Assessment of Predictive Capabilities of Detached Eddy Simulation to Simulate Flow and Mass Transport Past Open Cavities

Chang, Keun Sick; Constantinescu, George; Park, Seung O

doi:10.1115/1.2786529

Cited by 54 publications

(45 citation statements)

References 26 publications

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“…The interest in LES and hybrid RANS-LES methods like detached eddy simulation (DES) is mainly motivated by their greater accuracy over RANS for flows dominated by large-scale unsteady coherent structures and massive separation. (e.g., see results of a combined RANS, DES and LES study of flow and ejection of contaminant from bottom river cavities reported in [3], [4] and [5]). Such 3D simulations provide the full mean and instantaneous flow fields, as well as the distribution of the turbulence fluctuations and the bed shear stress.…”

Section: Review Of Relevant Experimental and Numerical Studiesmentioning

confidence: 95%

Mass exchange in a shallow channel flow with a series of groynes: LES study and comparison with laboratory and field experiments

2009

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The exchange of dissolved matter between a straight open channel and a series of shallow embayments present at one of its sides is investigated using large eddy simulation (LES). The direct link between the mechanism of mass exchange and the dynamics of coherent structures is demonstrated. It is shown that for the geometrical configuration considered in the present study, the mass exchange process is very non-uniform over the depth in the vicinity of the channel-embayment interface. Most of the contaminant is ejected from the embayments close to the free surface. The amount of contaminant re-entrained into the embayments situated downstream of the one in which contaminant was introduced is quantified. The mass exchange coefficient predicted by LES does not vary significantly with the embayment rank and is in very good agreement with the one predicted by the model proposed by Weitbrecht et al. (J Hydraul Eng 134(2):173-183, 2008) based on the value of a dimensionless morphometric groyne-field parameter. Field experiments were purposely performed in a natural stream with embayments whose length over width ratios were close to the ratio in the LES study. The concentration fields predicted by LES are compared with video-records of colored dye used to visualize the mass exchange in the field experiment. It is shown that, for both LES and the field experiment, the dominant passage frequency of the eddies inside the interfacial mixing layer is well predicted by the analytical model of Sukhodolov and Sukhodolova (in: Cowen et al (eds) Hydraulic measurements & experimental methods.123 588 Environ Fluid Mech (2009) 9:587-615 showing the temporal evolution of the concentration field. The results of the comparison indicate several similarities in the mixing process, despite the differences in the bathymetry and the large difference in the Reynolds number between LES and the field experiment. This proves the usefulness of performing detailed LES and laboratory studies in well-controlled environments to understand mass-exchange processes around river groyne fields.

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Section: Review Of Relevant Experimental and Numerical Studiesmentioning

confidence: 95%

Mass exchange in a shallow channel flow with a series of groynes: LES study and comparison with laboratory and field experiments

2009

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“… Constantinescu and Squires [2003, 2004], Constantinescu et al [2003], and Chang et al [2007] discuss results of grid sensitivity and validation studies for simulations of the flow past spheres and channel flow over a bottom cavity conducted using the same code. In particular, Chang et al [2007] showed that the agreement between highly resolved LES and DES conducted on a much coarser mesh improved significantly when the inflow contained turbulent fluctuations obtained from a preliminary straight channel flow calculation. This is the approach adopted in the present study.…”

Section: Numerical Methods and Simulation Set Upmentioning

confidence: 99%

Flow and turbulence structure around an in‐stream rectangular cylinder with scour hole

Kirkil

Constantinescu

2010

Water Resources Research

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[1] Most of the erosion around obstacles present in alluvial streams takes place after the formation of a scour hole of sufficiently large dimensions to stabilize the large-scale oscillations of the horseshoe vortex (HV) system. The present paper uses eddy resolving techniques to reveal the unsteady dynamics of the coherent structures present in the flow field around an in-stream vertical cylinder (e.g., bridge pier) with a large scour hole at a channel Reynolds number defined with the channel depth and the bulk channel velocity of 2.4 × 10 5 . The cylinder has a rectangular section and is placed perpendicular to the incoming flow. The geometry of the scour hole is obtained from an experiment conducted as part of the present work. The mechanisms driving the bed erosion during the advanced stages of the scour process around the vertical plate are discussed. Simulation results demonstrate the critical role played by these large-scale turbulent eddies and their interactions in driving the local scour. The paper analyzes the changes in the flow and turbulence structure with respect to the initial stages of the scour process (flat bed conditions) for a cylinder of identical shape and orientation. Results show the wake loses its undular shape due to suppression of the antisymmetrical shedding of the roller vortices. Also, the nature of the interactions between the necklace vortices of the HV system and the eddies present inside the detached shear layers (DSLs) changes as the scour process evolves. This means that information on the vortical structure of the flow at the initiation of the scour process, or during its initial stages, are insufficient to understand the local scour mechanisms. The paper also examines the effect of the shape of the obstruction on the dynamics of the vortical eddies and how it affects the bed erosion processes during the advanced stages of the local scour. In particular, the paper provides an explanation for the observed increase in the maximum scour depth for bed-mounted cylinders of rectangular section compared to cylinders of same width but of circular section. This increase is explained by the larger coherence of the HV system, the increased regularity of the interactions between the legs of the necklace vortices and the eddies shed in the DSLs, and the stronger coherence of the wake eddies, during both the initial and the later stages of the local scour process, for cases in which the obstruction has sharp edges that fix the separation point on the in-stream obstacle at all flow depths (e.g., rectangular cylinder).Citation: Kirkil, G., and G. Constantinescu (2010), Flow and turbulence structure around an in-stream rectangular cylinder with scour hole, Water Resour. Res., 46, W11549,

