"Onset of ventilation of surface-piercing hydrofoils" - June 12, 2025, Thursday, 2:30 pm, Pavilhão de Civil, amphitheatre VA5

Date: June 12, 2025, Thursday
Time: 2:30 pm
Place: Pavilhão de Civil, amphitheatre VA5 (Floor -1)

• Speaker: Manuel Aguiar Ferreira (Research Associate, Delft University of Technology)

• Title: "Onset of ventilation of surface-piercing hydrofoils"

• Abstract:

Hydrofoils have become extremely popular in recent decades for application to fast passenger ferries and high-performance sailing. They lift the hull up and out of the water as speed increases, significantly reducing the hydrodynamic resistance and improving the overall sailing efficiency. However, operating near the free surface, where they are most efficient, makes them prone to ventilation. This phenomenon leads to a sudden drop in lift and flutter that may have potentially catastrophic consequences.

To improve the design and safe operation of these devices, a significant effort has been made to map flow stability regions. The usual approach involves a systematic survey of the parameter space, defined by the depth-based Froude number and the angle of attack. This approach assumes that the steady-state flow regime depends only on the local values of the parameters, provided they are varied under suitable quasi-steady-state conditions. In this Seminar, we present experimental evidence that challenges this assumption. Tests were conducted by increasing the Froude number at a constant angle of attack and, conversely, by increasing the angle of attack at a constant Froude number. We show that the boundary between bistable and globally stable regions is not uniform and extends to significantly higher angles of attack than previously estimated. A revised stability map is proposed to reconcile the discrepancy between published and present data, illustrating how two alternative paths to a steady-state condition can lead to different flow regimes. We additionally provide insights into complex flow dynamics governing natural ventilation, particularly its trigger mechanisms, contributing to refining predictive models for hydrofoil performance in practical applications.

• Short Biographic Note:

Manuel Aguiar Ferreira completed his PhD at the University of Southampton, within the Aeronautical and Astronautical Department, where he investigated the development of turbulent boundary layers over rough surfaces. He was also involved in research on the acoustics of separated aerofoils, the interaction between turbulence and wind turbines, as well as the development of new experimental facilities and measurement instruments. Following a period working as Project Manager Seakeeping at the Maritime Research Institute Netherlands (MARIN), he returned to academia as a Postdoctoral Researcher at Delft University of Technology, in the Netherlands, within the Department of Process and Energy. His current research explores the phenomenon of ventilation of surface-piercing hydrofoils.

This is another Seminar of the “Seminars@DEM” cycle.
Next Seminar, June 20, 2025, Friday, 3:00 pm.