The Low Reduced Frequency Limit of Vibrating Airfoils—Part I: Theoretical Analysis

  1. Corral, Roque 12
  2. Vega, Almudena 2
  1. 1 Advanced Engineering Direction, Industria de TurboPropulsores S.A., Francisca Delgado, 9, Alcobendas, Madrid 28108, Spain
  2. 2 Universidad Politécnica de Madrid
    info

    Universidad Politécnica de Madrid

    Madrid, España

    ROR https://ror.org/03n6nwv02

Revista:
Journal of Turbomachinery

ISSN: 0889-504X,  1528-8900

Año de publicación: 2015

Volumen: 138

Número: 2

Tipo: Artículo

DOI: 10.1115/1.4031776 GOOGLE SCHOLAR lock_openAcceso abierto editor

Otras publicaciones en: Journal of Turbomachinery

Resumen

This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced frequency regime with special emphasis on its impact on the scaling of the work-per-cycle curves, using an asymptotic approach. A perturbation analysis of the linearized Navier–Stokes equations for real modes at low reduced frequency is presented and some conclusions are drawn. The first important result is that the loading of the airfoil plays an essential role in the trends of the phase and modulus of the unsteady pressure caused by the vibration of the airfoil. For lightly loaded airfoils, the unsteady pressure and the influence coefficients (ICs) scale linearly with the reduced frequency whereas the phase departs from π/2 and changes linearly with the reduced frequency. As a consequence, the work-per-cycle scales linearly with the reduced frequency for any interblade phase angle (IBPA), and it is independent of its sign. For highly loaded airfoils, the unsteady pressure modulus is fairly constant exhibiting only a small correction with the reduced frequency, while the phase departs from zero and varies linearly with it. In this case, only the mean value of the work-per-cycle scales linearly with the reduced frequency. This behavior is independent of the geometry of the airfoil and the mode shape in first-order approximation in the reduced frequency. For symmetric cascades, the work-per-cycle scales linearly with the reduced frequency irrespective of whether the airfoil is loaded or not. These conclusions have been numerically confirmed in Part II of the paper.

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