Structural optimization of rotor blades with straight and swept tips subject to aeroelastic constraints

The main conclusions obtained in the present study are summarized. Their application to the structural optimization of a helicopter blade should be limited by the assumptions used in obtaining the numerical results presented here. The optimum design procedure described here is very efficient, and can produce improved designs with a very limited number of precise analyses. The method of constructing the approximate problem is such that previously conducted aeroelastic analyses can be reused in a new optimization problem. For example, if an optimization study is preceded by a parametric study in which the effect of various combinations of blade design parameters is examined, all the aeroelastic analyses performed for the parametric study can be reutilized in the optimization study. This is not possible when the approximate problem is built from Taylor series expansions. The results of the optimization are quite sensitive to the aeroelastic stability margins required of the blade. In the optimization of case 2, changing the aeroelastic stability constraints from simply requiring that the blade be stable in hover, to requiring that the stability margins be maintained during the course of the optimization, reduced the gains in n/rev vibration levels by more than 50 percent. The introduction of tip sweep can reduce the n/rev vertical hub shears beyond the level that can be obtained by just modifying the mass and stiffness distributions of the blade

Rotary-wing aeroelasticity-current status and future trends

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77277/1/AIAA-2001-427-803.pd

Selected topics on the active control of helicopter aeromechanical and vibration problems

This paper describes in a concise manner three selected topics on the active control of helicopter aeromechanical and vibration problems. The three topics are as follows: (1) the active control of helicopter air-resonance using an LQG/LTR approach; (2) simulation of higher harmonic control (HHC) applied to a four bladed hingeless helicopter rotor in forward flight; and (3) vibration suppression in forward flight on a hingeless helicopter rotor using an actively controlled, partial span, trailing edge flap, which is mounted on the blade. Only a few selected illustrative results are presented. The results obtained clearly indicate that the partial span, actively controlled flap has considerable potential for vibration reduction in helicopter rotors

Aeroelastic and Aerothermoelastic Analysis in Hypersonic Flow: Past, Present, and Future

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90637/1/AIAA-54556-145.pd

Hypersonic Aeroelastic and Aerothermoelastic Studies Using Computational Fluid Dynamics

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140678/1/1.j053018.pd

Actuator saturation and its influence on vibration reduction by actively controlled flaps

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77213/1/AIAA-2001-1467-982.pd

Approximate Aerodynamic and Aeroelastic Modeling of Flapping Wings in Forward Flight

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140673/1/1.j052596.pd

Aeroelastic Response of Bird-Damaged Fan Blades Using a Coupled CFD/CSD Framework

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140712/1/6.2014-0334.pd

Forced and Aeroelastic Responses of Bird-Damaged Fan Blades: A Comparison and Its Implications

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140641/1/1.C033424.pd

Aeroelastic simulation of higher harmonic control

This report describes the development of an aeroelastic analysis of a helicopter rotor and its application to the simulation of helicopter vibration reduction through higher harmonic control (HHC). An improved finite-state, time-domain model of unsteady aerodynamics is developed to capture high frequency aerodynamic effects. An improved trim procedure is implemented which accounts for flap, lead-lag, and torsional deformations of the blade. The effect of unsteady aerodynamics is studied and it is found that its impact on blade aeroelastic stability and low frequency response is small, but it has a significant influence on rotor hub vibrations. Several different HHC algorithms are implemented on a hingeless rotor and their effectiveness in reducing hub vibratory shears is compared. All the controllers are found to be quite effective, but very differing HHC inputs are required depending on the aerodynamic model used. Effects of HHC on rotor stability and power requirements are found to be quite small. Simulations of roughly equivalent articulated and hingeless rotors are carried out, and it is found that hingeless rotors can require considerably larger HHC inputs to reduce vibratory shears. This implies that the practical implementation of HHC on hingeless rotors might be considerably more difficult than on articulated rotors