Particle image velocimetry measurement of steady, transitional, and turbulent flow in a randomly packed porous media

Abstract:

The sequential transient regime of the flow through randomly packed porous media has been observed experimentally from steady inertial to turbulent flow. Considering the inherent constraints in visualization and measurements in porous media, the characterization has been performed using time resolved PIV in a randomly packed ordered array of spheres with uniform size. The size of the spheres are 15 mm and the pore Reynolds numbers are set to be 300, 500, and 900. The test bed has a cross-section of 70×70 mm and a height of 15mm. In addition to the difficult accessibility to the interrogation window, the challenges of visualizing the flow in this porous structure is matching of refractive indices of the fluid and solid phase as slight mismatches have been shown to cause significant tracking errors. The 2-D velocity field has been captured at discrete planar locations along the optical axis through the test bed to study the physics and statistics of the flow. Variations occur in the imaging magnification, and if not taken into consideration may lead to increased error. This study addresses three forms of error in PIV as they pertain to porous media flow: tracking error, bias error due to displacement gradients and perspective error. The bias error due to displacement gradients was evaluated from correlation peak width. Direct Numerical Simulation is also being performed to investigate the transitional and turbulent flow in porous media in detail.