Leonard Shaw

ACTIVE CONTROL FOR CAVITY ACOUSTICS

To increase the range and payload of both existing and future aircraft, while maintaining or increasing mission survivability, weapons must be carried in low drag/low observable configurations. Existing external weapons carriage technology accounts for as much as 30% of total vehicle drag and prohibitive increases in radar signature. Internal weapons carriage solves signature issues, but substantially increases aircraft size while limiting weapon payloads to the size of weapon bays. New innovate and novel ways of both internal and external weapons carriage will be crucial to fighters of the next century. However, the new internal bays create a challenge to develop methods to suppress and control the internal flow induced acoustic environment in the weapons bay.The objective of the current wind tunnel test program was to define the baseline acoustic environment in a cavity and evaluate the effectiveness of active suppression concepts. The concepts consisted of leading edge oscillating flaps and leading edge pulsed fluidic actuation. Both concepts were evaluated for a range of parameters and the results indicate that either will successfully control the instabilities in the shear layer and thus suppress the flow induced acoustic environment in the cavity. The pulsed fluidic actuator was found to be more robust.

CLOSED LOOP ACTIVE CONTROL FOR CAVITY ACOUSTICS

To increase the range and payload of both existing and future aircraft, while maintaining or increasing mission survivability, weapons must be carried in low drag/low observable configurations. Existing external weapons carriage technology accounts for as much as 30% of total vehicle drag and prohibitive increases in radar signature. Internal weapons carriage solves signature r issues, but substantially increases aircraft size while limiting weapon payloads to the size of weapon bays. New innovative and novel ways of both internal and external weapons carriage will be crucial to fighters of the next century. However, the new internal bays create a challenge to develop methods to suppress and control the internal flow induced acoustic environment -in the weapons bay. The objective of the current wind tunnel test programwas to test pulsed fluidic injection at the leading edge of the cavity at --higher ifrequencies and evaluate closed -loop control. Suppression effectiveness was shown to be frequency dependent and closed loop control was shown to optimize suppression for most set of constraints.

Full-Scale Flight Demonstration of Active Control of a Pod Wake

Pods and externally carried stores can generate unsteady flows in their wakes with high acoustic loads capable of damaging aircraft structure. Active flow control technology has the potential to modify unsteady shedding in the wake of the pod, thereby reducing acoustic loads. In this work, an active flow control system was developed and tested on an F16 Aircraft. Using open loop flow control actuation, the frequency of the acoustic loads can be modified and their amplitude reduced. In addition, wake location can also be manipulated by the active control system. During the development process, small, mid, and full-scale wind tunnel tests were conducted with synthetic jet flow control actuators. Wind tunnel tests leading up to the flight test were conducted from Mach numbers from 0.2 up to 0.85. Synthetic jet exit velocities in excess of 800 feet per second were achieved. As was the case for wind tunnel pod wake control tests, the frequency of shedding was controlled, the location of the wake also was controlled, and the amplitude of the pressure fluctuations was reduced during the flight tests. Full-scale flight data were obtained for various actuator frequencies and aircraft flight conditions such as speed, altitude, angle-of-attack and yaw angle.

Acoustic Measurements for a Pulse Detonation Engine

The acoustic environment of a pulse detonation engine was measured. The engine consisted of one to four detonation tubes which were detonated at 20 or 40 Hertz. Fill fractions and equivalence ratios of 1 and 0.5 were tested. All of the testing was conducted in a test cell which was not acoustically treated. Measurements were made near the exit of the tubes and up to a distance 12 feet. Time histories and narrow band spectral analysis were generated. Comparisons of sampling frequencies of 200K and 20K were conducted. Numerous potential noise suppression approaches were evaluated. The results indicate that a very high level pulse is generated near the exit of the tubes but tends to decrease in amplitude fairly quickly with distance since the higher frequency energy dissipates in the atmosphere.

Active Control of a Pod Wake-Mid-Scale Application

Pods and externally carried stores can generate unsteady flows in their wakes with high acoustic loads capable of damaging aircraft structure. Active flow control technology has the potential to modify unsteady shedding in the wake of the pod, thereby reducing acoustic loads. In this work, an active flow control system was developed and tested on a generic pod configuration. Using open loop flow control actuation, the frequency of the acoustic loads can be modified and their amplitude reduced. In addition, wake location can also be manipulated by the active control system. A larger scale wind tunnel test on an eighth inch diameter pod with synthetic jet flow control actuators was conducted with the flow field being defined with and without the actuators operating. It was tested up to a Mach number of 0.5. Synthetic jet exit velocities in excess of 800 feet per second were achieved. As was the case for previous smaller scale pod wake control, the frequency of shedding was controlled, the location of the wake also was controlled, and the amplitude of the pressure fluctuations was reduced. Data were obtained for various actuator frequencies, amplitudes, and ejection locations on the aft end of the pod.

Effectiveness of an Integrated Aerodynamic Wake and Structural Vibration Control System at Transonic Speeds

** Wakes of aircraft external stores can generate high acoustic loads on downstream structures that lead to fatigue and failure of structural components. Structural vibration control systems have been employed to dampen structural loads but can become ineffective at high dynamic pressures. A recent wind tunnel study conducted at low subsonic speeds demonstrated that active flow control can enhance the effectiveness of a structural vibration control system on a fin submerged in the wake of an external store. This study continues this research and development effort through a transonic wind tunnel demonstration of an integrated aerodynamic wake and structural vibration control system. Results confirm that suppression strategies demonstrated at low subsonic speeds are applicable at transonic speeds and indicate that the integrated wake and structural vibration control system with limited control authority can provide suppression comparable to a highly capable vibration control system alone with only a fraction of the input power requirements.