Cold-flow patterns and mixing index behind/near rifled bluff-body frustums

Abstract

Rifled fillisters milled on cannular frustums were utilized to increase turbulence intensity (T.I.). Four configurations of unrifled, inner-rifled, outer-rifled, and two-faced rifled frustums were utilized to increase T.I. and mixing index (η). The mixing indices were calculated by measuring the concentrations of carbon dioxide ( $$ C_{{{\text{CO}}_{ 2} }} $$ ) and oxygen ( $$ C_{{{\text{O}}_{ 2} }} $$ ) behind the pure-jet nozzle and bluff-body frustums. The riled helical fillisters intensify the interaction and mixing between central flow and annular-air flow. Flow characteristics behind the pure-jet nozzles and bluff-body frustums were analyzed by smoke-wire flow visualization, vortex-shedding anemometry, and gas analyzer. The smoke-streak flow patterns behind the pure-jet nozzle were characterized by jet-flow and vortex-shedding patterns. Three flow patterns of jet-flow, recirculation-flow, and turbulent-flow were characterized behind the bluff-body frustums. The experimental results showed that Strouhal number (St) increases with T.I., and high central-jet Reynolds number (Re c) induces a low St. The $$ \eta_{{{\text{CO}}_{ 2} }} $$ increases with T.I. and the maximum $$ \eta_{{{\text{CO}}_{ 2} }} $$ of 64 % occurs behind the two-faced rifled frustum when T.I. = 4.5 %. The $$ \eta_{{{\text{O}}_{ 2} }} $$ increases with T.I., and $$ \eta_{{{\text{O}}_{ 2} }} $$ has maximum of 98 % occurring behind the two-faced rifled frustum when T.I. = 3.5 %. .