Measurements of the free-surface behind a backward facing step are made using laser-induced fluorescence and a digital video camera. Tests are conducted for two Reynolds numbers and a range of Froude numbers. An edge detection algorithm is used to locate the free surface from the digital images, and the ensemble of images are used to calculate the mean and root mean square of the elevation. The results of amplitude, length, and steepness are determined from the mean profiles and compared to existing potential flow theories. It is found that the potential flow theories overpredict the real-fluid measured mean-wave amplitude. The experimentally determined wavelength is much shorter than the nominal length, and an existing stream function theory is implemented to explain how the viscous wake acts to shorten the steady wavelength.
Stern flow field of a container ship in turning motion
