×

Large scale structures in LES of an oscillating open channel flow under the influence of surface cooling. (English) Zbl 1390.76173

Summary: Large-eddy simulation (LES) of open channel flow driven by an oscillating pressure gradient with zero surface shear stress was performed. The flow is representative of a tidal boundary layer in the coastal ocean under weak or no wind forcing. For a neutrally stratified water column, during peak pressure gradient forcing or peak tide, the flow develops large scale structures secondary to the mean flow consisting of streamwise-elongated, counter-rotating cells engulfing the bulk of the water column. These structures are similar to the classical Couette cells found in turbulent Couette flow driven by parallel no-slip plates moving in opposite direction. Application of a constant cooling flux of 200W/m\(^2\) at the surface of the open channel flow with an adiabatic bottom wall leads to what we term convective supercells consisting of streamwise-elongated cells of greater intensity and cross-stream width than Couette cells. The signature of the convective supercells is observed even during times when the oscillating mean flow is decelerating, unlike the signature of Couette cells in the case without surface cooling. The signature of the cells is visualized and quantified in terms of instantaneous fields such as streamwise-averaged velocity fluctuations, streamwise velocity averaged over streamwise and cross-stream directions and turbulent structure revealed through depth trajectories of Lumley invariant maps. Investigation of these convective supercells is deemed important due to their strong influence on vertical mixing of momentum and scalars and their potential role in determining the wake behind turbines in tidal flows.

MSC:

76F65 Direct numerical and large eddy simulation of turbulence
76B65 Rossby waves (MSC2010)
PDFBibTeX XMLCite
Full Text: DOI

References:

[1] Armenio, V.; Sarkar, S., An investigation of stably stratified turbulent channel flow using large-eddy simulation, J Fluid Mech, 459, 1-42, (2002) · Zbl 1022.76027
[2] Bredberg, J., Technical report, (2000), Department of Thermo and Fluid Dynamics, Chalmers University of Technology, 2000
[3] Fernandez, A. (2016) Personal communication.; Fernandez, A. (2016) Personal communication.
[4] Gargett, A. E., Couette vs. Langmuir circulations: comment on “on the helical flow of Langmuir circulation - approaching the process of suspension freezing” by dethleff, kempema, Koch and chubarenko, Cold Regions Sci Technol, 56, 58-60, (2009)
[5] Germano, M.; Piomelli, U.; Moin, P.; Cabot, W., A dynamic subgrid-scale eddy viscosity model, Phys Fluids, 3, 1760-1765, (1991) · Zbl 0825.76334
[6] Li, M; Sanford, L.; Chao, S. Y., Effects of time dependence in unstratified tidal boundary layers: results from large eddy simulations, Estuarine Coastal Shelf Sci, 62, 193-204, (2005)
[7] Lilly, D., A proposed modification of the Germano subgrid-scale closure, Phys Fluids, 3, 2746-2757, (1992)
[8] Papavassiliou, D. V.; Hanratty, T. J., Interpretation of large-scale structures observed in a turbulent plane Couette flow, Int J Heat Fluid Flow, 18, 55-69, (1997)
[9] Pope, S. B., Turbulent flows, (2000), Cambridge University Press · Zbl 0802.76033
[10] Radhakrishnan, S.; Piomelli, U., Large-eddy simulation of oscillating boundary layers: model comparison and validation, J Geophys Res, 113, C02022, 1-14, (2008)
[11] Thorpe, S. A., Langmuir circulation, Ann Rev Fluid Mech, 36, 55-79, (2004) · Zbl 1076.76075
[12] Walker, R; Tejada-Martínez, A. E.; Martinat, G.; Grosch, C. E., Large-eddy simulation of open channel flow with surface cooling, Int J Heat Fluid Flow, 50, 209-224, (2015)
[13] Walker, R; Tejada-Martínez; Grosch, C. E., Large-eddy simulation of a coastal Ocean under the combined effects of surface heat fluxes and full-depth Langmuir circulation, J Phys Oceanogr, (2016), in press
[14] Weller, H. G.; Tabor, G.; Jasak, H.; Fureby, C., A tensorial approach to computational continuum mechanics using object-oriented techniques, Comput Phys, 12, 620-631, (1998)
This reference list is based on information provided by the publisher or from digital mathematics libraries. Its items are heuristically matched to zbMATH identifiers and may contain data conversion errors. In some cases that data have been complemented/enhanced by data from zbMATH Open. This attempts to reflect the references listed in the original paper as accurately as possible without claiming completeness or a perfect matching.