On a puzzle posed by the Kurien-Sreenivasan boundary layer experiment

The Kolmogorov inertial range ratio of the mixed- to- longitudinal third-order structure functions of isotropic and homogeneous turbulence is $\frac{S_{1,2}}{S_{3,0}}=1/3$. Recent measurements by Kurien and Sreenivasan (Phys. Rev. E {\bf 64}, 056302 (2001)), showed that, while the longitudinal structure function was extremely close to Kolmogorov's, the measured ratio was very far: $\frac{S_{1,2}}{S_{3,0}}\approx 0.43$. Explanation of this puzzle is presented in this letter.