self-excited subsynchronous rotor vibrations.
Distinguishing Primary and Secondary Loads to Support Gas Turbine Blades and Vanes Design
Authors: Riva Andrea , Elli Stefano , Nussbaum Julien
Published: August 2017

Creep mechanisms are present in heavy duty gas turbine blades and vanes due to the simultaneous presence of high temperature and high stresses. Therefore, the microstructural phenomena (dislocation movement and atomic diffusion) that occur and accumulate during service are able to convert part of the initial elastic field of strain into permanent creep strain. This also induces a global redistribution of stresses. The progressive accumulation of creep strain can, in some extreme cases, produce changes and damage in the material (gamma prime rafting, porosity) and can eventually lead to component failure.

This work shows how the understanding of the nature of the load significantly affect the capability of creep strain to produce damage. In fact, it is shown how both primary (non-self-limiting) and secondary (self-limiting) loads are both capable to generate a significant amount of creep strain, but the microstructural damage is more easily generated by relentless primary loads, generated by external forces such as the rotor blade centrifugal force (or, in other components, external gas pressure, dead weight). In the case of turbine blades and vanes, due to the complexity of the component, it is challenging to quantitatively distinguish relentless primary from self-limiting secondary stresses or simply thermal from mechanical contributions. This work is aimed to provide the designer with tools to perform such distinction and support the interpretation of the creep calculations. The proposed methodologies are developed to improve the accuracy of the prediction of the creep damage in turbine blades and vanes, but they can also be used for other purposes (e.g. predict the hysteresis cycle shift, support the estimation of the plastic strain on the basis of an elastic FE calculation), as illustrated in the paper.
The Effect of Non-Equilibrium Boundary Layers on Compressor Performance
Authors: Wheeler Andrew P. S. , Dickens Anthony M. J. , Miller Robert J.
Published: August 2017

The paper investigates the effect of non-equilibrium behaviour of boundary layers on the profile loss of a compressor. The investigation is undertaken using both direct numerical simulation (DNS) of a mid-height section of a compressor blade and a reduced order model, MISES. The solutions are validated using experimental measurements made in the embedded stage of a multistage low speed compressor. The paper shows that up to 35% of the suction surface boundary layer of the compressor blade exhibits non-equilibrium behaviour. The size of this region reduces as the Reynolds number is increased. The non-equilibrium behaviour was found to reduce profile loss in most cases, however, in a range of cases where transition occurs through a small separation the presence of non-equilibrium behaviour was found to increase profile loss.
An Explicit-Implicit Time Integration Approach for Finite Element Evaluation of Engine Load Following an FBO Event
Authors: Weng Yiliu , Zheng Lipeng
Published: August 2017

Engine fan blade-off (FBO) is an extreme event that could well place the flight safety at risk. When it happens, the engine will experience high-velocity impact at first, and then enter into a “high-power” stage due to huge unbalance before coming to a steady state called “windmilling”. The analytical process for FBO can be split into two phases, one for impact simulation and the other for obtaining the FBO load to pylon. Typically, explicit method with fine mesh finite elements is used in the first phase, and implicit method with coarse meshes is adopted in the second one. In most cases, the only connection between these two analyses may be the unbalance level caused by FBO. More structural responses other than the unbalance level due to fan blade impact are actually ignored in the succeeding implicit analysis. Attempts have been made by Boeing, GE and MSC to integrate these two processes by adding some features in MD Nastran. Yet the intermediate binary files created and the restricted input entries make the integration process quite inflexible.

This paper introduces an explicit-implicit time integration approach for finite element analysis of engine load following an FBO event. The proposed method attempts to connect the two stages more closely, yet in a more flexible manner. In this approach, the engine structural response under FBO obtained from explicit analysis is transferred to the implicit analysis, together with the unbalance level caused by blade loss. The necessity of the approach is discussed, and sensitivity analysis is conducted to understand the factors that play significant roles in the approach. As the models for explicit and implicit analyses are different in mesh sizes and scales, the authors also develop a tool that can interpolate the load information and further, smooth it to fit calculation. Finally, the approach is tested on a full engine model to show its applicability and advantages over the traditional method for load evaluation of FBO event.
LES Analysis of Flow and Heat Transfer in a Rib-Roughened Duct in Clockwise and Anti-Clockwise Rotation Regimes
Authors: Salvagni Alessandro , Borello Domenico
Published: August 2017

