Franck, J. A. | Search bioRxiv

bioRxiv2021

Simulations of flow over a bio-inspired undulated cylinder with dynamically morphing topography

Inspired by the geometric properties of seal whiskers, the addition of spanwise undulations on a cylinder have been shown to lower the mean and oscillatory forces and modify the frequency of flow-induced vibration when compared to smooth cylinders. Previously, computational fluid dynamics (CFD) has been used to characterize the hydrodynamic response with respect to specific geometric features. However simulations are time intensive due to complex three-dimensional meshing and computation time, limiting the number of geometric perturbations explored. A method is proposed in which the specific geometric features of this complex topography can be modified during a simulation thereby decreasing the time per geometric modification and removing the need for manual meshing of the complex structure. The surface of the seal whisker inspired geometry is parameterized into seven defining parameters, each of which is directly controlled in order to morph the surface into any realization within the defined parameter space. Once validated, the algorithm is used to explore the undulation amplitudes in the chord and thickness directions, by varying each independently from 0 to 0.3 thicknesses in increments of 0.05 at a Reynolds number of 500. The force and frequency response are examined for this matrix of geometric parameters, yielding detailed force trends not previously investigated. The impact of the bio-inspired morphing algorithm will allow for further optimization and development of force-mitigating underwater devices and other engineering applications in need of vibration suppression, frequency tuning, or force reduction.

biophysics↗

bioRxiv2020

Flow over seal whiskers: significance of geometricfeatures on force and frequency response

The complex undulated geometry of seal whiskers has been shown to substantially modify the turbulent structures directly downstream, resulting in a reduction of hydrodynamic forces as well as modified vortex-induced-vibration response when compared with smooth whiskers. Although the unique hydrodynamic response has been well documented, an understanding of the fluid flow effects from each geometric feature remains incomplete. In this computational investigation, nondimensional geometric parameters of the seal whisker morphology are defined in terms of their hydrodynamic relevance, such that wavelength, aspect ratio, undulation amplitudes, symmetry and undulation off-set can be varied independently of one another. A two-factor fractional factorial design of experiments procedure is used to create 16 unique geometries, each of which dramatically amplifies or attenuates the geometric parameters compared with the baseline model. The flow over each unique topography is computed with a large-eddy simulation at a Reynolds number of 500 with respect to the mean whisker thickness and the effects on force and frequency are recorded. The results determine the specific fluid flow impact of each geometric feature which will inform both biologists and engineers who seek to understand the impact of whisker morphology or lay out a framework for biomimetic design of undulated structures.

biophysics↗