Zonal flows driven by the turbulent energy flux and the turbulent toroidal Reynolds stress in a magnetic fusion torus

2017 ◽  
Vol 24 (10) ◽  
pp. 102508 ◽  
Author(s):  
Shaojie Wang
Keyword(s):  
Reynolds Stress ◽  
Energy Flux ◽  
Turbulent Energy ◽  
Magnetic Fusion ◽  
Zonal Flows

A Numerical Investigation to Study Roughness Effects in Oscillatory Flows

2017 ◽  
Author(s):  
Chaitanya D. Ghodke ◽  
Sourabh V. Apte
Keyword(s):  
Shear Rate ◽  
Reynolds Stress ◽  
Large Diameter ◽  
Turbulent Energy ◽  
Sand Particle ◽  
Roughness Effects ◽  
Oscillatory Flows ◽  
Wake Field ◽  
Double Averaging ◽  
Acceleration Cycle

Effects of roughness on the near-bed turbulence characteristics in oscillatory flows are studied by means of particle-resolved direct numerical simulations (DNS). Two particle sizes of diameter 375 and 125 in wall units corresponding to the large size gravel and the small size sand particle, respectively, in a very rough turbulent flow regime are reported. A double-averaging technique is employed to study the nature of the wake field, i.e., the spatial inhomogeneities at the roughness length scale. This introduced additional production and transport terms in double-averaged Reynolds stress budget, indicating alternate pathways of turbulent energy transfer mechanisms. Budgets of normal components of Reynolds stress reveal redistribution of energy from streamwise component to other two components and is attributed to the work of pressure in both flow cases. It is shown that the large diameter gravel particles significantly modulate the near-bed flow structures, leading to pronounced isotropization of the near-bed flow; while in the sand case, elongated horseshoe structures are found as a result of high shear rate. Effect of mean shear rate on the near-bed anisotropy is significant in the sand case, while it is minimal for the gravel-bed. Redistribution of energy in the gravel case showed reduced dependence on the flow oscillations, while for the sand particle it is more pronounced towards the end of an acceleration cycle.

A turbulence velocity scale for curved shear flows

1975 ◽  
Vol 70 (1) ◽  
pp. 37-57 ◽  
Author(s):  
Ronald M. C. So
Keyword(s):  
Reynolds Stress ◽  
Shear Flows ◽  
Turbulent Energy ◽  
Streamline Curvature ◽  
Velocity Scale ◽  
Dimensional Boundary ◽  
Free Constant ◽  
Turbulence Velocity ◽  
Turbulence Length ◽  
Energy Balances

Assuming the turbulence length scale to be unaffected by streamline curvature, a turbulence velocity scale for curved shear flows is derived from the Reynolds-stress equations. Closure of the equations is obtained by using the scheme of Mellor & Herring (1973), and the Reynolds-stress equations are simplified by invoking the two-dimensional boundary-layer approximations and assuming that production of turbulent energy balances viscous dissipation. The resulting formula for the velocity scale has one free parameter, but this can be determined from data for non-rotating unstratified plane flows. Consequently there is no free constant in the derived expression. A single value of the constant is found to give good agreement between calculated and measured values of the velocity scale for a wide variety of curved shear flows.The result is also applied to test the validity and extent of the analogy between the effects of buoyancy and streamline curvature. This is done by comparing the present result with that obtained by Mellor (1973). Excellent agreement is obtained for the range −0·21 [les ]Rif[les ] 0·21. Therefore the present result provides direct evidence in support of the use of a Monin–Oboukhov (1954) formula for curved shear flows as proposed by Bradshaw (1969).

scholarly journals Key impact of phase dynamics and diamagnetic drive on Reynolds stress in magnetic fusion plasmas

2021 ◽  
Author(s):  
Yanick Sarazin ◽  
Guilhem Dif-Pradalier ◽  
Xavier Garbet ◽  
Philippe Ghendrih ◽  
Anatole Berger ◽  
...  
Keyword(s):  
Reynolds Stress ◽  
Magnetic Fusion ◽  
Fusion Plasmas ◽  
Phase Dynamics

Measurement on the Structure of the Reynolds Stress for the Turbulent Boundary Layer Flow Over a Two-Dimensional Escarpment With Mild Upwind Slope

