bluuebunny/crossref_metadata_2025 huggingface dataset:
NOx Reduction in a Swirl Combustor Firing Ammonia for a Micro Gas Turbine
Authors: Iki Norihiko , Kurata Osamu , Matsunuma Takayuki , Inoue Takahiro , Tsujimura Taku , Furutani Hirohide , Kobayashi Hideaki , Hayakawa Akihiro , Okafor Ekenechukwu
Published: August 2018

Ammonia is expected to be a hydrogen carrier that has potential as a carbon-free fuel. Ammonia is known as a nonignitable fuel, and it is not easy to hold ammonia flames under atmospheric conditions. A demonstration test with the aim of showing the potential of ammonia-fired power plants was conducted using a micro gas turbine. A 50-kW-class turbine system firing kerosene was selected as a base model. More than 40 kW of power generation was achieved by firing ammonia gas or a mixture of ammonia and methane by modifying the combustor, the fuel control device, and the gas turbine startup sequence. The prototype bifuel combustor is a swirl combustor employing a non-premixed flame and a decreased air flow rate near a gas fuel injector for flame holding. Ammonia combustion in the prototype bifuel combustor was enhanced by supplying hot combustion air and by modifying the air inlets. However, the exhaust gases from the ammonia flames had high NOx concentrations. NOx removal equipment using selective catalytic reduction can reduce NOx emission levels to below 10 ppm from more than 1000 ppm (converted value of NOx to 15% O2) as already reported. However, downsizing of NOx removal equipment should be achieved for practical use. Therefore, a low NOx combustor was developed. As the first step of the development of the combustor, flame observation in the gas turbine combustor was tried. Although the observation area was limited, an inhomogeneous swirling orange flame of ammonia gas was observed. Then, a combustor test rig was prepared for a detailed observation of ammonia flame under various combustion conditions. The combustor test rig used a regenerative heat exchanger for heating combustion air, and it used an orifice for pressure drop instead of a turbine. Combustion air and cooling air were supplied from two air compressors. At startup of the combustor test rig, a spark plug was used to ignite non-premixed methane and air. After heating the regenerative heat exchanger, ammonia gas was supplied to the combustor instead of methane gas. The exhaust gases from the combustor were analyzed using FTIR (Fourier transform infrared spectroscopy) under various conditions, such as methane firing, methane–ammonia firing, and ammonia firing. Although there are several concepts for NOx reduction, a rich–lean combustion method was applied first for ammonia firing. The rich–lean combustor modified from the prototype bifuel combustor also could burn ammonia well in cases of both methane–ammonia firing and ammonia firing. The rich–lean combustor succeeded in reducing NOx emission from methane–ammonia combustion to half the value measured in the case of the prototype bifuel combustor.
Numerical Investigation of Particles Deposition on Leading Edge of Nozzle Guide Vane
Authors: Yang Xiaojun , Li Zishuo , Cui Mohan
Published: August 2018

A numerical simulation was performed to determine the factors that affect particle deposition on the leading edge in a nozzle guide vane passage. In this study, a new computational particle sticking model in the high temperature environment combining the critical viscosity model with the critical velocity model was developed, which both particle viscosity and elasticity properties were considered in the process of deposition. New numerical implementations were used to simulate the deposition layer thickness evolution. For validating the new sticking model, some low temperature experiments of wax deposition on a vertical plate were performed, which numerical results in the same conditions were compared with. Afterwards, the new particle sticking model was used to predict the deposition on a simplified leading edge with 3 rows of shower cooling holes of nozzle guide vane in aeroengine. A structural mesh of the nozzle guide vane containing a dynamic mesh region around the leading edge for the deposition layer thickness evolution calculation was developed. To match the real condition in high pressure turbine of aero-engine during the airplane’s flight, this study focus on the particles with a diameter less than 100nm. The simulation results showed that the capture rate of the nano-particles in the leading edge was less than 2%. The evolution of the deposition layer thickness changing with the aero-engine operational duration were quantified and analysed. Results showed that shower cooling air could reduce the deposition rate in the leading edge, and features such as particle size, blowing ratio and inlet turbulent dispersion have a strong correlation with the deposition rate and deposition distribution.
Safety Design Methods for Rotor-Bearing System and Dynamic Analysis in Aero-Engines
Authors: Hong Jie , Li Tianrang , Liang Zhichao , Zhang Dayi , Ma Yanhong , Wang Yongfeng
Published: August 2018

One typical fusing structure (fused device or load reduction device, a variable supporting stiffness structure used in bearing supporting in aero-engine design) was introduced in this paper. Based on the rotor-bearing system simulation model, a dynamic calculation under the condition of variable supporting stiffness was conducted aimed at providing data for the rotor system safety design. Results showed that: rotor working in supercritical state had a benefit to the dynamic characteristics, as when the supporting stiffness suddenly lost, transient excessively increasing vibration was restrained, steady vibration also remained at a low level. Transient response peak value and impact response increased with the increase of stiffness loss, steady vibration ratio decreased with the increase of stiffness loss. Therefore, a compromise on the choosing of an optimal stiffness loss value was necessary. We also got some other significant conclusions that are instructive for further engineering applications.
The Unsteady Pre-Stall Behavior of the Spike-Type Rotating Stall Within an Airfoil Vaned-Diffuser
Authors: Zhao Jiayi , Xi Guang , Wang Zhiheng , Zhao Yang
Published: August 2018

