scholarly journals Friction drag reduction achievable by near-wall turbulence manipulation in spatially developing boundary-layer

2016 ◽  
Vol 28 (3) ◽  
pp. 035108 ◽  
Author(s):  
Amaury Bannier ◽  
Eric Garnier ◽  
Pierre Sagaut
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Wall Turbulence ◽  
Friction Drag ◽  
Friction Drag Reduction ◽  
Near Wall Turbulence ◽  
Turbulence Manipulation ◽  
Near Wall

High-Reynolds-number turbulent boundary layer friction drag reduction from wall-injected polymer solutions

2009 ◽  
Vol 621 ◽  
pp. 259-288 ◽  
Author(s):  
E. S. WINKEL ◽  
G. F. OWEIS ◽  
S. A. VANAPALLI ◽  
D. R. DOWLING ◽  
M. PERLIN ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Free Stream ◽  
Polymer Concentration ◽  
Friction Drag ◽  
Molecular Weights ◽  
Development Region ◽  
High Reynolds ◽  
Friction Drag Reduction ◽  
Near Wall

A set of controlled high-Reynolds-number experiments has been conducted at the William B. Morgan Large Cavitation Channel (LCC) in Memphis, Tennessee to investigate the friction drag reduction achieved by injecting aqueous poly(ethylene oxide) (PEO) solutions at three different mean molecular weights into the near-zero-pressure-gradient turbulent boundary layer that forms on a smooth flat test surface having a length of nearly 11m. The test model spanned the 3.05m width of the LCC test section and had an overall length of 12.9m. Skin-friction drag was measured with six floating-plate force balances at downstream-distance-based Reynolds numbers as high as 220 million and free stream speeds up to 20ms−1. For a given polymer type, the level of drag reduction was measured for a range of free stream speeds, polymer injection rates and concentrations of the injected solution. Polymer concentration fields in the near-wall region (0 < y+ < ~103) were examined at three locations downstream of the injector using near-wall planar laser-induced-fluorescence imaging. The development and extent of drag reduction and polymer mixing are compared to previously reported results using the traditional K-factor scaling. Unlike smaller scale and lower speed experiments, speed dependence is observed in the K-scaled results for the higher molecular weight polymers and it is postulated that this dependence is caused by molecular aggregation and/or flow-induced polymer degradation (chain scission). The evolution of near-wall polymer concentration is divided into three regimes: (i) the development region near the injector where drag reduction increases with downstream distance and the polymer is highly inhomogeneous forming filaments near the wall, (ii) the transitional mixing region where drag reduction starts to decrease as the polymer mixes across the boundary layer and where filaments are less pronounced and (iii) the final region where the polymer mixing and dilution is set by the rate of boundary layer growth. Unlike pipe-flow friction-drag reduction, the asymptotic maximum drag reduction (MDR) either was not reached or did not persist in these experiments. Instead, the nearest approach to MDR was transitory and occurred between the development and transitional regions. The length of the development region was observed to increase monotonically with increasing polymer molecular weight, injection rate, concentration and decreasing free stream speed. And finally, the near-wall polymer concentration is correlated to the measured drag reduction for the three polymer molecular weights in the form of a proposed empirical drag-reduction curve.

scholarly journals Global effect of local skin friction drag reduction in spatially developing turbulent boundary layer

2016 ◽  
Vol 805 ◽  
pp. 303-321 ◽  
Author(s):  
A. Stroh ◽  
Y. Hasegawa ◽  
P. Schlatter ◽  
B. Frohnapfel
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Control Region ◽  
Reduction Rate ◽  
Wall Turbulence ◽  
Local Skin ◽  
Control Schemes ◽  
Local Skin Friction ◽  
Friction Drag Reduction

