Particle image velocimetry for velocity measurement of muzzle flow: Detailed experimental study

A deep understanding of muzzle flow fields is essential for optimizing muzzle devices and projectile design. This flow characterization has been heretofore limited to local and intrusive measurement techniques such as pressure measurements using pencil probes. Consequently, the quantitative experimental data are limited, so are the number of numerical codes validated in this field. The objective of the present work is to demonstrate the applicability of the Particle Image Velocimetry (PIV) technique to provide accurate velocity measurements in the challenging environment of the propellant flow of a.300 blackout weapon. During this work, we have studied the feasibility of PIV on the muzzle flow using: (i) the naturally existing particles in the combustion gas as tracers, (ii) two different solid tracers; namely TiO₂ and ZrO₂ particles with a nominal size of 100 nm, seeded using two different methods. The first method implies coating the propellant grains with the tracer powder, in the second one the tracer is added directly inside the cartridge case. The experiments aim to demonstrate in particular: (i) the capability of PIV to resolve the main structures of the flow, (ii) the assessment of particle response across the Mach disk, and (iii) the non-alteration of the weapon's ballistics. To achieve this goal, an experimental setup with five different measurements was installed: (i) PIV system, (ii) classical high-speed schlieren visualization, (iii) optical particle counter, (vi) pressure transducer in the combustion chamber, and (v) projectile velocity measurement. The experimental results demonstrated (i) the ability of PIV to accurately resolve the main features of the flow as well as the instantaneous velocity field; (ii) that the combustion products contain sub-micrometric particles which can follow with high fidelity the gas flow; (iii) that solid ZrO₂ particles, when coated on the propellant grains, are suitable as tracers presenting a good flow fidelity and that the seeding of these inert particles is recommended in subsonic conditions (or whenever there is a lack of unburned particles); and (iv) that the TiO₂ particles intended to act as tracers, surprisingly not only melted but also functioned as a combustion accelerator and decreased the number of particles in the propellant gas.