Cavitation patterns on a plano-convex hydrofoil in a highspeed cryogenic cavitation tunnel

Abstract

Cavitation around a plano-convex hydrofoil has been observed using a cryogenic cavitation tunnel of a blowdown type. An approximately 300mm long test section with flow visualization was set between the 100L upper and lower tanks. The working fluids were water and liquid nitrogen. Experiments with emphasis on periodical shedding of cloud cavitation were performed for three channels, 20, 30 and 60 mm in width, and two hydrofoils, 20 and 60mm in chord length LC. Inlet velocity uin and cavitation number ? were varied between 3.8 and 19.5 m/sec, and ?1.83 and 19.35, respectively. Incident angle was fixed at 8º. Observed cavitation patterns are sorted according to the maximum cavitation length Lmax compared to LC. Type X is defined as no cavitation, type A as 0<Lmax?LC, type B as LC<Lmax?2LC, and type C as Lmax>2LC. Type B has either the periodical shedding mode or the steady mode, so type PB is defined as type B with periodical shedding and type SB as type B under steady condition. Apparently types A and C are almost steady. Type PB solely occurs in the case that Lmax is comparable to LC. The cavitation patterns are mapped in the diagram of the degree of subcooling Pin?Psat versus the dynamic pressure ?uin2/2 because they are not organized only by ? =(Pin?Psat )/(?uin2/2). It is suggested that the maximum cavitation thickness is controlled by the similarity laws of hydrofoils for types SB and C.