Numerical investigation on the recovery process of the flow field in a rotating duct

Abstract

Turbulent flow inside a rotating duct widely exists in revolving hydromachines. The Coriolis force and the centrifugal force generated in the rotation greatly modify the development of the flow field and consequently affect the efficiency of these hydromachines. A deviation of the mainstream to the pressure sidewall of the duct, which occurs as soon as the fluid flows to the rotating duct, is commonly observed and previously thought to remain throughout the flow field. However, this study discovers a recovery process of the modified flow field and numerically investigates that process for the first time. The recovery process begins very close to the entrance of the duct and ends when the same fully developed flow field as that without rotation is obtained. The results indicate that the recovery process can be divided into four phases: the linear recovery phase, stationary mixing phase, nonlinear recovery phase, and finish of the recovery process. The characteristic details of the four phases and the evolving mechanisms of the recovery process are discussed. The algebraic relationships between the characteristic parameters of the recovery process and the inflow conditions (the rotation velocity, rotation numbers, mean inflow velocity, and height of the duct) are obtained. It is found that the characteristic deviation distance of the velocity peak in the linear recovery phase linearly moves toward the centerline of the duct with a slope of k=−0.0023ω+0.0748. The recovery distance linearly increases with the product of the mean streamwise velocity U and the rotation velocity ω as follows: (XsH)0.2=0.025U·ω+b. It also denotes that the recovery process can be accelerated by reducing the height H of the duct. Accelerating the recovery process and reaching the ideal optimal velocity distribution as soon as possible can effectively improve the efficiency of the flow field.