Parametric Study on Ridges Inducing Secondary Motions in Turbulent Channel Flow

Deyn, Lars H. von; Gatti, Davide; Stroh, Alexander

doi:10.1002/pamm.202000139

Cited by 3 publications

(5 citation statements)

References 7 publications

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“…The observed increase in friction drag is slightly larger for triangular ridges, which is in agreement with the assumption that a larger friction increase is found for stronger secondary motions (Türk et al 2014;von Deyn et al 2020;Medjnoun et al 2020). Note that the increase in wetted surface area compared to the smooth wall reference case is larger for the rectangular ridges (11.7% ) than for the triangular ones (6.7% ) and thus does not appear to primarily govern the measured drag increase.…”

Section: Reynolds Number Dependency Of the Friction Coefficientsupporting

confidence: 86%

Ridge-type roughness: from turbulent channel flow to internal combustion engine

et al. 2021

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While existing engineering tools enable us to predict how homogeneous surface roughness alters drag and heat transfer of near-wall turbulent flows to a certain extent, these tools cannot be reliably applied for heterogeneous rough surfaces. Nevertheless, heterogeneous roughness is a key feature of many applications. In the present work we focus on spanwise heterogeneous roughness, which is known to introduce large-scale secondary motions that can strongly alter the near-wall turbulent flow. While these secondary motions are mostly investigated in canonical turbulent shear flows, we show that ridge-type roughness—one of the two widely investigated types of spanwise heterogeneous roughness—also induces secondary motions in the turbulent flow inside a combustion engine. This indicates that large scale secondary motions can also be found in technical flows, which neither represent classical turbulent equilibrium boundary layers nor are in a statistically steady state. In addition, as the first step towards improved drag predictions for heterogeneous rough surfaces, the Reynolds number dependency of the friction factor for ridge-type roughness is presented. Graphic abstract

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Section: Reynolds Number Dependency Of the Friction Coefficientsupporting

confidence: 86%

Ridge-type roughness: from turbulent channel flow to internal combustion engine

et al. 2021

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“…The rectangular shaped smooth ridges induce a drag increase of the order of 1 %-2 % only, almost independent of Re b . Note that this value is significantly lower than the drag increase for ridges reported in previous studies (von Deyn et al 2022b) due the present choice of reference channel height. If evaluated based on δ empty , the relative drag increase of the smooth ridges is of the order of 10 %.…”

Section: Turbulent Drag Of Sandpaper Stripscontrasting

confidence: 60%

“…Figure 18 shows data of the case protruding_rgh_δ in comparison to previous numerical results from our group (von Deyn et al 2022b) which has similar ridge dimensions as case ridge_δ. In this case, the ridge has a width of s = δ empty and a height of h = 0.05δ empty .…”

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confidence: 74%

“…The channel test section is divided into three segments of 76δ, 119δ and 119δ streamwise extent. As in previous investigations with the same facility (Gatti et al 2015(Gatti et al , 2020von Deyn et al 2021von Deyn et al , 2022a, the flow is tripped at the inlet of the first segment.…”

Section: Experimental Facilitymentioning

confidence: 99%

“…It is interesting to note that the secondary flow topology induced by smooth ridges differs from that of protruding rough strips. While we do not have a DNS data set that directly matches the dimensions of the experimentally investigated ridges, data for a similar ridge geometry are available from previous numerical work (von Deyn et al 2022b). These data are presented in the Appendix.…”

Section: Turbulent Secondary Motions Induced By Sandpaper Stripsmentioning

confidence: 99%

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Flow resistance over heterogeneous roughness made of spanwise-alternating sandpaper strips

Frohnapfel,

von Deyn,

Yang

et al. 2024

J. Fluid Mech.

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The Reynolds number dependent flow resistance of heterogeneous rough surfaces is largely unknown at present. The present work provides novel reference data for spanwise-alternating sandpaper strips as one idealised case of a heterogeneous rough surface. Experimental data are presented and analysed in direct comparison with drag measurements of homogeneous sandpaper surfaces and numerical simulations. Based on the homogeneous roughness data, the related challenges and sensitivities for the evaluation of roughness functions from experiments and simulations are discussed. A hydraulic channel height is suggested as an alternative measure for the drag impact of rough surfaces in internal flows. For the investigated heterogeneous roughness, it is found that turbulent flow does not exhibit a fully rough flow behaviour, indicating that the assignment of an equivalent sand grain height as commonly applied for homogeneous roughness is not possible. A prediction of the drag behaviour of rough strips based on an average between rough and smooth drag curves appears promising, but requires further refinement to capture the impact of turbulent secondary flows and spatial transients linking smooth and rough surface parts. While turbulent secondary flow induced by the roughness strips yield significant spanwise variation of the mean velocity profile for the investigated rough strips, we show that the spanwise averaged velocity profiles collapse reasonably well with a smooth or homogeneous rough wall flow. This allows to extract a global roughness function from the spanwise averaged flow field in good agreement with the one deduced from global pressure drop measurements.

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Influence of Ridge Spacing, Ridge Width, and Reynolds Number on Secondary Currents in Turbulent Channel Flow Over Triangular Ridges

Zhdanov,

Jelly,

Busse

2023

Flow Turbulence Combust

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Most studies of secondary currents (SCs) over streamwise aligned ridges have been performed for rectangular ridge cross-sections. In this study, secondary currents above triangular ridges are systematically studied using direct numerical simulations of turbulent channel flow. The influence of ridge spacing on flow topology, mean flow, and turbulence statistics is investigated at two friction Reynolds numbers, 550 and 1000. In addition, the effects of ridge width on SCs, which have not previously been considered for this ridge shape, are explored. The influence of SCs on shear stress statistics increases with increased ridge spacing until SCs fill the entire channel. One of the primary findings is that, for ridge configurations with pronounced secondary currents, shear stress statistics exhibit clear Reynolds number sensitivity with a significant growth of dispersive shear stress levels with Reynolds number. In contrast to rectangular ridges, no above-ridge tertiary flows are observed for the tested range of ridge widths. Flow visualisations of SCs reveal the existence of corner vortices that form at the intersection of the lateral ridge sides and the smooth-wall sections. These are found to gradually disappear as ridges increase in width. Premultiplied spectra of streamwise velocity fluctuations show strong dependency on the spanwise sampling location. Whereas spanwise averaged spectra show no strong modifications by SCs, a significant increase of energy levels emerges at higher wavelengths for spectra sampled at the spanwise locations that correspond to the centres of the secondary currents.

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Parametric Study on Ridges Inducing Secondary Motions in Turbulent Channel Flow

Cited by 3 publications

References 7 publications

Ridge-type roughness: from turbulent channel flow to internal combustion engine

Ridge-type roughness: from turbulent channel flow to internal combustion engine

Flow resistance over heterogeneous roughness made of spanwise-alternating sandpaper strips

Influence of Ridge Spacing, Ridge Width, and Reynolds Number on Secondary Currents in Turbulent Channel Flow Over Triangular Ridges

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