Large Eddy Simulation of Microbubble Drag Reduction in Fully Developed Turbulent Boundary Layers

Abstract

Microbubble drag reduction has good application prospects. It operates by injecting a large number of bubbles with tiny diameters into a turbulent boundary layer. However, its mechanism is not yet fully understood. In this paper, the mechanisms of microbubble drag reduction in a fully developed turbulent boundary layer over a flat-plate is investigated using a two-way coupled Euler-Lagrange approach based on large eddy simulation. The results show good agreement with theoretical values in the velocity distribution and the distribution of fluctuation intensities. As the results show, the presence of bubbles reduces the frequency of bursts associated with the sweep events from 637.8 Hz to 611.2 Hz, indicating that the sweep events, namely the impacting of high-speed fluids on the wall surface, are suppressed and the streamwise velocity near the wall is decreased, hence reducing the velocity gradient at the wall and consequently lessening the skin friction. The suppression on burst frequency also, with the fluid fluctuation reduced in degree, decreases the intensity of vortices near the wall, leading to reduced production of turbulent kinetic energy.

Performance of a Drip Irrigation System under the Co-Application of Water, Fertilizer, and Air

“…Compared with the mm-sized bubbles produced by Venturi aeration, micro-nano aeration produces tiny bubbles with a diameter between 200 nm and 50 µm, which have super stability and a larger specific surface area [34] and can effectively adsorb small fertilizer particles in irrigation water bodies. In addition, micro-nano bubbles can generate strong long-range hydrophobic forces during the bridging process, which can improve the adhesion ability between fertilizer particles and bubbles [35], reduce the probability of their detachment, and promote the transport of water to fertilizers. Therefore, compared with increasing the pressure of Venturi aeration on the total amount of fertilization, micro-nano aeration can significantly weaken the effect of pressure on the total amount of fertilization and improve the uniformity of the co-application of water, fertilizer, and air drip irrigation system's total amount of fertilization.…”

Numerical Study of the Influence of the Type of Gas on Drag Reduction by Microbubble Injection

“…For other methods of microbubble drag reduction, Lyu et al [20] proposed a gas-liquid two-phase flow model based on the mixed-flow model, and numerically simulated the MBDR process of the SUBOFF rotating model. Wang et al [21] used a two-way coupled Euler-Lagrange approach based on a large eddy simulation to study the MBDR mechanism in a fully developed turbulent boundary layer over a flat-plate. Zhao et al [22] used an OpenFOAM frame to study the two-phase micro-bubble flow over an axisymmetric body.…”

Untangling the Mysteries of Turbulence: A Data-Driven Visualization Study of Active Flow Control in Channel and Pipe Flows Using Numerical Simulations

“…A lot of researchers have done work in this domain focussed on developing various active and passive techniques of ow control in case of turbulent ows for bounded as well as unbounded ows. Various types of active drag reduction techniques are available such as using wall motion 4 , wall vibration 5 , wall deformation [6][7] , blowing 8-9 , suction [10][11] , span-wise oscillations [12][13] , Air injection [14][15] , synthetic jets [16][17] , unsteady jets [18][19] , Large eddy breakup devices [20][21] , microbubbles [22][23] , electromagnetic wall excitations [24][25] etc. The main difference between active and passive drag reduction techniques is that active techniques of ow control use some external source of energy to obtain drag reduction, while passive techniques do not need an external source of energy but active techniques of drag control are usually more effective as compared to the passive ow control techniques in terms of overall drag reduction but passive techniques can be less costly as compared to the active ones 26 .…”