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Abstract
An experimental investigation was conducted on an Air Jet Vortex Generator (AJVG) consisting of a closely spaced set of four, geometrically related sub-orifices. The jet was a discretised version of an ideal nozzle featuring an injection width that smoothly increased by a function of Euler’s number (e). The exponential AJVG was used to suppress flow separation about a two-dimensional, NACA 6 series airfoil, with testing conducted at a Reynolds number of 6.5 × 105.
The exponential jet was designed to be used with a set of blowing profiles that also increased in velocity by a function of Euler’s number, with three groups of injection schemes devised for testing. The first set of blowing profiles were a discretised version of the ideal injection scheme and featured a four part, step-wise increase in velocity. The second set of blowing profiles had an injection velocity that was constant across the four sub-orifices of the jet. The final set of blowing profiles issued air from one sub-orifice only to mimic conventional manifestations of AJVG.
Under conditions of a turbulent boundary layer, the discretised exponential blowing profiles consumed less energy to produce incremental recovery of lift coefficient up to 0.38 when compared to the blowing profiles featuring a constant injection velocity. An 18% reduction in energy consumption was noted for a 0.34 incremental recovery of lift coefficient. Both of these sets of blowing profiles proved superior to the third set of “conventional” blowing profiles beyond incremental recoveries of lift coefficient of 0.32.
The literature on Tandem Jet In Cross Flow (TJICF) configurations and fluid jets was analysed to provide an explanation for the energy efficiency benefit provided by the multiple orifice AJVG operating with exponential blowing profiles. It is likely that the exponential qualities of the jet reduced the near field entrainment of ambient fluid into the resulting vortex preventing premature weakening of the structure, which resulted in elevated levels of vorticity in the near-field of injection. The natural decay of the structure from this initial, elevated magnitude of strength provided enhanced suppression of flow separation and recovery of lift coefficient.