K. Ravindra

Reduction of Vertical Tail Buffet Response Using Active Control

The active vertical tail (AVT) successfully reduced the buffet response of structures by utilizing piezoelectric actuators, strain gauge sensors, and simple control techniques. The AVT is a 5%-scale aeroelastically tailored structure that exhibits vibration response similar to a full-scale aircraft structure, and was designed such that its piezoelectric actuators could provide control authority in the first two bending modes. The AVT was wind-tunnel tested on a generic twin-tailed double-delta fighter model at angles of attack and dynamic pressures representative of actual aircraft flight envelopes. At high angles of attack, the models leading-edge vortices impinge upon the AVT. Simple control algorithms were used with piezoelectric actuators and collocated strain gauge sensors to either minimize the acceleration at the AVTs tip or the strain at the root of the tail. Control gains were verified to be a nonlinear function of angle of attack, dynamic pressure, and location of the actuator/sensor pair. Spectral analysis showed that the peak response of the controlled AVT was up to 65% lower than the uncontrolled response. This represents approximately an order of magnitude improvement in the fatigue life of a similar aircraft structure. The rms response below 200 Hz was reduced by over 20%.

Aerospace Structures Course Revisited

In nearly all undergraduate aerospace programs, there is at least one course devoted to aerospace structures. The availability of modern tools for structural analysis and new technologies for flight vehicle structures such as advanced composite structures, begs the question of course content revisions that are needed in a traditional flight vehicle structures course. In addition, graduates entering the workforce are expected to” hit the ground running” in the work place. This clearly necessitates that graduates are reasonably well versed in the modern tools used in the industry while simultaneously well-grounded in the fundamentals. In this paper, an attempt is made to describe some innovative ways where the “fundamentals” and “modern tools” can coexist and prepare the student to get a holistic view of aerospace structures and function successfully in the workforce.

Unsteady Gaseous Diffusion Associated With a Fully Cavitating Oscillating Flat-Plate Hydrofoil

We give an analysis of convective gaseous diffusion into a full cavity behind an oscillating flat-plate hydrofoil in a turbulent flow. The unsteady diffusion theory accounts for fluctuations of cavity gas pressure and length which are assumed to be harmonic oscillations but are not necessarily in phase with the hydrofoil motion. A diffusive lag function is found which, for a given reduced frequency, determines the instantaneous diffusion rate as a product of the lag function and the quasisteady mass diffusion.