Experimental study on tail cavity structure and pressure characteristics of underwater vehicle with tail jet

Abstract

The tail of an underwater vehicle with a tail jet often creates an attached tail cavity when moving at high speed. The strong coupling between the tail cavity and high-speed jet affects the kinematics characteristics of underwater vehicles. This paper compares the influence of Froude number (Fr) and ventilation coefficient (CQv) on the tail cavity at area ratio A/Ae = 92.5 and 236.7 by water tunnel experiment. It was found that at a small Fr, the critical ventilation coefficient of the transition from intact (IC) to partially broken (PBC) and PBC to pulsating foam (PFC) at A/Ae = 92.5 is greater than that of A/Ae = 236.7. The cavitation number (σc) at A/Ae = 92.5 is generally smaller than that of A/Ae = 236.7. With increased CQv, PBC's dimensionless time-averaged length (Lc‾/D) decreases sharply and then gradually flattens. The Lc‾/D of A/Ae = 236.7 is larger than that of A/Ae = 92.5. The fluctuation amplitude of the PBC length is smaller than that of the PFC, and the fluctuation frequency (fLc) of the PFC length is about 120 Hz. The change in the tail cavity will affect the pressure characteristics of the vehicle's bottom. With the increase of CQv, the peak frequency of the bottom pressure fluctuation (fpeak) will continue to rise in the PBC until the transition to the PFC, and the fpeak will remain at about 120 Hz. The correlation coefficient is 0.74 between the fLc and the fpeak. In addition, the pressure oscillation intensity at the vehicle's bottom (pbrms) is small in the IC region. When the tail cavity changes from PBC to PFC, pbrms increases gradually at first, then tends to be flat.