Известия Томского политехнического университета: Инжиниринг георесурсов (Sep 2016)
Numerical and experimental investigation of cavitation flow around NACA0015 hydrofoil
Abstract
Hydropower resources, used for power generation in hidraulic power plants, are one of the major renewable energy sources. A significant scientific and technical challenge for designing the equipment of hydroelectric power plants is a cavitation caused by high velocity of water flow near the runner blades. Cavitation is also typical for other turbomachinery, pumps, hydraulic equipment, ship propulsors, etc. Cavitation leads to decrease in energy efficiency and increased wear of equipment. The needs in modeling turbulent flow around blade assemblies, the operation of which is accompanied by cavitation, require the development of modern numerical approaches capable of forecasting the cavitation occurrence and describing flow dynamics with satisfactory accuracy. The main aim of the research is to investigate cavitation flow in a vicinity of NACA0015 hydrofoil by means of experimental and numerical methods, to compare the simulation and measurement results, to analyze the effect of turbulence model on calculation of the boundary layer flow over the suction side of a hydrofoil. The methods used in the study. The spatial structure and dynamics of partial gas-vapor cavities were studied by high-speed imaging which was also used to estimate integral parameters of the cavities. Two-dimensional distributions of mean velocity and turbulent characteristics around the hydrofoil were measured by Particle Image Velocimetry (PIV) in both single- (non-cavitating) and two-phase (cavitating) flows. In numerical simulation of flows the authors have applied the methods of computational fluid dynamics based on solving the Reynolds equations for turbulent flow, using the control volume approach on a three-dimensional mesh consisting of hexahedral cells. The dispersed phase (cavitation bubbles and their clouds) was calculated by solving the equation of vapor fraction transfer. Turbulence was described by means of k-[omega] SST two-equation model, differential model of the Reynolds stress transfer (RSM) and the detached eddy simulation method (DES). The results. The authors obtained full set of data in the experiments. The data allow direct analysis of the results of numerical modeling and measurements and comparing the computational models. The carried out calculations showed that, even in the case of a small vapor cavity behind the leading edge of the hydrofoil, the use of the second-order closure method - differential model of the Reynolds stress transfer - was required to describe correctly the flow reattachment to the wall downstream. When the cavity became long, the flow unsteadiness was a determinant factor of turbulent transfer. Modeling with the eddy-resolving approaches allowed identifying the periodic dynamics of vapor cavities at low frequencies. In an unsteady case, the flow reattachment downstream of the cavity was better predicted by the model of the Reynolds stress transfer.
