Stochastic design of high altitude propellers

Abstract

High-Altitude Platform Stations or High-Altitude Pseudo-Satellites (HAPS) use propulsion systems which are commonly based on propellers. In this paper, an algorithm for the design of those propellers considering uncertainties is developed and applied. The algorithm is based on the non intrusive polynomial chaos expansion scheme, which converts the stochastic design problem into an equivalent deterministic one. Two uncertainties are studied and characterized: 1) the stratospheric wind fluctuations using reanalysis datasets and 2) the variability of the aerodynamic coefficients caused by the low Reynolds number. The results of the method are analyzed to tackle how relevant the uncertainties are in the propulsion of the stratospheric platforms. The case of study is an ideal stratospheric airship that operates at a mean wind speed of 9 m/s and requires a thrust of 100 N, both uncertain magnitudes. The propeller is built on NACA4412 airfoils and the cost function to be maximized is the mean net propulsion efficiency. The new method provides a relevant gain in the mean efficiency when compared with the deterministic optimization.