The spike-type rotating stall (RS) inception inside the vaned-diffuser, which seriously restricts the performance range and brings the problems of blade fatigue, still seems to be a ‘mystery’ since its randomness. The paper intends to explain the mechanisms of this stall inception. To quantitatively assess the critical unsteady behavior to the initiation of RS inception, the transient measurement characterizes the process falling into the RS through the parameter of ‘blade passing irregularity’. The underlying vortex disturbance, related to the growing of the flow complexity and the final spike-type precursor, is further revealed by the full-annulus simulation. The results show the propagation principle of the vortexes from the design to the stall inception point, reflected by the distribution of ‘blade passing irregularity’. The performance change of different sub-components due to the vortex behavior is presented. At the RS limit, the sudden ramp-up of the ‘blade passing irregularity’ near the leading edge (LE), accompanied with the drop of the static pressure rise in the sub-component between the semi-vaneless and throat, corresponds to the spike-type inception in the form of a clockwise vortex connecting the suction side of the diffuser vane and the pressure side of the adjacent vane. Besides, when approaching the spike-type inception point, the couple effect of the growing potential of the diffuser vane and the enhanced vortex disturbance at the impeller outlet degrades the diffuser inlet flow.
Multi-Objective Optimization Design and Analysis of High-Turning Tandem Cascade
Authors: Song Zhaoyun , Liu Bo , Cheng Hao , Mao Xiaochen
Published: August 2018

To improve the flow characteristics of tandem cascades on design and off design incidence angle and increase the stable operation range, a multi-objective optimization methodology based on CO-kriging and parallel multi-point sampling strategy is presented to realize multi-objective optimization of tandem cascades. Co-kriging model created by a greater quantity of low-fidelity samples coupled with a small amount of high-fidelity samples is introduced to reduce the compute cost of multi-objective optimization problems. The prediction performances of Co-kriging are much better than those of Kriging based on two numerical examples. The multi-point sampling strategy based on the fuzzy c-means clustering method can realize a good balance between exploitation known regions and exploration unknown regions for selecting new samples to update the Co-kriging. And the multi-objective optimization methodology can obtain the approximate Pareto frontier at a less compute cost and was validated by applying it to achieve the multi-objective optimization of a high-turning tandem cascade. After optimization, for the optimal tandem cascade, the static pressure ratio is higher and the total pressure loss coefficient is smaller at all incidence angle conditions. At inlet Mach number of 0.7, when incidence angle is −6° and 3°, the total pressure loss coefficient is respectively decreased by 21% and 35%. Tandem cascades with a high PP (about 0.92) and a negative KBB (about −6°) can realize good flow performances on design and off design incidence angle. And a large TR can improve the flow characteristics of tandem cascades on design and off design incidence angle and increase the stable operation range.
On the Stability Influence of Trimmed Vaneless Diffusers in Turbocharger Applications
Authors: Dragan Valeriu , Mihaescu Mihai
Published: August 2018

One key aspect of centrifugal compressor performance is the stability range, in particular at lower than optimal mass flows. This paper focuses on the stability improvement of a turbocharger-relevant compressor stage equipped with a trimmed vaneless diffuser, incorporated into its interior volute. Evidence in the literature suggests that such a diffuser might increase the stall margin, especially for the high speed lines. As is the case with all supercharged internal combustion engines, this would lead to improved overall efficiency, operational flexibility and lower emissions. Using advanced RANS turbulence modeling, a batch of test cases was setup in order to assess the feasibility of the concept as well as its potential drawbacks. Spalart-Allmaras and k-ω SST models, both with rotation and curvature corrections, were benchmarked against the baseline experimental data. The new diffuser was compared with conventional diffuser pinching and shelving and the fully trimmed embodiment was found to be superior to all others. Stability was assessed through a number of user defined parameters, tailored to reveal the signs of flow instability even under steady state assumptions. In addition to monitoring the mass flow imbalance, individual loading of blade passages and radial force magnitude and orientation were also monitored. Stability was found to be increased with the degree of diffuser trimming, alas this came at an ever increasing pressure loss. Most entropy was found to be generated across the volute as the flow velocity was significantly higher than the baseline. Another aspect was the static pressure distortion across the outlet of the vaneless diffuser, which paradoxically is linked with higher stability. Hence, in order to maximize both stability and mitigate pressure losses, further optimization on the scroll area distribution will have to be carried out after considering the new scroll inlet angle and speed circumferential distributions.
Numerical Investigations to Assess the Impact of Shaft Speed on the Performance of Scoop Devices
Authors: Prabhakar Arun , Abakr Yousif Abdalla , Simmons Kathy
Published: August 2018

The demand for continuous and efficient lubrication in aeroengine bearing assemblies has encouraged the development of scoop based lubrication systems. Using a scooped rotor in conjunction with axial passages within the shaft, a scoop system can provide lubrication to bearings and other components at a different axial location to the oil supply jet, optimizing the use of space.

