bluuebunny/crossref_metadata_2025 huggingface dataset:
Aero-Thermal Performance of a Nozzle Vane Cascade With a Generic Non Uniform Inlet Flow Condition: Part II — Influence of Purge and Film Cooling Injection
Authors: Barigozzi G. , Abdeh H. , Perdichizzi A. , Henze M. , Krueckels J.
Published: September 2016

In the present paper, the influence of the presence of an inlet flow non uniformity on the aerodynamic and thermal performance of a film cooled linear nozzle vane cascade is fully assessed. Tests have been carried out with platform cooling, with coolant ejected through a slot located upstream of the leading edge. Cooling air is also ejected through a row of cylindrical holes located upstream of the slot, simulating a combustor cooling system. An obstruction was installed upstream of the cascade at variable tangential and axial position to generate a flow non uniformity. The cascade was tested at a high inlet turbulence intensity level (Tu1 = 9%) and at a constant inlet Mach number of 0.12 and nominal cooling condition. Aero-thermal characterization of vane platform was obtained through 5-hole probe and end wall adiabatic film cooling effectiveness measurements. Results show a relevant negative impact of inlet flow non uniformity on the cooled cascade aerodynamic and thermal performance. Higher film cooling effectiveness and lower aerodynamic losses are obtained when the inlet flow non uniformity is located at mid pitch, while lower effectiveness and higher losses are obtained when it is aligned to the vane leading edge. Moving the non uniformity axially or changing its blockage only marginally influences the platform thermal protection.
Body Force Modeling of the Aerodynamics of the Fan of a Turbofan at Windmill
Authors: Dufour Guillaume , Thollet William
Published: September 2016

The windmilling regime of a turbofan corresponds to a freewheeling mode of the fan rotor, driven by the ram pressure at the inlet. Early in the design process, determination of the windmilling rotational speed of the fan can be critical in the design of the supporting structure of the engine. Therefore, prediction of key parameters in windmilling is an important part of engine design. In particular, given the very high bypass ratio obtained at windmill (typically around 50), the flow in the fan stage and bypass duct is of prime interest, as it drives the establishment of the rotational speed of the low pressure spool and the overall drag. Classical CFD simulations have been shown to provide an adequate representation of the flow, but extensive parametric studies can be needed, which underlines the need for reduced-cost modeling of the flow in the engine. In this context, a body force modeling (BFM) approach to windmilling simulations is examined in the present contribution. The main objective is to assess the capability of the BFM approach to reproduce the aerodynamics of the flow in the fan rotor of a turbofan at windmill, and to propose a method to predict the rotational speed of the fan. The test case considered is a high-bypass ratio geared turbofan (the DGEN 380), which has been tested in an experimental facility designed to reproduce ground level windmilling conditions. The available global and local experimental data are used to validate the model. Furthermore, classical RANS simulations are also provided as reference simulations to assess the accuracy of the BFM results.

It is found that the overall performance of the fan is well predicted by the BFM simulations, in particular at the low rotational regime associated to windmilling. In terms of local validation, radial profiles are also found to be in good agreement, except close to the shroud. Analysis of the CFD results shows this can be traced back to massive flow separation in the rotor tip area. In terms of cost, a BFM simulation is about 80 times faster than the baseline CFD computation, making this approach very efficient in term of accuracy-to-cost ratio. Finally, assuming zero-work exchange across the rotor, a transient equation for the rotational speed is derived and included in the time-marching process to the steady state. As a result, the rotational speed of the fan becomes an output of the simulations. The rotational speed predicted by the present model shows good agreement with engine experimental data. However, as only the rotor is modeled, the internal losses are not fully accounted for, and the massflow has to be specified from the experimental data. Further improvement of the approach will consist in modeling the stator and the complete secondary duct so that the loss, and therefore the massflow, can be predicted.
Efficient Modeling Strategy of an Axial Compressor Fan-Stage Under Inlet Distortion
Authors: Lobo Bryan , Zori Laith , Galpin Paul , Holmes William
Published: September 2016

The front fan of a turbofan aircraft engine often operates under distorted inlet flow conditions. This distortion is caused by either flight operating conditions, such as a crosswind or boundary layer ingestion, or due to its nacelle installation. These flow conditions negatively impact the aerodynamic performance of the compression system. Moreover, the asymmetry of the flow causes non-uniform circumferential pressure distortions which can trigger a strong aeromechanical response in the fan blades.

Numerical simulation can contribute to the design process if it can accurately predict the aerodynamic performance penalties and the loads experienced by the fan blades, thereby identifying potential problems early in the design phase. This requires accurate accounting of the pressure loads on the fan from the upstream inlet distortion and the potential effect of the downstream stator row. The loads are inherently transient in nature, requiring solutions on the full wheel geometry. However, full wheel modeling is expensive and not practical early in the design cycle. In this work, an efficient modeling strategy is proposed for an axial compressor fan with a downstream stator row (NASA Stage 67, rotor/stator) undergoing inlet distortion.

