Holographic microscopy and microfluidics platform for measuring wall stress and 3D flow over surfaces textured by micro-pillars

Evans, Humberto Bocanegra; Gorumlu, Serdar; Aksak, Burak; Castillo, Luciano; Sheng, Jian

doi:10.1038/srep28753

Cited by 29 publications

(6 citation statements)

References 46 publications

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“…Consequently, this microscale surface passively modulates the small scales of the flow in the wall region, which in turn affects the large scales in the outer flow. Given the size of the pillars, this result is surprising, but it is consistent with the findings by Bocanegra Evans et al ( 29 ), who observed the propagation of the pressure perturbation over 35 times the pillar height.…”

Section: Resultssupporting

confidence: 90%

Engineered bio-inspired coating for passive flow control

Evans

Hamed

Gorumlu

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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Flow separation and vortex shedding are some of the most common phenomena experienced by bluff bodies under relative motion with the surrounding medium. They often result in a recirculation bubble in regions with adverse pressure gradient, which typically reduces efficiency in vehicles and increases loading on structures. Here, the ability of an engineered coating to manipulate the large-scale recirculation region was tested in a separated flow at moderate momentum thickness Reynolds number, Re θ = 1,200. We show that the coating, composed of uniformly distributed cylindrical pillars with diverging tips, successfully reduces the size of, and shifts downstream, the separation bubble. Despite the so-called roughness parameter, k + ≈ 1, falling within the hydrodynamic smooth regime, the coating is able to modulate the large-scale recirculating motion. Remarkably, this modulation does not induce noticeable changes in the near-wall turbulence levels. Supported with experimental data and theoretical arguments based on the averaged equations of motion, we suggest that the inherent mechanism responsible for the bubble modulation is essentially unsteady suction and blowing controlled by the increasing cross-section of the tips. The coating can be easily fabricated and installed and works under dry and wet conditions, increasing its potential impact on a diverse range of applications.flow control | bio-inspired surface | engineered surface | flow separation | adverse pressure gradient D uring the past few decades, considerable effort has been placed on controlling flow separation (1-4). This phenomenon is usually responsible for increased vibration and drag on bluff bodies as well as higher energy consumption in vehicles. The drag experienced by a body under subsonic motion mostly embodies viscous and pressure (form) effects. The former is a result of friction induced by the near-wall fluid, and the latter is a result of pressure imbalance around the surface of the body. The separation phenomenon is well exemplified in the canonic case of flow around a foil at a sufficiently high angle of attack. There, the adverse pressure gradient (APG) in the suction side leads to flow deceleration and eventually flow detachment. The direct consequence of this process is a change of the aerodynamic force components, namely lift and drag.Surface roughness plays a significant role in the turbulence dynamics near the wall and, in particular, in the separation regions (5-8). Evidence suggests that randomly distributed roughness, e.g., sand grain roughness, may move the separation point against the flow direction in the case of foils (9, 10); this shift results in drag increase and lift decrease. Experiments by Song and Eaton (11) showed an upstream shift of the separation point in a channel expansion with rough walls. However, various studies have shown that triggering transition to turbulence may reduce separation (12). These findings have motivated the use of flow control strategies such as vortex generators (13) and synthetic jets (3) t...

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Section: Resultssupporting

confidence: 90%

Engineered bio-inspired coating for passive flow control

Evans

Hamed

Gorumlu

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

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“…The design freedom available with direct write methodologies was also exploited to introduce pillars with specific spatial distribution (Figure 5c) or height (Figure 5d) with the intent to demonstrate the possibility of device manufacturing with custom surface properties, for potential applications in the field of microfluidics. 30 In particular, a uniform array of pillars exhibits a high contact angle with water due to a Cassie−Baxter state (Figure S7). By introducing regions devoid of pillars (Figure 5c) or with variations in pillar height (Figure 5d), the behavior of water droplets can be manipulated (Video S2).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Aerosol Jet Printing of Phase-Inversion Graphene Inks for High-Aspect-Ratio Printed Electronics and Sensors

Gamba,

Diaz-Arauzo,

Hersam

et al. 2023

ACS Appl. Nano Mater.

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Aerosol jet printing is a technology particularly suited for additive manufacturing of functional microstructures, offering resolutions as high as 10 μm, broad compatibility for electronic nanomaterials, and noncontact deposition, making it compelling for device prototyping and conformal printing. To adapt this method from thin film patterns to taller features, both ink rheology and drying kinetics require careful engineering. Printing in a solvent-rich, low-viscosity state commonly results in a puddle, with liquid-phase spreading and susceptibility to instabilities, whereas printing solvent-depleted aerosol results in a granular morphology with high overspray. Here, we demonstrate a strategy to mitigate this trade-off by tailoring the evolution of ink rheology during the process, using a graphene ink containing the nonsolvent glycerol as an exemplar. During droplet transport to the nozzle, evaporation of volatile primary solvents increases the glycerol concentration, resulting in gel formation. This switch in the ink rheology between the cartridge and substrate maintains the print resolution at high deposition rates. Moreover, multiple layers can be printed in rapid succession to build up high aspect ratio microstructures, as demonstrated by continuously printed cylindrical pillars with diameters on the order of ∼100 μm and aspect ratios as high as ∼10. Finally, the efficacy of this ink formulation strategy for a CuO nanoparticle ink confirms the generalizability of this strategy for a broader scope of colloidal nanomaterial inks. In addition to its utility for microscale additive manufacturing of 2.5D structures, this strategy provides insights into higher deposition rate patterning to improve scalability and throughput of aerosol jet printing.

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“…Similarly, in microfluidic devices for cell sorting, the efficiency of cell capture and separation depends on the contact area between the cells and the solid surfaces. One approach for enhancing the contact area is to employ arrays of micro-pillars, as suggested in [13,14], but this can result in a substantial increase in dissipated power [15,16]. A more powerful approach is to use multi-scale structures, illustrated in fig.…”

Section: Introductionmentioning

confidence: 99%

TOMAS: Topology Optimization of Multiscale Fluid-Flow Devices using Variational Autoencoders and Super-Shapes

Padhy,

Suresh,

Chandrasekhar

2023

Preprint

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In this paper, we present a framework for multiscale topology optimization of fluid-flow devices. The objective is to minimize dissipated power, subject to a desired contact-area. The proposed strategy is to design optimal microstructures in individual finite element cells, while simultaneously optimizing the overall fluid flow. In particular, parameterized super-shapes are chosen here to represent microstructures since they exhibit a wide range of permeability and contact area. To avoid repeated homogenization, a finite set of these super-shapes are analyzed a priori, and a variational autoencoder (VAE) is trained on their fluid constitutive properties (permeability), contact area and shape parameters. The resulting differentiable latent space is integrated with a coordinate neural network to carry out a global multi-scale fluid flow optimization. The latent space enables the use of new microstructures that were not present in the original data-set. The proposed method is illustrated using numerous examples in 2D Overview of the proposed method: A dataset of shape parameters of super-shapes, contact areas, and homogenized permeability tensors is used to train a variational autoencoder (VAE). The resulting latent space is then used for global multiscale optimization of fluid flow.

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Holographic microscopy and microfluidics platform for measuring wall stress and 3D flow over surfaces textured by micro-pillars

Cited by 29 publications

References 46 publications

Engineered bio-inspired coating for passive flow control

Engineered bio-inspired coating for passive flow control

Aerosol Jet Printing of Phase-Inversion Graphene Inks for High-Aspect-Ratio Printed Electronics and Sensors

TOMAS: Topology Optimization of Multiscale Fluid-Flow Devices using Variational Autoencoders and Super-Shapes

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