scholarly journals Energy efficiency and performance limitations of linear adaptive control for transition delay

2016 ◽  
Vol 810 ◽  
pp. 60-81 ◽  
Author(s):  
Nicolò Fabbiane ◽  
Shervin Bagheri ◽  
Dan S. Henningson
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Skin Friction ◽  
Linear Control ◽  
Transition To Turbulence ◽  
Control Technique ◽  
Net Energy ◽  
Nonlinear Behaviour ◽  
Friction Drag ◽  
Budget Analysis

A reactive control technique with localised actuators and sensors is used to delay the transition to turbulence in a flat-plate boundary-layer flow. Through extensive direct numerical simulations, it is shown that an adaptive technique, which computes the control law on-line, is able to significantly reduce skin-friction drag in the presence of random three-dimensional perturbation fields with linear and weakly nonlinear behaviour. An energy budget analysis is performed in order to assess the net energy saving capabilities of the linear control approach. When considering a model of the dielectric-barrier-discharge (DBD) plasma actuator, the energy spent to create appropriate actuation force inside the boundary layer is of the same order as the energy gained from reducing skin-friction drag. With a model of an ideal actuator a net energy gain of three orders of magnitude can be achieved by efficiently damping small-amplitude disturbances upstream. The energy analysis in this study thus provides an upper limit for what we can expect in terms of drag-reduction efficiency for linear control of transition as a means for drag reduction.

Direct numerical simulation of spatially developing turbulent boundary layers with uniform blowing or suction

2011 ◽  
Vol 681 ◽  
pp. 154-172 ◽  
Author(s):  
YUKINORI KAMETANI ◽  
KOJI FUKAGATA
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Drag Reduction ◽  
Skin Friction ◽  
Reduction Factor ◽  
Stream Velocity ◽  
Normal Velocity ◽  
Friction Drag ◽  
Local Skin

Direct numerical simulation (DNS) of spatially developing turbulent boundary layer with uniform blowing (UB) or uniform suction (US) is performed aiming at skin friction drag reduction. The Reynolds number based on the free stream velocity and the 99% boundary layer thickness at the inlet is set to be 3000. A constant wall-normal velocity is applied on the wall in the range, −0.01U∞ ≤ Vctr ≤ 0.01U∞. The DNS results show that UB reduces the skin friction drag, while US increases it. The turbulent fluctuations exhibit the opposite trend: UB enhances the turbulence, while US suppresses it. Dynamical decomposition of the local skin friction coefficient cf using the identity equation (FIK identity) (Fukagata, Iwamoto & Kasagi, Phys. Fluids, vol. 14, 2002, pp. L73–L76) reveals that the mean convection term in UB case works as a strong drag reduction factor, while that in US case works as a strong drag augmentation factor: in both cases, the contribution of mean convection on the friction drag overwhelms the turbulent contribution. It is also found that the control efficiency of UB is much higher than that of the advanced active control methods proposed for channel flows.

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.

Skin Friction Drag Reduction in Turbulent Boundary Layer Conditions over Riblet Surfaces

2019 ◽  
Author(s):  
Hidetoshi Iijima ◽  
Hidemi Takahashi ◽  
Seigo Koga ◽  
Monami Sasamori ◽  
Yoshimi Iijima ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Skin Friction ◽  
Friction Drag ◽  
Friction Drag Reduction

Freeman Scholar Review: Passive and Active Skin-Friction Drag Reduction in Turbulent Boundary Layers

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Marc Perlin ◽  
David R. Dowling ◽  
Steven L. Ceccio
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Skin Friction ◽  
Practical Implementation ◽  
Friction Drag ◽  
Polymer Injection ◽  
Morphological Alterations ◽  
Air Layers ◽  
Layer Flow ◽  
Friction Drag Reduction

A variety of skin-friction drag reduction (FDR) methods for turbulent boundary layer (TBL) flows are reviewed. Both passive and active methods of drag reduction are discussed, along with a review of the fundamental processes responsible for friction drag and FDR. Particular emphasis is given to methods that are applicable to external hydrodynamic flows where additives are diluted by boundary layer entrainment. The methods reviewed include those based on engineered surfaces (riblets, large eddy breakup devices (LEBUs), and superhydrophobic surfaces (SHS)), those based on additives (polymer injection and gas injection), and those based on morphological alterations in the boundary layer flow (air layers and partial cavity formation). A common theme for all methods is their disruption of one or more of the underlying physical processes responsible for the production of skin-friction drag in a TBL. Opportunities and challenges for practical implementation of FDR techniques are also discussed.

Experimental study of skin friction drag reduction of turbulent boundary layer over shallow dimples

2022 ◽  
Author(s):  
Md Abdur Razzak ◽  
Yong Dong Cui ◽  
Jonathan Tay ◽  
Zhen Wei Teo ◽  
Thirukumaran Nadesan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Skin Friction ◽  
Friction Drag ◽  
Friction Drag Reduction

scholarly journals Research on Skin-Friction Drag Reduction by Hydrogen Injection in Supersonic Boundary Layer

2019 ◽  
Vol 37 (3) ◽  
pp. 449-456
Author(s):  
Shuai Wang ◽  
Guoqiang He ◽  
Fei Qin
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Skin Friction ◽  
Friction Reduction ◽  
Confined Space ◽  
Friction Drag ◽  
Wall Shear ◽  
Friction Drag Reduction

In order to investigate the applicability of the skin-friction reduction technique using hydrogen injecting into turbulent boundary layer, three-dimensional numerical simulation was carried out for a constant-cross-confined-space with rearward facing steps. The flow characteristics near wall surface and development of wall shear stress were analyzed and compared under different coming flow and injection conditions. The simulation results show that the hydrogen injection can achieve around 13.5% skin-friction drag reduction under the coming flow Mach number of 2.3Ma or 2.8Ma. At 2.8Ma, the optimal reduction profit is 13.5% which is obtained when the equivalent ratio is 0.06. The gases mixings are gradually enhanced along the flow path. At the positions of shock wave-boundary-layer interactions, the mixings are first strengthened and then suppressed, and meanwhile, the wall shear stress and density changes with similar law that first decreases and then rebounds at the positions. The declines of skin-friction drag decrease along the flow direction, the best reduction area can profit nearly 60%.

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