Call JTI-CS-2009-1-GRA-02-003 required an effective, efficient and reliable Synthetic Jet Actuator (SJA) system to be supplied as a complete plug-and play unit for wind tunnel testing.
Based on recent experience gained in the EU FP6 AVERT programme in which this capability was demonstrated, the University of Manchester (UoM) proposed to develop such a system in conjunction with the manufacturing and wind tunnel operational expertise of the Aircraft Research Association (ARA).
The proposal had the potential to considerably advance the state of the art in SJA technology through use of a novel scalable cantilever based electro-mechanical conversion element. The AVERT system and others show that UoM and ARA had the ability to produce an advanced system based on the best realisation of the current diaphragm-based concept as a risk reduction measure, in order to ensure that the objectives of the call were met.
Synthetic Jet Actuators (SJAs) have been routinely used for wind tunnel applications for around the last ten years. These actuators are typically Helmholtz resonator devices based on an actuated membrane, cavity and orifice. With the membrane natural frequency matched with cavity/orifice Helmholtz frequency to improve maximum jet velocity from the device. The orifice axis may be normal or inclined relative to the local wetted surface (skin) depending on the type of flow control actuation input required (single vortex or counter rotating vortex pair). The membranes are typically based on using a polycrystalline piezoelectric (PZT) patch applied to a metallic disc. These discs are commercially available components typically used for buzzers or low quality speakers. The typical operating frequency of the devices is around 2kHz consistent with audio applications. The currently achievable maximum velocity is around 150m/s with a power conversion efficiency of around 10%. Device mechanical/electrical reliability is an issue and health monitoring on arrays of devices is typically not available.
The University of Manchester (UNIMAN) and Aircraft Research Association (ARA) have delivered a single, linear spanwise array of 30 synthetic jet actuators with integrated health monitoring.
The VELOCIRAPTOR project has advanced the state of the art in SJA technology by...
1) Producing a sealant-free array with reduced number of parts
Manufacture of the module using stereolithography rapid prototyping technique has been achieved which, relative to the AVERT array, has enabled:
- the ability to include more complex geometry
- 33% reduction in part count per SJA
- 75% reduction in leadtime
2) Increasing power density of the SJA array
To meet the application requirements proposed by CIRA (placement of module at the 20% chord point of the inboard main flap element of a three element wing), a skewed opposite SJA configuration was utilised consisting of an array of overlapping SJAs. Relative to the AVERT array, the module reduces usable depth requirements by 50% while maintaining comparable performance in terms of peak jet exit velocity, i.e. ~90ms-1 at f = 2.7kHz.
3) Providing real-time actuator health monitoring
Distributed sensors in the array (in the form of small microphones housed in each SJA) demonstrate real-time monitoring via a 2-colour LED, the output of which is dependent on a pre-set threshold. The system provides a more rapid and continuous method of actuator health monitoring, as opposed to the previous practice of measuring actuator performance via hot-wire anemometry, which can be done only infrequently. The health monitoring system is expected to form a fundamental requirement towards the future certification of in-flight active flow control systems.