טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGuy Bar-Yosef
SubjectThe Flow Field at the Vicinity of Porous Media Boundaries
DepartmentDepartment of Agricultural Engineering
Supervisor Professor Shavit Uri


Abstract

This work deals with the problems encountered in the flow field at the interface of a porous medium while emphasizing the profile of the average velocity in the area between the flow above and within the porous medium. A solution in this area is required for runoff, rainfall events, furrow irrigation, flood events and others. As a result of shear, surface and subsurface flows affect each other and the boundary conditions at the interface are ill defined.


Despite an extensive history of research, to date no model has been found that would provide a full prediction of the flow at the porous media interface, given the characteristics of the porous media and the flow conditions.


The goal of this research is to examine a possible solution to the problem of laminar flow in the border region, between free flow and flow in porous media. The research hypothesis postulates that by using a PIV (Particle Imager Velocimetry) system and a numerical solution, it will be possible to determine the flow field both above and within the porous medium.


The research includes a theoretical development of the average flow equations, experiments and numerical solutions that were used to predict the micro-scale flow field and a comparison between the micro-scale flow field and a solution of the Modified Brinkman Equation (MBE), which was developed during the course of this research.


The porous medium physical model was developed based on a Canton Taylor Brush configuration. This configuration simplifies the interface problem, since the micro-scale flow field inside the porous media is unidirectional, symmetric, and fully developed. PIV measurements showed that the Stokes equation provides an accurate prediction of the flow field at the microscopic level. This conclusion was found to be correct with regard to the laminar flow conditions examined during this study.


The research found that the MBE solution depends on the height of the representative elementary volume, HREV. For a correct value of HREV the MBE predicts well the average velocities both above and within the porous medium, given that flow is laminar, that the porous medium is composed of an array of parallel grooves, and that the fluid viscosity, pressure gradient and water level above the porous medium are known.