Effect of dimensional variation, manufacturing process, and material on performance of fluidic oscillator
Jhaveri, Viyat Viral
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The use of active flow control (AFC) on civil transport aircraft flaps can delay stall at low aircraft speeds. This can lead to reducing the size of flaps or removing them from aircraft, which can reduce the part count, weight, and manufacturing cost of the aircraft. In addition to these changes, the cruise drag can also be reduced, which leads to lower fuel burn, hence lower costs and emissions. This technology works by energizing the boundary layer using an AFC device, a fluidic oscillator (FO) in this thesis, to prevent flow separation. However, the effects of material, manufacturing process, and dimensional variation on these parts is not entirely known. In this work, the key performance characteristics, also referred to as the functional requirements of the FO, were identified to be the coefficient of momentum and the oscillation frequency. The operational requirements of the FO were identified to be the fluidic power requirement and the ability to withstand pressure, significant temperature variations, and fluctuations in humidity. The materials that are explored include aluminum and carbon fiber PEKK. The manufacturing processes that were explored include machining, selective laser sintering (SLS), stereolithography (SLA), and injection molding. Variations in the dimensions were explored: nozzle width, nozzle length, nozzle radius, nozzle symmetry, nozzle curvature, and interaction chamber width. These were tested using a bench test setup. It was concluded that material had no impact on the performance of the FO, given stiff enough materials and those that can be manufactured to the required tolerances. The manufacturing process did affect the performance of the FO as it caused changes in the geometry of the FO. The changes included the inability of SLS, SLA, and injection molding to produces edges as sharp as can be produced by machining. As a result, the devices had lower pressure drops and higher oscillation frequencies, which are beneficial. It was also identified that nozzle width, shoulder width, and nozzle radius affected the oscillation frequency and that the nozzle width and nozzle radius affected the pressure drop. Nozzle symmetry and nozzle length did not affect the oscillation frequency and pressure drop; however, they did affect the jet profile. Lastly, the nozzle curvature did not have any effect on the performance of the FO. Additionally, the point at which the performance of the FO deviates from the model was identified, which corresponds to where the oscillation frequency is no longer dependent on the flow rate. Using this information, a dimensionless model was developed that can be used by FO designers to predict the pressure drop and oscillation frequency of the FO based on the dimensions of the FO.