Effect of Fuel Weight Distribution on the Aeroelastic Instability of Swept Wings

In this work, a study has been conducted to observe the influence of fuel weight distribution on the flutter characteristics of a high aspect ratio swept wing. In this paper, B777-200 wing model having a 34º sweptback angle is used as a baseline and two other models with the swept angles of 0º (straight wing) and 30º (forward swept) are considered in this study. Aeroelastic analysis is performed ranging from sea level up to 35,000 ft and the influence of in-flight fuel management in several flight altitudes is also investigated. There are four different fuel distribution model are investigated and it was found that some fuel distribution configuration are more critical which may lead to flutter. Moreover it was found that the flight altitude significantly affects the aeroelastic instability.

Numerical Stability Analysis of Oil Collector Case Self-Excited Vibrations

The investigation subject is an Oil Collector Case which is a thin axisymmetric stator part with console binding to the turbine rear frame. It had been suffering from high level vibrations and needed fixing measures to apply. Self-excited vibrations supposed as the main reason for defects to occur. The problem was examined in the engine and test rig conditions. The energetic method which is usually applied to blade flutter problems was used for aeroelastic stability analysis. Radial surface displacements were set according to the harmonic oscillation function that corresponds to the oil collector’s first bending eigenmode with two nodal diameters. 3D aerodynamic model represents a 180° sector, thus ensures that surface displacements and gas parameters on periodic surfaces are equal. A set of simulations was carried out and calculated; the aerodynamic damping coefficient values showed aeroelastic instability predisposition in both the engine and test rig conditions for most test cases. Influence of such model parameters as seal radial clearance, pressure ratio, inlet air temperature, wave propagation direction and rotor speed was investigated. A detailed analysis showed that for instability case positive aerodynamic work region lies inside the oil collector cavern downstream labyrinth seal where pressure wave and surface displacement speed wave are close to synchrony. Probable excitation mechanisms were described and discussed. It was demonstrated that aeroelastic instability of the same type as it was in the engine conditions can be reproduced in the test rig conditions.

Determination of the minimum wind speed leading to the galloping of conductors

The object of research in this paper is the split phase of overhead power lines. The study of the aeroelastic instability of the icy conductors of the split phase for a multi-span system has already been explored using the method of determining the Hurwitz stability criterion. In multi-span systems, where conductors are interconnected through a garland of insulators, the garlands themselves are involved in an oscillatory process. As a result of this, mutual influence of adjacent spans is observed energy is transferred from one span to another. The paper investigates the aeroelastic instability of the icy conductors of the split phase in the anchor span, which is characterized by two intrinsic features: the attachment point of conductors on the supports is fixed and mutual effects between adjacent spans are not observed. The study of motion instability is carried out by the first approximation method, that is, on the basis of linearization of the nonlinear equation at the equilibrium point and further investigation of the linearized equation in the vicinity of this point. The results of the study are based on the novelty of the carried out experiments - taking into account the peculiarities of the anchor span and the findings based on the analysis of empirical data.

Numerical and Experimental Studies of Labyrinth Seal Aeroelastic Instability

A labyrinth seal is commonly used to decrease the flow leakage loss between rotating and static components in aero engines. It is susceptible to aeroelastic instability because of its low stiffness. The aim of this study was to establish methods to predict and suppress it effectively. To achieve this, both numerical and experimental investigations are conducted using ansyscfx and ansys mechanical. These solvers are coupled to simulate the flutter precisely. Also, to assess the accuracy of the simulation qualitatively and quantitatively, a test rig is built. In the first part of this study, the accuracy of the numerical method is confirmed for several test cases with different seal clearance variations. Flutter inception is evaluated in detail for various pressure ratios and rotation speeds. The numerical results show good agreement with the experimental results. It is also confirmed that the aeroelastic instability is very sensitive to the seal clearance variations. These results show the same tendency as those in previous works. In the second part of this study, this paper tries to develop a flutter suppression method with higher leakage performance. This is achieved by changing the seal geometry. To detect the important geometric parameters, the contribution of each geometric component to aeroelastic instability is carefully analyzed. On the basis of this, the seal geometry is modified and its performance is evaluated. The optimized labyrinth seal shows good performance in terms of flow leakage and aeroelastic stability. Through this study, a new flutter suppression method is established.