Design and Optimization of Wing Internal Structure to Study the Flutter Frequency of Aircraft Wing

Abstract

The field of aviation has reached a lot of milestones in the 19th and early 20th century, but the supersonic commercial flights are still a nightmare in 21st century. The major obstacle to reach this milestone is the effect of flutter, which is an aeroelastic phenomenon. It is very important to understand the effect of flutter to reduce it. In this paper effect of flutter is studied by varying the wing internal structures. A scaled down model of the AGARD 445.6 wing having 65A004 aerofoil is designed using Catia V5, for which the experimental data is available for validation. Grid independence study is carried out to obtain more reliable mesh quality. Since flutter is a transient phenomenon time-step independence study is carried out for the time steps of, 0.005s, 0.0025s and 0.00125s. Since there is no difference between the flutter frequency readings for 0.0025 seconds and 0.00125 seconds, 0.0025 seconds is chosen to reduce the computation time. The baseline case is validated with an experimental data available and an error of 0.2-5.32% is observed. Aircraft wing is mainly made out of aluminium alloys. Hence a suitable aluminium alloy is selected by comparing the flutter frequencies. To choose a suitable material, three materials each from wood, alloys and composite are considered i.e., mahogany, aluminium alloy 7075 T6 and Aluminium Metal Matrix Composite (AMC) which are widely used in the Aviation industry. AMC is considered on the basis of frequency charts whose flutter frequency is 30Hz. In this paper in order to supress the flutter we have introduced optimization of ribs and spars in the wing. Variation in the number of ribs, flange width and rib thickness are considered individually. Wing configuration with 10 ribs, flange width of +10% and 10mm rib thickness respectively are having the best flutter frequencies. The wing with above features is further optimised by keeping weight as a constraint by introducing circular and triangular cut-outs section. Flutter frequency for without cut-out, circular cut-out and triangular cut-out are 77.84 Hz, 78.27Hz and 78.43Hz respectively. Hence it is concluded that ribs with triangular cut-outs can be able to reach maximum flutter frequency.