M.Sc Thesis


M.Sc StudentValentin Ognev
SubjectDerivation of a Model to Analyze Propeller Flutter Including
Inter-Blade Influences
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Rosen Aviv
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

During the current research a new aeroelastic model of a propeller, that takes into account the aerodynamic interaction between the blades and their wakes, was developed. These phenomena are important in flutter problems of multibladed propellers.

In the first part of the research a system of second order, non linear, differential, equations of motion of the blades were developed. These equations included inertia, structural and aerodynamic contributions

Assuming further that the blades perform small harmonic vibrations superimposed on a steady basic axisymmetric state, the system of differential equations was converted into an eigenvalue problem. The solution of this eigenvalue problem defined the frequencies and stability of the various perturbation modes.

The aerodynamic loads that act along the blades at the steady state were calculated by the combined momentum/blade element theory.

The aerodynamic loads that act on the oscillating blades were calculated using various models. All these models assumed an inviscid fluid and included: Theodorsen model, Cascade models and Iosilevskii model.

These models were verified by comparing their results with test results of a single bladed propeller that had been carried out by NACA. The present calculations showed a fairly good agreement with the test results of bending and bending torsion flutter.

The last part of the research included the development of a simplified model having two degrees of freedom: flapping and torsion. The results of the simplified model were compared with results of the detailed model, after it was adjusted to represent the simple case.

The simplified model was used for a parametric study of the influence of various parameters on the blades’ stability. The results of various aerodynamic models were compared. It was shown that inter-blade influences reduce the blade stability as the number of blades is increased. The research also showed the importance of taking into account all the aerodynamic effects (shed and trailing vortices), which requires the use of three dimensional models.