Velocity Measurements and Flow Visualization in Low Viscosity Jets

Abstract

Mixing of a liquid jet into a surrounding fluid is a commonly encountered phenomenon in both natural and engineering systems. Understanding the influence of viscosity ratio on jet stability can help design fluid systems with enhanced or suppressed mixing characteristics. Experiments were conducted with low viscosity axisymmetric liquid jets to characterize the behavior of instabilities as a function of viscosity ratio. In the experiment, viscosity ratios M (ambient-to-jet) from 1 to 50 were imaged in a constant density environment at jet Reynolds numbers ranging from 794 to 2464. Images display a change from axisymmetric jet breakup to a helical mode at high Reynolds numbers and high ambient-to-jet viscosity ratios. Additionally, hot film velocity measurements were taken to characterize the jet profile and quantitatively measure both the mean and fluctuating velocity fields. The spectral data captured singular peaks in the frequency domain, in the range of 6-30 Hz. This peak frequency was further shown to have a dependence on both the jet Reynolds number and the ambient-to-jet viscosity ratio. Images of jet breakup, jet velocity profiles, and velocity instability spectra are shown and discussed.