Impeller Design for a Microjet Engine

The use of microjets has found application areas in the propulsion of target drones and missiles. These propulsion systems have their own challenging topics due to their small sizes and very high rotational speeds (in the order of 100000 rpm). The complete engine consists of the following main components: Inlet, Impeller, Diffuser, Combustion Chamber, Turbine and Nozzle. In this paper, the focus was given to present the methodologies used in the design of the impeller (radial compressor) only, which is one of the most critical components of an engine. The main function of an impeller is to efficiently compress the air coming from the inlet and to deliver it to the combustion chamber via a diffuser. The compressor pressure ratio is highly dependent on the impeller tip speed. Hence, high tip speeds are essential to obtain high pressure ratios. Therefore, in microjets, high rotational speeds are inevitable. This results in many challenges such as vibratory behavior, transonic flow, shock waves in diffusers and high stresses. Furthermore, tip clearance is one of the most important concerns affecting impeller performance. Special care must be taken to maintain tip clearance close to an optimum value under operating conditions.

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