Infl uences of aeration induced turbulence on growth and competition of Microcystis and Scenedesmus in the presence of sediments with varying particle sizes

Aeration is an important measure to prevent cyanobacterial growth in eutrophic lakes and reservoirs.The purpose of this study is to clarify the infl uence of aeration induced turbulence on growth and competition of Microcystis and Scenedesmus in the presence of sediments with varying particle sizes.Microcystis aeruginosa and Scenedesmus obliquus were selected as the model organisms.Sediments with varying particle sizes were added into mono and mixed cultures of the organisms.In the absence of sediment,both low-and high-intensity aerations(the turbulent dissipation rates were 1.60×10^(-6)and 1.16×10^(-5)m^(2)/s^(3),respectively)promoted the growth of Scenedesmus,but the growth of Microcystis was inhibited particularly obvious under the high-intensity aeration conditions.In the presence of sediment,Scenedesmus was promoted under all aeration conditions,while Microcystis was inhibited.The inhibition rate of Microcystis decreased with the increase of sediment size when treated with low-intensity aeration in the nighttime.The highest inhibition rate of M.aeruginosa(89.2%)was identifi ed under the condition of low-intensity aeration in the nighttime with small sediment addition.Furthermore,our results indicated that the impacts of sediment-induced light intensity reduction on algal growth were insignifi cant.In the mixed culture,the growth of Microcystis was inhibited by Scenedesmus in all treatments with aeration.Our results provided a theoretical basis for the practice in controlling cyanobacteria by aeration.

Analytical estimation of mixing coefficient induced by surface wave-generated turbulence based on the equilibrium solution of the second-order turbulence closure model

Based on the equations of motion and the assumption that ocean turbulence is of isotropy or quasi-isotropy, we derived the closure equations of the second-order moments and the variation equations for characteristic quantities, which describe the mechanisms of advection transport and shear instability by the sum of wave-like and eddy-like motions and circulation. Given that ocean turbulence generated by wave breaking is dominant at the ocean surface, we presented the boundary conditions of the turbulence kinetic energy and its dissipation rate, which are determined by energy loss from wave breaking and entrainment depth respectively. According to the equilibrium solution of the variation equations and available data of the dissipation rate, we obtained an analytical estimation of the characteristic quantities of surface-wave-generated turbulence in the upper ocean and its related mixing coefficient. The derived kinetic dissipation rate was validated by field measurements qualitatively and quantitatively, and the mixing coefficient had fairly good consistency with previous results based on the Prandtl mixing length theory.

Prediction and test of cavity＇s hydrodynamic self-noise induced by turbulent boundary layer

The self-noise in cavity is tested in the circling tank, prediction method of cavity＇s self-noise induced by turbulent boundary layer is established. The window＇s vibration is using the simply supported boundary condition, the sound wave in the cavity is expanded using the rigid wall boundary condition, the modal coupling vibration equation between them is established using the radiation boundary condition. The turbulent boundary layer pulsating pressure is random, the self-noise power spectrum in the cavity is solved. Test of self-noise and turbulent pressure is carried out in the circling tank when the flow velocity is 5 m/s and 8 m/s, the result verifies that the theoretical method can predict the real cavity＇s hydrodynamic noise approximately, the trends are similar, this provides one analytical method for sonar dome＇s material selection and noise control.