Spray characteristics of swirl coaxial injector and its modeling

The spray characteristics of swirl coaxial injector was investigated experimentally, and the spray formation model was made using the theoretical analysis of liquid film flow on the inner wall of center post of the injector and the breakup model of liquid film. The liquid film thickness at the injector exit was measured using contact needle probe. The liquid film flow on the inner wall of the injector was analyzed theoretically. The empirical equations of the sheet breakup length and the sheet cone angle were deduced, and they were compared with the measurements. The liquid sheet breakup model was made using analyzed film thickness and sheet cone angle. The spray characteristics of liquid sheet injected from swirl coaxial injector were measured using the phase Doppler particle analyzer, and were compared with the numerical simulations. Nomenclature a* constant in eq.(l9) bconstant in eq.(l9) Cconstant in eq.(2l) dc diameter of gas core at liquid inlet as shown in Fig.2 de exit diameter of center post as shown in Fig.2 D constant in eq.(22) Ds2 Sauter mean diameter Econstant in eq.(23) hliquid film thickness as shown in Fig.2 * Professor, Faculty of Science and Technology, Member AIAA § Graduate Student, Faculty of Science and Technology H Head, Kakuda Research Center, Senior Member AIAA # Researcher, Kakuda Research Center Copyright © 2001 The American Institute of Aeronautics and Astronautics Inc. All rights reserved. h average liquid film thickness ho liquid film thickness at center post exit as shown in Fig.2 hiliquid film thickness at liquid inlet as shown in Fig.2 k^ cavity factor (=dc/de) Katomizer constant Llength of center post as shown in Fig.l Lbu breakup length of injected liquid sheet Mmass flow rate Pinjection pressure Qliquid volume flow rate per unit width Re Reynolds number defined by eq.(lO) u liquid velocity in x-direction Uliquid surface velocity in axial direction Uo liquid injection velocity at center post exit Ud droplet velocity Uiconstant liquid axial velocity at x=0 as shown in Fig.2 Ur relative velocity between air and liquid vliquid velocity in y direction xcoordinate along liquid stream line as shown in Fig.2 xo x at point where laminar boundary layer reaches film surface as shown in Fig.2 xt x at point where transition of boundary layer from laminar to turbulent occurs as shown in Fig.2 y coordinate perpendicular to x axis as shown in Fig.2 zcoordinate in axial direction (origin is at x=0) Zdistance from injector exit Greek Symbol asheet cone angle at z^O OCRsheet cone angle at z=L v kinetic viscosity 0: azimuthal angle as shown in Fig.l pdensity a surface tension t,'wave amplitude at liquid film breakup £o initial wave amplitude Subscript g gas 1 liquid American Institute of Aeronautics and Astronautics (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. Nitrogen l 34> 0.81