Combined Optical Connectivity And Optical Flow Velocimetry For Measurement Of The Interfacial Velocity Of A Liquid Jet In Gas Cross-Flow
T. Wang, Y. Hardalupas
Imperial College London, Mechanical Engineering Department, London SW7 2AZ, UK
Liquid jet in crossflow (LJIC) is a process in which a high-speed gas crossflow deforms and shears a continuous liquid flow into tiny droplets. This study quantifies the liquid surface motion of LJIC during the primary breakup process, which has not been fully assessed due to limited optical access close to the nozzle exit. The interfacial velocity of a breaking liquid jet indicates the interaction of the gas and liquid flows and the initial velocity of the stripped droplets. However, the local interfacial liquid velocities have not been measured, since no measurement technique is available, and they have only been estimated from theoretical and computational studies. Optical Connectivity (OC) is a new optical technique, which introduces a laser beam through an atomiser nozzle and relies on total internal reflection at the liquid interface to propagate the laser light inside the continuous liquid. This allows the recording of the instantaneous features of the disintegrating continuous liquid and its interface during the primary atomisation at the near nozzle region through imaging of the emitted fluorescent intensity from the liquid flow. The current research reports time-dependent OC measurements of the temporal evolution of the liquid interface structures along a LJIC. The LJIC breakup behaviour is reported for different atomisation regimes, as determined by non-dimensional parameters. Optical Connectivity is combined with Optical Flow Velocimetry (OFV) to quantify the local interfacial liquid velocities of liquid interface structures of the LJIC for a range of gas Weber numbers between 14.9 - 112.6 and liquid-to-gas momentum ratios between 2.1 - 36.4. The combined OC-OFV measurements report the spatial distribution of interfacial velocities along the surface of LJIC and reveal the physics of the contribution of gaseous shear and liquid jet geometry on the atomisation process.