|Ph.D Thesis||Department of Aerospace Engineering|
|Supervisor:||Prof. Rosen Aviv|
|Full Thesis text - in Hebrew|
The importance of an air-vehicle’s propulsion system requires a careful design of its different components. The propeller is, in many cases, the simplest and cheapest element of a propeller based propulsion system. Yet, a proper design of the propeller can increase significantly the efficiency of the entire propulsion system. This makes the propeller design an important part in the process of designing a new air-vehicle, or improving an existing one.
Most of the present existing methods of propeller design are based on the well known work of Betz from 1919. These approaches are based on optimizing the propeller geometry at a certain specific operating condition (a certain combination of airspeed, altitude and propeller angular speed) in a way that the power, which is required to obtain a certain propulsive force at that operating point, is minimized. Alternatively, a designer can maximize the thrust produced by a certain power. Yet, practical optimization of propellers is usually much more complicated
The current research offers a new design method of optimizing a propeller, while considering the characteristics of the air-vehicle. This includes the use of a variety of cost functions and taking in account various constraints that may include: geometric (side) constraints, performance constraints, acoustic constraints, and stress constraints. The new approach is not based on a specific aerodynamic model, but allows the use of any aerodynamic model.
The new design method uses a modern MDO (Multidisciplinary Design Optimization) approach to the above mentioned design problems. A new mixed optimization approach is used, where the advantages of various optimization schemes are coupled into a single process. During the new design process the designer has a very important role of monitoring the optimization process and defining the optimization scheme that will be used at each stage.
The use of the new method is demonstrated by two different test cases. The first test case deals with a mini-UAV equipped with an electric engine. The second case deals with an Ultralight category air-vehicle. This vehicle is equipped with internal combustion engine which is presented by a typical engine model. The two cases include the design of several propellers for different goals, under various design constraints. The test cases demonstrate the capabilities of the new design method and emphasize its advantages, mainly the ability to deal with any kind and combination of: cost function, constraints, and design variables. The optimization is performed while considering the characteristics of the entire air-vehicle.