A multi-frequency frozen gust analysis using the Fourier-Transformation (FT) pitch-change method is utilized to solve this flow problem on a reduced geometry (two rotor-passages only). A once-per-revolution inlet distortion modeled as a cosine variation in total pressure is imposed upstream of the rotor. The influence of the stator row on the fan is accounted for within a transient simulation by imposing a 360 degree profile at the exit of the rotor. The profile from the stator row is obtained previously from a steady-state simulation using a multiple mixing-plane approach. In this approach the stator potential flow and the pressure variation in the stator row due to inflow distortion are accounted for.

The paper compares the reduced geometry model with full wheel transient predictions, thereby demonstrating the efficiency of the proposed method both in terms of accuracy and solution speedup. Important aerodynamic performance parameters as well as flow field solution monitors are compared to assess the viability of this modeling strategy.
Experimental Investigation on Double Anti-Stall Ring Effects on Reversible Ventilation Fan Performance
Authors: Corsini Alessandro , Delibra Giovanni , Sheard Anthony G. , Volponi David
Published: September 2016

Stall margin improvement is a crucial issue during fan design, selection and installation. In fact, several industrial fans are operated in extreme applications and requested to be highly flexible in order to be able to withstand abrupt changes in operating conditions. This is the case of fans operated under distorted inlet conditions or interacting with other fans or used for reversible operations in tunnel and metro applications.

This paper reports on a systematic experimental study on the effects of the use of casing treatments on the performance of a single stage, reversible, axial fan. Tests focused on the performance of up-stream single treatment and up- and downstream double treatment, respectively designed to prevent the fan to run into stall in forward-only operations and forward- and reverse- operations. The study reports on the assessment of the change in performance, in normal and stalled operations, with an emphasis on the relative axial position between casing treatments and the impeller blades. The analysis demonstrates the achievement of significant improvements in performance in the unstable region for all the tested configurations with marginal losses in the stable counter-part.
Investigation of Thermal and Stress States of the Annular Combustion Chamber Flame Tube Walls
Authors: Anisimov Vladislav M. , Zubrilin Ivan A. , Orlov Mikhail Y.
Published: September 2016

Durability and reliability are the most important parameters of gas turbine engines combustion chamber. Combustion chamber flame tube walls are the most temperature-loaded engine components. Therefore, eliminating wall burnout is an key issue as well as keeping temperature of combustion chamber elements within the materials operating temperature range. Thus, there is a need to define thermal state of these elements. Currently, the problem of flame tube wall burnout is exacerbated by trends of increasing the compressor pressure ratio and temperature before the turbine. It is important to resolve this problem during the gas turbine engine design phase. This will reduce time and material costs for launch of their serial production. CFD is one way of resolving this problem.

The numerical method of simulating thermal state of flame tube walls was applied and tested. This method takes into account a thermal barrier coating and a cooling system. Three-dimensional geometric model consists of the flow area and the flame tube walls with multi-layer thermal barrier coating. Flow area is needed to simulate fluid dynamic processes. Flame tube walls geometry was created for heat transfer simulation. Mathematical model of the workflow in the combustion chamber had been created previously and was validated. The study is carried out by numerical methods, using the commercial software Ansys. Temperature distribution on the combustion chamber flame tube walls was obtained by the simulation. It agrees well with the results of the experiments.

The maximum temperature of the walls was reduced from 1400 K to 1100 K through the reallocation of holes area between the cooling system belts. This ensures the operability of the wall material. Then, the simulations of the flame tube walls deformation were conducted. As a result, the deformations and stresses, that occurred due to the walls heating, were evaluated using the one-way Fluid-Structure-Interaction (FSI) module. The maximum displacement along the axis of the combustion chamber was less than 2 mm, when the acceptable move in telescopic connection is 6 mm. It was found that the outer flame tube wall exposed the highest heat load. The area of the outer annular channel decreased by 18% and the area of the internal annular channel increased by 7%. Air distribution of the cooling system was changed due to walls deformation and velocity changes in annular channels, therefore the additional simulations and some modification in the design are required. The methodology created on the base of this study can be used for the simulation of the various combustion chamber designs.
Large Eddy Simulation of a Realistic Gas Turbine Combustor
Authors: Xu Baopeng , Liu Ya , Xie Rong
Published: September 2016

This paper proposes a large eddy simulation approach for the modeling of combusting flow with spray in realistic gas turbine combustors. A one equation subgrid model is used to model the effect of the unresolved subgrid scales on the resolved large scales. Subgrid combustion is modeled by an extended eddy dissipation model in which the filtered reaction rate is controlled by the turbulent mixing rate between the fine structures and the surrounding fluids. An Eulerian-Lagrangian approach is used to model the two-phase spray flow, and spray particles are tracked by a two-way coupling Lagrangian approach.

