scholarly journals Impact of burner plenum acoustics on the sound emission of a turbulent lean premixed open flame

2020 ◽  
Vol 12 ◽  
pp. 175682772095690
Author(s):  
S Herff ◽  
K Pausch ◽  
H Nawroth ◽  
S Schlimpert ◽  
CO Paschereit ◽  
...  
Keyword(s):  
Sound Pressure ◽  
Stokes Equations ◽  
Turbulent Flame ◽  
Jet Flow ◽  
Combustion Noise ◽  
Sound Emission ◽  
Open Flame ◽  
Quarter Wave ◽  
Experimental Findings ◽  
Wave Modes

The acoustic field of a turbulent lean cpremixed open flame is numerically investigated by a hybrid method solving the Navier-Stokes equations in a large-eddy simulation formulation and the acoustic perturbation equations. The interaction of acoustic modes of a burner plenum and the turbulent flame is analyzed with respect to the sound emission of the flame. It is investigated if a simplified computation yields a good broadband agreement of the sound pressure spectrum with experimental measurements. The results of two numerical setups, i.e., the first configuration consists of the burner plus the plenum geometry while in the second configuration the plenum is neglected, which is often done in technical applications due to computational efficiency reasons, are compared with experimental findings. It can be concluded that the plenum has a pronounced impact on the dynamics and combustion noise of the open flame. To be more precise, the comparative juxtaposition of the numerical and experimental results shows a good agreement only for the full burner-plenum computation since the interaction of the acoustic quarter-wave modes of the burner plenum with the jet flow has to be captured. The interaction of these quarter-wave modes with the flow is analyzed and the acoustic response to heat release fluctuations of the flame of the full burner-plenum computation is compared to that of the simplified burner computation, in which the plenum acoustics is neglected. Due to the excitation by the plenum acoustics, the jet flow of the full burner plenum contains higher turbulent kinetic energy and the flame is excited at several additional frequencies which result in distinct peaks in the acoustic spectrum and a higher overall sound pressure level.

scholarly journals Hydrodynamics of flagellated microswimmers near free-slip interfaces

2016 ◽  
Vol 789 ◽  
pp. 514-533 ◽  
Author(s):  
D. Pimponi ◽  
M. Chinappi ◽  
P. Gualtieri ◽  
C. M. Casciola
Keyword(s):  
Numerical Solutions ◽  
Stokes Equations ◽  
Slip Surface ◽  
Initial Conditions ◽  
Aerobic Bacteria ◽  
Slip Boundary ◽  
Experimental Findings ◽  
Micro Organisms ◽  
Air Interfaces ◽  
Shed Light

The hydrodynamics of a flagellated micro-organism is investigated when swimming close to a planar free-slip surface by means of numerical solutions of the Stokes equations obtained via a boundary element method. Depending on the initial conditions, the swimmer can either escape from the free-slip surface or collide with the boundary. Interestingly, the micro-organism does not exhibit a stable orbit. Independently of escape or attraction to the interface, close to a free-slip surface, the swimmer follows a counter-clockwise trajectory, in agreement with experimental findings (Di Leonardo et al., Phys. Rev. Lett., vol. 106 (3), 2011, 038101). The hydrodynamics is indeed modified by the free surface. In fact, when the same swimmer moves close to a no-slip wall, a set of initial conditions exists which result in stable orbits. Moreover, when moving close to a free-slip or a no-slip boundary, the swimmer assumes a different orientation with respect to its trajectory. Taken together, these results contribute to shed light on the hydrodynamical behaviour of micro-organisms close to liquid–air interfaces which are relevant for the formation of interfacial biofilms of aerobic bacteria.

Indirect combustion noise

2010 ◽  
Vol 659 ◽  
pp. 267-288 ◽  
Author(s):  
M. S. HOWE
Keyword(s):  
Mach Number ◽  
Sound Pressure ◽  
Effective Rate ◽  
Combustion Noise ◽  
Strongly Correlated ◽  
Mean Flow ◽  
Jet Formation ◽  
Jet Engine ◽  
Hot Gas ◽  
Numerical Predictions

An analysis is made of the noise generated during the passage of quiescent temperature/entropy inhomogeneities through regions of rapidly accelerated mean flow. This is an important source of jet engine core noise. Bake et al. (J. Sound Vib., vol. 326, 2009, pp. 574–598) have used an ‘entropy wave generator’ coupled with a converging–diverging nozzle to perform a series of canonical measurements of the sound produced when the inhomogeneity consists of a nominally uniform slug of hot gas. When flow separation and jet formation occur in the diffuser section of the nozzle, it is shown in this paper that the vortex sound generated by the jet is strongly correlated with the entropy noise produced by the slug and that the overall noise level is significantly reduced. Streamwise ‘stretching’ of the hot slug during high subsonic acceleration into the nozzle and the consequent attenuation of the entropy gradient in the nozzle are shown to significantly decrease the effective rate at which indirect combustion noise increases with the Mach number. Numerical predictions indicate that this is responsible for the peak observed by Bake et al. in the entropy-generated sound pressure at a nozzle Mach number near 0.6.

