Rapid mix concepts for low emission combustors in gas turbine engines

NASA LeRC has identified the Rich burn/Quick mix/Lean burn (RQL) combustor as a potential gas turbine combustor concept to reduce NOx emissions in High Speed Civil Transport (HSCT) aircraft. To demonstrate reduced NOx levels, NASA LeRC soon will test a flametube version of an RQL combustor. The critical technology needed for the RQL combustor is a method of quickly mixing combustion air with rich burn gases. Two concepts were proposed to enhance jet mixing in a circular cross-section: the Asymmetric Jet Penetration (AJP) concept; and the Lobed Mixer (LM) concept. In Phase 1, two preliminary configurations of the AJP concept were compared with a conventional 12-jet radial-inflow slot design. The configurations were screened using an advanced 3-D Computational Fluid Dynamics (CFD) code named REFLEQS. Both non-reacting and reacting analyses were performed. For an objective comparison, the conventional design was optimized by parametric variation of the jet-to-mainstream momentum flux (J) ratio. The optimum J was then employed in the AJP simulations. Results showed that the three-jet AJP configuration was superior in overall mixedness compared to the conventional design. However, in regards to NOx emissions, the AJP configuration was inferior. The higher emission level for AJP was caused by a single hot spot located in the wake of the central jet as it entered the combustor. Ways of maintaining good mixedness while eliminating the hot spot were identified for Phase 2 study. Overall, Phase 1 showed the viability of using CFD analyses to evaluate quick-mix concepts. A high probability exists that advancing mixing concepts will reduce NOx emissions in RQL combustors, and should be explored in Phase 2, by parallel numerical and experimental work

Modeling Supersonic Missile Fin-body Interference For Preliminary Design

Aerodynamic interference between adjacent surfaces plays an important role in the performance of missiles. Fin-body interference factors are used in the Missile Datcom method to predict missile aerodynamic characteristics using the equivalent angle-of-attack method. This investigation presents a simple, accurate, and rapid method to determine fin-body interference factors for preliminary design. Linearized potential theory is used to evaluate the effect of body upwash on the local velocity along the fin leading edge as a function of fin span. A panel method is applied to determine the change in equivalent angle of attack due to body upwash. Planar fin configurations are considered with the fins located symmetrically on the missile body; however, the results also apply to cruciform configurations. The fin-body interference factors are presented as a function of Mach number and changes in missile geometry, such as fin leading and trailing edge sweep, fin vertical position on the fuselage, and fuselage cross-sectional shape. Circular and elliptic fuselage cross sections are considered. The method is shown to be quite accurate. © 1989 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved