MODELING AND EXPERIMENTAL ANALYSIS OF PHASED ARRAY SYNTHETIC JET CROSS-FLOW INTERACTIONS

Abstract

Synthetic Jet Actuators (SJAs) are fluidic devices capable of adding momentum to static or non-static bodies of fluid without adding mass. They are therefore categorized as zero-net-mass-flux (ZNMF) momentum source. In its simplest compact form a SJA consists of an oscillatory surface connected to a cavity with a single exit orifice through which the fluid enters and exits. SJA technology has been utilized in applications ranging from boundary layer control over aerodynamic surfaces to fluidic mixing in dispersion applications. The ZNMF nature of the technology means it is not subject to constraints experienced by traditional momentum sources that require the addition of mass in order to impart momentum. The momentum that can be added by a single SJA is limited by the energy transfer capabilities of the oscillating surface. In modern SJAs this surface usually is a piezoceramic/metal composite subjected to a high voltage AC signal. For applications such as flow control over aerodynamic surfaces, modern SJAs are used in an array configuration and are capable of altering the flow momentum by values ranging from 0.01-10%. While it is possible to build larger actuators to increase this value the benefits associated with the compact size would be lost. It is therefore desirable to tune other parameters associated with SJA arrays to increase this value. The specific motivation for this study comes from the desire to control the momentum addition capacity of a specific SJA array, without having to alter any geometric parameters. In a broader sense this study focuses on understanding the physics of SJA interaction in array configuration through experiments which are then used to guide in the design of modeling technique that predicts SJA array behavior in cross-flows.

The first half of the project focused on understanding SJA behavior through modeling. Numerical techniques were initially used to model SJA and SJA arrays in cross-flows. Reduced numerical models were then developed from the full momentum equations. Analytical methods to solve these reduced order models were then implemented in order to cut down on solution time. A wave equation based solution to the stream and vorticity formulation of the momentum equations was implemented to predict SJA behavior.

For the experimental component of the project, a finite span high aspect ratio orifice SJA was designed and characterized through Constant Temperature Anemometry (CTA). Two of these SJA were then placed in close proximity to one another. The relative phase of operation between the two jets was altered and the resulting flow field was measured through Particle Image Velocimetry (PIV). This process was repeated for different sets of array spacing, and SJA to cross-flow velocity ratio. For specific choices of these parameters a 40% increase in momentum addition was observed. The experimental results were used to validate the modeling techniques. In general reasonable agreement between the modeling and experiment was observed in specific domains of the flow field.