An experimental study on the erosion of solid propellant by cavitation water jet in submerged environment

Abstract

The submerged cavitation water jet (SCWJ) is a promising technology for removing solid propellant from old solid rocket engines and recycling them. In this study, the feasibility of using SCWJ to break solid propellant is investigated. The structure of the cavitation cloud was captured by a high-speed camera and then analyzed using the Proper Orthogonal Decomposition (POD) and Frame Difference Method (FDM) method for exploring the unsteady characteristic of SCWJ, the HTPB propellant erosion experiments were performed, and the relationship of the SCWJ unsteady characteristic and the erosion results on HTPB propellant was analyzed. The results show that the SCWJ develops in the flow field including inception, development, shedding, and collapse stages, the maximum density of cavitation cloud changes exponentially, and the cavitation cloud length grows as the cavitation numbers increase. Lower cavitation number is always beneficial to high penetration rate and low energy consumption when erosion on the HTPB propellant. When the erosion time of 120 s, in high cavitation number under the least amount of energy consumed, the unit energy consumption minimum. The mass loss curve is double peak, the first peak is caused by water jet effect, standoff distance is located on the stage of development, the formation of erosion pit diameter is small, the depth is larger, the second peak is caused by cavitation effect, and its standoff distance is located on the shedding phase, forming the erosion pit diameter is bigger, the depth is shallow. The optimum standoff distance for the cavitation effect for the cavitation numbers 0.0135, 0.0081, 0.0058 and 0.0045 is 35 mm, 50 mm, 60 mm and 70 mm in order, and the mass loss rate of HTPB propellant is 90 mg s⁻¹, 200 mg s⁻¹, 277 mg s⁻¹ and 521 mg s⁻¹, respectively. At best cavitation effect standoff distance, cavitation number by 2 times, mass loss rate can increase 3 times. The matrix brittle fractures occur when the SCWJ strikes the HTPB propellant at a high strain rate. Besides, the erosion mechanism of HTPB propellant is discussed.