Surface Of Hydrofoil Research Articles

Measurement of the Bubbly Flow Beneath Partial Attached Cavities Using Electrical Impedance Probes

Surface electrical impedance probes are used to examine the bubbly flow beneath and in the closure region of partial attached cavities. A series of electrodes were mounted flush to the surface of a cavitating hydrofoil to detect the presence of liquid or vapor through changes in the impedance of the local fluid medium. Signals from the electrical probes were used to determine the near-surface gas-phase velocity and the shedding frequency of the gas phase. The impedance technique is shown to have the potential to measure advection velocities within a partial cavity, and the frequency content of the signal is used to determine the dynamics of the vapor shedding process. [S0098-2202(00)00501-0]

Non-linear Theory for Partially Cavitating Hydrofoils

Present linearized theories can not predict cavity flow around a hydrofoil with rounded nose. The authors propose a non-linear theory for a partially cavitating hydrofoil with arbitrary profile where cavity does not generate from the leading edge of the hydrofoil. Transient cavity flow model is adopted in the present theory. According to Hess and Smith's method for a two-dimensional steady flow, line sources and vortex are distributed on the surface of hydrofoil and that of cavity to treat the hydrofoil and cavity thickness exactly. Boundary conditions are as follows : (1) flow direction is parallel to the surface on wetted portion of the hydrofoil(2) flow velocity is constant on the cavity surface except for the collapsing region(3) position of cavity tip coincides with laminar separation point or transition point of boundary layer on cavitating hydrofoilThe solution is derived by an iterative procedure. In the cavity collapsing region, cavity shape and collapsing length are determined by solving Rayleigh's equation for a single spherical bubble and connected to the constant velocity region. The laminar separation point and transition point are derived from theoretical calculation.Experiments were made with a hydrofoil with symmetrical section whose chord was 150 mm and thickness was 12 mm. The position of cavity tip and end, cavity volume and cavity shape were measured. The results of present theory were found to be in good agreement with experimental results.

Limiting Pressure on Hydrofoils at Small Submergence Depths

It is shown that the magnitude of the local velocity and the surface pressure coefficient can be limited over the entire upper surface of a two-dimensional hydrofoil as it approaches the free water surface. In this limiting condition the flow over the upper surface is governed by the shallow water wave propagation phenomenon, and the limiting pressure or velocity is determined by the maximum depth attainable from the hydraulic jump relations. The experimental data verifies this new theory and proves that the previous two-dimensional hydrofoil theories are valid only for relatively deeply submerged bodies.