Experimental and Computational Analysis of Periodic Flow Structure in Oscillatory Gas Flow Meters

Abstract

The oscillatory characteristics and dynamic structure of periodic flow in an oscillatory gas flow meter were studied experimentally and numerically. The flow oscillations were triggered by the Coanda effect and an universal correlation between Strouhal number and Reynolds number, Str = 1.09 x 1(T 3 for ReHD > 800, was deduced based on spectral analysis of the pressure fluctuations in the flow channel. Numerical simulation indicated that the evolution of the flow patterns was classified into stages of induction and sustainable periodic oscillation. The transformation between the two stages was noticeably affected by the design of the feedback channels. The results further revealed that the development of the main vortex in the oscillating chamber and the small vortices at the entrance of the feedback channels concurrently modulate the mechanism of oscillation. The small vortices located at both entrances of the feedback channels play the role of a pair of modulating valves, which alternatively switch on and off the bypass flow through each feedback channel, thus reinforcing the periodic oscillation.

A novel fluidic oscillator incorporating step-shaped attachment walls

“…A fluidic oscillator is widely applied to measure flow rates [1][2][3] because of a characteristic that its oscillating frequency is linearly proportional to the inlet flow rate for Reynolds numbers over a broad range. The basis of operation is that a jet entering a divergent cross-section or a sudden-expansion channel generally diverts toward either side, due to the Coanda effect, then develops to become a periodically oscillating flow at a fixed frequency [4][5][6].…”

“…Previous researchers reported specific correlations among the oscillation characteristics and geometric parameters. Based on the channel structure and the operating principle, previous investigations of fluidic oscillators are classified into three types: feedback oscillator [1][2][3][7][8][9], Karman vortex oscillator [11,12], and concave-type oscillator (Vee-gutter or U concavity) [13][14][15][16][17][18]. Tippetts et al [19,20] deduced four major parameters for feedback fluidic oscillator of relaxation type, namely its Strouhal number (Sr), Reynolds number (Re), Euler number (Eu), and a dimensionless control loop inductance (L ), which serve also for dimensionless analysis in discussion, defined as follows:…”