bluuebunny/crossref_metadata_2025 huggingface dataset:
Difference in the Working Principle of Axial Slot and Tip Blowing Casing Treatments
Authors: Inzenhofer André , Guinet Cyril , Hupfer Andreas , Becker Bernd , Grothe Patrick , Heinichen Frank
Published: September 2016

Tip blowing and axial slot casing treatments have shown their ability to enhance the stability of a transonic axial compressor with different effects on efficiency. For an effective application of these casing treatments, a good knowledge of the influence of the casing treatment on the rotor flow field is important. There is still a need for more detailed investigations, in order to understand the interaction between the treatment and the near casing 3D flow field. For transonic compressor rotors this interaction is more complex, as super- and subsonic flow regions alternate while interacting with the casing treatment.

In the present study, an axial slot and a tip blowing casing treatment, which have been developed and optimized for the same tip critical transonic axial compressor rotor (reference rotor) by Streit et al. [1] and Guinet et al. [2], are subject of the investigation. Both casing treatment types showed their capabilities to enhance the compressor stability without losing by means of CFD simulations. Since the higher compressor stability allows a higher blade loading, Streit et al. reduced the blade number of the rotor. Thus, the efficiency was increased due to the reduction of friction losses. However, applying the tip blowing casing treatment to the reduced rotor shows a negative effect on the efficiency.

Both casing treatment types recirculate flow from a downstream to an upstream location of the rotor and reinject it to enhance the near casing flow field. Although the working principle of the two casing treatment types are similar, the transfer of the casing treatments from the reference to the reduced rotor show different trends in efficiency. Therefore, the effect of recirculation cannot explain the difference in efficiency. Hence, applying axial slots must include additional flow features, compared to recirculation channels.

Compensating effects as in circumferential groove casing treatments and other flow interactions between the near casing flow field and the slot flow are considered. These additional mechanisms of the axial slot casing treatment will be identified and isolated by comparing the two different casing treatment types. The numerical simulations are carried out on a 1.5 stage transonic axial compressor using URANS simulations.
Unsteady Rotating Radial Load of a Single Stage Radial Inflow Turbine
Authors: Marlier Jonathan , Barbieux Virginie , Tartinville Benoît
Published: September 2016

Radial inflow turbines with pivoting stator vanes are known to keep a high level of efficiency over a large flow range. This turbine type maintains a good efficiency level at reduced speed because the turbine wheel is not very sensitive to negative incidence. For these reasons variable geometry radial inflow turbines are used where a large operating map is required.

However, it is known from literature that impeller blades undergo significant unsteady aerodynamic forces due to upstream stator vanes, especially with transonic conditions at stator exit, which are quite common for these machines. From a mechanical point of view, the number of stator vanes is therefore crucial since it determines the excitation frequency. Over a large operating map, it is not possible to avoid all eigenmodes. The vane count shall avoid excitation of impeller critical eigenmodes, especially if their mode shape matches.

Amongst unsteady phenomena occurring in turbomachinery, rotor/stator interactions are of primary importance. Independently from impeller eigenmodes, this study discusses the unsteady rotating radial load on the impeller that can be generated under specific blade count combinations, for a single stage radial inflow turbine. This radial load can indeed be large and impact the rotordynamics. The rotating frequency of the load is given by Tyler-Sofrin theory. In order to compute its amplitude, unsteady CFD is performed, with the use of the non-linear harmonic method implemented into FINE™/Turbo software from NUMECA. The effects of the fluid, of the operating conditions and of the rotational speed are also quantified. Under specific conditions, resonance may occur and is discussed.
Automated Mode Identification of Airfoil Geometries to Be Used in an Optimization Process
Authors: Martin Ivo , Bestle Dieter
Published: September 2016

Extending the lifetime of modern gas turbines is becoming increasingly challenging. A proper method for exploiting further improvement potential is to utilize automatic design optimization techniques, where for example, optimization may help to prevent excitations of eigenmodes of compressor airfoils thus, decreasing service costs, by reducing the risk of high cycle fatigue. However, in some cases the avoidance of any excitation may be not possible or too expensive due to the loss of aerodynamic efficiency. Since different eigenmodes do not share the same risk of failure, this is also not always necessary. Numerical optimization may account for this by penalizing the various eigenmodes differently which, however, requires that a proper mode-recognition technique be robust against design and mesh changes during the optimization process. This paper will introduce such a technique based on self-organizing maps (SOM). It will be used to project the suction-side surface of different blade geometries and mesh types onto a standard map in order to make deformations comparable for classification techniques. This enables to apply e.g. the mode-assurance criteria (MAC) in order to find correlations between the actual and already classified reference modes. The method will be demonstrated on two rotor blades.
Sampling Strategies and Metamodeling Techniques for Engineering Design: Comparison and Application
Authors: Liu Haitao , Xu Shengli , Wang Xiaofang
Published: September 2016

