scholarly journals Atmospheric depths of Jupiter, Saturn, and Uranus

1971 ◽  
Vol 40 ◽  
pp. 371-374
Author(s):  
S. F. Dermott
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
Strong Correlation ◽  
Planetary Atmosphere ◽  
Satellite Systems ◽  
Orbital Radius ◽  
Boundary Layer Turbulence ◽  
The Mean

The presence of numerous near-commensurabilities among pairs of mean motions and the strong correlation between orbital radius and mass in the satellite systems of the three major planets (particularly in the Saturn system) suggest that the orbits of the satellites have evolved considerably under the action of tides. It is shown that the source of dissipation could be boundary layer turbulence at the base of the planetary atmosphere. If this is the source of dissipation then it should be possible to estimate the depths of these atmospheres from the mean rates of energy dissipation.

Some dynamical effects of heat on a turbulent boundary layer

1970 ◽  
Vol 40 (2) ◽  
pp. 361-384 ◽  
Author(s):  
C. I. H. Nicholl
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Mechanical Energy ◽  
Turbulent Energy ◽  
Strong Discontinuity ◽  
Sudden Increase ◽  
Boundary Layer Turbulence ◽  
Heated Air ◽  
Order Of Magnitude ◽  
The Mean

The dynamical effects of a sudden increase of as much as 100°C in boundary temperature upon fully turbulent boundary layers at low Reynolds numbers in air have been investigated in a wind tunnel. A section of the floor or the roof of the tunnel could be heated, so that the rate of working of gravitational forces on the turbulence could be made to represent either a gain or a loss of turbulent mechanical energy. Techniques of hot-wire anemometry were employed which enabled the instantaneous temperature and the instantaneous velocity to be measured simultaneously at a point in the non-homogeneous turbulent flow field.In the case of a strong discontinuity in the floor temperature, a fine-scale convective structure developed from the highly unstable interface between the heated air just above the surface and the turbulent boundary layer; and the motion in this region was sufficiently vigorous that the mean pressure in the vicinity of the floor was reduced and a local wall jet was generated. The deduced pressure distribution is regarded as evidence of coupling between the free and forced convection modes which may lead to a series of local wall jets downstream of the discontinuity.In the case of a strong discontinuity in the roof temperature, the interface between the heated air and the turbulent boundary layer was stable; and the boundary-layer turbulence, acting to spread this stable gradient over the vertical extent of the boundary layer, was required to do work against the gravitational field. A rate of working against gravity which was an order of magnitude less than the rate of supply of turbulent energy from the mean shear proved sufficient to suppress the turbulence in a very short time.

A Single Column Model Evaluation of Mixing Length Formulations and Constraints for the sa-TKE-EDMF Planetary Boundary Layer Parameterization

2021 ◽  
Author(s):  
Edward J. Strobach
Keyword(s):  
Boundary Layer ◽  
Weather Prediction ◽  
Eddy Diffusivity ◽  
Mixing Length ◽  
Boundary Layer Turbulence ◽  
Pbl Scheme ◽  
Mean Structure ◽  
The Mean ◽  
Planetary Boundary Layer Parameterization ◽  
A Minor

AbstractParameterizing boundary layer turbulence is a critical component of numerical weather prediction and the representation of turbulent mixing of momentum, heat, and other tracers. The components that make up a boundary layer scheme can vary considerably, with each scheme having a combination of processes that are physically represented along with tuning parameters that optimize performance. Isolating a component of a PBL scheme to examine its impact is essential for understanding the evolution of boundary layer profiles and their impact on the mean structure. In this study we conduct three experiments with the scale-aware TKE eddy-diffusivity mass-flux (sa-TKE-EDMF) scheme: 1) releasing the upper limit constraints placed on mixing lengths, 2) incrementally adjusting the tuning coefficient related to wind shear in the modified Bougeault and Lacarrere (BouLac) mixing length formulation, and 3) replacing the current mixing length formulations with those used in the MYNN scheme. A diagnostic approach is adopted to characterize the bulk representation of turbulence within the residual layer and boundary layer in order to understand the importance of different terms in the TKE budget as well as to assess how the balance of terms changes between mixing length formulations. Although our study does not seek to determine the best formulation, it was found that strong imbalances led to considerably different profile structures both in terms of the resolved and subgrid fields. Experiments where this balance was preserved showed a minor impact on the mean structure regardless of the turbulence generated. Overall, it was found that changes to mixing length formulations and/or constraints had stronger impacts during the day while remaining partially insensitive during the evening.