We report on an LES study of effects of stabilising/destabilising rotation on heat transfer over a ribbed surface in a rectangular duct at Re = 15000. The duct bottom wall, ribbed by flow-normal, equally-spaced square-sectioned ribs, was uniformly heated (except for the ribs) by a constant heat flux. The duct was rotated with angular velocity corresponding to the rotation number of 0.3, around an axis parallel to the ribs in counter-clockwise (clockwise) direction, thus destabilising (stabilising) the ribbed-wall adjacent flow.

These well-resolved LES gave some new insight into the rotation effects on flow and heat transfer providing information that are not easily accessible by experiments. An attempt was made to identify the heat transfer effects due to the rotation-induced modifications of the secondary motion.
Nozzle Guide Vane Film Cooling Effectiveness for Radial Showerheads With Restricted Cooling Hole Surface Angles
Authors: Holgate Nicholas E. , Ireland Peter T. , Self Kevin P.
Published: August 2017

Adiabatic film cooling effectiveness measurements are made on nozzle guide vane leading edges in an engine-realistic flow environment. The tested leading edges feature radial showerheads with different spanwise distributions of hole surface angle. The showerheads blow towards the midspan, except for one model with showerhead holes orthogonal to the vane surface. The results show that low surface angle radial showerhead holes generate high effectiveness within their rows and further downstream, but neglect the stagnation region lying between the two most upstream cooling hole rows. This downstream effectiveness gain is due to both the continued surface attachment of this coolant as it progresses downstream, and its beneficial interactions with downstream cooling jets. Moderate radial showerhead surface angles cause moderate coolant jet penetration into the mainstream, which promotes near-surface mixing of the coolant with the mainstream, increasing stagnation region effectiveness. The mixing effect is enhanced by the intense turbulence generated by combustor dilution jets. High surface angles may cause the stagnation region coolant to penetrate too far for either of these gains to be realised. Considering also the presence of endwall film cooling, these effects, taken together, suggest the superiority of radial showerheads which blow towards the midspan, as against those which blow towards each endwall. Surface temperature data is acquired by a novel infrared thermography technique which permits measurement of both heat transfer coefficient and film effectiveness from a single heated test.
Mistuned Higher-Order Mode Forced Response of an Embedded Compressor Rotor: Part II — Mistuned Forced Response Prediction
Authors: Li Jing , Aye-Addo Nyansafo , Kielb Robert , Key Nicole
Published: August 2017

This paper is the second part of a two-part paper that presents a comprehensive study of the higher-order mode mistuned forced response of an embedded rotor blisk in a multi-stage axial research compressor. The resonant response of the second-stage rotor (R2) in its first chordwise bending (1CWB) mode due to the second harmonic of the periodic passing of its neighboring stators (S1 and S2) is investigated computationally and experimentally at three steady loading conditions in the Purdue Three-Stage Compressor Research Facility. A Non-Intrusive Stress Measurement System (NSMS, or blade tip-timing) is used to measure the blade vibration. Two reduced-order mistuning models of different levels of fidelity are used, namely the Fundamental Mistuning Model (FMM) and the Component Mode Mistuning (CMM), to predict the response. Although several modes in the 1CWB modal family appear in frequency veering and high modal density regions, they do not heavily participate in the response such that very similar results are produced by the FMM and the CMM models of different sizes. A significant response amplification factor of 1.5∼2.0 is both measured and predicted, which is on the same order of magnitude of what was commonly reported for low-frequency modes. This amplification is also a strong, non-monotonic function of the steady loading. Moreover, on average, the mistuned blades respond at an amplitude only approximately 40% that of the tuned, much lower than what was commonly reported (75∼80%). This is due to the very low level of structural coupling associated with the 1CWB family of the rotor blisk. In this study, a very good agreement between predictions and measurements is achieved for the deterministic analysis. This is complemented by a sensitivity analysis which shows that the mistuned system is highly sensitive to the discrepancies in the experimentally determined blade frequency mistuning.
Experimental and Numerical Investigation of Turbulent Mixing in Film Cooling Applications
Authors: Straußwald Michael , Schmid Karin , Müller Hagen , Pfitzner Michael
Published: August 2017

