Noise Generated by a Lifted Flame in a Vitiated Co-Flow

2008 ◽  
Author(s):  
Robert Z. Szasz ◽  
Christophe Duwig ◽  
Laszlo Fuchs
Keyword(s):  
Acoustic Field ◽  
Hybrid Approach ◽  
Low Frequency ◽  
Lifted Flame ◽  
Inhomogeneous Wave Equation ◽  
Large Eddy ◽  
Ignition Region ◽  
Acoustic Sources ◽  
Pod Analysis ◽  
Low Frequency Waves

The acoustic field generated by a lifted flame is studied by a hybrid approach. First, Large Eddy Simulations (LES) are used to compute the flow and the acoustic sources. Next, an inhomogeneous wave equation is solved to obtain the resulting acoustic field. The flow computations show good agreement with experimental data. The dominant acoustic sources are found to be located in the ignition region and at the tip of the flame. The acoustic computations revealed the presence of low-frequency waves radiated in the far-field. The shape of the most energetic acoustic modes are identified by POD analysis to be axial modes.

Scattering of Plane Waves by a Constriction

2011 ◽  
Author(s):  
E. Alenius ◽  
M. A˚bom ◽  
L. Fuchs
Keyword(s):  
Acoustic Waves ◽  
Plane Waves ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Flow Noise ◽  
Times Series ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Low Frequency Waves ◽  
Good Agreement

Liner scattering of low frequency waves by an orifice plate has been studied using Large Eddy Simulation and an acoustic two-port model. The results have been compared to measurements with good agreement for waves coming from the downstream side. For waves coming from the upstream side the reflection is over-predicted, indicating that not enough of the acoustic energy is converted to vorticity at the upstream edge of the plate. Furthermore, the sensitivity to the amplitude of the acoustic waves has been studied, showing difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the relatively short times series available in LES.

Computation of the Acoustic Field in an Annular Gas Turbine Combustion Chamber Using a Hybrid Approach

2006 ◽  
Author(s):  
Robert Z. Szasz ◽  
Mihai Mihaescu ◽  
Laszlo Fuchs
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Acoustic Field ◽  
Stokes Equations ◽  
Hybrid Approach ◽  
Time Instant ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Flow Solver ◽  
Inhomogeneous Wave Equation

The acoustic field generated by flow unsteadiness in a model annular gas turbine (GT) combustion chamber is determined using a hybrid approach. In the flow solver the semi-compressible Navier-Stokes equations are resolved using LES as turbulence model. The acoustic solver is based on an inhomogeneous wave equation, where the instantaneous source terms are computed from the LES data in each time-instant. The flow and the acoustics in a GT combustor with co- and counter-rotating swirler burners have been considered. The results have shown that significant differences can be observed between the co- and counter-rotating configurations both in the flow and acoustic fields.

PEMANFAATAN RADIASI ENERGI TEGANGAN 150 KV UNTUK LAMPU LED PENERANGAN JALAN

Jurnal Teknik ◽  
2018 ◽  
Vol 7 (1) ◽  
Author(s):  
Mauludi Manfaluthy
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
High Voltage ◽  
Low Frequency ◽  
Energy Utilization ◽  
World Health ◽  
Electromagnetic Signals ◽  
Health Organization ◽  
The Magnetic Field ◽  
Low Frequency Waves

WHO (World Health Organization) concludes that not much effect is caused by electric field up to 20 kV / m in humans. WHO standard also mentions that humans will not be affected by the magnetic field under  100 micro tesla and that the electric field will affect the human body with a maximum standard of 5,000 volts per meter. In this study did not discuss about the effect of high voltage radiation SUTT (High Voltage Air Channel) with human health. The research will focus on energy utilization of SUTT radiation. The combination of electric field and magnetic field on SUTT (70-150KV) can generate electromagnetic (EM) and radiation waves, which are expected to be converted to turn on street lights around the location of high voltage areas or into other forms. The design of this prototype works like an antenna in general that captures electromagnetic signals and converts them into AC waves. With a capacitor that can store the potential energy of AC and Schottky diode waves created specifically for low frequency waves, make the current into one direction (DC). From the research results obtained the current generated from the radiation is very small even though the voltage is big enough.Keywords : Radiance Energy, Joule Thief, and  LED Module.

scholarly journals Integral Equations for Problems on Wave Propagation in Near-Earth Plasma

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1395
Author(s):  
Danila Kostarev ◽  
Dmitri Klimushkin ◽  
Pavel Mager
Keyword(s):  
Magnetic Field ◽  
Integral Equations ◽  
Field Potential ◽  
Low Frequency ◽  
Fredholm Equation ◽  
Compression Waves ◽  
Parallel Component ◽  
Electric Field Potential ◽  
The Magnetic Field ◽  
Low Frequency Waves

We consider the solutions of two integrodifferential equations in this work. These equations describe the ultra-low frequency waves in the dipol-like model of the magnetosphere in the gyrokinetic framework. The first one is reduced to the homogeneous, second kind Fredholm equation. This equation describes the structure of the parallel component of the magnetic field of drift-compression waves along the Earth’s magnetic field. The second equation is reduced to the inhomogeneous, second kind Fredholm equation. This equation describes the field-aligned structure of the parallel electric field potential of Alfvén waves. Both integral equations are solved numerically.

