Peculiarities of operation of a tandem fan with a unifying toroidal-helical blade tip in a confined space

Abstract

The operation of a thrust fan in a confined space is becoming an increasingly urgent problem due to the miniaturization of aircraft and, as a result, the expansion of their functionality. However, the traditional problems for small UAVs immediately arise: acoustic noise, low thrust, and, as a result, low payload. And the influence of the ground, walls, and ceiling creates an additional problem: low stability and controllability when approaching an obstacle. Another problem is the aerodynamic characteristics of the blades, especially the sleeve losses and end flows. That is, when approaching an obstacle, the pressure and shape of the inlet and outlet flows undergo significant changes and affect the basic characteristics of the aircraft. The deterioration of the aerodynamic characteristics of the blades contributes to an increase in noise, dust suction when operating in the ground impact zone, overturning of the aircraft when approaching the wall due to an increase in lateral force, etc. This significantly limits the functional capabilities of a small UAV. Exactly those for which they were created. When taking measures aimed at improving the tactical and technical characteristics of small UAVs, it is necessary to take into account their cost, based on the mass of their use. All these problems can be solved in two ways - by using toroidal fans, the manufacturing technology of which is a rather complicated problem, or by using traditional blades with a unifying toroidal-helical tip. The latter option looks the most attractive from the point of view of utilizing the previously achieved results. In addition, the interaction of the fan with the wall and ceiling at the same time is of undoubted interest. These problems are practically not considered by most researchers, although the problems of controllability and stability of small UAVs in these conditions are quite significant. And if for traditional fans with classical blade aerodynamics the issues of fan interaction with the wall, ground, and ceiling are considered quite extensively, then for toroidal fans, especially for tandem or tandem with a toroidal-helical tip, there are practically no such works. Of particular interest is the operation of an open rotor in a quadrotor system, when at high rotor speeds with tandem blades, the toroidal-helical unifying blade tip practically plays the role of a kind of channel (the effect of a ducted fan).