Swirl Flame Response to Simultaneous Axial and Transverse Velocity Fluctuations

2016 ◽  
Author(s):  
Aditya Saurabh ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Relative Phase ◽  
Transverse Velocity ◽  
Experimental Investigations ◽  
Velocity Fluctuations ◽  
Transverse Acoustic ◽  
Flame Response ◽  
Acoustic Velocities ◽  
Acoustic Forcing ◽  
Swirl Flame ◽  
The Impact

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.

Swirl Flame Response to Simultaneous Axial and Transverse Velocity Fluctuations

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Aditya Saurabh ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Experimental Study ◽  
Relative Phase ◽  
Transverse Velocity ◽  
Acoustic Velocity ◽  
Velocity Fluctuations ◽  
Thermoacoustic Instability ◽  
Transverse Acoustic ◽  
Flame Response ◽  
Swirl Flame ◽  
The Impact

In this experimental study, we investigate the impact of transverse acoustic velocity fluctuations on flame response to axial velocity fluctuations. Such a scenario where a flame is under the influence of a 2D acoustic field occurs in annular gas turbine combustors during thermoacoustic instability. A generic premixed swirl flame is exposed to simultaneous transverse and axial acoustic forcing. The amplitude of axial forcing was kept constant, while the amplitude and relative phase (with respect to axial forcing) of the transverse forcing was systematically varied. Results obtained indicate that transverse velocity affects flame response, and that both the magnitude of transverse velocity and its phase with respect to axial forcing are important factors.

Numerical Investigation of a Non-Confined Spray Flame Exposed to Acoustic Forcing

2015 ◽  
Author(s):  
Virginia Fratalocchi ◽  
Jim B. W. Kok
Keyword(s):  
Velocity Field ◽  
Numerical Investigation ◽  
Acoustic Waves ◽  
Slip Velocity ◽  
Evaporation Rate ◽  
Momentum Exchange ◽  
Velocity Fluctuations ◽  
Spray Flame ◽  
Acoustic Forcing ◽  
The Impact

A numerical investigation of the interaction between a spray flame and an acoustic forcing of the velocity field is presented in this paper. The test-case which is the focus of this work is a non-confined flame1,2 burning at atmospheric pressure and therefore the velocity fluctuations play a key role. Acoustic waves will eventually affect the rate of combustion, and the oscillating fluctuation of the heat released by the flame might be increased by the evaporation process. The dynamic interaction between the evaporating fuel spray and the velocity fluctuations induced by an acoustic perturbation is investigated to understand the impact of the acoustic waves on the droplet dispersion and on the evaporation rate. The influence of the initial droplet diameter has been observed to be irrelevant, when two monodispersed sprays of 20 μm and 80 μm were numerically simulated. In this work the main question to address is how the interphase heat and mass transfer, and the momentum exchange are influenced, at low amplitude velocity fluctuations, by the forcing frequency, under two different imposed velocity profiles of the liquid fuel. A fast decay of the slip velocity is predicted under both steady and perturbed conditions. Thus, slip velocity fluctuations do not have a significant influence on the solved spray field. Finally, the impact of the forcing frequency and of the pilot are the main effects acting on the forced flame response. At low frequency, the entrainment of hot gases into the spray results in a clearly visible stretching of the flame which causes a high level of temperature fluctuation. At high frequency, despite the weak response of the gas velocity field, the dynamics of the combustion show a faster evaporation rate than the acoustic–free case.

Swirl Flame Response to Traveling Acoustic Waves

2014 ◽  
Author(s):  
Aditya Saurabh ◽  
Richard Steinert ◽  
Jonas P. Moeck ◽  
Christian O. Paschereit
Keyword(s):  
Acoustic Wave ◽  
Acoustic Waves ◽  
Test Rig ◽  
Pressure Oscillations ◽  
Acoustic Interaction ◽  
Transverse Pressure ◽  
Transverse Acoustic ◽  
Flame Response ◽  
Swirl Flame ◽  
Insight Into

The advent of annular combustors introduced a new facet of flame-acoustic interaction: flame coupling with standing and spinning azimuthal acoustic waves. Such coupling involves an acoustic field that is essentially transverse to the flame. Recent experiments on single burner test rigs have provided significant insight into flame interaction with transverse standing waves. However, experiments that focus on the spinning/rotating nature of azimuthal instabilities are still lacking. In this report, we demonstrate a methodology for studying spinning azimuthal instabilities on a single burner test rig. This methodology is based on analyzing flame response to a traveling acoustic wave generated in the combustor. We generate traveling acoustic waves in our transverse acoustic forcing test-rig by converting one end of the transverse extensions to a non-reflecting end. This is achieved through the implementation of the technique of impedance tuning. In the paper, we have discussed this implementation, followed by discussions on the effects of a traveling acoustic wave on a swirl-stabilized flame. The discussion is in the form of a comparison of flame oscillations for traveling wave and standing wave transverse forcing cases. Results show that the effect of transverse pressure oscillations dominates the flame response to traveling acoustic waves.

