Possibility of drag reduction using d-type roughness

Choi, Kwing-So; Fujisawa, Nobuyuki

doi:10.1007/978-94-011-1701-2_8

Cited by 12 publications

(4 citation statements)

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“…Most have focused on the enhanced form drag induced by pressure forces acting upon roughness elements of various types. [5][6][7] A somewhat different approach was taken by Mulhearn,8 who examined the influence of a step increase in roughness height ͑from slightly to fully rough conditions, for two-dimensional transverse rectangular-grove k-type elements͒ upon the surface pressure intensity and spectra. By comparing these results with those from the smooth-wall case, it was inferred that the interaction between the inner and outer layers is qualitatively different for the rough-wall flow, in that only for the rough-wall case is the surface-pressure signature affected by the details of the outer region.…”

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confidence: 99%

Effect of roughness on pressure fluctuations in a turbulent channel flow

2007

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Direct numerical simulation is used to investigate the nature of pressure fluctuations induced by surface roughness in a turbulent channel flow at Re = 400 for three-dimensional periodic roughness elements, whose peaks overlap approximately 25% of the logarithmic layer. The three-dimensional roughness elements alter the pressure statistics significantly, compared to the corresponding smooth-wall flow, in both the inner and outer ͑core͒ regions of the channel. The direct consequence of roughness is an increased form drag, associated with more intense pressure fluctuations. However, it also alters the pressure fluctuations in the outer layer of the flow, and modifies the length scales defined by two-point correlations. We also find that the depth of the roughness sublayer defined by the pressure fluctuations is very different from that given by the large-and small-scale statistics from the velocity field. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2482883͔ This paper focuses on the influence of surface roughness on pressure fluctuations for a better understanding of inner/ outer layer interactions in wall-bounded turbulence. We consider incompressible turbulent flow in a plane channel, the lower wall of which is covered by a regular array of threedimensional "egg-carton"-shaped elements. 1 The elements extend well above the viscous sublayer of the equivalent smooth-wall flow, with their peak-to-valley height h given by h + = hu s / = 21.6 ͑based on the friction velocity from the smooth-wall side of the channel, u s ͒, corresponding to h = 0.054␦ ͑␦ is the half-height of the channel͒. The roughness is prescribed via a virtual no-slip surface whose mean height is at y = −0.96␦, using an immersed boundary technique. For the Reynolds number used here, Re = 400, the halfwidth-toroughness ratio is ␦ / h Ϸ 18.5. Assuming the top of the logarithmic layer reaches to about 0.2␦, this implies that the peaks of the roughness elements extend approximately onequarter of the way into the logarithmic region. As a consequence, the roughness can be expected to directly affect the bottom of the logarithmic layer but not completely destroy it. This case is relevant in a number of engineering and especially meteorological contexts.Much remains to be learned about rough-wall boundary layers. In light of existing experimental results, it now appears that rough-wall boundary layers can be categorized according to whether the surface roughness does not affect the outer layer 2,3 or if it does affect the outer layer.

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confidence: 99%

Effect of roughness on pressure fluctuations in a turbulent channel flow

2007

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“…These were initially linked to the length scale involved [23]. However, the conceptualization and distinctive characteristics of these two types of roughness have been significantly discussed and expanded [21,22,[24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Effect of Surface Roughness on Aerodynamic Loads of Bluff Body in Vicinity of Smoothed Moving Wall

Oliveira,

Alcântara Pereira

2024

Applied Sciences

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This paper contributes to a new Lagrangian vortex method for the statistical control of turbulence in two-dimensional flow configurations around a rough circular cylinder in ground effect when considering higher subcritical Reynolds numbers, namely 3 × 104 ≤ Re ≤ 2 × 105. A smoothed moving wall (active control technique) is used to include the blockage effect in association with the variation in cylinder surface roughness (passive control technique), characterizing a hybrid approach. In contrast with the previous approaches of our research group, the rough cylinder surface is here geometrically constructed, and a new momentum source term is introduced and calculated for the investigated problem. The methodology is structured by coupling the random Discrete Vortex Method, the Lagrangian Dynamic Roughness Model, and the Large Eddy Simulation with turbulence closure using the truncated Second-Order Velocity Structure Function model. This methodological option has the advantage of dispensing with the use of both a refined near-wall mesh and wall functions. The disadvantage of costly processing is readily solved with Open Multi-Processing. The results reveal that intermediate and high roughness values are most efficient for Reynolds numbers on the orders of 105 and 104, respectively. In employing a moving wall, the transition from the large-gap to the intermediate-gap regime is satisfactorily characterized. For the conditions studied with the hybrid technique, it was concluded that the effect of roughness is preponderant and acts to anticipate the characteristics of a lower gap-to-diameter ratio regime, especially with regard to intermittency.

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“…All the previous studies were done experimentally and it has been suggested that transverse square grooves, optimally sized and located, could result in a reduction in skin-friction drag. Choi and Fujisawa (1993) studied the effect of a transverse square with w/d 0 = 0.4 and reported a reduction in skin-friction drag of about 1% while ignoring the pressure drags on the groove walls. _______________ This paper was presented at the 5 th National Conference on Applicable Mathematics in Wave Mechanics and Vibrations (WMVC-2010) held at Kakatiya University, Warangal, India,13-15 March,2010.…”

Section: Introductionmentioning

confidence: 99%

Computational analysis of frictional drag over transverse grooved flat plates

Ranjan¹,

Ranjan²,

Singh³

2011

Int. J. Eng. Sci. Tech

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Skin-friction coefficient of turbulent boundary layer flow over a smooth-wall with transverse square grooves is investigated for four grooved-wall cases. The four grooved-wall configurations is like'd' type rough wall, which is characterized by regularly spaced two-dimensional square cavities (grooves) placed normal to the flow. This is made up of 5 mm square grooved-wall, where square grooves are spaced 10, 20 and 40 element widths apart in the streamwise direction. A commercial CFD code-'Fluent 6.3' is used for the mean velocity and turbulence intensity calculation. Hexahedral meshing is used to mesh the domain, with the first grid point placed at a height of 0.001 mm till the dimensionless wall distance, y+ = 10 and afterwards the grid spacing was increased by aspect ratio of 1.1 to get a structured mesh. A steady state renormalized group (RNG) k-ε model is used for turbulence modeling with non-equilibrium wall functions for near wall treatment. CFD code is validated against the experimental data reported by Stuardi and Ching. The skin-friction coefficient determined from the velocity profile increases sharply just downstream of the groove. This overshoot is followed by an undershoot and then relaxation back to the smooth-wall value. This behavior is observed in most grooved-wall cases. Integrating the skin-friction coefficient in the streamwise direction indicates that there is an increase in the overall drag with maximum to be 3.54% for the single groove case.

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Possibility of drag reduction using d-type roughness

Cited by 12 publications

References 10 publications

Effect of roughness on pressure fluctuations in a turbulent channel flow

Effect of roughness on pressure fluctuations in a turbulent channel flow

Effect of Surface Roughness on Aerodynamic Loads of Bluff Body in Vicinity of Smoothed Moving Wall

Computational analysis of frictional drag over transverse grooved flat plates

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