# Bulletin of the American Physical Society

# 76th Annual Meeting of the Division of Fluid Dynamics

## Sunday–Tuesday, November 19–21, 2023; Washington, DC

### Session L11: Boundary Layers: Turbulent I

8:00 AM–10:36 AM,
Monday, November 20, 2023

Room: 143A

Chair: Ricardo Garcia-Mayoral, University of Cambridge

### Abstract: L11.00006 : Interscale causality in near-wall turbulence*

9:05 AM–9:18 AM

#### Presenter:

Ricardo Garcia-Mayoral

(Univ of Cambridge)

#### Authors:

James de Salis Young

(University of Cambridge)

Zengrong Hao

(University of Cambridge)

Ricardo Garcia-Mayoral

(Univ of Cambridge)

*x*) and spanwise (

*z*) lengthscales. The flow can then be viewed as a dynamical system where the state space variables

*Φ= {u,w,v,p}*are the three velocity components and the pressure, which depend on the

*x*- and

*z*-wavenumbers

*k = (k*,

_{x},k_{z})*y*, and

*t*. The evolution equations for

*Φ*are the Navier-Stokes equations plus the continuity equation, which can then be written as

*F(Φ*, where

_{k,y,t}) = N(Φ_{k′,y,t},Φ_{k′′,y,t})*k*,

*k′*,

*k′′*and satisfy a triadic relationship,

*F*represents the linear part of the equations and

*N*the nonlinear terms, which are responsible for the transfer of information from other lengthscales into lengthscale

*k*. The objective of this work is to characterize and quantify the relative importance of the different contributions to

*N*. While intimately connected to triadic interactions, which are derived from energy considerations, this analysis, based instead on the momentum equations, aims to provide additional cause-effect information to the inter-scale interactions. For the near-wall cycle, for instance, we observe that the most significant interactions are of

*w*structures of wavelengths

*λ*≈100,

_{x}^{+}*λ*≈1000 advecting

_{z}^{+}*u*structures of wavelengths

*λ*≈1000,

_{x}^{+}*λ*≈100, to produce a signature in

_{z}^{+}*u*at wavelengths

*λ*≈100,

_{x}^{+}*λ*≈100. This interaction is essentially the generation of meandering in streamwise streaks.

_{z}^{+}*This work was supported in part by the European Research Council under the Caust grant ERC-AdG-101018287. Computational resources were provided by the University of Cambridge Research Computing Service under EPSRC Tier-2 grant EP/P020259/1 (projects cs066 and cs155), and by the UK 'ARCHER2' system under PRACE project pr1u1702 and EPSRC project e776.

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