Bluff Body Flows in the Presence of a Free Surface

Author: Valluri, Siddhartha

Year: 1996

Degree: Dissertation (Ph.D.)

Advisors: Roshko, Anatol; Gharib, Morteza

Committee Members: Roshko, Anatol; Gharib, Morteza; Hornung, Hans G.; Leonard, Anthony; Wu, Theodore Yao-tsu

Option: Aeronautics; Electrical Engineering

DOI: 10.7907/2wbk-9k81

Abstract

An experimental study is performed in a water tunnel (Re = 40,000 to Re = 60,000) to study the interaction between the wake of a circular disk and the free surface. The deformation of the free surface is correlated with the behavior of the wake by utilizing surface pictures, wake flow visualization, drag measurement and Digital Particle Image Velocimetry techniques. It is observed that the wake can exist in two modes with different stabilities. The flow can switch between these two modes and the switching process exhibits hysteresis. The topological differences between these modes and their relation to the observed surface patterns are discussed. The changes in the wake are reflected by an increase in Cd which reaches a maximum value when the upper edge of the disk is 0.125 diameters from the surface. Comparison is also made with a disk approaching a solid boundary.

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