This thesis presents the results of two 2-D computational studies of a circulation control Inlet Guide Vane (IGV) that takes advantage of the Coanda effect for flow vectoring. The IGV in this thesis is an uncambered airfoil that alters circulation around itself by means of a Coanda jet that exhausts along the IGV's trailing edge surface. The IGV is designed for an axial inlet flow at a Mach number of 0.54 and an exit flow angle of 11 degrees. These conditions were selected to match the operating conditions of the 90% span section of the IGV of the TESCOM compressor rig at the Compressor Aero Research Laboratory (CARL) located at Wright-Patterson AFB. Furthermore, using the nominal chord (length from leading edge of the IGV to the jet exit) for the length scale, the Reynolds number for the circulation control IGV in this region was 5e⁵. The first study was a code and turbulence model comparison, while the second study was an optimization study which determined optimal results for parameters that affected circulation around the IGV. Individual abstracts for the two studies are provided below. To determine the effect of different turbulence models on the prediction of turning angles from the circulation control IGV, the commercial code GASP was employed using three turbulence models. Furthermore, to show that the results from the optimization study were code independent a code comparison was completed between ADPAC and GASP using the Spalart-Allmaras turbulence model. Turbulence models employed by GASP included: two isotropic turbulence models, the one equation Spalart-Allmaras and the two-equation Wilcox 1998 k-ω. The isotropic models were then compared to the non-isotropic stress transport model Wilcox 1998 Stress-ω. The results show good comparison between turning angle trends and pressure loss trends for a range of blowing rates studied at a constant trailing edge radius size. When the three turbulence models are compared for a range of trailing edge radii, the models were in good agreement when the trailing edge is sufficiently large. However, at the smallest radius, isotropic models predict the greatest amount of circulation around the IGV that may be caused by the prediction of transonic flow above the Coanda surface. The optimization study employed the CFD code ADPAC in conjunction with the Spalart-Allmaras turbulence model to determine the optimal jet height, trailing edge radius, and supply pressure that would meet the design criteria of the TESCOM (TESt COMpressor) rig while minimizing the mass flow rate and pressure losses. The optimal geometry that was able to meet the design requirements had a jet height of h/C_n = 0.0057 and a trailing edge Radius R/C_n = 0.16. This geometry needed a jet to inflow total pressure ratio of 1.8 to meet the exit turning angle requirement. At this supply pressure ratio the mass flow rate required by the flow control system was 0.71 percent of the total mass flow rate through the engine. The optimal circulation control IGV had slightly lower pressure losses when compared to the cambered IGV in the TESCOM rig. / Master of Science

The objective of this thesis was to develop an experimental method to research circulation control wings using numerical analysis. Specifically, it is of interest to perform 3D wind tunnel testing on a circulation control wing in the Cal Poly Low Speed Wind Tunnel (CPLSWT). A circulation control wing was designed and analyzed to determine the feasibility of this testing. This study relied on computational fluid dynamics (CFD) simulations as a method to predict the flow conditions that would be seen in a wind tunnel test. A CFD simulation was created of a wing model in a wind tunnel domain. Due to high computational requirements, reliable 3D CFD results were not obtained. This led to utilizing 2D CFD models to make estimations about the flow conditions that would be encountered in an experimental environment. The 2D CFD model was validated with previous experimental data on circulation control wings and was shown to accurately capture the flow physics. These 2D CFD results were used to create a set of guidelines to help improve the effectiveness of a future wind tunnel test campaign and demonstrate where further design work needs to be done. The key finding is that it is feasible to perform circulation control testing in the CPLSWT with limitations on the maximum momentum coefficient. Due to internal plenum pressures reaching 66 psi at Cμ=0.35, a limitation should be placed on experimental testing below the choked condition of at Cμ=0.15. This provides a more feasible operating range for the equipment available. The main performance parameter of the airfoil was met with CLMAX=5.01 at Cμ=0.35 which required 0.9 lb/s/m mass flow rate for the 2D model.

