Experimental Studies on Co-flowing Subsonic and Sonic Jets

Abstract

Effect of an annular co-flow jet on the center jet at subsonic, correctly expanded and underexpanded sonic conditions was studied experimentally. It is found that the co-flow retards the mixing of the primary jet, leading to potential core elongation. The characteristic decay of the jet is also retarded in the presence of co-flow. With co-flow core length elongation of 40% and 80% were achieved for correctly expanded and underexpanded (NPR 7) sonic jets, respectively. Shadowgraph pictures show that the co-flow is effective in preserving the shock-cell structures of the inner jet, making the jet to propagate to a greater axial distance which otherwise would have decayed faster. NomenclatureD inner nozzle (primary) exit diameter M local Mach number M e jet Mach number NPR nozzle pressure ratio P a atmospheric pressure P b backpressure 116 Flow Turbulence Combust (2011) 87:115-132 P 0 stagnation chamber pressure P t pitot pressure R co-ordinate along jet radial direction X co-ordinate along jet axis Y co-ordinate along transverse direction Z co-ordinate along normal direction

Numerical Characterization of Lip Thickness on Subsonic and Correctly Expanded Sonic Co-flowing Jets

“…The primary jet potential core length (PCL) is defined as the axial extension until the primary exit nozzle velocity prevails for subsonic jets. 14) Figure 6 plots centerline total pressure variation for lip thickness 0:2D p co-flowing jet, Mach 0.6, for the seven different turbulence models and for the experiment. It is evident that the SA model produces data that agrees well with the experimental data, consistent with its advantage in predicting the flow field characteristics, and the k-¾ standard model decays slower than the experiment in the characteristic decay region.…”

“…This is because co-flow protects the main jet from interacting with the atmosphere thereby inhibiting mixing. 14) For lip thicknesses 1.0D p and 1:5D p , core length gets shortened up to 2.8D p and 2:4D p with a percentage reduction of 68 and 72% compared to lip thickness 0:2D p , respectively, due to the formation of the recirculation zone. The effect of lip thickness is well pronounced both in the potential core and characteristic decay region.…”

“…Hence, even in the far-field, the co-flowing jet with lip thickness 0:2D p possesses more kinetic energy compared to a single jet. 14) This implies that co-flow, with relatively lower values of lip thickness, inhibits the jet mixing of the main jet both in the near and far fields significantly.…”

“…For compressible co-flowing jets with small values of lip thickness, say a lip thickness of 0.7 mm, an 80% increase in potential core length was obtained when compared to a single jet. 13) Lovaraju and Rathakrishnan 14) experimentally studied co-flowing jets with a lip thickness 2.65 mm, and reported that co-flow inhibits mixing compared to the single jet at high subsonic and sonic underexpanded levels. The characteristic decay region of the central jet was also retarded in the presence of co-flow.…”

Investigation of the influence of co-flow velocity ratio on a compressible plane jet exhausting into parallel streams

“…Deo et al [28] investigated experimentally the effect of the initial conditions on the turbulent plane jet. Lovaraju and Rathakrishnan [24] studied experimentally the effect of coflow jet on the centered subsonic and sonic jets and observed that the co-flow is effective in preserving the shock-cell structure of the inner jet. Sandberg et al [29] computed two-dimensional compressible pipe flow into a co-flow with direct numerical simulation and demonstrated self-preserving behavior of turbulence statistics at nozzle exit.…”