Structure of into Water Plane Underexpanded Air Jets

An experimental and numerical investigation of the structure of plane underexpanded turbulent air jets in water was conducted to characterize their structure and mixing properties. Measurements included void fraction profiles, static pressure distributions, entrainment rates, and high speed flow visualization. A locally homogeneous flow model was also developed with compressibility effects treated using an effective adapted jet condition. Static pressure measurements confirmed the presence of a shock-wave-containing external expansion region for underexpanded air jets in water, similar to results observed for underexpanded air jets in air. In addition, the plane jets exhibited half-widths (based on void fractions) that were two to three times greater than half-widths (based on scalar properties) observed for single-phase jets. This behavior follows from the strong sensitivity of void fraction to mixing levels due to the large density ratio of the flow. Predictions of void fraction and mass entrainment were encouraging, but performance was found to be sensitive to initial conditions and effects of large-scale unsteadiness near the jet exit. Eric Loth Gerard M. Faeth Department of Aerospace Engineering Univeristy of Michigan Ann Arbor, MI 48109