Showing papers by "Steven L. Ceccio published in 2003"

Time-averaged flow over a hydrofoil at high Reynolds number

Abstract: At high Reynolds number, the flow of an incompressible viscous fluid over a lifting surface is a rich blend of fluid dynamic phenomena. Here, boundary layers formed at the leading edge develop over both the suction and pressure sides of the lifting surface, transition to turbulence, separate near the foil's trailing edge, combine in the near wake, and eventually form a turbulent far-field wake. The individual elements of this process have been the subject of much prior work. However, controlled experimental investigations of these flow phenomena and their interaction on a lifting surface at Reynolds numbers typical of heavy-lift aircraft wings or full-size ship propellers (chord-based Reynolds numbers, investigated.

Traveling-wave excitation and optical measurement techniques for non-contacting investigation of bladed disk dynamics

Abstract: In this paper we present the design of an experimental facility for measuring the vibration of bladed disks, such as those used in turbomachinery. In particular, a method for simulating the effects of rotating a bladed disk past stationary sources of excitation is described, in which acoustic excitation sources in the vicinity of each blade receive harmonic signals with precise phase differences. Optical measurement techniques, including laser vibrometry and holographic interferometry, are used to observe the vibration, so that neither excitation sources nor measurement devices contact the test specimen physically. The result is a versatile test facility appropriate for the investigation of complex bladed disk dynamics, including the effects of small variations in parameters, such as blade mistuning.

Microbubble Drag Reduction at High Reynolds Number

Abstract: This paper presents the preliminary results from a friction drag reduction experiment conducted at high Reynolds numbers. The experiments were conducted in two phases at the U. S. Navy’s William B. Morgan Large Cavitation Channel (LCC) in Memphis, TN on a flat, hydraulically smooth plate (12.9 meters long by 3.0 meters wide by 0.18 meters thick) at flow speeds ranging from 0.5 to 20 m/s. The employed drag reduction technique involved the injection of microbubbles into the boundary from a line source over a range of injection flow rates from 100 to 800 scfm. These results include mean velocity data and spatially averaged shear stress data acquired in the single-phase flow, as well as spatially averaged shear stress data, bubble images, and void fraction measurements made in the bubble-injected flow.Copyright © 2003 by ASME

Singularity image method for electrical impedance tomography of bubbly flows

Abstract: A singularity image method is applied to the electrical impedance tomography of gas-liquid flows in a two-dimensional circular domain. Algorithms that use analytic complex functions, dipoles and the Milne-Thomson circle theorem are described. Numerical experiments are provided to demonstrate the robustness of this technique. Numerical results show excellent reconstruction properties.

Dynamics and Noise Emission of Laser Induced Bubbles in a Vortical Flow Field

Abstract: The sound produced by the collapse of discreet cavitation bubbles was examined. Laser-generated cavitation bubbles were produced in both a quiescent and a vortical flow. The sound produced by the collapse of the cavitation bubbles was recorded, and its spectral content was determined. It was found that the rise time of the sound pulse produced by the collapse of single, spherical cavitation bubbles in quiescent fluid exceeded that of the slew-rate of the hydrophone, which is consistent with previously published results. It was found that, as the collapsing bubbles were deformed by the vortical flow, the acoustic impulse of the bubbles was reduced. Collapsing non-spherical bubbles often created a sound pulse with a rise time that exceeded that of the hydrophone slew-rate, although the acoustic impulse created by the bubbles was influenced largely by the degree to which the bubbles became non-spherical before collapse. The noise produced by the growth of cavitation bubbles in the vortex core was not measurable. These results have implications for the interpretation of hydrodynamic cavitation noise.Copyright © 2003 by ASME

Tip leakage vortex (tlv) variability from a ducted propeller under steady operation and its implications on cavitation inception

Abstract: The flow in the close vicinity of the blade-tip region of ducted propellers and similar hydro-machines can be quite complex due to the presence and dynamic interactions of the tipleakage vortex (TLV), the blade trailing edge vortex, (TEV) the gap shear flow, the wall (casing) boundary layer, and the wake from the blade boundary layer. This tip region flow is important as it has the potential to contribute to a substantial loss in total efficiency and pumping head. In hydro-machinery, there is the additional issue of cavitation. In the present study, Laser Doppler Velocimetry (LDV) and Particle Imaging Velocimetry (PIV) measurements were performed on the TLV from a ducted marine propulsor 33.4" in diameter at the blade TEV under steady operating conditions. The measurements were synchronized with the propeller angular position. Analysis of the velocity fields revealed considerable variations among the instantaneous realizations at a given spatial position in the tip vortex strength, its core size, and its overall structure. The implications of vortex variability on cavitation inception are discussed. In addition, significant differences exist between the averaged vortex properties from the instantaneous flow fields and the averaged vortex properties from the mean flow field. We will discuss these differences and their influence on cavitation performance and scaling.