CBET-0644640 K. Christensen, University of Illinois Urbana-Champaign
Intellectual merit: Canonical smooth-wall turbulence has been studied for many years and a relatively clear picture of its underlying structure now exists. However, the direct applicability of these efforts to technologically relevant flows, which often occur in complex geometries and in the presence of multiple noncanonical influences, like strong pressure gradients and highly-irregular surface roughness, is still unknown. The PI plans to expand his AFOSR research in the area of highly-irregular surface roughness by tackling two crucial topics central to advancing the science of modeling, predicting and controlling technologically-relevant turbulent flows in the presence of noncanonical influences. The majority of this effort will involve the study of turbulent boundary layers under the coupled influence of roughness replicated from turbine blades damaged by deposition and favorable-pressure-gradient (FPG) conditions. The PI has already made detailed PIV measurements under zero-pressure-gradient (ZPG) conditions at momentum thickness Reynolds numbers of 3900 and 11000. The PI plans to make similar measurements over smooth and rough walls with FPG conditions. This planned effort will address whether synergy between the two influences is similar in the transitionally- and fully-rough regimes and if wall similarity is valid under FPG conditions.
A second research area will involve the design of topological models for highly-irregular surface roughness, specifically replicated from damaged turbine blades, using proper orthogonal decomposition (POD) with only the most energetic topological scales. Short fetches of the model topologies will be replicated and tested in turbulent channel flow using PIV to assess their ability to reproduce the flow features observed over the actual surface. Understanding issues such as the importance of the largest roughness scales compared to the finer scales of the surface topology will provide "guidelines" for the design of more representative simulated roughness topologies and would also assist in relating past simulated roughness studies to flows over practical roughness.
Broader Impacts: The results of the proposed effort will have a direct impact on improved modeling and control of practical engineering flows, many of which have considerable influence on society (increased fuel efficiency of transportation systems for reduced oil consumption, for example). The students who will perform the bulk of this research will be actively recruited from under-represented groups using established programs at the University of Illinois (SURGE, MERGE, etc.) and will receive an exceptionally strong education in the areas of turbulence and advanced diagnostics.
The educational component of this CAREER award includes the development of a graduate-level microscale fluid mechanics course and the revision of a graduate-level experimental methods of fluid mechanics course to include microscale measurement methods. The PI also plans to establish a student seminar series in fluid and thermal science to foster the growth of and collaboration amongst graduate students in the College of Engineering with similar research interests.
