Turbulence characteristics of flow over a series of 2‐D bed forms in the presence of surface waves

Ojha, Satya P.; Mazumder, B. S.

doi:10.1029/2008jf001203

Cited by 34 publications

(22 citation statements)

References 59 publications

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“…Apart from this, the normalized turbulence intensities in the stream-wise and vertical directions above the rigid flat surface agreed well with those of Nezu and Rodi (1986), Clifford (1998), Ojha and Mazumder (2010), and Chatterjee et al (2018), with slight changes of empirical coefficients. The dimensionless stream-wise mean velocity over the flat rigid surface followed the log-law at all the measuring locations.…”

Section: Discussionsupporting

confidence: 69%

Development of bedforms due to waves blocked by a counter current

Chatterjee

Ghosh

Mazumder

et al. 2019

Earth Surf Processes Landf

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Experiments are conducted in a laboratory flume on the propagation of a surface wave against unidirectional flow with a sediment bed. This article presents the spatial variation of bedforms induced by the wave‐blocking phenomenon by a suitably tuned uniform fluid flow and a counter‐propagating wave. The occurrence of wave‐blocking is confirmed by finding a critical wave frequency in a particular flow discharge in which the waves are effectively blocked and is established using the linear dispersion relation. The purpose of this work is to identify wave‐blocking and its influence on the development of bedforms over the sediment bed. Interestingly bedform signatures are observed at a transition of bedforms in three zones, with asymmetric ripples having a steeper slope downstream face induced by the incoming current, followed by flat sand bars beneath the wave‐blocking zone and more symmetric ripples below the wave‐dominated region at the downstream. This phenomenon suggests that the sediment bed is segmented into three different regions of bed geometry along the flow. The deviations of mean flows, Reynolds stresses, turbulent kinetic energy, and power spectral density due to the wave‐blocking phenomenon are presented along the non‐uniform flow over sediment bed. The bottom shear stress, bed roughness and stochastic nature of the bedform features are also discussed. The results are of relevance to engineers and geoscientists concerned with contemporary process as well as those interested in the interpretation of palaeoenvironmental conditions from fossil bedforms. © 2019 John Wiley & Sons, Ltd.

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Section: Discussionsupporting

confidence: 69%

Development of bedforms due to waves blocked by a counter current

Chatterjee

Ghosh

Mazumder

et al. 2019

Earth Surf Processes Landf

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“…The mean velocities (ū,w); streamwise turbulence intensities ( u , w ) vertical bottom-normal turbulence intensity ( w ) and time-averaged Reynolds shear stress ( u ′ w ′ ) were computed by standard procedure (Nezu and Rodi 1986;Ojha and Mazumder 2010;Singh et al 2015). To ensure the fully developed flow at the experiment section we performed three experiments at three different locations (9, 10 and 12 m at downstream of the flume entrance) along the centre line of the flume and found almost no changes amongst the results of those tests.…”

Section: Methodsmentioning

confidence: 99%

“…The zero-plane position is evaluated by the method based on the inverse of the velocity profile derivative suggested in Nikora et al (2002) and Ojha and Mazumder (2010).…”

Section: Mean Velocity Profiles Over Cubical Rough Bedmentioning

confidence: 99%

“…Nevertheless, very few experimental studies have been carried out on the wavecurrent interaction problem over a rough-bed (e.g. Brevik and Aas 1980;Fredsoe et al 1999;Kemp and Simons 1983;Ojha and Mazumder 2010). In spite of the considerable work on flow over rough-bed in wave-current coexisting environment using Reynolds-averaged Navier-Stokes equations, no work has been reported for flow over rough-bed in wave-current coexisting environment using spatial-averaging to Reynoldsaveraged Navier-Stokes equations.…”

Section: Introductionmentioning

confidence: 96%

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Changes in turbulent flow structure over rough-bed under combined wave-current motions