The capture efficiency of a scoop system is the percentage of oil from the jet that is delivered to the desired end location. It is dependent on a number of factors such as shaft rotational speed, oil jet speed and other geometrical features. In this paper the impact of shaft speed on the capture efficiency of a scoop system is predicted numerically using Computational Fluid Dynamics (CFD). An analytical study has been also carried out to aid the understanding of the system’s behaviour. A simplified 2D geometry is used for the computational domain in the numerical simulations. The Volume of Fluid (VOF) multiphase model has been implemented to simulate the flow of oil and air. The effects of turbulence are modelled using the RNG K-ε turbulence model. Results obtained using CFD are compared to experimental results obtained from tests conducted on the same geometry.

It is evident from CFD and experiments that for a fixed oil jet velocity there is an optimum shaft speed at which maximum capture efficiency is obtained. This is somewhat higher than the threshold value identified by the analytical study at which 100% capture becomes theoretically possible. Maximum capture efficiencies of around 80% are predicted. Some oil is uncaptured because it forms a plume ahead of the scoop tip and deflects outwards and some is initially captured but leaves the scoop through centrifugal effects.

The analytical model suggests that the point of jet strike on the scoop may affect/control losses due to centrifugal effects with more oil being lost when the point of strike is closer to the scoop tip. Pluming losses become more significant at higher shaft speeds because the angle over which oil is captured decreases.

Predicted scoop capture efficiencies obtained using CFD are within 5.5% of experimentally obtained results for the configuration investigated here. Trends in behavior are the same experimentally and computationally highlighting the usefulness of a 2D CFD modelling approach.
The Role of Recirculation Zones in Soot Formation in Aircraft Combustors
Authors: Chong Shao Teng , Raman Venkat , Mueller Michael E. , Im Hong G.
Published: August 2018

Recirculation zone plays an important role in flame stabilization in combustors and gas turbines. The location, size, and strength of recirculation zones are important features of a combustor. However, the quantitative role of recirculation zones in affecting soot formation from an aero combustor is not fully understood. In a turbulent flow field with swirling flows and high frequency oscillations of the inflow jets, inner recirculation zones and outer recirculation zones have different functions in determining soot evolution. In this study, large-eddy simulation (LES) of soot formation with detailed physical and chemical models is used in order to study the dynamic aspects of soot formation. The soot population is modeled using the hybrid method of moments (HMOM), while the gas phase precursor evolution is modeled using detailed chemical kinetics. A model aero combustor, studied experimentally at DLR, is used as the baseline flow configuration. The simulations are used to understand the transport of soot particles within such complex flows. In particular, the ability of recirculation regions to increase soot formation by increasing residence times is explored. A Lagrangian particle tracking (LPT) analysis is carried out and statistical roles of recirculation zones are determined from these streamlines. Furthermore, source term analysis of these particles are performed to determine the key physical processes that contribute to soot mass in the recirculation zones. From a numerical stand-point, such soot evolution introduces limitations for statistical convergence, which will also be discussed. In particular, a time-scale analysis will be conducted to determine total computational time needed to obtain converged soot statistics.
Numerical Investigation of a Lean Premixed Swirl-Stabilized Hydrogen Combustor and Operational Conditions Close to Flashback
Authors: Mira D. , Lehmkuhl O. , Stathopoulos P. , Tanneberger T. , Reichel T. G. , Paschereit C. O. , Vázquez M. , Houzeaux G.
Published: August 2018

The current study presents a numerical investigation of the flow field of a swirl-stabilized burner featuring a non-swirling axial air jet on the central axis of the mixing tube. The system has been designed and optimized to burn hydrogen at the Technische Universität Berlin over the last 6 years in the context of the EU-funded projects GREENEST and AHEAD. As the burner design was based on experimental work, high-fidelity large-eddy simulations (LES) are used to provide deeper understanding on the non-reacting and reacting flow fields to elucidate the occurrence of flashback under certain operating conditions. The experimental measurements suggest that flashback is produced by a velocity deficit at the mixing tube outlet and these conditions are analyzed here using LES. The work includes code validation for non-reacting and reacting conditions by comparison to water tunnel and combustion test rig data, and aims to evaluate the accuracy of LES with a combustion model based on premixed flamelets to predict the reacting flow field under conditions close to flashback.
Experimental and Numerical Investigations of MILD Combustion in a Model Combustor Applied for Gas Turbine
Authors: Zhang Huan , Zhang Zhedian , Xiong Yan , Liu Yan , Xiao Yunhan
Published: August 2018

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, stable combustion and low noise for various kinds of fuel. MILD combustion is a promising combustion technology for gas turbine. The model combustor composed of an optical quartz combustor liner, four jet nozzles and one pilot nozzle has been designed in this study. The four jet nozzles are equidistantly arranged in the combustor concentric circle and the high-speed jet flows from the nozzles will entrain amount of exhaust gas to make MILD combustion occur. The combustion characteristics of the model combustor under atmosphere pressure have been investigated through experiments and numerical simulations. The influence of equivalence ratio and jet velocity on flow pattern, combustion characteristics and exhaust emissions were investigated in detail, respectively.

