Abstract: A circular jet has broad and important applications in practical engineering. Most research in this area has focused on a free jet, a wall jet or a vertical jet in a bounded domain. In this study, the mean velocities of circular offset jets were studied for four jet exit Froude numbers (Fr), three offset heights (S) (S/d=1, 2, 3) and three submergence ratios (ht/S) (surface jet, mixed jet, and submerged jet) in a bounded basin. Based on the results, we propose a velocity decay formula for a circular jet. The lateral velocity spread was more consistent with Gaussian and Cauchy–Lorentz distributions than the vertical velocity. Moreover, Fr had little effect on the decay of the mean velocity for a circular jet when Re>1×10⁴. The lateral and vertical spreads showed a quadratic relationship with the streamwise distance for different values of Fr at X/d<10. The positions of maximum mean velocity decay were independent of Fr and S/d when X/d<10. The spread rate was more uniform in the lateral direction than that in the vertical direction in a certain region for different S/d and ht/S. Therefore, the decay, spread, and maximum velocity position of the mean velocity for a circular offset jet can remain stable under different values of Fr, offset height, and submergence ratio.

Key words: Circular jet; Velocity decay; Froude number (Fr); Offset height; Submergence ratio

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