For some annular-type jet pump applications, it is important to avoid formation of a recirculation zone in the mixing region. The goals of this research were to find (i) when recirculation occurs and (ii) the size and location of the resulting recirculation zone. Experiments were performed using air in a straight-walled, annular-type, ducted jet. Area ratio Aj/As varied from 0.39 to 0.89; here, A is flow area, and j and s identify the jet and secondary flows, respectively. Data showed that recirculation correlates with J, where J ≈ Pj/(Pj + Ps), and P is rate of momentum. For the area ratios studied, recirculation begins when J exceeds a value ranging from 0.89 to 0.94. This paper also presents data showing the recirculation zone boundaries and presents a discussion of jet pump design.

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