Laser Doppler velocity (LDV) was utilized to measure the speed of a series of points in the model combustor. The measurement results show that a central recirculation existed in the combustion chamber. As the jet velocity of the nozzles increases, the amount of entrained mass by the jet increases simultaneously, however, the central recirculation zone is similar in shape and size. The recirculation of the model combustor will remain self-similar when the jet velocity varies in the range. The calculation model and method were verified through comparing with experimentally LDV data and be used to optimize the model combustor. Planar laser-induced fluorescence of hydroxyl radical (OH-PLIF) approaches were adopted to investigate the flame structure, the reaction zone and the OH distribution. OH distribution of the paralleled and crossed sections in the model combustor were measured, the whole reaction zone have been analyzed. The results show that the OH distribution was uniform in whole combustor. The exhaust gas composition of the combustor was measured by the “TESTO 350” Exhaust Gas Analyzer. All measurements emission results were corrected to 15% O2 in volume. Experimental results showed that NOx and CO emissions were less than 10 ppm@15%O2 when the equivalence ratio ranges from 0.63 to 0.8.
Hermetically Sealed Squeeze Film Damper for Operation in Oil-Free Environments
Authors: Ertas Bugra , Delgado Adolfo
Published: August 2018

The following work advances a new concept for a hermetically sealed squeeze film damper (HSFD), which does not require an open-flow lubrication system. The hermetically sealed concept utilizes a submersed plunger within a contained fluidic cavity filled with incompressible fluid and carefully controlled end plate clearances to generate high levels of viscous damping. Although the application space for a hermetic damper can be envisioned to be quite broad, the context here will target the use of this device as a rotordynamic bearing support damper in flexibly mounted gas bearing systems.

The effort focused on identifying the stiffness and damping behavior of the damper while varying test parameters such as excitation frequency, vibration amplitude, and end plate clearance. To gain further insight to the damper behavior, key dynamic pressure measurements in the damper land were used for identifying the onset conditions for squeeze film cavitation. The HSFD performance is compared to existing gas bearing support dampers and a conventional open-flow squeeze film dampers (SFD) used in turbomachinery. The damper concept yields high viscous damping coefficients an order of magnitude larger than existing oil-free gas bearing supports dampers and shows comparable damping levels to current state of the art open-flow SFD. The force coefficients were shown to contribute frequency dependent stiffness and damping coefficients while exhibiting amplitude independent behavior within operating regimes without cavitation. Finally, using experimentally based force density calculations the data revealed threshold cavitation velocities, approximated for the three end seal clearance cases. To complement the experimental work, a Reynolds based fluid flow model was developed and is compared to the HSFD damping and stiffness results.
Numerical Investigation of the Cooling Performance on the Endwall With and Without Fillet
Authors: Xu Qingzong , Du Qiang , Wang Pei , Liu Jun , Liu Guang
Published: August 2018

High inlet temperature of turbine vane increases the demand of high film cooling effectiveness. Vane endwall region was extensively cooled due to the high and flat exit temperature distribution of combustor. Leakage flow from the combustor-turbine gap was used to cool the endwall region except for preventing hot gas ingestion. Numerical predictions were conducted to investigate the flow structure and adiabatic film cooling effectiveness of endwall region in a linear cascade with vane-endwall junction fillet. The simulations were completed by solving the three-dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with shear stress transport(SST) k-ω turbulence model, meanwhile, the computational method and turbulence model were validated by comparing computational result with the experiment. Three types of linear fillet with the length-to-height ratio of 0.5, 1 and 2, named fillet A, fillet B and fillet C respectively, were studied. In addition, circular fillet with radius of 2mm was compared with linear fillet B. The interrupted slot, produced by changing the way of junction of combustor and turbine vane endwall, is introduced at X/Cax = −0.2 upstream of the vane leading edge. Results showed that fillet can significantly affect the cooling performance on the endwall due to suppressing the strength of the secondary flow. Fillet C presented the best cooling performance comparing to fillet A and fillet B because a portion of the coolant which climbs to the fillet was barely affected by secondary flow. Results also showed the effect of fillet on the total pressure loss. The result indicated that only fillet A slightly decreases endwall loss.
Numerical and Experimental FSI-Study to Determine Mechanical Stresses Induced by Rotating Stall in Unshrouded Centrifugal Compressor Impellers
Authors: Mischo B. , Jenny P. , Mauri S. , Bidaut Y. , Kramer M. , Spengler S.
Published: August 2018

Unshrouded industrial centrifugal compressor impellers operate at high rotational speeds and volume flow rates. Under such conditions the main impeller blade excitation is dominated by high frequency interaction with stationary parts, i.e. vaned diffusers or inlet guide vanes. However, at severe part load operating conditions sub-synchronous rotating flow phenomena (rotating stall) can occur and cause resonant blade vibration with significant dynamic (von-Mises) stress in the impeller blades. To ensure high aerodynamic performance and mechanical integrity, part load conditions must be taken into account in the aero-mechanical design process via CFD and FEM analyses anchored by experimental verification.

