Universality hypothesis for the small wave-number range of decaying turbulence

1995 ◽  
Vol 45 (6) ◽  
pp. 517-520
Author(s):  
L. Ts. Adzhemyan ◽  
M. Hnatich ◽  
M. Stehlik
Keyword(s):  
Wave Number ◽  
Number Range ◽  
Wave Number Range ◽  
Small Wave ◽  
Small Wave Number ◽  
Decaying Turbulence

Inviscid instability of an unbounded heterogeneous shear layer

1971 ◽  
Vol 48 (2) ◽  
pp. 405-415 ◽  
Author(s):  
S. A. Maslowe ◽  
R. E. Kelly
Keyword(s):  
Growth Rate ◽  
Froude Number ◽  
Mixing Layer ◽  
Density Variation ◽  
Wave Number ◽  
Unstable Wave ◽  
Number Range ◽  
Spatial Growth ◽  
Wave Number Range ◽  
Low Froude Number

Stability curves are computed for both spatially and temporally growing disturbances in a stratified mixing layer between two uniform streams. The low Froude number limit, in which the effects of buoyancy predominate, and the high Froude number limit, in which the effects of density variation are manifested by the inertial terms of the vorticity equation, are considered as limiting cases. For the buoyant case, although the spatial growth rates can be predicted reasonably well by suitable use of the results for temporal growth, spatially growing disturbances appear to have high group velocities near the lower cutoff wave-number. For the inertial case, it is demonstrated that density variations can be destabilizing. More precisely, when the stream with the higher velocity has the lower density, both the wave-number range of unstable disturbances and the maximum spatial growth rate are increased relative to the case of homogeneous flow. Finally, it is shown how the growth rate of the most unstable wave in the inertial case diminishes as buoyancy becomes important.

The scattering of acoustic waves by a spherically stratified inhomogeneous medium

1977 ◽  
Vol 76 (4) ◽  
pp. 345-350 ◽  
Author(s):  
David Colton
Keyword(s):  
Inhomogeneous Medium ◽  
Acoustic Waves ◽  
Index Of Refraction ◽  
Wave Number ◽  
Direct And Inverse Problems ◽  
Large Index ◽  
Small Wave ◽  
Small Wave Number ◽  
Limiting Case ◽  
Scattering Of Acoustic Waves

SynopsisIntegral operators are used to solve the direct and inverse problems of the scattering of acoustic waves by a spherically stratified inhomogeneous medium of compact support. The results are valid for all values of the wave number and an arbitrarily large index of refraction. In the limiting case of small wave number or small inhomogeneities the results are in agreement with those of Rorres and Born.

Hydromagnetic Stability of Two Rivlin-Ericksen Elastico-Viscous Superposed Conducting Fluids

1997 ◽  
Vol 52 (6-7) ◽  
pp. 528-532
Author(s):  
R. C. Sharma ◽  
P. Kumar
Keyword(s):  
Magnetic Field ◽  
Wave Number ◽  
Horizontal Magnetic Field ◽  
Number Range ◽  
Wave Number Range ◽  
Unstable Configuration ◽  
The Stability ◽  
Superposed Fluids ◽  
The Magnetic Field ◽  
Conducting Fluids

Abstract The stability of the plane interface separating two Rivlin-Ericksen elastico-viscous superposed fluids of uniform densities when the whole system is immersed in a uniform horizontal magnetic field has been studied. The stability analysis has been carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities and equal kinematic viscoelasticities. It is found that the stability criterion is independent of the effects of viscosity and viscoelasticity and is dependent on the orientation and magnitude of the magnetic field. The magnetic field is found to stabilize a certain wave-number range of the unstable configuration. The behaviour of growth rates with respect to kinematic viscosity and kinematic viscoelasticity parameters are examined numerically.

Absorption coefficient of Dupont Teflon FEP in the 20–130 wave-number range

1985 ◽  
Vol 24 (17) ◽  
pp. 2746 ◽  
Author(s):  
Mark A. Ordal ◽  
Robert J. Bell ◽  
Ralph W. Alexander ◽  
Raymond E. Paul
Keyword(s):  
Absorption Coefficient ◽  
Wave Number ◽  
Number Range ◽  
Wave Number Range

Liquid Turbulence Spectra in Two-Phase Bubbly Flow Under Turbulence Augmentation and Suppression Conditions

2006 ◽  
Author(s):  
Mohamed E. Shawkat ◽  
Chan Y. Ching ◽  
Mamdouh Shoukri
Keyword(s):  
Void Fraction ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Optical Probe ◽  
Wave Number ◽  
Two Phase ◽  
Number Range ◽  
Turbulence Spectra ◽  
Turbulence Suppression ◽  
Wave Number Range

