Session: 10-06-01: Fluid Measurements and Instrumentation

Paper Number: 145987

145987 - Characterization of Droplet Dynamics Under Impact of a Shock Wave Interacting With a Solid Surface 

This paper presents an experimental study on the transient deformation and breakup morphology of a water droplet as it approaches a solid surface driven by an interaction with a supersonic shock wave. This experiment is conducted in the Shock Tube Research Facility available in the Aero-Thermal Fluids Laboratory at the City College of New York. A droplet injection system integrated into the top of the Shock Tube Test Section produces consistently sized and spaced water droplets of a prescribed diameter. A shock wave, of Mach number greater than one, is then shot at the falling water droplet via the rupture of a mylar diaphragm after its subsequent burst pressure has been achieved in the Driver Section of the Shock Tube. Shock waves of varying Mach numbers are generated by loading differing mylar diaphragm thicknesses into the Shock Tube. Mylar thicknesses include 2, 5, 7, & 10 MIL (1/1000^th of an inch). As the shock wave travels down the length of the Shock Tube Driven Sections, its speed and pressure are monitored and recorded through digital pressure transducers and conventional pressure gauges mounted in the Driver Section and Test Section. After shock wave-droplet impact, the incident shockwave encounters a three-inch square metal plate mounted inside the test section to be visible through its horizontal viewports. It rebounds and impacts the falling water droplet a second time, causing significant deformation and its eventual breakup and failure.  

Well-synchronized control of all sub-systems enables the reproduction of shock-droplet-surface interactions under various test conditions. Multiple droplet-releasing ports were designed and manufactured to offer variable distances between the surface and the droplet upon impact by the shock waves. A high-speed imaging system, consisting of two high-speed cameras, a high-intensity LED point light source, and a series of optics, is used to visualize the complex shock-droplet-surface interactions. One of the high-speed cameras witnesses the impact through Schlieren conditions, to clearly visualize the large alterations of the density field generated by the shock wave. The other receives a collimated light beam through a cubic beam splitter, more clearly able to visualize the breakup morphology of the droplet.

It was found that the droplet breakup morphology and eventual failure depends largely on its size. Smaller droplets, around 1 mm in diameter, are deformed immediately and fail upon the second, weaker rebound impact. They then suffer a catastrophic break-up and rapid vaporization, their mist transported backwards through the post-shock cross flow. Larger droplets, around 5 mm in diameter survive almost unmoved through both incident and rebound impact. After the wave has cleared the droplet entirely, it begins to flatten and deform vertically in the post shock flow. This can lead to a bag deformation in the droplet, as it has become elongated enough to be filled by the remaining air flowing behind the initial shock. Should the water droplet have been dropped close enough to the plate, the inflating droplet can impact the plate, imparting energy upon it.  

Presenting Author: Jorge Ahumada Lazo The City College of New York

Presenting Author Biography: Dr. Jorge Ahumada Lazo is a Postdoctoral Research Associate in the Department of Mechanical Engineering at the City College of New York. He obtained his PhD degree in Mechanical Engineering from the University of Maryland Baltimore County in 2024. Prior to that, he earned a M.S. degree in Mechanical Engineering and a B.S. in Aerospace Engineering from New Mexico State University in 2018 and 2015, respectively.

Authors:

Jordan Giacoma City College of New York
Jorge Ahumada Lazo The City College of New York
Haipeng Zhang The City College of New York
Yang Liu The City College of New York