On the mechanisms of secondary flows in a gas vortex unit

Abstract

The hydrodynamics of secondary flow phenomena in a disc‐shaped gas vortex unit (GVU) is investigated using experimentally validated numerical simulations. The simulation using ANSYS FLUENT® v.14a reveals the development of a backflow region along the core of the central gas exhaust, and of a counterflow multivortex region in the bulk of the disc part of the unit. Under the tested conditions, the GVU flow is found to be highly spiraling in nature. Secondary flow phenomena develop as swirl becomes stronger. The backflow region develops first via the swirl‐decay mechanism in the exhaust line. Near‐wall jet formation in the boundary layers near the GVU end‐walls eventually results in flow reversal in the bulk of the unit. When the jets grow stronger the counterflow becomes multivortex. The simulation results are validated with experimental data obtained from Stereoscopic Particle Image Velocimetry and surface oil visualization measurements. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 1859–1873, 2018

An experimental and numerical study of the suppression of jets, counterflow, and backflow in vortex units

“…A smaller slot angle also results in the presence of smaller (or no) jets (and consequently, smaller counterflow region) in the unit, which subsequently reduces or eliminates the counterflow region. A detailed computational analysis of this phenomenon has already been by provided by Niyogi et al Less inclined inlet slots give smaller intensity jets. The smaller the counterflow region, the faster it disappears.…”

“…From the work of Niyogi et al, it is observed that jet formation can result in the presence of a counterflow region in the unit. The size of the counterflow region depends on the slot inclination.…”

“…Swirl decay due to the exhaust wall friction generates an adverse pressure gradient along the exhaust line resulting in an extended backflow. The latter is discussed in more detail by Niyogi et al…”

“…This research has led to demonstrating various remarkable flow features in these devices. In gas vortex units (GVUs), primary and secondary flow patterns like jets, recirculation, and backflow were observed . For gas–solid vortex units (GSVUs), minimum and maximum solids capacities have been predicted based on a dimensional analysis of various data from literature.…”

“…Along with these jets, the gas flow inside the unit also has secondary flow features . The central gas exhaust and the pressure reversal in the exiting gas result in a backflow region in the exhaust pipe.…”