On Internal Hydraulics with Entrainment

Gerdes, Frank; Garrett, Chris; Farmer, David M.

doi:10.1175/1520-0485(2002)032<1106:oihwe>2.0.co;2

Cited by 23 publications

(29 citation statements)

References 9 publications

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“…This balance (for the vertical direction only) can be represented, following McDougall (1984), as: Gerdes et al (2002). In order to adequately characterize turbulent vertical transport from observations of total vertical transport, the effect of this mean vertical transport must be considered.…”

Section: Entrainment Velocitymentioning

confidence: 99%

Mixing processes and hydraulic control in a highly stratified estuary

MacDonald¹

2003

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This thesis utilizes field data from the Fraser River Estuary, a highly stratified system located in southwestern British Columbia, Canada, to investigate the nature of mixing processes in a highly stratified environment, and to extend two-dimensional hydraulic theory to a three dimensional environment.During the late ebb, a stationary front exists at the Fraser mouth. Although densimetric Froude numbers in the vicinity of the front are supercritical in a frame of reference parallel to the local streamlines, the front itself is oriented such that the value of the Froude number is equal to the critical value of unity when taken in a frame of reference perpendicular to the front. This observation presents a robust extension of established two-dimensional, two-layer hydraulic theory to three dimensions, and implies similarity with trans-sonic flows, in that a Froude angle can be used to identify critical conditions in a manner similar to the Mach angle.Mixing processes were evaluated at the mouth during the late ebb using a control volume approach to isolate mean vertical entrainment processes from turbulent processes, and quantify the vertical turbulent salt and momentum fluxes. Observed turbulent dissipation rates are high, on the order of 10 -3 m 2 s -3 , with vertical entrainment velocities on the order In the estuarine channel, the variability of mixing processes was investigated through the tidal cycle using control volume and overturn scale methods. Spatially, mixing was observed to be more intense near a width constriction on the order of 25%. Temporally, more dominant mixing was observed during ebbs, due to increases in both vertical shear and stratification. Mixing is active and important throughout the tidal cycle, and was found to be the dominant process responsible for removing salt from the estuarine channel during the ebb. AcknowledgementsThis work could never have been accomplished without assistance and encouragement from a large number of people. It has truly been a pleasure to work with my advisor, Rocky Geyer, over the last four years. His enthusiasm for his work has been inspiring and I have learned a lot from him. I also appreciate the timely advice and input I have received from the other members of my committee, John Trowbridge, Eric Adams, and Ole Madsen, and I would like to thank Jim Ledwell for chairing my defense.The Fraser River cruises would not have been possible without help from David Jay, Philip Orton and Doug Wilson. The crew of the R/V Clifford A. Barnes, Ray McQuin and Nikki Hix, was fantastic to work with. Alex Horner was a tremendous help during both cruises, particularly with the collection of the data described in Chapter 4, and its subsequent analysis. Here at WHOI, Terry Donoghue and Jim Irish provided a tremendous amount of assistance in preparation for the two cruises.The Coastal and Estuarine GFD course at Friday Harbor Labs during the summer of 1999 was a great experience and provided me with a good foundation for the research presented here. I'd like to thank...

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Section: Entrainment Velocitymentioning

confidence: 99%

Mixing processes and hydraulic control in a highly stratified estuary

MacDonald¹

2003

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“…2a) has velocity (u 2 , 0), and the entrainment dimensionless parameter E is assumed to be ∼ 10 −4 (Ellison and Turner, 1959;Turner, 1986). Entrainment also implies an exchange of momentum between layers, and thus an additional resistive force (Baringer and Price, 1997b;Gerdes et al, 2002) that should be considered in the momentum balance. However, if u is ∼ u 2 (Tables 1 and 2), momentum variations due to entrainment can be reasonably neglected as previously discussed.…”

Section: Continuity Equation and Vertical Entrainmentmentioning

confidence: 99%

Friction and mixing effects on potential vorticity for bottom current crossing a marine strait: an application to the Sicily Channel (central Mediterranean Sea)

Falcini

Salusti

2015

Ocean Sci.

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Abstract. We discuss here the evolution of vorticity and potential vorticity (PV) for a bottom current crossing a marine channel in shallow-water approximation, focusing on the effect of friction and mixing. The purpose of this research is indeed to investigate the role of friction and vertical entrainment on vorticity and PV spatial evolution in channels or straits when along-channel morphology variations are significant. To pursue this investigation, we pose the vorticity and PV equations for a homogeneous bottom water vein and we calculate these two quantities as an integral form. Our theoretical findings are considered in the context of in situ hydrographic data related to the Eastern Mediterranean Deep Water (EMDW), i.e., a dense, bottom water vein that flows northwestward, along the Sicily Channel (Mediterranean Sea). Indeed, the narrow sill of this channel implies that friction and entrainment need to be considered. Small tidal effects in the Sicily Channel allow for a steady theoretical approach.We argue that bottom current vorticity is prone to significant sign changes and oscillations due to topographic effects when, in particular, the current flows over the sill of a channel. These vorticity variations are, however, modulated by frictional effects due to seafloor roughness and morphology. Such behavior is also reflected in the PV spatial evolution, which shows an abrupt peak around the sill region. Our diagnoses on vorticity and PV allow us to obtain general insights about the effect of mixing and friction on the pathway and internal structure of bottom-trapped currents flowing through channels and straits, and to discuss spatial variability of the frictional coefficient. Our approach significantly differs from other PV-constant approaches previously used in studying the dynamics of bottom currents flowing through rotating channels.

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“…Initial-value experiments were performed in order to establish exchange flows having an interfacial region of finite thickness due to mixing (Figure 1). A previous theory based on a homogeneous shallow water formulation with cross-interface entirainment (Gerdes, et al 2002) was tested. Effects on neighboring basins have been investigated using a numerical model of a basin flow drained by a single sti-ait.…”

Section: Approachmentioning

confidence: 99%

Determining the Stratification of Exchange Flows in Sea Straits

Pratt¹,

Helfrich²

2003

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid 0MB control number. PLEASE DO NOT RETURN YOUR SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)Office of Naval Research Regional Office Boston 495 Summer Street, Room 627 Boston, MA 02210-2109 SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENT APPROVED FOR PUBLIC RELEASE -DISTRIBUTION IS UNLIMITED SUPPLEMENTARY NOTES 20031217 005 ABSTRACTOur long-term goal is to contribute to the understanding of the dynamics and stratification of exchange flows such as in the Bab al Mandab and to understand the consequences for the circulation in the neighboring basins and/or marginal seas. One of the original objectives of the proposed work is to understand the effect of critical level mixing on the dynamics and stratification of sill flows. In particular, what happens when the mixing is limited to only the middle part of the water column, as appears to be the case in Bab al Mandab? When are such flows hydraulically controlled and to what extent are layer models with interfacial entrainment able to describe the hydraulic behavior. We also sought to formulate a model that captures the communication between the strait/sill system and the circulation and stratification in a connected basin. A separate objective was to convene a meeting of the world's leading investigators of the physics of flow in sea straits in order to review the current state of knowledge and identify important topics of future research. SUBJECT TERMS

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On Internal Hydraulics with Entrainment

Cited by 23 publications

References 9 publications

Mixing processes and hydraulic control in a highly stratified estuary

Mixing processes and hydraulic control in a highly stratified estuary

Friction and mixing effects on potential vorticity for bottom current crossing a marine strait: an application to the Sicily Channel (central Mediterranean Sea)

Determining the Stratification of Exchange Flows in Sea Straits

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