An experimental investigation was performed in air-water bubbly flow to study the liquid turbulence spectra in a 200mm diameter vertical pipe. A dual optical probe was used to measure the local void fraction and bubble diameter while the liquid velocities were measured using hot-film anemometry. Experiments were performed at two liquid superficial velocities of 0.2 and 0.68m/s for gas superficial velocities in the range of 0 to 0.18m/s. Generally, as the void fraction increases there is a turbulence augmentation. However, a turbulence suppression was observed near the pipe wall at the higher liquid flow rate for low void fraction. In the augmentation case, the turbulence spectra showed a significant increase in the energy at the wave number range comparable to the bubble diameter. In the suppression case, the spectra showed that suppression initially occurs at the low wave number range and then extends to higher wave numbers as suppression increased.

scholarly journals Dynamics of turbulence under the effect of stratification and internal waves

2015 ◽  
Vol 22 (3) ◽  
pp. 337-348 ◽  
Author(s):  
O. A. Druzhinin ◽  
L. A. Ostrovsky
Keyword(s):  
Vertical Direction ◽  
Internal Gravity Wave ◽  
Turbulent Energy ◽  
Horizontal Layer ◽  
Wave Number ◽  
Small Scale ◽  
Number Range ◽  
Wave Number Range ◽  
Order Of Magnitude ◽  
Scale Turbulence

Abstract. The objective of this paper is to study the dynamics of small-scale turbulence near a pycnocline, both in the free regime and under the action of an internal gravity wave (IW) propagating along a pycnocline, using direct numerical simulation (DNS). Turbulence is initially induced in a horizontal layer at some distance above the pycnocline. The velocity and density fields of IWs propagating in the pycnocline are also prescribed as an initial condition. The IW wavelength is considered to be larger by the order of magnitude as compared to the initial turbulence integral length scale. Stratification in the pycnocline is considered to be sufficiently strong so that the effects of turbulent mixing remain negligible. The dynamics of turbulence is studied both with and without an initially induced IW. The DNS results show that, in the absence of an IW, turbulence decays, but its decay rate is reduced in the vicinity of the pycnocline, where stratification effects are significant. In this case, at sufficiently late times, most of the turbulent energy is located in a layer close to the pycnocline center. Here, turbulent eddies are collapsed in the vertical direction and acquire the "pancake" shape. IW modifies turbulence dynamics, in that the turbulence kinetic energy (TKE) is significantly enhanced as compared to the TKE in the absence of IW. As in the case without IW, most of the turbulent energy is localized in the vicinity of the pycnocline center. Here, the TKE spectrum is considerably enhanced in the entire wave-number range as compared to the TKE spectrum in the absence of IW.

scholarly journals Summer planetary-scale oscillations: aura MLS temperature compared with ground-based radar wind

2009 ◽  
Vol 27 (4) ◽  
pp. 1763-1774 ◽  
Author(s):  
C. E. Meek ◽  
A. H. Manson
Keyword(s):  
Temperature Data ◽  
Wave Number ◽  
Medium Frequency ◽  
Period Range ◽  
Number Range ◽  
Data Presentation ◽  
Continuous Sampling ◽  
Planetary Scale ◽  
Mesospheric Temperature ◽  
Wave Number Range

Abstract. The advent of satellite based sampling brings with it the opportunity to examine virtually any part of the globe. Aura MLS mesospheric temperature data are analysed in a wavelet format for easy identification of possible planetary waves (PW) and aliases masquerading as PW. A calendar year, 2005, of eastward, stationary, and westward waves at a selected latitude is shown in separate panels for wave number range −3 to +3 for period range 8 h to 30 days (d). Such a wavelet analysis is made possible by Aura's continuous sampling at all latitudes 82° S–82° N. The data presentation is suitable for examination of years of data. However this paper focuses on the striking feature of a "dish-shaped" upper limit to periods near 2 d in mid-summer, with longer periods appearing towards spring and fall, a feature also commonly seen in radar winds. The most probable cause is suggested to be filtering by the summer jet at 70–80 km, the latter being available from ground based medium frequency radar (MFR). Classically, the phase velocity of a wave must be greater than that of the jet in order to propagate through it. As an attempt to directly relate satellite and ground based sampling, a PW event of period 8d and wave number 2, which appears to be the original rather than an alias, is compared with ground based radar wind data. An appendix discusses characteristics of satellite data aliases with regard to their periods and amplitudes.

An experimental study of gas-hydrate formation by measuring viscosity and infrared spectra

2003 ◽  
Vol 81 (1-2) ◽  
pp. 485-492 ◽  
Author(s):  
H Oyama ◽  
T Ebinuma ◽  
W Shimada ◽  
S Takeya ◽  
J Nagao ◽  
...  
Keyword(s):  
Experimental Study ◽  
Infrared Spectrum ◽  
Infrared Spectra ◽  
Hydrate Formation ◽  
Wave Number ◽  
Gas Hydrate Formation ◽  
Spectrum Change ◽  
Small Wave ◽  
Before And After ◽  
Small Wave Number

We measured the viscosities and infrared (IR) spectra before and after hydrate nucleation. During the induction period, the viscosity increases and the infrared spectrum shifts to higher energy. After nucleation, the viscosity decreases abruptly, and the peak positions in the IR spectrum change to the small wave-number side. These results indicate that water acts as a precursor to hydrate nucleation. PACS Nos.: 66.20td, 78.30.30-j, 64.60Qb

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