2011 ◽  
Author(s):  
Bao-Shi Shiau ◽  
Ben-Jue Tsai
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Reynolds Stress ◽  
High Speed ◽  
Slope Angle ◽  
Turbulent Energy ◽  
Quadrant Analysis ◽  
Two Dimensional ◽  
Spectrum Distribution ◽  
Layer Flow

Experimental measurement study on the structure of the Reynolds stress and turbulence spectrum for wind flows over a two-dimensional escarpment with mild upwind slope (slope angle θ = 15°) were performed in the wind tunnel. The Quadrant analysis was applied to analyze the experimental data and yield the structure of the Reynolds stress. In according to the quadrant analysis, the Reynolds stress is composed of four events of the stress components, i.e. outward interaction, ejection (low-speed fluid upward), inward interaction, and sweep (high-speed fluid downward). Measured results show that: (1) Measurements of the structure of the Reynolds stress reveal that both the sweep and ejection events are the major contributors to the Reynolds stress for flow around the two dimensional escarpment with mild upwind slope. (2) The contributions to the Reynolds stress made by ejection events and sweep events are almost the same at heights Z/Zref greater than 0.2 for different downstream distances along the mild slope of escarpment. Here Zref is the turbulent boundary layer thickness. When flow reached the top of the slope of escarpment, stress fractions of ejection event and sweep event, S2 and S4 increased significantly. (3) The he turbulent energy spectrum distribution was not found very dominant spectrum peak as winds flow over the mild upwind slope and top surface of escarpment.

Algebraic turbulent energy flux models for hypersonic shear flows

2010 ◽  
Vol 46 (2-3) ◽  
pp. 49-61 ◽  
Author(s):  
Rodney D.W. Bowersox ◽  
Simon W. North
Keyword(s):  
Energy Flux ◽  
Shear Flows ◽  
Turbulent Energy

scholarly journals Reynolds Stress and Turbulent Energy Production in a Tidal Channel

2002 ◽  
Vol 32 (4) ◽  
pp. 1242-1251 ◽  
Author(s):  
Tom P. Rippeth ◽  
Eirwen Williams ◽  
John H. Simpson
Keyword(s):  
Reynolds Stress ◽  
Energy Production ◽  
Turbulent Energy ◽  
Tidal Channel

scholarly journals Experimental study of oscillating-grid turbulence interacting with a solid boundary

2017 ◽  
Vol 813 ◽  
pp. 768-798 ◽  
Author(s):  
Mark W. McCorquodale ◽  
R. J. Munro
Keyword(s):  
Reynolds Stress ◽  
Energy Flux ◽  
Velocity Component ◽  
Vertical Plane ◽  
Vertical Flux ◽  
Solid Boundary ◽  
Grid Turbulence ◽  
Normal Velocity ◽  
Particle Imaging ◽  
Oscillating Grid

The interaction between oscillating-grid turbulence and a solid, impermeable boundary (positioned below, and aligned parallel to, the grid) is studied experimentally. Instantaneous velocity measurements, obtained using two-dimensional particle imaging velocimetry in the vertical plane through the centre of the (horizontal) grid, are used to study the effect of the boundary on the root-mean-square velocity components, the vertical flux of turbulent kinetic energy (TKE) and the terms in the Reynolds stress transport equation. Identified as a critical aspect of the interaction is the blocking of a vertical flux of TKE across the boundary-affected region. Terms of the Reynolds stress transport equations show that the blocking of this energy flux acts to increase the boundary-tangential turbulent velocity component, relative to the far-field trend, but not the boundary-normal velocity component. The results are compared with previous studies of the interaction between zero-mean-shear turbulence and a solid boundary. In particular, the data reported here are in support of viscous and ‘return-to-isotropy’ mechanisms governing the intercomponent energy transfer previously proposed, respectively, by Perot & Moin (J. Fluid Mech., vol. 295, 1995, pp. 199–227) and Walkeret al.(J. Fluid Mech., vol. 320, 1996, pp. 19–51), although we note that these mechanisms are not independent of the blocking of energy flux and draw parallels to the related model proposed by Magnaudet (J. Fluid Mech., vol. 484, 2003, pp. 167–196).

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