An analysis of the exhaust diffuser section of a gas turbine is presented by incorporating the reduced order mathematical model "actuator disc concept" that represents the last stage of the turbine. The actuator disc model is one of the simplified numerical methods for analyzing the aerodynamic performance of axial turbine stage. In which, the rotor and the stator of the turbine stages are modeled as zero thickness discs with a specified blade speed and zero speed respectively. Finite volume based commercial CFD package ANSYS FLUENT was employed for the numerical investigation of the applicability of the proposed simplified model. The compressible Navier-Stoke equations along with k- turbulent model were solved in the computational domain by incorporating suitable boundary conditions. The implementation of actuator disc boundary conditions is described in detail. The numerical results obtained from the proposed model are in good agreement with the experimental data available in the literature. The effect of casing angle on the performance of diffuser is presented.
Aerodynamic aspects of train shapes suitable for Vacuum Tube Train System are investigated in this paper. Three feasible geometries for the vacuum tube train system have been considered and modelled in three dimensions and have been computationally studied using the commercial software Ansys Fluent. Aerodynamic drag loads on these geometries have been calculated under different tube pressures and speeds of the train, which provide insight on various operating parameters that need to be considered while designing the vacuum tube train system. The present computational research shows that, the suitable vacuum pressure, and different shapes of head and tail of the train have significantly effects the drag force of the vacuum train in the tunnel. Overall, the elliptical train shape with a height to base ratio of 2:1 is more efficient for aerodynamic drag reduction of the vacuum tube train at the vacuum tube pressure of 1013.25 Pa.
A proper design of exhaust hood geometry is very much essential in order to improve the overall efficiency of the steam turbine plant. The geometry of the non-axisymmetric exhaust hood makes the fluid flow at the exit of the steam turbine to be radially and circumferentially non-uniform. This work involves computational simulation of steam turbine asymmetric exhaust hood flows by incorporating the actuator-disc concept. The ANSYS FLUENT, finite volume based CFD solver is used for the present computational study. In the present simulation, the implementation of actuator disc boundary conditions with and without tip leakage is described in detail. The Actuator disc model approach exhibits a similar steam turbine exhaust hood flow asymmetry and static pressure recovery compared with the results reported in the literature, highlighting the applicability of the present model in coupling the rotor tip leakage jet with the steam turbine hood flow structure with less computational effort.
This paper presents a detailed literature review on the studies carried out in the last three decades, for understanding the factors affecting the performance of the ejector. An ejector is one of the important components in many industrial applications in the field of refrigerant expansion, circulation of fluids, vacuum creation, etc. From the analysis of the reported works of the ejector, the CFD modeling has proved to be a convenient method for analyzing the complex phenomenon in the ejector like mixing process, turbulence characteristics, shock interactions, and condensation process. The first part of this paper discusses the operation of ejector, flow structure, parameters required for the computational modeling, governing equations, etc. The second part discusses the influence of geometrical parameters and various operating conditions on the ejector performance. The shape and position of shock waves in the ejector for various operating conditions are also narrated under the same section. Third part of this paper is devoted to discussions on advances in modeling to be considered for the performance improvement of ejectors. Finally, the paper concludes with clear guidelines for the effective ejector modeling. Future scope of ejector research, pathways to progress, etc., mentioned in the conclusion section should help researchers and designers in this field.
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