scholarly journals Drag Reduction of a Turbulent Boundary Layer over an Oscillating Wall and Its Variation with Reynolds Number

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Martin Skote ◽  
Maneesh Mishra ◽  
Yanhua Wu
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Downstream Distance ◽  
The Past ◽  
Layer Flow ◽  
Reynolds Number Dependency ◽  
Downstream Development

Spanwise oscillation applied on the wall under a spatially developing turbulent boundary layer flow is investigated using direct numerical simulation. The temporal wall forcing produces a considerable drag reduction over the region where oscillation occurs. Downstream development of drag reduction is investigated from Reynolds number dependency perspective. An alternative to the previously suggested power-law relation between Reynolds number and peak drag reduction values, which is valid for channel flow as well, is proposed. Considerable deviation in the variation of drag reduction with Reynolds number between different previous investigations of channel flow is found. The shift in velocity profile, which has been used in the past for explaining the diminishing drag reduction at higher Reynolds number for riblets, is investigated. A new predictive formula is derived, replacing the ones found in the literature. Furthermore, unlike for the case of riblets, the shift is varying downstream in the case of wall oscillations, which is a manifestation of the fact that the boundary layer has not reached a new equilibrium over the limited downstream distance in the simulations. Taking this into account, the predictive model agrees well with DNS data. On the other hand, the growth of the boundary layer does not influence the drag reduction prediction.

Effect of Reynolds number on drag reduction in turbulent boundary layer flow over liquid–gas interface

2020 ◽  
Vol 32 (12) ◽  
pp. 122111
Author(s):  
Hongyuan Li ◽  
SongSong Ji ◽  
Xiangkui Tan ◽  
Zexiang Li ◽  
Yaolei Xiang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Boundary Layer Flow ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

Flow-induced degradation of drag-reducing polymer solutions within a high-Reynolds-number turbulent boundary layer

2011 ◽  
Vol 670 ◽  
pp. 337-364 ◽  
Author(s):  
BRIAN R. ELBING ◽  
MICHAEL J. SOLOMON ◽  
MARC PERLIN ◽  
DAVID R. DOWLING ◽  
STEVEN L. CECCIO
Keyword(s):  
Boundary Layer ◽  
Molecular Weight ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
High Reynolds Number ◽  
Polymer Degradation ◽  
Rheological Analysis ◽  
Downstream Distance ◽  
High Reynolds

Polymer drag reduction, diffusion and degradation in a high-Reynolds-number turbulent boundary layer (TBL) flow were investigated. The TBL developed on a flat plate at free-stream speeds up to 20ms−1. Measurements were acquired up to 10.7m downstream of the leading edge, yielding downstream-distance-based Reynolds numbers up to 220 million. The test model surface was hydraulically smooth or fully rough. Flow diagnostics included local skin friction, near-wall polymer concentration, boundary layer sampling and rheological analysis of polymer solution samples. Skin-friction data revealed that the presence of surface roughness can produce a local increase in drag reduction near the injection location (compared with the flow over a smooth surface) because of enhanced mixing. However, the roughness ultimately led to a significant decrease in drag reduction with increasing speed and downstream distance. At the highest speed tested (20ms−1) no drag reduction was discernible at the first measurement location (0.56m downstream of injection), even at the highest polymer injection flux (10 times the flux of fluid in the near-wall region). Increased polymer degradation rates and polymer mixing were shown to be the contributing factors to the loss of drag reduction. Rheological analysis of liquid drawn from the TBL revealed that flow-induced polymer degradation by chain scission was often substantial. The inferred polymer molecular weight was successfully scaled with the local wall shear rate and residence time in the TBL. This scaling revealed an exponential decay that asymptotes to a finite (steady-state) molecular weight. The importance of the residence time to the scaling indicates that while individual polymer chains are stretched and ruptured on a relatively short time scale (~10−3s), because of the low percentage of individual chains stretched at any instant in time, a relatively long time period (~0.1s) is required to observe changes in the mean molecular weight. This scaling also indicates that most previous TBL studies would have observed minimal influence from degradation due to insufficient residence times.

Vorticity Modification in a Turbulent Channel Flow by Microbubble Injection

2004 ◽  
Author(s):  
Claudia del C. Gutierrez-Torres ◽  
Jose A. Jimenez-Bernal ◽  
Elvis E. Dominguez-Ontiveros ◽  
Yassin A. Hassan
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Turbulent Channel Flow

Investigation of the drag reduction phenomenon has been carried out for several years. Several techniques to reduce the drag have been applied and researched for a number of years. Microbubbles injection within a turbulent boundary layer is one method utilized to achieve reduction of drag. In this work, the effects of the presence of microbubbles in the boundary layer of a turbulent channel flow are discussed.

Bubble friction drag reduction in a high-Reynolds-number flat-plate turbulent boundary layer

2006 ◽  
Vol 552 (-1) ◽  
pp. 353 ◽  
Author(s):  
WENDY C. SANDERS ◽  
ERIC S. WINKEL ◽  
DAVID R. DOWLING ◽  
MARC PERLIN ◽  
STEVEN L. CECCIO
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Flat Plate ◽  
High Reynolds Number ◽  
Friction Drag ◽  
High Reynolds ◽  
Friction Drag Reduction

Characterization of Visually Detected Coherent Motions in the Turbulent Boundary Layer

2001 ◽  
Author(s):  
Christopher Robin Hirschi
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Flow Characteristics ◽  
Viscous Sublayer ◽  
Vertical Transport ◽  
Momentum Transport ◽  
Coherent Motion ◽  
The Past

Abstract Research over the past 40 years indicates that coherent motions within the turbulent boundary layer account for disproportionate contributions to momentum transport (Robinson, 1991). To better understand these motions, low-Reynolds number turbulent boundary layer experiments were conducted to investigate the instantaneous velocity and vorticity fields associated with near-wall coherent motion interactions. The present study identifies and explores the most prevalent flow characteristics associated with the vertical transport of injected passive marker from the viscous sublayer.

Hydroacoustics of Transitional Boundary-Layer Flow

1991 ◽  
Vol 44 (12) ◽  
pp. 517-531 ◽  
Author(s):  
Gerald C. Lauchle
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Pressure Fluctuations ◽  
Local Pressure ◽  
Turbulent Spots ◽  
Layer Flow

Transitional boundary layers exist on surfaces and bodies operating in viscous fluids at speeds such that the critical Reynolds number based on the distance from the leading edge is exceeded. The transition region is composed of a simultaneous mixture of both laminar and turbulent regimes occurring randomly in space and time. The turbulent regimes are known as turbulent spots, they grow rapidly with downstream distance, and they ultimately coalesce to form the beginning of fully-developed turbulent boundary-layer flow. It has been long suspected that such a region of unsteadiness may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. This article reviews the available literature on this subject. The emphasis of this literature is on natural and artificially created transitional boundary layers under mostly incompressible conditions; hence, the word hydroacoustics in the title. The topics covered include the dynamics and local wall pressure fluctuations due to the passage of turbulent spots created in a deterministic way, the pressure fluctuations under transitioning boundary layers where the formation and location of spots are random, and the acoustic radiation from transition and its pre-cursor, the Tollmien-Schlichting waves. The majority of this review is for zero-pressure gradient flat plate flows, but the limited literature on axisymmetric body and plate flows with pressure gradient is included.

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