Numerical investigation on jet characteristics and performance of SparkJet actuator based on pressure wave behavior inside a cavity

Abstract

Thrust and total impulse performance of a SparkJet actuator are affected by pressure waves inside the cavity, so it is important to understand these effects. The two objectives of the present study are to characterize the jet performance of a SparkJet actuator and to investigate pressure waves inside the cavity and correlate them with actuator performance. To this end, a SparkJet actuator is solved numerically based on equilibrium gas assumption. Loss of thrust occurs because of the pressure drop caused by the pressure wave, flow separation at the orifice throat, and vortex above the orifice exit. A fast Fourier transform of thrust reveals pressure wave components at two natural frequencies that originate from the pressure waves inside the cavity. The reflected pressure waves inside the cavity affect natural frequencies. The pressure wave reflected in the r-axis direction is affected by the energy deposition aspect ratio which influenced the total impulse by as much as ∼3.21%. The pressure wave reflected in the z-axis direction is affected by the effective height distance. However, this rarely affects the total impulse directly. The use of an appropriate taper angle affects the total impulse by as much as ∼8.49%. Approximately, 11% of the total impulse is originated from oscillations by the reflected wave in the r-axis direction, whereas 4% of it is from the reflected wave in the z-axis direction. This work contributes to improving the design of electrode and cavity configurations for SparkJet actuators and showing the importance of oscillations made by reflected pressure waves.