City Research Online

Abstract

The present study experimentally investigates the onset of ventilation of surface-piercing hydrofoils. Under steady-state conditions, the depth-based Froude number �� and the angle of attack � define regions in which distinct flow regimes are either locally or globally stable. To map the boundary between these stability regions, the parameter space (�,��) was systematically surveyed by increasing � until the onset of ventilation while maintaining a constant �� . Two simplified model hydrofoils were examined: a semi-ogive with a blunt trailing edge and a modified NACA 0010-34. Tests were conducted in a towing tank under quasi-steady-state conditions for aspect ratios of 1.0 and 1.5 , and for �� ranging from 0.5 to 2.5 . Ventilation occurred spontaneously for all test conditions as � increased. Three distinct trigger mechanisms were identified: nose, tail and base ventilation. Nose ventilation is prevalent at �� <1.0 and �� <1.25 for aspect ratios of 1.0 and 1.5 , respectively, and is associated with an increase in the inception angle of attack. Tail ventilation becomes prevalent at higher �� , and the inception angle of attack exhibits a negative trend. Base ventilation was only observed for the semi-ogive profile, but it did not lead to the development of a stable ventilated cavity. Notably, the measurements indicate that the boundary between bistable and globally stable regions is not uniform and extends to significantly higher � than previously estimated. A revised stability map is proposed to reconcile previously published and current data, demonstrating how two alternative paths to a steady-state condition can lead to different flow regimes.

Publication Type:	Article
Additional Information:	© The Author(s), 2026. Published by Cambridge University Press. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Publisher Keywords:	waves/free-surface flows, multiphase flow, flow control
Subjects:	Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology School of Science & Technology > Department of Engineering
SWORD Depositor:	Symplectic Administrator

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