
Accession Number : AD0718121
Title : A Theoretical Investigation of a Circular Lifting Jet in a CrossFlowing Mainstream.
Descriptive Note : Final rept. Jul 69Dec 70,
Corporate Author : LOCKHEEDGEORGIA CO MARIETTA
Personal Author(s) : Hackett,James E. ; Miller,H. Ronald
Report Date : JAN 1971
Pagination or Media Count : 60
Abstract : Finiteelement potentialflowmodeling theoretical techniques are described which predict, from first principles, both the rolledup geometry and the path of a round lifting jet convergent into a crossflowing mainstream, as on VTOL or direct liftassisted STOL aircraft. Starting with a straightcylinder geometry, 'point' vortex elements are perturbed using a pre dictorcorrector stepping method to give a first estimate of the bentback shape, using assumed circulation values. A collocation scheme is next used to revise the circulation values, and after three or four iterations, a final exitplane pressure distribution may be calculated. The faninduced total pressure rise is simulated by injecting vortex rings at a chosen position in th duct which feeds the jet. Since the scope of the method is entirely nonviscous, separations toward the rear of real jets and the associated pressure changes are not simulated and basepressure type of pressures cannot be expected. Nevertheless, for forward speed ratios of 0.1, 0.2, 0.3 and 0.4, the lowpressure contours at each side of the jet do show an increasing rearward shift, just as is found experimentally. Somewhat surprisingly, the simulated plumes were more stable at higher velocity ratios. At lower forward speeds, there was a tendency to flap, rather like a hose end when freed. It is anticipated that, if viscous effects were simulated, these motions might damp out. (Author)
Descriptors : (*VERTICAL TAKEOFF AIRCRAFT, *LIFT), (*JETS, LIFT), MATHEMATICAL PREDICTION, THEORY, PRESSURE, VORTICES, POTENTIAL THEORY
Subject Categories : Aerodynamics
Fluid Mechanics
Distribution Statement : APPROVED FOR PUBLIC RELEASE