Microjet Flow Control on an Airfoil Flap: Particle Image Velocimetry Characterization

Normal-blowing microjets near the trailing edge of a flap can improve the aerodynamic performance of high-lift systems, potentially without some of the system-integration drawbacks of traditional systems. Previous two-dimensional simulations and a preliminary wind-tunnel test demonstrated the effectiveness of the microjet concept on a deployed flap. To further validate microjet effectiveness, this study uses a specially developed particle image velocimetry technique to estimate the momentum injected by a microjet on a deployed Fowler flap of a two-element NLR7301 airfoil while simultaneously measuring the lift enhancement provided by the microjet via surface pressure taps. The test results are broadly consistent with numerical simulations that predict lift increases proportionally to the square root of momentum injection. Within the experimental uncertainties, the test results show slightly less lift benefit for a given level of estimated momentum injection compared to the simulations, possibly due to three-dimensional effects such as spanwise variability and spanwise velocity components of the injected air, which could not be measured with the current instrumentation.