A Study on Some Periodically Oscillating Flows in a Circular Pipe : Experimental Results and Numerical Analysis of Cross-Sectional Mean Velocity

Abstract

This paper describes experimental and theoretical bulk speeds in a circular pipe for some periodically oscillating air flows produced by two pistons with arbitrary phase differences including 180°. The following facts are found for the experimental conditions having a Reynolds number R_e= 1.32×10⁴-5.94×10⁴ and a reduced frequency √(ω')=10.9∼18.8. (1) The results of numerical simulation fairly well coincide with those of experiments. Therefore, the method of characteristics can predict, with good accuracy, the bulk speed of oscillating flows produced by two pistons. (2) The flows are almost axisymmetric. (3) When the piston phase difference is equal to 180°, the compressibility has no effect on the flow. But that effect becomes more remarkable as the phase difference becomes smaller from 180° to 90°. (4) If the effect of compressibility is comparatively small. the bulk speed is controlled by the time-averaged piston speed.