A study on a lobed jet mixing flow by using stereoscopic particle image velocimetry technique An experimental investigation of the non-reactive mixing processes associated with a lobed fuel injector in a coflowing air stream is presented. The lobed fuel injector is a device which generates streamwise vorticity, producing high strain rates which can enhance the mixing of reactants while delaying ignition in a controlled manner. The lobed injectors examined in the present study consist of two corrugated plates between which a fuel surrogate, CO 2 , is injected into coflowing air. Acetone is seeded in the CO 2 supply as a fuel marker. Comparison of two alternative lobed injector geometries is made with a straight fuel injector to determine net differences in mixing and strain fields due to streamwise vorticity generation. Planar laser-induced fluorescence ͑PLIF͒ of the seeded acetone yields two-dimensional images of the scalar concentration field at various downstream locations, from which local mixing and scalar dissipation rates are computed. It is found that the lobed injector geometry can enhance molecular mixing and create a highly strained flowfield, and that the strain rates generated by scalar energy dissipation can potentially delay ignition in a reacting flowfield.

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.

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