To help engineers perform engineering design and optimization efficiently, this article systematically compares the performance of typical sampling strategies and metamodeling techniques based on nine engineering responses with different levels of dimensionality and nonlinearity. In the comparative study, four metamodels, three characteristics of sample data, and four evaluation criteria are considered. Compared with the existing comparative studies for evaluating different metamodeling techniques, the contributions provided by the comparative study in this article are: (1) sample data with only space-filling property and, both space-filling and projective properties are compared; (2) newly developed radial basis functions-based high dimensional model representation (RBFHDMR) model is involved in the study to compare with other metamodels; and (3) we offer a guideline for the use of sampling methods, and furthermore, rather than empirical recommendations, we introduce and compare some recently developed ensemble strategies for the use of metamodels.
Investigations on the Generation and Weakening of Shock Wave in a Radial Turbine With Variable Guide Vanes
Authors: Yang Dengfeng , Lao Dazhong , Yang Ce , Hu Leon , Sun Harold
Published: September 2016

The turbocharger, with its advantages in increasing fuel economy and reducing emission, has been widely used in internal combustion engines. Aiming to achieve both fast transient response and high boost at low engine speeds of the diesel engines, variable nozzle turbine (VNT) turbochargers are necessary to match well with the engines in various operating conditions. At different engine speeds, both the mass flow rate and expansion ratio of the exhaust gas could be controlled by changing the opening of the guide vanes to adjust the nozzle throat area. At low engine speeds, the small opening of the VNT nozzle can accelerate the exhaust gas, resulting in the increase of the compressor boost pressure. The large opening of the VNT nozzle is capable of avoiding the excessive boost pressure at high engine speeds.

The high exhaust gas pressure accompanying the small opening of the guide vane at the engine braking condition leads to shock waves. Loading fluctuation on the surface of the rotor blade, in response to the shock wave at the variable guide vanes, could increase the high cycle fatigue (HCF) risk of the rotor blade significantly. In this study, the generation and weakening mechanism of the shock wave in the VNT have been investigated by adopting three guiding vanes with different span chord ratios. Numerical simulation indicates that two shock waves are produced in the geometry throat and the trailing edge of the guide vane, named throat shock wave and trailing edge shock wave, respectively.

The trailing edge shock wave at mid-span area of the rotor-stator interface has the largest intensity, and it is gradually weakened towards both the rotor blade leading edge and the guide vane trailing edge. As the distance between the guiding vane and rotor blade changes, the trailing edge shock wave also varies in intensity, shape, and relative position to the blade, while the throat shock wave has no variations. Further analysis shows that the generation of the shock wave is mainly due to the excessive acceleration of the exhaust gas. Reduction of the gas expansion ratio across the variable guide vane and the channel shrinkage degree between the nozzle vane trailing edge and the rotor blade can eliminate the throat shock wave and weakens the trailing edge shock wave. As the trailing edge shock wave weakens, pressure fluctuation inside the rotor blade can be reduced, which will significantly reduce the turbine blades forced response and enhance the reliability of the VNT turbine.
Effects of Tip Clearance and Operating Conditions on the Flow Structure and Turbulence Within an Axial Compressor Rotor Passage
Authors: Li Yuanchao , Chen Huang , Tan David , Katz Joseph
Published: September 2016

The flows in the tip regions of two rotors with blades of similar geometry but different tip clearance are studied experimentally to determine the effect of gap on the flow structure at different operating conditions. The experiments have been performed in the JHU optically index-matched facility, where the refractive index of the fluid is matched with that of the acrylic rotor blades and casing, facilitating unobstructed Stereo Particle Image Velocimetry (SPIV) measurements. The blade geometries are based on the first one and a half stages of the Low Speed Axial Compressor (LSAC) facility at NASA Glenn. The tip gap sizes are 0.49% and 2.3% of the blade chordlength, and measurements are performed for two flow rates, the lower of which is just above stall conditions. The presence and trajectories of the tip leakage vortex (TLV) and secondary structures are visualized by recording high speed movies of cavitation at lower pressures. The results consist of performance curves, distributions of velocity, circumferential vorticity and turbulent kinetic energy, as well as the strength and trajectory of vortices. Increasing the tip gap reduces the static-to-static pressure coefficient for all flow conditions. For the higher flow rate, a wider tip gap has several effects: (i) It delays the rollup of the TLV and its detachment from the suction side (SS) corner of the blade, presumably due to the larger distance from the endwall casing and the ‘image vortex’. (ii) It alters the blade loading and reduces the circulation shed from the blade. (iii) It delays the onset of TLV bursting in the aft part of the rotor passage. (iv) For both gaps, the endwall boundary layer separates at the point where the leakage flow meets the opposite-direction main passage flow. For the wide gap, the separated layer with opposite sign vorticity remains above the TLV; while for the narrow gap, the TLV entrains this layer around itself. And (v) consistent with the major differences in flow structure, the spatial distributions and magnitudes of all the turbulence intensity are also very different. Trends and flow structure are quite different at pre-stall conditions. Most notably, TLV rollup is still delayed for the wide gap, but vortex bursting and associated arrival of multiple secondary structures to the pressure side (PS) of the next blade occur earlier. Consequently, the turbulence level on both sides of the blade tip is substantially higher, and remnants of the previous TLV are ingested into the next tip gap.
Large-Scale DES Analysis of Stall Inception Process in a Multi-Stage Axial Flow Compressor
Authors: Yamada Kazutoyo , Furukawa Masato , Tamura Yuki , Saito Seishiro , Matsuoka Akinori , Nakayama Kentaro
Published: September 2016

