Flow Characteristics of a Fully Developed Concentric Annular Turbulent Flow

The hydraulic transportation technology of piped vehicles is a new type of pipeline transportation mode. A concentric annular turbulent flow with different boundaries is formed between the barrel of the piped vehicle and the pipe wall. The study on the annular turbulent flow can provide basic support for the application and promotion of this technology. Therefore, in this paper, the PIV technique was utilized to experimentally investigate the statistical characteristics of the annular turbulent flow in a fully developed smooth concentric annular pipe. The results showed that the position of the maximum velocity in the annular turbulent flow was not at the center but biased towards the barrel wall. Moreover, the smaller the radius ratio, the more it shifted towards the barrel wall. The position of the maximum velocity was independent of the Reynolds number and was a univariate function of the radius ratio; it was obtained by fitting experimental data that rmt*=k0.3491+k0.349. The resistance coefficient of annular turbulence was independent of the radius ratio and was a univariate function of the Reynolds number; it was obtained by fitting experimental data that λ=0.3183Rea0.2487. The shear stress on the barrel wall was greater than that on the pipe wall in annular turbulent flow. Moreover, as the radius ratio increased, the shear stress on the barrel wall decreased, while that on the pipe wall increased. The velocity distribution in annular turbulent flow was divided into an inner region and an outer region. In the inner region, the uc+−yc+ curves were greatly affected by the Reynolds number, and the average gradient increased with the increase in the Reynolds number, while in the outer region, the average gradient of the up+−yp+ curves decreased with the increase in the Reynolds number. The velocity distribution in annular turbulent flow cannot be expressed by a unified relationship. However, at high Reynolds numbers, there existed a region where the velocity distribution satisfied the logarithmic law in the outer region, and the slope of the logarithmic region was greater than that in circular pipe flow and parallel-plate flow.