ID 200

High Speed Visualization and Measurement of Liquid Velocity and Volume Fraction Distributions in Turbulent Cavitation Flow in a Tiny Nozzle using Synchrotron X-Ray

 

Abstract:

A number of experimental and numerical studies on turbulent cavitation flow in the nozzle of fuel injectors have been carried out. However, the planar distributions of local instantaneous liquid velocity and liquid volume fraction in cavitation region have not been measured quantitatively, which makes it difficult to quantitatively establish a numerical model on turbulent cavitation flow. In this study, we develop a new measurement method to quantitatively and simultaneously measure the planar distributions of local instantaneous liquid velocity and liquid volume fraction in a turbulent cavitation flow inside a two-dimensional (2D) rectangular nozzle by using synchrotron high-flux x-ray at SPring-8 (Super Photon ring-8 GeV). Hollow glass microspheres are mixed in filtered tap water, which can be visualized by X-ray phase contrast imaging technique and then detected by image analysis, since almost all the cavitation bubbles are not spherical and their diameters are different from those of the glass particles. The PTV and PIV analyses of the high speed images of turbulent cavitation flow with the glass particles in a 2D nozzle with 0.5 mm in width and 2 mm in length are carried out to measure the planar distribution of local instantaneous liquid velocity in cavitating flow. We simultaneously measure the planar distribution of local instantaneous liquid volume fraction based on the local number density of the glass particles, by assuming that αL = 1 when the number n of the glass particles in an inspection volume is the largest, αL = 0 when n = 0, and αL is proportional to the particle number. As a result, we obtain liquid velocity distributions in recirculating cavitation flows in the nozzle by X-ray PTV and PIV, and the distributions of liquid volume fraction for various cavitation regimes, such as incipient cavitation and super cavitation regimes.