scholarly journals Electromagnetic power of lightning superbolts from Earth to space

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
J.-F. Ripoll ◽  
T. Farges ◽  
D. M. Malaspina ◽  
G. S. Cunningham ◽  
E. H. Lay ◽  
...  
Keyword(s):  
Low Frequency ◽  
Optical Emission ◽  
High Energy ◽  
Very Low Frequency ◽  
Electromagnetic Power ◽  
Power Spectral ◽  
High Energy Tail ◽  
Van Allen Probes ◽  
Long Time ◽  
Low Frequency Waves

AbstractLightning superbolts are the most powerful and rare lightning events with intense optical emission, first identified from space. Superbolt events occurred in 2010-2018 could be localized by extracting the high energy tail of the lightning stroke signals measured by the very low frequency ground stations of the World-Wide Lightning Location Network. Here, we report electromagnetic observations of superbolts from space using Van Allen Probes satellite measurements, and ground measurements, and with two events measured both from ground and space. From burst-triggered measurements, we compute electric and magnetic power spectral density for very low frequency waves driven by superbolts, both on Earth and transmitted into space, demonstrating that superbolts transmit 10-1000 times more powerful very low frequency waves into space than typical strokes and revealing that their extreme nature is observed in space. We find several properties of superbolts that notably differ from most lightning flashes; a more symmetric first ground-wave peak due to a longer rise time, larger peak current, weaker decay of electromagnetic power density in space with distance, and a power mostly confined in the very low frequency range. Their signal is absent in space during day times and is received with a long-time delay on the Van Allen Probes. These results have implications for our understanding of lightning and superbolts, for ionosphere-magnetosphere wave transmission, wave propagation in space, and remote sensing of extreme events.

scholarly journals Large Eddy Simulation of Periodic Transient Pressure Fluctuation in a Centrifugal Pump Impeller at Low Flow Rate

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 311
Author(s):  
Renfei Kuang ◽  
Xiaoping Chen ◽  
Zhiming Zhang ◽  
Zuchao Zhu ◽  
Yu Li
Keyword(s):  
Large Eddy Simulation ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Low Frequency ◽  
Pump Impeller ◽  
Eddy Simulation ◽  
Inlet Flow Rate ◽  
Large Eddy ◽  
Centrifugal Pump Impeller

This paper presents a large eddy simulation of a centrifugal pump impeller during a transient condition. The flow rate is sinusoidal and oscillates between 0.25Qd (Qd indicates design load) and 0.75Qd when the rotating speed is maintained. Research shows that in one period, the inlet flow rate will twice reach 0.5Qd, and among the impeller of one moment is a stall state, but the other is a non-stall state. In the process of flow development, the evolution of low-frequency pressure fluctuation shows an obviously sinusoidal form, whose frequency is insensitive to the monitoring position and equals to that of the flow rate. However, inside the impeller, the phase and amplitude in the stall passages lag behind more and are stronger than that in the non-stall passages. Meanwhile, the strongest region of the high-frequency pressure fluctuation appears in the stall passages at the transient rising stage. The second dominant frequency in stall passages is 2.5 times to that in non-stall passages. In addition, similar to the pressure fluctuation, the evolution of the low-frequency head shows a sinusoidal form, whose phase is lagging behind that by one-third of a period in the inlet flow rate.

Collective oscillations in bubble clouds

2011 ◽  
Vol 680 ◽  
pp. 114-149 ◽  
Author(s):  
ZORANA ZERAVCIC ◽  
DETLEF LOHSE ◽  
WIM VAN SAARLOOS
Keyword(s):  
Frequency Response ◽  
Acoustic Field ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Viscous Damping ◽  
Edge States ◽  
Bubble Cloud ◽  
Collective Oscillations ◽  
The Individual ◽  
Bubble Oscillations

In this paper the collective oscillations of a bubble cloud in an acoustic field are theoretically analysed with concepts and techniques of condensed matter physics. More specifically, we will calculate the eigenmodes and their excitabilities, eigenfrequencies, densities of states, responses, absorption and participation ratios to better understand the collective dynamics of coupled bubbles and address the question of possible localization of acoustic energy in the bubble cloud. The radial oscillations of the individual bubbles in the acoustic field are described by coupled linearized Rayleigh–Plesset equations. We explore the effects of viscous damping, distance between bubbles, polydispersity, geometric disorder, size of the bubbles and size of the cloud. For large enough clusters, the collective response is often very different from that of a typical mode, as the frequency response of each mode is sufficiently wide that many modes are excited when the cloud is driven by ultrasound. The reason is the strong effect of viscosity on the collective mode response, which is surprising, as viscous damping effects are small for single-bubble oscillations in water. Localization of acoustic energy is only found in the case of substantial bubble size polydispersity or geometric disorder. The lack of localization for a weak disorder is traced back to the long-range 1/r interaction potential between the individual bubbles. The results of the present paper are connected to recent experimental observations of collective bubble oscillations in a two-dimensional bubble cloud, where pronounced edge states and a pronounced low-frequency response had been observed, both consistent with the present theoretical findings. Finally, an outlook to future possible experiments is given.

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