Anomalous scaling of passive scalar fluctuations in experiments of turbulent pipe flow

The anomalous scaling of passive scalar fluctuations is experimentally investigated in turbulent pipe flow with a Taylor-microscale Péclet number of $\mathcal{O}(10^5)$ , where the turbulence is known to deviate from the homogeneous isotropic turbulence. The scalar structure functions and intermittency in the mixing are examined. The experimental results consolidate that the scaling exponents of scalar structure functions saturate at high-order even moments, evidenced previously in homogeneous isotropic turbulence with a Taylor-microscale Péclet number of $\mathcal{O}(10^3)$ . The saturation scaling exponent decreases to approach unity as the Taylor-microscale Péclet number increases. This saturation scaling exponent is further corroborated by the fractal codimension of sharp scalar fronts.