Feasibility of applying small particle in-line holography to determine 3-D velocity fields within automobile engine compartments



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Texas Tech University


This thesis presents an investigation into the feasibility of using particle field holography to determine air flow velocities typical of those within an automobile engine compartment. Three primary objectives are considered in this study. The first objective is to investigate the behavior of spherical microparticles of different sizes in order to determine a suitable particle size that would accurately represent local air velocities and could be resolved holographically. The second objective is to determine the velocity error due to the fluid acceleration to allow estimates of how well a given particle will represent the air flow. The third objective is to investigate the theoretical aspects of in-line particle field holography and to estimate particle velocity measurement errors.

Particle velocity behavior is investigated by developing a computer program determine particle trajectories in an inviscid air stream flowing past a cylinder. The program predicted velocity errors and total accelerations. It was found that a 5-micron diameter water droplet could tolerate accelerations up to 900m/s^2 and still represent the air flow with an error of less than 1.5 percent.

A theoretical investigation of in-line holography and experimental results from the literature indicates that a particle of 5 microns can be imaged throughout a sample volume of about 2.5 to 5 cm''. The longitudinal focal tolerance is the largest source of error when determining particle displacements. However, this error can be reduced if the longitudinal measurement is repeated several times. If three longitudinal measurements are made at each particle location, and if the particle travels 1 mm and the fluid acceleration is within the allowable limit for the particle size, then the local air velocity can be measured with an error of about 1.4 percent.

Two serious disadvantages of using particle field holography to measure fluid velocities are the high equipment costs and the time required to analyze holograms. The construction of a low cost miniature ruby laser to experimentally verify air flow measurements is suggested.