Let u formaciji već je više od stotinu godina predmet istraživanja raznih znanstvenih disciplina te je do danas znanstveno dokazano da takva strategija letenja može dovesti do značajnih ušteda u potrošnji energije. Kako bi se ovaj potencijal u potpunosti iskoristio potrebno je unaprijediti postojeće sustave upravljanja letom, do razine djelomične ili potpune autonomije. Cilj istraživanja bio je unaprijediti model aerodinamičke interferencije pri letu u formaciji kojim se može pouzdanije simulirati složene aerodinamičke pojave u takvom letu. Ovo se ostvarilo sprezanjem nestacionarne metode vrtložne rešetke s 2D viskoznim optjecanjem profila te proširivanjem modela uvodenjem koncepta slobodnog traga. Razvijeni model validiran je u stacionarnim i nestacionarnim uvjetima strujanja. Primjenjiv je za proizvoljnu geometriju nosećih površina, pri različitim vrijednostima Reynoldsovog i Machovog broja te za veliki raspon napadnih kutova, uključujući i područje nakon pojave sloma uzgona. Glavna primjena modela razmatrana u ovom radu je primjena za let u formaciji, bez ograničenja na vrstu, broj članova, raznolikost letjelica ili na medusobni položaj letjelica u formaciji. Na primjeru leta složenom putanjom za dvije bespilotne letjelice u formaciji prikazane su mogućnosti razvijenog modela u nestacionarnom strujanju i pri prijelaznim režimima leta. Posebna pozornost pridana je numeričkoj efikasnosti te se procedura, uz nekoliko modifikacija, približila izvodenju simulacije u stvarnom vremenu.
|Sažetak (engleski)|| |
Formation flight has been a subject of research in various scientific fields for over a hun dred years, and it has already been scientifically proven that such strategy can result in significant energy savings. In order to take advantage of this potential, existing flight control systems need to be enhanced to the level of partial or full autonomy. The aim of the research was to improve the aerodynamic interference model of formation flight achieving more accurate simulation of the aerodynamic effects in a such flight. This was accomplished by coupling the unsteady vortex lattice method with 2D viscous flow aro und the airfoil and by extending the model with the free wake rollup model. Developed model was successfully validated for both steady and unsteady flow. It is applicable for arbitrary lifting surface geometry, for different Reynolds and Mach numbers, for large range of angle of attack including values beyond the stall angle. The main application of the developed model considered in this thesis was the formation flight, of any type, of any number of formation members, geometry diversity of formation members, or its mutual position in formation. Simulation of complex scenario of formation flight, that also included transient flight regimes, was successfully conducted. A special attention was given to the possibility of time effective calculation and a simulation close to the real time simulation was achieved with several adaptations of the procedure. The thesis is organized in six chapters as follows. First chapter presents relevance and motivation for this research, its goals, hypothesis and methodology. There is also an overview of the relevant literature defining the base ground and scope of the research described in this thesis. The essential aerodynamic model as described in chapter two is based on the poten tial flow and its elements are: standard vortex lattice method, unsteady vortex method method, and free-wake method. Standard vortex lattice method is based on vortex rings with extension for unsteady flow and extension for free wake rollup. Previously described model is extended with viscous effects of the airfoil as described in chapter three. This extension included coupled potential flow and 2D airfoil flow which included viscous and compressibility effects. This coupling was achieved with iterative process of correction of angle of attack for each section of discretized lifting surface. Developed model has a capability of application for arbitrary lifting surface geometry and for different flow parameters, both in steady and unsteady flow. Several examples were presented that validated the developed model in steady and unsteady flow. Fourth chapter introduces specifics of formation flight, and metrics for the evaluation of the formation flight efficiency as a whole but also for each aircraft in the formation. As a measure of formation efficiency a new parameter is introduced a formation drag ratio KDF , and a measure of efficiency of flight in formation for one formation member a formation member drag ratio kDF . These metric parameters can be used to evaluate formation performance, evaluate formation strategy and scenarios. An example of ap plication of the developed model for the analysis of close formation with two members is presented. In fifth chapter results of several numerical experiments for close echelon formations with two or more members with same geometry are presented. Example for the aircraft used in these experiments is unmanned aircraft Aerosonde, while its geometry and aerodynamic data are given in the Appendix. Numerical experiments in steady and unsteady conditions with main variable being a relative position of follower aircraft with respect to the leader. This analysis resulted in definition of optimal position of follower aircraft in the formation. This chapter also presents of two modification of the procedure that benefited of significantly shorter computation time. Sixth and last chapter briefly states main conclusion of the research described in this thesis, summarizing achieved scientific contributions, and discuses topics and tasks for future research work that would contribute to the further development of the model and its enhancements, offering its different potential applications.