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Easom, Gary
Languages: English
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arxiv: Physics::Fluid Dynamics
The fundamental errors in the numerical modelling of the turbulent component of fluid flow are one of the main reasons why computational fluid dynamics techniques have not yet been fully accepted by the wind engineering community. This thesis is the result of extensive research that was undertaken to assess the various methods available for numerical simulation of turbulent fluid flow. The research was undertaken with a view to developing improved turbulence models for computational wind engineering. Investigations have concentrated on analysing the accuracy and numerical stability of a number of different turbulence models including both the widely available models and state of the art techniques. These investigations suggest that a turbulence model, suitable for wind engineering applications, should be able to model the anisotropy of turbulent flow as in the differential stress model whilst maintaining the ease of use and computational stability of the two equation k-e models. Therefore, non-linear expansions of the Boussinesq hypotheses, the quadratic and cubic non-linear k-e models, have been tested in an attempt to account for anisotropic turbulence and curvature related strain effects. Furthermore, large eddy simulations using the standard Smagorinsky sub-grid scale model have been completed, in order to account for the four dimensional nature of turbulent flow. This technique, which relies less heavily on the need to model turbulence by utilising advances in computer technology and processing power to directly resolve more of the flow field, is now becoming increasingly popular in the engineering community. The author has detailed and tested all of the above mentioned techniques and given recommendations for both the short and longer term future of turbulence modelling in computational wind engineering. Improved turbulence models that will more accurately predict bluff body flow fields and that are numerically stable for complex geometries are of paramount importance if the use of CFD techniques are to gain wide acceptance by the wind engineering community.
  • The results below are discovered through our pilot algorithms. Let us know how we are doing!

    • 3. Solution Procedures and Numerical Analysis 3.1 - Introduction. ……………………………………………… 3.2 - The Navier-Stokes Equations. ……………………… 3.3 - The Reynolds Stresses. ……………………………… 3.4 - Common Discretisation Schemes. ……………………… 3.5 - Common Differencing Schemes - Discretisation of the Convection Term. ……………………………… 3.5.1 - The Central Differencing Scheme. ……………………… 3.5.2 - The Upwind Differencing Scheme. ……………………… 3.5.3 - The Hybrid Differencing Scheme. ……………………… 3.5.4 - The QUICK Differencing Scheme. ……………………… 3.5.5 - The CCCT Differencing Scheme. ……………………… 3.6 - Calculation of the Flow Field and Pressure Equation. ……. 3.6.1 - Solving the Simultaneous Equations. ……………………… 3.7 - Summary. ………………………………………………
    • 4. Turbulence Modelling 4.1 - Introduction. ……………………………………………… 4.2 - Reynolds Averaged Navier-Stokes Equations. ……………………………………… 4.2.1 - The Eddy Viscosity Concept. ……………………………… 4.2.2 - The Mixing Length Model. ……………………………… 4.2.3 - The Standard k - e Turbulence Model. ……………… 4.2.3.1 - Discussion. ……………………………………………… 4.2.4 - The Low Reynolds number k - e Turbulence Model. ……. 4.2.5 - The k - w Equation Model. ……………………………… 4.2.6 - The Renormalisation Group (RNG) k-e Turbulence Model. ……………………………… 4.2.6.1 - Discussion. ……………………………………………… 4.2.7 - The Differential Stress Equation Model (DSM). ……… 4.2.7.1 - Discussion. ……………………………………………… 4.2.8 - The Algebraic Stress Model. ……………………………… 4.2.8.1 - Discussion. ……………………………………………… 4.3 - Turbulent Wall Boundary Conditions. ……………… 4.3.1 - The Linear Sub-Layer. ……………………………… 4.3.2 - The Log Law Layer. ……………………………………… 4.4 - Alternatives to the Navier-Stokes Equations.……………… 4.4.1 - Chaos. ……………………………………………………… 4.4.2 - The Discrete Vortex Method. ……………………………… 4.5 Summary. ………………………………………………
    • 5. Developments in Turbulence Modelling 5.1 - Introduction. ……………………………………………… 5.2 - The MMK k - e Turbulence Model. ……………………… 5.3 - Two Layer Turbulence Models. ……………………… 5.3.1 - Discussion. ……………………………………………… 5.4 - Revisions to the Boussinesq Hypothesis - The Non-Lineark-e Model. ……………………………… 5.5 - Wall Reflection Terms / The Pressure Strain Relationship for the Differential Stress Model. ……… 5.5.1 - Theory. ……………………………………………… 5.5.2 - Modelling. ……………………………………………… 5.6 - Direct Numerical Simulation. ……………………… 5.7 - Large Eddy Simulation. ………………………………
    • 6. Results: A Comparison of Data Obtained from Both CFD Simulations and Full Scale Experimental Studies.
    • 8.1 - Introduction. ………………………………………………… 128 8.2 - Conclusions. ……………………………….………………………….. 128 8.3 - Recommendations for Future work. …..………………………….. 131
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