The paper describes the flow mechanism of the rotating stall inception in a multi-stage axial flow compressor for an actual gas turbine. Large-scale numerical simulations have been conducted. The compressor investigated is a test rig compressor which was used for development of the industrial gas turbine, Kawasaki L30A. While the compressor consists of 14 stages, the front half stages of the compressor were analyzed in the present study. According to the test data, it is considered that the 5th or 6th stage is the one most suspected of leading to the stall.

In order to capture precise flow physics that could happen at stall inception, a computational mesh was made dense, giving at least several million cells to each passage. It amounted to about two billion cells for the first 7 stages (three hundred million cells in each stage). Since the mesh was still not enough for the large-eddy simulation (LES), the detached-eddy simulation (DES) was employed. In the DES, a flow field is calculated by LES except near-wall and near-wall turbulent eddies are modeled by RANS. The computational resource required for such large-scale simulation was still quite large, so the computations were conducted on the K computer (RIKEN AICS in Japan). Unsteady flow phenomena at the stall inception were analyzed by using data mining techniques such as vortex identification and limiting streamline drawing with the LIC (line integral convolution) method.

The present compressor has stall started from the separation on the hub side instead of the commonly observed leading-edge separation near the tip. The flow phenomenon first observed in the stalling process is the hub corner separation, which appears in some passage of the 6th stator when approaching the stall point. This hub corner separation expands with time, and eventually leads to the leading-edge separation on the hub side for the stator. Once the leading-edge separation happens, it rapidly develops into the rotating stall, causing another leading-edge separation for the neighboring blade in sequence. Finally, the rotating stall spreads to the upstream and downstream bladerows due to its large blockage effect.
Demonstration Plant and Combustion System for an Oxy-Fuel Gas Turbine Cycle
Authors: Saanum Inge , Ditaranto Mario , Schönborn Alessandro , Janczewski Jacek
Published: September 2016

A semi-closed oxy-fuel retrofit gas turbine demonstration plant (DEMOXYT) is described and preliminary results of the oxy-fuel burner under relevant conditions are presented. The plant consists of a 100 kWel radial turbine with a pressure ratio of 4.25, featuring a recuperator, to which a specific oxy-fuel burner has been designed and constructed, and a condensing scrubber in the flue gas recirculation loop. An overview and salient thermodynamic data of the plant are provided, as well as important parameters governing its limits of operation. Results from combustion experiments obtained in a pressurized oxyfuel combustor are presented in terms of a burner operation map for 4.2 bar. The combustion testing results describe the stability maps of the burner and the influence of excess oxygen and total oxygen concentration in the reactants on the formation of CO. It was found that excess oxygen values below about 5% could result in excessive CO concentrations in the undiluted product gases of the flame, but that CO formation was relatively independent of the oxygen concentration in the reactants.
Cogenerative Performance of a Wind–Gas Turbine–Organic Rankine Cycle Integrated System for Offshore Applications
Authors: Bianchi Michele , Branchini Lisa , De Pascale Andrea , Melino Francesco , Orlandini Valentina , Peretto Antonio , Haglind Fredrik , Pierobon Leonardo
Published: September 2016

Gas Turbines (GT) are widely used for power generation in offshore oil and gas facilities, due to their high reliability, compactness and dynamic response capabilities. Small heavy duty and aeroderivative units in multiple arrangements are typically used to offer larger load flexibility, but limited efficiency of such machines is the main drawback. A solution to enhance the system performance, also in Combined Heat and Power (CHP) arrangement, is the implementation of Organic Rankine Cycle (ORC) systems at the bottom of the gas turbines. Moreover, the resulting GT-ORC combined cycle could be further integrated with additional renewable sources.

Offshore wind technology is rapidly developing and floating wind turbines could be combined with offshore GT-ORC based power plants to satisfy the platform load.

