The effects of drag reduction measures on boundary layer turbulence structure - Implications of an inviscid model

1985 ◽  
Author(s):  
M. LANDAHL ◽  
D. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Turbulence Structure ◽  
Boundary Layer Turbulence

Investigation of Microbubble Boundary Layer Using Particle Tracking Velocimetry

2005 ◽  
Vol 128 (3) ◽  
pp. 507-519 ◽  
Author(s):  
Javier Ortiz-Villafuerte ◽  
Yassin A Hassan
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Buffer Zone ◽  
Continuous Phase ◽  
Velocity Fields ◽  
Turbulence Structure ◽  
Mean Velocity ◽  
Measured Velocity

Particle tracking velocimetry has been used to measure the velocity fields of both continuous phase and dispersed microbubble phase, in a turbulent boundary layer, of a channel flow. Hydrogen and oxygen microbubbles were generated by electrolysis. The average size of the microbubbles was 15μm in radius. Drag reductions up to 40% were obtained, when the accumulation of microbubbles took place in a critical zone within the buffer layer. It is confirmed that a combination of concentration and distribution of microbubbles in the boundary layer can achieve high drag reduction values. Microbubble distribution across the boundary layer and their influence on the profile of the components of the liquid mean velocity vector are presented. The spanwise component of the mean vorticity field was inferred from the measured velocity fields. A decrease in the magnitude of the vorticity is found, leading to an increase of the viscous sublayer thickness. This behavior is similar to the observation of drag reduction by polymer and surfactant injection into liquid flows. The results obtained indicate that drag reduction by microbubble injection is not a simple consequence of density effects, but is an active and dynamic interaction between the turbulence structure in the buffer zone and the distribution of the microbubbles.

Turbulence Structure Modification and Drag Reduction by Microbubble Injections in a Boundary Layer Channel Flow

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
C. C. Gutiérrez-Torres ◽  
Y. A. Hassan ◽  
J. A. Jimenez-Bernal
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Single Phase ◽  
Pure Water ◽  
Channel Height ◽  
Turbulence Structure ◽  
Two Phase ◽  
Flow Measurements ◽  
Phase Water

Turbulent boundary layer modification in a channel flow using injection of microbubbles as a means to achieve drag reduction was studied. The physical mechanism of this phenomenon is not yet fully understood. To obtain some information related to this phenomenon, single-phase (pure water) flow and two-phase (water and microbubbles) channel flow measurements are taken. The void fraction conditions were varied while maintaining a Reynolds number of 5128 based on the half channel height. The study indicates that the presence of microbubbles within the boundary layer modifies the turbulence structure such that variations in time and space turbulent scales are observed, as well as ejection and sweep phenomena.

A Method of Predicting the Behavior of a Turbulent Boundary Layer With Discrete Transpiration Jets

1975 ◽  
Vol 97 (2) ◽  
pp. 214-224 ◽  
Author(s):  
H. J. Herring
Keyword(s):  
Heat Transfer ◽  
Energy Source ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Differential Equations ◽  
Ordinary Differential Equations ◽  
Equations Of Motion ◽  
Turbulence Structure ◽  
Boundary Layer Turbulence ◽  
Interaction Terms

A method is proposed for predicting the behavior of a turbulent boundary layer with heat transfer under the influence of transpiration with discrete jets. The boundary layer is treated as a laterally averaged flow and the effects of nonuniformity are introduced through additional momentum and energy source terms in the equations of motion. These nonuniformity interaction terms are obtained using solutions of a set of ordinary differential equations governing the trajectory of jets. The effects of interaction between the jet and boundary layer turbulence structure are also treated. The predictions of the theory are shown to compare well with available discrete jet-boundary layer data.

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