Large-scale control strategy for drag reduction in turbulent channel flows

2017 ◽  
Vol 2 (6) ◽  
Author(s):  
Jie Yao ◽  
Xi Chen ◽  
Flint Thomas ◽  
Fazle Hussain
Keyword(s):  
Drag Reduction ◽  
Control Strategy ◽  
Large Scale ◽  
Channel Flows ◽  
Turbulent Channel Flows ◽  
Scale Control

Drag Reduction Due to Streamwise Grooves in Turbulent Channel Flow

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
C. T. DeGroot ◽  
C. Wang ◽  
J. M. Floryan
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Turbulent Channel Flow ◽  
Surface Modifications ◽  
Channel Flows ◽  
Wave Number ◽  
Stress Profile ◽  
Bulk Fluid ◽  
Geometry Model ◽  
Turbulent Channel Flows

Drag reduction in turbulent channel flows has significant practical relevance for energy savings. Various methods have been proposed to reduce turbulent skin friction, including microscale surface modifications such as riblets or superhydrophobic surfaces. More recently, macroscale surface modifications in the form of longitudinal grooves have been shown to reduce drag in laminar channel flows. The purpose of this study is to show that these grooves also reduce drag in turbulent channel flows and to quantify the drag reduction as a function of the groove parameters. Results are obtained using computational fluid dynamics (CFD) simulations with turbulence modeled by the k–ω shear-stress transport (SST) model, which is first validated with direct numerical simulations (DNS). Based on the CFD results, a reduced geometry model is proposed which shows that the approximate drag reduction can be quantified by evaluating the drag reduction of the geometry given by the first Fourier mode of an arbitrary groove geometry. Results are presented to show the drag reducing potential of grooves as a function of Reynolds number as well as groove wave number, amplitude, and shape. The mechanism of drag reduction is discussed, which is found to be due to a rearrangement of the bulk fluid motion into high-velocity streamtubes in the widest portion of the channel opening, resulting in a change in the wall shear stress profile.

scholarly journals Effect of finite Weissenberg number on turbulent channel flows of an elastoviscoplastic fluid

2021 ◽  
Vol 927 ◽  
Author(s):  
Daulet Izbassarov ◽  
Marco E. Rosti ◽  
Luca Brandt ◽  
Outi Tammisola
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Weissenberg Number ◽  
Channel Flows ◽  
Viscoplastic Flow ◽  
Turbulent Structures ◽  
Turbulent Dissipation ◽  
Flow Equations ◽  
Turbulent Channel Flows ◽  
Nonlinear Elastic

Direct numerical simulations are carried out to study the effect of finite Weissenberg number up to $Wi=16$ on laminar and turbulent channel flows of an elastoviscoplastic (EVP) fluid, at a fixed bulk Reynolds number of $2800$ . The incompressible flow equations are coupled with the evolution equation for the EVP stress tensor by a modified Saramito model that extends both the Bingham viscoplastic and the finite extensible nonlinear elastic-Peterlin (FENE-P) viscoelastic models. In turbulent flow, we find that drag decreases with both the Bingham and Weissenberg numbers, until the flow laminarises at high enough elastic and yield stresses. Hence, a higher drag reduction is achieved than in the viscoelastic flow at the same Weissenberg number. The drag reduction persists at Bingham numbers up to 20, in contrast to viscoplastic flow, where the drag increases in the laminar regime compared with a Newtonian flow. Moreover, elasticity affects the laminarisation of an EVP flow in a non-monotonic fashion, delaying it at lower and promoting it at higher Weissenberg numbers. A hibernation phenomenon is observed in the EVP flow, leading to large changes in the unyielded regions. Finally, plasticity is observed to affect both low- and high-speed streaks equally, attenuating the turbulent dissipation and the fragmentation of turbulent structures.

Frictional drag reduction promoted by generating void waves in high-speed turbulent channel flows

2019 ◽  
Vol 2019.24 (0) ◽  
pp. A122
Author(s):  
Taiji TANAKA ◽  
Hyun Jin PARK ◽  
Yuji TASAKA ◽  
Yuichi MURAI ◽  
Chiharu KAWAKITA
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Channel Flows ◽  
Frictional Drag ◽  
Turbulent Channel Flows

Drag reduction promoted by repetitive bubble injection in turbulent channel flows

2015 ◽  
Vol 75 ◽  
pp. 12-25 ◽  
Author(s):  
Hyun Jin Park ◽  
Yuji Tasaka ◽  
Yoshihiko Oishi ◽  
Yuichi Murai
Keyword(s):  
Drag Reduction ◽  
Channel Flows ◽  
Turbulent Channel Flows
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