Computational analysis on fluid flow characteristics in a modified annular dump combustor of a ship

The improvement of systems of aeronautical and marine propulsion able to meet the forthcoming drastic certification requirements on the reduction of the level of pollutants emission heavily relies on the development of new concepts of combustion chamber technologies. In view of this, a novel numerical investigation has been performed on the basis of characteristics of the flow of a fluid passing over a simple annular-shaped dump combustor and a modified dump combustor with certain central restrictions like rectangular and spherical shapes. The restrictions are located at a fixed distance of 0.14 m from the inlet. Flow characteristics and patterns are presented sequentially in the form of streamline contours, velocity contour, pressure contour, axial velocity profiles, and centerline velocity profiles. The above-mentioned flow characteristics are studied at several locations in the flow field for various Reynolds numbers (Re), ranging from 103 to 106 for all considered models. The flow regulating mass and momentum conservation partial differential governing equations along the x-axis and y-axis are discretised with the help of the control volume-based finite volume approach. The SIMPLE algorithm and second-order upwind scheme are used to solve iteratively the discretised equations for the case of a fixed aspect ratio of 3 and for a central abstraction of 120 %. The analysis corroborates and concludes that more numbers of bubbles are formed in a geometrically modified dump combustor than in a plain dump combustor. Additionally, it has been found that the number of recirculating bubbles increases along with the value of the Reynolds number. Consequently, the core recirculation zone is improved, which ensures the desirable mixing of fluids in the ship combustor and helps significantly in the reduction of NOx emission and combustion residuals. Furthermore, as the Reynolds number (Re) increases, the variation in axial velocity also raises for all considered Reynolds numbers, indicating an improved chance of better mixing. At a Re of 106, the axial velocity profile reaches its peak for both the modified combustors, although at different locations. Specifically, the magnitude of the axial velocity profile is 1.05 at the position of 0.14 m for the rectangular restriction and 0.10 m for the spherical restriction. Consequently, a higher Reynolds number may be recommended for optimal mixing.