Bubble-induced pseudo turbulence in laminar pipe flows

Abstract

Turbulence intensities and Reynolds stresses of bubble-induced pseudo turbulence in air–water laminar bubbly flows in a vertical pipe of 20mm diameter are measured at a low liquid Reynolds number, Re=900. A pipe made of fluorinated ethylene propylene resin, which has the same refractive index as water, is utilized to enable the LDV measurement of Reynolds stresses. Experimental data show that (1) turbulence kinetic energy of bubble-induced turbulence is proportional to local void fraction, (2) the ratio among axial, radial and azimuthal components of turbulence intensity is 2:1:1, (3) Sato’s eddy viscosity model underestimates the Reynolds shear stress of bubble-induced pseudo turbulence, whereas it qualitatively well represents the Reynolds stress distribution, (4) the Reynolds shear stress of bubble-induced turbulence depend not only on velocity gradient but also on gradient of void fraction and (5) the dissipation process of bubble-induced turbulence is analogous to that of shear-induced turbulence.