An experimental investigation of the effect of heat release on the planar countercurrent reacting turbulent shear layer
Naing, Sann Myint
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The flow characteristics of planar, incompressible, reacting and non-reacting countercurrent shear layers were investigated. The primary stream velocity was fixed at U 1 =12 m/s and the suction driven secondary counter current stream U 2 was varied over 0-29% of U 1 . Scani-valve pressure measurement instrumentation was used to sample the pressure variations along the sidewall, finding that the pressure gradient was close to zero under nonreacting condition and naturally slight favorable pressure gradient under reacting conditions. The pressure varied 1.32% to 7.1% under non-reacting and reacting conditions for a secondary wall oriented at a 30 degree angle. Particle image velocimetry (PIV) was used for both non-reacting and reacting flow to acquire detailed velocity field measurements. The shear layer under non-reacting conditions experiences an 88% growth as counterflow velocities up to 30% are applied. Chemiluminescence and schlieren flow visualization were used to measure the fluctuations in the flow field and observe the behaviors of the reacting mixing layer. Overall, more wrinkling, bulging and fluctuations are pronounced at low counterflow and at slightly fuel rich conditions; an increase in the counterflow reduced the growth rate and the flame becomes more contained, but the effect has little impact in the fuel rich cases. At λ=1.62 and [varphi]=1.8, it is found that the mixing layer achieves new an instability mode where the flame starts to flap at low frequency. The spatio-temporal transition is believed to take place at 1.5<λ<1.86 and at [varphi]=1.5. Similar to the characteristics of the co-flowing shear layer, the heat release suppresses the shear layer growth rate and Reynolds shear stress.