Fundamental knowledge on the flow dynamics and in particular the turbulent heat flux in film cooling flows is essential for the future design process of efficient cooling geometries. Thermographic PIV has been used to measure temperature and velocity fields in flows emanating from cylindrical effusion holes simultaneously. The measurements were carried out in a closed-loop, heated wind tunnel facility at a repetition rate of 6 kHz. Due to the high frame rate of the measurements, the unsteady flow dynamics could be resolved. For a density ratio of DR = 1.6 and a momentum ratio of I = 8, the jet ejected from the cylindrical effusion hole lifts off the surface. From the instantaneous measurements it could be observed that pockets of hot air are entrained into the coolant forcing the relatively fast cooling air to dodge the slow main flow air. These shear layer fluctuations result in turbulent heat fluxes that do not follow the gradient diffusion hypothesis which is often used in RANS models. In addition to these experimental investigations, numerical results from RANS simulations with the k-ω-SST turbulence model are presented that were carried out as basis for future investigations on turbulent heat flux modeling.
Forcing Superposition and Decomposition of an Embedded Compressor Rotor
Authors: Li Jing , Kielb Robert
Published: August 2017

This paper investigates superposition and decomposition methods when determining the forcing function on an embedded rotor in a multistage axial compressor. Under investigation is a 3-row stator/rotor/stator configuration where two stators, having the same vane count, can be circumferentially clocked to change the rotor excitation. The combined forcing function on the rotor in any arbitrary clocking arrangement is assumed to be a linear combination of two known clocking positions. In this study, the forcing function from these known positions are first approximated by two 2-row CFD solutions, namely stator/rotor and rotor/stator. It is found that theses approximations are poor, since they do not include the significant effect of stator-stator interaction. Next, these two forcing components are obtained via a linear decomposition using two 3-row CFD solutions at two clocking positions. A linear superposition is performed based on these decomposed results to estimate the combined rotor forcing for any arbitrary clocking position. It is found that although the trend of rotor forcing with respect to clocking is qualitatively captured, considerable quantitative discrepancies exist that refute the proposed linearity assumption. This assumption oversimplifies the multi-row aerodynamic interactions: a change in the stator-stator clocking position does not only alter the relative phase between two stator-induced forcing functions to the rotor, but also these two components themselves.
An Approach for Efficient CFD Simulations of an Ejector Air Injection System for Active Aerodynamic Compressor Stabilization
Authors: Brehm Sebastian , Kern Felix , Raub Jonas , Niehuis Reinhard
Published: August 2017

The Institute of Jet Propulsion at the University of the German Federal Armed Forces Munich has developed and patented a novel concept of air injection systems for active aerodynamic stabilization of turbo compressors. This so-called Ejector Injection System (EIS) utilizes the ejector effect to enhance efficiency and impact of the aerodynamic stabilization of the Larzac 04 two-spool turbofan engine’s LPC. The EIS design manufactured recently has been subject to CFD and experimental pre-investigations in which the expected ejector effect performance has been proven and the CFD set-up has been validated. Subsequently, optimization of the EIS ejector geometry comes into focus in order to enhance its performance. In this context, CFD parameter studies on the influence of in total 16 geometric and several aerodynamic parameters on the ejector effect are required. However, the existing and validated CFD set-up of the EIS comprises not only the mainly axisymmetric ejector geometry but also the highly complex 3D supply components upstream of the ejector geometry. This is hindering large scale CFD parameter studies due to the numerical effort required for these full 3D CFD simulations. Therefore, an approach to exploit the overall axissymmetry of the ejector geometry is presented within this paper which reduces the numerical effort required for CFD simulations of the EIS by more than 90%. This approach is verified by means of both experimental results as well as CFD predictions of the full 3D set-up. The comprehensive verification data set contains wall pressure distributions and the mass flow rates involved at various Aerodynamic Operating Points (AOP).

