Passive mixing control via lobed injectors in high speed flow

Abstract

The near-eld ow and mixing characteristics of nonreactive lobed fuel injectors in subsonic and transonic airstreams were studied experimentally. Three alternative injector geometries were explored, two of which had lobed shapes. These lobed injectors mixed gas-phase injectant (nitrogen) and co owing air to different extents, straining uid interfaces due to streamwise vorticity generation. The experiments were conducted in a "trisonic" wind tunnel, with co owing airstream Mach numbers ranging from 0.4 to 1.2. Visualization of the downstream evolution of the injectant was achieved via planar laser-induced uorescence imaging of acetone seeded in the nitrogen. Comparisons of near-eld ow evolution, mixing properties, and scalar dissipation and strain rates were made among different injectors for the different experimental ow conditions. It was observed that lobed injector geometries produced greater near-eld mixing as well as higher effective interfacial strain rates than nonlobed injectors in the subsonic (Mach 0.4) regime, although at higher subsonic Mach numbers mixing increases were accompanied by a reduction in the effective strain rate. Flow evolution observed in the experiments was also compared with numerical simulations of vorticity evolution and rollup, with good correspondence.

A review of jet mixing enhancement for aircraft propulsion applications

“…Lobed nozzles (Fig. 1) have long been used on civil aircraft turbojet engines as jet noise suppressors and, more recently, on the core of mixed-flow turbofans to enhance thermal efficiency [25] and fuel injectors for improved combustion [26]. In both cases, they work by promoting rapid mixing of the propulsive jet with the freestream in the former case and of the core jet flow with the annular fan flow before exhausting through a common nozzle in the latter case.…”

Experimental and numerical study of mixing characteristics of a rectangular lobed mixer in supersonic flow

“…The most widely application of the lobed mixer is in the exhaust systems of turbofan engines for nozzle noise reduction (5)(6)(7)(8) , as well as for thrust augmentation and infrared radiation suppression in ejector systems (9)(10)(11) . Recently, the mixers are widely exploited in the combustion of scramjets, referred to as the petal nozzles (12,13) or lobed injectors (14)(15)(16) , to improve the molecular mixing of chemical species.…”

Mixing Enhancement in a Coaxial Jet Mixer

“…If active methods (acoustic radiation, jet oscillation, nozzle vibration and so on) require an additional energy to influence the flow, passive ones solve the same problem using the flows energy by changing initial conditions of the mixing layer formation. For this purpose nozzles of different forms (square, triangle and lobed nozzles [1][2][3][4][5][6]) and nozzles with vortex generators [1, [7][8][9][10][11] are usually used. These tools enhance mixing in comparison with round nozzles of correspondent sizes in subsonic and supersonic flows [9].…”