Numerical Investigation on Acoustic Energy Flux Distribution in a Lined Duct

AbstractThe octic fluid dispersion equation, the kinetic Boltzmann–Vlasov equation and the MHD (scalar pressure) analysis, programmed for a two-species collisionless magnetoplasma in a form permitting direct comparison between them, have been applied to the study of the Alfvén modes in both low- and high-β plasmas. In the low-βregime all methods give essentially the same solutions for the isotropic fast magnetosonic and the field-guided shear Alfvén modes. The real part of the refractive index of the field-guided slow magnetosonic acoustic mode is almost identical in the fluid and kinetic analyses, but is 50% too high in the MHD analysis owing to neglect of the trace-free part of the pressure tensor which drives almost half of the acoustic energy flux. The strong damping of the acoustic mode in both low- and high-β plasmas is drastically reduced by increase of electron temperature, whereas a moderate increase in the perpendicular ion temperature is sufficient to eliminate shear Alfvén damping in high-β plasmas and even to produce wave growth, the effect being more pronounced the higher the plasma β. The fluid analysis shows the electromagnetic energy flux to be negligible in the acoustic mode, in which the acoustic flux is driven both by the trace-carrying and trace-free parts of the pressure tensor, but is usually the dominant component in the (fast) magnetosonic mode.

Download Full-text

Investigation of High-Intensity Beam Characteristics on Welding Cavity Shape and Temperature Distribution

Journal of Heat Transfer ◽

10.1115/1.2910339 ◽

1990 ◽

Vol 112 (1) ◽

pp. 163-169 ◽

Cited By ~ 25

Author(s):

P. S. Wei ◽

T. H. Wu ◽

Y. T. Chow

Keyword(s):

Temperature Distribution ◽

Thermal Property ◽

Energy Flux ◽

High Intensity ◽

Flux Distribution ◽

Welding Process ◽

Local Heat Transfer ◽

Distribution Parameter ◽

Beam Power ◽

Cavity Shape

A model for investigating the characteristics of a high-intensity beam on welding cavity shape and temperature distribution is developed. The beam power density is assumed to have a Gaussian distribution. The local heat transfer rate to the liquid-vapor interface depends on this distribution and on the interface contour. This contour as determined by an iterative procedure involves simultaneously satisfying the heat conduction rate into the liquid and equilibrium of the normal forces. Computed shapes of the cavity and the free surface temperature distributions agree well with experimental data. The beam energy flux distribution parameter is found to have the strongest effect on the welding process. The predicted dimensionless curve of the beam power-penetration depth parameter versus the welding velocity-thermal property parameter is also in accord with experimental results. The use of the energy flux distribution parameter instead of the fusion zone width at the workpiece surface for the welding velocity-thermal property parameter is recommended.

Download Full-text

Disturbance energy transport and sound production in gaseous combustion

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.264 ◽

2012 ◽

Vol 707 ◽

pp. 53-73 ◽

Cited By ~ 32

Author(s):

Michael J. Brear ◽

Frank Nicoud ◽

Mohsen Talei ◽

Alexis Giauque ◽

Evatt R. Hawkes

Keyword(s):

Energy Flux ◽

Sound Production ◽

Energy Transport ◽

Source Term ◽

Sole Source ◽

Conservation Equation ◽

Acoustic Energy ◽

Far Field ◽

Source Terms ◽

Mean Flow

AbstractThis paper presents an analysis of the energy transported by disturbances in gaseous combustion. It extends the previous work of Myers (J. Fluid Mech., vol. 226, 1991, 383–400) and so includes non-zero mean-flow quantities, large-amplitude disturbances, varying specific heats and chemical non-equilibrium. This extended form of Myers’ ‘disturbance energy’ then enables complete identification of the conditions under which the famous Rayleigh source term can be derived from the equations governing combusting gas motion. These are: small disturbances in an irrotational, homentropic, non-diffusive (in terms of species, momentum and energy) and stationary mean flow at chemical equilibrium. Under these assumptions, the Rayleigh source term becomes the sole source term in a conservation equation for the classical acoustic energy. It is also argued that the exact disturbance energy flux should become an acoustic energy flux in the far-field surrounding a (reacting or non-reacting) jet. In this case, the volume integral of the disturbance energy source terms are then directly related to the area-averaged far-field sound produced by the jet. This is demonstrated by closing the disturbance energy budget over a set of aeroacoustic, direct numerical simulations of a forced, low-Mach-number, laminar, premixed flame. These budgets show that several source terms are significant, including those involving the mean-flow and entropy fields. This demonstrates that the energetics of sound generation cannot be examined by considering the Rayleigh source term alone.