Furthermore, limitations of the approach are revealed concerning its suitability e.g. to judge the response of the attached compressor of future EIS designs concerning aerodynamic stability or cyclic loading.
Understanding the Effect of Systematic Errors on the Accuracy of Experimental Measurements of Fluid-Film Bearing Dynamic Coefficients
Authors: Schwartz Benstone , Fittro Roger , Knospe Carl
Published: August 2017

Designing high-performance industrial machinery with fluid-film bearings for safe and stable operation relies on accurate stability prediction. One element of accurate stability prediction is fluid-film bearing properties. Bearing codes are utilized to predict fluid-film bearing properties and these prediction models are validated using various test rigs. Due to systematic errors present in test rigs, estimated bearing coefficients have associated uncertainty. Uncertainty in fluid-film bearing coefficient estimation due to displacement measurement error, force measurement error, and rotor flexibility is analyzed. A single-degree-of-freedom system model is analyzed to understand trends in uncertainties. Computer modeling software is used to develop a modular, high-fidelity model to analyze a test rig for worst-case uncertainty in fluid-film bearing coefficient estimation for a tilting-pad journal bearing. The results show that for high excitation frequencies the uncertainty is large enough that estimated coefficients are practically useless.
Development of High Frequency Virtual Thermocouples
Authors: Braun James , Lu Shengqi , Paniagua Guillermo
Published: August 2017

This paper presents a numerical procedure to enhance the frequency response of temperature probes equipped with two thermocouple junctions of different diameter. The output of the two thermocouples exposed to the same flow transient can be used to predict the output of a virtual smaller thermocouple, which cannot be physically realized. The approach is demonstrated numerically, with the aid of conjugate heat transfer simulations performed with 3D Unsteady Reynolds Averaged Navier-Stokes. The dual junction thermocouple with wire diameters of 50 μm, 25 μm were exposed to several inlet temperatures and pressures to analyze the overall recovery factor. Then multiple unsteady tests were performed. The analysis of those transient tests was used to determine the transfer function in the time domain between the two wires and to perform a digital compensation to predict the performance of a much thinner wire thermocouple. This method was assessed by recovering the theoretical response of the 12.5 μm thermocouple with our dual-junction thermocouple probe for several pressures and wall temperatures. Finally, the procedure was applied to a virtual fine wire thermocouple of 6 μm and a frequency response around 700 Hz.
Numerical Simulation With Adaptive Boundary Method for Predicting Time Evolution of Erosion Processes
Authors: Castorrini Alessio , Corsini Alessandro , Morabito Francescogiuseppe , Rispoli Franco , Venturini Paolo
Published: August 2017

In the present study a new approach to simulate the time evolution of erosion of a target body is presented. An interface algorithm connecting two in-house codes for flow field and particle motion and deposition simulations is developed and presented. The flow solver produces the flow field which is taken as input by the particle tracking and deposition solver, which, in turn, provides the displacements of all the grid nodes due to erosion. The approach is still one-way coupling, since particle motion is governed only by the flow field which is not affected by the particles. However, the interface allows to account for the effect of erosion on flow field and particle motion.

This approach shows a big potential for those applications where a long time simulation is important but not possible with the classical numerical techniques.
Numerical Testing of a Trailing Edge Passive Morphing Control for Large Axial Fan Blades
Authors: Castorrini A. , Corsini A. , Sheard A. G. , Rispoli F.
Published: August 2017

The concept of morphing geometry to control and stabilize the flow has been proposed and applied in several aeronautic and wind turbine applications. We studied the effect of a similar passive system applied on an axial fan blade, analysing potential benefits and disadvantages associated to the passive coupling between fluid and structure dynamics.

The present work completes a previous study made at the section level, giving a view also on the three-dimensional effects.

