# Experiments and data analysis of non-equilibrium turbulent boundary layers

**Project Leader: **Joseph Klewicki**Staff: **Jimmy Philip, Spencer Zimmerman, Ivan Marusic**Student: **Sylvia Romero**Collaborators: **Greg Chini (UNH), Chris White (UNH), Beverley McKeon (Caltech)**Sponsors: **US Office of Naval Research**Primary Contact: **Joseph Klewicki (klewicki@unimelb.edu.au)**Keywords: **fluid dynamics; turbulence**Disciplines: **Mechanical Engineering**Domains: **

As first described by Prandtl, a boundary layer forms when there is a fluid flow tangential to a no-slip material surface, eg, a solid wall. The flow state of a boundary layer, or wall-flow, becomes turbulent at sufficient Reynolds number. Once in the turbulent regime, the statistical properties of wall-flows continue to vary with increasing Re, and accordingly, so do the underlying instantaneous mechanisms of momentum and kinetic energy transport. The US Navy has long-standing interests in high Reynolds number wall-flows owing to the impact of these flows on application/device performance and energy consumption. As a result of intensive research over the past seven decades, a considerable body of research now informs the capacity to describe, both physically and mathematically, the behaviors of the so-called canonical wall-flows. Central elements here include an understanding of the important dynamical mechanisms, and the Reynolds number scaling of statistics, structural features, and spectral properties. Collectively, these advances have fostered the development of increasingly sophisticated predictive models of turbulent wall-flow dynamics. While critical aspects associated with Reynolds number dependence still remain to be claried in the canonical flows, signicantly much less is known about the dynamical structure and prediction of non-equilibrium wall-flows. Addressing the scaling, dynamics, and prediction of this class of flows is the goal of this research project.

Non-equilibrium conditions arise when an imposed forcing effect modifies momentum transport and turbulence production such that the flow no longer adheres to the scaling behaviors of the unperturbed canonical flow. Wall-flows of practical interest to the Navy are regularly subjected to non-equilibrium effects. Accordingly, the proposed research aims to advance flow prediction by connecting the structural modifications of the turbulence to the imposed forcing effects in ways that are mathematically well-founded, and that simultaneously expose the causative physical mechanisms. The research projects described here pertain to the experimental elements of this project – involving detailed measurements of turbulence in non-equilibrium boundary layer flows.