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“…Detailed grid sensitivity and validation studies for the flow past spheres and for flow and contaminant transport in a channel with a bottom cavity are discussed in the work of Constantinescu and Squires [2003, 2004], Constantinescu et al [2003], and Chang et al [2007]. An additional validation test case was conducted for the case of a relatively low‐Reynolds‐number flow (Re = 18,000) past a circular cylinder mounted on a flat‐bed channel.…”

Section: Methodsmentioning

confidence: 99%

“…For internal flows (e.g., flow past surface‐mounted bodies in a channel) the predictions of DES in terms of the large‐scale eddy content, their dynamics, and the prediction of the mean flow and turbulence statistics are dependent on the presence, or not, of resolved turbulence in the incoming flow. For instance, this is discussed on the basis of comparison with highly resolved LES by Chang et al [2007] in their DES study of flow and contaminant ejection from a bottom river cavity. As the incoming flow in all applications of relevance to river engineering is turbulent and the flow predictions can be significantly affected by the characteristics of the incoming flow, it is important to specify inflow conditions that match as close as possible those present in experiments and in the field.…”

Section: Introductionmentioning

confidence: 99%

Nature of flow and turbulence structure around an in‐stream vertical plate in a shallow channel and the implications for sediment erosion

Kirkil

Constantinescu

2009

Water Resources Research

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[1] Detailed knowledge of the dynamics of large-scale turbulence structures is needed to understand the geomorphodynamic processes around in-stream obstacles present in rivers. Detached Eddy Simulation is used to study the flow past a high-aspect-ratio rectangular cylinder (plate) mounted on a flat-bed relatively shallow channel at a channel Reynolds number of 2.4 Â 10 5 . Similar to other flows past surface-mounted bluff bodies, the large amplification of the turbulence inside the horseshoe vortex system is because the core of the main necklace vortex is subject to large-scale bimodal oscillations. The presence of a sharp edge at the flanks of the obstruction fixes the position of the flow separation at all depths and induces the formation and shedding of very strong wake rollers over the whole channel depth. Compared with the case of a circular cylinder where the intensity of the rollers decays significantly in the near-bed region because the incoming flow velocity is not sufficient to force the wake to transition from subcritical to supercritical regime, in the case of a high-aspect-ratio rectangular cylinder the passage of the rollers was found to induce high bed-shear stresses at large distances (6-8 D) behind the obstruction. Also, the nondimensional values of the pressure root-mean-square fluctuations at the bed were found to be about 1 order of magnitude higher than the ones predicted for circular cylinders. Overall, this shows that the shape of the in-stream obstruction can greatly modify the dynamics of the large-scale coherent structures, the nature of their interactions, and ultimately, their capability to entrain and transport sediment particles and the speed at which the scour process evolves during its initial stages.Citation: Kirkil, G., and G. Constantinescu (2009), Nature of flow and turbulence structure around an in-stream vertical plate in a shallow channel and the implications for sediment erosion, Water Resour. Res., 45, W06412,

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Assessment of Predictive Capabilities of Detached Eddy Simulation to Simulate Flow and Mass Transport Past Open Cavities

Cited by 54 publications

References 26 publications

Mass exchange in a shallow channel flow with a series of groynes: LES study and comparison with laboratory and field experiments

Mass exchange in a shallow channel flow with a series of groynes: LES study and comparison with laboratory and field experiments

Flow and turbulence structure around an in‐stream rectangular cylinder with scour hole

Nature of flow and turbulence structure around an in‐stream vertical plate in a shallow channel and the implications for sediment erosion

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