Measurement of the Free Surface in the Wake of a Submerged Foil

Author

Jamie Schicho, University of Rhode IslandFollow

Date of Award

2021

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

Jason Dahl

Abstract

This thesis investigates measurement techniques to measure the far field free surface wake of a submerged hydrofoil in a fluid flow. There were three independent variables adjusted during testing; 2 angles of attack (5 and 10 degrees), 3 depths of the foil (1*chord length, 5/4*chord length, and 3/2*chord length), and 6 flow speeds (between 0.70 m/s and 1.10 m/s). The Fr²_d values for these experiments were between 0.115 and 0.42 which was chosen to be similar to that of the Duncan Experiments in 1981.

For the surface elevation measurements two methods were explored through this research. The first method was Digital Image Correlation (DIC). This method proved effective for determining the surface elevation for waves that formed behind the foil at low flow speeds. At higher flow speeds (> 0:7 m/s) a steady state wake formed behind the foil. However at these higher speeds there was substantial turbulence at the surface which caused ray crossing in the images captured through the free surface. This meant that the DIC analysis had extremely inconsistent results at the flow speeds of interest in this research.

The second surface elevation measurement method was a side view image processing method. This proved to be a viable method to capture the surface elevation for run cases of interest in these experiments. The wave form created behind the submerged foil was steady state for most of Fr²_d values that were tested. For the majority of the run cases the wave form behind the submerged foil matched well with a curve fit based on a sum of sinusoidal waves, as expected. These experiments were only repeated once for a single angle of attack. For these repeated cases the results were consistent however this requires more testing to confirm repeatability of the experiments. In the Froude number analysis the experimental wavelength results agreed well with the expected wavelength results based on the linear dispersion relation. The results from Duncan (1981) align very well with breaking wave cases from these experiments for both wave height and wavelength.

Recommended Citation

Schicho, Jamie, "Measurement of the Free Surface in the Wake of a Submerged Foil" (2021). Open Access Master's Theses. Paper 1957.
https://digitalcommons.uri.edu/theses/1957