Boeing and the US Air Force have demonstrated that active flow control can enable safe munitions release from a weapons bay at high supersonic speed, paving the way for future strike aircraft to dispense weapons throughout their flight envelope.
In the rocket-sled test at Holloman AFB, New Mexico, a Mk82 JDAM was released from a weapons bay at about Mach 2. Windtunnel testing had indicated that, without active flow control, the bomb would have returned to the bay, Boeing says.
The test demonstrated the Air Force Research Laboratory's HIFEX concept for high-frequency excitation active flow control as an alternative to a passive weapons-bay spoiler for supersonic munitions release. Additional testing is planned for 2008.
A tandem array of microjets upstream of the weapons bay reduced the unsteady pressures inside the bay and modified the flow outside to ensure the JDAM was dispensed nose-up from the sled, says Bill Bower, Boeing Phantom Works HIFEX programme manager.
Supersonic flow over the open weapons bay creates a shear layer, and feedback between this and acoustic waves inside the cavity creates unsteady pressures in the bay. The two rows of evenly spaced supersonic microjets disrupt the resonance within the bay and also generate shocks that modify the external flow to ensure the weapon leaves the bay with the correct attitude.
In previous tests with a 10%-scale HIFEX weapons bay, Boeing evaluated different types of flow-control actuator, including powered resonance tubes, a jet screen and the supersonic microjets. The jets did better at controlling acoustic levels in the bay and substantially reduced dynamic pressures within the cavity. Supersonic drop tests showed the tandem array of jets provided the best weapon separation characteristics.
To generate the control authority needed to modify the supersonic airflow over the weapons bay, Bowers says the jets would be powered by engine bleed air and use a convergent-divergent passage to generate supersonic flow.
Source: Flight International
