Two numerical simulations of liquid motion driven by wind shear or syringe pump

Abstract

Liquid column breaking, called atomization, is of great interest in both geophysics and engineering. Particularly, the atomization occurs on the ocean surface, on fuel injection in engines, on ink injection in printers, and, perhaps, on spilt chemical in future needleless-syringe. Although there are many studies for the atomization, the atomization mechanism is not fully understood, because of complicated interfacial movement and deformation, accompanied with bubble entrainment. We, therefore, used a direct numerical simulation with Level-Set/VOF method as the interface tracking method. The method is coupling method of Level-Set method, which captures an interface shape smoothly, and VOF method with high-precision mass conservation of liquid. The calculation of wind waves was performed using the program code ‘FK’ developed in Kyoto University. The computational domain is set to be 140 mm, 20 mm, and 40 mm in streamwise, spanwise, and vertical directions, respectively. The upper half of the computational domain is set to be air, and lower one is set to be water. The initial constant air flow is set to be 5 m/s, and the water is initially set to be 1 m/s. The results show that we can reproduce the chop breaking, a kind of atomization on a liquid column breaking. Furthermore, we performed another numerical simulation using ANSYS FLUENT as a preliminary calculation for atomization of a water jet by syringe pumping. The computational domain is set to be 70 mm in total length, 60 mm in total length of the syringe barrel, and the syringe diameter is 20 mm. The length of needle is 10 mm and needle diameter is 2 mm. The piston wall is set to be a mobile wall by dynamic mesh function. The piston wall was moved 40 mm to needle direction with the frequency of 0.1 Hz. The PISO method is used for the unsteady flow. We calculated the flow rate spilt from the edge of the nozzle. The results show that the frequency of spilt flow rate agreed with 0.1Hz, which is the frequency of the mobile wall of the piston.