Mr. Austin Thombs Profile

Austin Thombs

at NRL SSC

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Proceedings Article | 12 April 2021 Presentation + Paper

Effects of actuated boundaries on Tollmien-Schlichting waves and developed boundary layer turbulence

Austin Thombs, Silvia Matt, Weilin Hou

Proceedings Volume 11752, 1175208 (2021) https://doi.org/10.1117/12.2586035

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The potential for hydrodynamic drag reduction using small-scale actuation to influence turbulent boundary layer flow is investigated. When coupled with lab data, numerical simulations allow for the most complete understanding of the effect of various parameters on boundary layer turbulence. Two computational fluid dynamics (CFD) model sets are created in COMSOL, a multiphysics software package, to compare to experimental data and inform future research in the flowSiTTE laminar-to-turbulent flow tank. Effects on boundary layer dynamics and turbulence are studied through the implementation of an actuated boundary along the tank lid, using a standing wave to counter shear stress streaks characteristic of fully developed boundary layer turbulence. Numerical velocity data from the tank lid model are consistent with laboratory data collected with Particle Image Velocimetry (PIV). Additionally, boundary layer actuation of transitional turbulence is studied by analyzing the formation and dampening of Tollmien-Schlichting (TS) waves on a NACA 0012 airfoil. Standing wave actuation with amplitudes of 10-100μm along the airfoil is shown to reduce hydrodynamic drag by up to 15% at a wide range of frequencies. Boundary actuation delays the formation of the separation layer along the airfoil’s trailing edge – the region of flow responsible for much of the airfoil’s drag – keeping the flow attached for nearly the entire chord length and significantly reducing pressure drag.

Proceedings Article | 6 May 2020 Presentation + Paper

Characterizing mixing and stress in a laboratory volume using CFD models

Austin Thombs, Weilin Hou, Silvia Matt, Nezam Uddin

Proceedings Volume 11420, 114200V (2020) https://doi.org/10.1117/12.2558184

KEYWORDS: Data modeling, Sensors, Particles, Velocity measurements, Fiber optics sensors, 3D modeling, Fluid dynamics, SolidWorks, Motion models, Magnetism

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Laboratory instruments used to measure velocity within a fluid, such as Acoustic Doppler Velocimetry (ADV) or Particle Image Velocimetry (PIV), often only gather data at one or a few points in the fluid, if using ADV, or values within a plane, when PIV is used. To get a complete picture of the total shear stress inside a container for the study of coupled biophysical interaction and stress impact on phytoplankton cells, it is best to complement measurements with a numerical model. Since the total shear stress is the primary driver in mechanical bioluminescence production, it is important to be able to accurately quantify fluid flow and dynamics at small spatial and temporal scales across the fluid domain. In this work, the fluid domains of different laboratory beakers were studied. They were modeled in Solidworks, and exported into a multi-physics software package (COMSOL) to be solved numerically. A rotating domain setup was used, and solved with a multiphase computational fluid dynamics (CFD) model, using both laminar and turbulent flow, as well as various rotational velocities. We further compare the model data to individual data points from measurements using a fiber flow sensor, to verify the model and constrain the total shear stress within the container.

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