Effect of low clay concentration on nearly isotropic turbulence*

An experimental investigation was conducted to investigate and quantify the effect of low clay concentrations on nearly isotropic turbulence created in a customized cubic mixing box. A novel approach using Laponite RD, a synthetic clay, produced a nearly transparent water-clay mixture suspension. This clay-laden flow allowed full optical access for high-speed particle image velocimetry (PIV) to characterize the spatio-temporal dynamics around the center of the mixing box. We investigated mass concentrations of C(%) = 0, 1, 1.5, and 2, which minimized non-Newtonian behavior. Clay particles significantly modulated the turbulence structure even at low concentrations of laponite with a monotonic reduction of turbulence kinetic energy, mean dissipation rate, and an increase of the Taylor microscale, λ, as clay concentration increased. Velocity spectra demonstrated a clear dependence on clay concentration and the Taylor microscale Reynolds number scaling correction, p, of the power law in the inertial subrange. The Taylor microscale estimation by p-factor agrees well with those obtained from structure function and direct PIV measurements. The energy budget suggests that the reduction in TKE and increase in λ are likely associated with the presence of clay particle aggregation.