Controlling Volumetric Heat Release Rates in a Dump Combustor Using Countercurrent Shear

Abstract

Research carried out in a backward-facing step combustor burning prevaporized JP10-air mixtures has examined the implementation of counterflow as a means to enhance turbulent combustion and increase volumetric heat release rates. The combustor is characterized by a nominally two-dimensional primary flow of lean reactants entering a rectangular channel before encountering a 2:1 single-sided step expansion. A secondary flow is created via suction at the dump plane as a fluidic control mechanism to enhance the naturally occurring countercurrent shear layer caused by separation. Counterflow is shown to elevate turbulence levels and volumetric heat release rates downstream of the step while concomitantly reducing the scale of the recirculation zone. Modifications to the rearward-facing step geometry are investigated using particle image velocimetry under isothermal flow conditions in an effort to extend the near-field interaction between the recirculation zone and the incoming primary flow, further exploiting the benefits of counterflow. Relative heat release rates quantified using chemiluminescence are shown to increase by 70% with a counterflow level of 6% of the primary mass flow rate in the step geometry, and by 150% when 3.5% counterflow is introduced into a modified step geometry.