scholarly journals Boundary Layer Turbulence over Surface Waves in a Strongly Forced Condition: LES and Observation

2019 ◽  
Vol 49 (8) ◽  
pp. 1997-2015 ◽  
Author(s):  
Nyla T. Husain ◽  
Tetsu Hara ◽  
Marc P. Buckley ◽  
Kianoosh Yousefi ◽  
Fabrice Veron ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Surface Waves ◽  
Wind Stress ◽  
Wind Profile ◽  
Wave Crest ◽  
Turbulent Stress ◽  
Boundary Layer Turbulence ◽  
The Mean ◽  
The Impact

AbstractThe impact of sea state on air–sea momentum flux (or wind stress) is a poorly understood component of wind–wave interactions, particularly in high wind conditions. The wind stress and mean wind profile over the ocean are influenced by the characteristics of boundary layer turbulence over surface waves, which are strongly modulated by transient airflow separation events; however, the features controlling their occurrence and intensity are not well known. A large-eddy simulation (LES) for wind over a sinusoidal wave train is employed to reproduce laboratory observations of phase-averaged airflow over waves in strongly forced conditions. The LES and observation both use a wave-following coordinate system with a decomposition of wind velocity into mean, wave-coherent, and turbulent fluctuation components. The LES results of the mean wind profile and structure of wave-induced and turbulent stress components agree reasonably well with observations. Both LES and observation show enhanced turbulent stress and mean wind shear at the height of the wave crest, signifying the impact of intermittent airflow separation events. Disparities exist particularly near the crest, suggesting that airflow separation and sheltering are affected by the nonlinearity and unsteadiness of laboratory waves. Our results also suggest that the intensity of airflow separation is most sensitive to wave steepness and the surface roughness parameterization near the crest. These results clarify how the characteristics of finite-amplitude waves can control the airflow dynamics, which may substantially influence the mean wind profile, equivalent surface roughness, and drag coefficient.

Entrance Region Heat Transfer in a Channel With a Ribbed Wall

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Koji Matsubara ◽  
Hiroyuki Ohta ◽  
Takahiro Miura
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Entrance Region ◽  
Turbulent Heat ◽  
Height Ratio ◽  
Ribbed Channel ◽  
Boundary Layer Turbulence ◽  
Smooth Channel ◽  
The Mean ◽  
Fuel Elements

Direct numerical simulation was performed for the heat transfer of airflow in the entrance region of a channel with repeated rib protrusions. The rib-pitch to rib-height ratio (Pi/H) was increased from 2.0 to 16.0 by four steps. The rib-height ratio (H/δ) was maintained constant at 0.20. The distribution of heat transfer coefficient numerically simulated agreed with the experiment by Kattchee and Mackewicz (1963, “Effects of Boundary Layer Turbulence Promoters on the Local Film Coefficients of ML-1 Fuel Elements,” Nucl. Sci. Eng., 16, pp. 31–38). The enhancement parameter was used to evaluate the heat transfer performance by a ribbed channel. This parameter was defined as the ratio of the mean Nusselt number for the ribbed channel against the smooth channel consuming the same pumping power. The simulation result revealed that the enhancement parameter was maximized for Pi/H = 2 to 4 over the upstream ribs (x/δ < 2) and was remained high for Pi/H = 4, 8, and 16 over the downstream ribs (x/δ > 4). Therefore, the optimal rib pitch was smaller for the upstream ribs, and increased to the developed region. The mechanisms underlying this trend were discussed through observation of the streamlines, mean temperature, turbulence statistics, and instantaneous structures. The turbulence was increased over the ribbed wall for the cases of medium to wide rib pitch (Pi/H = 4, 8, and 16), whereas the turbulence increase appeared only over the upstream ribs (x/δ < 2) for the cases of narrow rib pitch (Pi/H = 2). The excellent performance of the wider rib pitch (Pi/H = 4, 8, and 16) at the downstream ribs (x/δ > 2) was resulted from the turbulence increase activating the turbulent heat transport. Whereas, the superiority by the narrower rib pitch (Pi/H = 2, 4) comes from the turbulence activation, and the renewed thin boundary layer which continues due to the densely allocated ribs.

scholarly journals Energy dissipation caused by boundary layer instability at vanishing viscosity – ERRATUM

