Computational fluid dynamics vs. inverse dynamics methods to determine passive drag in two breaststroke glide positions

Abstract

Computational fluid dynamics (CFD) plays an important role to quantify, understand and "observe" the water movements around the human body and its effects on drag (D). We aimed to investigate the flow effects around the swimmer and to compare the drag and drag coefficient (CD) values obtained from experiments (using cable velocimetry in a swimming pool) with those of CFD simulations for the two ventral gliding positions assumed during the breaststroke underwater cycle (with shoulders flexed and upper limbs extended above the head-GP1; with shoulders in neutral position and upper limbs extended along the trunk-GP2). Six well-trained breaststroke male swimmers (with reasonable homogeneity of body characteristics) participated in the experimental tests; afterwards a 3D swimmer model was created to fit within the limits of the sample body size profile. The standard k-ε turbulent model was used to simulate the fluid flow around the swimmer model. Velocity ranged from 1.30 to 1.70 m/s for GP1 and 1.10 to 1.50 m/s for GP2. Values found for GP1 and GP2 were lower for CFD than experimental ones. Nevertheless, both CFD and experimental drag/drag coefficient values displayed a tendency to jointly increase/decrease with velocity, except for GP2 CD where CFD and experimental values display opposite tendencies. Results suggest that CFD values obtained by single model approaches should be considered with caution due to small body shape and dimension differences to real swimmers. For better accuracy of CFD studies, realistic individual 3D models of swimmers are required, and specific kinematics respected.

Assessment of passive drag in swimming by numerical simulation and analytical procedure

“…Vilas-Boas et al (2010) noted a gliding speed in breaststroke of 1.37 m • s −1 after the push-off in national level swimmers. Costa et al (2015) assessed the push-off at speeds between 1.1 and 1.7 m • s −1 . Shahbazi, Sanders, McCabe and Adams (2007) reported that experienced swimmers show a speed after the tumble turn of 2.42 m • s −1 .…”

“…Eventually, researchers started to investigate whether the different approaches would return the same results (i.e., goodness-of-fit), if they were sensitive enough to reflect the same phenomenon or not. It was reported that experimental data tend to overestimate the values in comparison to numerical simulations (Costa et al, 2015). Nevertheless, both CFD and experimental data were dependent on swimming velocity.…”

Individual–Environment Interactions in Swimming: The Smallest Unit for Analysing the Emergence of Coordination Dynamics in Performance?

“…By modifying disk orientation and flow characteristics (constant or variable acceleration), they found that hand acceleration (from 2.84 to 5.84 m/s) strongly increased propulsive drag by up to 40%. Following this study, interest turned to evaluating water resistances during glide periods [54,[66][67][68][69]. Investigators scanned the swimmer's whole body and tested resistances as a function of position (arms extended at the front or along the body) and depth.…”

Experimental and Numerical Investigation of Drag Force at High Speed Diver Motion in Different Depths from Free Surface

“…The importance of the flow effects around the swimmer has been introduced by Costa et al (2015) wherein k-ε model of turbulence had been used to simulate fluid flow around the model and their results were validated with swimming pool experiments. Zhan (2015) in another research by using of 3D numerical simulation analysis evaluated passive drag near free surface by RNG k-ε turbulence model.…”