scholarly journals Problems of an experimental study of a reverse flow in the turbulent channel flow

2021 ◽  
Vol 2057 (1) ◽  
pp. 012097
Author(s):  
D I Zaripov
Keyword(s):  
Experimental Study ◽  
Measurement Error ◽  
Channel Flow ◽  
Spatial Resolution ◽  
High Speed ◽  
High Spatial Resolution ◽  
Reverse Flow ◽  
Turbulent Channel Flow ◽  
Measurement Methods ◽  
Piv Measurements

Abstract The problems of experimental study of the near-wall reverse flow (NWRF) phenomenon observed in a turbulent channel flow are discussed. Until now, the problem of detecting the NWRF events has been associated with the lack of spatial resolution of measurement methods. The present study, using the example of high-speed PIV measurements, shows that problems associated with the influence of the measurement error arise even when a high spatial resolution is achieved.

scholarly journals Turbulent channel flow over an anisotropic porous wall – drag increase and reduction

2018 ◽  
Vol 842 ◽  
pp. 381-394 ◽  
Author(s):  
Marco E. Rosti ◽  
Luca Brandt ◽  
Alfredo Pinelli
Keyword(s):  
Drag Reduction ◽  
Channel Flow ◽  
High Speed ◽  
Vertical Direction ◽  
Porous Wall ◽  
Turbulent Channel Flow ◽  
Spanwise Direction ◽  
Normal Velocity ◽  
Porous Walls ◽  
The One

The effect of the variations of the permeability tensor on the close-to-the-wall behaviour of a turbulent channel flow bounded by porous walls is explored using a set of direct numerical simulations. It is found that the total drag can be either reduced or increased by more than 20 % by adjusting the permeability directional properties. Drag reduction is achieved for the case of materials with permeability in the vertical direction lower than the one in the wall-parallel planes. This configuration limits the wall-normal velocity at the interface while promoting an increase of the tangential slip velocity leading to an almost ‘one-component’ turbulence where the low- and high-speed streak coherence is strongly enhanced. On the other hand, strong drag increase is found when high wall-normal and low wall-parallel permeabilities are prescribed. In this condition, the enhancement of the wall-normal fluctuations due to the reduced wall-blocking effect triggers the onset of structures which are strongly correlated in the spanwise direction, a phenomenon observed by other authors in flows over isotropic porous layers or over ribletted walls with large protrusion heights. The use of anisotropic porous walls for drag reduction is particularly attractive since equal gains can be achieved at different Reynolds numbers by rescaling the magnitude of the permeability only.

Experimental Study of Polymer Drag Reduction in a Turbulent Channel Flow

2003 ◽  
Author(s):  
Xiaochun Shen ◽  
Kihyun Kim ◽  
Jamison L. Miller ◽  
Ryan Sun-Chee-Fore ◽  
Ana I. Sirviente
Keyword(s):  
Experimental Study ◽  
Polymer Solution ◽  
Channel Flow ◽  
Water Channel ◽  
Turbulent Channel Flow ◽  
Turbulence Characteristics ◽  
Polymer Injection ◽  
Turbulent Channel Flows ◽  
Polymer Drag Reduction ◽  
Turbulent Water

The effect of polymer injection on the turbulence characteristics of a fully developed turbulent water channel flow was studied. The main focus of this study was to assess the influence of the polymer solution injection concentration and consequent mixing. This study was conducted by measuring the turbulence characteristics of two fully developed turbulent channel flows for a Reynolds number of 5×104, with different injection concentrations of the same polymer solution but with the same homogeneous concentration at the test section. These measurements were complemented by visualizations of the flow, which revealed the presence of supra-molecular polymer structures. The development of such structures seems to enhance the drag reducing abilities of the polymer solution.

Sign in / Sign up

Export Citation Format

Share Document