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June 1984

NASA CR–174717

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WU–505–36–22–00

NSG–3206

315

Dilution Jets in Accelerated Cross Flows

Abraham Lipshitz and Isaac Greber

Dilution jets; Reverse flow; Combustors; Jet mixing

Unclassified -Unlimited

Subject Category: 07

Case Western Reserve University

Department of Mechanical and Aerospace Engineering

Cleveland, Ohio

A14

Final report. Project Manager, Stephen M. Riddlebaugh, Aerothermodynamics and Fuels Division, NASA Lewis

Research Center, Cleveland, Ohio 44135. This report was submitted by Abraham Lipshitz as a dissertation in partial

fulfillment of the requirements for the degree Doctor of Philosophy to Case Western Reserve University in May 1981.

Results of flow visualization experiments and measurements of the temperature field produced by a single jet and a row of dilution jets issued into a

reverse flow combustor are presented. The flow in such combustors is typified by transverse and longitudinal acceleration during the passage through its

bending section. The flow visualization experiments were designed to examine the separate effects of longitudinal and transverse acceleration on the jet

trajectory and spreading rate. A model describing a dense single jet in a lighter accelerating cross flow is developed. The model is based on integral

conservation equations, including the pressure terms appropriate to accelerating flows. It uses a modified entrainment correlation obtained from

previous experiments of a jet in a cross stream. The flow visualization results are compared with the model calculations in terms of trajectories and

spreading rates. Each experiment is typified by a set of three parameters: momentum ratio, density ratio, and the densimetric Froude number. When

injection velocities are large or densities are small, the Froude number becomes very large and hence, unimportant. Therefore, the Froude number is

generally significant in describing liquid experiments but is unimportant for the gas experiments in the combustor. Agreement between test and

calculated results is encouraging but tends to become poorer with increasing momentum ratio. The temperature measurements are presented primarily in

the form of consecutive normalized temperature profiles. Some interpolated isothermal contours are also shown. The single jet trajectories are

consistently found to be swept towards the inner wall of the bend, whether injection is from the outer or the inner wall. This behavior is explained by a

drifting effect which consists of a transverse velocity component across the combustor due to the developing nature of the flow along it. Plots of lateral

temperature distributions of the jet indicate that under longitudinal acceleration conditions the thermal spreading of the jet may be completely

suppressed. Comparison between combustor experimental results and model calculations shows poor agreement due to the drifting effect which is not

taken into consideration in the model calculations. The row of jets experiments are characterized by two additional parameters: spacing ratio and

confinement parameter. The results are shown in the form of consecutive normalized temperature profiles. The confinement parameter appears to

become increasingly important with decreasing spacing ratio, in particular when its effect is enhanced by the drifting phenomenon and associated

pressure field. A tightly spaced row of jets injected from the inner wall, prior to the bend, is surprisingly kept attached to the inner wall in spite of the

strong turning. A similar attachment for a jet injected from the outer wall is not observed.