• Version
• 34 Downloads
• 1.26 MB File Size
• 1 File Count
• December 14, 2016 Create Date
• December 14, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Further Comparisons of Theoretical and Experimental Lift and Pressure Distributions on Airfoils in Cascade at Low Subsonic Speed

Comparisons of theoretical and experimental lift coefficients and
pressure distributions were made for five compressor-type cascades of
highly cambered NACA 6-series airfoils. The experimental lift coef—
ficients, which were between 0.81 and 0.96, were 0.18 to 0.hl less than
the theoretical values for the same mean—flow direction. When the
theoretical lift coefficients were made equal to the experimental lift
coefficients by putting the circulation equal to the required value,
the Kutta condition being neglected, the agreements between the two pres—
sure distributions were very close, except for the configurations with
the highest pressure rise across the cascade (59 and 6% percent of the
upstream dynamic pressure). Interesting irregularities in the experi—
mental pressure distributions, not present in the calculated distri-
butions, were found to be caused by localized regions of laminar
separation.

The experimental data used in these comparisons were obtained by
the newer technique described in NACA TN 2028. The present paper is
thus to some extent a revision of an earlier paper, NACA TN 1376, where
substantially poorer comparisons were found for data obtained.by the
older techniques.

In reference l.several comparisons were made between theoretical
lift coefficients and pressure distributions on airfoils in cascade and
the corresponding experimental lift coefficients and pressure distri—
butions,reported in references 2 and 3. As with isolated airfoils, the
experimental lift coefficients were always less than the theoretical
lift coefficients; however, the differences were found to be remarkably
large, especially for compressor blading with large turning angles.

Furthermore, as is also true of isolated airfoils, a more or less
acceptable agreement between the pressure distributions could be
Obtained if the circulation was adjusted to correspond to the experi-
mental lift coefficient, either with superposition of sufficient nega-
tive camber, as in reference 4, so that the Kutta condition at the
trailing edge would still be obeyed, or with simple disregard of the
Kutta condition.