bluuebunny/crossref_metadata_2025_split huggingface dataset:
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 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.
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.
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.
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.
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.
Numerical Investigation on a High Endwall Angle Turbine With Swept-Curved Vanes
Authors: Meng Fusheng , Gao Jie , Fu Weiliang , Liu Xuezheng , Zheng Qun 
Published: August 2018

In a high endwall angle turbine, large meridional expansion can cause the strong secondary flow at the endwall, which results in a larger endwall flow loss than the small meridional expansion turbine. The endwall heat transfer is strongly affected by secondary flow effect. In order to optimize the endwall flow to reduce the flow loss and optimize the distribution of heat load, the swept-curved method was used in this study.
The swept-curved method was investigated on a transonic second stator (S2) with large meridional expansion in a Low-Pressure (LP) Turbine. Validation studies were performed to investigate the aerodynamic and the heat transfer prediction ability of shear stress transport (SST) turbulence model. The influence of different shapes of the stacking line, including forward-swept, backward-swept, positive-curved and negative-curved, were investigated through numerical simulation. The parameterized control of swept-curved height and angle were adopted to optimize the performance of the aerodynamic and heat transfer. 3D flow field calculation captured the relatively accurate flow structures in the parts of endwall and near endwall. Heat transfer behaviors were explored by means of isothermal wall temperature and Nusselt number (Nu) distribution. The results show that the maximal heat transfer coefficient at the leading edge, for the formation of horseshoe vortexes that cause the high velocity towards the endwall. The swept vane can improve the static pressure and heat load distribution at the endwall region, which decreases the area-averaged shroud heat flux by 2.6 percent and the loss coefficient 1.3 percent.
Modeling Partial Admission in Control Stages of Small Steam Turbines With CFD
Authors: Bellucci Juri , Rubechini Filippo , Arnone Andrea 
Published: August 2018

This work aims at investigating the impact of partial admission on a steam turbine stage, focusing on the aerodynamic performance and the mechanical behavior.
The partialized stage of a small steam turbine was chosen as test case. A block of nozzles was glued in a single “thick nozzle” in order to mimic the effect of a partial admission arc. Numerical analyses in full and in partial admission cases were carried out by means of three-dimensional, viscous, unsteady simulations. Several cases were tested by varying the admission rate, that is the length of the partial arc, and the number of active sectors of the wheel. The goal was to study the effect of partial admission conditions on the stage operation, and, in particular on the shape of stage performance curves as well as on the forces acting on bucket row.
First of all, a comparison between the flow field of the full and the partial admission case is presented, in order to point out the main aspects related to the presence of a partial arc. Then, from an aerodynamic point of view, a detailed discussion of the modifications of unsteady rows interaction (potential, shock/wake), and how these ones propagate downstream, is provided. The attention is focused on the phenomena experienced in the filling/emptying region, which represent an important source of aerodynamic losses. The results try to deepen the understanding in the loss mechanisms involved in this type of stage. Finally, some mechanical aspects are addressed, and the effects on bucket loading and on aeromechanical forcing are investigated.
Experimental Investigation of Droplets Splashing With Varying Pressures and Impact Angles to Predict Behaviour During Wet Compression
Authors: Bröder Jascha , Günther Christoph , Joos Franz 
Published: August 2018

Wet compression is a powerful means to increase gas turbine power output and to perform fast load changes. These characteristics make this process suitable to compensate the unsteady supply of electric energy from renewable sources or to increase overall power output in times of high demand without the necessity to invest in higher peak capacity.
In case of high fogging water sprays are injected inside the intake duct of the gas turbine compressor resulting in droplets entering the first stages of the compressor. Inside, droplets above a specific size cannot follow the airflow properly, which makes it likely for them to collide with compressor surfaces and disintegrate. Characteristics of the ejected secondary droplets influence evaporation and condensation processes and thereby the thermodynamics of the compression process.
To investigate the characteristics of ejected secondary droplets, collisions between droplets and surfaces were recorded with a high-speed camera using the shadowgraphy method. From these recordings, quantity, diameter and velocity of secondary droplets were obtained. To resemble conditions at the first stages of a compressor under high fogging conditions, the experiments were conducted at elevated pressures up to 500 kPa and with varying impact angles from 0° to 30°. The Weber number normal to the surface was held constant at 550 and 700. The paper discusses the measured influence of splashing at simulated compressor conditions.