A fixed-pitch propeller design and performance evaluation tool for a free turbine, micro turboprop application

Abstract

In recent times, the conversion of thrust-producing micro gas turbine (MGT) engines to a power-based, free turbine configuration has been increasingly investigated. In such applications, free turbine power loads often include electrical generation systems, turboshaft, and turboprop configurations. In a converted micro turboprop configuration, simplicity often dictates the use of fixed-pitch propellers. In such a configuration, the rotational velocity of the propeller is not controllable and is entirely dictated by engine input power and platform advance velocity. A propeller design and performance evaluation tool for a fixed-pitch, free turbine micro turboprop configuration is presented. The propeller design tool provides the designer with the ability to accurately predict the propeller performance and tip Mach number limits throughout an appropriate advance speed range. The propeller design tool is developed in Python® and features a user-friendly graphical user interface. Propeller performance is evaluated using combined blade-element and momentum theory. Blade element lift and drag characteristics are determined using thin-foil theory and a generic drag coefficient formulation. The performance prediction accuracy of the propeller design tool is evaluated by designing four test propellers covering a design power input range of between 7.5 and 30 kW. The performance results of these four test propellers are verified using commercial computational fluid dynamics (CFD) software (Cadence FINE/Turbo™). It is shown that the results from the propeller design tool correlate well with the CFD results. Peak efficiency and static revolutions per minute differences of below 4% and 5%, respectively, are observed for all the test propellers.