We use the numerical computation to simulate the system which defines a complex fluid-structure interaction problem. In order to do that, an in-house finite element solver, already used in the previous study, is applied to solve the coupled dynamics.
Design of Directional Probes for High-Frequency Turbine Measurements
Authors: Liu Zhe , Paniagua Guillermo
Published: August 2017

Aerodynamic probes are prevalent in turbomachinery research and gas turbine monitoring. Regrettably, this measurement technique experiences limitations in the transonic range as well as high frequency. Calibrated numerical tools offer an alternative procedure to design suitable instrumentation for each turbine application. In this paper, all the numerical analyses were performed using unsteady Reynolds Averaged Navier Stokes (URANS), two and three-dimensional.

Firstly, two different probe geometries, oval and trapezoidal probe geometries were characterized at different incidence angles. In particular, the pressure recovery, angle sensitivity, induced vortex shedding unsteadiness at several yaw angles were evaluated. The studies were performed over a wide range of Mach numbers from subsonic to the transonic regime. The vortex shedding of the probe was also carefully analyzed. In a second evaluation, we selected the oval probe geometry including the line-cavity effects into the pressure tappings. The resonance frequency of line-cavity system was evaluated and compared with analytical calculations, as well as with the detailed analysis of Bergh and Tijdeman. The comparison of the pressure tapping readings with the actual input signal allowed the identification of the transfer functions, as well as the physical mechanisms that should be corrected during the measurements. Finally, 3D unsteady evaluations were implemented to compute the blockage effects, as well as the final frequency attenuation experienced by the piezo-resistive sensors.
Statistical Anomaly Based Study of Rotating Stall in a Transonic Axial Compressor Stage
Authors: Heinlein G. S. , Chen J. P. , Chen C. M. , Dutta S. , Shen H. W.
Published: August 2017

Tip clearance flow in transonic rotors is known to have a significant effect on compressor performance and stability. The purpose of this study is to employ a novel statistical analysis method as a stall precursor detector and investigate the flow physics underlying stall inception. To allow for natural stall evolution, a full annulus simulation of a transonic axial compressor stage (NASA Stage 35) was utilized. Due to the size of the data set, a statistical analysis was employed to rapidly analyze the entire spatial and temporal simulation domain. The statistical analysis method was performed pointwise on the domain and utilized Entropy in a Grubb’s test to reveal statistically anomalous regions, times, and trends which would be of interest for future evaluation with more standard visualization techniques. Through use of the statistical anomaly detecting Grubbs’ test, rotating stall, which developed in the stage, was tracked back in time to immediately after mass flow stabilization of the stalled operating condition. The Grubbs’ analysis showed a rotating stall cell formed from a rotating disturbance region with a once per revolution mode. Oscillations were also observed in a spiral-type vortex breakdown of the tip clearance vortex. The interaction between the disturbance region and the spiral-type vortex breakdown caused the amplitude of oscillation in the tip vortex to increase in the radial and circumferential directions. The behavior caused local decreases in the mass flow and high loading to the blades in the disturbance region. Eventually, the oscillations led to leading edge spillage and the disturbance region broke down into rotating stall. By tracking anomalies of Entropy in time and space the statistical Grubbs’ test showed the efficacy of the method at detecting the earliest signs of rotating stall.
Sensitivity of Large Eddy Simulations to Inflow Condition and Modeling if Applied to a Transonic High-Pressure Cascade Vane
Authors: Harnieh Mael , Gicquel Laurent , Duchaine Florent
Published: August 2017

Large Eddy Simulation (LES) prediction of the flow around transonic high-pressure turbine cascade vanes is an active subject of research. For such problems, the flow topology is dictated by the geometry, inflow conditions and irreversibilities. When studied experimentally, input specifications necessarily suffer from uncertainties inherent to experimental measurement facilities. Such limits are also present in numerical applications. The following paper proposes to evaluate the relative importance of uncertainty sources in determining the adequate LES flow behaviour for the T120 transonic blade experimentally tested at UniBw (Munich) during the European project AITEB II. To do so, the nominal operating point is targeted and different simulations are obtained by changing inflow specifications with and without turbulence injection. As expected, changes in the static pressure ratio between the inlet and the outlet by more or less 4%, alter significantly the flow topology and the aerodynamic losses. Impact of turbulence injection at inlet is also addressed. Investigation of dissipation fields, including the laminar and sub-grid model contributions, allows the identification of the underlying mechanisms. Although irreversibilities have a smaller impact on the flow prediction relative to the static pressure ratio (and associated uncertainties), its relevance on the flow prediction and topology is found to be of primary importance.
Dynamic Simulation of Startup Characteristics for the Advanced Humid Air Turbine System
Authors: Watanabe Yutaka , Takahashi Toru , Nakamoto Masashi
Published: August 2017

