bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of a FLOX®-Based Combustor for a Micro Gas Turbine With Exhaust Gas Recirculation
Authors: Hasemann S. , Huber A. , Naumann C. , Aigner M.
Published: August 2017

Micro gas turbines (MGT) offer interesting advantages for the use in combined heat and power (CHP) systems. A possibility to raise the total efficiency of a MGT is the introduction of an external exhaust gas recirculation (EGR). The composition of the working fluid due to EGR affects the combustion process and the formation of pollutants. Changes in flame position, flame volume and flame intensity as well as rising CO emissions in state of the art industrial burners have been described by several authors before. This paper describes the experimental investigation of a single stage FLOX®-based combustor for a MGT in the power range of 1–3 kWel applied with EGR. The tests were performed on an atmospheric test rig with optical access. The combustion air was preheated up to 718 °C and diltued with N2, CO2 and steam. A probe of the exhaust gas was analyzed for emissions and OH* chemiluminescence measurements were performed. In addition to the experiments, chemical kinetic simulations were performed. Results show, that the examined combustor is able to work stable even at very low oxygen levels (down to 12.6 %) at combustor inlet, although the possible range of operation under EGR conditions is reduced. The measured increase of CO emissions matches to the performed simulations.
The Relevance of Damper Pre-Optimization and its Effectiveness on the Forced Response of Blades
Authors: Gastaldi Chiara , Berruti Teresa M. , Gola Muzio M.
Published: August 2017

The paper presents a calculation procedure for the design of turbine blades with underplatform dampers. The procedure involves damper “pre-optimization” before the coupled calculation with the blades.

The pre-optimization procedure excludes, since the early design stage, all those damper configurations leading to low damping performance. Pre-optimization involves plotting a design “damper map” with forbidden areas, corresponding to poorly performing damper geometries and admissible design areas, where effective solutions for the damper shape can be explored. Once the candidate damper configurations have been selected, the damper equilibrium equations are solved by using both the multi-harmonic balance (MHB) method, and the direct time integration method (DTI). Direct time integration of the damper dynamic equations is implemented in order to compute the trend of the contact forces in time and the shape of the hysteresis cycles at the different contact points. Based on these trends, the correct number of Fourier terms to represent the contact forces on the damper is chosen. It is shown that one harmonic term together with the static term, are enough in the MHB calculation of a pre-optimized damper.

The proposed method is applied to a test case of a damper coupled with two blades. Experimental forced response functions of the test case with a nominal damper are available for comparison. The purpose of this paper is to show the effectiveness of the “damper maps” in excluding all those damper configurations, leading to undesirable damper behavior and to highlight the strong influence of the blades mode of vibration on the damper effectiveness. From the comparison of dampers with different geometrical parameters, the pre-optimized damper proved to be not only the most effective, in terms of damping capability, but also the one that leads to a faster and more flexible calculation of the damper, coupled with the blades.
Fan Blade Tip Aerodynamics With Realistic Operational Casing Geometries and Clearances
Authors: John Alistair , Qin Ning , Shahpar Shahrokh
Published: August 2017

During engine operation fan casing abradable liners are worn by the blade tip, resulting in the formation of trenches. This paper investigates the influence of these trenches on the fan blade tip aerodynamics. A detailed understanding of the tip flow features for the fan blade under investigation is developed. A parametric model is then used to model trenches in the casing above the blade tip. It is shown that increasing clearance via a trench reduces performance by less than increasing clearance through cropping the blade tip. A response surface method is then used to generate a model that can predict fan efficiency for a given set of clearance and trench parameters. It is shown that the efficiency sensitivity to clearance is greater for cropped tips than trenches, and is biased towards the leading edge for cropped tips, and the trailing edge for trenches.
Determining Stress in Turbocharger Impellers due to Component Machining Process
Authors: Barrans Simon M. , Tabriz Md Shams E. , Ellis Christian F.
Published: August 2017

Turbocharger impeller wheels are traditionally manufactured using a casting process. However, with the improvement of multi-axial machining technology, machined impeller wheels are becoming popular among turbo machinery manufacturers due to their enhanced durability. Nonetheless, machining a complex impeller shape from a solid billet, results in tool marks being left on the component surface. As presented in this paper, repeatedly running a wheel to 5% beyond the design speed limit can result in fatigue failure initiating from the machining marks.

In this paper, the ‘as machined’ geometry of sample wheels has been determined using both CT scanning and optical surface measurement techniques. The data from these measurements has been used to generate solid CAD models suitable for finite element analysis to simulate the stress distribution of reverse engineered wheels. The maximum principal stress predicted is 15% higher than that obtained from the nominal CAD model. In order to model the measured geometry efficiently, a novel technique has been used to enforce cyclic symmetry on geometry that is not precisely cyclically symmetric.

