Experimental study on the modulation effect of dissipation scale neutrally buoyant particles on approximate isotropic turbulence generated by horizontal oscillating grids

Investigating the turbulent modulation effects due to dissipation scale particles is essential for the development of a more refined interphase interaction model for particle-laden two-phase turbulence. This study used Particle Image Velocimetry (PIV) to measure the approximately isotropic turbulence generated by oscillating grids, and investigated the turbulence modulation of dissipation scale neutrally buoyant particles. In the range of grid motion parameters studied in this research, the turbulence integral length scale is approximately 1 cm, while the Taylor microscale is about an order of magnitude smaller than the integral scale. The turbulence dissipation scale ranges from 188 to 1358 μm. Experiments were conducted to investigate the effects of particles with diameters of 150 μm, 270 μm, and 500 μm on isotropic turbulence, with particle volume fractions ranging from 0 to 0.1%, which make the flow belongs to dilute particle-laden turbulence. It was found that in the approximate isotropic turbulence, particles exhibit the effects of energy dissipation, storage, and redistribution. Particles are also capable of absorbing the energy from the secondary mean flow and converting it into turbulent fluctuation energy through particle-fluid interactions. These mechanisms together constitute the modulation of turbulence by particles. The ability of particles to dissipate, store, and redistribute energy varies with particle diameter, making the influence of particle volume fraction closely related to the relative size of the particle diameter. Overall, when the particle scale is larger than the turbulence dissipation scale, the particles tend to enhance the turbulence, and vice versa. Since the presence of particles alters the turbulence dissipation scale, the relative size of the particle scale to the turbulence dissipation scale is an important but not the only parameter influencing particle-induced turbulence modulation. Observations from the local flow field around the particles indicate that when the particle diameter is less than the turbulence dissipation scale, the flow structures surrounding the particles remain dominated by turbulence. However, larger particles dominate the surrounding flow structures, leading to a more orderly arrangement of velocity contours around them.