Force coefficients for modelling the drift of a victim of river drowning

The global annual death toll due to drowning is of the order of 105. Rescue and search operations in urban rivers show a low rate of success. Operational computational drift models have been developed for marine environments but not for the case of river drowning. In the latter case, no scale separation occurs between the body and flow length scales. To model them, three hydrodynamic force coefficients of representative bodies, such as drag, side and lift coefficients, are needed. So far, their value was not characterized for the typical positioning of the body of a drowning victim. In this work, we used full-scale laboratory experiments to identify the range of value of these hydrodynamic coefficients based on 249 tests conducted in a wind tunnel. Observations in the air can be transferred to water environment thanks to flow similarity. For the typical body positioning of a drowning victim, the drag coefficient was found to vary in the range 0.5–1.2. Changing the yaw angle of the body, induces variations in the drag coefficient by about 50%. Considering loose clothes instead of tight clothes leads to an increase in the drag coefficient by about 30%, whereas adding a backpack has a limited influence (less than 5%). With the available experimental setup, it has been difficult to detect distinctive patterns and trends for the side and lift coefficients. This study is part of a multidisciplinary effort for developing scientific knowledge and technologies contributing to a reduction of drowning-induced fatalities in rivers.