Umlauf, Lars
:
Turbulence Parameterisation in Hydrobiological Models for Natural Waters.
[OnlineEdition]
Technische Universität, Darmstadt
[Ph.D. Thesis], (2001)

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Item Type:  Ph.D. Thesis  

Title:  Turbulence Parameterisation in Hydrobiological Models for Natural Waters  
Language:  English  
Abstract:  In this thesis different turbulence models are tested with respect to their applicability to oceanographical and limnological problems. Twoequation models for rotating stratified flows are emphasized. After a short introduction in Chapter 1, the transport equations for the turbulent fluxes of momentum, heat and the variance of the temperature fluctuations are derived in Chapter 2. Several closure models for the pressurestrain correlation and the pressuretemperaturegradient correlation are introduced. After their algebraization, the closed transport equations are presented in the socalled boundary layer approximation. With this approximation it is possible to describe the essential features of turbulence models in terms of socalled stability functions. The chapter closes with the presentation of some stability functions, new or already known in the literature. In Chapter 3 different twoequation models (in particular the kepsilon model, the komega model and the model of Mellor and Yamada are formulated and compared in some standard situations. Considered are: The logarithmic lawofthewall, the decay of homogeneous turbulence, homogeneously stratified and sheared homogeneous turbulence in full equilibrium and in structural equilibrium, and the balance between turbulent transport of turbulent kinetic energy and its rate of dissipation. The following results are presented: 1. Stability functions for the structural equilibrium, depending only on the Richardson number, are introduced. Analogous expressions for the turbulent Prandtl number and for the ratios of different lengthscales are derived. Even though the twoequation models investigated are isomorphic in structural equilibrium, they are sensible with respect to different values of the model parameters. The best results are achieved with the komega model. 2. Analytical solutions (in agreement with numerical computations) of twoequation models for the balance between turbulent transport of turbulent kinetic energy and its dissipation are derived. It is demonstrated that the kepsilon model exhibits a singularity for physically reasonable parameters and that the model of Mellor and Yamada is in accordance with the measurements only without its compulsory wall function. Only the komega model reproduces the experimental decay satisfactorily in all situations. Chapter 4 is concerned with applications of twoequation models to problems in limnology and oceanography. The main results are as follows: 1. The mixed layer depth and hence the temperature of the mixed layer in sheardriven entrainment situations is determined by the steadystate Richardson number, an intrinsic property of the models. This quantity, which can be adjusted by parameter calibration, is thus crucial for biological submodels generally being very sensible with respect to temperature differences. 2. The turbulent bottom boundary layer in Lake Alpnach (Switzerland), induced by internal oscillations, could be modelled in agreement with all significant measurements. However, the phaselag between the rate of dissipation and the current shear was underestimated by all models. This part of the work was based on a cooperation with the EAWAG (Switzerland) and includes the first reported comparison of continuous turbulence measurements and models in such a boundary layer. 3. A coupled oxygenturbulence model is suggested that reproduces the measured oxygen profiles in Lake Ammer (Germany) adequately. In Chapter 5 the numerical FiniteVolume method is introduced. The properties of a new discretization of the boundary volumes are discussed. This chapter closes with some tests of the numerical robustness of twoequation models. In contrast to traditional program codes for the computation of turbulent flows, the program architecture suggested in Chapter 6 is based on an objectoriented technique. It is illustrated how turbulence models can be expressed by the abstract vocabulary of an objectoriented language, superior in terms of clarity, reliability, and extendibility compared to structural languages. 

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Place of Publication:  Darmstadt  
Uncontrolled Keywords:  turbulence, turbulence modelling, turbulence modeling, oceanography, lakes, internal seiches, coupled modelling, coupled modeling  
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Classification DDC:  500 Naturwissenschaften und Mathematik > 550 Geowissenschaften  
Divisions:  Studienbereiche > Studienbereich Mechanik  
Date Deposited:  17 Oct 2008 09:21  
Last Modified:  07 Dec 2012 11:47  
Official URL:  http://elib.tudarmstadt.de/diss/000177  
URN:  urn:nbn:de:tudatuprints1776  
Referees:  Hutter, Prof. Kolumban and Oberlack, Prof. Martin  
Advisors:  Hutter, Prof. Kolumban  
Refereed:  4 July 2001  
URI:  http://tuprints.ulb.tudarmstadt.de/id/eprint/177  
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