Then the proposed approach is applied to simulate a combusting spray flow in an industrial annular combustor. The objectives of this study are to demonstrate its capability to investigate the complex flow and combustion dynamics in realistic gas turbine combustors. The predicted instantaneous and time averaged fields of velocity, temperature, pressure, fuel mass fraction are investigated. The precessing vortex core caused by the swirling flow as well as pressure oscillations is examined. The predicted results nicely reproduce the flow, spray and combustion dynamics and successfully capture the main features of the studied combustor, such as the processing vortex core. Finally, the predicted exit temperature and the total pressure loss are compared with experimental data and good agreements are obtained.
Numerical Study on the Effect of a Volute on Surge Phenomena in a Centrifugal Compressor
Authors: Jeon S. H. , Hwang D. H. , Park J. H. , Kim C. H. , Baek J. H. , Kim H. W.
Published: September 2016

Numerical investigation of the effect of the volute on stall flow phenomenon is presented by solving three-dimensional Reynolds-averaged compressible Navier-Stokes equations. Two different configurations of a centrifugal compressor were used to compare their performance: One is an original centrifugal compressor which is composed of impeller, splitter, vaned diffuser and a volute and the other is the one without a volute. Steady calculations were performed to predict aerodynamic performance in terms of the pressure ratio, efficiency and mass flow rate. The results show that the operating range of the compressor with a volute is narrower than that of the compressor without a volute. This can be interpreted that flow instability is strongly influenced by the tongue of a volute which is highly asymmetric.

Unsteady calculations were also performed with a time-step size of 38μs corresponding to a pitch angle of 5 degrees at the given rotational speed. The flow characteristics for two configurations are analyzed and compared at various instantaneous times showing unsteady dynamic features. Based on the unsteady flow simulation, fast Fourier transform at several discrete points in semi-vaneless space was performed at peak efficiency and near surge point in order to illustrate the unstable flow physics in both configurations. It is found that the blade passing frequency is dominant, indicating that diffuser passages have a periodicity of 40 degrees due to the rotational blades. Besides blade passing frequency, there were several noticeable frequencies which affect the instability of the whole system. Those frequencies in both configurations are compared and analyzed in various aspects.
Analysis of Time-Signal of an Industrial Gas Turbine Combustor Under an Unstable Condition
Authors: Lengani D. , Zunino P. , Romoli F. , Bertolotto E. , Rizzo S.
Published: September 2016

This paper analyzes the time-signals of pressure sensors mounted in an industrial gas turbine combustor under an unstable condition. The present investigation is aimed at the discussion of the sudden increase in amplitude due to the limit-cycle oscillations and of its temporal evolution. To this purpose, different post-processing tools are described and adopted: i.e. wavelet transform, cross-correlations, time-space Fourier transform and proper orthogonal decomposition (POD).

The properties of the wavelet transform are used in order to identify the time of occurrence and the frequency of the limit-cycle oscillations. They occur at the second harmonic of the natural frequency of the annular combustion chamber. The amplitude of the pressure fluctuations at this characteristic frequency increases to a critical value with very large amplitude in about 0.15s that corresponds to about 26 periods of the phenomenon. Within this period, the pressure signals from two neighboring burners have a quite large and increasing degree of correlation as it is observed from the cross-correlation of the signals. The time-space Fourier transform suggests that the instability couples with a natural mode of the combustion chamber. The azimuthal wave length of such mode is half of the combustion chamber circumference (this corresponds to an azimuthal mode 2). According to this findings, the POD is used to provide an identifier for the occurrence of the limit-cycle oscillations. In fact, POD is known to isolate the deterministic fluctuations based on an energy rank. Hence, the first POD mode isolates the effect of specific frequency forcing and its energy content is retained in the first POD eigenvalue which is used as identifier.
Secondary Flow and Extra Heat Transfer Enhancement of Ribbed Surface After Jet Impingement
Authors: Wang Z. , Zhang Q. , Yan Y. , Liu K.
Published: September 2016

It has been recognized by previous experiments that substantial heat transfer augmentation can be achieved by adding ribbed turbulators after jet impingement in a cross flow. This study investigates the fundamental working mechanism in a typical turbulent channel flow. Conjugate CFD simulations were carried out for ribs, jet impingement, and their combinations. The flow characteristics and drawbacks for the two individual enhancement techniques are highlighted. Further analysis on the coupling design reveals that the counter-rotating vortices generated by the jet flow can energize the inter-rib recirculating vortices and promote the span-wise convection. With an optimal combination design, extra heat transfer benefit could be achieved beyond the simple superposition of rib and jet impingement techniques. This general thermal design philosophy is useful for design optimization in practice and has also been confirmed by published experimental data.
An Experimental Investigation of Impingement Heat Transfer in Narrow Space With Full-Height Pin Fins
Authors: Rao Yu , Wan Chaoyi , Liu Yuyang , Qin Jiang
Published: September 2016

