Turbulent boundary layers on rough surfaces

Acharya, Mukund; Bornstein, J.; Escudier, M. P.

doi:10.1007/bf00316784

Cited by 88 publications

(32 citation statements)

References 19 publications

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“…It can be seen that our data using both methods are consistent with previous results in the literature. The indirect measurements results (via equation 2.1) compare well with the direct measurements (within 10%) given the uncertainty in determination of the skin-friction velocity (Acharya et al 1986) and the log-law boundaries used to determine the roughness length . The skin friction values obtained via the floating-element dragbalance are used in all our analysis.…”

Section: Effect Of Surface Morphology On Aerodynamic Parametersmentioning

confidence: 55%

“…It is important to highlight that, although is of common practice, fitting velocity profiles to determine the unknowns in equation 1.1, bares great uncertainty. This is due to the difficulties, particularly at the large h/δ, in determining both the skin friction velocity and the log-law boundaries (Acharya et al 1986;Castro 2007;Segalini et al 2013). The reduction of the wall-normal range of the logarithmic layer, due to the increasing importance of the RSL is another important factor to take into account.…”

Section: Determination Of Aerodynamic Parametersmentioning

confidence: 99%

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

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

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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

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Section: Effect Of Surface Morphology On Aerodynamic Parametersmentioning

confidence: 55%

Section: Determination Of Aerodynamic Parametersmentioning

confidence: 99%

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

Placidi

Ganapathisubramani

2015

J. Fluid Mech.

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“…There are very few detailed studies of real roughness and they are briefly summarized here. Acharya et al (1986) studied the influence of four rough surfaces on a turbulent boundary layer. The four surfaces included a stochastically rough surface representative of a newly-finished turbomachinery blading, a variant of this surface with different roughness parameters, a sand-cast surface and a mesh surface.…”

Section: Studies Of Turbulent Flow Over Irregular Roughnessmentioning

confidence: 99%

Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

Christensen¹,

Wu²

2008

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The public reporting burden for this collection of information is estimated to average 1 hour per response. including the time for reviewing instructions, sea"hing existing data soUrces, gathering and maintaining the data needed, and completing and reviewving the collection of infomation. Send comments regaliong this burden estimate or any otiler aspect of tts collection of information. including suggestions for reducing fhe burden, to the Department of Defense, Executive Service Directorate (0704-0188). Respondents should be aware that notwithstanding any other provision of law. no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a curently valid OMB control number. PLEASE DO NOT RETURN YOUR A F R L S R SUPPLEMENTARY NOTES ABSTRACTThe present effort investigates the effects of practical roughness replicated from a turbine blade damaged by deposition of foreign material. statistical and structural characteristics of wall turbulence. Two-dimensional particle image velocimetry (PIV) measurements are performed in the streamwise-wall-normal plane of turbulent boundary layers at momentum Reynolds numbers of 8000 and 13000. The surface conditions include a smooth wall and two highly-irregular rough walls. These rough surfaces have the same roughness topography but differ in spatial scaling. The validity of Townsend's wall similarity hypothesis in the presence of practical roughness is assessed and the impact of this roughness on the spatial structure of the flow is investigated. In addition, stereoscopic PIV measurements are made in streamwise-spanwise planes of smooth-and rough-wall turbulent boundary layers both within and at the outer edge of the roughness sublayer. This data is used to explore the impact of dominant topographical features on the near-wall flow as well as the influence of practical roughness on the spatial organization of the flow.Understanding such effects provides a stepping stone toward efficient modeling and control of practical flows in the presence of roughness. SUBJECT TERMS

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“…Up to now, all the correlations of the sand roughness ks and some geometrical length scale as e.g. parameter Ra have a very limited validity see Acharya, Bornstein and Escudier (1986).…”

Section: Introductionmentioning

confidence: 99%

Numerical modelling of turbulent flow over rough walls

Louda

Příhoda

Kozel

2007

Proc Appl Math and Mech

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The numerical simulation of turbulent flow over rough walls was carried out for various types of roughness. The mathematical model was based on the Reynolds averaged Navier-Stokes equations for incompressible flow. The two-equation SST and oneequation Spalart-Allmaras turbulence models were used. Boundary conditions on rough walls were prescribed directly on the wall using the SST model modified to account for wall roughness by Hellsten and Laine (1997) and the SA model modified by Aupoix and Spalart (2003). Turbulence models were tested for the constant pressure turbulent boundary layer on the rough wall formed by commercial abrasive paper and by tightly packed spheres. The effect of wall roughness on the decelerated flow over a smoothly contoured ramp with flow separation was investigated. Obtained results were compared with experimental data.

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Turbulent boundary layers on rough surfaces

Cited by 88 publications

References 19 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

Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

Numerical modelling of turbulent flow over rough walls

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