Browsing by Subject "DRE"
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Item In-Flight Measurements of Freestream Atmospheric Turbulence Intensities(2012-11-05) Fanning, Joshua 1987-The last key to implementing laminar flow control on swept-wings is controlling the crossflow instability. One promising technology is spanwise-periodic discrete roughness elements (DREs). Previous work has shown success with applique DREs and extending the region of laminar flow. This work seeks to extend the DRE technology to include dielectric barrier discharge plasma actuators as well as recreate past experiments with applique DREs. One major need in implementing DREs and controlling crossflow is attaining an accurate measurement of the freestream atmospheric turbulence intensities. Knowing the atmospheric turbulence intensity will allow for comparing wind tunnel experiments to the flight environment and help produce better wind tunnel experiments by allowing them to better match the flight environment. Also, knowledge of the turbulence intensity at the specific instance of an experimental data point will allow for determining if differences in experimental results are the result of a difference in turbulence intensity. It has been determined through this work that the levels of freestream turbulence range from 0.023% - 0.047% with an average of 0.035%. These levels were reached through the use of temporal correlations to remove electronic noise as well as acoustic sound from the hotwire measurements and hence are lower than previously calculated.Item Sensitivity of Swept-Wing, Boundary-Layer Transition to Spanwise-Periodic Discrete Roughness Elements(2014-12-12) West, David EdwardMicron-sized, spanwise-periodic, discrete roughness elements (DREs) were applied to and tested on a 30? swept-wing model in order to study their effects on boundary-layer transition in flight where stationary crossflow waves are the dominant instability. Significant improvements have been made to previous flight experiments in order to more reliably determine and control the model angle of attack (AoA) and unit Reynolds number (Re'). These improvements will aid in determining the influence that DREs have on swept-wing, laminar-turbulent transition. Two interchangeable leading-edge surface-roughness configurations were tested: polished and painted. The baseline transition location for the painted leading edge (increased surface roughness) was unexpectedly farther aft than the polished. Transport unit Reynolds numbers were achieved using a Cessna O-2A Skymaster. Infrared thermography, coupled with a post-processing code, was used to globally extract a quantitative boundary-layer transition location. Each DRE configuration was compared to curve-fitted baseline data in order to determine increases or decreases in percent laminar flow while accounting for the influence of small differences in Re' and AoA. Linear Stability Theory (LST) guided the DRE configuration test matrix. In total, 63 flights were completed, where only 30 of those flights resulted in useable data. While the results of this research have not reliably confirmed the use of DREs as a viable laminar flow control technique in the flight environment, it has become clear that significant computational studies, specifically direct numerical simulation (DNS) of these particular DRE configurations and flight conditions, are a necessity in order to better understand the influence that DREs have on laminar-turbulent transition.Item Sensitivity of Swept-Wing, Boundary-Layer Transition to Spanwise-Periodic Discrete Roughness Elements(2014-12-12) West, David EdwardMicron-sized, spanwise-periodic, discrete roughness elements (DREs) were applied to and tested on a 30? swept-wing model in order to study their effects on boundary-layer transition in flight where stationary crossflow waves are the dominant instability. Significant improvements have been made to previous flight experiments in order to more reliably determine and control the model angle of attack (AoA) and unit Reynolds number (Re'). These improvements will aid in determining the influence that DREs have on swept-wing, laminar-turbulent transition. Two interchangeable leading-edge surface-roughness configurations were tested: polished and painted. The baseline transition location for the painted leading edge (increased surface roughness) was unexpectedly farther aft than the polished. Transport unit Reynolds numbers were achieved using a Cessna O-2A Skymaster. Infrared thermography, coupled with a post-processing code, was used to globally extract a quantitative boundary-layer transition location. Each DRE configuration was compared to curve-fitted baseline data in order to determine increases or decreases in percent laminar flow while accounting for the influence of small differences in Re' and AoA. Linear Stability Theory (LST) guided the DRE configuration test matrix. In total, 63 flights were completed, where only 30 of those flights resulted in useable data. While the results of this research have not reliably confirmed the use of DREs as a viable laminar flow control technique in the flight environment, it has become clear that significant computational studies, specifically direct numerical simulation (DNS) of these particular DRE configurations and flight conditions, are a necessity in order to better understand the influence that DREs have on laminar-turbulent transition.