INJECTION OF BUBBLING LIQUID JETS FROM MULTIPLE INJECTORS INTO A SUPERSONIC STREAM

Multiple (12 injectors) bubbling liquid jets (helium microbubbles in water) were injected transverse to a M = 2.4 airflow. Penetration and spray plume spreading angle were measured directly using nanoshadowgraphs and front-lighted pictures, respectively. The experiments were performed at two conditions, i.e., the constant supply pressure condition and the constant liquid mass flow rate condition. For the case of a parallel arrangement of the injector orifices to the airflow, the penetration of the jet array increased steadily from front to back. The last jet (12th jet) has over 5 times the penetration of the first jet for the water only case. The usual similarity law for the penetration, h is-proportional-to q-0.5, was approximately valid also for the multiple water-only jets. For the bubbling jet case, the penetration of the first jet doesn't change with increasing gas concentration gamma, but the rear jets have less penetration height than that of liquid-only jets at the constant injection pressure condition. For the constant injection pressure condition, the resulting penetration of the jet plume decreased with increasing gamma. On the other hand, for the constant liquid mass flow rate condition, the penetration of the multiple bubbling jets increased a little with increasing gamma. Straight coherent jets just coming out of orifice were observed for the gamma = 0 case. Conical jet plumes were obtained for the bubbling jet case. Therefore, the width of the jet plume increased by using the bubbling jet. The effects of the angle between the orifice array and the freestream direction and the surfactant concentration on the penetration and mixing of multiple bubbling jets were also clarified.