Discussion of “Verification and validation of a computational fluid dynamics (CFD) model for air entrainment at spillway aerators” Appears in the Canadian Journal of Civil Engineering 36(5): 826-838.

Abstract

The Authors presented the outputs of some numerical modelling of a spillway aerator conducted using a commercial package (Aydin and Ozturk 2009). A spillway aeration device is located on the spillway bottom and sometimes on the sidewalls. It is designed to deflect high-velocity flow away from the chute surface (and walls) to artificially introduce air into the flow and protect the spillway invert from cavitation erosion. The main flow regions are: (a) the approach flow region, which characterizes the initial nappe flow conditions; (b) the transition region, which coincides with the length of the deflector; (c) the aeration region; (d) the impact point region; and (e) the downstream flow region (Chanson 1989a, 1989b; Kramer et al. 2006). A key feature of the flow abovestream and downstream of an aerator is the strong mixing of air and water yielding a complicated high-velocity airnwater flow. Herein, it is argued that the validation and certification of the commercial CFD package were ill-performed and that the physical modelling technique based upon a proper dimensional analysis remains the basic design tool.In summary, we believe that the validation and certification of the Authorsr numerical results were improper. These should be conducted on the detailed airnwater flow properties of the flow abovestream and downstream of the spillway aerators, and several extensive datasets are freely accessible (e.g., Chanson 1988; Kramer 2004; Toombes 2002). The physical modelling and theoretical calculations remain the basic tools of the design engineers to size the spillway aeration devices on a large spillway, although the physical model dimensions must be carefully selected to address the potential scale effects (e.g., Kramer 2004; Chanson 2009).