The work has demonstrated that it is possible to predict the stress raising effect of the machining marks at the design stage. The analysis methodology presented in the paper will enable future integrated optimisation of both the design and manufacture of impeller wheels to ensure that wheels with a specified operating envelope are machined as efficiently as possible.
Analysis of the Thermodynamic Potential of Supercritical Carbon Dioxide Cycles: A Systematic Approach
Authors: Crespi Francesco , Gavagnin Giacomo , Sánchez David , Martínez Gonzalo S.
Published: August 2017

Since the renewed interest in supercritical carbon dioxide cycles, a large number of cycle layouts have been proposed in literature. These analyses, which are essentially theoretical, consider different operating conditions and modelling assumptions and thus the results are not comparable.

There are also works that aim to provide a fair comparison between different cycles in order to assess which one is most efficient. These analyses are very interesting but, usually, combine thermodynamic and technical restrictions thus making it difficult to draw solid and general conclusions with regards to which the cycle of choice in the future should be .

With this background, the present work provides a systematic thermodynamic analysis of twelve supercritical carbon dioxide cycles under similar working conditions, with and without technical restriction in terms of pressure and/or temperature. This yields very interesting conclusions regarding which the most interesting cycles are amongst those proposed in literature. Also, useful recommendations are extracted from the parametric analysis with respect to the directions that must be followed when searching for more efficient cycles.

The analysis is based on efficiency and specific work diagrams with respect to pressure ratio and turbine inlet temperature in order to enhance their applicability to plant designs driven by fuel economy and/or footprint.
A Numerical Study of Ethanol-Water Droplet Evaporation
Authors: Lupo Giandomenico , Duwig Christophe
Published: August 2017

The present effort focuses on detailed numerical modelling of the evaporation of an ethanol-water droplet. The model intends to capture all relevant details of the process: it includes species and heat transport in the liquid and gas phases, and detailed thermo-physical and transport properties, varying with both temperature and composition. Special attention is reserved to the composition range near and below the ethanol/water azeotrope point at ambient pressure. For this case, a significant fraction of the droplet lifetime exhibits evaporation dynamics similar to those of a pure droplet. The results are analysed and model simplifications are examined. In particular, the assumptions of constant liquid properties, homogeneous liquid phase composition and no differential volatility may not be valid depending on the initial droplet temperature.
Direct and Indirect Noise Generated by Injected Entropic and Compositional Inhomogeneities
Authors: Rolland Erwan O. , De Domenico Francesca , Hochgreb Simone
Published: August 2017

Flow disturbances are generated inside a duct via pulsed injection of helium into a flow of air. This leads to the generation of an acoustic pulse (direct noise), as well as the production of entropic and compositional inhomogeneities which are convected with the mean flow. As these inhomogeneities are convected through a choked nozzle, they generate indirect noise. The resulting acoustic pressure fluctuations are measured experimentally using pressure transducers upstream of the nozzle. Insight obtained from theoretical models and a time-delay analysis can be used to isolate and extract the contributions of direct and indirect noise in the experimental signal. These results are directly compared to existing one-dimensional direct and indirect noise models. The experimental measurement of indirect noise is found to be in good agreement with the theoretical models for entropy noise and compositional noise for a compact one-dimensional isentropic nozzle.
Effect of Heat Transfer on Pipe Flow Stability
Authors: Zhang Ce , Ma Wei , Yu Wensheng , Teng Jinfang
Published: August 2017

The compressibility of flow field has an important effect on flow stability. However, when the compressibility is considered, the effect of Mach number is often considered while the effect of heat transfer is always neglected in the existing flow stability studies. Linear stability analysis tools based on compressible Orr-Sommerfeld (O-S) equations and linearized Navier-Stokes equations in cylindrical coordinate system are established in this paper. These equations are numerically solved by using Chebyshev spectral collocation method and pseudo-modes are eliminated. Linear stability analysis of pipe flow with heat transfer whose average flow field is obtained by CFD simulation is carried out. The results show that for spatial modes, the heating effect of the wall makes pipe flow more unstable, while cooling effect of the wall makes pipe flow more stable. For global modes of pipe flow, the frequency of global mode decreases when the wall cools the flow and the decrease of mean temperature of pipe flow leads to the improvement of global mode stability.
Numerical Study on the Influence of Tip Clearance on Rotating Stall in an Unshrouded Centrifugal Compressor
Authors: Ju Wenying , Xu Shengli , Wang Xiaofang , Chen Xudong , Yang Shuhua , Meng Jigang
Published: August 2017

Whole annulus unsteady simulations are performed by CFD with the whole flow passage model from inlet guide vanes to volute of an unshrouded centrifugal compressor. Characteristics and development mechanism of rotating stall are analyzed including the flow field and the impeller blade load in time and frequency domain. Rotating stall with three cells is observed in both two actual operation conditions but the cell rotating speed and the forming process is different. Leading edge tip clearance leakage is a criterion to predict the formation of a spike stall in centrifugal compressors. Tip clearance flow also plays an important role in the moving of rotating instabilities and the propagation of stall cells. It can effectively slow down the stall forming and decrease the pressure load on blade by reduced the tip clearance size at the leading edge.
Parametric Investigation of Gurney Flaps for the Use on Wind Turbine Blades
Authors: Alber Joerg , Pechlivanoglou Georgios , Paschereit Christian Oliver , Twele Jochen , Weinzierl Guido
Published: August 2017

This paper presents a strategy to model the aerodynamic Gurney flap effect on two-dimensional airfoils and subsequently on the rotor blade performance of horizontal axis wind turbines.