Thermal power generation systems have played an important role to adjust power supply and demand balance in power grid due to the high operational flexibility. It is required for next future thermal power generation systems to have higher thermal efficiency and operational flexibility, not only to reduce CO2 emission but also to cope with the increase of electricity generation by renewable energy sources which are changeable depending on the weather. The Advanced Humid Air Gas Turbine (AHAT) system is expected to meet these requirements and now proceeding with the development by Mitsubishi Hitachi Power Systems Ltd., Central Research Institute of Electric Power Industry (CRIEPI) and Sumitomo Precision Products Co., Ltd. So far, the system concept and cycle performance of the AHAT system were verified by operational tests of a 3MW-class pilot plant and a 40MW-class test facility. However, the characteristics of operational flexibility, such as load following capability and fast startup speed, have not been clarified sufficiently. It is considered that dynamic characteristics analysis is useful to evaluate and improve operational flexibility. On the other hand, CRIEPI is now developing the dynamic analysis tool for thermal power generation systems based on Modelica language using Dymola, in the aim of evaluating operational characteristics of both a new thermal power system and existing thermal power plant. The component models of this tool are basically developed based on mass and energy conservation equations. In this paper, we try to construct the dynamic model using this tool for the startup characteristics analysis and to investigate the possibility of shortening startup speed of AHAT system. First, the validity of the dynamic model of AHAT system was verified compared with the 3MW-class pilot plant operational data. As a result, the simulation result agrees almost well with the operational data and the validity of this dynamic model was confirmed. And next, the startup characteristics in the case of increasing startup load ratio by dynamic simulation were investigated. The simulation result show that it is difficult to achieve the rated power output only by changing startup load ratio because the humidification rate of humidification tower is rate-limiting and the gas turbine exhaust gas temperature reaches the limit value before achieving the rated power output. And it is found that the effects of the water valve operational speed of humidification tower and of the heat capacity of the recuperator are important to shorten the startup time of AHAT system.
An Onion Peeling Reconstruction of the Spatial Characteristics of Entropy Waves in a Model Gas Turbine Combustor
Authors: Wassmer Dominik , Pause Felix , Schuermans Bruno , Paschereit Christian Oliver , Moeck Jonas P.
Published: August 2017

Entropy noise affects thermoacoustic stability in lean pre-mixed gas turbine combustion chambers. It is defined as acoustic noise that is emitted at the first turbine stage due to the acceleration of entropy waves that are advected from the reaction zone in the combustor to the turbine inlet. These non-isentropic temperature waves are caused by equivalence ratio fluctuations which are inherently present in a technically premixed combustion system. To experimentally study the generation and transport of entropy waves, an estimation of the spatial distribution of the entropy spots is highly valuable as it allows the accurate determination of the cross-section averaged entropy, which is the relevant quantity for the formation mechanism of entropy noise at the turbine stage. In this work, a time-of-flight based temperature measurement method is applied to a circular combustion test rig equipped with a premixed swirl-stabilized combustor. Downstream of the burner, an electric spark discharge is employed to generate a narrow acoustic pulse which is detected with a circumferentially arranged microphone array. The measured time of flight of the acoustic signal corresponds to the line-integrated inverse of the speed of sound between the acoustic source and each microphone. By modulating a share of the injected gaseous fuel, equivalence ratio fluctuations are generated upstream of the reaction zone and consequently entropy spots are advected through the axial measurement plane. The spark discharge is triggered at distinct phase angles of the entropy oscillation, thus allowing a time resolved-analysis of the thermo-acoustic phenomenon. Estimating the spatial temperature distribution from the measured line integrated inverse speed of sounds requires tomographic reconstruction. A Tikhonov regularized Onion Peeling is employed to deduce radial temperature profiles. To increase the number of independent data, the spark location is radially traversed, which enhances the resolution of the reconstructed temperature field. A phantom study is conducted, which allows the assessment of the capabilities of the reconstruction algorithm. By means of the reconstructed radial entropy field, spatially resolved entropy waves are measured and their amplitudes and phases are extracted. The characteristics of the entropy waves measured in this way correspond well to former studies.
Numerical Combustion and Heat Transfer Simulations and Validation for a Hydrogen Fueled “Micromix” Test Combustor in Industrial Gas Turbine Applications
Authors: Striegan C. , Haj Ayed A. , Kusterer K. , Funke H. H.-W. , Loechle S. , Kazari M. , Horikawa A. , Okada K. , Koga K.
Published: August 2017

