Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J25: Flow Control: Surface Modification and Permeability |
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Chair: Mitul Luhar, Univeristy of South California Room: 150B |
Sunday, November 19, 2023 4:35PM - 4:48PM |
J25.00001: Wrinkle patterns of an elastic loop coupled with a transient gap flow Seyoung Joung, Changhwan Jang, Daegyoum Kim Thin elastic materials subjected to a compressive force can undergo wrinkling which results in a regular surface pattern characterized by specific length scales. One can manipulate the wavelength of wrinkle patterns by tuning material properties, while controlling the applied compressive force during dynamic buckling provides an alternative way. To genuinely control the pattern of a wrinkling surface, an experimental approach based on hydrodynamic coupling between transient loading and wrinkling is attempted. Here, we consider wrinkling on an elastic loop in a gap flow, which is induced by expanding a fluid-filled gap between a bottom substrate and a moving plate. Vortices formed across the elastic loop contribute to pressure difference between the inner and outer surfaces of the loop, and cause in-plane compression along its perimeter. Various modes of wrinkling emerge on the elastic loop depending on the time scale of the plate motion, such that shorter wavelength appears with the smaller time scale. Our results suggest the possibility of temporally controlling wrinkle patterns by dynamic hydrodynamic loading. |
Sunday, November 19, 2023 4:48PM - 5:01PM |
J25.00002: Reactive control using an active deformable surface and real-time PIV Findlay McCormick, Bradley Gibeau, Sina Ghaemi This study investigates turbulence control strategies that utilize an active deformable surface and real-time particle image velocimetry (RT-PIV). The control strategies target the sweep and ejection motions of the vortices shed from a spherical cap placed in a laminar boundary layer. The strategies consisted of wall-normal surface deformations that opposed to or complied with the wall-normal (v) or streamwise (u) velocity fluctuations measured using RT-PIV. The results show that the control approach hindered the advancement of sweep motions toward the wall. It also disrupted the periodic shedding of vortices. The v-control with opposing wall motions and u-control with compliant wall motions demonstrated strong inhibition of sweep motions, while the v-control with compliant and u-control with opposing wall motions showed weaker inhibition. All reactive control cases disrupted vortex shedding. In some instances, this disruption was accompanied by increased turbulent kinetic energy due to secondary flow motions. However, the v-control with opposing wall motions reduced the vortex-shedding energy while maintaining total turbulent kinetic energy close to or below that of the unforced flow. Overall, the experiments show the effectiveness of reactive control strategies in inhibiting sweep motions and disrupting vortical structures. |
Sunday, November 19, 2023 5:01PM - 5:14PM |
J25.00003: Effect of added wall-transpiration and pressure gradient on the plane Couette flow using resolvent analysis Toni Dokoza, Martin Oberlack, Joao Vinicius Hennings de Lara The resolvent analysis is applied on the plane Couette flow with constant wall-transpiration velocity V_{0} and wall velocity U_{w} with emphasis on the effect of V_{0} on the coherent structures and the amplification rate σ_{1}. Various invariant scaling laws for the most amplified first singular value σ_{1} and the flow parameters are found. For a constant ratio of the wall-transpiration and streamwise Reynolds numbers γ=Re_{V0}/Re=V_{0} /U_{w}, σ_{1} is the largest for an invariant relationship Re·γ^{a} = C reaching a peak value for a specific Re for each γ. It is shown that the streamwise structures not only move closer to the upper wall, but also become more confined in the wall-normal and spanwise direction for an increasing Re_{V0} while keeping the streamwise Reynolds number Re constant. Direct numerical simulations (DNS) showed that added wall-transpiration could not lead to the destruction of the coherent structures of the plane Couette flow, whereas it was only possible by imposing a pressure-gradient, i.e. for the plane Couette-Poiseuille flow. |
Sunday, November 19, 2023 5:14PM - 5:27PM |
J25.00004: Near wall flow topology at superhydrophobic surfaces in turbulent channel flow Albert J Baars, Daniel Matz, Christoph Wilms The effect of superhydrophobic surfaces on drag reduction and flow topology in turbulent channel flow is investigated at Re_{τ} = 180 and different wave length of the structure (pillars, 10 ≤ L^{+}≤ 80) using direct numerical simulation. The gas-liquid interface and the interface between pillar tip and liquid are considered as one plane. The gas-liquid interface is modeled by a slip boundary condition. The ratio of no-slip / total area of the surface structure amounts to 1/4. The drag reduction increases under-proportionally with L^{+} from 11% at L^{+}= 10 up to 37% at L^{+}= 80. Fully developed flow in streamwise direction appears for wall-normal distances of y_{d}^{+ }≥ 4 (L^{+}= 10) and y_{d}^{+} ≥ 28 (L^{+}= 80). The region smaller y_{d}^{+} differs significantly from the typical velocity profile of a turbulent wall-bounded flow. Above the slip area velocity profiles with ∂u^{+}/ ∂y^{+} ≈ 0 appear for y^{+}≤ 0.2. Above the pillar tips almost linear velocity profiles arise with a minimum thickness at the leading edge and a maximum downstream at 0.55 times the pillar edge length (y^{+}< 1.8 at L^{+} = 80). In both wall near domains, viscous momentum transfer dominates turbulent momentum transfer. Above, non-linear velocity profiles and growing turbulent momentum transfer arise. In this contribution a detailed description of governing transport phenomena related to drag reduction is given for the mentioned regions. |
Sunday, November 19, 2023 5:27PM - 5:40PM |
