Transient analysis of laminar twin semi-confined jets and development of a time step optimizing fuzzy controller

Abstract

Transient laminar simulations of two parallel jets issuing into a semi-confined space were conducted. Critical Reynolds numbers were noted when two dimensional flows transitioned from a steady state symmetrical flow to the formation of secondary downstream recirculations and ultimately to transient flow. New non-dimensionalizations for Reynolds number and recirculation size are proposed which incorporate both inlet size and channel height. The effects of jet spacing on near inlet mixing in two dimensional geometries were also studied. It was seen that the majority of mixing occurred in the space between the two jets. Placing the jets along the walls of the confined space allowed for the most efficient mixing.

A time step optimizing fuzzy controller is also described. Simulations were run at three Reynolds numbers marking different transient intensities. The fuzzy controller was seen to logically modify the time step according to changes in computational signals. It is shown that a fuzzy in situ time step controller can reduce computing costs of two dimensional unsteady transient simulations.

Critical Reynolds number analysis was then extended to a three dimensional semi-confined duct with circular inlets. The growth of large recirculation zones and their effect on inflow deformation were measured under increasing Reynolds number. The confinement stifles the growth of the recirculation regions as the Reynolds number is increased, causing a deformation of the inflow circular profile. The deformation of the inflow by the recirculation zones appear to be the driving cause of instability in the three dimensional flows.