Team for Advanced Flow Simulation and Modeling
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Opening of a Round Parachute
The interactions between the parachute system and the surrounding flow field are dominant in most parachute operations and thus the ability to predict parachute fluid-structure interaction phenomena is of interest to the Army. The dynamics of parachutes are complex and difficult to model accurately. During both the inflation process and the terminal descent stage, the dynamics of a parachute are governed by a highly nonlinear coupling between the structural dynamics of the parachute system and the surrounding fluid flow. Semiempirical parachute models require experimental data in order to adjust the model to represent parachute phenomena. However, these models break down if the simulated problem deviates from the problem the empirical data supports. In order to capture accurately time-variant parachute dynamics, the structural dynamics and fluid dynamics must be addressed as a coupled system.
For the coupled parachute simulation shown, the time-dependent Navier-Stokes equations governing the flow were solved using a stabilized space-time finite element formulation. The fluid dynamics model used an unstructured triangular mesh in which the parachute surface is defined by a set of adjacent nodes interior to the mesh. An automatic mesh moving scheme (with occasional remeshing) was used to handle deformations in the spatial domain due to the motions of the parachute canopy. The structural dynamics equations of motion were solved using a finite element formulation for a "tension structure" composed of cables, membranes, and concentrated masses. This formulation is being developed in collaboration with University of Connecticut to be extended to a large class of parachutes. The initial condition for the problem was that the parachute system was dropped from rest in its nonstressed configuration.
The figures below show for an axisymmetric simulation the computed geometries and vertical position of the structural model at equally spaced instances in time. These plots show the inflation sequence as the canopy inflates, overinflates and collapses due to wake recontact and approaches a fully inflated "steady-state" geometry.
The following figures show the computed flow fields at six equally spaced instances in time during the overinflation of the parachute. The left side of each frame shows the canopy shape and surrounding vector velocity field with respect to the vertical motion of the skirt node. The right side shows the pressure field with blue representing low pressures and red representing high pressures.
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