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%.

The Effect of a Spanwise Body Force on Skin-Friction Reduction and its Connections to Low-Drag States in Turbulent Flow

2018 ◽  
Author(s):  
Thomas A. Hafner ◽  
Jae Sung Park
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Skin Friction ◽  
Body Force ◽  
Friction Reduction ◽  
Friction Drag ◽  
Turbulent Channel Flows ◽  
Wall Shear ◽  
Skin Friction Reduction

Reducing turbulent skin-friction drag is a subject of great interest due to the potential benefits. These benefits are reflected in applications such as aircraft and vehicles for which skin-friction drag constitutes a significant fraction of the total drag. For example, commercial airliners have up to 50% of their fuel consumption associated with turbulent drag. Thus, any drag reduction would result in substantial savings with regards to the operational cost of the airline industry. In this study, we investigated the effects of a spanwise body force on reducing skin-friction drag in turbulent channel flows. To this end, we performed direct numerical simulations (DNS) of turbulent channel flows with an applied spanwise body force. The body force consists of four control parameters: the amplitude of excitation, penetration depth, period of oscillation, and wavelength. A series of DNS were performed to investigate the effect of these parameters on drag reduction. We observed different levels of drag reduction and the magnitude of skin-friction varied considerably. The DNS results showed that the skin friction is reduced by as much as 20% with values for penetration lengths from 0.03 to 0.09 and periods between 10 and 20. An optimal combination of the four adjustable control parameters is yet to be concluded. In addition to skin-friction reduction, we found an intriguing observation from a time series of wall shear stress. When the wall shear stress is sufficiently lower than its mean value (i.e., low-drag intervals), the spanwise body force appears to significantly affect turbulent dynamics to make the wall shear stress not as chaotic as in other intervals. Specifically, the standard deviations of the peak-to-peak magnitudes of the wall shear stress during low-drag intervals are significantly lower than that of other intervals. This observation could be crucial in that it may lead to a further fundamental understanding of the drag reduction process. Moreover, it may aid in the development of more effective control schemes by way of anticipating that low-drag intervals are promising targets for drag reduction.

Proposal of control laws for turbulent skin friction reduction based on resolvent analysis

2019 ◽  
Vol 866 ◽  
pp. 810-840 ◽  
Author(s):  
Aika Kawagoe ◽  
Satoshi Nakashima ◽  
Mitul Luhar ◽  
Koji Fukagata
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Skin Friction ◽  
Friction Reduction ◽  
Suboptimal Control ◽  
Spectral Space ◽  
Control Laws ◽  
Wall Shear ◽  
Skin Friction Reduction

This paper evaluates and modifies the so-called suboptimal control technique for turbulent skin friction reduction through a combination of low-order modelling and direct numerical simulation (DNS). In a previous study, Nakashima et al. (J. Fluid Mech., vol. 828, 2017, pp. 496–526) employed resolvent analysis to show that the efficacy of suboptimal control was mixed across spectral space when the streamwise wall shear stress (case ST) was used as a sensor signal, i.e. specific regions of spectral space showed drag increment. This observation suggests that drag reduction may be attained if control is applied selectively in spectral space. DNS results presented in the present study, however, do not show a significant effect on the flow with selective control. A posteriori analyses attribute this lack of efficacy to a much lower actuation amplitude in the simulations compared to model assumptions. Building on these observations, resolvent analysis is used to design and provide a preliminary assessment of modified control laws that also rely on sensing the streamwise wall shear stress. Control performance is then assessed by means of DNS. The proposed control laws generate as much as $10\,\%$ drag reduction, and these results are broadly consistent with resolvent-based predictions. The physical mechanisms leading to drag reduction are assessed via conditional sampling. It is shown that the new control laws effectively suppress the near-wall quasi-streamwise vortices. A physically intuitive explanation is proposed based on a separate evaluation of clockwise and anticlockwise vortices.

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

Large-scale contribution to mean wall shear stress in high-Reynolds-number flat-plate boundary layers up to 13650

2014 ◽  
Vol 743 ◽  
pp. 202-248 ◽  
Author(s):  
Sébastien Deck ◽  
Nicolas Renard ◽  
Romain Laraufie ◽  
Pierre-Élie Weiss
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flat Plate ◽  
Skin Friction ◽  
High Reynolds Number ◽  
Large Scale ◽  
Wall Shear ◽  
High Reynolds

AbstractA numerical investigation of the mean wall shear stress properties on a spatially developing turbulent boundary layer over a smooth flat plate was carried out by means of a zonal detached eddy simulation (ZDES) technique for the Reynolds number range $3060\leq Re_{\theta }\leq 13\, 650$. Some asymptotic trends of global parameters are suggested. Consistently with previous findings, the calculation confirms the occurrence of very large-scale motions approximately $5\delta $ to $6 \delta $ long which are meandering with a lateral amplitude of $0.3 \delta $ and which maintain a footprint in the near-wall region. It is shown that these large scales carry a significant amount of Reynolds shear stress and their influence on the skin friction, denoted $C_{f,2}$, is revisited through the FIK identity by Fukagata, Iwamoto & Kasagi (Phys. Fluids, vol. 14, 2002, p. L73). It is argued that $C_{f,2}$ is the relevant parameter to characterize the high-Reynolds-number turbulent skin friction since the term describing the spatial heterogeneity of the boundary layer also characterizes the total shear stress variations across the boundary layer. The behaviour of the latter term seems to follow some remarkable self-similarity trends towards high Reynolds numbers. A spectral analysis of the weighted Reynolds stress with respect to the distance to the wall and to the wavelength is provided for the first time to our knowledge and allows us to analyse the influence of the largest scales on the skin friction. It is shown that structures with a streamwise wavelength $\lambda _x >\delta $ contribute to more than $60\, \%$ of $C_{f,2}$, and that those larger than $\lambda _x >2\delta $ still represent approximately $45\, \%$ of $C_{f,2}$.

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.

Skin Friction Coefficient and Boundary Layer Trend on UKM Aster i-Bond

2014 ◽  
Vol 629 ◽  
pp. 450-455
Author(s):  
Zambri Harun ◽  
Muhammad Syafiq ◽  
Mohd Rasidi Rasani ◽  
Shahrum Abdullah ◽  
Rozli Zulkifli ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Skin Friction ◽  
Aerodynamic Drag ◽  
Skin Friction Coefficient ◽  
Front Part ◽  
Rear Part ◽  
Wall Shear ◽  
Cfd Method

This study concerns with aerodynamic drag on a passenger car. By using computational fluid dynamics (CFD) method, we found that values of skin friction coefficients for three different parts of the car: front, top and rear parts, are different. This study addresses three different basic possible flows around a car: favourable, zero and adverse pressure gradients. Generally, cars use approximately 20% of their engine power to overcome aerodynamic drag, which is generally proportional to the frontal area. The boundary layer at each position has been analyzed to ascertain the effect of wall shear stress on the car surface. It is found that the value of wall shear stress velocity is highest at the rear part, followed by front and top parts. Subsequently, it is shown that the front part has the thinnest viscous region despite not being the part with the highest local ambient velocity compared with the top and rear parts. Despite its supposed aerodynamic shape, the rear part of the car sees separation of flow and the total drag per unit area here is the largest, twice as large as front part and more than seven times larger than the top part.

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
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