Investigation of thermal effect on aeroelastic flutter speed

Aeroelasticity is a discipline that examines the behavior of elastic structures in fluid flow. One of the critical phenomena within this field is flutter, a potentially catastrophic instability where aerodynamic forces couple with structural vibrations, leading to uncontrolled oscillations. Determining flutter speed is vital for aircraft safety, as exceeding this limit can result in structural failure. Therefore, flutter speed must remain outside the flight envelope. Traditionally, thermal effects are often neglected in flutter calculations, despite their potential influence on structural characteristics. This study investigates the effects of thermal loads on the flutter characteristics of aircraft structures. Initially, a modal analysis is conducted by using MSC Nastran Software to determine the natural frequencies under varying thermal loads. The numerical method is validated through experimental vibration tests performed at different temperatures, comparing the experimentally obtained natural frequencies with those derived numerically. Subsequently, a generic fighter aircraft mission profile is developed to create a thermal map for an AGARD wing. Thermal computational fluid dynamics (CFD) analyses are performed by using STAR-CCM+ software to simulate temperature distribution across the wing structure. The generated thermal loads are then applied as pre-loads onto the AGARD wing, and modal analyses are conducted by using the validated numerical methodology in MSC Nastran. Finally, flutter speeds for different thermal load conditions are calculated using the ZAERO software. Comparations reveal that increased thermal loads result in a reduction of both flutter speed and flutter frequency. The findings emphasize the necessity of incorporating thermal effects into flutter analysis for a more accurate assessment of aircraft structural stability.