A Model for the Thermo-Acoustic Feedback of Transverse Acoustic Modes and Periodic Oscillations in Flame Position in Cylindrical Flame Tubes

2012 ◽  
Author(s):  
Joachim Schwing ◽  
Felix Grimm ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
High Frequency ◽  
Circular Cross Section ◽  
Experimental Investigations ◽  
Constant Density ◽  
Rayleigh Criterion ◽  
Velocity Fluctuations ◽  
Acoustic Modes ◽  
High Frequency Oscillations ◽  
Transverse Acoustic

In the past decades, several feedback mechanisms for longitudinal acoustic modes in gas turbine combustors have been investigated. These mechanisms are successfully used in predictive tools like acoustic network models to analyze low-frequency instabilities in combustion systems. In contrast, little is known about high-frequency oscillations — fluctuations at several kHz. Most theories are derived from experimental investigations of afterburners in the 1950s and 1960s, indicating an interaction of vortex shedding, fluctuating vorticity and heat release. In this work a different feedback mechanism for high-frequency oscillations in cylindrical flame tubes related to transverse acoustic modes is suggested and analysed: Transverse acoustic pressure fluctuations are linked to an oscillating velocity field. A time-dependent but periodic displacement field can be derived from these velocity fluctuations. The model assumes that the zone of heat release is displaced by the velocity fluctuations. Pressure oscillations and periodically deflected heat release lead to a contribution to the Rayleigh criterion without fluctuations in the global heat release. This effect is studied in a circular cross section presuming a circular zone of heat release. Expressions for the displacement of the flame front are derived from the analytical solution of the wave equation in cylindrical geometries assuming a quiescent medium, constant density and speed of sound. The Rayleigh criterion is integrated and growth rates are evaluated whereas damping effects are neglected as they are not subject to this study. Characteristics of the model are assessed and compared to experimental observations to check the validity and the applicability of the theory.

scholarly journals Experimental investigations on diesel engine using alumina nanoparticle fuel additive

2021 ◽  
Vol 13 (2) ◽  
pp. 168781402098840
Author(s):  
Mohammed S Gad ◽  
Sayed M Abdel Razek ◽  
PV Manu ◽  
Simon Jayaraj
Keyword(s):  
Diesel Engine ◽  
Diesel Fuel ◽  
Alumina Nanoparticles ◽  
Experimental Investigations ◽  
Fuel Additive ◽  
Alumina Nanoparticle ◽  
Fuel Injectors ◽  
Performance And Emission ◽  
And Performance ◽  
The Impact

Experimental work was done to examine the impact of diesel fuel with alumina nanoparticles on combustion characteristics, emissions and performance of diesel engine. Alumina nanoparticles were mixed with crude diesel in various weight fractions of 20, 30, and 40 mg/L. The engine tests showed that nano alumina addition of 40 ppm to pure diesel led to thermal efficiency enhancement up to 5.5% related to the pure diesel fuel. The average specific fuel consumption decrease about neat diesel fuel was found to be 3.5%, 4.5%, and 5.5% at dosing levels of 20, 30, and 40 ppm, respectively at full load. Emissions of smoke, HC, CO, and NOX were found to get diminished by about 17%, 25%, 30%, and 33%, respectively with 40 ppm nano-additive about diesel operation. The smaller size of nanoparticles produce fuel stability enhancement and prevents the fuel atomization problems and the clogging in fuel injectors. The increase of alumina nanoparticle percentage in diesel fuel produced the increases in cylinder pressure, cylinder temperature, heat release rate but the decreases in ignition delay and combustion duration were shown. The concentration of 40 ppm alumina nanoparticle is recommended for achieving the optimum improvements in the engine’s combustion, performance and emission characteristics.

scholarly journals A FEM-Based 2D Model for Simulation and Qualitative Assessment of Shot-Peening Processes

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2784
Author(s):  
Georgios Maliaris ◽  
Christos Gakias ◽  
Michail Malikoutsakis ◽  
Georgios Savaidis
Keyword(s):  
Process Parameters ◽  
Material Properties ◽  
Shot Peening ◽  
Qualitative Assessment ◽  
Experimental Investigations ◽  
Elastoplastic Material ◽  
Size Distributions ◽  
User Friendly ◽  
The Impact ◽  
2D Model

Shot peening is one of the most favored surface treatment processes mostly applied on large-scale engineering components to enhance their fatigue performance. Due to the stochastic nature and the mutual interactions of process parameters and the partially contradictory effects caused on the component’s surface (increase in residual stress, work-hardening, and increase in roughness), there is demand for capable and user-friendly simulation models to support the responsible engineers in developing optimal shot-peening processes. The present paper contains a user-friendly Finite Element Method-based 2D model covering all major process parameters. Its novelty and scientific breakthrough lie in its capability to consider various size distributions and elastoplastic material properties of the shots. Therewith, the model is capable to provide insight into the influence of every individual process parameter and their interactions. Despite certain restrictions arising from its 2D nature, the model can be accurately applied for qualitative or comparative studies and processes’ assessments to select the most promising one(s) for the further experimental investigations. The model is applied to a high-strength steel grade used for automotive leaf springs considering real shot size distributions. The results reveal that the increase in shot velocity and the impact angle increase the extent of the residual stresses but also the surface roughness. The usage of elastoplastic material properties for the shots has been proved crucial to obtain physically reasonable results regarding the component’s behavior.

