Dear all,
We are pleased to invite you to the next WISE Webinar on the topic of Wave-turbulence interaction taking place on 27/02/2025 at 17:00-18:00 Norway time; 10 - 11AM Minnesota time.
Join us via https://tudelft.zoom.us/my/wisezoominars on 27th Feb. 2025.
First speaker: Simen Ådnøy Ellingsen, Norwegian University of Science and Technology (NTNU)
Title: Waves interacting with small-scale turbulence: laboratory investigations
Abstract:
Waves invariably coexist with turbulent flow in natural flows and interact to produce mean flow properties that are significantly different from the mere sum of the two. When waves encounter a turbulent current, the flow goes through a period of transition before a new, combined “equilibrium” state is reached. This fact has consequences for wave-ocean modelling, as transfer of energy and momentum, Lagrangian-mean current, directional wave spectrum and ocean-atmosphere fluxes are all potentially affected. A number of open questions remain, however, and systematic investigations remain relatively scarce. We will focus on laboratory studies of waves interacting with turbulent flows where the turbulent lengthscales are of the order of a wavelength or less. The history of experiments is briefly reviewed, then several experimental campaigns from the NTNU wave-turbulence water channel are presented, including glimpses from an ongoing experiment. Results include measurements of the reorientation and intensification of ambient turbulence due the action of the Stokes drift, the directional spectral broadening due to scattering of waves by turbulence, and an Eulerian-mean “anti-Stokes” flow present in the “equilibrium state” which can approximately cancel the Stokes drift nearest the surface.
Second speaker: Lian Shen, University of Minnesota
Title: Effect of an incoming Gaussian wave packet on underlying turbulence
Abstract:
We present a simulation-based study of the effect of a passing wave packet on underlying fully developed turbulence. We propose a novel wave-phase-resolved simulation method inspired by Helmholtz decomposition to directly couple the turbulence simulation with instantaneous wave orbital motions without wave-phase averaging. We also introduce a boundary condition treatment for the turbulence at the wave surface, which allows the turbulence simulation to be conducted in a rectangular domain while retaining the wave-phase effect. The results obtained from the proposed method reveal considerable variations in turbulence statistics, including the enstrophy and Reynolds normal stresses, during wave packet passage. Most changes occur rapidly when the narrow bandwidth around the wave packet core passes. Further analyses of the energy spectra indicate that the enhancement of turbulence occurs across a wide range of scales, with the near-surface small-scale motions experiencing the most significant intensification. Meanwhile, large-scale motions with scales comparable to the boundary layer depth are also enhanced. The mechanisms underlying the Reynolds normal stress variation at different length scales are related to the energy transfer from the wave orbital straining to turbulence through production, the pressure–strain effect, the pressure diffusion and the wave advection. By assessing the turbulence statistics and dynamics impacted by a wave packet in detail, this study provides an improved understanding of the response of a developed turbulent flow to a transient wave field. The proposed simulation method also proves to be a promising phase-resolved approach for efficiently modelling the wave effect on turbulence.
Please note that WISE Webinars including the Q&A will be recorded and posted on the WISE YouTube Channel afterwards (https://www.youtube.com/@wisezoominars). By participating, you consent to any information you share to be included in the recording and shared.
Best wishes,
Alvise, Ton, Bernard, Tripp, Morteza and Qingxiang.
(The WISE Webinar organizing committee)