A numerical study of energy separation in a jet flow

Redistribution of the total energy of a fluid in motion, which is called "energy separation," has been observed in various flow situations. Understanding the underlying mechanism of this interesting phenomenon has been limited due to lack of the temporal information on flow and temperature fields. In the present study, numerical simulation of a viscous circular jet was performed to provide detailed temporal information on pressure, vorticity, and total temperature fields. Nondimensionalized governing equations, including mass, momentum, and total energy conservation equations, were simultaneously solved by an equal-order linear finite element and fractional four-step method. The results show that the formation and transport of vortices induce a pressure fluctuation in the flow field. The fluid, which flows through the disturbed pressure field, exchanges pressure work with the surroundings, and gains or loses total energy. This work exchange leads to higher and lower total temperature regions than the surroundings. In addition to the presence and movement of the vortices, the results indicate that the vortex-pairing process significantly intensifies the pressure fluctuation and corresponding total temperature difference. This implies that the vortex-pairing process is a very important process in intensifying energy separation and might explain the enhancement of energy separation in a jet using acoustic excitation.