2018 ◽  
Vol 857 ◽  
pp. 952-952
Author(s):  
Natacha Nguyen van yen ◽  
Matthias Waidmann ◽  
Rupert Klein ◽  
Marie Farge ◽  
Kai Schneider
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
Vanishing Viscosity ◽  
Boundary Layer Instability

The effect of Reynolds number on boundary layer turbulence

1998 ◽  
Vol 18 (4) ◽  
pp. 341-346 ◽  
Author(s):  
David B. DeGraaff ◽  
Donald R. Webster ◽  
John K. Eaton
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layer Turbulence

Frontogenesis and frontal arrest of a dense filament in the oceanic surface boundary layer

2017 ◽  
Vol 837 ◽  
pp. 341-380 ◽  
Author(s):  
Peter P. Sullivan ◽  
James C. McWilliams
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Shear Instability ◽  
Upper Ocean ◽  
Surface Boundary ◽  
Horizontal Shear ◽  
Boundary Layer Turbulence ◽  
Filament Axis ◽  
Small Width ◽  
The Cross

The evolution of upper ocean currents involves a set of complex, poorly understood interactions between submesoscale turbulence (e.g. density fronts and filaments and coherent vortices) and smaller-scale boundary-layer turbulence. Here we simulate the lifecycle of a cold (dense) filament undergoing frontogenesis in the presence of turbulence generated by surface stress and/or buoyancy loss. This phenomenon is examined in large-eddy simulations with resolved turbulent motions in large horizontal domains using${\sim}10^{10}$grid points. Steady winds are oriented in directions perpendicular or parallel to the filament axis. Due to turbulent vertical momentum mixing, cold filaments generate a potent two-celled secondary circulation in the cross-filament plane that is frontogenetic, sharpens the cross-filament buoyancy and horizontal velocity gradients and blocks Ekman buoyancy flux across the cold filament core towards the warm filament edge. Within less than a day, the frontogenesis is arrested at a small width,${\approx}100~\text{m}$, primarily by an enhancement of the turbulence through a small submesoscale, horizontal shear instability of the sharpened filament, followed by a subsequent slow decay of the filament by further turbulent mixing. The boundary-layer turbulence is inhomogeneous and non-stationary in relation to the evolving submesoscale currents and density stratification. The occurrence of frontogenesis and arrest are qualitatively similar with varying stress direction or with convective cooling, but the detailed evolution and flow structure differ among the cases. Thus submesoscale filament frontogenesis caused by boundary-layer turbulence, frontal arrest by frontal instability and frontal decay by forward energy cascade, and turbulent mixing are generic processes in the upper ocean.

Observations of Small-Scale Turbulence and Energy Dissipation Rates in the Cloudy Boundary Layer

2006 ◽  
Vol 63 (5) ◽  
pp. 1451-1466 ◽  
Author(s):  
Holger Siebert ◽  
Katrin Lehmann ◽  
Manfred Wendisch
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
Wind Velocity ◽  
Turbulence Theory ◽  
Horizontal Wind ◽  
Inertial Subrange ◽  
Intermittent Flow ◽  
Small Scale ◽  
Dissipation Rates ◽  
Wide Range

Abstract Tethered balloon–borne measurements with a resolution in the order of 10 cm in a cloudy boundary layer are presented. Two examples sampled under different conditions concerning the clouds' stage of life are discussed. The hypothesis tested here is that basic ideas of classical turbulence theory in boundary layer clouds are valid even to the decimeter scale. Power spectral densities S( f ) of air temperature, liquid water content, and wind velocity components show an inertial subrange behavior down to ≈20 cm. The mean energy dissipation rates are ∼10−3 m2 s−3 for both datasets. Estimated Taylor Reynolds numbers (Reλ) are ∼104, which indicates the turbulence is fully developed. The ratios between longitudinal and transversal S( f ) converge to a value close to 4/3, which is predicted by classical turbulence theory for local isotropic conditions. Probability density functions (PDFs) of wind velocity increments Δu are derived. The PDFs show significant deviations from a Gaussian distribution with longer tails typical for an intermittent flow. Local energy dissipation rates ɛτ are derived from subsequences with a duration of τ = 1 s. With a mean horizontal wind velocity of 8 m s−1, τ corresponds to a spatial scale of 8 m. The PDFs of ɛτ can be well approximated with a lognormal distribution that agrees with classical theory. Maximum values of ɛτ ≈ 10−1 m2 s−3 are found in the analyzed clouds. The consequences of this wide range of ɛτ values for particle–turbulence interaction are discussed.

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