An experimental study has been conducted on multiple-jet impingement heat transfer in a narrow space with full-height pin fins under maximum cross flow scheme. Transient liquid crystal thermography method has been used to obtain the detailed impingement heat transfer distribution for the Reynolds numbers from 15,000 to 30,000. The experimental study shows that the spanwisely-averaged Nusselt number ratio Nu/(Re0.8 Pr1/3) is almost independent of Reynolds numbers, and the full-height pin-fin arrays can slightly improve the average Nusselt number on the endwall of the target plate by about 5.0%, and increase the pressure loss by up to about 17.9%. It is also found that heat transfer uniformity is also improved on the endwall of the target plate with pin fin arrays.
Development of a Model for Auto-Ignition Delays and its Use for the Prediction of Premix Combustion Reliability
Authors: Bounaceur Roda , Glaude Pierre-Alexandre , Sirjean Baptiste , Fournet René , Montagne Pierre , Vierling Matthieu , Molière Michel
Published: September 2016

Except in diesel engine applications, auto-ignition is an unwanted event from a general safety and reliability standpoint. It is especially undesirable in the premixing process involved in most low NOx combustion technologies. Therefore, in addition to auto-ignition temperature, autoignition delay (AID) is a key data for the design of modern combustors including gas turbine ones. The authors have investigated the detailed kinetic mechanisms leading to autoignition and established practical AID correlations involving the fuel composition, its temperature, pressure and equivalence ratio. The correlations brought about during this program offer a good reconciliation between calculated and experimental AID through a wide range of fuel composition, initial temperature and pressure. Validations were mainly done against data acquired with experimental setups consisting in shock tubes and rapid compression machines. The auto-ignition delay times of methane, pure light alkanes and various blends representative of several natural gas and process-derived fuels have been reviewed. For each fuel mixture, this study procures a simple equation linking the auto-ignition delay time to the temperature, pressure and equivalence ratio. As a direct application of this work, the authors have evaluated the risk of auto ignition in the premixing zone of a combustor characterized by a residence time and an associated probability density function. The results of this simulation stress the key role of larger hydrocarbon in the risk of flash-back events.
Some Perspectives on the Treatment of Three-Dimensional Flows on Axial Compressor Blading
Authors: Obaida Hayder M. B. , Kawase Motoyuki , Rona Aldo , Gostelow J. Paul
Published: September 2016

The unsteady and three-dimensional nature of the flow past axial compressor blading poses substantial challenges to the design of the main flow passage. High aspect ratio blading is amenable to the approach of splitting the design task between the cascade and the meridional planes. However, the three-dimensional flows increasingly affect the stage aerodynamic performance with decreasing blade aspect ratios. At very high load conditions, corner vortices can grow to two-thirds of the blade span, under the influence of the pitchwise pressure gradient, causing significant blockage and loss. A survey of treatments for three-dimensional flows highlights a variety of approaches, including longitudinal and tangential slots for suction and blowing, fences, turning vanes, fillets, and grooves. The merits and issues exposed by past implementations of these end-wall treatments are summarized. Considered together, these arrangements display a variable and open approach, which points towards an opportunity for considering a more common framework, led by a greater understanding of the flow physics. Preliminary work on the parametrization of end-wall grooves has highlighted some promising topological features of end walls generated by using the Beta distribution function as the guide curve. This seemingly unexplored application of the Beta function to axial compressor end wall design promises a better fit with the pitchwise periodic axial compressor geometry than other guide curve functions considered herein and used in the past.
Impact of Flame Stretch and Heat Loss on Heat Release Distributions in Gas Turbine Combustors: Model Comparison and Validation
Authors: Klarmann Noah , Sattelmayer Thomas , Geng Weiqun , Zoller Benjamin Timo , Magni Fulvio
Published: September 2016

The work presented in this paper comprises the application of an extension for the Flamelet Generated Manifold model which allows to consider elevated flame stretch rates and heat loss. This approach does not require further table dimensions. Hence, the numerical overhead is negligible, preserving the industrial applicability. A validation is performed in which stretch and heat loss dependent distributions are obtained from the combustion model to compare them to experimental data from an atmospheric single burner test rig operating at lean conditions. The reaction mechanism is extended by OH*-kinetics which allows the comparison of numerical OH*-concentrations with experimentally obtained OH*-chemiluminescence. Improvement compared to the Flamelet Generated Manifold model without extension regarding the shape and position of the turbulent flame brush can be shown and are substantiated by the validation of species distributions which better fit the experimental in situ measurements when the extension is used. These improvements are mandatory to enable subsequent modeling of emissions or thermoacoustics where high accuracy is required. In addition to the validation, a qualitative comparison of further combustion models is performed in which the experimental data serve as a benchmark to evaluate the accuracy. Most combustion models typically simplify the combustion process as flame stretch or non-adiabatic effects are not captured. It turns out that the tested combustion models show improvement when stretch or heat loss is considered by model corrections. However, satisfactory results could only be achieved by considering both effects employing the extension for the Flamelet Generated Manifold model.
Analysis of the Unsteady Flow in Compressor Cascade With POD Method
Authors: Yangang Wang , Yue Li , Junxu Chen
Published: September 2016