Assessment of Unsteady Flows in Turbines

1992 ◽  
Vol 114 (1) ◽  
pp. 79-90 ◽  
Author(s):  
O. P. Sharma ◽  
G. F. Pickett ◽  
R. H. Ni
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Research Activities ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Design ◽  
The Impact

The impacts of unsteady flow research activities on flow simulation methods used in the turbine design process are assessed. Results from experimental investigations that identify the impact of periodic unsteadiness on the time-averaged flows in turbines and results from numerical simulations obtained by using three-dimensional unsteady Computational Fluid Dynamics (CFD) codes indicate that some of the unsteady flow features can be fairly accurately predicted. Flow parameters that can be modeled with existing steady CFD codes are distinguished from those that require unsteady codes.

Mistuning and Damping of a Radial Turbine Wheel. Part 1: Fundamental Analyses and Design of Intentional Mistuning Pattern

2021 ◽  
Author(s):  
Alex Nakos ◽  
Bernd Beirow ◽  
Arthur Zobel
Keyword(s):  
High Stress ◽  
Forced Response ◽  
Experimental Investigations ◽  
Detailed Knowledge ◽  
Turbine Wheel ◽  
Operation Conditions ◽  
Radial Turbine ◽  
Influence Coefficients ◽  
Modes Of Vibration ◽  
The Impact

Abstract The radial turbine impeller of an exhaust turbocharger is analyzed in view of both free vibration and forced response. Due to random blade mistuning resulting from unavoidable inaccuracies in manufacture or material inhomogeneities, localized modes of vibration may arise, which involve the risk of severely magnified blade displacements and inadmissibly high stress levels compared to the tuned counterpart. Contrary, the use of intentional mistuning (IM) has proved to be an efficient measure to mitigate the forced response. Independently, the presence of aerodynamic damping is significant with respect to limit the forced response since structural damping ratios of integrally bladed rotors typically take extremely low values. Hence, a detailed knowledge of respective damping ratios would be desirable while developing a robust rotor design. For this, far-reaching experimental investigations are carried out to determine the damping of a comparative wheel within a wide pressure range by simulating operation conditions in a pressure tank. Reduced order models are built up for designing suitable intentional mistuning patterns by using the subset of nominal system modes (SNM) approach introduced by Yang and Griffin [1], which conveniently allows for accounting both differing mistuning patterns and the impact of aeroelastic interaction by means of aerodynamic influence coefficients (AIC). Further, finite element analyses are carried out in order to identify appropriate measures how to implement intentional mistuning patterns, which are featuring only two different blade designs. In detail, the impact of specific geometric modifications on blade natural frequencies is investigated.

scholarly journals Fuzzy rules based model for solute dispersion in an open channel dead zone

2002 ◽  
Vol 4 (1) ◽  
pp. 39-51
Author(s):  
Helen Kettle ◽  
Keith Beven ◽  
Barry Hankin
Keyword(s):  
Finite Volume ◽  
Fuzzy Number ◽  
Open Channel ◽  
Transverse Velocity ◽  
Dead Zone ◽  
Fuzzy Rules ◽  
Turbulent Velocity ◽  
Velocity Fluctuations ◽  
Laboratory Flume ◽  
The Mean

A method has been developed to estimate turbulent dispersion based on fuzzy rules that use local transverse velocity shears to predict turbulent velocity fluctuations. Turbulence measurements of flow around a rectangular dead zone in an open channel laboratory flume were conducted using an acoustic Doppler velocimeter (ADV) probe. The mean velocity and turbulence characteristics in and around the shear zone were analysed for different flows and geometries. Relationships between the mean transverse velocity shear and the turbulent velocity fluctuations are encapsulated in a simple set of fuzzy rules. The rules are included in a steady-state hybrid finite-volume advection–diffusion scheme to simulate the mixing of hot water in an open-channel dead zone. The fuzzy rules produce a fuzzy number for the magnitude of the average velocity fluctuation at each cell boundary. These are then combined within the finite-volume model using the single-value simulation method to give a fuzzy number for the temperature in each cell. The results are compared with laboratory flume data and a computational fluid dynamics (CFD) simulation from PHOENICS. The fuzzy model compares favourably with the experiment data and offers an alternative to traditional CFD models.

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