Spectral and modal analysis of a cavitating flow through an orifice

• Published in: Experimental thermal and fluid science 2021-02, Vol.121, p.110251, Article 110251
• Main Authors: Esposito, C., Mendez, M.A., Steelant, J., Vetrano, M.R.
• Format: Article
• Language: English
• Subjects: Attenuation; Cavitation; Cavitation number; Cloud cavitation; Downstream effects; Flow rates; Flow velocity; High speed; High-speed visualization; Modal analysis; Multiscale modal analysis; Orifice flows; Orifices; Pressure; Pressure oscillations; Proper Orthogonal Decomposition; Supercavitating flow; Transducers; Video
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2020.110251

•The mPOD decomposed videos of cavitating flows into modes with band-limited spectra.•A larger amount of vapor broadens the frequency spectra of the shedding modes.•Higher frequencies are linked to the regular shedding of the vapor clusters.•Low frequencies produced at the orifice exit are dominant in the far-field. Cavitation phenomena, produced when a flow is accelerated through a restriction, are of fundamental importance because of the large pressure oscillation they induce on pipelines. This paper presents an experimental investigation of various cavitation regimes produced at the exit of an orifice and its downstream propagation and attenuation. A cylindrical and a conical orifice are investigated over a range of cavitation number σ=0.2-1, keeping the ratio between saturation pressure (Psat) and downstream pressure (Pdw) at two different values ξ=Psat/Pdw=0.05,0.3. The range of operating conditions allows to investigate cavitation from the inception to the cloud, the developed, and the super-cavitation regime. For each configuration, the experimental analysis includes flow rate measurements, pressure signals via fast pressure transducers, and high-speed videos. The videos are analyzed using Multiscale Proper Orthogonal Decomposition (mPOD), to extract the coherent patterns that arise during the cloud cavitation and the developed cavitation regimes. The simultaneous analysis of the high-speed video in the proximity of the orifice and the time-resolved downstream pressure signal allows highlighting the effect of the cavitation intensity on the downstream evolution of these fundamental flows.