Spatial resolution effects on measurements in a rough wall turbulent boundary layer

Ghanadi, Farzin; Djenidi, L.

doi:10.1007/s00348-021-03272-x

Cited by 9 publications

(11 citation statements)

References 31 publications

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“…This observation is qualitatively in agreement with the findings by Shah et al (2008). In contrast, Ghanadi and Djenidi (2021) reported no attenuation of the streamwise variance with increasing wire length. In addition, Ghanadi and Djenidi (2021) observed that the application of the correction scheme of Smits et al (2011) to the ⟨uu⟩ + -profiles obtained from spatially filtered velocity data results in a strong over-correction that also produces an artificial near-wall peak for fully rough flows.…”

Section: Spatial Resolution Effects In Rough Wall Flowssupporting

confidence: 92%

“…While there is a clear understanding of the severity of spatial resolution effects in measurements of canonical smoothwall flows, there has been little account on spatial resolution effects in rough wall flows so far. To the best authors' knowledge, the works by Shah et al (2008) and Ghanadi and Djenidi (2021) are the only ones addressing this aspect and show contrasting evidence, prompting the present study.…”

Section: Spatial Resolution Effects In Rough Wall Flowsmentioning

confidence: 69%

“…In contrast, Ghanadi and Djenidi (2021) reported no attenuation of the streamwise variance with increasing wire length. In addition, Ghanadi and Djenidi (2021) observed that the application of the correction scheme of Smits et al (2011) to the ⟨uu⟩ + -profiles obtained from spatially filtered velocity data results in a strong over-correction that also produces an artificial near-wall peak for fully rough flows. With our data, we confirm that the correction scheme by Smits et al (2011) is not able to reconstruct the unfiltered ⟨uu⟩ + -profile when applied to rough wall-bounded turbulent flows.…”

Section: Spatial Resolution Effects In Rough Wall Flowsmentioning

confidence: 85%

“…An interesting observation by Ghanadi and Djenidi (2021) was that their measurements did not show any effect of attenuation when increasing the wire length. The answer to this conundrum could lie in the type of fully rough flow they have considered, namely "a rough wall consisting of [a] series of transverse bar [s] spanning the entire width of the wind tunnel."…”

Section: Spatial Resolution Effects In Rough Wall Flowsmentioning

confidence: 96%

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Spatial resolution issues in rough wall turbulence

Gatti

Stroh

2022

Exp Fluids

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The question whether spatial resolution effects should be accounted for when performing hot-wire (or particle image velocimetry) measurements in turbulent wall-bounded flows over rough surfaces in the fully rough regime is addressed and answered by exploiting an existing direct numerical simulation database of open-channel flows at $$Re_\tau =500$$ R e τ = 500 over a rough surface consisting of randomly distributed roughness elements. The results show sizeable attenuation effects of the streamwise velocity fluctuation intensity, similar to smooth-wall flows with up to 70% for a wire width of around 100 viscous units. A suitable correction scheme is applied to successfully compensate for the spatial resolution effects. Both results indicate that spatial resolution effects are relevant also in fully rough flows and can be corrected a posteriori when the state-of-the-art criteria on sensor size cannot be achieved in experiments. Graphical Abstract

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Section: Spatial Resolution Effects In Rough Wall Flowssupporting

confidence: 92%

Section: Spatial Resolution Effects In Rough Wall Flowsmentioning

confidence: 69%

Section: Spatial Resolution Effects In Rough Wall Flowsmentioning

confidence: 85%

Section: Spatial Resolution Effects In Rough Wall Flowsmentioning

confidence: 96%

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Spatial resolution issues in rough wall turbulence

Gatti

Stroh

2022

Exp Fluids

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“…A wire diameter (d) of 2.5 μm with an etched length (l HW ) of 0.4-0.6 mm is used to achieve l + HW 54, an l HW /d ratio of around 200, as recommended by Ligrani & Bradshaw (1987) and Hutchins et al (2009). However, we showed previously (Ghanadi & Djenidi 2021b) that for the present rough wall there is no attenuation associated with a spatial resolution for l + HW up to 160. The wire is operated with an in-house constant-temperature circuit at an overheat ratio of 1.8.…”

Section: Experimental Set-up and Proceduresmentioning

confidence: 93%

Study of a rough-wall turbulent boundary layer under pressure gradient

Ghanadi

Djenidi

2022

J. Fluid Mech.

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The behaviour of a fully rough-wall turbulent boundary layer subjected to different pressure gradients is investigated for different Reynolds numbers using hot-wire measurements. Mean velocity and velocity root-mean-square measurements indicate that the boundary layer remains in a self-preserving state regardless of the pressure gradient. However, different pressure gradients lead to different self-preservation states, as suggested by the lack of collapse of the velocity profile between the pressure gradient cases. The results also indicate that the roughness effect is more important than the pressure gradient; particularly, the closer the wall, the more dominant the roughness effect over the pressure gradient effect on the boundary layer. Finally, both spectral and proper orthogonal decomposition analyses applied to the hot-wire measurements indicate that the pressure gradient impacts predominantly the large-scale motion.

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Evaluation of spatial resolution effects in rough wall-bounded turbulence

Xia,

Chung,

Marusic

et al. 2024

Exp Fluids

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This study investigates the impact of insufficient spanwise spatial resolution on the measurement accuracy of streamwise velocity fluctuations over rough walls. We use a direct numerical simulation (DNS) database of turbulent open-channel flow over three-dimensional sinusoidal roughness with varied wavelengths and roughness heights. Employing a triple decomposition, we investigate both the attenuation of the turbulent fluctuations (about the local mean), $$u^\prime$$ u ′ and the dispersive stresses (roughness-induced fluctuations of the time-averaged mean about the global mean), $${\tilde{U}}$$ U ~ . A boxcar filter on DNS data is applied to investigate the effects of spanwise spatial filtering on these quantities. Our analysis reveals the significance of two key length-scale ratios for velocity measurements over rough walls: the wire length relative to the spatially and temporally plane-averaged Kolmogorov scale at the roughness crest ($$l/\langle \eta \rangle _k$$ l / ⟨ η ⟩ k ), and the wire length relative to the roughness spanwise wavelength ($$l/\Lambda _y$$ l / Λ y ). We observe that maintaining $$l/\langle \eta \rangle _k$$ l / ⟨ η ⟩ k constant while increasing $$l/\Lambda _y$$ l / Λ y attenuates the variance of $${\tilde{U}}$$ U ~ and $$u^\prime$$ u ′ within the roughness sublayer. When fixing $$l/\Lambda _y$$ l / Λ y , an increase in $$l/\langle \eta \rangle _k$$ l / ⟨ η ⟩ k influences the turbulent fluctuations across all wall-normal locations. These findings highlight the necessity of considering both length scales when evaluating spanwise spatial resolution in turbulence measurements over rough walls.

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Spatial resolution effects on measurements in a rough wall turbulent boundary layer

Cited by 9 publications

References 31 publications

Spatial resolution issues in rough wall turbulence

Spatial resolution issues in rough wall turbulence

Study of a rough-wall turbulent boundary layer under pressure gradient

Evaluation of spatial resolution effects in rough wall-bounded turbulence

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