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Experimental study of the boundary layer over an airfoil in plunging motion

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Abstract

This is an experimental study on the boundary layer over an airfoil under steady and unsteady conditions. It specifically deals with the effect of plunging oscillation on the laminar/turbulent characteristics of the boundary layer. The wind tunnel measurements involved surfacemounted hot-film sensors and boundary-layer rake. The experiments were conducted at Reynolds numbers of 0.42×106 to 0.84 × 106 and the reduced frequency was varied from 0.01 to 0.11. The results of the quasi-wall-shear stress as well as the boundary layer velocity profiles provided important information about the state of the boundary layer over the suction surface of the airfoil in both static and dynamic cases. For the static tests, boundary layer transition occurred through a laminar separation bubble. By increasing the angle of attack, disturbances and the transition location moved toward the leading edge. For the dynamic tests, earlier transition occurred with increasing rather than decreasing effective angle of attack. The mean angle of attack and the oscillating parameters significantly affected the state of the boundary layer. By increasing the reduced frequency, the boundary layer transition was promoted to the upstroke portion of the equivalent angle of attack, but the quasi skin friction coefficient was decreased.

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Abbreviations

A :

Amplitude of the plunging motion (cm)

C f :

Skin friction coefficient

E :

Hot-film output voltage (V)

E 0 :

Offset voltage (V)

H :

Shape factor

PSD:

Power spectrum density

Re :

Reynolds number

U ∞ :

Free stream velocity (m/s)

U e :

Velocity at the boundary layer edge (m/s)

c :

Airfoil chord (cm)

f :

Plunging frequency (Hz)

h :

Plunging displacement (cm)

\(\bar h\) :

Dimensionless plunging amplitude, \(\bar h = {{2A} \mathord{\left/ {\vphantom {{2A} c}} \right. \kern-\nulldelimiterspace} c}\)

k :

Reduced frequency, k = π f c/U ∞

s :

Sensor

t :

Time (s)

u :

Rake velocity (m/s)

x :

Distance from the leading edge of the airfoil (cm)

y :

Distance normal to the airfoil surface (m)

α :

Angle of attack (°)

α 0 :

Mean incidence angle (°)

α eq :

Equivalent angle of attack (°)

δ :

Boundary-layer thickness (m)

δ*:

Displacement thickness (m)

θ :

Momentum thickness (m)

ω :

Angular frequency (rad/s)

ρ :

Air density (kg/m3)

τ :

Quasi-wall-shear stress (N/m2)

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Authors and Affiliations

  1. Aerospace Research Institute, Tehran, Iran

    F. Rasi Marzabadi

  2. Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran

    M. R. Soltani

Authors
  1. F. Rasi Marzabadi
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  2. M. R. Soltani
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Correspondence to F. Rasi Marzabadi.

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Marzabadi, F.R., Soltani, M.R. Experimental study of the boundary layer over an airfoil in plunging motion. Acta Mech Sin 28, 372–384 (2012). https://doi.org/10.1007/s10409-012-0039-1

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  • DOI: https://doi.org/10.1007/s10409-012-0039-1

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