A method is presented for determining the aeroelastic stability boundaries of a cascade with aerodynamic, inertial, and structural coupling between the bending and torsional degrees of freedom. A computer program has been written to systematically investigate the effect of this coupling on cascade stability over a wide range of design parameters. Results presented illustrate that the bending-torsion interaction has a pronounced effect on the cascade flutter boundary, despite no appreciable tendency toward frequency coalescence as flutter is approached. The analysis also indicates that bending flutter is possible even in the absence of finite mean lift.

Coupled bending-torsion flutter in cascades.

Wake impacts on aerodynamic and aeroelastic behaviors of a horizontal axis wind turbine blade for sheared and turbulent flow conditions

The present invention relates to a centrifugal compressor. The compressor is a compact magnetic bearing based on technology and efficient compressor, and the compressor may have a high speed operation and reliable control system. The present invention employs a compressor installed on a single common motor so that a driving means shared two separate compressors. Balance the axial force at high speed is achieved by employing a pair of electromagnetic bearing.

A centrifugal compressor

This paper is devoted to solve the problem of stall flutter suppression for an absolutely divergent blade of small scale wind turbine. The blade is specially designed with absolutely divergent motions for the purpose of determining the most effective methods of active control for stall flutter suppression. A 2-DOF blade section is considered, with a simplified stall nonlinear aerodynamic model being applied. H-infinity mixed-sensitivity synthesis method with a new three-weight regulation is designed to control the time-domain instability of aeroelastic equations, with a third weight being chosen to weight complementary sensitivity for tracking problems and noise attenuation to robust stabilization in H- infinity control. Effects on flutter suppression are investigated based on different structural and external parameters. Apparent effects of H-infinity mixed-sensitivity method are displayed in the paper, when the other common intelligent control methods fail. The research provides a control way for absolutely divergent turbine blade motions. As typical nonlinear aeroelastic instable vibration, stall flutter is an important reason of fatigue damage for wind turbine. How to effectively avoid flutter instability has become an important subject needed to be investigated. Meanwhile in this area, the investigation of typical blade section based on the simplified stall flutter of 2-DOF flap/lag motions plays an important role due to its simplicity and high efficiency (1). Hence in this study, stall flutter suppression will be depicted based on 2-DOF blade section. In recent years, a number of issues related to the modeling, vibration analysis, and control methods for stall flutter are investigated. Shantanu experimentally studies and demarcates the stall flutter boundaries of an airfoil by measuring the forces and flow fields around the airfoil when it is forced to oscillate (2). S. Sarkar investigates the effect of system parametric uncertainty on the stall flutter bifurcation behavior of a pitching airfoil, with the aerodynamic moment on the two-dimensional rigid airfoil being computed using the ONERA dynamic stall model (3). J. Peiro investigates the dynamics of a typical airfoil section and demonstrates the importance of the added mass terms, with structural behavior being modeled by linear springs and the aerodynamic loading being exerted by Beddoes-Leishman (B-L) model (4). Zhiwei adopts a nonlinear time-domain aeroservoelastic model and designs flutter suppression control systems, with a novel state-space model being descripted for control design (5). Ananth presents a method to predict cascade flutter under subsonic stalled flow condition in a quasi-steady

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Stall Flutter Suppression for Absolutely Divergent Motions of WindTurbine Blade Base on H-Infinity Mixed-Sensitivity Synthesis Method

Aerodynamic Formulation for Stability Analysis of Lightly Cambered Airfoils in Cascade

Quasi-steady prediction of coupled bending–torsion flutter under rotating stall

This paper presents the results of a feedback technique for controlling low frequency surge oscillations in an axial compressor. To simulate surge a hybrid model is developed, by coupling the Moore - Greitzer potential flow model and the Navier - Stokes solution, to result in more realistic flow predictions. This hybrid model incorporates the viscous effect on the flow behaviour, which is neglected in the Moore - Greitzer model. The present model is shown to capture the existence of rotating stall disturbances in the combustor during a typical classic surge cycle as has been reported in the experiments. After modelling the surge we propose a steady feedback control scheme to minimise the adverse effect of the surge oscillations on the combustor operation. The results for a four hole and six hole feedback control mechanisms are reported and it is seen that the existing high frequency fluctuations in the unsteady variation of plenum pressure before control are virtually eliminated in the presence of a stead...

S. M. Ananth

Papers

Quasi-steady prediction of coupled bending–torsion flutter under rotating stall

A Simple Feedback Control Strategy for Controlling the Axial Compressor Surge

Aerodynamic Formulation for Stability Analysis of Lightly Cambered Airfoils in Cascade