Theoretical Solutions for the Jet Flap Diffuser

Citation

Morel, Jean-Pierre Georges (1969) Theoretical Solutions for the Jet Flap Diffuser. Engineer's thesis, California Institute of Technology. doi:10.7907/Y75H-MC77. https://resolver.caltech.edu/CaltechETD:etd-11152005-140840

Abstract

This study proposes a jet sheet as an alternative to a rigid diffuser for a momentum propulsor. This appears attractive technically. The diffuser shape can be tailored by modulating jet momentum and angle and can be switched off in forward flight since its main function is increasing thrust/power ratio at static speeds. Theoretical analysis for a steady inviscid incompressible flow predicts impressive thrust augmentations. Taking into account the energy required to feed the jet sheet, it appears that in some cases propulsor thrust can be more than doubled. It could be applied to ducted fans, jet engines and seems particularly attractive for ejector thrust systems. A first approach of the study of the flow is made in the planar and axisymmetric cases by assuming that the velocity is uniform in each section. For the planar problem a linearized solution is presented. A conformal mapping transforms it into a half-plane boundary value problem of the Riemann-Hilbert-Poincare type. It is solved by combining Filbert Transforms, asymptotic expansion and a digital computer program. Then the nonlinear two-dimensional problem is presented with some references to the way it could be solved.

Thesis Files