Model of the Aerodynamic Behavior of a Pararotor

Abstract

A simple semi-empirical model for the aerodynamic behavior of a low-aspect ratio pararotor in autorotation at low Reynolds numbers is presented. The paper is split into three sections: Sec. II deals with the theoretical model derivation, Sec. III deals with the wind-tunnel measurements needed for tuning the theoretical model, and Sec. IV deals with the tuning between the theoretical model and the experimental data. The study is focused on the effect of both the blade pitch angle and the blade roughness and also on the stream velocity, on the rotation velocity, and on the drag of a model. Flow pattern visualizations have also been performed. The value of the free aerodynamic parameters of the semi-empirical model that produces the best fit with the experimental results agrees with the expected ones for the blades at the test conditions. Finally, the model is able to describe the behavior of a pararotor in autorotation that rotates fixed to a shaft, validated for a range of blade pitch angles. The movement of the device is found to be governed by a reduced set of dimensionless parameters.

Pararotor Dynamics: Center of Mass Displacement from the Blade Plane—Analytical Approach

“…For rJ3 = 0 (the blades plane is aligned with the center of mass), and neglecting the higher-order terms, theequations developed in [10,15] are recovered.…”

“…However, the effect of induced velocity is included in the values of lift, lift slope, and drag coefficients, C L , C La , and C D , which are determined from experiments [15]. This experimental work was performed in operational conditions of a pararotor model, and so the effect of Vf will result on an increment of the magnitudes of lift and drag if the freestream velocity over the blades is considered.…”

“…As analyzed in [15,16], it is considered that 0)3 remains constant when the system is perturbed around an equilibrium point. In a smallaspect-ratio blade pararotor, the induced power correction factor K is considerably larger than in large-aspect-ratio rotary-wing decelerators.…”

“…The eigenvectors define the type of evolution (node, spiral, focus). In the case of a two-variable systems, the following stable cases appear [10,15]. 1) A stable node X\ < 0 and X 2 < 0> ^1,2 werea l and different,…”

“…Previous work has been done to model the stability of a pararotor, mainly by Nadal Mora, Sanz, and Piechocki [9][10][11][12][13][14][15][16]. They conducted investigations that present the stability behavior of pararotors whose blades were aligned with the center of mass of the whole device.…”