Prediction of Aerodynamic Characteristics of Ram-Air Parachutes

Abstract

The focus of this work is on the computational methodology for aerodynamic modeling of ram-air parachutes and increasing confidence and understanding in their concept designs including new parachute control methods. The complex geometries of ram-air parachutes are modeled by two-dimensional rigid airfoil geometries with or without trailing-edge deflections and bleed air spoilers. The aerodynamic forces are then calculated from steady or unsteady Reynolds-averaged Navier–Stokes simulations using Cobalt and Kestrel flow solvers. The effects of the grid size and type, the time step, and the choice of solver parameters are investigated. The flow solvers are then used to study the flow around three-dimensional wings with open/closed ram-air inlets by comparing lift and drag coefficients with available experimental data. The results show that computational fluid dynamics simulations are a valuable aid in understanding the flow structure of ram-air parachutes, which resemble a rectangular wing with open inlets. However, the computational solutions of these geometries have initial oscillations of large amplitude and converge slowly compared to closed wings/airfoils. The simulation of open geometry should run unsteady and for a large number of time steps. It is also shown that an open-inlet geometry has smaller lift and larger drag, and it stalls earlier than a closed-inlet geometry. Although the air reaches stagnation conditions inside the cavity present in an open airfoil, the air pressure inside the wing cells is less than the stagnation pressure. The flow investigations show that eddies are formed on the lower surface of the open airfoil and wings; however, the wing eddy size varies in the spanwise direction. Finally, the grid sensitivity results show that the solutions of open geometries are very sensitive to the grid quality.