A Study of Cold and Combusting Flow Around Bluff-Body Combustors

Abstract

The results from visual observations and measurements of flows over axisymmetric conducted, and vertically mounted bluff-body combustors are presented for low Reynolds number. The flow visualization is accomplished by adding TiCI₄ vapor into the central gaseous propane jet for cole reacting and combusting flows, or by injecting TiCI₄-N₂ mixture into the flow field behind bluff-body combustors through a probe for pure annular air jet. Vertical laser light sheets provide a remarkably detailed visualization of the dynamic structures in the recirculating zone behind the bluff-body combustors. For the pure annular air jet, an analytical expression was used to correlate the experimental data for the length of the recirculating zone as a function of annular Reynolds number This expression is used in the laminar, transitional and fully turbulent regimes. For the cold reacting flow, another analytical expression is used to correlate the experimental data for the axial location o Forward stagnation point as a function of flow conditions at the nozzle exit as well as the nozzle diameters. The introduction of the central jet into the flow enlarges the recirculating zone. For the combusting flow, the annular vortices in the recirculating zone appear more organized, stationary and intense for attached flames compared to the cold reacting flows. The size of the recirculating zone and the height of the central jet are reduced by at least half. For the detached flame, the height of the centra jet is greatly reduced; whereas the length of the recirculating zone is increased slightly, when comparer to corresponding cold flow. The detached flame well reattach if the central jet velocity (propane) is increased. Photographs are presented to reveal the structures of the recirculating zones for the three different kinds of flows.