The pioneering stand alone power system, for an oil and gas platform, examined in this paper comprises a 10MW offshore wind farm and three gas turbines rated for 16.5MW, each one coupled with an 4.5MW ORC module. The ORC main parameters are observed under different wind power fluctuations. Due to the non-programmable availability of wind and power demand, the part-load and dynamic characteristics of the system should be investigated. A dynamic model of the power system based on first principles is used, developed in the Modelica language. The model is integrated with a time series-based model of two offshore wind mills. Various thermodynamic indexes, available in the literature, are identified and evaluated to compare the actual combined heat and power performances of single components and of the overall integrated system in the considered wind scenarios.
Effect of Rotation on a Gas Turbine Blade Internal Cooling System: Numerical Investigation
Authors: Burberi E. , Massini D. , Cocchi L. , Mazzei L. , Andreini A. , Facchini B.
Published: September 2016

Increasing turbine inlet temperature is one of the main strategies used to accomplish the demands of increased performance of modern gas turbines. As a consequence, optimization of the cooling system is of paramount importance in gas turbine development. Leading edge represents a critical part of cooled nozzles and blades, given the presence of the hot gases stagnation point and the unfavourable geometry for cooling. This paper reports the results of a numerical investigation aimed at assessing the rotation effects on the heat transfer distribution in a realistic leading edge internal cooling system of a high pressure gas turbine blade. The numerical investigation was carried out in order to support and to allow an in-depth understanding of the results obtained in a parallel experimental campaign. The model is composed of a trapezoidal feeding channel which provides air to the cold bridge system by means of three large racetrack-shaped holes, generating coolant impingement on the internal concave leading edge surface, whereas four big fins assure the jets confinement. Air is then extracted through 4 rows of 6 holes reproducing the external cooling system composed of shower-head and film cooling holes. Experiments were performed in static and rotating conditions replicating the typical range of jet Reynolds number (Rej) from 10000 to 40000 and Rotation number (Roj) up to 0.05, for three crossflow cases representative of the working condition that can be found at blade tip, midspan and hub, respectively. Experimental results in terms of flow field measurements on several internal planes and heat transfer coefficient on the LE internal surface have been performed on two analogous experimental campaigns at University of Udine and University of Florence respectively. Hybrid RANS-LES models were used for the simulations, such as Scale Adaptive Simulation (SAS) and Detached Eddy Simulation (DES), given their ability to resolve the complex flow field associated with jet impingement. Numerical flow field results are reported in terms of both jet velocity profiles and 2D vector plots on symmetry and transversal internal planes, while the heat transfer coefficient distributions are presented as detailed 2D maps together with radial and tangential averaged Nusselt number profiles. A fairly good agreement with experimental measurements is observed, which represent a validation of the adopted computational model. As a consequence, the computed aerodynamic and thermal fields also allow an in-depth interpretation of the experimental results.
Study on the Reverse Rotating Character Driven by the Backflow on a Centrifugal Fan System
Authors: Qu Xiaoyun , Wang Tong , An Jongho
Published: September 2016

In the turbo-compressor driving system, working fluid of large capacity and high pressure is stored in the system. Once an accident happened unexpectedly, the driving power of the rotor would be shut off quickly. Owing to the pressure difference between the inlet and the outlet of the compressor, the original downstream fluid might flow back from the volute to the impeller. The backflow might propel the impeller rotating reversely compared with its working status. It would damage the bearing and sealing system. Therefore, it is necessary to avoid the rotor reversal. With the development of the economies of scale, the capacity of the compressor unit becomes larger and larger, the possibility of the rotor reversal accident might be in consideration. The reverse performance of the centrifugal impeller is related to the mass flowrate of the backflow, the backflow pressure, moment of inertia as well as the initial working rotating speed of the rotor. In order to get the quantitative relation of the parameters, a test rig was set up with a centrifugal fan. The parameter was tested on the idle processes with different initial rotating speeds. Compared with the idle process, the reduction processes of the rotating speed driven by the backflow were tested. The processes varied with the pressure and the flowrate of the backflow. In addition, three-dimension simulation on the fan was performed. Corresponding to the experimental data, numerical performance of the fan was got to verify the numerical method. The flow information in the fan with backflow was analyzed. Even the backflow passing through the impeller, there is small flowrate to the volute by the operating fan. Combined with experimental data and the numerical parameters, the theoretical analysis on the reduction process of rotating speed was carried out. The critical values of the initial working rotating speed, the pressure and the flowrate of the backflow were derived to avoid the reverse rotation. Therefore, it can be used for the fan system in the design process to prevent the reverse rotation.
Effects of Rotor-Speed-Ratio and Crosswind Inlet Distortion on Off-Design Performance of Contra-Rotating Propelling Unit
Authors: Vouros Stavros V. , Chasoglou Alexandros C. , Efstathiadis Theofilos G. , Kalfas Anestis I.
Published: September 2016

This paper presents an investigation of the effects of rotor-speed-ratio (RSR) and inlet crosswind distortion on the off-design performance of a contra-rotating propelling unit. A dedicated wind tunnel has been built in order to study the off-design performance in distorted and undistorted conditions. A miniature 8-hole pressure rake has been calibrated to measure the total and static pressure field across the blade span, upstream and downstream of the propellers. A data analysis algorithm has been developed for the rapid exportation of desensitized and reliable mass-averaged characteristics, while wall blockage effects are accounted for incorporating a correction factor. Investigation of rotor-speed-ratio effects at undistorted inlet conditions show that, efficiency is the highest when the front rotor operates at rotational speed equal to 90% of the aft rotor’s speed.

