High-frequency subsonic flow past a pulsating thin airfoil. II - Gust-type upwash

A theoretical model is developed for the sound generated when a convected disturbance encounters a cambered airfoil at non-zero angle of attack. The model is a generalization of a previous theory for a flat-plate airfoil, and is based on a linearization of the Euler equations about the steady, subsonic flow past the airfoil. High-frequency gusts, whose wavelengths are short compared to the airfoil chord, are considered. The airfoil camber and incidence angle are restricted so that the mean flow past the airfoil is a small perturbation to a uniform flow. The singular perturbation analysis retains the asymptotic regions present in the case of a flat-plate airfoil: local regions, which scale on the gust wavelength, at the airfoil leading and trailing edges; a ‘transition’ region behind the airfoil which is similar to the transition zone between illuminated and shadow regions in optical problems; and an outer region, far away from the airfoil edges and wake, in which the solution has a geometric-acoustics form. For the cambered airfoil, an additional asymptotic region in the form of an acoustic boundary layer adjacent to the airfoil surface is required in order to account for surface curvature effects. Parametric calculations are presented which illustrate that, like incidence angle, moderate amounts of airfoil camber can significantly affect the sound field produced by airfoil–gust interactions. Most importantly, the amount of radiated sound power is found to correlate very well with a single aerodynamic loading parameter, αeff, which is an effective mean-flow incidence angle for the airfoil leading edge.

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Numerical Investigation of Subsonic Flow Past a Flat Plate Aerofoil

Lecture Notes in Mechanical Engineering - Applications of Fluid Dynamics ◽

10.1007/978-981-10-5329-0_17 ◽

2017 ◽

pp. 251-260

Author(s):

Shailesh Kumar Jha ◽

S. Narayanan ◽

L. A. Kumaraswamidhas

Keyword(s):

Flat Plate ◽

Numerical Investigation ◽

Subsonic Flow ◽

Flow Past

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Unsteady subsonic flow past two relatively moving flat cascades of thin weakly loaded oscillating blades

Fluid Dynamics ◽

10.1007/bf01055089 ◽

1989 ◽

Vol 23 (4) ◽

pp. 620-625 ◽

Cited By ~ 4

Author(s):

K. K. Butenko ◽

A. A. Osipov

Keyword(s):

Subsonic Flow ◽

Flow Past

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Second order theory for steady or unsteady subsonic flow past slender lifting bodies of finite thickness

10.2514/6.1968-75 ◽

1968 ◽

Cited By ~ 1

Author(s):

J. REVELL

Keyword(s):

Subsonic Flow ◽

Finite Thickness ◽

Order Theory ◽

Second Order ◽

Flow Past

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Approximate unsteady thin-airfoil theory for subsonic flow

AIAA Journal ◽

10.2514/3.7188 ◽

1976 ◽

Vol 14 (8) ◽

pp. 1083-1089 ◽

Cited By ~ 14

Author(s):

Nelson H. Kemp ◽

Gregory Homicz

Keyword(s):

Subsonic Flow ◽

Thin Airfoil

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High Frequency Characteristics of the Near Wake and Vortex Past a Triangular Cylinder

Journal of Fluids Engineering ◽

10.1115/1.4049060 ◽

2020 ◽

Vol 143 (3) ◽

Author(s):

Lei Sun ◽

Yong Huang ◽

Xiwei Wang ◽

Xiang Feng ◽

Wei Xiao

Keyword(s):

Reynolds Number ◽

Circular Cylinder ◽

Vortex Core ◽

High Frequency ◽

Vortex Formation ◽

Flame Stabilization ◽

Near Wake ◽

Freestream Velocity ◽

Formation Region ◽

Flow Past

Abstract The flow past a triangular cylinder is one of the fundamental flows and widely utilized in flame stabilization and heat transfer. In this study, the near wake and vortex characteristics of the flow past an equilateral triangular cylinder are experimentally measured by a high frequency particle image velocimetry (PIV) system at 3 kHz. The triangular cylinder is installed in a wind tunnel with Reynolds numbers ranging from 10,700 to 17,700. The Reynolds-averaged and phase-averaged methods are utilized to analyze the flow field. Based on the flow fields, the length of the vortex formation region is about 1.5 times of the length of the equilateral triangle side. The residence time of a vortex in the vortex formation region is equal to a vortex shedding period. The stream wise velocity of the vortex core center downstream the vortex formation is about 0.8 times of the freestream velocity, which is slightly larger than the value about 0.7 for the flow past a circular cylinder at the same Reynolds number. The maximum tangential velocity at the periphery of the vortex core maybe occurs slightly in advance of the vortex reaching the boundary of the vortex formation region. The normalized lengths of the recirculation zone of the triangular cylinder keep nearly unchanged and are about 1.55 to 1.9 times of those of the circular cylinder at the same Reynolds number. The normalized normal wise instead of stream wise turbulence intensity has stronger effects on the distribution of the normalized turbulent kinetic energy.

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