Experiments in Fluids 17 (1994) 68-74 9 Springer-Verlag 1994 of the cross-flow separation region of 68 Abstract The flow in the cross-flow separation region of a 1.37 m long, 6:1 prolate spheroid at lO ~ angle of attack was investigated with a novel 3-D fiber-optic Laser Doppler Velocimeter (LDV). The probe was used to measure three simultaneous, orthogonal velocity components from within the model. The design and operation of this LDV probe is described and velocity, Reynolds stress, and velocity triple-product measurements are presented from the inner boundary layer through the boundary-layer edge. IntroductionThe phenomenon of three-dimensional separation of the flow about a body, though quite common, is both difficult to model and poorly understood. Indeed, since -unlike in two-dimensional flow separation -three-dimensional flow separation is rarely associated with the vanishing of the wall shear stress, it can often be difficult to even identify the presence or precise location of 3-D flow separation.In order to better understand three-dimensional flow separation, several groups have studied the flow about a 6 to i prolate spheroid at angle of attack. This flow is a well-defined, relatively simple 3-D flow which exhibits all the fundamental transition and separation phenomena of three-dimensional flow. The flow about the prolate spheroid is schematically illustrated in Fig. 1. The flow separating from the lee-side of the prolate speroid, at the point marked S x, rolls up into a strong vortex on each side of the body. This primary vortex is accompanied by several smaller vortices, which separate from the surface at the points $2 and $3. The flow reattaches at points, R, and R2. The complex interactions between vortices result in a highly skewed, and thus three-dimensional, boundary layer.Previous works by Meier et al. (1984 and, Kreplin et al. (1985) and Vollmers et al. (1985) at the DFVLR (now the DLR) and Barveris and Chanetz (1986) and Chanetz and D~lery (1988) at ONERA have documented the surface flow, surface pressure, skin friction and mean velocity around the prolate spheroid. Previous work at VPI by Ahn (1992) has documented the Reynolds number and angle of attack effects on the boundary layer transition and separation phenomena for this flow. Barber and Simpson (1991) thoroughly documented the mean and turbulent velocities in the cross-flow separation region, but due to the limitations of their instrumentation -five-hold pressure probes and crossed hot wires -they obtained no data within the inner boundary layer.Because of simple geometry and the extent of the experimental data obtained, this flowfield has made an excellent test case for three-dimensional computational models. A recent study by AGARD (199o) used the DFVLR and ONERA data for comparison to three-dimensional computations utilizing integral boundary layer, algebraic mixing-length, and eddyviscosity turbulence models. The AGARD study found that all of the computational models experienced difficulties in calculating the f...
An extensive experimental investigation was carried out to examine tip-vortex induced cavitation on a ducted propulsor. The flowfield about a 3-bladed, ducted rotor operating in uniform inflow was measured in detail with three-dimensional LDV; cavitation inception was measured; and a correlated hydrophone/high-speed video system was used to identify and characterize the early, sub-visual cavitation events. Two geometrically-similar, ducted rotors were tested over a Reynolds number range from 1.4×106 to 9×106 in order to determine how the tip-vortex cavitation scales with Reynolds number. Analysis of the data shows that exponent for scaling tip-vortex cavitation with Reynolds number is smaller than for open rotors. It is shown that the parameters which are commonly accepted to control tip-vortex cavitation, vortex circulation and vortex core size, do not directly control cavitation inception on this ducted rotor. Rather it appears that cavitation is initiated by the stretching and deformation of secondary vortical structures resulting from the merger of the leakage and tip vortices.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.