The experimental description and quantification of unsteady interaction between rotating stall cells and an unshrouded centrifugal compression stage in two different full scale compression units by Jenny and Bidaut [1] were reproduced in a scaled model test facility to enhance the understanding of the fluid-structure interaction mechanisms and to improve design guide lines. Measurements with strain gauges and time-resolved pressure transducers on the stationary and rotating parts at different positions identified similar rotating stall patterns and induced stress levels. Rotating stall cell induced resonant blade vibration was discovered for severe off-design operating conditions and the measured induced dynamic von-Mises stress peaked at 15% of the mechanical endurance limit of the impeller material.

Unsteady full annulus CFD simulations predicted the same rotating stall pressure fluctuations as the measurements. The unsteady RANS simulations were then used in FEM fluid-structure interaction analyses to predict the stress induced by rotating stall and assess the aerodynamic damping of the corresponding impeller vibration mode shape. Excellent agreement with the measurements was obtained for the stall cell pressure amplitudes at various locations. The relative difference between measured and mean predicted stress from fluid-structure interaction was 17% when resonant blade vibration occurred. The computed aerodynamic damping was 27% higher compared to the measurement.
A Meta-Model for Aerodynamic Properties of a Reversible Profile in Cascade With Variable Stagger and Solidity
Authors: Angelini Gino , Bonanni Tommaso , Corsini Alessandro , Delibra Giovanni , Tieghi Lorenzo , Volponi David
Published: August 2018

In this paper, a systematic CFD work is carried out with the aim to inspect the influence of different cascade parameters on the aerodynamic performance of a reversible fan blade profile. From the obtained results, we derive a meta-model for the aerodynamic properties of this profile. Through RANS simulations of different arrangements in cascades, the aerodynamic performance of airfoils are analyzed as Reynolds number, solidity, pitch angle and angle of attack are varied. The definition of a trial matrix allows the reduction of the minimum number of simulations required. The computed CFD values of lift and drag coefficients, stall margin and the zero-lift angle strongly depend on cascade configuration and differ significantly from standard panel method software predictions. In this work, X-Foil has been used as a benchmark. Particularly, the high influence of pitch angle and solidity is here highlighted, while a less marked dependence from the Reynolds number has been found.

Meta-models for lift and drag coefficients have been later derived, and an analysis of variance has improved the models by reducing the number of significant factors. The application of the meta-models to a quasi-3D in-house software for fan performance prediction is also shown. The effectiveness of the derived meta-models is proven through a spanwise comparison of a reversible fan with the X-Foil based and meta-model based versions of the software and 3D fields from a standard CFD simulation. The meta-model improves the software prediction capability, leading to a very low global overestimation of the specific work of the fan.
Technology-Based Re-Contouring of Blade Integrated Disks After Weld Repair
Authors: Denkena B. , Mücke A. , Schumacher T. , Langen D. , Hassel T.
Published: August 2018

The widespread adoption of blade integrated disks (blisks) made of titanium demands tailored re-generation processes to increase sustainability and economic efficiency. High standards regarding geometrical accuracy and functional properties as well as the unique characteristics of each type of damage complicate the repair. Thus, flexible and well-designed processes are necessary. Typically, material deposit is followed by a milling or grinding process to restore the original shape. Here, not only the individual repair processes have to be controlled, but also their interaction. For example, depending on the resulting microstructure of the welded seam, the re-contouring process needs to be adapted to minimize tool wear as well as shape deviations of the complex blade geometries. In this paper, the process chain for a patch repair is examined, consisting of a TIG welding process followed by 5-axis ball nose end milling. Conventional TIG as well as a modified TIG process producing a finer grain structure and enhanced mechanical properties of deposited material were investigated. Grain refinement was achieved by SiC particles added to the weld pool. Based on the characteristics of the fusion material and static stiffness of the component, a methodology is introduced to minimize shape deviation induced by the subsequent milling process. Special attention is given to tool orientation, which has a significant impact on the kinematics and resulting process forces during milling. An electromagnetic guided machine tool is used for compensation of workpiece deflection.
Prediction of Unsteady Tip Leakage Flow of a Transonic Compressor Rotor by Reynolds-Stress-Constrained Large Eddy Simulation
Authors: Zhuang Yueqing , Liu Hui
Published: August 2018

