Boundary Layer Multi-Property Flow Measurements Using a Micro-Plasma Sensor

When voltage is applied between two electrodes situated in close proximity to each other (10–100 μm), a weakly ionized, low temperature plasma discharge can be generated. This in turn creates a plasma sheath, an electrically ionized boundary layer (typically of the order of 10’s to 100’s of microns), where space charge effects dominate. The sheath acts like a virtual capacitor, with the plasma behaving as an inductor. Aerodynamic effects influence the plasma morphology (shape, thickness), thus making the plasma the transduction mechanism. The attraction to the use of plasma discharge as a transduction method for fluid flow property measurement stem from the fact that it lends itself to a probe implementation that is simple in design, can be miniaturized, and at the same time offers unmatched capability for handling ultra-high temperature environments. Sensing plasma discharge characteristics and their variation due to flow interaction can be done electrically, but also optically to yield time-varying intensity and spectral information from fluid-plasma interaction. The current paper focuses on the deployment of a micro-plasma sensor system as a new novel multi-parameter sensing approach for surface flow measurement. Results on pressure dynamics, shear flow, and other possible engineering parameters will be discussed in the context of results from several bench-level experiments.