Singh

Debnath

Mazumder

2016

ISH Journal of Hydraulic Engineering

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This paper presents the result of an experimental study carried out in a laboratory flume to investigate the interaction of surface wave and unidirectional current over cube-mounted rough-bed. The cubes were made of wood and were positioned at the channel-bed with different spacing. The study particularly focuses on the changes induced in the spatially averaged velocity profile, turbulent intensity and Reynolds stress due to the superposition of waves of different frequencies on current-induced flow.The spatially averaged velocity profile shows two distinct regions: the linear or exponential distribution below the roughness tops and logarithmic profile above the roughness top. The profile of streamwise turbulent intensity is similar to that of current-only flow except in the region near the water surface. In contrast, the profile of bottom-normal turbulent intensity is almost constant over the entire depth. Below the roughness crest, the form-induced stress changes significantly with switching from negative to a positive value with change in roughness spacing, but is not affected much by the presence of surface wave.

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“…The oscillatory velocity amplitude close to the bed was influenced by vortex formation. Other studies, Dimas & Kolokythas (2011);Hurther & Thorne (2011) and Ojha & Mazumder (2010) have noticed this up to six ripple heights above the ripple crest. When waves and current are combined the velocity profile of following current get a maximum value then regularly decreases toward the surface (Klopman, 1994;van Doorn, 1981).…”

Section: Horizontal Velocity Time Series and Analysismentioning

confidence: 99%

Aspects of inlet geometry and dynamics

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This thesis contains new analytical approaches as well as laboratory-and field experiments conducted to understand the hydrodynamic and morphodynamic responses of tidal inlets to forcing from tides, river flow and waves on the time scales of closure, flood or storm events. The thesis outcome is effective new tools for authorities managing coastal zones balancing navigation-, shore protection-and socio-economic development purposes.A new method of coastal inlet classification based on dimensionless parameters is presented. These parameters represent the relative strength of the three main forcing agents: tides, river flow and waves. This new classification is applied to 178 inlets along the NSW coast of Australia, and compared with other widely used classification schemes available in the literature.The inlet hydraulic analysis is presented in Chapter 2 with given inlet geometry and wave climate with overwash discharge (Q over ) added into the usual governing equations. The hydraulic analysis of inlets in terms of the frequency response function for the linearised system is illustrated for cases of monochromatic and mixed diurnal/semi-diurnal tides. This analysis quantifies the influence of the entrance invert level, river flow and bay surface area. A case of inland flooding at Lake Conjola, Australia is used to test different methods resulting in a successful illustration of the importance of wave overwash as a driving force.For each hydrodynamic condition, the inlet system and its elements have a corresponding morphological equilibrium state. New relationships for inlets in equilibrium were constructed based on dimensional analysis and tested on a data set of 36 natural inlets in the USA. These new relations depend not only on the tidal prism but also the tidal period, and mean annual significant wave height s H .During unusual weather, the morphology of tidal inlets runs out of equilibrium.Subsequently, they may return to the previous equilibrium or move towards a new equilibrium or get closed. Inlet morphodynamics analysis is ideally carried out from topographical surveys. These are however costly and usually not available. Process based numerical models are still unreliable. A more economical and reliable new method, a 24.5hour moving window method, is introduced to infer hydraulic-and morpho-dynamic changes from tidal records. The morphological time scales are thus determined from time series of mean water levels, standard deviation, or the gain of the primary tidal components. This analytical method is successfully applied to inlet closure events and flood or storm events.The morphological time scale, T morph has been derived from the 24.5hour moving window analysis for many closure events with bay area (A b <0.7km 2 ) in Australia. The results show a clear trend of T morph decreasing with increasing relative wave strength -i.e., more rapid closure with iii bigger waves. However, for larger inlets or inlets with training works the morphology changes, at the time scale of individual storms, are usua...

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Turbulence characteristics of flow over a series of 2‐D bed forms in the presence of surface waves

Cited by 34 publications

References 59 publications

Development of bedforms due to waves blocked by a counter current

Development of bedforms due to waves blocked by a counter current

Changes in turbulent flow structure over rough-bed under combined wave-current motions

Aspects of inlet geometry and dynamics

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