Direct numerical simulations of turbulent channel flow with transverse square bars on one wall

Leonardi, Stefano; Orlandi, P.; Smalley, Robert; Djenidi, L.; Antonia, R. A.

doi:10.1017/s0022112003005500

Cited by 332 publications

(344 citation statements)

References 10 publications

Supporting

Mentioning

279

Contrasting

Unclassified

Order By: Relevance

“…It is shown in figures 8(a) & (b) that the behaviour of the roughness length as a function of frontal and plan solidity is drastically different. Figure 8(a) shows that the roughness length (which is related to the total drag) increases in the sparse regime, and indicates a marginal decrease after the peak for increased values of frontal solidity, as in Leonardi et al (2003) and Leonardi & Castro (2010). Within the range of solidity explored herewith, the bulk drag seems to reach a peak at λ F = 0.21 for a fixed λ P = 0.27.…”

Section: Effect Of Surface Morphology On Aerodynamic Parametersmentioning

confidence: 78%

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

View full text Add to dashboard Cite

Citation: Placidi, M. & Ganapathisubramani, B. (2015). Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers. Journal of Fluid Mechanics, 782, pp. 541-566. doi: 10.1017Mechanics, 782, pp. 541-566. doi: 10. /jfm.2015 This is the accepted version of the paper.This version of the publication may differ from the final published version. Experiments were conducted in the fully-rough regime on surfaces with large relative roughness height (h/δ ≈ 0.1, where h is the roughness height and δ is the boundary layer thickness). The surfaces were generated by distributed LEGO TM bricks of uniform height, arranged in different configurations. Measurements were made with both floating-element drag-balance and high-resolution particle image velocimetry on six configurations with different frontal solidity, λ F , at fixed plan solidity, λ P , and vice versa, for a total of twelve rough-wall cases. Results indicate that the drag reaches a peak value λ F ≈ 0.21 or a constant λ P = 0.27, whilst it monotonically decreases for increasing values of λ P for a fixed λ F = 0.15. This is in contrast with previous studies in the literature based on cube roughness that show a peak in drag for both λ F and λ P variations. The influence of surface morphology on the depth of the roughness sublayer (RSL) is also investigated. Its depth is found to be inversely proportional to the roughness length, y 0 . A decrease in y 0 is usually accompanied by a thickening of the the RSL and vice-versa. Proper orthogonal decomposition analysis was also employed. The shapes of the most energetic modes calculated using the data across the entire boundary layer are found to be selfsimilar across the twelve rough-walls cases, however, when the analysis is restricted to the roughness sublayer, differences that depend on the wall morphology are apparent. Moreover, the energy content of the POD modes within the RSL suggest that the effect of increased frontal solidity is to redistribute the energy towards the larger-scales (i.e. larger portion of energy is within the first few modes) whilst the opposite is found for variation of plan solidity. Permanent

show abstract

Section: Effect Of Surface Morphology On Aerodynamic Parametersmentioning

confidence: 78%

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…This position is located at x/D h = 28, where x is the distance of the seventh rib from the inlet, and D h is the hydraulic diameter of the channel. According to Leonardi et al [3], the roughness elements are virtually isolated as the cavity width to roughness height ratio is greater than 7 (or the pitch ratio is greater than 8). Throughout this paper, reference quantities for length and velocity are e and U 0 , respectively.…”

Section: Methodsmentioning

confidence: 99%

“…Even though numerous studies have been carried out to study the thermal and flow characteristics in ribbed channels, the understanding of this phenomenon is not complete. In direct numerical simulations (DNS) of turbulent channel flow with square ribs on one wall, Leonardi et al [3] showed that main flow features, such as the size and strength of the recirculation zones, do not change significantly and reoccur along the channel as the cavity width to roughness height ratio is greater than 7. Using liquid crystals, Rau et al [4] found a second maximum of heat transfer rate as the rib pitch ratio is greater than 10.…”

Section: Introductionmentioning

confidence: 99%

Turbulent flow in a ribbed channel: Flow structures in the vicinity of a rib

Wang

Salewski

Sundén

2010

Experimental Thermal and Fluid Science

View full text Add to dashboard Cite

PIV measurements are performed in a channel with periodic ribs on one wall. The emphasis of this study is to investigate the flow structures in the vicinity of a rib in terms of mean velocities, Reynolds stresses, probability density functions (PDF), and two-point correlations. The PDF distribution of u is bimodal in the separated shear layer downstream of the rib. The maximum Reynolds shear stresses occur at the leading edge of the rib. Based on quadrant analysis, it is found that ejection motions make a dominant contribution to the Reynolds shear stress in this region. Moreover, topology-based visualization is applied to the separation bubble upstream of the rib. Salient critical points and limit cycles are extracted, which gives clues to the physical processes occurring in the flow.

show abstract

“…Probability of negative u versus wall-normal coordinate z for different Reynolds numbers: (a) graphite case and (b) grit-blasted case. (Maass & Schumann 1994;Cherukat et al 1998;Leonardi et al 2003;Napoli et al 2008). For the current surfaces, the situation is more complex, since the surfaces also show variations in the transverse direction, which allows the near-wall flow to circumnavigate some of the roughness features.…”

Section: Reverse Flowmentioning

confidence: 99%

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

2016

View full text Add to dashboard Cite

The Reynolds-number dependence of turbulent channel flow over two irregular rough surfaces, based on scans of a graphite and a grit-blasted surface, is studied by direct numerical simulation. The aim is to characterise the changes in the flow in the immediate vicinity of and within the rough surfaces, an area of the flow where it is difficult to obtain experimental measurements. The average roughness heights and spatial correlation of the roughness features of the two surfaces are similar, but the two surfaces have a significant difference in the skewness of their height distributions, with the graphite sample being positively skewed (peak-dominated) and the grit-blasted surface being negatively skewed (valley-dominated). For both cases, numerical simulations were conducted at seven different Reynolds numbers, ranging from Re τ = 90 to Re τ = 720. The positively skewed surface gives rise to higher friction factors than the negatively skewed surface in all cases. For the highest Reynolds numbers, the flow has values of the roughness function U + well in excess of 7 for both surfaces and the bulk flow profile has attained a constant shape across the full height of the channel except for the immediate vicinity of the roughness, which would indicate fully rough flow. However, the mean flow profile within and directly above the rough surface still shows considerable Reynolds-number dependence and the ratio of form to viscous drag continues to increase, which indicates that at least for some types of rough surfaces the flow retains aspects of the transitionally rough regime to values of U + or k + well in excess of the values conventionally assumed for the transitionally to fully rough threshold. This is also reflected in the changes that the near-wall flow undergoes as the Reynolds number increases: the viscous sublayer, within which the surface roughness is initially buried, breaks down and regions of reverse flow intensify. At the highest Reynolds numbers, a layer of near-wall flow is observed to follow the contours of the local surface. The distribution of thickness of this 'blanketing' layer has a mixed scaling, showing that viscous effects are still significant in the near-wall flow.

show abstract

Direct numerical simulations of turbulent channel flow with transverse square bars on one wall

Cited by 332 publications

References 10 publications

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Effects of frontal and plan solidities on aerodynamic parameters and the roughness sublayer in turbulent boundary layers

Turbulent flow in a ribbed channel: Flow structures in the vicinity of a rib

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

Contact Info

Product

Resources

About