yes / A two dimensional (2D) RNG k-ε sediment model including the effects of secondary currents is developed to simulate sediment transport and bed deformation in rivers with continuous bends. Nonuniform suspended and bedload sediment transports and variation of effective bed material size distribution are included in the model. A semi-coupled scheme for sediment model is proposed, which can be used for simulating both the long- and short-term sediment transport whenever riverbed changes. The model is applied to simulate the flow and sediment transport in the Shapotou reservoir in the upper reach of the Yellow River which is a typical natural river reach with continuous bends. River bed deformations caused by suspended and bedload sediment transport are investigated. Good agreement between the numerically simulated results and the field measurements is obtained, indicating that the model is capable of simulating the sediment transport and predicting the bed deformation of rivers having continuous bends with reasonable accuracy. / the Major Research Plan Project, National Natural Science Foundation of China(Grant No.: 91230111 and 51279071); National Key BasicResearch Development Program of China (973 Program, Grant No.: 2010CB429002);Project of Science and Technology of Colleges in Ningxia, China (Grant No.:NGY2012097)

The primary purpose of this thesis is to quantify the effects of RANS turbulence modeling on the resolution of free shear vortical flows. The simulation of aerodynamic wing-tip vortices is used as a test bed. The primary configuration is flow over an isolated finite wing with aspect ratio, , and Reynolds number, . Tip-vortex velocity profiles, vortex core and wake turbulence levels, and Reynolds stresses are compared with wind tunnel measurements. Three turbulence models for RANS closure are tested: the Lumley, Reece, and Rodi full Reynolds stress transport model and the Sparlart-Allmaras model with and without a proposed modification. The main finding is that simulations with the full Reynolds stress transport model show remarkable mean flow agreement in the vortex and wake due to the proper prediction of a laminar vortex core. Simulations with the Spalart-Allmaras model did not indicate a laminar core and predicted over-diffusion of the tip-vortex. Secondary investigations in this work include the study of wall boundary layer treatment and simulating the wake-age of an isolated rotorcraft in hover using a steady-state RANS solver. By comparing skin friction plots over the NACA 0012 airfoil, it is shown that wall functions are most effective in the trailing edge half of the airfoil, while high velocity gradient and curvature of the leading edge make them more vulnerable to discrepancies. The rotorcraft simulation uses the modified Spalart-Allmaras turbulence model and shows proper, qualitative, resolution of the interaction between the vortex sheet and the tip vortex. / Master of Science

A numerical study of turbulent combustion systems was pursued to examine different computational modeling techniques, namely computational fluid dynamics (CFD) and chemical reactor network (CRN) methods. Both methods have been studied and analyzed as individual techniques as well as a coupled approach to pursue better understandings of the mechanisms and interactions between turbulent flow and mixing, ignition behavior and pollutant formation. A thorough analysis and comparison of both turbulence models and chemistry representation methods was executed and simulations were compared and validated with experimental works. An extensive study of turbulence modeling methods, and the optimization of modeling techniques including turbulence intensity and computational domain size have been conducted. The final CFD model has demonstrated good predictive performance for different turbulent bluff-body flames. The NOx formation and the effects of fuel mixtures indicated that the addition of hydrogen to the fuel and non-flammable diluents like CO2 and H2O contribute to the reduction of NOx. The second part of the study focused on developing chemical models and methods that include the detailed gaseous reaction mechanism of GRI-Mech 3.0 but cost less computational time. A new chemical reactor network has been created based on the CFD results of combustion characteristics and flow fields. The proposed CRN has been validated with the temperature and species emission for different bluff-body flames and has shown the capability of being applied to general bluff-body systems. Specifically, the rate of production of NOx and the sensitivity analysis based on the CRN results helped to summarize the reduced reaction mechanism, which not only provided a promising method to generate representative reactions from hundreds of species and reactions in gaseous mechanism but also presented valuable information of the combustion mechanisms and NOx formation. Finally, the proposed reduced reaction mechanism from the sensitivity analysis was applied to the CFD simulations, which created a fully coupled process between CFD and CRN, and the results from the reduced reaction mechanism have shown good predictions compared with the probability density function method. / Ph. D. / Turbulent combustion has been regarded as one of the most typical occurrences with industrial burners, where turbulent flow is produced by large vortex eddies when fuel and oxidizer mixes. Due to increasing demands for energy and concerns for environmental pollution, it is important to have a comprehensive understanding of turbulent combustion processes. To help provide information related to turbulent combustion, computational modeling can be used to give physical insights of the combustion process. A numerical study of turbulent combustion systems was pursued to examine different computational modeling techniques and to understand the mechanisms in terms of fluid dynamics and chemical kinetics. Computational fluid dynamics (CFD) was used to predict the flow field, including gas velocities, temperatures and fuel characteristics. Another computational technique known as the chemical reactor network (CRN) was used to provide information related to the chemical reactions and pollutant production. A method was developed as part of the study to couple the computational methods to pursue better understandings of the mechanisms and interactions between turbulent flow and mixing, ignition behavior and pollutant formation. Results have been compared with experimental data to optimize the modeling techniques and validate the developed model. The CRN model with the detailed gaseous reaction mechanism from the Gas Research Institute GRI-Mech 3.0 created a reacting network across the combustor with flame chemistry details. By post-processing the CRN results using a sensitivity analysis, the reduced reaction mechanism was summarized, which provided a promising method to generate representative reactions of the system from hundreds of species and reactions that occur in the combustion process. The proposed reduced reaction mechanism was applied to the CFD simulations, which created a fully coupled process between CFD and CRN. The results from the reduced reaction mechanism have shown good predictions compared with the probability density function method, which is a simplified way to model combustion. Pollutant emission such as NOx has also been studied in both CFD and CRN models, in terms of the effects of fuel mixtures, the formation mechanisms and influential factors as well as reactions to the formation process. The work provides guidance for an integrated framework to model and study turbulence and chemical reactions for turbulent combustion systems.