The leading edge vortex’s frequency characteristics and flow separation due to adverse pressure gradient are found to be dominant in the determination of compressor performance. For deep understanding of the unsteady gas flow in compressor cascade, the numerical study with Proper Orthogonal Decomposition (POD) reconstructed method is performed in the present study. And, the Fast Fourier Transform (FFT) is implemented to get the vortex fluctuation frequency to fully understand flow separation. Furthermore, the comparisons between the baseline results and the reconstructed flow field by POD method are conducted for investigating the feasibility of POD method. It demonstrated that a few POD modes are adequate to reconstruct main flow field and higher POD modes reflect more detailed flow structure. And also, the characteristic of mode coefficient is analyzed with the detailed explanations of POD. Then, the POD method, which decouples flow field in space and time, is found to be effective in the depiction of the vortex structure and the representation of the flow mechanism. The present study can be regarded as the first step to determine the number of POD modes and evaluates the error of reconstructed flow field.
Predictive Emissions Monitoring System for Small Siemens Dry Low Emissions Combustors: Validation and Application
Authors: Hackney R. , Sadasivuni S. K. , Rogerson J. W. , Bulat G.
Published: September 2016

Predictions of the Siemens 1D reactor network model, GENE-AC, are validated against emissions measurements from high pressure tests of an industrial gas turbine combustor. The same modelling approach is then applied to the Siemens SGT-400 production engine, where trends predicted by a reactor network model of the SGT-400 combustor are used as the basis for a Predictive Emissions Monitoring System. Input parameters include: load, pilot/main fuel split, equivalence ratio, and inlet air temperature and pressure. Comparison with a sample of 90 engine tests demonstrates reasonably accurate prediction of NOx and CO without tuning the model to match individual engines.
A Kinetics Model for the Shockless Explosion Combustion
Authors: Berndt Phillip , Klein Rupert , Paschereit C. Oliver
Published: September 2016

The shockless explosion combustion (SEC) is a novel approach to constant volume combustion in gas turbines. It promises an efficiency gain comparable to that of pulse detonation combustion (PDC), but without the drawbacks associated with detonations. It utilizes homogeneous combustion of a volume of fuel/air to avoid strong shock waves, similar to the RCCI process in internal combustion engines. Recharging is handled analogous to a pulse jet through the pressure waves in the combustion chamber. To achieve homogeneous auto ignition, the process involves setting up a stratified layer of fuel/air such that it homogeneously auto ignites in an approximately constant volume combustion (CVC). This becomes feasible by using fuels with small dependence of their auto ignition time on temperature, e.g. blends involving fuels with negative temperature coefficient (NTC) behaviour. The ignition process of such fuels is complex and often involves multi-stage ignition on time scales comparable to the acoustic time scale. It is hence expected that even though a SEC effectively is CVC, the ignition can not be modeled in 0D, but that it instead involves complex interaction between gas dynamics and chemical kinetics. The stratification process therefore has to be numerically optimized in CFD calculations. Optimization, especially if whole cycles are to be simulated, requires small kinetics models, even if restricted to one dimension, to be computationally feasible. On the other hand, the interaction of kinetics and gas dynamics at ignition rules out an easy to evaluate optimization goal for reduction of the chemical kinetics using offline methods like directed relation graphs and the techniques based on sensitivity analysis introduced by Williams/Peters. Even if sufficient computation power was invested, the accuracy constraints on the auto ignition times severely limit the usability of a conventional reduced mechanism. Online tools like CSP or ILDM would be an option for practical purposes, but do not provide insight into the ignition process and are therefore of little help for fundamental research. For a CFD simulation of a SEC, a new ansatz has therefore been developed. We exploit the constraint of a small temperature dependence of the auto ignition time on temperature to introduce a model specialized for SEC simulation that is sufficiently small to allow optimization of a fuel/air stratification, yet features correct auto ignition delay times for each ignition stage to the accuracy of experimental measurements. We then proceed to present simulation results which a posteriori justify our approach and demonstrate that shockless explosion combustion is feasible.
Shockless Explosion Combustion: Experimental Investigation of a New Approximate Constant Volume Combustion Process
Authors: Reichel Thoralf G. , Bobusch Bernhard C. , Paschereit Christian Oliver , Schäpel Jan-Simon , King Rudibert , Klein Rupert
Published: September 2016