For the optimum RSR, the effects of crosswind inlet distortion are investigated. Crosswind mass-flow is generated by a 16-fan array, accommodated in a secondary square wind-tunnel, with its center axis perpendicular to propeller main flow direction. In order to achieve realistic crosswind flow characteristics, the pressure side of the secondary wind tunnel is being used, after proper flow conditioning. Total and static pressure distribution highlights the location of a primary and a secondary stall cell, both upstream and downstream of the propellers. The results indicate a spanwise shift of the inlet pressure profile towards the direction of crosswind. A rotation of the wake is also observed due to propellers’ remaining swirl. Finally, the effect of distortion on the overall performance is being investigated, by the exportation of averaged total pressure rise for the various examined inlet distortion cases. Mass-flow is slightly increased; however, total pressure rise is dramatically reduced due to crosswind flow effects. Especially for the case of landing under extremely strong crosswind, the ratio between total pressure rise and inlet dynamic head is 4.2 times lower, compared to undistorted inlet operating conditions.
Stabilizing and Accelerating Solution of Harmonic Balance Equation System Using the LU-SGS and Block Jacobi Methods
Authors: Huang Xiuquan , Wang Ding Xi
Published: September 2016

The paper presents the combination of the Lower Upper Symmetric Gauss Seidel (LU-SGS) method and the block Jacobi method for stabilizing and accelerating the solution of a harmonic balance equation system. First the baseline LU-SGS procedure for a harmonic balance equation system with explicit discretization of the time spectral source term is derived. The LU-SGS method, different from its original application as an implicit time marching scheme, is used as an implicit residual smoother, allowing big CFL numbers (in order of 1000s), within the Runge-Kutta explicit time marching loops. Then the block Jacobi method is introduced to augment solution stability for the solution of a harmonic balance equation system under situation where grid reduced frequency is in the order of 10. Results are presented to show the effectiveness of the combination of LU-SGS and the block Jacobi method on the solution stabilization and acceleration. The influence of the number of Jacobi iterations on solution convergence is also investigated.
Turbines and Structures for Ultra-High Pressure Ratio Aero-Engines
Authors: Lundbladh Anders , von der Bank Ralf , Avellán Richard , Forsman Stefan , Donnerhack Stefan , Sturm Wolfgang , Versluis Joris , Rae Anthony , Stokes Mark , Caballero Oscar , Soldevilla Natalia , Ornat Artur , Mrugala Tomasz , Kraj Lucjan , Bourgois Sebastien
Published: September 2016

This paper describes the research carried out in the European Commission co-funded project LEMCOTEC (Low Emission Core Engine Technology) on aerodynamics for turbines and structures for compressors, combustors and turbines. The aim is to significantly contribute to the reduction of the environmental footprint of aviation with regard to emissions from aero engines.

The LEMCOTEC turbine and structure technologies are directed primarily to act as enablers for higher thermal efficiency arising from increased overall pressure ratio. Thus the work is supporting increased operating temperatures, reduced core deformation, reduced cooling flows and increased performance to weight ratio, in addition to direct reduction of flow losses and associated component efficiency increases.

The article details the targets for performance improvements, the validation of the technologies and how they, together with LEMCOTEC’s improved technologies on compressors and combustors, relate to the goal of building ultra-high pressure ratio engines.
Numerical Investigation of Intermittent Corner Separation in a Linear Compressor Cascade
Authors: Ma Wei , Gao Feng , Ottavy Xavier , Lu Lipeng , Wang A. J.
Published: September 2016

Recently bimodal phenomenon in corner separation has been found by Ma et al. (Experiments in Fluids, 2013, doi:10.1007/s00348-013-1546-y). Through detailed and accurate experimental results of the velocity flow field in a linear compressor cascade, they discovered two aperiodic modes exist in the corner separation of the compressor cascade. This phenomenon reflects the flow in corner separation is high intermittent, and large-scale coherent structures corresponding to two modes exist in the flow field of corner separation. However the generation mechanism of the bimodal phenomenon in corner separation is still unclear and thus needs to be studied further. In order to obtain instantaneous flow field with different unsteadiness and thus to analyse the mechanisms of bimodal phenomenon in corner separation, in this paper detached-eddy simulation (DES) is used to simulate the flow field in the linear compressor cascade where bimodal phenomenon has been found in previous experiment. DES in this paper successfully captures the bimodal phenomenon in the linear compressor cascade found in experiment, including the locations of bimodal points and the development of bimodal points along a line that normal to the blade suction side. We infer that the bimodal phenomenon in the corner separation is induced by the strong interaction between the following two facts. The first is the unsteady upstream flow nearby the leading edge whose angle and magnitude fluctuate simultaneously and significantly. The second is the high unsteady separation in the corner region.
GT13E2 Low Part Load Operation: Extended Flexibility Down to 30% Load
Authors: Magni Fulvio , Grimm Frank , Sorato Sebastiano , Micheli Marco
Published: September 2016

This paper describes the development work of the Low Part Load upgrade package for the GT13E2 gas turbine fleet and the related test results of the engine validation phase.

