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Technical Memorandum

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National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135–3191

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Available electronically at http://gltrs.grc.nasa.gov/GLTRS

June 1991

NASA TM–104411

AIAA–91–2460

E–6238

WU–537–02–21–00

22

A03

A CFD Study of Jet Mixing in Reduced Flow Areas

for Lower Combustor Emissions

C.E. Smith, M.V. Talpallikar, and J.D. Holdeman

Dilution; Can; Emissions; Jet mixing flow; Gas turbines; Combustion chamber

Unclassified -Unlimited

Subject Category: 07

Prepared for the 27th Joint Propulsion Conference cosponsored by the AIAA, SAE, ASME, and ASEE, Sacramento,

California, June 24–27, 1991. C.E. Smith and M.V. Talpallikar, CFD Research Corporation, Huntsville, Alabama 35805

(work funded by NASA Contract NAS3–25967). J.D. Holdeman, NASA Lewis Research Center. Responsible person,

J.D. Holdeman, (216) 433–5846.

The Rich-burn/Quick-mix/Lean-burn (RQL) combustor has the potential of significantly reducing NOx emissions in

combustion chambers of High Speed Civil Transport (HSCT) aircraft. Previous work on RQL combustors for industrial

applications suggested the benefit of “necking down” the mixing section. In this study, a 3D numerical investigation was

performed to study the effects of neckdown on NOx emissions and to develop a correlation for optimum mixing designs in

terms of neckdown area ratio. The results of the study showed that jet mixing in reduced flow areas does not enhance

mixing, but does decrease residence time at high flame temperatures, thus reducing NOx formation. By necking down the

mixing flow area by four, a potential NOx reduction of sixteen-to-one is possible for annular combustors. However, there is

a penalty that accompanies the mixing neckdown: reduced pressure drop across the combustor swirler. At conventional

combustor loading parameters, the pressure drop penalty does not appear to be excessive.