This presentation was made at CAASE18, The Conference on Advancing Analysis & Simulation in Engineering. CAASE18 brought together the leading visionaries, developers, and practitioners of CAE-related technologies in an open forum, to share experiences, discuss relevant trends, discover common themes, and explore future issues.

Resource Abstract

The present work describes the use of the CFD software – FloEFD during the conceptual and preliminary design of the tailless multi-variant sUAS which is being developed at the National Institute for Aviation Research (NIAR). The sUAS will act as a technology demonstrator to showcase the capabilities of NIAR in design, analysis and manufacturing. It has a pusher configuration and is designed to cruise at 50 mph with a maximum take-off weight of 55 lbs. It relies on electric propulsion for VTOL flight and on piston engine propulsion for forward flight. As it does not have a tail, its longitudinal stability is dependent on the reflex shape of the airfoils and the wing sweep angle. Multiple design iterations are carried out on a parametric CAD model to size the wings and to achieve a nearly trimmed condition for the cruise flight regime. The aerodynamic characteristics of the final configuration of the sUAS are presented here. A one-third scale Wind Tunnel model is fabricated using additive manufacturing techniques and is tested at the NIAR Walter H. Beech Wind Tunnel. A comparison between the CFD results and the Wind Tunnel test results is made.



The CFD simulations are performed for cruise conditions (V = 50 mph, Re ? 750,000). The aerodynamic parameters are calculated for an angle of attack range of -10° to 13° (? = 0°) and for a sideslip angle range of 0° to 25° (? = 0°). The results for sideslip angle range of -25° to 0° are assumed to be symmetric. The thin boundary layer approach and the solution adaptive refinement approach are used in this study. The mesh size is approximately 4.5 million cells at the end of all the refinements. Results are compared to the wind tunnel test results which are performed at the same Re ? 750,000. The computational domain, mesh plots and correlation of results are shown in the figures below.



It is seen that there is a very good agreement between the FloEFD simulation results and the Wind Tunnel test results at small and moderately high angles of attack and sideslip angles. It is evident from the results that the sUAS possesses natural static stability about all its axis (negative Cm – ? slope, positive Cn – ? slope and negative Cl – ? slope). At higher angles of attack and sideslip angles, there is a deviation in the results predicted by FloEFD and wind tunnel data. Efforts are being made to improve the existing CFD model.