Electrostatic instability for azimuthal mode number l = 1 induced by electron-neutral collisions in a strongly-magnetized nonneutral electron plasma

1996 ◽  
Vol 219 (1-2) ◽  
pp. 95-101 ◽  
Author(s):  
Ronald C. Davidson ◽  
Edward H. Chao
Keyword(s):  
Electron Plasma ◽  
Mode Number ◽  
Azimuthal Mode

Coherent structure in a turbulent jet via a vector implementation of the proper orthogonal decomposition

2007 ◽  
Vol 571 ◽  
pp. 281-326 ◽  
Author(s):  
M. O. IQBAL ◽  
F. O. THOMAS
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Coherent Structure ◽  
Near Field ◽  
Orthogonal Decomposition ◽  
Turbulent Jet ◽  
Mode Number ◽  
Azimuthal Mode ◽  
Proper Orthogonal ◽  
Energy Convergence ◽  
Jet Structure

The coherent structure in the near-field of an axisymmetric turbulent jet at a Reynolds number of 3.8 × 105 and Mach number of 0.3 is experimentally characterized by a vector implementation of the proper orthogonal decomposition (POD). The POD eigenfunctions and associated eigenvalues are extracted at several selected streamwise locations in the initial region. The focus on the near-field is motivated by its importance in numerous technical applications. Results show a rapid energy convergence with POD mode number. Examination of the relative energy contained in the combined azimuthal and radial components of the POD modes reveals that it is comparable to that in the streamwise component. The streamwise evolution of the eigenvalue spectra is characterized by a remarkable variation in the azimuthal mode number energy distribution, leading to the dominance of azimuthal mode m = 1 beyond the end of the jet core. In contrast, a scalar implementation using only the streamwise component shows the dominance of mode m = 2 which is consistent with previous scalar implementations of the POD. For a given azimuthal mode number, the eigenvalue spectra exhibit a broad peak which occurs at a constant value of Strouhal number based on local shear layer momentum thickness and local jet maximum velocity. The phase information required for a local reconstruction of the jet structure is obtained by projecting the POD eigenmodes onto instantaneous realizations of the flow at fixed streamwise locations. The instantaneous realizations are obtained by utilizing cross-stream arrays of multi-sensor probes in conjunction with linear stochastic estimation (LSE). Results clearly show the local dynamic behaviour of each component of the jet structure.

scholarly journals Control of stationary cross-flow modes in a Mach 3.5 boundary layer using patterned passive and active roughness

2013 ◽  
Vol 718 ◽  
pp. 5-38 ◽  
Author(s):  
Chan Yong Schuele ◽  
Thomas C. Corke ◽  
Eric Matlis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Three Dimensional ◽  
Cross Flow ◽  
Active Surface ◽  
Mode Number ◽  
Test Model ◽  
Integrated Sensor ◽  
Azimuthal Mode ◽  
Langley Research Center

AbstractSpanwise-periodic roughness designed to excite selected wavelengths of stationary cross-flow modes was investigated in a three-dimensional boundary layer at Mach 3.5. The test model was a sharp-tipped $1{4}^{\circ } $ right-circular cone. The model and integrated sensor traversing system were placed in the Mach 3.5 supersonic low disturbance tunnel (SLDT) equipped with an axisymmetric ‘quiet design’ nozzle at NASA Langley Research Center. The model was oriented at a $4. {2}^{\circ } $ angle of attack to produce a mean cross-flow velocity component in the boundary layer over the cone. The research examined both passive and active surface roughness. The passive roughness consisted of indentations (dimples) that were evenly spaced around the cone at an axial location that was just upstream of the first linear stability neutral growth branch for cross-flow modes. The active roughness consisted of an azimuthal array of micrometre-sized plasma actuators that were designed to produce the effect of passive surface bumps. Two azimuthal mode numbers of the passive and active patterned roughness were examined. One had an azimuthal mode number that was in the band of initially amplified stationary cross-flow modes. This was intended to represent a controlled baseline condition. The other azimuthal mode number was designed to suppress the growth of the initially amplified stationary cross-flow modes and thereby increase the transition Reynolds number. The results showed that the stationary cross-flow modes were receptive to both the passive and active patterned roughness. Only the passive roughness was investigated at a unit Reynolds number where transition would occur on the cone. Transition front measurements using the Preston tube approach indicated that the transition Reynolds number had increased by 35 % with the subcritical wavenumber roughness compared with the baseline smooth tip cone, and by 40 % compared with the critical wavenumber roughness. Based on the similarities in the response of the stationary cross-flow modes with the active roughness, we expect it would produce a similar transition delay.

