Flow stabilization by subsurface phonons

Abstract

The interaction between a fluid and a solid surface in relative motion represents a dynamical process that is central to the problem of laminar-to-turbulent transition (and consequent drag increase) for air, sea and land vehicles, as well as long-range pipelines. This problem may in principle be alleviated via a control stimulus designed to impede the generation and growth of instabilities inherent in the flow. Here, we show that phonon motion underneath a surface may be tuned to passively generate a spatio-temporal elastic deformation profile at the surface that counters these instabilities. We theoretically demonstrate this phenomenon and the underlying mechanism of frequency-dependent destructive interference of the unstable flow waves. The converse process of flow destabilization is illustrated as well. This approach provides a condensed-matter physics treatment to fluid-structure interaction and a new paradigm for flow control.

Thermal Conductivity Reduction in a Nanophononic Metamaterial versus a Nanophononic Crystal: A Review and Comparative Analysis

“…The dispersion diagram for the unit cell provides a rather comprehensive description of these effects. Applications of phononic crystals include vibration isolation, wave focusing, flow control, topological insulators, and nonreciprocal materials, among others . Downsizing a phononic crystal to the nanoscale brings rise to the notion of a nanophononic crystal.…”

“…[107] The simulations are subsequently allowed to run under the NVE ensemble (constant number of atoms, volume, and energy) for either calculation of the thermal conductivity using the Green-Kubo method (as described in Section 4) or the SED distribution as a function of frequency and wavenumber. For the SED calculations, the NVE simulations are run for 2 22 time steps covering 2 ns, and information is extracted every 2 5 steps. Both sets of NVE calculations are based on Δt = 0.5 fs as earlier.…”

Highly Localized and Efficient Energy Harvesting in a Phononic Crystal Beam: Defect Placement and Experimental Validation

“…The passband resonance modes are in general larger than 0 dB in the displacement transmission. Although the considered PC beam is also truncated from an ideally infinite PC beam, we note that the defect modes are different from the truncation modes or surface modes in that wave will be localized around the mismatched unit cell at the frequency of the defect mode [29][30][31]. The insets in Figure 2a show the predicted output voltage around the two band gaps when an external load resistance of 500 kΩ is applied in the FEM simulation using the module "Piezoelectric Devices" in COMSOL MULTIPHYSICS.…”

“…(c) Full-field strain distribution at the frequency of the second defect mode of the defect and perfect PC beam. Crystals 2019, 9, x FOR PEER REVIEW 5 of 13mode[29][30][31]. The insets inFigure 2(a)show the predicted output voltage around the two band gaps when an external load resistance of 500 k is applied in the FEM simulation using the module "Piezoelectric Devices" in COMSOL MULTIPHYSICS.…”

Nonlinear Bloch waves and balance between hardening and softening dispersion

“…In the ordered case, phononic materials are constructed from a repeated array of identical unit cells which enables the calculation of the elastic band structure for a given topological configuration. This direct exposure, and access, to the inherent dynamical properties of phononic materials has vigorously chartered a new direction in materials physics, at a multitude of scales, and has already begun to impact numerous applications ranging from vibration control [1,2], through subwavelength sound focusing [3,4] and cloaking [5,6], to reducing the thermal conductivity of semiconductors [7][8][9] and stabilizing a wall-bounded fluid flow [10]. A discussion of applications and references are provided in recent review articles [11][12][13] and books [14][15][16][17], and special journal issues on the topic assemble some of the latest advances in the field [18][19][20][21][22][23][24].…”