Turbulence collapses at a threshold particle loading in a dilute particle-gas suspension

Direct Numerical Simulations (DNS) of the flow of a particle-gas suspension in a channel have been carried out to examine the turbulence attenuation due to particles. As the volume fraction is increased in the range $0\text{--}3.5\times 10^{-3}$ , there is a discontinuous decrease in the turbulent velocity fluctuations at a critical volume fraction. The turbulent energy production rate decreases by an order of magnitude, accompanied by a much smaller increase in the energy dissipation due to particle drag, resulting in a decrease in the total energy dissipation. In contrast to the current understanding, the results show that turbulence attenuation is a discontinuous process, and is due to a disruption of the turbulent energy production mechanism, and not due to the increased dissipation due to the particles