Flexible composite propeller design using constrained optimization techniques
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An investigation of a conventional propeller, made from composite materials, was conducted in which its characteristics were studied under quasi-static aerodynamic loading. Also, optimized designing of a composite propeller was performed for various constrained and unconstrained design objectives. Only symmetric ply stacking sequences were considered to eliminate the effect of centrifugal force on the propeller. Results show that the ply stacking sequence has an effect on the propeller characteristics of a conventional propeller. Proper stacking sequence of the composite propeller improves its performance as compared to its metallic counterpart. An improvement of about 47% in the propeller thrust coefficient was observed for one of the cases. Similarly, improvement was observed in other propeller characteristics as well. The classical blade element theory of propellers is used to calculate propeller characteristics and the aerodynamic force distribution on the propeller blades. The finite element method is used to calculate the resulting deformation of the propeller blades. In the present study, the propeller is modeled as a variable thickness plate, discretized into a number of quadrilateral shear-deformable finite elements. Propeller characteristics are calculated for ply orientation angles ranging from -90 degrees to +90 degrees to study these parameters as a function of orientation angle. These analyses were performed for six different values of advance ratios and at two different initial blade setting angles. Improvement in propeller design, by only changing the stacking sequence, was also considered using techniques of numerical optimization. It is shown that different design objectives can be achieved by changing the stacking sequence. For carrying out design optimization of propeller, Fortran subroutine "CONMIN" was used.