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Seminar: Effects of Structural Motion on Separation and Separation Control: Numerical Simulations, Theory, Wind/Water-Tunnel and Free-Flight Experiments

Dr. Hermann F. Fasel, University of Arizona
Friday, April 21, 2017, 3:00 pm
E001 Scott Lab
201 W. 19th Ave.
Columbus, OH 43210

In most of the past research addressing separation for wing sections, the effect of wing motion on the aerodynamic behavior has been neglected. With the current trend towards aerodynamically more efficient high-aspect-ratio composite wings, wing elasticity and, as a consequence of this, the effect of wing motion on aerodynamic performance will become increasingly more important. Our combined research effort at the University of Arizona addresses this issue by employing CFD simulations, wind-tunnel and free-flight experiments for investigating the fundamental flow physics of transition and separation for wing sections that are undergoing temporal (oscillatory, or impulse) motions as resulting from fluid-structure interactions, atmospheric unsteadiness, engine vibrations, etc. The focus of our research is not on the fluid-structure interaction per se, but rather on the effect of the wing motion on the fundamental flow physics of separation and laminar turbulent transition.

For most of the published research considering separation control for wing sections the effect of wing motion on the fluid dynamics is neglected. In the near-stall and/or full-stall regime, where separation control is of interest, some degree of wing movement is always present. With the current trend towards aerodynamically more efficient flexible high-aspect-ratio composite wings this effect will become even more pronounced in the future. Therefore, the consideration of the wing motion is crucially required for the successful implementation of flow control strategies in future advanced military and civilian aircraft. Our combined research approach addresses this critical issue by employing CFD simulations, wind-tunnel and free-flight experiments for investigating the fundamental flow physics of separation and its control for wing sections that are undergoing temporal (oscillatory, or impulse) motions resulting from fluid-structure interactions, atmospheric unsteadiness, engine vibrations, etc. By directly describing the wing movement in the investigations, the proposed research sets itself apart from existing fluid-structure interaction research. The focus here is not on the fluid-structure interaction per se, but rather on the effect of the airfoil motion on the fundamental flow physics of separation and its control. The parameter range for the proposed research (w.r.t., Reynolds number, pitching and/or plunging amplitude and frequency) is very different from the parameter range for flapping wing research, and is therefore highly relevant for larger Air Force UAVs and/or full-size aircraft. The objective of the current research is to provide a fundamental physics-based understanding of how unsteady wing motion affects separation and its control for lifting surfaces. This improved understanding will ultimately lead to guidelines for the design of novel flexible composite wings with reduced fatigue loads (which can also result from fluid-structure interactions when using flow control) or tailored elastic properties, such that the structural motion can be exploited for flow control.Free-flight experiments will be carried out to map out the relevant parameter space (amplitudes, frequencies and Reynolds numbers). Two different dynamically scaled models of the X-56A were designed for the planned scientific flight experiments.

The X-56A, also known as the MUTT (Multi-Use Technology Testbed) flight demonstrator, is a product of the AFRL-led Multi-Utility Aeroelastic Demonstration (MAD) programWe are collaborating with the project leaders at AFRL (P. Flick) and NASA. The airplane was designed and constructed by Lockheed Martin’s Skunk Works. At the University of Arizona a  the 1:3 dynamically scaled model of the X-56A was designed and built. The aircraft is currently getting instrummented for scientific flight tests.

A In addition, a 1:2 dynamically scale model aircraft of the X-56A was designed and is currently under construction. The models are designed such that they will allow options for straight and swept wings. The new aircraft will be equipped with multiple inertial measurement units (IMUs) and accelerometers along the span that are synchronized via Bluetooth to record the wing displacement in flight. The 1:2 scale model has the advantage that the Reynolds number range in flight is close to that of the wind-tunnel experiments and numerical simulations. The upcoming planned flight tests will provide the required information regarding flight-typical structural motion (amplitude, frequency, etc.) which will then be used for the CFD simulations and wind-tunnel experiments.

Wing sections with the X-56A airfoil are investigated in the new low freestream turbulence subsonic wind tunnel at the UA.26 A plunging apparatus was designed and built for investigating the effects of oscillatory plunging motions up to 20Hz. In parallel, Implicit Large Eddy Simulations (ILES) are performed at New Mexico State University (NMSU). Furthermore, the fundamental flow physics of the of the effect of wing sweep on transition and separation is investigated by high-fidelity DNS and water-tunnel experiments of a model geometry where the pressure gradient of the suction side of the airfoil is imposed on a flat plate boundary layer. This multi-tiered approach allows for the cross-validation of the different investigative tools (free-flight & wind/water-tunnel experiments, simulations) and thus increases chances for making major progress in this difficult field of research.

About the Speaker

Hermann Fasel is Professor of Mechanical and Aerospace Engineering at the University of Arizona. He has worked in Computational Fluid Dynamics for over 35 years with particular emphasis on Direct Numerical Simulations (DNS). He pioneered the use of DNS for investigating laminar-turbulent boundary-layer transition. He and his students investigated numerous aspects of stability and transition for a large range of flow speeds, from low subsonic to hypersonic, including also the interaction of transition and separation, as well as passive and active flow control.

He is an active pilot, for both power and glider airplanes.

Hosted by Professor Jim Gregory.