Date of Award


Document Type


Degree Name

Master of Science


Department of Aeronautics and Astronautics

First Advisor

Thomas Buter, PhD

Second Advisor

Rodney Bowersox, PhD

Third Advisor

Philip Beran, PhD


The effect of blowing vortex generator jets (VGJs) on the performance of a highly-offset (s-duct) diffuser was investigated experimentally. VGJs are pitched, skewed jets which generate streamwise vortices as well as injecting high-momentum fluid into the boundary layer. Diffuser performance with and without VGJs was measured for an inlet Mach number of 0.6 (Re/x = 1.27x107 per cm). Pitot static and hot-film instrumentation was used to measure flow properties at the diffuser inlet and exit planes. Without blowing, the flow on the lower surface of the diffuser was massively separated. Blowing at 0.48% mass flow ratio through three lower-surface VGJs reduced the size of the separated flow region, reduced the thickness of the boundary layer at the exit plane, increased pressure recovery by 1.3%, and increased the static pressure rise achieved in the diffuser by over 50%. Turbulence intensity, turbulent shear stress, and turbulent kinetic energy were reduced as well. Distortion of the exit plane flowfield increased with blowing.

AFIT Designator


DTIC Accession Number