The first part consists of the parametric investigation of 26 airfoil polar data-sets, derived from different, but comparable, wind tunnel experiments. They are evaluated and processed in terms of the lift and drag increase caused by Gurney flaps in comparison to each Baseline configuration. Consequently, a model is developed, transforming Baseline- into Gurney flap polar data for varying flap-heights. The results of the emerging Gurney Flap Polar Calculator are validated against the experimental lift and drag curves.

In the second part, the blade design of the NREL 5 MW Reference Turbine is modified by implementing polar data-sets of varying Gurney flap-heights, which are imported into the rotor simulation software QBlade. Thereupon, blade optimization strategies are examined regarding the two main Gurney flap applications on rotor blades: the retrofit and the design solution. The optimized retrofit solution on existing blades indicates power performance improvements, albeit at the expense of increasing structural loads. The optimized design solution on to-be-constructed blades, on the other hand, suggests chord-length reductions, while keeping the performance characteristics on a similar or even enhanced level.

It is concluded that aerodynamic improvements are achieved by relatively small Gurney flap-heights, which are applied at specific blade positions.
Experimental Study of Aeronautical Ignition in a Swirled Confined Jet-Spray Burner
Authors: Marrero-Santiago J. , Verdier A. , Brunet C. , Vandel A. , Godard G. , Cabot G. , Boukhalfa M. , Renou B.
Published: August 2017

Aeronautical gas turbine ignition is still not well understood and its management and control is mandatory for new lean-burner designs. The fundamental aspects of swirled confined two-phase flow ignition are addressed in the present work. Two facilities enable the analysis of two characteristic phases of the process. The KIAI-Spray single-injector burner was investigated in terms of local flow properties, including the air velocity and droplet fuel (n-heptane) size-velocity characterization by phase Doppler anemometry (PDA), and the study of local equivalence ratio by means of planar laser induced fluorescence (PLIF) on a tracer (toluene). The initial spark location inside the chamber is vital to ensure successful ignition. An ignition probability map was elaborated varying the location of a 532 nm laser-induced spark in the chamber under ultra-lean nominal conditions (ϕ = 0.61). The outer recirculation zone (ORZ) was found to be the best region for placing a spark and successfully igniting the mixture. A strong correlation was found between the ignition probability field and the airflow turbulent kinetic energy and velocity fields. Local equivalence ratio enhances the importance of the ORZ. Once a successful ignition is accomplished on one injector, the injector-to-injector flame propagation must be examined. High-speed visualization through two synchronized perpendicular cameras was applied on the KIAI-Spray linear multi-injector burner. Four different injector-to-injector distances and four fuels of different volatilities (n-heptane, n-decane, n-dodecane and jet-A1 kerosene) were evaluated. Spray branches and inter-injector regions changed with the inter-injector distance. Two different flame propagation mechanisms were identified: the direct radial propagation and the arc propagation mode. Ignition delay times were modified with the injector-to-injector distance and with the different fuels.
Multi-Fidelity Modelling of a Fully-Featured HP Turbine Stage
Authors: Occhioni Giorgio , Shahpar Shahrokh , Li Haidong
Published: August 2017

An improvement in overall efficiency and power output for gas turbine engines can be obtained by increasing the combustor exit temperature, but the thermal management of metal parts exposed to hot gases is challenging. Discrete film cooling, combined with internal convective cooling is the current state-of-the-art available to aerothermal designers of these components. To simplify the simulation problem in the aerodynamic design phase, it is common practice to replace the cooling holes with source strips applied to the blade. This could lead to inaccuracies in high pressure turbine performance prediction. This study has been carried out on a fully-featured high pressure turbine stage using high-fidelity simulations. The film cooling holes on the nozzle guide vane and on the rotor are initially modelled using a strip model approach. Then, to increase the model fidelity, the strips on the suction side of the rotor are replaced with discrete fan shaped film cooling holes. A rigid body rotation is also applied to the nozzle guide vane to vary the stage capacity and reaction. The effects of the mesh topology & resolution are also taken into account. The results obtained with these two approaches are then compared, giving the designers a better understanding on film cooling modelling and relationship between capacity, reaction and performance. The accurate prediction of the complex interaction between cavity inflows and the main-flow, still represent a challenge for the state of the art RANS solvers. Hence, an unsteady phase-lag approach has been used to overcome the RANS limitations. A validation of the unsteady solutions has been carried out with respect to experimental data.
Numerical Study on the Reduction of NOx Emissions From Pulse Detonation Combustion
Authors: Djordjevic Neda , Hanraths Niclas , Gray Joshua , Berndt Phillip , Moeck Jonas
Published: August 2017

