Neil S. Rodrigues

A Parametric Investigation of Gelled Propellant Spray Characteristics Utilizing Impinging Jet Geometry

Phase Doppler anemometry is used to experimentally measure and compare the drop size and drop velocity of two gel propellant simulants – 1.0 wt.-% Agar and 1.0 wt.-% Kappa Carrageenan with deionized water. A parametric study is conducted to observe the influence of geometry on the drop characteristics. A like-on-like impinging jet doublet is used with varying impingement angles, free jet length-to-orifice diameter ratios, and internal lengthto-orifice diameter ratios. The impingement angle and free jet length-to-orifice diameter ratio are not observed to show strong drop characteristics correlations. Increasing the internal length-to-orifice diameter ratio is observed to produce larger drop diameters.

Spatially Resolved Gelled Propellant Spray Characteristics of Impinging Jets

The spatially resolved spray characteristics created by the like-on-like impingement of two gelled propellant simulants was experimentally investigated using Phase Doppler Anemometry (PDA). Water based gels of 1.0 wt.-% agar and 1.0 wt.-% kappa carrageenan, which were characterized using the Herschel-Bulkley rheological model, were used as the gel propellant simulants. Spatially resolved measurements for drop size and drop velocity were obtained up to 10 mm away from the centerline along the transverse axis in the plane of the sheet and up to 20 mm away from the centerline along the transverse axis in the plane normal to the sheet. All measurements were obtained at an axial plane 5 cm downstream of the impingement point. Larger D10 and D32 mean diameters and lower mean axial drop velocity Uz-mean were observed for transverse distances away from the centerline of the spray along both the axis in the plane of the sheet and in the plane normal to the sheet.Copyright

Impinging Jet Spray Formation using Viscoelastic Liquids

The impinging jet spray formation of viscoelastic liquids was experimentally studied using water-based solutions of xanthan gum at three different concentrations (0.1 wt.-%, 0.5 wt.-%, and 4.0 wt.-%). Unique spray patterns were observed depending on the generalized Bird-Carreau jet Reynolds number, jet Weber number, and jet Weissenberg number. The maximum instability wavelength and sheet breakup lengths were extracted from the shadowgraphs. Drop formation was only observed for the 0.1 wt.-% xanthan gum solution and Phase Doppler Anemometry was used to measure means and distribution of drop diameter and drop axial velocity.

Measurement of Aerodynamic Breakup of Non-Newtonian Drops by Digital In-Line Holography

Aerodynamic fragmentation of bulk liquid into small droplets is an essential spray process that occurs in a variety of combustion systems. The aerodynamic breakup of non-Newtonian fluids, such as aerospace propellants, bio-fuels, fire-fighting liquids, thermal barrier coatings, water-gel explosives, paints, etc, is involved in many important applications. Non-Newtonian fluids differ from Newtonian fluids in that they do not exhibit a linear shear stress-strain rate relationship. They are employed when the liquid is desirable to have a low viscosity during spray formation (high strain rate) and a higher viscosity when on a target (low strain rate). This useful rheological behavior leads to a significantly different breakup mechanism of non-Newtonian fluids compared to that of Newtonian liquids. Unfortunately, there are limited experimental studies on the aerodynamic breakup of non-Newtonian drops. This is probably due to the difficulty in measuring fragments of complex morphologies. Digital in-line holography (DIH) provides simultaneous measurements of the particle size and position with unique access to three-dimensional (3D) information. Previous applications have demonstrated its applicability to arbitrary-shape particles, capability of extracting 3D morphologies, and effectiveness in characterizing the aerodynamic breakup of Newtonian drops. In the present study, the aerodynamic breakup of non-Newtonian drops is characterized using DIH. The measured characteristics including breakup morphologies, fragment/droplet size distribution and velocity distributions, demonstrate the effectiveness of DIH as a diagnostic tool for non-Newtonian fluids.Copyright