ASCE has honored the writing team of Benjamin Hohermuth, Robert Boes, and Stefan Felder, Ph.D., Aff.M.ASCE, with the 2023 Karl Emil Hilgard Hydraulic Prize for the paper “High-Velocity Air-Water Flow Measurements in a Prototype Tunnel Chute: Scaling of Void Fraction and Interfacial Velocity,” Journal of Hydraulic Engineering, November 2021.

Aeration occurs in many natural and human-made flows and must be considered in engineering design. In water infrastructure, air–water flows can be violent and of very high velocity. To date, most fundamental research and engineering design guidelines involving air–water flows have been based upon laboratory-scale measurements with limited validation at prototype scale with larger Reynolds numbers.

In the paper, unique measurements were conducted in high-velocity air–water flows in the tunnel chute of the 225-meter-high Luzzone arch Dam in Switzerland. For each of the two test series, an array of 16 double-tip conductivity probes was installed in the circular tunnel chute of 3-meter diameter and slope of ≈37° measuring void fraction, bubble count rate, interfacial velocity, and droplet sizes for four different discharges of up to 15.9 m3=s corresponding to Reynolds numbers of up to 2.4 × 107 and mean flow velocities of up to 38 m=s. Void fraction and interfacial velocity distributions, as well as design parameters such as depth-averaged void fractions and flow resistance, compared well with previous laboratory studies and empirical equations. The droplet chord sizes exhibited scale effects, and care must be taken if air–water mass transfer and droplet momentum exchange processes are assessed at the laboratory scale.

The Karl Emil Hilgard Hydraulic Prize is presented to the author or authors of the paper that is judged to be of superior merit in dealing with a problem of flowing water, either in theory or in practice.