Experimental Study of Wall Shear Rates in the Entry Region of a Curved Tube.

摘要

Very few studies of entry flow and wall shear rates in curved tubes have been made because of the theoretical difficulties of solving the full three-dimensional Navier-Stokes equations and the experimental difficulties of requiring direct non-disturbing techniques for the measurements of curved tube flows characterized by secondary flows. Recently,the precise distribution of wall shear rates in curved tubes has been of considerable concern to fluid dynamicists,engineers,and physiologists. In this study local wall shear rates in steady and pulsatile flows in the entry region of a curved tube have been measured by the limiting current method. A semi-circular rigid tube of circular cross section with radius ratio 1/7has been employed for a range of Dean number between 139to 2868. Corresponding pulsatile flow experiments have been performed at a mean Dean number of 613and at several frequencies. The circumferential and axial distributions of the wall shear rates have been measured at 20degrees circumferential increments at five different sections of the entry region. The experimental data have been compared with those estimated from the corresponding velocity measurements and some theoretical and numerical results. This work suggests that the distribution of atherosclerotic lesions corresponds to locations of low shear rather than high shear,and may be facilitated by boundary layer separation. The results of the present work should also be useful in developing a realistic mathematical model for curved tube flow and in designing coiled heat exchangers and refrigerators.