J25.00005: Drag reduction based on vapor stabilized surfaces on underwater superhydrophobic surfaces. Deepak J, Arindam Das Superhydrophobic surfaces have proven to be beneficial for marine and submarine vehicles as they effectively reduce drag. This drag reduction is achieved through the creation of a thin layer of air known as the "plastron," which forms within the asperities of the textured surface between the solid material and the surrounding liquid. However, this plastron layer is inherently unstable due to factors such as hydrostatic pressure, air diffusion in water, and the instability caused by the shearing flow over the surface. |
Sunday, November 19, 2023 5:40PM - 5:53PM |
J25.00006: Toward a physical model for the effective slip length of superhydrophobic surfaces in turbulent flows Jae Sung Park, Siamak Mirfendereski, Simon Song Superhydrophobic surfaces are microscopically textured surfaces that reduce skin friction in turbulent flows thanks to the nearly shear-free boundary created by entrapping air pockets within surface textures. Owing to their heterogeneity, it is desirable to model these surfaces with a single effective slip length. However, the relationship between the heterogeneity of superhydrophobic surfaces and their effective slip length is not fully explored for turbulent flows. In this talk, we will present our recent efforts to systematically develop a model that captures the effective slip length of superhydrophobic surfaces in terms of surface features such as texture size and solid fraction. Firstly, we perform direct numerical simulations of turbulent channel flows with an effective slip length for friction Reynolds numbers up to 600 to derive a correlation between drag reduction and effective slip length. Secondly, from the literature, we collect the drag reduction of superhydrophobic surfaces with various texture sizes and solid fractions. Lastly, a physical model for an effective slip length of superhydrophobic surfaces as a function of texture size and solid fraction is developed by utilizing the derived correlation and the drag reduction of superhydrophobic surfaces. The physical model will be validated against experimental and computational data. |
Sunday, November 19, 2023 5:53PM - 6:06PM |
J25.00007: Analytical formulae for flow resistance of a periodic heat sink Hiroyuki Miyoshi, Toby L Kirk, Marc Hodes, Darren G Crowdy Analytical formulae are developed for the friction factor times Reynolds number (fRe) for fully-developed flow through a 5-sided duct. The value fRe is relevant to the flow resistance of longitudinal-fin heat sinks with or without clearance between the tips of the fins and a shroud as per the classic problem numerically resolved by Sparrow et al. [ASME J. Heat Transfer, 100, 1978]. Simple formulae for fRe in the limit of vanishing fin thickness are derived via matched asymptotic expansions in two settings: (i) when the fin spacing to fin height is small, and (ii) when the fin clearance to fin height is small. Numerical calculations show that the asymptotic formulae remain good approximants for fRe even outside the asymptotic parameter range for which they were derived. |
Sunday, November 19, 2023 6:06PM - 6:19PM |
J25.00008: Pressure Drop Measurements over Anisotropic Porous Substrates in Channel Flow Shilpa Vijay, Mitul Luhar The use of varying surface microstructures has the potential to be an effective passive flow control method for wall-bounded turbulent flows. Previous numerical simulations have shown drag reduction over streamwise preferential substrates that yield larger effective slip lengths for the streamwise mean flow compared to the turbulent cross-flows. A deterioration in performance is typically observed when the normalized wall-normal permeability √K_{yy}^{+ }is greater than 0.4, linked to the presence of the large-scale motions associated with the K–H instability. However, it remains to be seen if the trends observed in the numerical simulations hold for physically-realizable materials. In this study, a family of anisotropic periodic lattices is manufactured using 3D printing, whereby rod size and spacing in different directions can be varied systematically to achieve different ratios of streamwise, wall-normal, and spanwise bulk permeabilities (K_{xx},_{ }K_{yy}, K_{zz}.) The 3D-printed materials are then flush-mounted in a benchtop water channel. Pressure drop measurements are made in the fully developed region of the flow to systematically characterize drag as a function of bulk permeability for materials with K_{xx}/K_{yy}∈ [0.15,6.8]. Although drag reduction as compared to a smooth wall is not observed in the range of bulk Reynolds numbers tested (Re_{b} ∈[500,4000]), the relative increase in drag is lower for streamwise-preferential materials. |
Sunday, November 19, 2023 6:19PM - 6:32PM |
J25.00009: The influence of surface-embedded phononic crystals on the amplification of Tollmien-Schlichting waves Theodoros Michelis, Angka Bayu Putranto, Marios Kotsonis This study explores a novel approach to control convective boundary layer instabilities (TS-waves) by leveraging metamaterial concepts, specifically using one-dimensional phononic crystals (PCs) embedded in the surface, leveraging on the inherent frequency band stop characteristic of PCs. By employing analytical models derived from transfer matrix and interface response theories, the PC is fine-tuned to match the desired TS wave properties. The accuracy of the models is verified through finite elements analysis. To investigate the interaction between TS waves and a single PC, coupled two-dimensional fluid structure interaction simulations are conducted in the frequency domain. The study demonstrates that the behavior of TS-waves is determined by the phase relationship between the displacement of the PC's free-face surface and the unsteady perturbation pressure at the wall. When these two factors are in-phase, TS waves are amplified, while they are attenuated when out-of-phase. The mechanical oscillation of the PC is solely driven by the perturbation pressure. The hydrodynamic coupling between TS waves and the PC is governed by a combination of the Orr mechanism and wall-normal velocity linear superposition near the wall. Furthermore, the effectiveness of a metasurface composed of a streamwise-distributed array of PCs is evaluated. The metasurface results in a delay in the amplitude growth of the TS wavelength along its extent, achieving an 11.3% increase in wavelength delay. |
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