Comparative studies on flow control in rectangular S-duct diffuser using submerged-vortex generators

The paper presents an effective design of a passive-type submerged-vortex generator (SVG) and uses it in rectangular S-duct diffuser in different combination to establish its effectiveness in improving the flow pattern. Because of high curvature (45°/45°), S-duct diffuser remains a challenging task to engineers for controlling flow separation. Experiments were performed with bare S-duct diffuser (i.e., duct without SVG) as well as duct with SVG for limited combinations. A finite-volume technique based commercial CFD code using RNG k–εk–ε turbulence model has been used to study the effectiveness of SVG installed at the various locations inside the duct.The geometry of the SVG is simpler and easy to fabricate as compared to ‘wishbone’ and ‘doublet’ type vortex generators reported in literature. The combination of SVG proved pretty effective in controlling flow distortion at the duct exit. The performance parameters like static pressure recovery coefficient (CSPCSP) and total pressure loss coefficient (CTLCTL), depict that the 3 SVG pairs attached to both the sidewalls at plane-4 offers the best performance (27.26% increase in CSPCSP and 14.58% reduction in CTLCTL) among all configurations tested including the bare duct. The said configuration also exhibits a considerable decrease in distortion coefficient (∼27%), a drop in non-uniformity index (∼24.58%) and a reduction in momentum thickness (∼61.54%) with respect to the bare S-duct diffuser near the exit (plane-5).