Prevention of cavitation corrosion

Abstract

The present invention directly deals with the problem of cavitation corrosion by modifying the hub of a propeller to eliminate low pressure areas. The present invention is the placement, formation, and / or insertion, on a propeller, of a non-smooth area in each facet of the hub between each of the blades. This area is also sometimes referred to as the “blade root”. The exact configuration of the raised area can vary from a longitudinal raised area to single or multiple bumps or buttons to single or multiple pointed projections. By modifying the hub, whether by casting a new propeller with a redesigned hub, or by retrofitting an existing hub, the elimination of corrosion occurs when a high Developed Area Ratio (DAR) propeller hub has one or more raised protrusions on the surfaces of the propeller hub between each blade seat. The addition of the raised protrusions discourages the formation of low pressure areas around the hub. By removing the low pressure areas from the immediate area around the hub, the shock waves caused by the collapse of the low pressure areas is moved away from the propeller, thus eliminating corrosion impact damage.

Description

CROSS-REFERENCE TO RELATED PATENTS [0001] This application claims the benefit, under Title 35, United States Code, Sec. 119(e), of U.S. provisional Application No. 60 / 636,176 filed Dec. 14, 2004, titled PREVENTION OF CAVITATION CORROSION, the disclosure of which, including all appendices and all attached documents, is hereby incorporated by reference in its entirety.FIELD OF THE INVENTION [0002] The present invention relates generally to design of propulsion devices, more specifically to the design of high efficiency propellers. BACKGROUND OF THE INVENTION [0003] Cavitation is the formation of partial vacuums in a liquid by a swiftly moving solid body or by high intensity sound waves. These partial vacuums are caused by a low pressure in the liquid. When the local ambient pressure at a point in the liquid falls below the liquid's vapor pressure, the liquid undergoes a phase change to a gas, creating “bubbles” or, more accurately, partial vacuums in the liquid. [0004] When the vacuum...

AI Technical Summary

Benefits of technology

[0008] By modifying the hub, whether by casting a new propeller with a redesigned hub, or by retrofitting an existing hub, applicant has discovered that the elimination of corrosion occurs when a high Developed Area Ratio (DAR) propeller hub has one or more raised protrusions on the surfaces of the propeller hub between each blade seat. The addition of the raised protrusions discourages the formation of low pressure areas around the hub. By removing the low pressure areas from the immediate area around the hub, the shock waves caused by the collapse of the low pressure areas is moved away from the propeller, thus eliminating corrosion impact damage.

Problems solved by technology

When the vacuums of cavitation collapse, they create large amounts of noise.

The collapse also produces very high energy and can cause major damage.

A solid body can become pitted and worn away due to the repeated collapse of these vacuums.

Cavitation corrosion occurs frequently on propellers, such as those used by aircraft and marine vessels.

When the vacuums collapse, they typically cause strong shockwaves in the fluid, which can cause damage to the blades or the propeller's hub.

This is particularly troublesome in high speed propellers, as the damage to the propeller reduces overall efficiency.

However, this approach does not completely solve the problem as the partial vacuums still can form around the hub and cause pitting and damage to the hub.

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