Development of a porous media model with application to flow through and around a net panel

The flow characteristics through and around a net panel have been investigated through computational fluid dynamics (CFD) and measurements. A finite volume approach was used for solving the Reynolds averaged Navier–Stokes equations combined with a k–εk–ε turbulence model for describing the flow. For computational efficiency, the net was modeled as a sheet of porous media rather than a large number of cylinders connected by knots. The model resistance coefficients needed for the porous media equations were found by optimizing the fit between computed lift and drag forces on the net panel and lift and drag measured in tow tank experiments. Lift and drag acting on a flat panel of knotless nylon net (2.8 mm twine thickness and 29 mm mesh size) stretched on a frame were measured at different speeds and angles of attack, and fluid velocity was recorded in the region behind the net. The optimization process used to obtain the best fit porous media coefficients was simplified through the use of an analytical model. Final comparisons between CFD predictions and measurements of lift and drag coefficients and velocity reduction behind the net panel were made for two of the speeds and angles of attack. The agreement between measured and modeled data was good with a mean normalized absolute error of 6.2%.