Suppression of the cavity oscillation using high-speed mass injection

The cavity flow oscillation is a typical unsteady, nonlinear flow phenomenon, accompanied by resonance with strong pressure oscillation and intense turbulence. A control method is proposed to suppress the cavity oscillation using high-speed mass injection. Wind-tunnel experiments are performed to validate the control method. A length-to-depth six cavity is employed in the experiments with a Mach number 1.8 of the incoming flow. The upstream injection is generated in the leading edge of the cavity with a large momentum coefficient (more than 10%). Effects of the high-speed mass injection on the cavity oscillation are validated by a significant reduction of the overall sound pressure level inside the cavity. The broadband cavity noise is reduced by more than 10 dB, with a great suppression of the cavity tones. Owing to the high-speed mass injection, the cavity oscillation has been effectively suppressed in the supersonic condition. Because there is no need of additional gas supply in the control system, the control strategy is considered to be a potential and practical candidate for engineering applications.

Dielectric and energy storage properties of PVDF/Nd-BaTiO3@Al2O3 composite films

Flexible Nd-doped BaTiO3@Al2O3/polyvinylidene fluoride (PVDF) composites have been successfully developed. With the reaction temperature of 70∘C, Nd-doped BaTiO3@Al2O3 particles display uniform core–shell structures and disperse well in the PVDF matrix. Due to the benign dielectric properties of Nd-doped BaTiO3 and great suppression of the Al2O3 coating on the leakage current and dielectric loss, the Nd-doped BaTiO3@Al2O3/PVDF composites with different Nd-doped BaTiO3@Al2O3 filling ratios (0–4[Formula: see text]vol.%) exhibit relatively good dielectric and energy storage performance. Among them, the maximum discharged energy density of 8.6[Formula: see text]J/cm3 was achieved in the composite with 1[Formula: see text]vol.% Nd-doped BaTiO3@Al2O3 loading.