High Resolution Simulation of the Turbulent Wake Behind a Sphere in a Stratified Fluid PDF Download

Author: Matthew Bronson De Stadler
Publisher:
ISBN: 9781303429675
Category :
Languages : en
Pages : 241

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Book Description
The wake of a bluff body is significantly modified by the presence of a stable density stratification. Buoyancy effects introduce a complex coupling between kinetic and potential energy which results in a significantly longer wake lifetime, internal wave radiation, and long lived coherent structures. This dissertation presents results obtained from high resolution numerical simulations of stratified turbulent wakes. The dissertation is divided into two parts. The first part of the dissertation uses the well established temporal approximation to simulate from the near wake to the far wake. In this part of the dissertation, the effect of the Prandtl number on a stratified turbulent wake was considered. For 0.2 Pr

Author: Sheel Nidhan
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Turbulent wakes are pervasive in man-made and natural environments. In the ocean and the atmosphere, these wakes interact with the background ambient stratification to give rise to a myriad of interesting phenomena, e.g., multistage decay of mean and turbulence, long-lived coherent structures, and the appearance of internal gravity waves, to name a few. With the rise in supercomputing power, high-fidelity numerical simulations have become an increasingly feasible way to investigate the phenomenology of these wakes. As these simulations become commonplace in research, there is an increased focus on the use of data-driven techniques to uncover the rich dynamics from the obtained datasets. This dissertation is an examination of turbulent wakes using data-driven techniques and numerical simulations. In the first part, spectral proper orthogonal decomposition is used to investigate a turbulent disk wake database at Re = 5 x 104 and Fr = [infinity], 10, 2. We first study the evolution of the vortex shedding mode and double helix mode in the unstratified wake (Fr = [infinity]), building on and refining the previous experimental studies. Thereafter, the SPOD analysis of the stratified wakes is performed that uncovers two new results: (a) coherence originating at the body gets stronger and lives longer with progressively increasing stratification levels and (b) for Fr [greater than and approximately equal to] 2, vortex shedding is the dominant mechanism of internal gravity wave generation. In the second part of the work, large eddy simulations (LES) are used to investigate the flow past a prolate 6:1 spheroid. Firstly, high-resolution hybrid simulation is used to simulate the far wake of a 6:1 spheroid at 0-degree angle of attack and Re = 105, Fr = 2 and 10. The far wake is compared to the above-mentioned disk database. The spheroid wakes show differences in locations at which mean wake transitions take place. These differences are explained in light of energy budgets. Secondly, large eddy simulations of flow past a 6:1 spheroid at Re = 5000, Fr = [infinity], 6, 1.9, 1, and a moderate angle of attack [alpha] = 10[superscript circle] are carried out. Body forces, mean wake and vorticity dynamics, and flow spectra are analyzed in detail and presented in the dissertation.

Author: W. S. Lewellen
Publisher:
ISBN:
Category :
Languages : en
Pages : 134

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A computational model has been developed for the turbulent wake of a body moving through a stably stratified fluid. Details of the wake growth, collapse and generation of internal waves were examined by the application of a second-order closure approach to turbulent flow developed at A.R.A.P. over the past few years. Predictions of the model have been verified by comparison with a wide variety of wake flows including wakes with no momentum, wakes with axial momentum, wakes with angular momentum, and for wakes in both stratified and unstratified fluids. A sensitivity investigation reveals that the primary variable affecting the strength of the generated internal waves is the initial Richardson number, with the first local maximum of the vertical height of the wake scaling inversely with the 1/8th power of the initial Richardson number.

Author: Edward Y. T. Kuo
Publisher:
ISBN:
Category :
Languages : en
Pages : 14

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The modeling of the turbulent wake of a self-propelled body in a stratified fluid is discussed. The scaling parameter is taken to be the internal Froude number, using the speed and diameter of the body and Vaisala frequency of the fluid. The ratio of the time for the wake to collapse to the characteristic time of the turbulence is related to model scale when the wake is turbulent up to and including the collapse. A number of criteria for turbulent wake are discussed. Numerical estimates are made, assuming typical values of the model speed and of the Vaisala frequency, of the minimum model size necessary for the existence of a turbulent wake at collapse.

Author: Walter P. M. van de Watering
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 74

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In a laboratory experiment, turbulent mixed regions were generated in a linearly density-stratified fluid and their behavior was studied. Such regions may occur in nature in the atmosphere and in the ocean. Particularly during their early history, the shape of such regions is influenced by the interacting effects of turbulence and buoyancy, culminating in the occurrence of a maximum thickness and subsequent vertical collapse. A Richardson number (equivalent to the ratio of the characteristic turbulence time and the Vaisala period) was found satisfactorily to correlate the data obtained, together with those previously obtained by other investigators with self-propelled bodies. An estimate is made of the degree of mixing that takes place inside a turbulent mixed region during its growth in stably-stratified surroundings: the effectiveness of this mixing determines the ultimate thickness to which the mixing region collapses. (Author).

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 102

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The primary goal of our work was to provide accurate information about velocity and density field in the near wake region of a flow around a sphere in a stratified fluid. This is a canonical configuration used in investigating a structure of stratified wakes and in numerical simulations.

Author: National Research Council
Publisher: National Academies Press
ISBN: 0309065372
Category : Science
Languages : en
Pages : 1039

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Book Description
The Twenty-Second Symposium on Naval Hydrodynamics was held in Washington, D.C., from August 9-14, 1998. It coincided with the 100th anniversary of the David Taylor Model Basin. This international symposium was organized jointly by the Office of Naval Research (Mechanics and Energy Conversion S&T Division), the National Research Council (Naval Studies Board), and the Naval Surface Warfare Center, Carderock Division (David Taylor Model Basin). This biennial symposium promotes the technical exchange of naval research developments of common interest to all the countries of the world. The forum encourages both formal and informal discussion of the presented papers, and the occasion provides an opportunity for direct communication between international peers.

Author: Jorg Imberger
Publisher: Academic Press
ISBN: 0120885719
Category : Science
Languages : en
Pages : 446

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Book Description
A broad cross-section of scientists working in aquatic environments will enjoy this treatment of environmental fluid dynamics, a foundation for elucidating the importance of hydrodynamics and hydrology in the regulation of energy.

Author: Robert M. Kerr
Publisher: Springer Science & Business Media
ISBN: 9401009287
Category : Science
Languages : en
Pages : 298

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This symposium continues a long tradition for IUGGjIUTAM symposia going back to "Fundamental Problems in Thrbulence and their Relation to Geophysics" Marseille, 1961. The five topics that were emphasized were: turbulence modeling, statistics of small scales and coherent structures, con vective turbulence, stratified turbulence, and historical developments. The objective was to consider the ubiquitous nature of turbulence in a variety of geophysical problems and related flows. Some history of the contribu tions of NCAR and its alumni were discussed, including those of Jackson R Herring, who has been a central figure at NCAR since 1972. To the original topics we added rotation, which appeared in many places. This includes rotating stratified turbulence, rotating convective turbulence, horizontal rotation that appears in flows over terrain and the role of small scale vorticity in many flows. These complicated flows have recently begun to be simulated by several groups from around the world and this meeting provided them with an excellent forum for exchanging results, plus inter actions with those doing more fundamental work on rotating stratified and convective flows. New work on double diffusive convection was given in two presentations. The history of Large Eddy Simulations was presented and several new approaches to this field were given. This meeting also spawned some interesting interactions between observational side and how to inter pret the observations with modeling and simulations around the theme of particle dispersion in these flows.

Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 400

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