Temporal evolution of the near wake of an impulsively started parachute canopy

The flow field in the near wake of an impulsively started rigid impermeable parachute canopy was studied computationally by a finite element scheme. The separated shear layer surrounding the canopy created a starting vortex ring. As time evolved, flow instabilities caused the vortex ring to become convoluted and eventually led to the breakup of the ring. This phase of the flow took a time of about 16D/U, where D is the effective projected diameter of the canopy and U is the freestream velocity. After the initial phase, the flow went through a transition phase where the drag reached a local peak prior to settling into its steady state. In the steady state phase, the drag and base pressure coefficient of the canopy were nearly constant. The computed drag coefficient matched very well against experimental data. The time to reach the steady state was 45D/U. During the steady state phase, a complex vortex shedding pattern was observed in the near wake despite the nearly constant drag coefficient.