Behavior of hydrofoil cavitation in a slit channel

The paper presents the results of a cavitation in a slit channel study and offers an analytical description of cavity development. Special emphasis was placed on examining partial cavitation near a NACA 0012 hydrofoil (NACA - the National Advisory Committee for Aeronautics) inside slit channels of different geometries. Experimental investigation was carried out via high-speed imaging and the laser Doppler anemometry (LDA) method. The experimental data showed that the local flow velocity in hydrofoil leading edge area increased abruptly under arising cavitation. In addition, occurrence of cavitation raised flow velocity pulsation by 20%. In the case of a shorter channel, cavity growth occurred at higher cavitation numbers than for a longer channel. The cavity growth velocity was higher for a shorter channel. We showed that the tendency of partial cavitation development in the slit channel can be described as follows: L/C similar to sigma(-1), where L is the cavity length; C is the hydrofoil chord; sigma is the cavitation number; and parameter A changes as the slit channel length is varied. Comparison of cavitation development near hydrofoil at different attack angles alpha inside the slit channel with a three-dimensional (3D) cavitation tunnel was conducted. Cavitation in the slit channel occurred at lower sigma/2 alpha values compared to 3D cavitation flow around the hydrofoil. To directly compare lengths of the attached cavities arising in slit channels and 3D cavitation tunnels, an additional parameter is proposed, taking into account friction of the slit channel: K = lambda<middle dot>l/D. This parameter allowed us to quantitatively compare the characteristics of cavitating hydrofoils in slit channels and 3D tunnels. The paper provides the governing criteria of the cavitation in the slit channel. Our results propose the physical foundations for the development of cavities in the slit channel.