Near-bed turbulence characteristics in unsteady hydrograph flows over mobile and immobile gravel beds

TY - GEN

T1 - Near-bed turbulence characteristics in unsteady hydrograph flows over mobile and immobile gravel beds

AU - Kean, Jonathan

AU - Cuthbertson, Alan

AU - Beevers, Lindsay

PY - 2016/9

Y1 - 2016/9

N2 - Improvements to current deterministic sediment transport prediction methods requires enhanced understanding of the changes in near-bed turbulent flowcharacteristics occurring during the unsteady hydrograph flow conditions, under which sediment transport is most likely to occur. This paper investigates specifically at relative influence of mobile and immobile bed conditions on the near-bed turbulent structure, focusing specifically on the generation of so-called burst and sweep events, as well as the reciprocal influence of unsteady flow on the nature of these turbulent flow events over both mobile and immobile gravel beds. Quadrant analysis is used to determine the number and strength of turbulent burst and sweep events from detailed three-dimensional ADV velocity data collected over both types of bed. Results indicate that the mobile bed experiences less, but higher magnitude, near-bed burst and sweep events compared to the immobile bed. Further consideration of the results using a hole-size analysis within the quadrant plots may permit the correlation with observed higherorder turbulence events with sediment transport under unsteady hydrograph flows. In this respect, the results demonstrated that higher strength, rather than a higher volume, of turbulent burst/sweep events are found during unsteady flow conditions that are favorable for sediment transport.

AB - Improvements to current deterministic sediment transport prediction methods requires enhanced understanding of the changes in near-bed turbulent flowcharacteristics occurring during the unsteady hydrograph flow conditions, under which sediment transport is most likely to occur. This paper investigates specifically at relative influence of mobile and immobile bed conditions on the near-bed turbulent structure, focusing specifically on the generation of so-called burst and sweep events, as well as the reciprocal influence of unsteady flow on the nature of these turbulent flow events over both mobile and immobile gravel beds. Quadrant analysis is used to determine the number and strength of turbulent burst and sweep events from detailed three-dimensional ADV velocity data collected over both types of bed. Results indicate that the mobile bed experiences less, but higher magnitude, near-bed burst and sweep events compared to the immobile bed. Further consideration of the results using a hole-size analysis within the quadrant plots may permit the correlation with observed higherorder turbulence events with sediment transport under unsteady hydrograph flows. In this respect, the results demonstrated that higher strength, rather than a higher volume, of turbulent burst/sweep events are found during unsteady flow conditions that are favorable for sediment transport.

UR - http://www.isrs2016.de/index.html

M3 - Conference contribution

SN - 9781138029453

T3 - River Sedimentation - Proceedings of the 13th International Symposium on River Sedimentation, ISRS 2016

SP - 259

EP - 266

BT - River Sedimentation - Proceedings of the 13th International Symposium on River Sedimentation, ISRS 2016

A2 - Wieprecht, Silke

A2 - Haun, Stefan

A2 - Weber, Karolin

A2 - Noack, Markus

A2 - Terheiden, Kristina

PB - CRC Press/Balkema

T2 - 13th International Symposium on River Sedimentation, ISRS 2016

Y2 - 19 September 2016 through 22 September 2016

ER -