  In this paper, we propose a novel reduced order model (ROM) lengthscale
definition that is based on energy distribution arguments. This novel ROM
lengthscale is fundamentally different from the current ROM lengthscales, which
are generally based on dimensional arguments. As a first step in the assessment
of the new, energy based ROM lengthscale, we compare it with a standard,
dimensional based ROM lengthscale in the mixing-length ROM (ML-ROM) simulation
of the turbulent channel flow at $Re_{\tau} = 395$. The numerical investigation
shows that the energy based ROM lengthscale yields a significantly more stable
ML-ROM than the dimensional based ROM lengthscale. The new energy based
lengthscale definition could allow the development of scale-aware reduced order
modeling strategies that are better suited for flow-specific applications.
