Holographic diffraction image velocimetry for three-dimensional measurements of fluid and solid motions.

摘要

Of continuous importance in experimental fluid dynamics and solid mechanics is the accurate measurement of three-dimensional (3-D) three-component (3-C) velocity or displacement fields of an extended region. For example, such capability can be a powerful aid in the understanding and characterization of such complex flow phenomena as turbulence and vortex formation/shedding for the development of new aircraft and turbomachines. Such flows generally involve a broad range of 3-D 3-C velocities over a large spatial domain, making instantaneous gross-field evaluation difficult. Likewise, an important and necessary stage in the development and application of new materials is the accurate assessment of their physical properties and behaviors under various geometrical configurations and loading conditions. Especially with the rapid development of new composites, knowledge of various mechanical properties such as strain, fracture propagation, debonding, etc., is critical to their use, but current measurement techniques can be intrusive and cumbersome.; To meet these challenges, an optical nonintrusive technique for the measurement of 3-D 3-C fluid flows as well as solid deformations has been developed and tested. Termed Holographic Diffraction Image Velocimetry (HDIV), the technique utilizes a double-reference-beam, double-exposure, off-axis holographic recording and reconstruction technique to measure gross-field velocity and displacement components of particle seeded flows and solid deformations, respectively.; The feasibility and accuracy of the HDIV method were experimentally verified for both simulated and actual flows. Simulations involved measurement of displaced planar and volume static particle fields by continuous-wave holography while pulsed-laser holography was implemented for viscous flow around a sphere. The results obtained with the HDIV method exhibit good spatial resolution, high data-point sampling, and wide dynamic range. While the technique is still in a developmental stage, the current results show application potential in many areas of fluid dynamics and solid mechanics.