Computational Fluid Dynamics Simulation

Objective: ATEX certification of turbine enclosure chamber for fire and safety.

Background: A full-scale model of enclosure chamber was considered and fluid volume was extracted from CAD file. A tet-prism mesh was considered adequate for capturing boundary layer effects and was generated using ICEM-CFD. A y+ value of 30-150 was maintained for a selection of k-epsilon turbulence model with wall functions where natural convection flow was simulated using FLUENT solver.

Results & Conclusion: A series of simulations were conducted such as cold flow, hot flow, tracer gas and gas leak analysis. Concentrations of hazardous gasses were observed and trapping zones of these gasses were identified. In order to obtain ATEX certification for safe operations containment plan was necessary. Therefore, venting of these hazardous gasses was proposed of potential problematic zones along with placements of early warning gas detectors. As a result, these enclosures were ATEX certified.

Objective: Assessment of Secondary Air System (SAS) of a gas turbine for cooling ventilation and bearing load balancing.

Background: More than 50 inter turbine cavities were analyzed from various engine lines by Rolls-Royce. In all these cavities the basic geometry was developed by extracting the right features from 2D CAD and 3D features such as nozzles, boreholes, and offtakes were introduced in a periodic sector model basing on details of 3D features. The resulting periodic model was meshed using tetrahedral cells and prismatic elements were created on all the wall boundaries using ICEM-CFD. Turbulent flow was then simulated using k-epsilon turbulence model with standard wall functions in FLUENT. In order to maintain the right pressure balance in the cavity, one pressure outlet boundary condition was used with the definition of reference pressure at the boundary and then other boundary conditions were specified as pressure inlet/outlet and mass flow inlet. The compressible flow in the cavities was simulated with appropriate convergence as per the best practices and was checked once the solution was obtained. These analyses included steady and unsteady flows and depended on the nature of vortex shedding by the 3D features and also by the whirling nature of the flow.

Results & Conclusion: This was a long-term project with individual tasks ranging from 3 to 6 months. The flow analysis provides an understanding of the complex flow in high speed rotating disc where there are regions of stagnant flow. This analysis also provides an understanding of metal shielding from the hot air or if the cavities are ventilated enough to flush the oil or oil vapors as this may catch fire and could result in engine shut down. Furthermore, estimates of cooling air were made that bypasses the cavities and used for blade cooling and pressurization.

Objective: Development of transfer functions for simplified pipe layout in Oil & Gas industry.

Background: A DoE approach was used to select the right set parameters and to come up with various dominant physical features of the pipes in terms of its diameter. A hexahedral mesh type was chosen that is exactly the same for all the different pipe bends. The mesh was generated with near wall mesh resolution and k-omega SST turbulence model was used for wall shear prediction to the desired accuracy. FLUENT solver was used for conducting the analysis and ICEM-CFD for grid generation.

Results & Conclusion: Most accurate loss prediction was achieved and various flow features were captured such as flow swirling and recirculation zones. This data was then used to develop transfer function that is currently used as a tool in the piping industry.

a. A generic 3D model for the hull/keel of the ship was prepared in Auto Cad.

b. The mesh was prepared in Fluent mesh (tetrahedral), ensuring sufficient no of nodes (60000+) and faces.

c. In Ansys Fluent the air cavity around the hull is provided as a ‘patch’.

d. Reynolds number of lower than 1000, hence laminar fluid dynamic simulations were performed.