Preliminary CFD Analysis of an Innovative Hybrid HAPS Configuration
Creators: name:  V.R. BARANIELLO 
name:   G. PERSECHINO 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLIGHT PHYSICS
COMPUTATIONAL AERODYNAMICS
EXPERIMENTAL AERODYNAMICS

description: CIRA is currently designing an innovative HAPS configuration for Earth Observation and Telecommunications named High Altitude Hybrid Airship. The configuration designed can generate both aerodynamic and aerostatic forces to balance the weight during the different phases of a mission. The design of a hybrid configuration for stratospheric platforms represents itself a novelty in the aerospace sector while some hybrid platforms have been proposed only for tropospheric applications. During the conceptual design phase, a first estimation of the aerodynamic properties has been based on a semi-empirical formulation, then some specific flight conditions have been investigated by CFD analyzes (as for example, at the maximun efficiency attitude). In order to validate the results of the conceptual design phase [1], a preliminary, but now complete, CFD analysis has been performed on the most promising configuration. In fact, the CFD analyzes allowed to improve the conceptual design, obtaining a final configuration able to carry on the same initial desired payload (in terms of weight) but having reduced overall weight and dimensions. The final configuration has a lenticular shape with an overall weight of about 180kg and a volume equal to 1220 m3. These preliminary CFD analyzes, on this configuration, have been carried out on the open source CFD solver OpenFoam, using its steady-state solver SimpleFoam. The configuration has been provided directly by the conceptual design tool we have implemented, which provides as output a CAD file with the geometry. From the CAD file, we have generated the .STL file used to generate the aerodynamic mesh. Several simulations at different angle of attack and sideslip have been carried out in order to investigate the steady-state air motion around the HAPS, at the mission altitude, and the computation of the typical aerodynamic force coefficient curves (lift, drag, side force and aerodynamic moments). Flow conditions at 18000 m altitude were simulated with an airspeed equal to 16 m/sec (this value represents the nominal mission airspeed) and variable angle of attack in the range [0 17 ] and sideslip angle range in the range [0 -30 ]. The computed values of the aerodynamic forces ad moments have been used to have a first estimation of the position of the center of pressure and to assess the preliminary static stability (longitudinal, lateral and directional) of the selected configuration. Moreover, the computed aerodynamic database will be used to build a flight simulator of the High Altitude Hybrid Airship. The paper will be organized in three main parts. In the first part we will briefly introduce the advantadges of a hybrid HAPS configuration, which, as expressed previously, allows a reduction of weight and dimensions, making easier operations. In the second part, we will describe the structure and the results of the conceptual design process we have implemented to obtain several candidate configurations, from whom we have selected the final one which is object of the analysis of this paper. In the third part, we will show and discuss the results of the aerodynamic analyzes. At the end of the paper we will also provide to the readers an overview of the next steps in our design process.