Session: 40-03: Compressor Secondary Flows and Interactions

Paper Number: 152175

Aerodynamic Force Modelling of Free and Shrouded Propellers in Incidence for Low Subsonic VTOL Operations 

Growing market demand for urban aerial mobility has led to the rise of electric Vertical Take-off and Landing (eVTOL) aircraft. A distributed propulsive system consisting of multiple lightly loaded rotors operating in low subsonic range is a typical feature of such aircraft. An architectural choice of shrouded or free propeller offers several benefits/drawbacks in terms of aerodynamic performance, and is a point of consideration for eVTOL aircraft design.

Tiltrotors, a growing preference for urban aerial applications, have a unique characteristic of rotors operating in a large range of incidence angles while transitioning from take-off to cruise. During such operation, the non-axisymmetric inflow leads to uneven loading over the rotating blades and additional forces in the tilted rotational plane. These unsteady oscillatory forces are referred to as ‘1P loads’ or in-plane forces. The current study presents existing low-order analytical models in the literature for the calculation of such aerodynamic forces for the free propellers. Starting with Glauert’s deflected momentum theory for the computation of in-plane force gradient with respect to incidence angle, the various limitations and modifications in the hypotheses over the years are explored. Some of the limitations are then improved by additional factors taking into account the rotor induced velocity components in incidence for more precise estimation of the in-plane forces. A scarcity of such models for shrouded propellers in incidence in the literature is observed and addressed to help with preliminary design of VTOL aircraft propellers. A similar analytical model to that of the free propeller is developed for shrouded propellers operating in incidence, to consider both the modified rotor flow field in the presence of a shroud and the additional loads on the shroud in incidence. The analytical models are compared against available experimental data in the literature, as well as numerical simulation results using designed propellers representative of a typical VTOL aircraft. The design methodology of these propellers can be referred to from a previous conference proceeding (ISABE_2024_264). The calculated results from the analytical models follow the observed trend of variation of in-plane force gradient with varying incidence, while the exactitude to the observed value varies with changing advance ratio (non-dimensional free stream velocity). This is owing to the increasing flow separation that sets in with increasing incidence, especially for the shrouded propeller, that introduces additional losses in the flow. While further improvements are recommended, the goal of a low-order analytical model for estimation of in-plane forces for free and shrouded propeller is satisfactorily reached.

Presenting Author: Sanjana Gummekeri Krishna Safran Tech

Presenting Author Biography: Sanjana Gummekeri Krishna is currently pursuing a PhD. in the field of propeller aerodynamics at ISAE-SUPAERO, France. She received her Bachelor’s degree in aerospace engineering (2019) from R.V.College of Engineering, India, followed by a Master’s degree in aerospace propulsion (2022) from Ecole Centrale de Lyon, France. Her research covers experimental and numerical studies of aerodynamics of turbomachinery.

Authors:

Sanjana Gummekeri Krishna Safran Tech
Ye-Bonne Maldonado Safran Tech
Ludovic Wiart Safran Tech
Benoit Rodriguez Safran Tech
Sébastien Duplaa ISAE-SUPAERO
Xavier Carbonneau ISAE-SUPAERO