The GT13E2 gas turbine was originally designed for operation at high combined cycle efficiency and low emissions in the range from about 60% to 100% load. The upgrade package improves the minimum environmental load of the GT13E2 making it possible to operate the GT with full flexibility down to 30% relative load. In fact, in today’s energy market operational flexibility is one of the key requirements for our customers. The extended low part load capability will allow the customers to operate the power plant in combined cycle mode with high efficiency and to rapidly change the load as soon as the grid demands. The upgrade package can be retrofitted to the installed service fleet with AEV burner technology.

The main challenge at low part load operation is to keep the NOx and especially the CO emissions under control. Increased emissions at lower loads were acceptable since it was not intended to operate for long periods of time at these loads. The low part load upgrade improves combustion of the gas turbine by keeping the flame temperature at higher levels. The key to success for improved combustion behavior at part load is mainly the reduction of the burner air mass flow and the redistribution of the corresponding fuel mass flow. The main measures used for the low part load concept are a further closing of the inlet guide vanes and a redistribution of the fuel gas to fewer burners. Additional measures for further reduction of the burner air mass flow at part load were also evaluated and tested. Only a combination of several measures really improves the minimum environmental load of the gas turbine and of the combined cycle efficiency, compared to the original operation concept.

During the development of the low part load project each single measure was extensively validated on GT13E2 engines independently. The combination of the different measures was finally validated on a customer engine and the projected emission targets down to 30% load were successfully confirmed.
Validation and Assessment of the Continuous Random Walk Model for Particle Deposition in Gas Turbine Engines
Authors: Forsyth Peter , Gillespie David R. H. , McGilvray Matthew , Galoul Vincent
Published: September 2016

Threats to engine integrity and life from deposition of environmental particulates that can reach the turbine cooling systems (i.e. <10 micron) have become increasing important within the aero-engine industry, with an increase of flight paths crossing sandy, tropical storm-infested, or polluted airspaces. This has led to studies in the turbomachinery community investigating environmental particulate deposition, largely applying the Discrete Random Walk (DRW) model in CFD simulations of air paths. However, this model was conceived to model droplet dispersion in bulk flow regimes, and therefore has fundamental limitations for deposition studies. One significant limitation is an insensitivity to particle size in the turbulent deposition size regime, where deposition is strongly linked to particle size. This is highlighted within this study through comparisons to published experimental data.

Progress made within the wider particulate deposition community has recently led to the development and application of the Continuous Random Walk (CRW) model. This new model provides significantly improved predictions of particle deposition seen experimentally in comparison to the DRW for low temperature pipe flow experiments. However, the CRW model is not without its difficulties. This paper highlights the sensitivities within the CRW model and actions taken to alleviate them where possible. For validation of the model at gas turbine conditions, it should be assessed at engine-representative conditions. These include high-temperature and swirling flows, with thermophoretic and wall-roughness effects. Thermophoresis is a particle force experienced in the negative direction of the temperature gradient, and can strongly effect deposition efficiency from certain flows. Previous validation of the model has centred on low temperatures and pipe flow conditions. Presented here is the validation process which is currently being undertaken to assess the model at gas turbine-relevant conditions. Discussion centres on the underlying principles of the model, how to apply this model appropriately to gas turbine flows and initial assessment for flows seen in secondary air systems. Verification of model assumptions is undertaken, including demonstrating that the effect of boundary layer modelling of anisotropic turbulence is shown to be Reynolds-independent. The integration time step for numerical solution of the non-dimensional Langevin equation is redefined, showing improvement against existing definitions for the available low temperature pipe flow data. The grid dependence of particle deposition in numerical simulations is presented and shown to be more significant for particle conditions in the diffusional deposition regime. Finally, the model is applied to an engine-representative geometry to demonstrate the improvement in sensitivity to particle size that the CRW offers over the DRW for wall-bounded flows.
Pilot-Pilot Interaction Effects on a Prototype DLE Gas Turbine Burner Combustion
Authors: Kundu Atanu , Klingmann Jens , Subash Arman Ahamed , Collin Robert
Published: September 2016

