Experimental Study of Through-Flowing Pneumatic Lines

Abstract

The complete linear two-port admittance parameters of a short uniform pneumatic line are experimentally determined as functions of driving frequency and the steady through-flow in the line. The measured through-flow influence (c.f. the driving point admittance increase) is found to be much greater than that predicted by known one-dimensional acoustic models (frequency dependent phase velocity and attenuation factor) with mean velocity Doppler shift correction. More satisfactory agreement is found with a model which considers the first-order effects of the through-flow velocity profile. High-frequency (up to 2500 Hz) laminar dynamic flow and pressure data is presented for lines on the order of 6 in. long and 1/8 in. ID, with Mach numbers from zero to 0.16. The experimental aspects of quantitative dynamic flow measurement with a hot-wire anemometer are discussed in detail. Details and calibration of the high-frequency line flow and pressure probes, and the low Reynolds number—high Mach number flow test setup are presented.