Investigation of the Behavior of Ventilated Supercavities in a Periodic Gust Flow

Abstract

A ventilated supercavity consists of a large, gas-filled bubble enveloped around an underwater vehicle that allows for significant drag reduction and increases in vehicle speed. Previous studies at the Saint Anthony Falls Laboratory (SAFL) focused on the behavior of ventilated supercavities in steady horizontal flows. In open waters, vehicles can encounter unsteady flows, especially when traveling near the surface, under waves. In supercavitation technology, it is critical that the vehicle remains within the cavity while traveling through water to avoid unwanted planing forces. A study has been carried out in the high-speed water tunnel to investigate the effects of unsteady flow on axisymmetric supercavities. An attempt is made to duplicate sea states seen in open waters. In an effort to track cavity dimensions throughout a wave cycle, an automated cavity-tracking script has been developed. Using a high-speed camera and the proper software, it is possible to synchronize cavity dimensions with pressure measurements taken inside the cavity. Results regarding supercavity appearance, cavitation parameters, and their relation to sea state conditions are presented. It was found that flow unsteadiness caused a decrease in the overall length of the supercavity while having only a minimal effect on the maximum diameter. The supercavity volume varied with cavitation number, and a possible relationship between the two was explored.

Numerical Study of the Behaviors of Ventilated Supercavities in a Periodic Gust Flow

“…The validation experiments are conducted in a high-speed water tunnel in the Saint Anthony Falls Laboratory at University of Minnesota with details provided in the past studies (Lee et al 2013, Karn et al 2015, Karn et al, 2016, Shao et al 2018and Wu et al 2019. It is a closed recirculating facility and the length of the horizontal test-section is 1.20 m long and the same cross section with the simulation.…”

“…The |/. and ~• €• in the experiments are measured through an automatic image processing technique described by Lee et al (2013) with an uncertainty around 8 %. It is depicted that aMp and its location are fluctuated periodically both in simulation and experiments.…”

“…However, there is only a very limited number of experimental works on supercavitation in unsteady flows. For example, Lee et al (2013) experimentally studied the ventilated supercavitation around a vehicle pitching up and down with the emphasis on the interaction between the vehicle aft body and supercavity boundary. Lee et al (2013) duplicated several sea states using a periodic gust generator in the high-speed cavitation tunnel at SAFL to investigate the effects of unsteady flows on the shape deformation of axisymmetric supercavities.…”

“…For example, Lee et al (2013) experimentally studied the ventilated supercavitation around a vehicle pitching up and down with the emphasis on the interaction between the vehicle aft body and supercavity boundary. Lee et al (2013) duplicated several sea states using a periodic gust generator in the high-speed cavitation tunnel at SAFL to investigate the effects of unsteady flows on the shape deformation of axisymmetric supercavities. Using the same setup, Karn et al (2015) provided further insight into the dependence of supercavity closure on the flow unsteadiness, and found the incoming unsteady flows would cause the transition of the supercavity closure and its shape.…”

“…Although synchronized measurements of cavity shape and pressure are conducted in the past (Lee et al 2013, Karn et al 2015, and Shao et al 2018, the pressure inside the ventilated supercavity is measured at a fixed location and the information regarding to the internal velocity and pressure field is still quite scarce in periodic gust flows due to the limitation of diagnostic approaches.…”