Solar energy is incident on the earth's surface in both short-wave and long-wave parts of the spectrum. The short-wave part of the spectrum is of special interest to oceanographers since the vertical distribution of temperature in the top layer of the ocean is mostly determined by the vertical attenuation of short-wave radiation. There are numerous studies regarding the temperature evolution as a function of time (see Chapter 2 for details). The diurnal and seasonal variation of the heat content (and hence temperature) of the ocean is explored in this thesis. The basis for such heat budget simulation lies in the fact that the heat budget is the primary driver of ocean currents (maybe secondary to wind effects) and these circulation features affect the biological and chemical effects of that region. The vertical attenuation of light (classified to be in the 300-700 nm range) in the top layer of the ocean has been parameterized by several authors. Simpson and Dickey (1981) in their paper have listed the various attenuation schemes in use till then. This includes a single-exponential form, a bimodal exponential form, and a spectral decomposition into nine spectral bands, each with their specific exponential functions with depth. The effects of vertical light attenuation have been investigated by integrating the light models into a 1D and a 3D turbulence closure model. The main part of the thesis is the inclusion of a bottom effect in the shallow waters. Bottom serves two purposes, it reflects some light based on its albedo and it radiates the rest of the light as heat. 1-D simulation including bottom effects clearly indicates the effect of light on the temperature profile and also the corresponding effect on salinity profiles. An extension of the study includes a 3D simulation of the heat budget and the associated circulation and hydrodynamics. Intense heating due to the bottom leads to the formation of hyper-saline waters that percolate down to depths of 50 m in the summer. Such plumes have been simulated by using a 3D numerical ocean model and it is consistent with observations from the Bahamas banks.

In this thesis study, Detached Eddy Simulation turbulence model is studied in two dimension mainly for flow over single element airfoils in high Reynolds numbers to gain experience with model before applying it to a three dimensional simulations. For this aim, Spalart-Allmaras and standard DES ,DES97, turbulence models are implemented to parallel, viscous, hybrid grid flow solver. The flow solver ,Set2d, is written in FORTRAN language. The Navier-Stokes equations are discretized by first order accurately cell centered finite volume method and solved explicitly by using Runge-Kutta dual time integration technique. Inviscid fluxes are computed using Roe flux difference splitting method. The numerical simulations are performed in parallel environment using domain decomposition and PVM library routines for inter-process communications. To take into account the effect of unsteadyness after the convergence is ensured by local time stepping technique for four order magnitude drop in density residual, global time stepping is applied for 20000 iterations. The solution algorithm is validated aganist the numerical and experimental studies for single element airfoils in subsonic and transonic flows. It is seen that Spalart-Allmaras and DES97 turbulence models give the same results in the non-seperated flows. Grey area is investigated by changing $C_{DES}$ coefficient. Modeled Stress Depletion which cause reduction of eddy viscosity is observed.

Simulation and modelling of turbulent flows under influence of streamline curvature and system rotation have been considered. Direct numerical simulations have been performed for fully developed rotating turbulent channel flow using a pseudo-spectral code. The rotation numbers considered are larger than unity. For the range of rotation numbers studied, an increase in rotation number has a damping effect on the turbulence. DNS-data obtained from previous simulations are used to perform a priori tests of different pressure-strain and dissipation rate models. Furthermore, the ideal behaviour of the coefficients of different model formulations is investigated. The main part of the modelling is focused on explicit algebraic Reynolds stress models (EARSMs). An EARSM based on a pressure strain rate model including terms that are tensorially nonlinear in the mean velocity gradients is proposed. The new model is tested for a number of flows including a high-lift aeronautics application. The linear extensions are demonstrated to have a significant effect on the predictions. Representation techniques for EARSMs based on incomplete sets of basis tensors are also considered. It is shown that a least-squares approach is favourable compared to the Galerkin method. The corresponding optimality aspects are considered and it is deduced that Galerkin based EARSMs are not optimal in a more strict sense. EARSMs derived with the least-squares method are, on the other hand, optimal in the sense that the error of the underlying implicit relation is minimized. It is further demonstrated that the predictions of the least-squares EARSMs are in significantly better agreement with the corresponding complete EARSMs when tested for fully developed rotating turbulent pipe flow. / QC 20100825

