Experimental, high-fidelity, and three-dimensional validation of near-wall airfoil grids

Verify the net drag reduction produced by near-wall NACA0006 airfoil-section grids through experiments and DNS or LES, and evaluate the performance using a three-dimensional grid geometry that includes effects omitted by the axisymmetric periodic RANS model, such as radial spokes, unsteadiness, bends, and fouling in actual pipes.

Background

The paper predicts that a periodic array of concentric NACA0006 airfoil rings concentrated near the pipe wall can produce a positive net drag reduction, with a maximum simulated flow-rate increase of 9.02% near Re ≈ 10^5. However, the simulations use an axisymmetric Reynolds-averaged Navier–Stokes model with periodic streamwise boundary conditions and omit radial spokes, unsteadiness, bends, fouling, and fully three-dimensional geometry.

The authors explicitly identify experimental verification, higher-fidelity numerical analysis using direct or large-eddy simulation, and evaluation of a three-dimensional implementation as unresolved work needed to establish whether the predicted drag reduction persists under realistic operating conditions.