A change in the combustion concept of gas turbines from conventional isobaric to constant volume combustion (CVC), such as in pulse detonation combustion (PDC), promises a significant increase in gas turbine efficiency. Current research focuses on the realization of reliable PDC operation and its challenging integration into a gas turbine. The topic of pollutant emissions from such systems has so far received very little attention. Few rare studies indicate that the extreme combustion conditions in PDC systems can lead to high emissions of nitrogen oxides (NOx). Therefore, it is essential already at this stage of development to begin working on primary measures for NOx emissions reduction, if commercialization is to be feasible.

The present study evaluates the potential of different primary methods for reducing NOx emissions produced during pulsed detonation combustion of hydrogen. The considered primary methods involve utilization of lean combustion mixtures or its dilution by steam injection or exhaust gas recirculation. The influence of such measures on the detonability of the combustion mixture has been evaluated based on detonation cell sizes modelled with detailed chemistry. For the mixtures and operating conditions featuring promising detonability, NOx formation in the detonation wave has been simulated by solving the one-dimensional reacting Euler equations. The study enables an insight into the potential and limitations of considered measures for NOx emissions reduction and lays the groundwork for optimized operation of pulse detonation combustion systems.
Transient Thermal Modelling of Whole GT Engine With a Partly Coupled FEM-Fluid Network Approach
Authors: Giuntini Sabrina , Andreini Antonio , Facchini Bruno , Mantero Marco , Pirotta Marco , Olmes Sven , Zierer Thomas
Published: August 2017

The present work aims at investigating a new methodology developed at Ansaldo Energia, for the transient finite element modelling of the whole engine with an axisymmetric approach.

The strong coupling and non linearity in the heat transfer process during transient thermal analyses are handled by a partly coupled scheme. The 2D axisymmetric finite element model includes a dedicated thermal fluid network where fluid-metal temperatures are computed. In the overall procedure the selected finite element solver is a customized version of CalculiX®, while mass flow rates and pressure distributions in each thermal fluid network element are provided by external fluid network solvers in terms of customized time series.

This paper represents a first insight about a fully integrated WEM (Whole Engine Modelling) procedure currently under development. Geometrical changes during operation, lead to different fluid properties affecting heat transfer coefficients too. These modified conditions in their turn impact the material temperature and displacements. The future implementation steps will be oriented on the adoption of a customized version of the native CalculiX® fluid network solver with the aim of developing a fully integrated procedure able to take into account the interaction between the secondary air system and the modifications in the clearances and gaps due to the thermal and mechanical loads.

In this paper, a detailed description of the procedure will be reported with comprehensive discussions about some fundamental modelling aspects. Preliminary results, related to the first application of the new methodology to the transient thermal modelling of a simplified test case representative of real engine geometries, will be presented.
Effect of Inflow Circumferential Distortion on a Transonic Axial Compressor
Authors: Li Yuyun , Wang Zhiheng , Xi Guang
Published: August 2017

The Inlet distortion, which may lead to the stability reduction or structure failure, is often non-ignorable in an axial compressor. In the paper, the three-dimensional unsteady numerical simulations on the flow in NASA rotor 67 are carried out to investigate the effect of inlet distortion on the performance and flow structure in a transonic axial compressor rotor. A sinusoidal circumferential total pressure distortion with eleven periods per revolution is adopted to study the interaction between the transonic rotor and inlet circumferential distortion. Concerning the computational expense, the flow in two rotor blade passages is calculated. Various intensities of the total pressure distortion are discussed, and the detailed flow structures under different rotating speeds near the peak efficiency condition are analyzed. It is found that the distortion has a positive effect on the flow near the hub. Even though there is no apparent decrease in the rotor efficiency or total pressure ratio, an obvious periodic loading exists over the whole blade. The blade loadings are concentrated in the region near the leading edge of the rotor blade or regions affected by the oscillating shocks near the pressure side. The time averaged location of shock structure changes little with the distortion, and the motion of shocks and the interactions between the shock and the boundary layer make a great contribution to the instability of the blade structure.
The Response to Incident Acoustic Waves of the Flow Field Produced by a Multi-Passage Lean-Burn Aero-Engine Fuel Injector
Authors: Treleaven Nicholas C. W. , Su Jialin , Garmory Andrew , Page Gary J.
Published: August 2017

Previous work has shown that compressible unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, with suitable acoustic boundary conditions, are capable of correctly predicting the acoustic impedance of simplified fuel injectors. In this work the method developed is applied to simulating the acoustically forced flow in and downstream of a realistic multipassage fuel injector. The simulations are validated by comparing the impedance of the injector with data obtained experimentally by a multi-microphone technique. Such results can then be used in conjunction with a suitable low-order thermo-acoustic network model to predict the stability of combustors. However the validated simulations can also be used to reveal further details about the effect of acoustic forcing on the flow field.

