Analysis of Bulb Turbine Hydrofoil Cavitation

Abstract

The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds’s number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties.

Control mechanisms of different bionic structures for hydrofoil cavitation

“…Passive control of hydrofoil cavitation refers to disturb the flow by changing the surface structure or material properties of hydrofoils, so as to inhibit the occurrence and development of cavitation [15] , [16] . There are many studies on the passive control methods, such as setting obstacles on the hydrofoil surface [17] , [18] and modifying the airfoil profiles [19] , [20] . Lin et al [17] found that circular obstacles on the plane hydrofoil could stabilize the leading-edge cavitation and reduce the shedding cavitation.…”

“…Che et al [18] focused on the obstacles on the suction side of hydrofoil, and found that the increase of wall pressure near the obstacles inhibited the development of sheet cavitation, verifying the effectiveness of obstacles in cavitation control. Podnar et al [20] studied the influence of spherical blade shape on flow characteristics, and found that modifying the design parameters of hydrofoil can reduce the occurrence and development of cavitation. In addition, setting surface roughness [21] , [22] , [23] , vortex generators [24] , [25] , [26] and jet holes [27] can also realize the passive control of hydrofoil cavitation.…”

Numerical Study of Cavitation Characteristics through Butterfly Valve under Different Regulation Conditions

“…They analyzed the morphological characteristics of cavitation bubble collapse at specific times and calculated the collapsed cavitation bubbles near the solid wall using the open FOAM program. Podnar et al [10] studied the influence of blade hydrofoil shape on flow characteristics by conducting experimental studies on a bulb turbine measuring station and a single hydrofoil in a cavitation tunnel. They also carried out the flow visualization of the suction surface of a hydrofoil in a cavitation channel.…”

Exploration of the mechanism of cavitation vortex rope and vortex development in the draft tube of tubular turbine units

“…The development of inter-leaf and tailwater rope vortices depends on the flow and velocity characteristics of the rotor inlet and outlet. Ji et al [10] used a scale-adaptive simulation method and a diffuser with cyclonic flow to simplify and simulate the non-contact flow inside a draft tube to reveal the potential mechanism between the structure of the vortex rope and the cavitation vortex. From the analysis of the vorticity transport equation, it was concluded that the vorticity expansion term is larger along the cavity interface and the vorticity field is modified in the region of higher density and pressure gradients.…”