Browsing by Subject "laminar flow control"
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Item Aerodynamic Design for Swept-wing Laminar Flow(2013-11-08) Belisle, Michael JosephThis work describes and compares processes for swept-wing laminar flow control (SWLFC) aerody-namic design. It focuses on results obtained during the preliminary outer-mold-line (OML) design of the Subsonic Aircraft Roughness Glove Experiment (SARGE), a natural laminar flow and passive laminar flow control wing glove flight experiment funded by the NASA Environmentally Responsible Aviation initiative. The experiment seeks to raise the technology readiness level of the spanwise-periodic discrete roughness element (DRE) SWLFC technique for transition delay on a swept wing. Changes to the SARGE project requirements necessitated numerous redesigns that lead to design process insights and reinforced the value of proven methodologies. Optimization-based wing design methods are compared to traditional processes in the context of issues specific to SWLFC design. A refined traditional process incorporates the lessons learned during SARGE design excursions. As 3D e?ects are often significant at transonic Mach numbers, they should be included in the analysis as soon as practical when allowing for available computational tools. In the initial experimental feasibility and OML design, Euler computational fluid dynamics was used to produce a series of 2.5D SWLFC airfoils with boundary-layer stability and transition predicted using linear stability theory and the e^(N) method. Two wing gloves were lofted onto the Gulfstream-III host aircraft wing: TAMU-05-04, a straight loft using the TAMU2D-04 airfoils, and TAMU-06-05, an optimized revision used in the preliminary design review (PDR) of the SARGE experiment conducted in June 2012. The target pressure distribution for the TAMU-06-05 glove was developed using a graphical B-spline method. The SARGE PDR identified a few issues that need to be addressed in order to ensure a successful experiment, which includes isobar unsweep that adversely a?ects boundary layer stability for DRE control and potential flow separation at the inboard fairing. Using the refined process, an alternate planform is evaluated as a potential starting point to address these issues and is shown to be feasible.Item Computational Evaluation of a Transonic Laminar-Flow Wing Glove Design(2012-07-16) Roberts, Matthew WilliamThe aerodynamic benefits of laminar flow have long made it a sought-after attribute in aircraft design. By laminarizing portions of an aircraft, such as the wing or empennage, significant reductions in drag could be achieved, reducing fuel burn rate and increasing range. In addition to environmental benefits, the economic implications of improved fuel efficiency could be substantial due to the upward trend of fuel prices. This is especially true for the commercial aviation industry, where fuel usage is high and fuel expense as a percent of total operating cost is high. Transition from laminar to turbulent flow can be caused by several different transition mechanisms, but the crossflow instability present in swept-wing boundary layers remains the primary obstacle to overcome. One promising technique that could be used to control the crossflow instability is the use of spanwise-periodic discrete roughness elements (DREs). The Flight Research Laboratory (FRL) at Texas A&M University has already shown that an array of DREs can successfully delay transition beyond its natural location in flight at chord Reynolds numbers of 8.0x10^6. The next step is to apply DRE technology at Reynolds numbers between 20x10^6 and 30x10^6, characteristic of transport aircraft. NASA's Environmentally Responsible Aviation Project has sponsored a transonic laminar-flow wing glove experiment further exploring the capabilities of DRE technology. The experiment will be carried out jointly by FRL, the NASA Langley Research Center, and the NASA Dryden Flight Research Center. Upon completion of a wing glove design, a thorough computational evaluation was necessary to determine if the design can meet the experimental requirements. First, representative CAD models of the testbed aircraft and wing glove were created. Next, a computational grid was generated employing these CAD models. Following this step, full-aircraft CFD flowfield calculations were completed at a variety of flight conditions. Finally, these flowfield data were used to perform boundary-layer stability calculations for the wing glove. Based on the results generated by flowfield and stability calculations, conclusions and recommendations regarding design effectiveness were made, providing guidance for the experiment as it moved beyond the design phase.Item Laminar Flow Control Flight Experiment Design(2012-11-29) Tucker, Aaron 1975-Demonstration of spanwise-periodic discrete roughness element laminar flow control (DRE LFC) technology at operationally relevant flight regimes requires extremely stable flow conditions in flight. A balance must be struck between the capabilities of the host aircraft and the scientific apparatus. A safe, effective, and efficient flight experiment is described to meet the test objectives, a flight test technique is designed to gather research-quality data, flight characteristics are analyzed for data compatibility, and an experiment is designed for data collection and analysis. The objective is to demonstrate DRE effects in a flight environment relevant to transport-category aircraft: [0.67 ? 0.75] Mach number and [17.0M ? 27.5M] Reynolds number. Within this envelope, flight conditions are determined which meet evaluation criteria for minimum lift coefficient and crossflow transition location. The angle of attack data band is determined, and the natural laminar flow characteristics are evaluated. Finally, DRE LFC technology is demonstrated in the angle of attack data band at the specified flight conditions. Within the angle of attack data band, a test angle of attack must be maintained with a tolerance of ? 0.1? for 15 seconds. A flight test technique is developed that precisely controls angle of attack. Lateral-directional stability characteristics of the host aircraft are exploited to manipulate the position of flight controls near the wing glove. Directional control inputs are applied in conjunction with lateral control inputs to achieve the desired flow conditions. The data are statistically analyzed in a split-plot factorial that produces a system response model in six variables: angle of attack, Mach number, Reynolds number, DRE height, DRE spacing, and the surface roughness of the leading edge. Predictions on aircraft performance are modeled to enable planning tools for efficient flight research while still producing statistically rigorous flight data. The Gulfstream IIB aircraft is determined to be suitable for a laminar flow control wing glove experiment using a low-bank-angle-turn flight test technique to enable precise, repeatable data collection at stabilized flight conditions. Analytical angle of attack models and an experimental design were generated to ensure efficient and effective flight research.Item Receptivity Studies on a Swept-Wing Model(2012-07-16) Woodruff, Matthew JefferyA series of flight tests was performed using a swept-wing model mounted on a Cessna O-2 aircraft. The crossflow waves on the airfoil were excited by pneumatic spanwise-periodic distributed roughness elements (DREs). The objective of the experiment was to determine the roughness receptivity i.e. the relationship between roughness height and the amplitude of the unstable crossflow wave. The local skin-friction variation was measured using an array of calibrated and temperature-compensated hotfilm sensors. The amplitudes of the disturbance shear stress were compared to the amplitudes of the DREs. It was found that there is a relationship between the shear stress and DRE amplitude that needs to be studied more before any definitely conclusions can be made. It was also found that the sensitivity of the crossflow to DREs is highly dependent on the freestream turbulence levels.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.