Planar imaging of jet mixing in crossflow

Abstract

AUNIQUE experiment has been developed for the study of jet mixing in crossflow. The scalar mixing of a round jet discharging normally into a ducted flow is studied through planar nephelometry. Simultaneous, multiple-point fluid concentration measurements are made for a variety of flow conditions in a simulated gas turbine combustor. The field measurements are in good agreement with the point-to-point measurements of other investigators. The potential for studying more practical, multijet configurations is evident. Contents Jet engine turbine lifetimes depend critically on the gas temperature distribution at the turbine inlet. The gas leaving the combustor primary zone must be cooled and the temperature profile flattened in order to preserve turbine integrity. Cooling is usually achieved by injecting compressor discharge air normal to the hot flow through holes in the combustor liner. The size, geometry, and location of these holes control the combustor exit temperature distribution. An improved understanding of mixing in crossflow is, therefore, of significant practical importance. A new approach to studying mixing in crossflow is described below. A generic experiment consisting of planar digital imaging of a single round jet discharging into a uniform crossflow is described. The study of more complex, multijet configurations is in progress. Experiment The configuration chosen for study represents a sector of an annular gas turbine combustor. In these initial experiments, the geometry and flow conditions at the boundaries are simplified to facilitate the interpretation of the data and to allow comparison of the results with those of other investigators. The apparatus is shown schematically in Fig. 1. The working section consists of three parallel contiguous ducts of rectangular cross section, simulating a sector of an annular gas turbine combustor. Sector width is 30.5 cm. The inner combustor duct is 10 cm high, and side viewing is allowed through a 30.5 cm X 10 cm x 0.16 cm pyrex window. The outer ducts, which supply the injectant gas and simulate gas turbine combustor shroud passages, are each 2.54 cm high and fed by a two-dimensional 2:1 ratio contraction nozzle to provide a more uniform approach flow. These are separated from the inner duct (combustor) by removable 3-mm-thick flat-plates. The injectant is fed to the combustor through holes of various sizes and shapes that are machined into the plates. In the present experiment, the injectant (air) was fed through a single round hole in the upper plate only. The hole was beveled inward at 40 deg and brought to a sharp edge at the discharge plane. The jet velocity was varied independently of the shroud velocity by regulating pressure drop across the