The Effect of Curvature on Boundary Layer Transition

Abstract

Discrepancies in the boundary layer profiles of NACA T.N. 613, * and recent work done at Cambridge University, England, on the effect of inclination on transition required the reinvestigation of the effect of curvature on boundary layer transition using a more fundamentally sound experimental technique than previously. This technique consisted in comparing velocity profiles taken at different speeds at each measuring station with the universal Blasius laminar profile; a further indication of transition was obtained by measuring the local shear coefficient with a small total head tube pressed against the surface. Agreement between the two methods was complete in all but one case. The effect of inclination was investigated by rotating the working section of the tunnel as a whole around a fixed pivot. Unfavorable inclination produced a decrease in transition Reynolds number on either side of the sheet but a neutral region was found to exist in which inclination had no effect on the transition and in which the effect of curvature alone acted. The effect of the curvature could be expressed as a function of the single variable 1000δm/rc. As to the exact nature of the (Rδm)T vs 1000δm/rc curve, little as yet can be said since a sufficient range of 1000δm/rc has not been investigated as yet. The results of T.N. 613 were thus validated qualitatively but the values of transition given there were found to be too large. * National Advisory Committee for Aeronautics Technical Note.