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Reduced frequency effect on an unsteady compressible boundary layer over an oscillating supercritical airfoil

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Abstract

Boundary layer states, including laminar, turbulent, attached or separated, have significant effects on an airfoil operation and aerodynamic forces; especially as the boundary layer becomes turbulent or separated, the drag forces increase significantly. In the compressible flow and the transonic regime, when the compressibility effects and shock–boundary layer interaction are also considered, the flow field is so complicated that it cannot be easily investigated using the theoretical and computational methods. In this study boundary layer is investigated experimentally in several static angles of attack and also, during sinusoidal pitching motions at M ∞ = 0.65, Reynolds number of 9.202 million per meter, using multiple hot film and pressure sensors. Transition and relaminarization points, supersonic region, and shock formation are detected on the upper surface of the airfoil, and, the reduced frequency effect is investigated in dynamic case. It is worth mentioning that the low-range oscillation amplitudes and reduced frequencies used in this research led to quite different and interesting results that have not been considered in the other investigations dealing with oscillating airfoils.

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Abbreviations

c :

Airfoil chord

C P :

Pressure coefficient

F :

Oscillation frequency

k :

Reduced frequency, πfc/U ∞

M ∞ :

Free-stream mach number

MHFS:

Multiple hot film sensor

PSD:

Power spectral density

RMS:

Root mean square

T :

Transition point

R :

Relaminarization point

x/c :

Non-dimensional distance from the leading edge

t :

Time

τ :

Time scale, ωt

U ∞ :

Free stream velocity

AOA:

Static angle of attack

α0 :

Mean angle of attack

αu :

Instantaneous angle of attack during pitch up

αd :

Instantaneous angle of attack during pitch down

αmin :

Minimum angle of attack in pitching motion

αmax :

Maximum angle of attack in pitching motion

α(t):

Instantaneous angle of attack, α0 + ∆α sin(ωt)

∆α:

Oscillation amplitude

ω :

Angular frequency, 2πf

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Authors and Affiliations

  1. Aerospace Engineering Department, Amirkabir University of Technology, Tehran, Iran

    N. Fallahpour, A. A. Haghiri & M. Mani

  2. Center of Excellence on Computational Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran

    M. Mani

Authors
  1. N. Fallahpour
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  2. A. A. Haghiri
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  3. M. Mani
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Correspondence to N. Fallahpour.

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Technical Editor: Francisco Ricardo Cunha.

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Fallahpour, N., Haghiri, A.A. & Mani, M. Reduced frequency effect on an unsteady compressible boundary layer over an oscillating supercritical airfoil. J Braz. Soc. Mech. Sci. Eng. 37, 1379–1390 (2015). https://doi.org/10.1007/s40430-014-0245-9

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  • DOI: https://doi.org/10.1007/s40430-014-0245-9

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