Hydrogen represents a possible alternative gas turbine fuel for future low emission power generation once it can be combined with the use of renewable energy sources for its production. Due to its different physical properties compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for Dry Low NOx (DLN) Hydrogen combustion. This makes the development of new combustion technologies an essential and challenging task for the future of hydrogen fueled gas turbines.

The newly developed and successfully tested “DLN Micromix” combustion technology offers great potential to burn hydrogen in gas turbines at very low NOx emissions. The mixing of hydrogen and air is based on the jet in cross-flow (JICF) principle, where the gaseous fuel is injected perpendicular into the crossing air stream. The reaction takes place in multiple miniaturized diffusion flames with an inherent safety against flashback and the potential of low NOx emissions due to a short residence time of the reactants in the flame region.

Aiming to further develop an existing burner design in terms of an increased energy density, a redesign is required in order to stabilize the flames at higher mass flows while maintaining low emission levels.

For this reason, a systematic numerical analysis using CFD is carried out, to identify the interactions of combustion, radiation and heat conduction in the adjacent burner wall by conjugate heat transfer (CHT) methods. Different combustion models are applied, starting from a hybrid eddy break-up model to more advanced turbulence-chemistry interaction approaches considering detailed chemical mechanisms. Those allow an improved prediction of the different NO-pathways of production and consumption. The results of the simulations are in good agreement with atmospheric test rig data of optical flame structure, measured combustor surface temperatures and NOx emissions.

The numerical methods help reducing the effort of manufacturing and testing to few designs for single validation campaigns, in order to confirm the flame stability and NOx emissions in a wider operating condition field. Further on, the more detailed CFD-simulations support the understanding of decisive mechanisms to reduce the numerical work to the most important models for further industrial applications in future.
Influence of Tip Geometry on Over Tip Leakage in Shrouded Rotor Blades With Cooling
Authors: Tessier Jeffrey , Vogel Gregory
Published: August 2017

Gas turbine blades can be shrouded and designed with “knife edges” to reduce over tip leakages as an attempt to improve turbine stage efficiency. The smaller the tip gap is, the less the amount of leakage and consequently the higher the turbine efficiency. However a zero tip gap between the rotating blade and the stationary casing is simply not practical and not achievable for typical engine operations. One approach often consists of making the stationary shroud at the casing of abradable coating or of softer material in a honeycomb structure. In some cases, it is also common practice to pretrench the honeycomb structure to a certain height to reduce rubbing that could naturally occur with brand new hardware.

This paper details the physical effects occurring between trenched and un-trenched configurations and quantifies the potential loss in turbine stage efficiency and power under such changes.

Because front turbine stages are also cooled, this paper is also detailing the physical effects that are occurring between trenched and un-trenched configurations for a shrouded cooled turbine blade and the associated impact on performance. Since gas turbine are set to run at a specific gas mass flow, the differences between un-trenched and trenched for un-cooled and cooled are compared at the same given gas mass flow conditions.

The paper concludes with key considerations for cooled turbine stage efficiency effects with and without trench.
ECAT: An Engine Component Aerothermal Facility at the University of Oxford
Authors: Kirollos Benjamin , Lubbock Roderick , Beard Paul , Goenaga Frédéric , Rawlinson Anton , Janke Erik , Povey Thomas
Published: August 2017

This paper describes a new engine-parts facility at the University of Oxford for high technology-readiness-level research, new technology demonstration, and for engine component validation.

