A study of flush air data system calibration using numerical simulation

Abstract

We describe the use of computational fluid dynamics (CFD) simulations for calibrating a flush air data system (FADS). In particular, the HYFLEX hypersonic vehicle FADS is used as a case study. The HYFLEX FADS consists of nine pressure ports located flush with the vehicle nose surface, connected to onboard pressure transducers. After appropriate processing, surface pressure measurements can be converted into useful air data parameters. The FADS processing algorithm requires a pressure model which relates air data parameters to the measured pressures. In the past, such pressure models have been calibrated using combinations of flight data, experimental results, and numerical simulation. In this paper, we perform a calibration of the HYFLEX FADS using CFD simulations exclusively. The CFD simulations are used to build an empirical pressure model which accurately describes the HYFLEX nose pressure distribution over a range of flight conditions. We believe that CFD provides a quick and inexpensive way to calibrate the FADS, and is applicable to a broad range of flight conditions. When tested with HYFLEX flight data, the calibrated FADS is found to work well. The system predicts vehicle angle of attack and angle of sideslip to accuracy levels which generally satisfy flight control requirements. Dynamic pressure is predicted to within the resolution of the onboard inertial measurement unit. We find that wind-tunnel experiments and flight data are not necessary to accurately calibrate the HYFLEX FADS for hypersonic flight.