Abstract
In this paper, swirl decay, swirling flow pitch and pressure loss in a straight pipe are described. Two types of experiments are performed. First, swirling angle, velocity and pressure measurements are conducted to estimate swirl decay and swirling flow pitch. Either the traditional swirl number, m, or a proposed swirling angle at r/R=0.95, Θsw, is employed as the definition of swirl strength for evaluating swirl decay. As a result, it is ascertained that both the swirl number and a proposed swirling angle at r/R=0.95 are useful for swirl strength definition. Change in swirling flow pitch due to swirl decay is confirmed by analyzing the swirling angle distribution. It is confirmed quantitatively that the pitch is long in the annular region and short in the central region of the pipe. When the swirl decays, swirling flow pitch at radius, r, is elongated far downstream. Second, the other equipment and a straight pipe, longer than 120 pipe diameters, are employed for confirming the relationship between swirl strength and pressure loss. Wall-pressure measurements are performed. An equation for pressure loss of swirling flow in a straight pipe which considers pressure loss influenced by the swirler, swirl and pipe friction is proposed by the author. The ratios of each types of pressure loss to the total loss are ascertained. In a straight pipe with a guide vanes type of swirler, inlet length is about 15 pipe diameters. Pressure loss in the transitional region where swirl effect remains decreases and the ratio of pipe friction loss to the total loss increases according to swirl decay.