In this study, the non-equilibrium Johnson and King Turbulence Model (JK model) is implemented in a three-dimensional, Navier-Stokes flow solver. The main program is a structured Euler/Navier-Stokes flow solver in which spatial discretization is accomplished by a finite volume formulation and a multigrid technique is used as a convergence accelerator. The aim is the validation of this in-house developed CFD (Computational Fluid Dynamics) tool with this enhanced enlarged capability in order to obtain a reliable flow solver that can solve flows over swept wings accurately. Various test cases were evaluated against reference solutions in order to demonstrate the accuracy of the newly implemented JK turbulence model. The selected test cases are NACA 0012 airfoil, ONERA M6 wing, DLR-F4 wing and two wings taken from the 3rd Drag Prediction Workshop. The solutions were analyzed and discussed in detail. The results show appreciably good agreement with the experimental data including force coefficients and surface pressure distributions.

Every type of current meter is different and has its proper characteristics. Knowing the performance of a current meter is essential in order to use it properly either for field or laboratory measurements (such as in the Offshore Technology Research Center wave basin). A study of the MAVS (Modular Acoustic Velocity Sensor) in a wave basin is a first step essential for later deployment in real studies. This thesis is based on data obtained from different series of laboratory measurements conducted in the OTRC wave basin. The objective of the first part of the study was to characterize the MAVS frequency response using benchmarks such as tow tests or wave tests. These benchmarks allowed us not only to characterize the sensor but also to eventually correct some of the measurement distortions due to flow blockage, vortex shedding, or vibrations of the mounting structure, for example. After the preliminary study was done, we focused on the potential use of the MAVS in the OTRC wave basin. Indeed, in the case of a study of a scale model in the wave basin, the stresses applied to the model have to be accurately known. In the case of current-induced loads, this includes contributions from both the mean flow and the turbulence. Thus, after correcting the values measured by the MAVS, a mapping of the current jet was executed to determine its three-dimensional structure in the wave basin. Knowing the structure of the current in the OTRC wave basin, it was then possible to define a domain in which the current can be considered uniform with a certain tolerable error. This domain of uniformity will allow us to validate the use of the OTRC wave basin to study large models such as FPSOs (Floating Production, Storage and Offloading Units).

An unstructured explicit, Reynolds averaged Navier-Stokes solver is developed to operate on inviscid flows, laminar flows and turbulent flows and one equation Spalart-Allmaras turbulence modeling is implemented to the solver. A finite volume formulation, which is cell-center based, is used for numerical discretization of Navier-Stokes equations in conservative form. This formulation is combined with one-step, explicit time marching upwind numerical scheme that is the first order accurate in space. Turbulent viscosity is calculated by using one equation Spalart-Allmaras turbulence transport equation. In order to increase the convergence of the solver local time stepping technique is applied. Eight test cases are used to validate the developed solver,for inviscid flows, laminar flows and turbulent flows. All flow regimes are tested on NACA-0012 airfoil. The results of NACA-0012 are compared with the numerical and experimental data.

A three-dimensional, parallel, finite volume solver which uses Roe&#039 / s upwind flux differencing scheme for spatial and Runge-Kutta explicit multistage time stepping scheme for temporal discretization on unstructured meshes is developed for the unsteady solution of external viscous flow around rotating bodies. The main aim of this study is to evaluate the aerodynamic dynamic stability derivative coefficients for rotating missile configurations. Arbitrary Lagrangian Eulerian (ALE) formulation is adapted to the solver for the simulation of the rotation of the body. Eigenvalues of the Euler equations in ALE form has been derived. Body rotation is simply performed by rotating the entire computational domain including the body of the projectile by means of rotation matrices. Spalart-Allmaras one-euqation turbulence model is implemented to the solver. The solver developed is first verified in 3-D for inviscid flow over two missile configurations. Then inviscid flow over a rotating missile is tested. Viscous flux computation algorithms and Spalarat-Allmaras turbulence model implementation are validated in 2-D by performing calculations for viscous flow over flat plate, NACA0012 airfoil and NLR 7301 airfoil with trailing edge flap. The ALE formulation is validated in 2-D on a rapidly pitching NACA0012 airfoil. Afterwards three-dimensional validation studies for viscous, laminar and turbulent flow calculations are performed on 3-D flat plate problem. At last, as a validation test case, unsteady laminar and turbulent viscous flow calculations over a spinning M910 projectile configuration are performed. Results are qualitatively in agreement with the analytical solutions, experimental measurements and previous studies for steady and unsteady flow calculations.