Memorias de investigación
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The Low Reduced Frequency Limit of Vibrating Airfoils. Part I: Theoretical Analysis

Research Areas
  • Aeroacustics and vibrations,
  • Turbomachinery

This paper studies the unsteady aerodynamics of vibrating air- foils in the low reduced frequency regime with special empha- sis in its impact on the scaling of the work per cycle curves using an asymptotic approach (Part I) and numerical simula- tions (Part II). A perturbation analysis of the linearized Navier- Stokes equations for real modes at low reduced frequency is pre- sented and some conclusions are drawn. The first important re- sult 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 scale linearly with the reduced frequency whereas the phase departs from ?/2 and changes linearly with the reduced frequency. As a conse- quence the work-per-cycle scales linearly with the reduced fre- quency for any inter-blade phase angle and it is independent of its sign. For highly loaded airfoils the unsteady pressure mod- ulus 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 modeshape in first approximation. For symmetric cascades the work-per-cycle scales linearly with the reduced frequency irre- spectively of whether the airfoil is loaded or not. Simulations using a frequency domain linearized Navier-Stokes solver have been carried out on a low-pressure turbine airfoil section, the NACA0012 and NACA65 profiles and a flat plate to show the generality and correctness of the analytical conclusions (Part II of the corresponding paper). Both, the traveling-wave and influ- ence coefficient formulations of the problem are used in combi- nation to increase the understanding and explore the nature of the unsteady pressure perturbations.
ASME Turbo Expo 2015: Turbine Technical Conference and Exposition
Montreal, Canada
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ASME Proceedings | Structural Mechanics and Vibration

Research Group, Departaments and Institutes related
  • Creador: Departamento: Mecánica de Fluidos y Propulsión Aeroespacial