Studying the gyroscopic forces and structural damping joint impact on the wing flutter of the aeroelastic euram model

Aeronautical and Space-Rocket Engineering

Strength and thermal conditions of flying vehicles


Аuthors

Zichenkov M. C.*, Ishmuratov F. Z.**, Kuznetsov A. G.*

Central Aerohydrodynamic Institute named after N.E. Zhukovsky (TsAGI), 1, Zhukovsky str., Zhukovsky, Moscow Region, 140180, Russia

*e-mail: stataer@tsagi.ru
**e-mail: fanil.ishmuratov@tsagi.ru

Abstract

The article deals with the structural damping role analysis while studying the gyroscopic forces impact on the flutter speed. The algorithm for accounting for gyroscopic forces in polynomial Ritz method while computing the aircraft aeroelasticity dynamic characteristics, developed earlier by the authors, was employed. The algorithm was realized in the KC-M software developed in TSAGI and validated while solving aeroelasticity problems in many practical applications.

The computations were performed on the example of the wing of the well-known aeroelastic research model of the four-engine long-distance aircraft EuRAM (European Research Aeroelastic Model), developed and studied in the framework of the European project 3AS (Active Aeroelastic Aircraft Structure). The model characteristic feature is the flutter form occurrence associated with the lateral vibrations of external engines. This form is affected by the gyroscopic forces due to the engines rotating rotors.

The flutter characteristics analysis at various levels of structural damping (characterized by logarithmic vibrations decrement δ ) revealed that the vibrations tones interaction character with account for gyroscopic effect was not principally changed. It was found herewith, that the gyroscopic forces impact on the speed of the considered flutter form might be of different sign depending on the level of the structural damping.

For example, at δ = 0.02 the flutter speed increases by 11.5%, with the maximum value of the engine rotor kinematic momentum (scaled to the model). While increasing the structural damping value, in the beginning, the gyroscopic forces' impact on the flutter speed decreases, it does not practically exist at δ = 0.04, and with further increase of the decrement the impact changes its sign, and the flutter speed decreases. The flutter absence was marked at δ > 0.046 in the range of small rotor rate speed, but while the rate speed increase the flutter may occur. Its speed decreases at that (about 10%) with the rate speed increase. This indicates the importance of accounting for the dynamics of rotor systems while the aircraft aeroelastic phenomena analysis.

The obtained the results were confirmed also by the finite element computing method in NASTRAN system using Rotordynamics module (accounting for the rotor systems dynamics). The computing results on gyroscopic forces impact on aeroelasticity characteristics at various structural damping values performed with KC-M software accord well with computations performed with NASTRAN software.

It was noted that while experimental validation of the gyroscopic impact on the flutter speed of the model in the wind tunnel various results might be obtained depending on the structural damping level. Thus, the detailed computational and experimental analysis of the model dynamic characteristics is required while such tests preparing and running.

Keywords:

aircraft, numerical modal, gyroscopic forces

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