Analysis of cavitating flow structure by experimental and numerical investigations

Abstract

The unsteady structure of cavitating flows is investigated by coupled experimental and numerical means. Experiments focus on the structure and dynamics of sheet cavitation on the upper side of a two-dimensional foil section in the ENSTA cavitation tunnel. Various flow conditions are investigated by varying the pressure, the flow velocity, and the incidence of the foil section. High-frequency local measurements of volume fractions of the vapour phase are performed inside the liquid/vapour mixture by a X-ray absorption method. The numerical approach is based on a macroscopic formulation of the balance equations for a two-phase flow. The assumptions required by this formulation are detailed and they are shown to be common to almost all the models used to simulate cavitating flows. In the present case we apply a single-fluid model associated with a barotropic state law that governs the mixture density evolution. Numerical simulations are performed at the experimental conditions and the results are compared to the experimental data. A reliable agreement is obtained for the internal structure of the cavity for incidence varying between 3° and 6°. Special attention is paid to the mechanisms of partial and transitional instabilities, and to the effects of the interaction between the two sides of the foil section.

Numerical Investigation into Effects of Viscous Flux Vectors on Hydrofoil Cavitation Flow and Its Radiated Flow Noise

“…Figures 12-14 compare the iso-contours of the predicted distributions of the stream-wise (x-direction) velocities, of the three different viscous models, during a single cycle. As reported in several previous studies [3,[42][43][44], the re-entrant jet is the most critical mechanism causing unstable cavitation behavior. The re-entrant jet causes adverse velocity gradients on hydrofoil surfaces in a stream-wise direction, and then back-flow toward the leading edge occurs.…”

Bubbly shock propagation as a mechanism for sheet-to-cloud transition of partial cavities

“…The shock propagation and sound mixture sound speed models also appear to adequately capture the shock dynamics. These models do not consider the bubble dynamics within the cavity flow, including the complex topology of the gas phase at high cavity void fractions, as discussed by Coutier-Delgosha et al (2006), nor is the constant production of vapour at the cavity detachment included in the modelling.…”

“…Also, a propagating bubbly shock would not have a sharp front but would have finite thickness related to the dynamics of the collapsing cavitation bubbles, as discussed by Brennen (2005). The length scale of the bubbles within the high void-fraction cavitating portion of the cavity, prior to the passage of the front, is expected to be of the order of 100 microns and the shape to be highly non-spherical, as shown by Coutier-Delgosha et al (2006). Therefore, we can expect the thickness of the front to be a multiple of this length scale.…”

An active method to control cavitation in a centrifugal pump by obstacles

“…Mou et al 15 analyzed the characteristics of non-smooth drag reduction influence on centrifugal pump impeller; the non-smooth surface well controls the near blade wall boundary layer flow and reduces the shear stress of the blade; and the pit-shaped nonsmooth surface can reduce the fluid turbulent flow in the centrifugal pump impeller, reduce the energy dissipation caused by the turbulent, make the fluid flow more stable in the impeller, and improve the efficiency of the centrifugal pump. Coutier-Delgosha et al 16 also studied the cavitating flow structure and analyzed a surge mode oscillation characterized by a global pulsation at low frequency by numerical and experimental methods. Pouffary et al 17 investigated the cavitating flow in turbomachinery with the help of numerical simulation using a barotropic state law to model cavitation phenomenon.…”