Sulfur hexafluoride pulsed jet visualization by the Resonant Schlieren method

• Published in: Optics continuum 2023-01, Vol.2 (1), p.205
• Main Authors: Machado, Danilo Almeida, de Souza Costa, Fernando, Carlos de Oliveira, Antonio, Junior, Annibal Hetem
• Format: Article
• Language: English
• ISSN: 2770-0208; 2770-0208
• DOI: 10.1364/OPTCON.474915

Resonant Schlieren technique combines the variation of the refractive index of the medium with the absorption of seeded particles, thus producing high contrast images. It presents low cost and a relatively easy implementation and operation, and allows visualization of low and high-density flows. This paper describes the application of the Resonant Schlieren method to visualize a pulsed free jet of sulfur hexafluoride. A piezoelectric valve with a duty cycle of 10 Hz and pulse width of 2 ms was used to control the flow through a nozzle with 1 mm diameter. Pressures in a vacuum chamber with optical windows were varied from 20 mbar to 1 bar and the flow was seeded with iodine molecules in order to increase the gas refractive index. The Schlieren images of the expanded flows presented a high contrast and the measured pulsed jet front velocities varied from 3 to 166 m/s, from subsonic to supersonic flow regimes. Numerical simulations were performed using the lattice Boltzmann method and the theoretical results showed a good agreement with experimental data.