Holger B. E. Kurz

Effects of a Discrete Medium-Sized Roughness in a Laminar Swept-Wing Boundary Layer

Direct numerical simulations of the effects of a cylindrical roughness element in the laminar 3-d boundary layer on the upper surface of a swept wing are performed. The roughness element generates streamwise vortices, where one is persistently growing in streamwise direction due to crossflow instability. By varying the roughness height, the onset of secondary instability of this crossflow vortex and ultimate transition to turbulence varies also in streamwise direction. When reaching the “effective”, i.e. the flow-tripping roughness height, the linear crossflow-instability regime is bypassed and breakdown to turbulence occurs in close vicinity to the element due to a global instability.

Near-Wake Behavior of Discrete-Roughness Arrays in 2-d and 3-d Laminar Boundary Layers

A spanwise row of medium-sized cylindrical roughness elements is introduced to two different base flows, a 2-d boundary layer and a respective 3-d boundary layer, as can be found on unswept and swept wings, respectively, both with strongly negative streamwise pressure gradient. For both cases, sub-effective and super-effective, i.e. directly flow tripping, elements are investigated. Similarities and differences in the flow fields around the roughness elements are highlighted. It turns out that, when comparing the results in a coordinate system aligned with the local flow direction at the boundary layer edge, the qualitative differences in the near wakes are rather subtle. Nevertheless, the elements in the 3-d boundary layer trigger steady crossflow vortices that will ultimately become secondarily unstable, and therefore lead at first to a continuously upstream-shifting transition location with increasing roughness height. Performance data for our direct numerical simulation code NS3D are given for the CRAY XE6 and the current test and development system CRAY XC40.

Rapid, International Design and Test of a Hybrid-Powered, Blended-Wing Body Unmanned Aerial Vehicle

Student engineering teams collaborated across three international universities to develop a 3 m wingspan unmanned aircraft in a single academic year. This aircraft, named Hyperion, is inspired by the NASA/Boeing X48-B blended wing body, and serves as a test platform for high efficiency aerodynamics and propulsion. The design concept includes a novel hybrid gas-electric propulsion system developed by a University of Colorado spinout company, Tigon EnerTec. The aircraft features a high-lift blended-wing body design, composite materials, and advanced flight controls, and was successfully flight tested in the Spring of 2011. Students at the University of Colorado, the University of Stuttgart, Germany, and the University of Sydney, Australia, benefited greatly from the multi-national design and delocalized manufacturing, which was conceived to simulate modern industry practices. Hyperion’s unique architecture and advanced subsystems establish novel technologies that can be incorporated into UAV, general aviation, or commercial markets.

Receptivity of a Swept-Wing Boundary Layer to Steady Vortical Free-Stream Disturbances

Direct numerical simulations (DNS) of steady vortical free-stream disturbances impinging on the leading edge of a swept wing are performed for a low- and a high-speed subsonic case at a Mach number of 0.16 and 0.65, respectively. The receptivity of the crossflow-instability dominated boundary layer downstream of the stagnation line to the forced disturbances is investigated. The introduced (spanwise) wavelengths are in the order of the most amplified steady crossflow mode in the low Mach-number case and induce respective low-amplitude disturbances in the boundary layer.

Hyperion Blended Wing Body Aircraft Technology

Student engineering teams develop a 3 m scale model inspired after the NASA-Boeing X48-B blended wing body to use as a test bed for advanced technical studies. The design concept implements a novel hybrid gas/biodiesel-electric power train as a green aircraft technology. The Hyperion aircraft will serve as a test-bed for research and development in the following focus areas: aerodynamics, structures and materials, weights and mass properties, handling and control, flight mechanics, and efficiency improvements on performance. additional authors as list is limited to 20: Dries Verstraete, Kai Lehmkuehler, University of Sydney; Ewald Kraemer, University of Stuttgart.