Search for: All records

One of the common hydrotherapeutic exercises is walking in water because buoyancy reduces joint loading and increases mobility for a patient. The fluid drag forces (the forces that act on the person from the fluid in the direction opposing the direction of motion) cause changes in muscle activations, as walking in water changes the forces that act on the leg compared with overground walking. Here, through a series of numerical simulations, we quantify how the flow forces that act on the leg due to its motion in water change over a walking gait cycle. We show that besides drag forces that act on the walking legs and peak when the leg is accelerated forward, relatively large lateral forces (in the direction perpendicular to the direction of motion) also act on the leg. These forces are caused by the rapid acceleration of the opposite leg when the two legs are close, creating an asymmetric pressure distribution around the leg. These results are unexpected and could have significant implications for designing hydrotherapeutic plans for patients by considering the lateral forces besides the drag forces that act on the body while walking in water. 

We investigate the effects of fluid elasticity on the flow forces and the wake structure when a rigid cylinder is placed in a viscoelastic flow and is forced to oscillate sinusoidally in the transverse direction. We consider a two-dimensional, uniform, incompressible flow of viscoelastic fluid at$$Re=100$$, and use the FENE-P model to represent the viscoelastic fluid. We study how the flow forces and the wake patterns change as the amplitude of oscillations,$$A^*$$, the frequency of oscillations (inversely proportional to a reduced velocity,$$U^*$$), the Weissenberg number,$$Wi$$, the square of maximum polymer extensibility,$$L^2$$, and the viscosity ratio,$$\beta$$, change individually. We calculate the lift coefficient in phase with cylinder velocity to determine the range of different system parameters where self-excited oscillations might occur if the cylinder is allowed to oscillate freely. We also study the effect of fluid elasticity on the added mass coefficient as these parameters change. The maximum elastic stress of the fluid occurs in between the vortices that are observed in the wake. We observe a new mode of shedding in the wake of the cylinder: in addition to the primary vortices that are also observed in the Newtonian flows, secondary vortices that are caused entirely by the viscoelasticity of the fluid are observed in between the primary vortices. We also show that, for a constant$$Wi$$, the strength of the polymeric stresses increases with increasing reduced velocity or with decreasing amplitude of oscillations.