Since the unsteadiness of tip leakage flow has profound effects on both aerodynamic performance and stall margin of axial compressors, it is important to accurately predict the transient tip flow at affordable computational cost. Limited by the high requirement of grid resolution of wall turbulence flow, large eddy simulation (LES) method is greatly restricted in engineering application. In the present work, a Reynolds-stress-constrained large eddy simulation (CLES) method has been introduced, in which the whole domain is simulated using LES while Reynolds stress constraint is enforced on the subgrid-scale (SGS) stress model for near-wall regions aiming at reducing the near-wall grid resolution. The CLES simulations have been performed to investigate the flow behaviors of the unsteady tip leakage flow in a transonic compressor NASA Rotor 67 at near-stall conditions. Reliability assessments have been conducted through comparisons of experimental measurements and numerical results obtained by RANS, DES, CLES as well as LES, respectively. Both the total pressure ratio and isentropic efficiency calculated by CLES agree well with experiment. The turbulence statistical results show three distinct high flow fluctuation regions near the blade tip. The first one is a long and narrow strip ahead of the leading edge of the rotor caused by the movement of the passage shock wave. The second one is formed on the suction side from the leading-edge of the rotor blade due to the oscillation of the tip leakage vortex. And the third one, which occupies most of the blade passage from the middle part of the rotor blade, is generated under multiple factors. The frequency characteristic of the unsteady tip leakage flow has been analyzed. The energy spectrums of the local transient pressure signals are highly related with the local unsteady flow features. The originating mechanisms of the flow unsteadiness in the rotor tip leakage flow have also been discussed, and the results show that the flow unsteadiness is mainly caused by a combined interaction effect of the double leakage flow, the tip leakage vortex flow spilled from the adjacent blade passage, as well as the involved main flow.
Extended Range of Fuel Capability for GT13E2 AEV Burner With Liquid and Gaseous Fuels
Authors: Zajadatz Martin , Güthe Felix , Freitag Ewald , Ferreira-Providakis Theodoros , Wind Torsten , Magni Fulvio , Goldmeer Jeffrey
Published: August 2018

The gas turbine market tends to drive development towards higher operational and fuel flexibility. In order to meet these requirements the GT13E21 combustion system with the AEV burner has been further developed to extend the range of fuels according to GE fuel capabilities.

The development includes operation with diluted natural gas, gases with very high C2+ contents up to liquefied petroleum gas on the gaseous fuels side and non-standard liquid fuels such as biodiesel and light crude oil. Results of full scale high pressure single burner combustion test in the test facilities at DLR-Köln are shown to demonstrate these capabilities. With these tests at typical pressure and temperature conditions safe operation ranges with respect to flame flashback and lean blow out were identified. In addition, the recent burner mapping at the DLR in Köln results in emission behavior similar to typical fuels as natural gas and fuel oil #2. It was also possible to achieve low emission levels with liquid fuels with a high fuel bound nitrogen content.

Based on these results the GT13E2 gas turbine has demonstrated capability with a high variety of gaseous and liquid fuel at power ranges of 200 MW and above. The fuels can be applied without specific engine adjustments or major hardware changes over a whole range of gas turbine operation including startup and GT acceleration.
Design of an Air-Cooled Radial Turbine: Part 1 — Computational Modelling
Authors: Zhang Yang , Duda Tomasz , Scobie James A. , Sangan Carl M. , Copeland Colin D. , Redwood Alex
Published: August 2018

This paper is part of a two-part publication that aims to design, simulate and test an internally air cooled radial turbine. To achieve this, the additive manufacturing process, Selective Laser Melting (SLM), was utilized to allow internal cooling passages within the blades and hub. This is, to the authors’ knowledge, the first publication in the open literature to demonstrate an SLM manufactured, cooled concept applied to a small radial turbine. In this paper, the internally cooled radial turbine was investigated using a Conjugate Heat Transfer (CHT) numerical simulation. Topology Optimisation was also implemented to understand the areas of the wheel that could be used safely for cooling. In addition, the aerodynamic loss and efficiency of the design was compared to a baseline non-cooled wheel. The experimental work is detailed in Part 2 of this two-part publication. Given that the aim was to test the rotor under representative operating conditions, the material properties were provided by the SLM technology collaborator.

The boundary conditions for the numerical simulation were derived from the experimental testing where the inlet temperature was set to 1023 K. A polyhedral unstructured mesh made the meshing of internal coolant plenums including the detailed supporting structures possible. The simulation demonstrated that the highest temperature at the blade leading edge was 117 K lower than the uncooled turbine. The coolant mass flow required by turbine was 2.5% of the mainstream flow to achieve this temperature drop. The inertia of the turbine was also reduced by 20% due to the removal of mass required for the internal coolant plenums. The fluid fields in both the coolant channels and downstream of the cooled rotor were analyzed to determine the aerodynamic influence on the temperature distribution. Furthermore, the solid stress distribution inside the rotor was analyzed using Finite Element Analysis (FEA) coupled with the CFD results.
Investigation of the Dihedral Angle Effect on the Boundary Layer Development Using Special-Shaped Expansion Pipes
Authors: Fei Teng , Ji Lucheng , Yi Weilin
Published: August 2018