The velocity flow field produced by the injector with and without acoustic forcing is analysed using snapshot POD to determine the large scale energy containing structures within the flow. In the non-acoustically forced simulations it was found that the first four POD modes correspond to two rotating spiral modes, designated as the m = 1 and m = 2 modes with a peak frequency content of 450 Hz for the first mode and 1000 Hz for the second mode corresponding to experimental Hot-Wire measurements made in a separate study. It is hypothesised that these spiral modes will affect the atomisation, evaporation and mixing of the fuel in subsequent planned two-phase simulations. POD analysis of the flow subjected to 300 Hz, 300 Pa acoustic excitation shows that the first four POD modes correspond to similarly shaped spiral modes. The acoustic excitation is responsible for the appearance of 4 POD modes within the injector body that correspond to two push-pull velocity modes with axes of symmetry perpendicular to each other. The acoustic forcing also produces two additional POD modes that most likely represent the non-linear interaction between the push-pull and spiral modes.

Further analysis of the fluctuations in pressure, mass flow rate, angular velocity and swirl number, within the passages and at the injector exit plane, show that the fluctuations in pressure and mass flow rate average across the passages while variations in angular velocity and swirl number sum across the passages. The relationship between mass flow rate, angular velocity and swirl number is discussed with reference to general observations of the sensitivity of flames to fluctuations in these quantities.
Effect of Rayleigh-Taylor Instability on Backward-Facing-Step Stabilized Turbulent Premixed Flames
Authors: Long Brandon S. , Briones Alejandro M. , Stouffer Scott D. , Rankin Brent A.
Published: August 2017

A computational investigation of centrifugal force effects on backward-facing-step stabilized turbulent premixed propane-air flames is conducted. The centrifugal force acts from the high-density reactants towards the low-density products creating a Rayleigh-Taylor instability. A straight channel with an infinite radius of curvature and a backward-facing step is used as the baseline. A curved channel (referred to as a centrifuge in this work) with a finite radius of curvature and a backward-facing step on the outer radius is used to evaluate the effects of centrifugal force on turbulent flame speeds. Three-dimensional simulations are performed using Reynolds-averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES). The computational results are compared with broadband chemiluminescence and shadowgraph images reported in the literature for similar conditions and geometries. The past experiments and current simulations show that increasing the inlet velocity in the straight channel and centrifuge results in a flame cannot withstand the high stretch rates and the flame is positioned behind the backward-facing step. The measured and computed shadowgraphs for the straight channel and centrifuge demonstrate that by increasing the inlet flow velocity the flame becomes hydrodynamically unstable, characterized by heterogeneous and anisotropic turbulent flow, and a large density variation occurs further downstream. The RANS and LES computations qualitatively capture these trends, but the LES results show better agreement with the experimental broadband chemiluminescence and shadowgraph images. It is challenging to decouple the combined effects of turbulence fluctuations and Rayleigh-Taylor induced centrifugal acceleration on turbulent flames speeds. However, the combined effects of turbulence fluctuations and centrifugal acceleration appear to promote increased turbulent flame speeds and at high enough inlet velocities, allow the flame to exist where it would otherwise blowout.
Continuous Closed-Loop Transonic Linear Cascade for Aero-Thermal Performance Studies in Micro-Turbomachinery
Authors: Yakirevich E. , Miezner R. , Leizeronok B. , Cukurel B.
Published: August 2017

The present work summarizes the design process of a new continuous closed-loop hot transonic linear cascade. The facility features fully modular design which is intended to serve as a test bench for axial micro-turbomachinery components in independently varying Mach and Reynolds numbers ranges of 0 – 1.3 and 2·104 – 6·105 respectively. Moreover, for preserving heat transfer characteristics of the hot gas section, the gas to solid temperature ratio (up to 2) is retained. This operational environment has not been sufficiently addressed in prior art, although it is critical for the future development of ultra-efficient high power or thrust devices.

In order to alleviate the dimension specific challenges associated with micro-turbomachinery, the facility is designed in a highly versatile manner, and can easily accommodate different geometric configurations (pitch, ±20° stagger angle, ±20° incidence angle), absent of any alterations to the test section. Owing to the quick swap design, the vane geometry can be easily replaced without manufacturing or re-assembly of other components. Flow periodicity is achieved by the inlet boundary layer suction and independently adjustable tailboard mechanisms. Enabling test-aided design capability for micro gas turbine manufacturers, aero-thermal performance of various advanced geometries can be assessed in engine relevant environments.
Research on Failure of Semi-Open Centrifugal Impeller Under Aerodynamic Load
Authors: Chen Xudong , Xu Shengli , Wang Xiaofang , Ju Wenying , Yang Shuhua , Meng Jigang
Published: August 2017

