LIFT AND DRAG OF HYDROFOILS: APPLICATION OF THEORY TO EXPERIMENTAL RESULTS
Abstract
It is shown that the induced drag of a hydrofoil of aspect ratio = or > 6 (the smallest investigated) can be computed with sufficient accuracy by a procedure similar to that used for airfoils in an infinite medium. The several methods for computing the wave-making drag of hydrofoil in mediums of finite or infinite depth are compared. An empirical correction factor depending on the ratio or velocity to critical velocity is applied to the equation for the 2- dimensional wave-making drag of a flat plate in a medium of infinite depth to approximate the decrease of the wave-making drag in a medium of finite depth. In the actual operation of a hydrofoil in open water, this correction factor becomes negligible. Wave-making and induced drags are subtracted from experimental total drag to give values of profile drag. An examination of the resulting profile drag curves and those obtained directly from NACA wind-tunnel tests showed very close agreement when the hydrofoil and airfoil sections were tested at the same Reynolds nos. Similar form and reasonable magnitude were obtained when the hydrofoil was tested at lower Reynolds nos. Since the wave-making and induced drags of a hydrofoil are independent of scale effect, it is possible, given the profile drag at a suitable Reynolds no., to find the full-scale total drag at that Reynolds no. It is also shown that the slop of the lift coefficient with angle of attack is a function of submergence and increases with depth toward a theoretical infinite-depth value depending on the aspect ratio.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1952
- Accession Number
- AD0008348
Entities
People
- B. V. Korvin-kroukovsky
- Robert J. Wernick
Organizations
- Stevens Institute of Technology