Compressibility Effects in Micro Synthetic Jets

Effects of including compressibility in the numerical modeling of flows produced by and in synthetic jet actuators — consisting of an oscillating diaphragm in a cavity with a small circular orifice in the face opposite the diaphragm — has been studied for axisymmetric configurations. Numerical results obtained on the assumption of incompressible and compressible flows with orifice diameters of the 20 and 40 μm and with an orifice length of 50 μm are compared. There are significant differences between compressible and incompressible flows for the 20 μm orifice, in that the jet velocity is greatly reduced when compressible flow is assumed, whereas the differences are much smaller in the 40 μm case. For both orifices the pressure rise upstream of the orifice is smaller when the fluid is compressible. It follows that results obtained on the assumption of incompressible flow cannot be extrapolated for micro-synthetic jet actuators handling compressible fluids.