The designs of centrifugal compressors are pushed towards higher pressure ratios, higher mass flow rates, and wider operating conditions. As the change of the actual condition, compressors often operate at low flow rates. There are some important unstable flow conditions at low flow rates such as rotating stall. The exciting forces may cause blade resonance and high dynamic stress level. High cycle fatigue failure is one of the main damage form of compressor impellers. Therefore, the dynamic stress prediction of impeller is an important part of compressor design and failure analysis. This paper is concerned with the prediction of dynamic stress of an actual damaged semi-open centrifugal impellers under unsteady aerodynamic load using a full nonlinear damping model which includes material and aerodynamic damping. Material damping is predicted based on an empirical equation and expressed as a function of stress amplitude. Aerodynamic damping is predicted through unidirectional fluid-structure interaction analysis. In this paper, the aerodynamic damping of the semi-open centrifugal impeller with various vibration amplitudes, modes and operation conditions is estimated. The numerical result indicates that, the material damping increases with the increasing stress amplitude while the aerodynamic damping is independent of the blade vibratory amplitude for a given blade mode. A nonlinear total damping model is then proposed, including both material and aerodynamic damping. The contribution of material damping plays an important part in total damping estimation as well as the aerodynamic damping. With this model, a procedure for dynamic stress estimation is proposed. Aerodynamic load on the surface of the impeller obtained by transient CFD calculation and the load in frequency domain obtained by Fast Fourier Transformation (FFT). Comparing normal condition with low flow condition, the main frequencies of the aerodynamic load are basically coincident and the load amplitude increases significantly under low flow rate. The main frequencies at the leading edge of blades are 4 times, 5 times and 6 times rotation frequency. They may be caused by rotating stall and excite the impeller. As the load of 5 times rotation frequency is maximum, harmonic analysis is performed to estimate the dynamic stress of the semi-open centrifugal compressor blades under the load. The result shows that the resonance stress at the leading edge of the blade under low flow condition is 22 times up on the stress under normal condition. The result of fatigue strength assessment shows that fatigue damage may occur at the leading edge of blades and it is consistent with the actual damaged position of the impeller. Therefore, fatigue damage is likely to happen under low flow rate condition. It is necessary to consider the situation carefully during the design of compressors.
Effect of Uneven Wall Heating Conditions Under Different Buoyancy Numbers for a One Side Rib-Roughened Rotating Channel
Authors: Wang Zhi , Corral Roque
Published: August 2017

This paper investigates the impacts of uneven wall heating conditions under different Buoyancy numbers on flow field and heat transfer performance of a rotating channel with one side smooth and one side roughened by 45 degree inclined ribs. Parametric RANS simulations were conducted under two different wall heating conditions: only ribbed wall heated, as in experiment setup, and all walls heated, under three different Buoyancy numbers. Results are compared, when available, with experimental results.

Numerical results show that uneven wall heating has only a minor impact on non-rotating cases and very low buoyancy rotating cases. However, it has a significant influence, on both, the heat transfer behaviour and the flow field, when the Buoyancy number is large. In the ribbed trailing rotating tests, the all walls heated cases show significantly higher heat transfer rate than only the ribbed wall heated cases. The discrepancy is enlarged as Buoyancy number increases. The heat transfer in the all walls heated case increases monotonically with the Buoyancy number whereas in the ribbed wall heated case is slight reduced. In the ribbed leading rotating tests, the heat transfer sensitivity to the heating conditions is not conspicuous, and for both cases, the heat transfer level slightly reduced as Buoyancy number increases.

The flow field investigation shows that, there is a significant displacement of main flow in the all walls heated cases than only the ribbed wall heated cases under high Buoyancy numbers. This displacement is due to the buoyancy effect and responsible for the heat transfer differences in uneven heating problems. According to the results obtained in the paper, we conclude that when buoyancy effects are relevant, the heating settings can play a significant role in the heat transfer mechanisms and therefore in the experimental and numerical results.
Measurements of Radial Vortices, Spill Forward and Vortex Breakdown in a Transonic Compressor
Authors: Brandstetter Christoph , Jüngst Maximilian , Schiffer Heinz-Peter
Published: August 2017

The phenomena prior to rotating stall were investigated in a high-speed compressor test rig using optical and pneumatic measurement techniques. A number of throttling procedures was performed at transonic and subsonic speedlines with the aim to detect the unsteady effects initiating rotating stall or large amplitude blade vibrations. At transonic speed radial vortices traveling around the circumference were detected in the upstream part of the rotor using phase-locked PIV measurements above 92% span and unsteady wall pressure measurements. When these radial vortices impinge on a blade leading edge, they cause a forward spill of fluid around the leading edge. The effects are accompanied by a large-scale vortex breakdown in the blade passage leading to immense blockage in the endwall region. At subsonic speeds, the observed flow phenomena are similar but differ in intensity and structure.