Physical processes influencing acoustic radiation from jet engine inlets

2013 ◽  
Vol 725 ◽  
pp. 152-194 ◽  
Author(s):  
Christopher K. W. Tam ◽  
Sarah A. Parrish ◽  
Edmane Envia ◽  
Eugene W. Chien
Keyword(s):  
Acoustic Radiation ◽  
Mode Number ◽  
Mean Flow ◽  
Physical Processes ◽  
Forward Flight ◽  
Azimuthal Mode ◽  
Jet Engine ◽  
Significant Difference ◽  
Radiated Sound ◽  
Flow Gradients

AbstractNumerical simulations of acoustic radiation from a jet engine inlet are performed using advanced computational aeroacoustics algorithms and high-quality numerical boundary treatments. As a model of modern commercial jet engine inlets, the inlet geometry of the NASA Source Diagnostic Test is used. Fan noise consists of tones and broadband sound. This investigation considers the radiation of tones associated with upstream-propagating duct modes. The primary objective is to identify the dominant physical processes that determine the directivity of the radiated sound. Two such processes have been identified. They are acoustic diffraction and refraction. Diffraction is the natural tendency for an acoustic duct mode to follow a curved solid surface as it propagates. Refraction is the turning of the direction of propagation of a duct mode by mean flow gradients. Parametric studies on the changes in the directivity of radiated sound due to variations in forward flight Mach number, duct mode frequency, azimuthal mode number and radial mode number are carried out. It is found there is a significant difference in directivity for the radiation of the same duct mode from an engine inlet when operating in static condition versus one in forward flight. It will be shown that the large change in directivity is the result of the combined effects of diffraction and refraction.

Acoustic Modes in the Annular Duct with Uniform Mean Flow

2011 ◽  
Vol 214 ◽  
pp. 554-558 ◽  
Author(s):  
Zhan Xin Liu
Keyword(s):  
Power Level ◽  
Angular Frequency ◽  
Acoustic Mode ◽  
Mode Number ◽  
Benchmark Problems ◽  
Energy Relation ◽  
Mean Flow ◽  
Azimuthal Mode ◽  
Sound Power Level ◽  
Annular Duct

There are many benchmark problems in computational aeroacoustics (CAA) and acoustic mode in the annular duct with uniform mean flow is a problem of this kind. The energy relation of the duct mode is deduced from the governing equation, Euler equations in this paper. If the sound power level, angular frequency, azimuthal mode number and radial mode number are given, the acoustic mode in the annular duct can be expressed explicitly by the deduced results. The simulation of two different cases shows the propagation of a single acoustic mode in annular duct pictorially.

40Gbit/s MDM-WDM Laguerre-Gaussian Mode with Equalization for Multimode Fiber in Access Networks

2018 ◽  
Vol 39 (2) ◽  
pp. 175-184 ◽  
Author(s):  
Yousef Fazea ◽  
Angela Amphawan
Keyword(s):  
Wavelength Division Multiplexing ◽  
Mode Number ◽  
Multimode Fiber ◽  
Azimuthal Mode ◽  
Wavelength Division ◽  
Modal Dispersion ◽  
Fiber To The Home ◽  
Mode Division Multiplexing ◽  
Fiber Mode ◽  
Gaussian Mode

AbstractModal dispersion is seen as the primary impairment for multimode fiber. Mode division multiplexing (MDM) is a promising technology that has been realized as a favorable technology for considerably upsurges the capacity and distance of multimode fiber in conjunction with Wavelength Division Multiplexing (WDM) for fiber-to-the-home. This paper reveals the importance of an equalization technique in conjunction with controlling the modes spacing of mode division multiplexing-wavelength division multiplexing of Laguerre-Gaussian modes to alleviate modal dispersion for multimode fiber. The effects of channel spacing of 20 channels MDM-WDM were examined through controlling the azimuthal mode number and the radial mode number of Laguerre-Gaussian modes. A data rate of 40Gbit/s was achieved for a distance of 1,500 m for MDM-WDM.

Excitation of the l=2 azimuthal mode in a pure electron plasma

2007 ◽  
Vol 14 (10) ◽  
pp. 102103 ◽  
Author(s):  
G. Bettega ◽  
F. Cavaliere ◽  
B. Paroli ◽  
M. Cavenago ◽  
R. Pozzoli ◽  
...  
Keyword(s):  
Electron Plasma ◽  
Azimuthal Mode
Sign in / Sign up

Export Citation Format

Share Document