Physics-Based Pressure Field and Fluid Forcing Inference for Cylindrical Bluff Body Experiments

Abstract

The proceeding work details contributions to the state-of-the-art of velocimetry-based experimental fluid mechanics through the application of novel pressure and force estimation methods to studies in bluff-body aerodynamics and the problem of vortex-induced vibrations. Together, these techniques allow the measurement of fluid velocity and pressure, in space and time, for an area of interest surrounding an immersed body, along with the estimation of the total forcing on the immersed body. Conditions for optimal data sampling from the velocimetry data for the estimation of pressure fields are approximated analytically, and a variety of common pressure integration techniques are compared. The assessed integration techniques are characterized as having similar accuracy, with minor differences in error sensitivity observed. The errors in the estimated pressure fields can be expressed by considering the conformity of the obtained velocimetry data with the governing equations of motion. Accordingly, an analytical framework is developed which propagates the errors in the velocity field measurement through the pressure calculation. A subset of the error terms may be resolved in practical experiments, while others must remain neglected, in the absence of an extended model. Once equipped with the time-resolved pressure field, a control-volume-based analysis then allows the estimation of time-resolved forcing data. The dependence of the time-resolved force estimations on an often neglected three-dimensional term in the planar momentum balance is shown analytically. As a result, specific recommendations are provided for experimental best practises and field of view selection for obtaining accurate time-resolved forcing data from planar velocimetry measurements. Finally, following the previous methodological verification studies, the post-processing techniques are applied to an experiment of a stationary cylinder and that undergoing forced oscillations in a steady free-stream. The three-dimensional flow field surrounding the body is statistically reconstructed along with the pressure estimates in order to resolve the velocity/pressure and force distributions in the volume immediately surrounding the cylinder.