Simulation of Cold Flow in Cavity-Ramp Combustor

2013-10-24T00:00:00Z (GMT) by Federico Lugnani
The main objective of this thesis is the analysis of a subsonic laminar cold flow in a dump combustor. This type of combustors have gained increasing attention because of their typical flow recirculation zone after a sudden change in geometry, a feature that makes them particu- larly suitable for applications where fuel residence time is a major issue. In this sense, dump combustors have interested the scramjet community, because of extremely high flow velocities that imply extremely low time to obtain a satisfactory completion of combustion. This work adopts the three-dimensional version of Chebyshev Multidomain Spectral Method, because of its high accuracy, its appliability to complex geometries and its convenient paral- lel implementation. To create an appropriate geometry input file, a mesh generator has been implemented, focusing on the possibility of refining the grid in areas where the flow structure requires it. To provide validation for the three-dimensional version of the numerical code, after a number of problems characterized by a simple setup, a laminar subsonic flow over a backward-facing step is tested, because of its analogy to a simplified version of the dump combustor. This kind of geometry has received wide attention in the literature, which makes it ideal to implement also a new type of boundary condition. Transmissive boundary conditions have been programmed and tested, believing that such type of boundary is more convenient than those already programmed. As a final flow geometry, the backward facing step is modified to assume the typical shape of a dump combustor, so that the main interest of this thesis is pursued. The main scope of this analysis is on the flow features in the cavity and in the proximity of geometrical discontinuities, with different Reynolds numbers, and also with different types of outflow boundary conditions.

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