Annular parachutes have a higher drag coefficient than most other hemispherical-type parachutes, and so also possess the capability to produce more drag force in comparison to other more traditional canopies of equivalent canopy area. However, these annular geometries also possess a higher tendency for unstable operation, including the collapse of the canopy during descent. To investigate the flow about these parachute geometries, a series of computational fluid dynamics simulations were performed in conjunction with wind tunnel experiment. Correlation between CFD simulation and PIV imagery shows that the simulations are a reliable match to experiment, especially in regions near the model. The flowfields resulting from these simulations were investigated through the use of contours of the coefficient of pressure, vorticity magnitude, and the Q-Criterion. These flowfields offer insight to the cyclic production of drag force on the surface of each of the geometries as well as the asymmetrical flow following in their wake. The production of streamwise drag-force is correlated to the shedding of low pressure structures and vortices from the rear of the simulated models, and the use of contours of the Q-Criterion is compared against contours of vorticity magnitudes. Fast Fourier Transform analysis of velocity time-history data and linear stability analysis of time-averaged contours using the Langley Stability and Transition Analysis Code (LASTRAC) help identify the approximate location of transition on the surface of the models, through the use of N-factor correlation. This analysis also identifies the most unsteady regions of the flow, such as the shedding region at the trailing edge of the inner side of the annular models.
展开▼