During the throttling procedure, blade vibration amplitudes were monitored using strain gauges and blade tip timing instrumentation. Non-synchronous blade vibrations in the first torsional eigenmode were measured as the rotor approached stall. Using the different types of instrumentation, it was possible to align the aerodynamic flow features with blade vibration levels. The results show a clear correlation between the occurrence of radial vortices and blade vibrations.
Comparison of 3D Unsteady Transient Conjugate Heat Transfer Analysis on a High Pressure Cooled Turbine Stage With Experimental Data
Authors: Liu Jong-Shang , Morris Mark C. , Malak Malak F. , Mathison Randall M. , Dunn Michael G.
Published: August 2017

In order to have higher power to weight ratio and higher efficiency gas turbine engines, turbine inlet temperatures continue to rise. State-of-the-art turbine inlet temperatures now exceed the turbine rotor material capability. Accordingly, one of the best methods to protect turbine airfoil surfaces is to use film cooling on the airfoil external surfaces. In general, sizable amounts of expensive cooling flow delivered from the core compressor are used to cool the high temperature surfaces. That sizable cooling flow, on the order of 20% of the compressor core flow, adversely impacts the overall engine performance and hence the engine power density. With better understanding of the cooling flow and accurate prediction of the heat transfer distribution on airfoil surfaces, heat transfer designers can have a more efficient design to reduce the cooling flow needed for high temperature components and improve turbine efficiency. This in turn lowers the overall specific fuel consumption (SFC) for the engine. Accurate prediction of rotor metal temperature is also critical for calculations of cyclic thermal stress, oxidation, and component life.

The utilization of three-dimensional computational fluid dynamics (3D CFD) codes for turbomachinery aerodynamic design and analysis is now a routine practice in the gas turbine industry. The accurate heat-transfer and metal-temperature prediction capability of any CFD code, however, remains challenging. This difficulty is primarily due to the complex flow environment of the high-pressure turbine, which features high speed rotating flow, coupling of internal and external unsteady flows, and film-cooled, heat transfer enhancement schemes. In this study, conjugate heat transfer (CHT) simulations are performed on a high-pressure cooled turbine stage, and the heat flux results at mid span are compared to experimental data obtained at The Ohio State University Gas Turbine Laboratory (OSUGTL). Due to the large difference in time scales between fluid and solid, the fluid domain is simulated as steady state while the solid domain is simulated as transient in CHT simulation. This paper compares the unsteady and transient results of the heat flux on a high-pressure cooled turbine rotor with measurements obtained at OSUGTL.
A Low Cycle Fatigue Life Prediction Model of Single Crystal Nickel-Based Superalloys Using Critical Plane Approach Combined With Crystallographic Slip Theory
Authors: Mu Lijuan , Dong Xuezhi , Gao Qing , Tian Yongsheng , Tan Chunqing
Published: August 2017

The anisotropy is the most remarkable characteristic for single crystal nickel-based superalloys, which makes fatigue behavior and life prediction highly correlate with the crystallographic orientation. Based on critical plane approach and preferred crystallographic slip mechanism, an anisotropic LCF life model is proposed to account for orientation-dependent fatigue life in this paper. In addition, the effects of the mean stress and stress-weakening caused by asymmetric loading are also considered. The critical plane is determined by searching for 30 potential slip systems. Moreover, the slip plane with the maximum resolved shear stress amplitude in the crystallographic microstructure of the single crystal nickel-based superalloy is chosen as the critical plane.

The LCF test data are utilized to obtain the regression equation by multiple linear fitting method. The presented LCF life model is applicable for more complex stress state and has higher prediction accuracy than the CDY model.
Long-Term Oxidation Resistance of Several Precipitation Strengthened Ni-Based Superalloys
Authors: Meyer Joseph , Deodeshmukh Vinay
Published: August 2017

Precipitation strengthened alloys are a staple material in the gas-turbine industry due to their excellent creep and mechanical strength. HAYNES® 282® alloy was developed to have excellent creep resistance while maintaining good fabricability and thermal stability. However, its long-term oxidation resistance has not been fully established. The purpose of this paper is to present yearlong oxidation data of 282 alloy at 871°C (1600°F) and to rank it with well-known gamma prime strengthened alloys: 263 alloy, R-41 alloy, and Waspaloy alloy. The oxidation resistance of each alloy was ranked based on weight change behavior, metal recession, Cr depletion, and microstructure. It was found that at 871°C, 282 alloy had oxidation resistance similar to 263 alloy but better than Waspaloy alloy.
Acoustic Combustor Forcing by Unsteady Air Injection Into a Nozzle With High Subsonic Mean Flow
Authors: Niether Sebastian , Hanraths Niclas , Paschereit C. Oliver , Panek Lukasz , Moeck Jonas P.
Published: August 2017