Approximate constant volume combustion (aCVC) is a promising way to achieve a step change in the efficiency of gas turbines. This work investigates a recently proposed approach to implement aCVC in a gas turbine combustion system: shockless explosion combustion (SEC). The new concept overcomes several disadvantages such as sharp pressure transitions, entropy generation due to shock waves, and exergy losses due to kinetic energy which are associated with other aCVC approaches like, e.g., pulsed detonation combustion. The combustion is controlled via the the fuel/air mixture distribution which is adjusted such that the entire fuel/air volume undergoes a spatially quasi-homogeneous autoignition. Accordingly, no shock waves occur and the losses associated with a detonation wave are not present in the proposed system. Instead, a smooth pressure rise is created due to the heat release of the homogeneous combustion. An atmospheric combustion test rig is designed to investigate the autoignition behavior of relevant fuels under intermittent operation, currently up to a frequency of 2Hz. Application of OH*- and dynamic pressure sensors allows for a spatially- and time-resolved detection of ignition delay times and locations. Dimethyl ether (DME) is used as fuel since it exhibits reliable autoignition already at 920K mixture temperature and ambient pressure. First, a model-based control algorithm is used to demonstrate that the fuel valve can produce arbitrary fuel profiles in the combustion tube. Next, the control algorithm is used to achieve the desired fuel stratification, resulting in a significant reduction in spatial variance of the auto-ignition delay times. This proves that the control approach is a useful tool for increasing the homogeneity of the autoignition.
Rapid Preliminary Combustor Design Using a Flow Network Approach
Authors: du Toit B. , Theron S.
Published: September 2016

Preliminary combustor design usually requires that an extensive number of geometrical and operational conditions be evaluated and compared. During this phase important parameters the designer sought after are typically the mass flow rate distribution through air admission holes, associated pressure losses as well as liner wall temperatures. The process is therefore iterative in nature and can become expensive in terms of engineering analysis cost considering the time required to build and execute 3D CFD models. Network codes have the potential to fill the gap during this stage of the design since they can be setup and solved in timeframes that are orders of magnitude less than comprehensive CFD models, essentially leading to cost savings since overall less time is spent on 3D simulations and rig tests. An additional advantage using this approach is that results from the network solution can be applied as boundary conditions to subsequent more detailed 3D models.

In this study a commercial flow network tool, Flownex®, was used to model a complete combustor including flow distribution, combustion and heat transfer. The integrated mass, momentum and energy balance is solved using the continuity, momentum and energy equations applied to nodes and elements. These nodes and elements are the modular building blocks, typically semi-empirical and allow users to either select appropriate built-in correlations, or to define using specific equations through scripting. Flow equations are fully compressible and applied to the gas mixture. The chemical composition of the reactants forming during combustion as well as the adiabatic flame temperature is determined from the NASA CEA package incorporated into the solution. Heat transfer mechanisms included in the model are gas-surface radiation, film convection, forced convection in ducts, surface-surface radiation, and 2D axially-symmetric conduction through solid walls. Results produced from the network were compared with test data obtained from the NASA E3 development combustor. Overall good agreement resulted, showcasing the success of the approach followed.
Control of the Precessing Vortex Core by Open and Closed-Loop Forcing in the Jet Core
Authors: Kuhn Phoebe , Moeck Jonas P. , Paschereit Christian Oliver , Oberleithner Kilian
Published: September 2016

The precessing vortex core (PVC) is the dominant coherent structure of swirling jets, which are commonly applied in gas turbine combustion. It stems from a global hydrodynamic instability that is caused by internal feedback mechanisms in the jet core. In this work, we apply open and closed-loop forcing in a generic non-reacting jet to control this mechanism and the PVC. Control is exerted by two oppositely facing, counter-phased zero-net mass flux jets, which are introduced radially into the flow through a thin lance positioned on the jet center axis. By using this type of forcing, the instability mode m = 1, corresponding to the PVC, can either be excited or damped. This markedly affects the PVC oscillation frequency and amplitude. The passive influence of the actuation lance on the mean flow field properties and the coherent flow dynamics is studied first without forcing. PIV and hot-wire measurements reveal an effect on the mean flow, but no qualitative changes of the PVC dynamics. Lock-in experiments are conducted, in which the synchronization behavior of the PVC with the forcing is determined. Here, two different cases are considered. First, actuation is applied at different streamwise positions in order to identify the region of highest receptivity towards external forcing. This region of lowest lock-in amplitude is shown to coincide with the location of the wavemaker, shortly upstream of the vortex breakdown bubble. Second, the lock-in behavior at a fixed axial position and various forcing frequencies ff is studied. A linear correlation between the lock-in amplitude and the deviation of the forcing frequency from the natural oscillation frequency |ff – fn| is observed. Closed-loop control is then applied with the aim to suppress the PVC. The actuator lance is positioned in the wavemaker region, where the flow is most receptive. Magnitude and phase of the natural flow oscillation associated with the PVC are estimated from four hot-wire signals using an extended Kalman filter. The estimated PVC signal is phase-shifted and fed back to the actuator. PIV measurements reveal that feedback control achieves a reduction of the PVC oscillation energy of about 40%.
Investigation of Siemens SGT-800 Industrial Gas Turbine Combustor Using Different Combustion and Turbulence Models
Authors: Lörstad Daniel , Ljung Anders , Abou-Taouk Abdallah
Published: September 2016

