Pressure Development in the Entrance Region and Fully Developed Region of Generalized Channel Turbulent Flows

1976 ◽  
Vol 43 (1) ◽  
pp. 13-19
Author(s):  
S. M. Hai
Keyword(s):  
Turbulent Flows ◽  
Reynolds Numbers ◽  
Channel Flows ◽  
Pressure Drops ◽  
Turbulent Channel Flows ◽  
Numerical Predictions ◽  
High Reynolds Numbers ◽  
Pressure Development ◽  
High Reynolds ◽  
Very High

In this paper, the pressure drops in the developing length of generalized turbulent channel flows are investigated, and the effects of Reynolds number and distance from the channel entrance are examined. The numerical method is also used to predict the pressure drops in simple channel flows for very high Reynolds numbers (of the order of 100,000). Excellent agreement is obtained between experimental data and numerical predictions.

scholarly journals Extreme dissipation and intermittency in turbulence at very high Reynolds numbers

2020 ◽  
Vol 476 (2243) ◽  
pp. 20200591
Author(s):  
Gerrit E. Elsinga ◽  
Takashi Ishihara ◽  
Julian C. R. Hunt
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Small Scale ◽  
Scaling Exponent ◽  
High Reynolds Numbers ◽  
Layer Structures ◽  
High Reynolds ◽  
Very High

Extreme dissipation events in turbulent flows are rare, but they can be orders of magnitude stronger than the mean dissipation rate. Despite its importance in many small-scale physical processes, there is presently no accurate theory or model for predicting the extrema as a function of the Reynolds number. Here, we introduce a new model for the dissipation probability density function (PDF) based on the concept of significant shear layers, which are thin regions of elevated local mean dissipation. At very high Reynolds numbers, these significant shear layers develop layered substructures. The flow domain is divided into the different layer regions and a background region, each with their own PDF of dissipation. The volume-weighted regional PDFs are combined to obtain the overall PDF, which is subsequently used to determine the dissipation variance and maximum. The model yields Reynolds number scalings for the dissipation maximum and variance, which are in agreement with the available data. Moreover, the power law scaling exponent is found to increase gradually with the Reynolds numbers, which is also consistent with the data. The increasing exponent is shown to have profound implications for turbulence at atmospheric and astrophysical Reynolds numbers. The present results strongly suggest that intermittent significant shear layer structures are key to understanding and quantifying the dissipation extremes, and, more generally, extreme velocity gradients.

Correction: Wall bounded turbulent flows up to high Reynolds numbers: LES resolution assessment

2019 ◽  
Author(s):  
Ghazaleh Ahmadi ◽  
Hassan Kassem ◽  
Bernhard Stoevesandt ◽  
Joachim Peinke ◽  
Stefan Heinz
Keyword(s):  
Turbulent Flows ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
High Reynolds

Wall bounded turbulent flows up to high Reynolds numbers: LES resolution assessment

2019 ◽  
Author(s):  
Ghazaleh Ahmadi ◽  
Hassan Kassem ◽  
Bernhard Stoevesandt ◽  
Joachim Peinke ◽  
Stefan Heinz
Keyword(s):  
Turbulent Flows ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
High Reynolds

scholarly journals Turbulent flows in channels and pipes

2007 ◽  
Vol 29 (3) ◽  
pp. 385-396
Author(s):  
Khanh Le Chau
Keyword(s):  
Variational Principle ◽  
Viscous Fluid ◽  
Turbulent Flows ◽  
Good Accuracy ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Pipe Flows ◽  
High Reynolds Numbers ◽  
Friction Factors ◽  
High Reynolds

A variational principle for channel and pipe flows of incompressible viscous fluid is proposed. For low Reynolds numbers this variational principle reduces to the principle of minimum dissipation. For high Reynolds numbers it enables one to calculate the velocity profiles and the corresponding friction factors with reasonably good accuracy.

Comparison and Scaling of the Bursting Period in Rough and Smooth Walls Channel Flows

1999 ◽  
Vol 121 (4) ◽  
pp. 735-746 ◽  
Author(s):  
S. Demare ◽  
L. Labraga ◽  
C. Tournier
Keyword(s):  
Turbulent Flows ◽  
Major Part ◽  
Reynolds Numbers ◽  
Channel Flows ◽  
Quadrant Analysis ◽  
Number Range ◽  
Mixed Variables ◽  
Detection Techniques ◽  
Turbulent Channel Flows ◽  
Bursting Process

The Structure of Smooth and k-type rough wall turbulent channel flows was examined over a Reynolds number range of 12,700–55,000 using a few of the most common detection techniques (Modified U_Level (MODUL), TERA, Quadrant analysis) and conditional averages. When grouping time is used and a threshold-independent range could be found, all of the above techniques yield approximately the same time between bursts in the major part of the turbulent flow. In the range of Reynolds numbers studied, the bursting frequency is best scaled on mixed variables. The conditional averaged patterns give a representation of the bursting process and show some differences between turbulent flows which develop on smooth and rough walls, in both inner and outer regions.

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