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 Dynamics of turbulence under the effect of stratification and internal waves

2015 ◽  
Vol 2 (1) ◽  
pp. 329-359
Author(s):  
O. A. Druzhinin ◽  
L. A. Ostrovsky
Keyword(s):  
Turbulent Mixing ◽  
Vertical Direction ◽  
Internal Gravity Wave ◽  
Turbulent Energy ◽  
Horizontal Layer ◽  
Small Scale ◽  
Turbulent Eddies ◽  
Order Of Magnitude ◽  
Scale Turbulence ◽  
Initial 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 IW propagating in the pycnocline are also prescribed as initial condition. The IW wavelength is considered to be by the order of magnitude larger 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 initially induced internal wave. The DNS results show that in the absence of 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 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 turbulent energy is localized in the vicinity of the pycnocline center. Here the TKE spectrum is considerably enhanced in the entire wavenumber range as compared to the TKE spectrum in the absence of IW.

scholarly journals Spectral properties of turbulent energy in the quilibrium wave number range.

1989 ◽  
pp. 109-118
Author(s):  
Toshimitsu KOMATSU ◽  
Yasushi MATSUMOTO ◽  
Toshihiko SHIBATA ◽  
Toichiro TSUBAKI
Keyword(s):  
Spectral Properties ◽  
Turbulent Energy ◽  
Wave Number ◽  
Number Range ◽  
Wave Number Range

‘Inactive’ motion and pressure fluctuations in turbulent boundary layers

1967 ◽  
Vol 30 (2) ◽  
pp. 241-258 ◽  
Author(s):  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Outer Layer ◽  
Pressure Fluctuations ◽  
Turbulent Energy ◽  
Viscous Sublayer ◽  
Wave Number ◽  
Noticeable Effect ◽  
Frequency Spectra ◽  
Active Motion ◽  
Order Of Magnitude

Townsend's (1961) hypothesis that the turbulent motion in the inner region of a boundary layer consists of (i) an ‘active’ part which produces the shear stress τ and whose statistical properties are universal functions of τ and y, and (ii) an ‘inactive’ and effectively irrotational part determined by the turbulence in the outer layer, is supported in the present paper by measurements of frequency spectra in a strongly retarded boundary layer, in which the ‘inactive’ motion is particularly intense. The only noticeable effect of the inactive motion is an increased dissipation of kinetic energy into heat in the viscous sublayer, supplied by turbulent energy diffusion from the outer layer towards the surface. The required diffusion is of the right order of magnitude to explain the non-universal values of the triple products measured near the surface, which can therefore be reconciled with universality of the ‘active’ motion.Dimensional analysis shows that the contribution of the ‘active’ inner layer motion to the one-dimensional wave-number spectrum of the surface pressure fluctuations varies as τ2w/k1 up to a wave-number inversely proportional to the thickness of the viscous sublayer. This result is strongly supported by the recent measurements of Hodgson (1967), made with a much smaller ratio of microphone diameter to boundary-layer thickness than has been achieved previously. The disagreement of the result with most other measurements is attributed to inadequate transducer resolution in the other experiments.

Aero-optics of subsonic turbulent boundary layers

2012 ◽  
Vol 696 ◽  
pp. 122-151 ◽  
Author(s):  
Kan Wang ◽  
Meng Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Dominant Role ◽  
Elevation Angle ◽  
Turbulent Boundary Layers ◽  
Density Field ◽  
Small Scale ◽  
Number Range ◽  
Scale Turbulence

AbstractCompressible large-eddy simulations are carried out to study the aero-optical distortions caused by Mach 0.5 flat-plate turbulent boundary layers at Reynolds numbers of ${\mathit{Re}}_{\theta } = 875$, 1770 and 3550, based on momentum thickness. The fluctuations of refractive index are calculated from the density field, and wavefront distortions of an optical beam traversing the boundary layer are computed based on geometric optics. The effects of aperture size, small-scale turbulence, different flow regions and beam elevation angle are examined and the underlying flow physics is analysed. It is found that the level of optical distortion decreases with increasing Reynolds number within the Reynolds-number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role, followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analysed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton’s linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.

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.

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.

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