Geometry and Flow Influences on Jet Mixing in a Cylindrical Duct

JOURNAL OF P ROPULSION AND POWER Vol. 11, No. 3, May-June 1995 Geometry and Flow Influences on Jet Mixing in a Cylindrical Duct M. S. Hatch ,* W. A. Sowat, and G. S. Samuelscn:j: University of California, Irvine, Irvine, California 92717 and J. D . Holdeman§ NASA Lewis Research Center, Cleveland, Ohio 44135 To examine the mjxing characteristics of jets in an axisymmetric can geometry, temperature measurements were obtained downstream of a row of cold jets injected into a heated cross stream. Parametric, nonreacting experiments were conducted to determine the influence of geometry and flow variations on mixing patterns in a cylindrical configuration. Re.~ults show that jct-to-mainstream momentum-flux ratio and orifice geometry significantly impact the mixing characteristics of jets in a can geometry. For a lixed number of orifices, the coupling between momentum-flux ra tio and injector geometry determines I) the degree of jet penetration at the inj ection plane and 2) the extent of circumferential mixing downstream of the injection plane. T he resu lts also s how that, at a fixed momentum-flux ratio, jet penetration decreases with I) a n increase in slanted slot aspect ratio and 2) an increase in the a ngle of the slots with respect to the mrunstream direction. Nomenclature DR f J MODl MOD2 MOD3 MOD4 MODS MOD6 MOD7 MR promising low NOx combustor concepts is the rich-burn/quick- mix/lean-burn (RQL) combustor. 2 The RQL deve lopmental effort poses new challenges in jet mixing in a confined cross- flow. 1.~ More specifically, the range of jet-to-mainstream mass flow ratios encountered in the quick-mix region of a RQL combustor differ significantly from those of a conventional combustor dilution zone.J--' Most of the previous research of jets in a crossflow has been performed in rectangular geometries. Examples of these stud- ies are provided in Table 1 and are summarized elsewhere.6 The influence of orifice geometry and spacing, jet-to-main- stream momentum-flux ratio J, and density ratio have been documented for single- and double-sided injection (e.g., Ref. 6). These studies have identified J and orifice spacing as the most significant parameters influencing the mixing pattern. jet-to-mainstream density ratio orifice angle with respect to mainstream mixture fraction jet-to-mainstream momentum flux ratio eight-hole baseline geometry 8: l aspect ratio slanted slots, cf> == 45 deg 4: l aspect ratio slanted slots, cf> = 0 deg 4:1 aspect ratio slanted slots, cf> == 22.5 deg 4:1 aspect ratio slanted slots. = 45 deg 4:1 aspect ratio slanted slots, cf> = 67.5 deg 4: l aspect ratio slanted slots, == 90 deg jet-to-mainstream mass ratio Introduction IXING of jets in a confined crossflow has a variety of practical applications and has motivated a number of studies over the past decades. In a gas turbine combustor, e.g., mixing of relatively cold air jets is important in the dilution zone where the products of combustion are mixed with air to reduce the temperatures to levels acceptable for the turbine blade materia l. Mixing of jets in a crossflow is also important in applications such as discharge of effluents in water, and in transition from hover to cruise of V/STOL aircraft. To meet the air quality standards affecting gas turbines, low emissions combustors are being developed. ' One of the M Presented as Pape r 92-0773 at the AIAA 30lh Aerospace Sciences Meeting and Exhibit. Reno, NV, Jan. 6-9, 1992; received March 18, 1993; revision received Ju ne 2, 1994; accepted for publication July 14, 1994. Copyright© 1992 by the American Institute of Aeronautics and Astronau1ics, Inc. No copyright is asserted in 1he United States under Title 17, U.S. Code. The U.S. Governmenl bas a roya lty-free license to exercise all rights under the copyrigh1 claimed here in for Govern menta l purposes. All other rights are reserved by the copy- right owner. *Grad uate Researcher , UC! Combustion Laboratory. Student Member AIAA. tAssociate Direc1or, UCI Combuslion Laboratory. Member AIAA. *Professor. Director. UC( Combustion Laboratory. Associate Fel- low AIAA. §Senior Research Engineer. Associate Fellow AIAA. Experiment A series of parametric experiments were conducted in this study to determine the influence ofJ and orifice configuration on mixing of jets in a can geometry. The parametric experi- ments investigated a range of J values, including 25, 52, and 80. A jet-to-mainstream mass ratio of 2.2 was maintained at each tested J value. An area discharge coefficient of 0.80 was assumed in designing the orifices. The modules tested in the parametric studies were fabri- cated from a 3-in.- (76-mm-) i.d., 0.125-in.- (3.18-mm-) thick Plexiglas® tubing. Plexiglas was selected for its optical quality and ease of fabrication . For each J value, configurations with eight, equally spaced orifices were evaluated. The geometries included: 1) round holes (module 1); 2) 4:1 aspect ratio slots oriented at various angles with respect to the mainstream Oow direction: 0 deg (module 3), 22.5 deg (module 4), 45 deg (module 5) 67.5 deg (module 6), and 90 deg (module 7); and 3) 8: 1 aspect ratio slots oriented at 45 deg (module 2). The modules were 6.5 in. (165 mm) long, with the center of the o rifice row placed at one radius from the edge. The orifice area for each module at the design J value was kept constant. As a result, the dimensions of a given orifice varied as a function of J. A representative module is shown in Fig. 1. (All modules are presented in Ref. 7.) While the leading edge of each orifice was fixed at the same axial location (z/R = 0.0), the axial extent of jet mass addition varied ac- cording to orifice size and, in the case of the slots, slot angle