Turbulence Modeling for CFD

A computational fluid dynamics (CFD) model of fully developed turbulent flow in a pipe is implemented with the help of StarCCM+ software and the variation of axial velocity and skin friction coefficient along the length of pipe is analyzed. The fluids used for this purpose are air and water. The results obtained computationally are compared with the results obtained analytically.

For a turbulent case of air, the centreline velocity for a fully developed region is around 1.19m/s while the value calculated analytically is 1.22m/s. Similarly, for the turbulent case of water, the value of centreline velocity for fully developed region according to figure 4 is 0.061m/s while the value obtained analytically is equal to 0.06122m/s.  Similarly, for the fully developed turbulent flow of air and water, the value of skin friction coefficient comes out to be 0.01 and 0.009 respectively while the values obtained computationally are 0.00795 and 0.01.

 It is also observed from the results that the axial velocity against the position of centreline also reveal that the axial velocity increases along the length of pipe and after some distance, it becomes constant which is in conformity to the results obtained experimentally. The results of the skin friction coefficient against the position of centreline also reveal that the skin friction decreases along the length of pipe and after some distance, it becomes constant which is in conformity to the results obtained experimentally.

In this study CFD simulation numerical analysis of fluid flow in a pressure vessel, having annular flow paths is carried out using finite volume scheme. Such turbulent fluid flow path and geometry is encountered in many applications like in heat exchangers, power plants, and pressure vessels. Determination of flow and temperature field and the change of thermal characteristics with the inlet water are of particular interest for design and safety of the vessel. The work involved developing computer code (in Fortran90) for obtaining flow field for two-dimensional flow model of the actual problem, wherein fluid flow from the bottom of the vessel upwards and gets distributed through different flow paths and fluid after reaching a pre-defined zone joins with large pool. The problem was solved by a finite volume method. The solution methodology involves a semi-implicit iterative algorithm (SIMPLE).

The CFD simulation results were used to identify the stagnation region in the vessel and improve upon the design.

To analyze the performance change of the combined VAWTs of different types compared to single VAWT.

The CFD analysis of the performance of the turbines using the turbulence modeling like RANS as well as LES in a commercial code STAR-CCM+

The LES turbulence model seems to be giving a good approximation of the forces, moments, as it computes instantaneous flow field that involves eddies with smaller length and time scale.

Savonius rotor increases the static torque of the Darrieus rotor which helps in quick initial rotation of the combined Savonius-Darrieus rotor turbine. However, after gaining the full rotational speed, its performance of the power output must be studied. It comes out that, for the 5% interference, the power output of one of the synchronized rotor increases by 62.78% compared to that of the single rotor when operated separately, and that for 11% interference, power increases by 72.97%, but it gives 49% rise in the case of 16% interference.

Simulation Objective: Thermosolutal buoyancy opposed free convection of a binary Ostwald-De Waele fluid

The Modified Marker and Cell (MMAC) method is used for obtaining the numerical solution of the governing equations (in-house developed code). A gradient-dependent consistent hybrid upwind scheme of second order (GDCHUSSO) is used for the discretization of the convective terms.

Heat and mass transfer and stability for a different arrangement of an active surface was studied for different power-law index and their effect on stability at critical buoyancy ratio is delineated.