Experimental Estimation of Turbulence Modification by Inertial Particles at Moderate $Re_\lambda$

Several experimental and numerical studies have aimed at quantifying the impact of inertial particles on turbulent kinetic energy, and turbulent kinetic energy dissipation ($\varepsilon$) of particle-laden flows. We propose a new experimental method to estimate the carrier-flow dissipation $\varepsilon_p$ in the presence of inertial sub-kolmogorov particles at moderate $Re_\lambda$ (Mora et al. PRF, 2019). Its foundations rely on the unladen flow dissipation calculation using the Rice theorem, and the density of zero crossings $n_s$ of the longitudinal velocity fluctuation coming from a laser doppler anemometry device. We show that, under some mild assumptions, that $\varepsilon_p$ can be deduced from the value of $n_s$. Our experimental results provide strong evidence, regarding the non-negligible effect that dense sub-kolmogorov particles have on the carrier flow energy cascade at $\phi_v=\mathcal{O}(10^{-5})$, and $Re_\lambda \in [200-600]$. Our observations are consistent with previous two-way coupling DNS studies at similar concentrations. Our results may also have an impact on distinct phenomena on particle-laden flows that depend on the coupling of the particles with the flow, such as preferential concentration and settling velocity modifications.