The corners between the blades and end walls are common geometric structures in turbomachinery, where boundary layers on the blade and end wall surface interact with each other. This boundary layer interaction enlarges the region of low momentum fluid which leads to the boundary layers grow thicker at the corner region. Then the corner separation is likely to occur, and even worse by the adverse pressure gradient along the streamwise as well as secondary flows along the pitchwise. The key issue to design the geometric structures of the corner region is to control the dihedral angle between the blade and end wall surface. However, from the current published literature, few researchers have studied the influence of dihedral angle on the flow structures at the corner region in detail. In this paper, a series of expansion pipes with different cross sections which represent different dihedral angles are simulated. Then, some useful conclusions about how the dihedral angle affects the flow structures at the corner region are drawn. Moreover, a new method to predict the boundary layer thickness at the corner region is introduced, and the predicted results are in good agreement with simulation results.
Analysis and Testing of Aerobatic Turboprop Aircraft Inlet
Authors: Faltot Pierre-Jean , Pitel Welnitz Daniela , Vertenoeuil Philippe , Vlach Tomas , Lombardi Luca , D’Ercole Michele
Published: August 2018

Aerobatic aircraft have become popular for the training of military pilots, and nowadays an increasing number of such airframes are being developed. Modern turboprop engines provide high performance allowing the pilots to get similar handling characteristics to military jet aircraft engines. Prior to the availability of high performance turboprops, the basic pilot training was conducted using jet aircraft. Furthermore, the introduction of electronic control systems on last-generation turboprop engines enables single lever control, making it an ideal candidate for this type of aerobatic and training airframes. This new type of engine operation is however accompanied by several challenges from the point of view of the engine design and installation aerodynamics.

GEAC has gone through a complex design process, in cooperation with the airframer, to validate the design of a new aerobatic aircraft inlet in the context of developing an aerobatic version of the H80 engine. In order to ensure a) surge-free operation, b) optimal engine performance and c) effective ice/FOD separation in inclement weather conditions and during any kind of aerobatic maneuver, the team has done extensive CFD predictions of the flow behaviour, performance/operability studies and finally a ground test campaign.

First, a back-to-back comparison of the aerobatic inlet geometry versus a reference commuter inlet geometry was conducted. Then, flight conditions were simulated in calm and crosswind environments. Distortion patterns were examined using in-house developed tools and the diverse sources of distortion were identified. One of the results is the introduction of geometry improvements to guarantee improved performance and extended engine operability range. Advanced propeller modeling techniques were introduced and benchmarked in order to have the most exact representation of the propeller aerodynamic effect on inlet flow.

Finally, a test campaign was conducted for validation purposes. An exhaustive instrumentation, data acquisition system and detailed test program were developed to validate CFD methods and assumptions made during the design phase, and to raise our confidence in the flight conditions simulation results.
Dynamic Properties of Water-Lubricated Double Clearance Squeeze Film Damper Supported by O-Rings
Authors: Shoyama Tadayoshi , Fujimoto Koji
Published: August 2018

In this study, the complex modulus of double clearance squeeze film dampers (DCSFD) were experimentally determined under low amplitude unidirectional vibration. A DCSFD consists of two layers of squeeze film separated by an annular floating ring. Influences of the ring mass and clearances were examined. In our experiment, an increase in the damping coefficient of the DCFSD was observed when compared with that of a single clearance squeeze film damper (SCSFD) with the same total clearance as the DCSFD. Compared to theoretical values based on the classical theory of SCSFD, the damping coefficient of water-lubricated DCSFD was significantly higher at frequencies exceeding 700 Hz. Furthermore, DCSFD with larger clearances exhibited higher damping than those with smaller clearances. The origin of the increase in damping coefficient and the decrease in the inertia coefficient were discussed by considering the effect of the ring’s eccentricity, cavitation and turbulence in the film.
Robust Film Cooling Hole Shape Optimization Considering Surface Roughness and Partial Hole Blockage
Authors: Lee Sanga , Hwang Wontae , Yee Kwanjung
Published: August 2018

High performance film cooling holes with complicated geometries have been regarded as impractical up to now because of manufacturability issues. However, recent advances in additive manufacturing (AM) technology have opened up new doors. Investigating characteristics of film holes built with AM, and finding the optimum shape considering these characteristics are now required to confirm their practical utility.