Siemens SGT-800 gas turbine is the largest industrial gas turbine within Siemens medium gas turbine size range. The power rating is 53MW at 39% electrical efficiency in open cycle (ISO) and, for its power range, world class combined-cycle performance of >56%. The SGT-800 convectively cooled annular combustor with 30 Dry Low Emissions (DLE) burners has proven, for 50–100% load range, NOx emissions below 15/25ppm for gas/liquids fuels and CO emissions below 5ppm for all fuels, as well as extensive gas fuel flexible DLE capability.

In this work the focus is on the combustion modelling of one burner sector of the SGT-800 annular combustor, which includes several challenges since various different physical phenomena interacts in the process. One of the most important aspects of the combustion in a gas turbine combustor is the turbulence chemistry interaction, which is dependent on both the turbulence model and the combustion model. Some turbulence-combustion model combinations that have shown reasonable results for academic generic cases and/or industrial applications at low pressure, might fail when applied to complex geometries at industrial gas turbine conditions since the combustion regime may be different.

Therefore is here evaluated the performance of Reynolds Averaged Navier-Stokes (RANS) and Scale Adaptive Simulation (SAS) turbulence models combined with different combustion models, which includes the Eddy Dissipation Model (EDM) combined with Finite Rate Chemistry (FRC) using an optimized reduced 4-step scheme and two flamelet based models; Zimont’s Burning Velocity model and Lindstedt & Vaos Fractal model. The results are compared to obtained engine data and field experience, which includes for example flame position in order to evaluate the advantages and drawbacks of each model. All models could predict the flame shape and position in reasonable agreement with available data; however, for the flamelet based methods adjusted calibration constants were required to avoid a flame too far upstream or non-sufficient burn out which is not in agreement with engine data. In addition both the flamelet based models suffer from spurious results when fresh air is mixed into fully reacted gases and BVM also from spurious results inside the fuel system. The combined EDM-FRC with a properly optimized reduced chemical kinetic scheme seems to minimize these issues without the need of any calibration, with only a slight increase in computational cost.
Identification of Multi-Parameter Flame Transfer Function for a Reheat Combustor
Authors: Scarpato Alessandro , Zander Lisa , Kulkarni Rohit , Schuermans Bruno
Published: September 2016

Lean premix technology is widely spread in gas turbine combustion systems, allowing modern power plants to fulfill very stringent emission targets. These systems are however also prone to thermoacoustic instabilities, which can limit the engine operating window. The thermoacoustic analysis of a combustor is thus a key element in its development process. GT24/GT26 reheat combustion system feature a unique technology where fuel is injected into a hot gas stream from a first combustor and auto-ignites in a sequential combustion chamber. Recently, a methodology was successfully developed and validated to analyze the dynamic response of an auto-ignition flame and to extract the Flame Transfer Function using unsteady Large-Eddy Simulations (LES) [GT2015-42622]. The flame was assumed to behave as a Single Input Single Output (SISO) system. The analysis qualitatively highlighted the important role of temperature and equivalence ratio fluctuations, but it was not possible to separate these effects from velocity perturbations. This is the main target of the present work: the flame is treated as a multi-parameter system, and compressible LES are conducted to extract the frequency-dependent flame transfer function. The simulations are forced with uncorrelated broadband signals in order to efficiently calculate the dynamic response over the frequency range of interest. The methodology introduced in this work will help to define stable operation concepts for gas turbines.
Industrial Gas Turbine Health and Performance Assessment With Field Data
Authors: Roumeliotis I. , Aretakis N. , Alexiou A.
Published: September 2016

The paper presents a thorough analysis of historical data and results acquired over a period of two years through an online real-time monitoring system installed at a Combined Heat and Power (CHP) plant. For gas turbine health and performance assessment, a Gas Path Analysis tool based on the adaptive modeling method is integrated into the system. An engine adapted model built through a semi-automated method is part of a procedure which includes a steam/water cycle simulation module and an economic module used for power plant performance and economic assessment. The adaptive modeling diagnostic method allowed for accurate health assessment during base and part load operation identifying and quantifying compressor recoverable deterioration and the root cause of an engine performance shift. Next the performance and economic assessment procedure was applied for quantifying the economic benefit accrued by implementing daily on-line washing and for evaluating the financial gains if the off-line washings time intervals are optimized based on actual engine performance deterioration rates.