Lean premixed dry low emission (DLE) combustion system in a gas turbine engine is a globally accepted concept to reduce pollutant emissions and to improve combustion efficiency. This study is focused on an industrial downscaled prototype burner (4th Generation Dry Low Emission Burner for SGT-750 designed and manufactured by Siemens Industrial Turbo machinery AB), which has been tested extensively at atmospheric conditions. To enhance the operability and alleviate flame dynamics behavior, multiple fuel and air circuits (i.e. Rich-Pilot-Lean (RPL), Pilot and Main) are engaged in the burner. Primarily, present study evaluates the RPL-Pilot interaction effect on the main combustion zone. A highly swirled flow from the burner exit produces a central recirculation zones (CRZ) to recirculate the hot vitiated gas for sustaining the combustion process. The main flame is stabilized in the inner shear layer (ISL), which is found in the diverging section (named as Quarl). The total power of the burner was varied between 70–140 kW and the fuel used for the experiment was 99.5% pure methane. A short length quartz liner was used for the experiment and the residence time of the combustor is 9 ms. At the liner exit, emission sampling (CO, NOx) has been conducted using a water-cooled emission probe. Optical measurements were permitted, as the Quarl and combustor liner were optically accessible. Planar laser-induced fluorescence of OH molecule (OH-PLIF) and natural chemiluminescence measurements were conducted to visualize the flame characteristics and its response by changing the RPL and Pilot fuel splits. A comprehensive study was performed by varying the RPL residence time to investigate the main flame stabilization and pollutant formation of the burner. Higher RPL residence time exhibits NOx benefits but at the same time flame instability was increased. Pilot fuel percentage modification demonstrate negative impact on NOx formation due to the limited mixing of fuel and air. With the increase of Pilot fuel split, CO emission decreases, which is advantageous for increasing the LBO margin. The study has identified a number of critical situations where the flame was stabilized without any RPL and Pilot combustion. Apart from the experimental results, a simple reactor network model has been applied for predicting NOx emission. Different kinetic mechanisms were assessed and the prediction results are compared to experimental results. Heat loss from the combustor wall played a significant role on emission formation and was included in the reactor model. This study provides a good understanding of the new DLE industrial burner concept and the RPL-pilot interaction effect on the emission.
End-Wall Secondary Flow Control Using Engineered Residual Surface Structure
Authors: Miao X. , Zhang Q. , Atkin C. , Sun Z.
Published: September 2016

Residual surface roughness is often introduced in the manufacture process with ball-end or fillet-end milling. Instead of paying extra cost to remove these small-scale residual surface structures, there is a potential usage of them as flow control device. This numerical study therefore explores the ability of engineered surface structure in controlling the endwall secondary flow in turbomachinery. The CFD method is validated against the existing experimental data obtained for a 90 degree turning duct flow with a single rib fence placed on the end-wall. The working principle of the engineered surface structure is revealed through detailed analysis on the flow produced by multiple small fences and grooves mimicking the residual surface. The results consistently show that addition of engineered residual structure on flow surface can effectively reduce the magnitude of stream-wise vorticity associated with secondary flow and alleviate its lift-off motion. In the end, a general working mechanism and design guideline for optimizing the residual structure are summarized.
Investigation of Unsteady Flow Phenomena in First Vane Caused by Combustor Flow With Swirl
Authors: Jacobi Simon , Mazzoni Cosimo , Chana Krishan , Rosic Budimir
Published: September 2016

The flow at the combustor turbine interface of power generation gas turbines with can combustors is characterized by high and non-uniform turbulence levels, lengthscales and residual swirl. These complexities have a significant impact on the first vanes aerothermal performance and lead to challenges for an effective turbine design. To date, this design philosophy mostly assumed steady flow and thus largely disregards the intrinsic unsteadiness. This paper investigates the steady and unsteady effects of the combustor flow with swirl on the turbines first vanes. Experimental measurements are conducted on a high-speed linear cascade that comprises two can combustors and four nozzle guide vanes. The experimental results are supported by a Large Eddy Simulation performed with the inhouse CFD flow solver TBLOCK. The study reveals the highly unsteady nature of the flow in the first vane and its effect on the heat transfer. A persistent flow structure of concentrated vorticity is observed. It wraps around the unshielded vane’s leading edge at midspan and periodically oscillates in spanwise direction due to the interaction of the residual low-pressure swirl core and the vane’s potential field. Moreover, the transient behavior of the horseshoe-vortex system due to large fluctuations in incidence is demonstrated.
Analysis of the Sources and the Modal Content of the Acoustic Field in a Radial Compressor Outflow
Authors: Banica Marius C. , Limacher Peter , Feld Heinz-Jürgen
Published: September 2016

In large modern turbochargers, compressors often constitute the main source of noise, with a frequency spectrum typically dominated by tonal noise at the blade passing frequency (BPF) and its harmonics. In transonic operation, inflow BPF noise is mainly generated by rotor locked shock fronts. These and the resulting acoustic fields can be predicted numerically with reasonable accuracy. Outflow noise, while also dominated by BPF tones, is linked to more complex source mechanisms. Its modal structure and the relationships between sources and modal sound pressure levels (SPL) are less well understood. Perhaps this is linked to the intrinsically non-axisymmetric geometries, which results in the need for full stage simulations if high accuracy is of paramount importance.