The Engine Component AeroThermal (ECAT) facility has a modular working section which houses a full annulus of engine components. The facility is currently operated with high-pressure nozzle guide vanes from a large civil jet-engine. A high degree of engine similarity is achieved, with matched conditions of Mach number, Reynolds number, and coolant-to-mainstream pressure ratio. For combustor-turbine interaction studies, a combustor simulator module is used, which is capable of both rich-burn and lean-burn combined temperature, swirl and turbulence profiles.

The facility is being used for aerothermal optimisation research (e.g., novel cooling systems, aerodynamic optimisation problems, capacity sensitivity studies), computational fluid dynamics validation (aerodynamic predictions, conjugate predictions), and for component validation to accelerate the engine design process.

The three key measurement capabilities are: capacity characteristic evaluation to a precision of 0.02%; overall cooling (metal) effectiveness measurements (using a rainbow set of parts if required); and aerodynamic loss evaluation (with realistic cooling, trailing-edge flow etc.). Each of these three capabilities have been separately developed and optimised in other facilities at the University of Oxford in the last 10 years, to refine aspects of facility design, instrumentation design, experimental technique, and theoretical aspects of scaling and reduction of experimental data. The ECAT facility brings together these three research strands with a modular test vehicle for rapid high technology-readiness-level research, demonstration of new technologies, and for engine component validation.

The purpose of this paper is to collect in one place — and put in context — the work that led to the development of the ECAT facility, to describe the facility, and to illustrate the accuracy and utility of the techniques by presenting typical data for each of the key measurements.

The ECAT facility is a response to the changing requirements of experimental turbomachinery testing, and it is hoped this paper will be of interest to engine designers, researchers, and those involved in major facility developments in both research institutes and engine companies.
A One-Dimensional Gas Dynamics Code for Turbocharger Turbine Pulsating Flow Performance Modelling
Authors: Feneley Adam , Pesiridis Apostolos , Chen Hua
Published: August 2017

As governments around the world ramp up their efforts to reduce CO2 emissions, downsizing internal combustion engines has become a dominant trend in the automotive industry. Air charging systems are being utilised to increase power density and therefore lower emissions by downsizing internal combustion engines. Turbocharging represents the majority of these air charging systems, which are commonly adopted for commercial and passenger vehicles. The process of matching turbomachinery to an engine during early-stage development is important to achieving maximum engine performance in terms of power output and the reduction of emissions.

Despite on-engine conditions providing highly unsteady gas flows, current turbocharger development commonly uses performance maps that are produced from steady state measurements. There are other significant sources of error to be found in early stage turbocharger performance prediction, such as the omission of heat transfer effects, and the use of data extrapolation methods to cover the entire operating range of a device from limited data sets. Realistic engine conditions provide a complex heat transfer scenario, which is dependent upon load history and the component layout of the engine bay. Heat transfer effects are particularly prevalent at low engine loads, whilst pulsating effects are significant at both high and low engine speeds (and therefore exhaust pulse frequency). Compressor maps are often provided by manufacturers with a level of heat transfer corresponding to a gas stand test, not realistic engine conditions. This causes a mismatch when using the aforementioned maps in commercial engine codes. This reduces the quality of overall engine performance predictions, since as the temperature of the exhaust gas on the turbine side rises, the performance prediction increasingly deviates from the usual adiabatic assumption used in simulations.

In the present work, a one-dimensional unsteady flow model has been developed to predict the performance of a vaneless turbine under pulsating inlet conditions, with scope to account for heat transfer effects. Flow within the volute is considered to be one-dimensional and unsteady, with mass addition and withdrawal used to simulate the gas flow between the volute and rotor. Rotor passages are also treated as one-dimensional and unsteady, with the equations being solved by the method of characteristics. This model is able to simulate the circumferential feeding of the rotor from the casing, unlike many previous zero and one-dimensional models. Building upon previous work, the basis of this code has been constructed in C++ with future integration with other modern gas dynamics codes in mind. By providing the appropriate instantaneous operating conditions at specified time intervals, a code such as this could theoretically negate the need for maps produced by steady-state data.