Modern stationary gas turbines potentially suffer from thermoacoustic instabilities due to emission constraints and the resulting need for lean premixed combustion. In the development process, thermoacoustic characteristics are assessed with combustion tests employing acoustic excitation. In this work an actuator principle is developed that allows for high amplitude, phase accurate excitation at multiple frequencies simultaneously, while being able to operate in the harsh environment of an industrial combustion test rig. It is based on a proportional valve for gas flow modulation that injects pressurized air into a nozzle-like section downstream of the combustion chamber. In this section the main air flow is accelerated, which simulates the first turbine stage. Injection of modulated air causes blockage of the exhaust gas flow, generating high sound pressure amplitudes. As a demonstration of the effectiveness of the proposed approach, the actuator is used to control combustion instability with a closed-loop algorithm. A reduction of over 55 % of the oscillation amplitude is achieved. Additionally, it is shown that the modulated air injection inside the nozzle throat generates similar sound pressure amplitudes as a siren-type actuation with the same stationary blockage level. The amplitude can be further increased by inclining the injection axis towards the incoming main air flow.
Catalytic Influence of Water Vapor on Lean Blowoff and NOx Reduction for Pressurised Swirling Syngas Flames
Authors: Pugh Daniel , Bowen Philip , Crayford Andrew , Marsh Richard , Runyon Jon , Morris Steven , Giles Anthony
Published: August 2017

It has become increasingly cost-effective for the steel industry to invest in the capture of heavily carbonaceous BOF (Basic Oxygen Furnace) or converter gas, and use it to support the intensive energy demands of the integrated facility, or for surplus energy conversion in power plants. As industry strives for greater efficiency via ever more complex technologies, increased attention is being paid to investigate the complex behavior of by-product syngases. Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O on heavily carbonaceous syngas mixtures. Direct formation of CO2 from CO is slow due to its high activation energy, and the presence of disassociated radical hydrogen facilitates chain branching species (such as OH), changing the dominant path for oxidation. The observed catalytic effect is non-monotonic, with the reduction in flame temperature eventually prevailing, and overall reaction rate quenched. The potential benefits of changes in water loading are explored in terms of delayed lean blowoff, and primary emission reduction in a premixed turbulent swirling flame, scaled for practical relevance at conditions of elevated temperature (423 K) and pressure (0.1–0.3 MPa). Chemical kinetic models are used initially to characterize the influence that H2O has on the burning characteristics of the fuel blend employed, modelling laminar flame speed and extinction strain rate across an experimental range with H2O vapor fraction increased to eventually diminish the catalytic effect. These modelled predictions are used as a foundation to investigate the experimental flame. OH* chemiluminescence and OH planar laser induced fluorescence (PLIF) are employed as optical diagnostic techniques to analyze changes in heat release structure resulting from the experimental variation in water loading. A comparison is made with a CH4/air flame and changes in lean blow off stability limits are quantified, measuring the incremental increase in air flow and again compared against chemical models. The compound benefit of CO and NOx reduction is quantified also, with production first decreasing due to the thermal effect of H2O addition from a reduction in flame temperature, coupled with the potential for further reduction from the change in lean stability limit. Power law correlations have been derived for change in pressure, and equivalent water loading. Hence, the catalytic effect of H2O on reaction pathways and reaction rate predicted and observed for laminar flames, are compared against the challenging environment of turbulent, swirl-stabilized flames at elevated temperature and pressure, characteristic of piratical systems.
Tackling Highly Constrained Design Problems: Efficient Optimisation of a Highly Loaded Transonic Compressor
Authors: Baert Lieven , Beaucaire Paul , Leborgne Michaël , Sainvitu Caroline , Lepot Ingrid
Published: August 2017

Turbomachinery components are designed to achieve high performances while being exposed to a complex flow environment with varying operating conditions. Whereas the purpose of a new design optimisation is straightforward — obtaining a better design than the already existing one — the actual process itself remains a challenging task, permanently confronted to the dual need to reduce the cycle time and to further integrate complexity and multiple physics. The extensive use of numerical simulations has contributed in a significant way to the design of state-of-the-art blade geometries. To deal with expensive high-fidelity computations, surrogate-based optimisation (SBO) has become an established and recognised approach. In order to be useful within an industrial context, it is crucial that this SBO process is capable of efficiently handling high-dimensional design spaces as well as managing highly constrained design problems.

This work presents innovative auto-adaptive surrogates, exploiting a blend of interpolation/regression and classification, implemented in the integrated optimisation platform Minamo. As a demonstrator based on NASA Rotor 37, an aero-mechanical multi-point optimisation has been performed. For a design space with 60 parameters, significant performance gains have been obtained (+4% after 250 evaluations or less than a fortnight’s runtime) while considering over 30 constraints. The proposed SBO approach offers therefore many opportunities for turbomachinery applications tackling highly constrained design problems. Despite the unavoidable curse of dimensionality, the proposed approach is able to efficiently achieve reliable results at a cost that is in line with industrial needs and it provides a conclusive asset in the frame of design specifications evolving along the design cycle.