HYDRODYNAMIC DRAG AND LIFT FORCES ON HUMAN HAND-ARM MODELS

Forces acting on the forearm and hand during swimming can be decomposed into drag forces and lift forces. In this study drag and lift forces were measured on two models of a human hand and forearm when towed in a towing tank. To compare the results of models with different size at different velocities force data were normalized to drag and lift coefficients (C-d and C-l). Influence of the orientation of the model with respect to the how, velocity, size of the model and the relative contribution of the hand and forearm on C-d and C-l were studied. The orientation of the model with respect to the line of motion was varied by rotating the models around three axes, and quantified using the angle of pitch (AP: the angle between the hand plane and how) and the sweep-back angle (SB: the orientation of the flow vector when projected on the hand plane). C-d was maximal when the palm of the hand is almost perpendicular to the how (AP =65 degrees, SB=342 degrees). C-l shows maximal values at two different orientations: with the hand in a thumb-leading position, AP= 31 degrees, SE=358 degrees, and with the hand in a little finger-leading position, AP=48 degrees, SE=193 degrees, The orientation of the hand was very critical in generating lift forces. By contrast, the influence of velocity and size of the model on the values of C-d and C-l was limited. The relative contribution of the hand and forearm on C, and CL was examined by varying the immersion depth of the model. In the experiments where only the hand was towed C-d was about the same as for the condition where hand and forearm together were towed. C-l reached the highest values in the experiments where only the hand was towed. The hands are the main contributors for the generation of lift force.