A numerical investigation of two locally applied drag-reducing control schemes is carried out in the configuration of a spatially developing turbulent boundary layer (TBL). One control is designed to damp near-wall turbulence and the other induces constant mass flux in the wall-normal direction. Both control schemes yield similar local drag reduction rates within the control region. However, the flow development downstream of the control significantly differs: persistent drag reduction is found for the uniform blowing case, whereas drag increase is found for the turbulence damping case. In order to account for this difference, the formulation of a global drag reduction rate is suggested. It represents the reduction of the streamwise force exerted by the fluid on a plate of finite length. Furthermore, it is shown that the far-downstream development of the TBL after the control region can be described by a single quantity, namely a streamwise shift of the uncontrolled boundary layer, i.e. a changed virtual origin. Based on this result, a simple model is developed that allows the local drag reduction rate to be related to the global one without the need to conduct expensive simulations or measurements far downstream of the control region.

Physics and control of wall turbulence for drag reduction

2011 ◽  
Vol 369 (1940) ◽  
pp. 1396-1411 ◽  
Author(s):  
John Kim
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Skin Friction ◽  
Linear Analysis ◽  
Wall Turbulence ◽  
Boundary Layer Control ◽  
Control Input ◽  
Friction Drag ◽  
Nonlinear Simulations ◽  
Layer Control

Turbulence physics responsible for high skin-friction drag in turbulent boundary layers is first reviewed. A self-sustaining process of near-wall turbulence structures is then discussed from the perspective of controlling this process for the purpose of skin-friction drag reduction. After recognizing that key parts of this self-sustaining process are linear, a linear systems approach to boundary-layer control is discussed. It is shown that singular-value decomposition analysis of the linear system allows us to examine different approaches to boundary-layer control without carrying out the expensive nonlinear simulations. Results from the linear analysis are consistent with those observed in full nonlinear simulations, thus demonstrating the validity of the linear analysis. Finally, fundamental performance limit expected of optimal control input is discussed.

Experimental Study on the Bursting Phenomenon in the Turbulent Boundary Layer on the Compliant Wall

2008 ◽  
Author(s):  
Yui Owaku ◽  
Isao Misu ◽  
Nobuyoshi Fujimatsu
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Solid Wall ◽  
Friction Drag ◽  
Contribution Rate ◽  
Compliant Wall ◽  
Bursting Phenomena ◽  
Four Quadrant ◽  
Friction Drag Reduction ◽  
Ejection Event

This paper describes an experimental study on the friction drag reduction on the compliant wall. In the fluid dynamics, the research on the turbulent friction drag reduction is one of the important subjects. The use of the compliant wall has the possibilities of the friction drag reduction. Many researchers have investigated the effects of the compliant wall since 1960’s. However, the past studies are focused on those effects such as dependency of the material properties and flow conditions. Those effects are intimately related with the turbulent flow fields. In order to clarify the mechanism of the drag reduction, the coherent structures near the wall surface must be investigated. The purpose of the present study is to investigate the vortical semi-periodic motions over the solid and compliant walls in detail. The experiments are conducted at Re = 5.0 × 105 based on unit length and the free stream velocity using the NPL type wind tunnel. The compliant wall is made of silicone resin with Young’s modulus E = 2.83 MPa. The boundary layer flows are measured using the single and X-array hot wire probe. The VITA and four quadrant analyses are applied to investigate the bursting phenomena in the turbulent flow structures. The experimental results show that the skin friction drag over the compliant wall is smaller than that on the solid wall about 15%. Further the bursting frequencies over the compliant wall are greater than those over the solid wall. The four quadrant analysis is also applied to investigate the turbulent coherent motions. These results show that the ejection event over the compliant wall is increased. The contribution rate of the ejection event to the Reynolds stress over the compliant wall is greater than that of the sweep event. The increment of the bursting frequency is consistent with that of the ejection event. The friction drag decreases because the velocity near the wall is decelerated when the contribution rates in second and third quadrants to the Reynolds stress increase. These tendencies are also confirmed over the compliant wall with the various thicknesses. The present results show that the friction drag reduction over the compliant wall is related with the increment of contribution rate of the ejection event in the bursting phenomena.

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