In order to shed some light on outflow noise generation, a transient simulation of a 360° model of a radial compressor stage, including a vaned diffuser and a volute, was carried out using state-of-the-art CFD. Additionally, experimental data was gathered at a multitude of data points downstream of the volute exit for post processing and modal analysis. The sources and the propagation were calculated directly. Optimized values for tempo-spatial acoustic wave resolution and buffer layer design were chosen, based on extensive studies on simplified models. Two grid refinement levels were used to check grid convergence and time step size independence of the results was ensured.

Numerical and experimental data match within 1% for total pressure ratio, volume flow and exit total temperature for the studied operating point. Both show the same modal content at the 1st BPF and indicate the presence of the same single dominating mode. The numerical results underpredict overall sound power levels (PWL) at the 1st BPF by 6.6dB. This difference is expected to decrease with further grid refinement and improved accounting for numerical damping. At the 2nd BPF, the experimental data show a significant broadening of the modal content with homogeneous modal PWL distributions. The multitude of modes leads to the generation of complex interference patterns, which shows that single-point acoustic measurements are often inadequate for component noise qualification and should be substituted by modal techniques. The dominating dipole sound sources are found in narrow areas around the vane leading edges and the rotor blade trailing edges. Because of the non-axisymmetric geometry, vane dipole source strengths become a function of circumferential position. The unsteady shedding of vortices from the vane suction surfaces is identified as a further possible source mechanism. However, the contributions of structural vibrations and mode scattering due to small manufacturing imperfections remain unclear.
CFD Analysis of a SGT-800 Burner in a Combustion Rig
Authors: Abou-Taouk Abdallah , Andersson Niklas , Eriksson Lars-Erik , Lörstad Daniel
Published: September 2016

This work focuses on 3D turbulent reacting flow modeling of a SGT-800 3rd generation dry low emission (DLE) burner at both atmospheric and engine-like conditions. At atmospheric pressure the burner is fitted in a test rig with high pre-heating of the incoming air. To reduce the computational cost, the M4 mechanism previously developed by Abou-Taouk et al. (2013) is used for operating pressure of 1 bar. A new novel optimized 4-step reaction mechanism for methane-air mixture is developed in the present work at an operating pressure of 20 bar. The mechanism is based on a large sample of detailed chemistry solutions that are processed by an iterative optimization procedure. This leads to a reduced 4-step mechanism, reproducing the targeted detailed chemistry solutions in terms of laminar flame speeds, species profiles and temperatures.

The CFD simulations are performed using the combined eddy dissipation model / finite rate chemistry (EDM/FRC) turbulence chemistry interaction model. The turbulence is modeled using both the k-ω SST and the scale adaptive simulation (SAS) turbulence models. A comprehensive testing and measurement campaign carried out at atmospheric pressure for this burner was previously performed in a combustion test rig. The CFD results are compared to measurement data which includes for example flame position and pressure drop.
Swirl Flame Response to Simultaneous Axial and Transverse Velocity Fluctuations
Authors: Saurabh Aditya , Moeck Jonas P. , Paschereit Christian Oliver
Published: September 2016

In this experimental study we investigate the impact of transverse acoustic velocity fluctuations on the flame transfer function in response to axial velocity fluctuations. A generic swirl flame is exposed to transverse acoustic velocities of varying amplitude and relative phase simultaneously with axial acoustic forcing. Results obtained indicate that transverse velocity affects flame response, and both the magnitude of transverse velocity and its phase with respect to axial forcing are important factors. In addition to this key results, considerations for experimental investigations dealing with transverse acoustic forcing have been discussed.
Experimental Investigation on Impingement Array Cooling Systems Through IR Thermography
Authors: Cocchi L. , Facchini B. , Giuntini S. , Winchler L. , Tarchi L. , Innocenti L. , Andrei L. , Bonini A.
Published: September 2016

This paper reports the results of an experimental campaign involving heat transfer measurements on the target surface of an impingement jet array. Test were performed with the help of an open loop wind tunnel test rig, housing a model of the cooling system. The model general layout consists of an impingement channel, designed as a straight duct with rectangular section. A side of the channel is a steel impingement plate, while the opposite side acts as the impingement target surface and is composed of an electrically heated Inconel sheet supported by a thin steel plate. The coolant flow is provided by a plenum located upstream the impingement plate. The combined use of an inverter controlled electric fan and four rotary vanes vacuum pumps allows air circulation inside the model.

Convective heat transfer coefficient on the impingement target surface is evaluated through a steady-state technique. The temperature of the target surface is measured through IR thermography: the outer side of the target surface is painted with a high-emissivity black coating and is observed by an IR camera; the inner temperature is then obtained through a simple finite difference model of the target plate.

In the present work, different impingement layouts were tested (3 ≤ Sx/d ≤ 10, 3 ≤ Sy/d ≤ 20, 2.5 ≤ H/d ≤ 3.33) for different values of jet Reynolds number (2000 ≤ Rej ≤ 19000).

Heat transfer results show a good agreement with the existing correlations, thus providing a validation for the adopted measurement technique, and extend the investigation to holes pitch values outside from correlations.