scholarly journals The primary instability of falling films in the presence of soluble surfactants

2013 ◽  
Vol 729 ◽  
pp. 123-150 ◽  
Author(s):  
George Karapetsas ◽  
Vasilis Bontozoglou
Keyword(s):  
Stokes Equations ◽  
Liquid Films ◽  
Solid Substrate ◽  
Navier Stokes ◽  
Desorption Kinetics ◽  
Order Of Magnitude ◽  
Soluble Surfactants ◽  
Experimental Findings ◽  
Adsorption Desorption ◽  
Primary Instability

AbstractWe investigate the linear stability of a film flowing down a solid substrate in the presence of soluble surfactants. The Navier–Stokes equations for the liquid motion are considered, together with advection–diffusion equations for the concentrations of the species involved, which include monomers dissolved in the bulk and adsorbed at the liquid–air and at the liquid–substrate interfaces. The adsorption–desorption kinetics of the surfactant at both interfaces is explicitly accounted for. An Orr–Sommerfeld eigenvalue problem is formulated, and solved analytically in the limit of long-wave disturbances and numerically for arbitrary wavelength using a finite element method. An extensive parametric study is performed to reveal the role of surfactant solubility and adsorption–desorption kinetics. The results quantify the stabilizing effect of soluble surfactants due to the presence of Marangoni stresses, and indicate that moderately soluble surfactants may be more effective than insoluble ones. Disturbances of finite wavelength are stabilized by more than an order of magnitude, and their detailed behaviour depends in a non-monotonic way on the amount of surfactant and on its solubility and kinetics. The above predictions provide insights for the interpretation of recent experimental findings on the primary instability and on the ensuing unstable dynamics of liquid films doped with soluble surfactants.

Sound emission from a turbulent flame

1988 ◽  
Vol 21 (1) ◽  
pp. 1543-1550 ◽  
Author(s):  
Masashi Katsuki ◽  
Yukio Mizutani ◽  
Mototaka Chikami ◽  
Taizo Kittaka
Keyword(s):  
Turbulent Flame ◽  
Sound Emission

Numerical Simulation of a High Pressure Supersonic Multiphase Jet Flow Through a Gaseous Medium

2004 ◽  
Author(s):  
Randy S. Lagumbay ◽  
Oleg V. Vasilyev ◽  
Andreas Haselbacher ◽  
Jin Wang
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Gaseous Medium ◽  
Fuel Injection ◽  
Stokes Equations ◽  
Complex Structure ◽  
Jet Flow ◽  
Multiphase Model ◽  
Mixture Density ◽  
Flow Through

Computational Fluid Dynamics (CFD) analysis is used to numerically study the structure and dynamics of a high-pressure, high-speed jet of a gas/liquid mixture through a gaseous medium close to the nozzle region. The complex structure of the jet near the nozzle region is captured before it breaks-up downstream. A new multiphase model based on a mixture formulation of the conservation laws for a multiphase flows is used in the simulation. The model does not require ad-hoc closure for the variation of mixture density with pressure and yields thermodynamically accurate acoustic propagation for multiphase mixtures. The numerical formulation has been implemented to a multi-physics unstructured code “RocfluMP” that solves the modified three-dimensional time-dependent Euler/Navier-Stokes equations for a multiphase framework in integral form. The Roe’s approximate Riemann solver is used to allow capturing of shock waves and contact discontinuities. For a very steep gradient, an HLLC scheme is used to resolved the isolated shock and contact waves. The developed flow solver provides a general coupled incompressible-compressible multiphase framework that can be applied to a variety of supersonic jet flow problems including fuel injection systems, thermal and plasma spray coating, and liquid-jet machining. Preliminary results for shock tube analysis and gas/liquid free surface jet flow through a gaseous medium are presented and discussed.

