Mechanisms of Force and Moment Generation by the Flow Over Oscillating Rectangular Cylinders
Abstract
The primary goal of this project is to develop an understanding of the underlying physics connecting the flow structures to the unsteady force and moment acting on a cylinder exhibiting flow-induced linear and/or rotational vibration. Of specific interest are cylinders of nominally square cross section exhibiting oscillation due to a type of movement-induced excitation, known as galloping, in the absence of interaction with vortex-induced vibration. For such configuration, the proposed work aims to address questions relating to: (1) the influence of canonical geometrical variations of the square cross section on the aero-elastic stability characteristics of the cylinder, (2) the validity of the typically-employed quasi-steady assumption in the analysis of gallop vibration at high amplitude of oscillation, and (3) the mechanisms leading to the generation of the force and moment on the cylinder by the flow. The investigation employs an experimental setup in which the cylinder is forced to oscillate at different frequencies and amplitudes under conditions corresponding to energy transfer from the flow to the cylinder. Measurements will be conducted over the Reynolds number range 1,000-10,000, based on the cylinder thickness, employing a six-component force/moment balance, planar whole-field molecular tagging two-component velocimetry, and a novel recently-developed molecular-tagging-based technique for measurement of the surface pressure and shear stress distribution. Synchronization of the phase-resolved data from all three measurement techniques will provide a unique database, enabling new insightful understanding of the relation hip between the flow features and the force and moment acting on the cylinder. This understanding will be aided by an analysis based on Poisson s equation for pressure through which the contribution to the force and moment by individual flow features is captured. The resulting physical understanding will be instrumental in facilitating the development of low-order physics-based models that capture the sensitivity of the characteristics of the unsteady flow force/moment to flow conditions and geometrical characteristics of the cylinder. These models could serve as useful design tools, particularly for cases where the quasi-steady assumption breaks down and knowledge of the static force characteristics would not be sufficient for analysis of gallop-induced vibrations. The outcome of the current project will impact a wide range of engineering applications, including flow-induced vibration of power lines, bridges and marine structures, in general, and of suspension lines of precision airdrop systems (PADS); a particular application of significant importance to the US Army.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 31, 2017
- Source ID
- W911NF1710153
Entities
People
- Ahmed Naguib
Organizations
- Army Contracting Command
- Michigan State University
- United States Army