This investigation concerns the complicated unsteady (pulsatile) flow around a protuberance, such as encountered in polyps or nodules on the vocal folds. Despite its prevalence in engineering and biological flows, the previous work on flow separation from a hemispheroid-like object, or bump, on a wall has all been limited to steady freestream flow conditions, thus creating a significant void in the knowledge base. The overall objective of the investigation is to understand flow structures produced by three-dimensional flow separation in pulsatile flow over a 2:1 aspect ratio prolate hemispheroid on a wall. The outcomes of this work will provide insight not only into bioengineering flow applications, but also contribute to the broader topic of unsteady three-dimensional flow separation from smoothly-contoured objects on a boundary. It will be determined how flow structures interact with the wall in order to elucidate their impact on the shear stress and pressure signature on the wall both upstream and downstream of the protuberance. This secondary objective is of great importance because bioengineering flows are most concerned with fluid-structure interactions that elicit a biological response (e.g. pressure loadings that drive the dynamics of voiced speech, and wall shear stresses that have been linked to atherosclerosis). A suite of experimental investigations will be performed in a wind tunnel, utilizing time-resolved particle image velocimetry, laser Doppler anemometry, wall pressure measurements, skin friction line visualization, and oil-film interferometry, in order to resolve the separated flow morphologies, and their interaction with flow parameters of interest on the wall. The transformative potential of the proposed study is to facilitate the development of an unprecedented ability to design systems that take advantage of inherent features of unsteady 3-D separated flows.
Detailed study and understanding of separated 3-D flows in pulsatile flows constitutes the intellectual merit of the proposed study. Vocal fold polyps and nodules are hemispheroidal protuberances that develop on the vocal folds, altering the fluid loading that drives voiced speech and produces sound. Magnetically-targeted drug delivery in the arteries results in hemispheroidal conglomerations on the arterial surface, disrupting the hemodynamics. In both scenarios, the protuberance interacts with a pulsatile flow field. Found not only in biomedical, but also engineering applications, pulsatile flow over a bump on a wall presents a fundamental fluid mechanics problem involving three-dimensional flow separation, complex vortex shedding patterns, and fluid-structure interactions along the downstream wall. The proposed research is applicable to the aforementioned examples of bioengineering flows, as well as to the broader case of flow separation from objects that are located in a buffeting wake (e.g. automobile and marine aerodynamics, wind turbine performance, etc.), and also to environmental flows and contaminant transport around hills and berms. The proposed research plan will achieve broader impacts by (1) benefiting engineering and societal environments, (2) increasing participation of undergraduates and underrepresented groups, and (3) K-12 outreach programs. Furthermore, the grant will facilitate the training of a Ph.D. student and a post-doctoral scholar. Dissemination of information will be achieved through scholarly publications, conference proceedings, and the archival of data on the PIs existing research website. Additionally, several mentoring activities for post-doctoral scientists, graduate, and high school students are underway.
