Modeling of Cavitating Flow through Waterjet Propulsors

Abstract

A computational-fluid-dynamics-based modeling effort to capture flow through an axial flow waterjet propulsor is presented. The effort covered the waterjet flow over a wide range of flow coefficients and into cavitation-driven breakdown. The computations are presented in cavitation at two values of flow coefficient through a series of decreasing operating inlet total pressure. The computational results are compared to experimental measurements. Suction-surface and tip-gap cavitation patterns are presented and compared to experimental photographs. Presented computational solutions are blade-passage steady and periodic. The computational results apply a powering iteration methodology to facilitate coupling of rotor, stator, and inflow and outflow ducting.

Numerical Assessment of a Two-Phase Model for Propulsive Pump Performance Prediction

“…As N * keeps decreasing and the values of T and H * start dropping steeply, the numerical model deviates significantly from the test data. A similar trend can be observed in the CFD results reported in the study of Lindau et al [32]. The reasons for this behaviour were first adduced by Chesnakas et al [51] and later confirmed by Tan et al [12] and Chen et al [13].…”

“…In particular, Zhao et al [41] and Guo et al [42] formulated modified versions of the ZGB cavitation model to account for the effect of vorticity on cavitation. In this path, Lindau et al [32] obtained good results for the same axial-flow waterjet pump described in the present paper, employing a steady-state RANS approach with homogeneous multiphase assumption and a mass-transfer rate cavitation model. The adopted cavitation model is characterized by empirical coefficients set to default values to provide good results for general applications, e.g., simple geometries like hydrofoils or complex machines.…”

“…In particular, l B is measured as the normalized streamwise distance between the two locations on the blade surface at which α v = 0, while V vap sums up the cells volume where α v > 0.1 and is then normalized with the coarse grid result. GCI parameters for both medium (GCI 32 medium ) and fine refinement (GCI 21 f ine ) are summarised in Table 1. These include the extrapolated variables, ϕ ext , and error, e ext .…”

“…In this path, numerous eddy viscosity models have been employed to account for the subgrid-scale terms in different hydraulic machinery analyses [29,30], with a marked predominance for the k − ω Shear Stress Transport (SST) model by Menter [31]. Examples are innumerable, and the reader can refer to [27,30,[32][33][34][35][36][37][38][39][40] for further insights.…”

On the Effects of Tip Clearance and Operating Condition on the Flow Structures Within an Axial Turbomachine Rotor Passage

“…There is a large body of literature on the effect of cavitation on the performance of axial turbomachines, including tests of waterjet pumps performed in the present facility [48,49]. They show that for cavitation to adversely affect the overall machine performance, almost the entire suction side of the rotor blades has to be covered by attached cavitation [50]. For a less developed extent of cavitation, such as the present conditions, it has a negligible effect on the overall machine performance.…”