Numerical Simulation of a Supersonic Three-Phase Cavitating Jet Flow Through a Gaseous Medium in Injection Nozzle

2005 ◽  
Author(s):  
Randy S. Lagumbay ◽  
Oleg V. Vasilyev ◽  
Andreas Haselbacher ◽  
Jin Wang
Keyword(s):  
Multiphase Flow ◽  
Gaseous Medium ◽  
Fuel Injection ◽  
Stokes Equations ◽  
Jet Flow ◽  
Injection Nozzle ◽  
Mixture Density ◽  
Three Phase ◽  
Flow Through ◽  
Cavitating Jet

A new multiphase mathematical model based on a mixture formulation of the laws of conservation for a multiphase flow is used to simulate a supersonic three-phase cavitating jet flow through a gaseous medium. The model does not require an adhoc closure for the variation of mixture density with regards to the attendant pressure and yields a thermodynamically accurate value for the acoustical propagation generated by the process. A source term for cavitation is added into the equations of the mixture formulation and the resultant cavitation is mathematically modeled accordingly. The new numerical formulation has been incorporated into a multi-physics unstructured code “RocfluMP” that solves the modified three-dimensional time-dependent Euler/Navier-Stokes equations for a multiphase framework in integral form. A modified form of the Harten, Lax and van Leer approximate Riemann equations are used to resolve the isolated shock and contact waves. The newly developed multiphase flow equations provide a general framework for analyzing coupled incompressible-compressible multiphase flows that can be applied to a variety of supersonic multiphase jet flow problems such as fuel injection systems and liquid-jet machining. Preliminary results for three-phase cavitating jet flow through a gaseous medium in injection nozzle are presented and discussed.

scholarly journals Theoretical Modelling and Effectiveness Study of Slotted Stand-Off Layer Damping Treatment for Rail Vibration and Noise Control

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Caiyou Zhao ◽  
Ping Wang
Keyword(s):  
Sound Pressure ◽  
Vibration Reduction ◽  
Pressure Level ◽  
Theoretical Modelling ◽  
Frequency Range ◽  
Sound Emission ◽  
Vertical Excitation ◽  
Railway Noise ◽  
Lateral Excitation ◽  
Selection Of

A promising means of reducing railway noise is to increase the damping of the rail, which decreases the vibration of the rail to reduce noise. To achieve this goal, a slotted stand-off layer damping treatment has been developed, and a compound track model with this treatment is developed for investigating the effectiveness of this treatment in terms of the vibration reduction. Through the dynamic analysis of the track undergoing the slotted stand-off layer damping treatment, some guidelines are proposed on the selection of materials and structure parameters for this treatment. In addition, the prototype of the optimal slotted stand-off layer damping treatment has been built and tested in the laboratory. It is found that the slotted stand-off damping treatment shows significant effects in decreasing the amplitude of the accelerance of the rail and a significant reduction of sound emission reflected as the radiation sound pressure level decreases by 8.2 and 9.4 dB at vertical excitation and lateral excitation, respectively, in the frequency range of 0–4000 Hz.

scholarly journals Quarter-wave modes of standing Alfvén waves detected by cross-phase analysis

2008 ◽  
Vol 113 (A8) ◽  
pp. n/a-n/a ◽  
Author(s):  
Yuki Obana ◽  
Frederick W. Menk ◽  
Murray D. Sciffer ◽  
Colin L. Waters
Keyword(s):  
Phase Analysis ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Quarter Wave ◽  
Wave Modes

Prediction of Jets and Flames in Co-Flowing Streams

1991 ◽  
Author(s):  
S. Ha ◽  
David G. Lilley
Keyword(s):  
Turbulent Flame ◽  
Computer Code ◽  
Solution Procedure ◽  
Theoretical Computation ◽  
Mean Velocity ◽  
Boundary Layer Equations ◽  
Fully Implicit ◽  
Flame Ignition ◽  
Experimental Findings ◽  
Hot Zone

Abstract The theoretical computation of jets and flames in co-flowing streams is of considerable interest in aerothermochemistry. Axisymmetric flowfields are considered with time-mean velocity, temperature and species concentrations (three components — fuel, oxygen, and products) being predicted via a version of the GENMIX computer code. It is equipped with the standard Prandtl mixing length model of turbulence and an Arrhenius-type reaction rate expression for kinetically-influenced turbulent flame simulation. The code solves the boundary layer equations using a fully-implicit forward-marching solution procedure. A variety of production runs have been made to show parameter effects, and results are tabulated, graphed and discussed. Complexities include: 1. The jet and surroundings may have different densities. 2. The surroundings may be co-flowing with nonzero axial velocity. 3. Flame ignition is via an outer annular hot zone. 4. Flames with typical hydrocarbon fuels burning in air are considered, and dissociation effects are included in a simple manner. Results confirm the previous experimental findings about jet development in co-flowing streams, and extend knowledge to more practical and burning situations.

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