In this paper, the performance of a high-efficiency film hole is numerically investigated. In-hole roughness and blade surface roughness are examined assuming an AM process, and contorted hole shape caused by partial blockage is also considered. A robust hole shape is obtained considering these uncertainties, utilizing a reference hole shape made by combining three cylindrical holes. Hole diameter, injection angle, and two angles for defining the two auxiliary holes are used as design variables to be optimized. For flow field and thermal analysis with roughness, compressible steady Reynolds averaged Navier-Stokes equations with a sand-grain roughness model are used. For the probabilistic assessment of each hole shape, Monte Carlo Simulations with the Kriging surrogate model is used, along with efficient global optimization (EGO) and a genetic algorithm. As a result, a high performance yet robust film cooling hole shape is obtained.
Reproducing Existing Nacelle Geometries With the Free-Form Deformation Parametrization
Authors: Rusch Konstantin , Siggel Martin , Becker Richard-Gregor
Published: August 2018

In the conceptual and preliminary aircraft design phase the Free-Form Deformation (FFD) is one of various parametrization schemes to define the geometry of an engine’s nacelle. This paper presents a method that is able to create a C2 continuous periodic approximation of existing reference nacelles with the B-spline based FFD, which is a generalization of the classical FFD. The basic principle of this method is to start with a rotational symmetric B-spline approximation of the reference nacelle, which is subsequently deformed with a FFD grid that is placed around the initial geometry. A method is derived that computes the displacement of the FFD grid points, such that the deformed nacelle approximates the reference nacelle with minimal deviations. As this turns out to be a linear inverse problem, it can be solved with a linear least squares fit. To avoid overfitting effects — like degenerative FFD grids which imply excessive local deformations — the inverse problem is regularized with the Tikhonov approach. The NASA CRM model and the IAE V2500 engine have been selected as reference geometries. Both resemble nacelles that are typically found on common aircraft models and both deviate sufficiently from the rotational symmetry. It is demonstrated that the mean error of the approximation decreases with an increase of the number of FFD grid points and how the regularization affects these results. Finally, the B-spline based FFD with the classical Bernstein based FFD are compared for both models. The results conceptually prove the usability of the FFD approach for the construction of nacelle geometries in the preliminary aircraft design phase.
Analysis of Unsteady Energy Fluxes in a Turbocharger by Using a Holistic Model Extrapolating Standard Lookup Tables in Full Engine Operating Map
Authors: Serrano José Ramón , García-Cuevas Luis Miguel , Inhestern Lukas Benjamin , Guilain Stephane , Tartoussi Hadi
Published: August 2018

One dimensional modeling can give important insights into the needs of engine and turbocharger design. In this paper a holistic turbocharger model that calculates besides transient effects also heat transfer, friction losses, extrapolated adiabatic turbine and compressor maps has been validated over the range of an entire diesel engine map. Due to its capability of calculating heat fluxes in very different conditions turbocharger maps measured in hot as well as maps measured in cold conditions can be used as input data of the model. The turbocharger model has been validated in a high number of running conditions and has been compared against a reference model to highlight its advantages. Since the model can calculate data that are difficult to measure as complex internal turbocharger heat transfer, entropy, and adiabatic efficiency pulses, these numbers have been analyzed. It has been found out that the analyzed turbocharger loses relatively high amounts of heat especially at its highest efficiency zone. Further, the importance of the isentropic power during the valley in engine exhaust gas flow pulses has been highlighted. Apart from the peak energy a big part of isentropic energy is available in the valley of the pulse. Finally, a specific coefficient has been proposed to quantify the available energy rate in the valley of the pulse.
A Modal Based Approach for the Lateral Dynamic Analysis of Rotating Shafts Supported by Elastic Substructures
Authors: Quattrone Flavio , Dugone Benjamin
Published: August 2018

It is well known that the detailed modelling of the structures supporting modern, heavy-duty gas turbines is essential for accurately estimating the dynamic behaviour of the complete coupled system. In this paper, the equations of motion governing the lateral dynamics of a rotating shaft supported by an elastic substructure are assembled by making exclusive use of modal parameters — such as modal damping ratios, undamped natural frequencies and modal shapes — of both the supporting structure and the undamped, non-rotating and unconstrained rotor. Thanks to the particular approach of considering the rotor in its unconstrained configuration, the modal base used to derive the equations of motion becomes independent on the rotational speed. It therefore needs to be extracted only once. Gyroscopic effects can then be effortlessly introduced by projecting the gyroscopic matrix on the modal base described above. Harmonic, modal and transient analyses can be carried out by means of the proposed set of equations. Additionally, since the mathematical expression of a modal tracking parameter is reduced to a simple scalar product by the particular shape of the proposed system matrices, Campbell’s diagram analyses result to be simplified.

An actual example of application to the modal and unbalance analyses of a heavy-duty gas turbine engine is presented. The proposed approach is used to produce the Campbell’s diagram of the complete rotor-structure system and extract bearing vibration velocities for a typical case of unbalance. Results are then compared on the one hand with those calculated by a well-known commercial tool and on the other hand with real measurement data. Since a key benefit of the present approach is that it is fully independent from the method used to extract the input modal parameters, it allows using results from models of the most appropriate complexity — 1D, 2D or 3D. Alternatively, and as shown in this paper, validated measurement data can also be used for fine-tuning of the input parameters in order to close potential gaps between numerical models and real machine dynamic behaviour.