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

Deyn, Lars H. von; Schmidt, Marvin; Stroh, Alexander; Kriegseis, Jochen; Böhm, Benjamin

doi:10.1007/s00348-021-03353-x

Cited by 7 publications

(9 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Based on oil-interferometry measurements, they report a decreasing skin-friction coefficient with increasing Reynolds number, indicating the absence of a fully rough regime for large 2-D structures, in agreement with channel flow pressure-drop measurements by von Deyn et al. (2019, 2021). The versus behaviour of ridges is included schematically in figure 1.…”

Section: Introductionsupporting

confidence: 83%

“…Recently, ridge-type 2-D structures have been investigated systematically by Medjnoun et al (2020), who considered skin-friction drag and its interplay with secondary currents for triangular, rectangular and half-sphere shapes of the order of l + g ≈ 200. Based on oil-interferometry C f measurements, they report a decreasing skin-friction coefficient C f with increasing Reynolds number, indicating the absence of a fully rough regime for large 2-D structures, in agreement with channel flow pressure-drop measurements by von Deyn et al (2019Deyn et al ( , 2021. The C f versus Re b behaviour of ridges is included schematically in figure 1.…”

Section: Introductionsupporting

confidence: 81%

“…The viscous-scaled mean velocity profile retrieved from DNS data (see von Deyn et al. 2021), which is available for the case di_13, hints at the applicability of the described framework also for large ridges.

Figure 6.Roughness function versus .…”

Section: Measurement Resultsmentioning

confidence: 72%

“…This methodology is also employed in other studies dealing with pressure-drop measurements of flows over irregular roughness (Barros, Schultz & Flack 2018;Flack, Schultz & Barros 2020). The viscous-scaled mean velocity profile retrieved from DNS data (see von Deyn et al 2021), which is available for the case di_13, hints at the applicability of the described framework also for large ridges.…”

Section: Drag Regimesmentioning

confidence: 99%

“…For the interested reader, note that the mean flow data of di_13 up to is discussed in von Deyn et al. (2021). Moreover, set dr_2 corresponds to the one discussed in Gatti et al.…”

Section: Experimental Matrixmentioning

confidence: 99%

See 4 more Smart Citations

From drag-reducing riblets to drag-increasing ridges

Deyn

Gatti

2022

J. Fluid Mech.

Self Cite

View full text Add to dashboard Cite

Small drag-reducing riblets and larger drag-increasing ridges are longitudinally invariant and laterally periodic surface structures that differ only in the details of their lateral periodicity and their size in viscous units. Due to their different drag behaviour, typically riblets and ridges have been analysed separately. By studying experimentally trapezoidal-grooved surfaces of different sizes, we address systematically the transition from riblet-like to ridge-like behaviour in a unified framework. The structure height and lateral wavelength are varied both physically, by considering eight different surfaces, and in their viscous-scaled form, by spanning a wide range of bulk Reynolds number $Re_b$ . The effective skin-friction coefficient $C_f$ is determined via pressure-drop measurement in a turbulent channel flow facility designed for accurate drag measurements. An unexpectedly rich drag behaviour is unveiled, in which different drag regimes are distinguished depending on the value of $l_g^+$ , the viscous-scaled square root of the groove area. The well-known drag-reducing regime of riblets that spans up to $l_g^+=17$ is followed by a regime in which the roughness function ${\rm \Delta} U^+$ increases logarithmically with $l_g^+$ , indicating an apparent fully rough behaviour up to $l_g^+\approx 40$ . Further increase of $l_g^+$ leads to a clear departure from the fully rough regime, and an unexpected non-monotonic behaviour of the roughness function ${\rm \Delta} U^+$ for $50< l_g^+<200$ is reported for the first time. For sufficiently large $Re_b$ and $l_g$ , it is shown that a single parameter, similar to the classical hydraulic diameter, is sufficient to describe the drag behaviour of ridges. We find that an appropriate definition of the effective channel height is crucial for interpreting the drag behaviour. When the longitudinal protrusion height of the structured surface is accounted for in the channel height definition, a laminar flow exhibits the same $C_f(Re_b)$ relation known for flat surfaces. This approach thus allows us to discern the modification of $C_f$ induced by turbulence. We provide predictive correlations for the fully rough regime and the high Reynolds number range of trapezoidal-grooved surfaces that become possible thanks to the chosen channel height definition.

show abstract

Section: Introductionsupporting

confidence: 83%

Section: Introductionsupporting

confidence: 81%

Figure 6.Roughness function versus .…”

Section: Measurement Resultsmentioning

confidence: 72%

Section: Drag Regimesmentioning

confidence: 99%

“…For the interested reader, note that the mean flow data of di_13 up to is discussed in von Deyn et al. (2021). Moreover, set dr_2 corresponds to the one discussed in Gatti et al.…”

Section: Experimental Matrixmentioning

confidence: 99%

See 3 more Smart Citations

From drag-reducing riblets to drag-increasing ridges

Deyn

Gatti

2022

J. Fluid Mech.

Self Cite

View full text Add to dashboard Cite

show abstract

Measurements in a Turbulent Channel Flow by Means of an LDV Profile Sensor

Pasch,

Leister,

Gatti

et al. 2023

Flow Turbulence Combust

View full text Add to dashboard Cite

Spatially and temporally resolved velocity measurements in wall-bounded turbulent flows remain a challenge. Contrary to classical laser Doppler velocimetry (LDV) measurements, the laser Doppler velocity profile sensor (LDV-PS) allows the combined measurement of tracer particle position and velocity, which makes it a promising tool. To assess its feasibility a commercial LDV-PS is employed in a turbulent channel flow at $$Re_\tau =350$$ R e τ = 350 . Additionally, the measurement and signal-processing accuracies of velocity and location are evaluated for various tracer-object sizes and velocities. On this basis, the turbulent channel flow measurements are evaluated and compared to reference data from direct numerical simulations. Thus, potentials of the LDV-PS are investigated for different regions of the flow and various data processing routines as well as the experimental practice are discussed from an application perspective.

show abstract

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

View full text Add to dashboard Cite

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.

show abstract

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

Cited by 7 publications

References 46 publications

From drag-reducing riblets to drag-increasing ridges

From drag-reducing riblets to drag-increasing ridges

Measurements in a Turbulent Channel Flow by Means of an LDV Profile Sensor

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

Contact Info

Product

Resources

About