Flow induced by a turbulent jet under random waves

Abstract

The flow characteristics of a vertical turbulent jet discharged in random-waves environment have been investigated experimentally to assess the dilution of wastewater discharge in coastal areas. The results show that additional wave induced mixing is significant, which is reflected from the substantial increase in jet width and turbulence, as well as the rapid decrease in centerline velocity and shortening of jet potential core. The jet–wave interaction generates two flow regimes; jet-momentum dominated near field (JDNF) and wave-momentum dominated far field (WDFF). Comparing to those of jet flow in regular waves, the transition point between the two regimes is closer to the jet outlet and the velocity decay in WDFF is milder. A Lagrangian integral model has been developed to predict the characteristics of jet in random waves. Using the commonly adopted values of the radial and forced entrainment coefficients, the computed results match the experimental data closely for cases of small to medium waves (u_sig/W₀ < 0.05, u_sig = mid-depth maximum orbital velocity, WW₀ = jet outlet velocity), while for large waves the jet width is underpredicted, showing that the entrainment coefficients are wave dependent.

Keywords:

• Jet
• jet–wave interaction
• random waves