Download Full-text

Observational study of chromospheric heating by acoustic waves

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038559 ◽

2020 ◽

Vol 642 ◽

pp. A52

Author(s):

V. Abbasvand ◽

M. Sobotka ◽

M. Švanda ◽

P. Heinzel ◽

M. García-Rivas ◽

...

Keyword(s):

Energy Flux ◽

Acoustic Waves ◽

Acoustic Energy ◽

Solar Chromosphere ◽

Echelle Spectrograph ◽

Quiet Sun ◽

Non Local ◽

Radiative Losses ◽

Semi Empirical

Aims. Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses. Methods. Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and in the Hα and Hβ lines with the echelle spectrograph attached to the Vacuum Tower Telescope on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux at frequencies up to 20 mHz was derived from Doppler velocities observed in line centers and wings. Radiative losses were computed by means of a set of scaled non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models obtained by fitting synthetic to observed line profiles. Results. In the middle chromosphere (h = 1000–1400 km), the radiative losses can be fully balanced by the deposited acoustic energy flux in a quiet-Sun region. In the upper chromosphere (h > 1400 km), the deposited acoustic flux is small compared to the radiative losses in quiet as well as in plage regions. The crucial parameter determining the amount of deposited acoustic flux is the gas density at a given height. Conclusions. The acoustic energy flux is efficiently deposited in the middle chromosphere, where the density of gas is sufficiently high. About 90% of the available acoustic energy flux in the quiet-Sun region is deposited in these layers, and thus it is a major contributor to the radiative losses of the middle chromosphere. In the upper chromosphere, the deposited acoustic flux is too low, so that other heating mechanisms have to act to balance the radiative cooling.

Download Full-text

Energy Flux Distribution and Thermal Performance of Linear Fresnel Collector System in Cold Region

Energy and Power Engineering ◽

10.4236/epe.2017.910039 ◽

2017 ◽

Vol 09 (10) ◽

pp. 555-567

Author(s):

Jing Ma ◽

Zheng Chang ◽

Rui Tian

Keyword(s):

Energy Flux ◽

Thermal Performance ◽

Flux Distribution ◽

Cold Region ◽

Collector System

Download Full-text

Energy flux distribution in a plane anisotropic optical waveguide

Journal of Applied Spectroscopy ◽

10.1007/bf00619046 ◽

1977 ◽

Vol 27 (1) ◽

pp. 939-942

Author(s):

N. I. Avdeeva

Keyword(s):

Optical Waveguide ◽

Energy Flux ◽

Flux Distribution

Download Full-text

Energetically Consistent Computation of Combustor Stability with a Model Consisting of a Helmholtz-Fem-Domain and a Low-Order Network

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4050024 ◽

2021 ◽

Author(s):

Gerrit Heilmann ◽

Christoph Hirsch ◽

Thomas Sattelmayer

Keyword(s):

Boundary Conditions ◽

Energy Flux ◽

Fundamental Problem ◽

Acoustic Energy ◽

Special Treatment ◽

Transfer Matrices ◽

Mean Flow ◽

Acoustic Damping ◽

Spatially Resolved ◽

Low Order

Abstract An efficient approach for the detection of the acoustic damping of gas turbine combustors is the combination of spatially resolved FEM approaches based on the Helmholtz equation with low-order networks for all elements leading to acoustic damping. A fundamental problem of such hybrid approaches is that the flow is considered in the networks, but not in the spatially resolved FEM area. Without special treatment of the boundary conditions this leads to serious errors in the calculation of the damping rate. The purpose of the paper is the derivation of the required correction procedures, which allow the energetically consistent formulation of such hybrid models and lead to correct damping rates. The time averaged equation of acoustic energy flux is expressed in terms of reflection coefficients and compared to the equivalent formulation for vanishing mean flows. An existing transformation for boundary conditions to obtain equal energy flux at the interface between network and Helmholtz domain is analyzed in detail. The findings are then used to derive energetically consistent transformations of transfer matrices to couple two FEM domains via a network model. The relevance of energetically consistent transfer matrices for stability analysis is demonstrated with a generic test case. The central partition is acoustically characterized via low order models considering mean flow. The resulting acoustic two-port is transformed to obtain an energetically consistent transfer matrix for a subsequent FEM discretized eigenvalue analysis of the remaining geometry. The eigenvalues of energetically consistent calculations are finally compared to eigenvalues of energetically inconsistent setups.

Download Full-text