The results demonstrate that this approach allows continuous health and performance monitoring at full and part load operation enhancing decision making capabilities and adding to the information that can be acquired through traditional analysis methods based on heat balance and base load correction curves.
Optimizing Separate Exhaust Turbofans for Cruise Specific Fuel Consumption
Authors: Khalid Syed
Published: September 2016

Cruise specific fuel consumption (SFC) of turbofan engines is a key metric for increasing airline profitability and for reducing CO2 emissions. Although increasing design bypass ratio (BPR) of separate exhaust turbofan configurations improves cruise SFC, further improvements can be obtained with control actuated variable geometry modulations of core nozzle throat area, bypass nozzle throat area, and compressor variable vanes (CVV). The scope of this paper is to show only the benefits possible, and the process used in determining those benefits, and not to suggest any particular control algorithm for searching the best combination of the control effectors. A parametric cycle study indicated that the effector modulations could increase the cruise BPR, core efficiency, transmission efficiency, propulsive efficiency, and ideal velocity ratio resulting in a cruise SFC improvement of as much as 2.6% depending upon the engine configuration. The changes in these metrics with control effector variations will be presented. Modulation of CVV is already possible in legacy digital controls, and modulation of nozzle areas should be explored in light of the low bandwidth requirements at steady-state cruise conditions.
Design Exploration of a Return Channel for Multistage Centrifugal Compressors
Authors: Jariwala Vishal , Larosiliere Louis , Hardin James
Published: September 2016

In this study, aerodynamic design improvement options are explored for a low vane count and high flow-coefficient stage return channel, which was found to produce larger than acceptable levels of residual swirl and distortion at the stage exit. A CFD-driven design exploration of three classes of return channel vanes was conducted with the goal of achieving a useful reduction in the stage exit residual swirl angle and its spanwise variance without compromising total pressure loss.

First, the approach taken to anchor the CFD model with test data and resultant aerodynamic diagnosis at design point for the baseline return channel are discussed. This is followed by a cursory parametric design screening to explore concepts that can potentially meet the design goal while adhering to the spatial envelope (stage spacing) and mechanical constraints. Results of this exploration are presented and some conclusions are offered concerning the suitability of a 3D return channel guide vane partially extended into the crossover bend.
Numerical Simulations of Unsteady Aerodynamic Effects in the Blade Tip Region of Cooling Fans
Authors: Na Gi-Don , Kameier Frank , Springer Nils , Mauß Michael
Published: September 2016

The acoustical characteristics of fans are an essential criterion of product quality and are continually growing in importance as for example cooling fan modules in the automotive industry have to suffice high comfort requirements. In order to locate dominant acoustic sources and to reduce the noise emission generated by a shrouded fan configuration, numerical simulations are performed. The working approach considers variously modified fan geometries and their evaluation regarding arising vortex flow phenomena and their effect on a decreased sound pressure level (SPL) in consideration of an improvement or the constancy of aerodynamic fan performance. Particular emphasis lies on the analysis of secondary flows in the blade tip region by postprocessing CFD-results. Due to the large number of geometrical modifications investigated and the importance of highly resolved eddy structures, a hybrid approach is chosen by applying the SAS-SST turbulence model in URANS simulations. The SAS (Scale Adaptive Simulation) delivers LES (Large Eddy Simulation) content in unsteady regions of a RANS-simulation and exhibits not nearly the high computational effort needed to perform a full scale LES. An assessment of the actual propagation of noise emission into the far-field is made by performing experimental investigations on the most promising modifications. The acoustic measurements are carried out in a fan test stand in the anechoic chamber of the University of Applied Sciences Duesseldorf. The aerodynamic performance is measured in a fan test rig with an inlet chamber setup in accordance with ISO 5801. The measured acoustical and aerodynamic performance is validated by the industrial partner. The results of the acoustic measurements are in turn utilized to determine indicators of noise radiation in the numerical simulation. Within this work an approach is presented where the analyses of secondary flows in the blade tip region provide the basis for an innovative noise reduction design in a shrouded fan configuration. The new design exhibits a reduced SPL (A-weighted) of approx. 4 dB over the entire operating range while showing no significant deterioration on the aerodynamic performance. The design was registered for patent approval cooperatively by the industrial partner and the University of Applied Sciences Duesseldorf, while minor design parameters are still subject to further improvements. All numerical simulations are performed with Ansys CFX, a commercial solver widely spread in the industry. Methods similar to those shown in this work can be implemented in the design phase of axial fans in order to develop acoustically optimized fan geometries.