Results from Cal Poly's recent wind tunnel test, during the Winter of 2011-2012, in the 40- by 80-foot test section at the National Full-Scale Aerodynamics Complex (NFAC) at NASA Ames Research Center are presented. AMELIA, the Advanced Model for Extreme Lift and Improved Aeroacoustics, is the first full-span, cruise efficient, short take-off and landing (CESTOL) model incorporating leading- and trailing-edge blowing wing circulation control and over-the-wing mounted turbine propulsion simulators (TPS) to date. Testing of the 10 foot span model proved successful and was the result of a 5 year NASA Fundamental Aeronautics Program Research Announcement. The test generated extensive low-speed experimental aerodynamic and acoustic measurements. All of the results associated with Cal Poly's effort will be available in an open-source validation database with the goal of advancing the state-of-the-art in prediction capabilities for modeling aircraft with next generation technologies, focusing on NASA's N+2 generation goals. The model's modular design allowed for testing of 4 major configurations. Results from all configurations are presented. Out of a total of 292 data runs, 14 repeat run configurations were obtained. Overall repeatability of test data are good. Factors contributing to non-repeatability in the test data were assessed and showed high pressure air line temperature to be a primary factor. Test data shows drastic improvements in performance are obtained when incorporating leading edge blowing: wing stall can be delayed to more than 25 degrees angle-of-attack at lift coefficients exceeding six. Without the introduction of leading edge blowing to increase boundary layer momentum and maintain flow attachment around the leading edge, STOL performance suffers. Similar runs for isolated trailing edge blowing show a reduction in maximum lift coefficient to three with stall occurring at zero angle-of-attack. Testing at two engine pylon heights allowed for the highly coupled propulsion and flow control system to be characterized.

In the past, research into Short Takeoff and Landing aircraft has led to the investigation of the coupling of a Circulation Control Wing and Upper Surface Blowing engine. The Circulation Control Wing entrains the flow of the engine to be deflected downward such that a component of the thrust is now in the vertical direction. The unfortunate consequence of the Upper Surface Blowing engine is the poor cruise performance due to scrub drag. Cal Poly's research into a Cruise Efficient Short Takeoff and Landing Aircraft offers a solution by pylon mounting over the wing engines. Analysis shows that the engine thrust is still deflected downward resulting in very high lift coefficients above 6.6. In the culmination of this project Cal Poly would like to find a correlation between the location of the engine and the deflection angle of the thrust. The results of this study show some engine deflection for an over the wing engine. The configurations explored were able to provide 3°-8.5° of deflection. The deflection falls short of the results by previous static and wind tunnel tests of upper surface blowing engines. The results show that the closer to the wing and further forward the engine is located the more engine deflection will be seen. This paper explores the trends of coupling an over the wing engine with a circulation control wing as well as compare the results to the idealized claims of previous experiments.

This package of programs is a result of the U.S.U. Library incorporating an automated control on the circulation of their books, which would provide the library with a daily record of all books in circulation, or not available for circu­lation, and send notices when books were overdue. Because of the long-range program of the Data Processing Department of the University, it was decided to develop the software for this project rather than purchase the hardware. The then existing hardware included the IBM 1401 computer (4K), 1402 card reader, 1403 on line printer, and a card sorter. The only additional hardware required by the Data Processing Department was the "read punch feed" feature on the card reader. This report includes information for operating the programs involved in pro­cessing the data. Any information required in setting up the data collection system may be obtained from the U.S. U. Library. These programs were developed to be compatible with the previously mentioned hardware and were used until the data processing facilities of the University were updated. All programs were written in the SSPS II symbolic language.

In the past, 2D CFD analysis of Circulation Control technology have shown poor comparison with experimental results. In Circulation Control experiments, typical results show a relationship between lift coefficient, CL, vs blowing momentum coefficient, Cμ. CFD analysis tend to over-predict values of CL due to gridding issues and/or turbulence model selection. This thesis attempted to address both issues by performing Richardson’s Extrpolation method to determine an acceptable mesh size and by using FLUENT’s 2-equation turbulence models. The experimental results and CAD geometry were obtained from Georgia Tech Research Institute for comparison with the CFD analysis. The study showed that 3D CFD analysis of circulation control showed similar results of over-predicting CL, which can also be attributed to gridding issues and turbulence model selection. When compared to the experimental results, the k − ω turbulence model produced the lowest errors in CL of approximately 15-17%. The other turbulence models produced errors within 5% of k − ω. A fully unstructured volume mesh with prismatic cells on the surfaces was used as the grid. The CCW con- figuration was analyzed with and without wind tunnel walls present, which produced errors of 20% and 15% in CL, respectively, when compared to experimental results. Despite the large errors in CL, CFD was able to capture the trend of increasing CL as Cμ was increased. Results reported in this thesis can be further calibrated to allow the CFD model to be used as a predictive tool for other CCW applications.

The rapid air travel growth during the last three decades, has resulted in runway congestion at major airports. The current airports infrastructure will not be able to support the rapid growth trends expected in the next decade. Changes or upgrades in infrastructure alone would not be able to satisfy the growth requirements, and new airplane concepts such as the NASA proposed Super Short Takeo and Landing and Extremely Short Takeo and Landing (ESTOL) are being vigorously pursued. Aircraft noise pollution during Takeoff and Landing is another serious concern and efforts are aimed to reduce the airframe noise produced by Conventional High Lift Devices during Takeoff and Landing. Circulation control technology has the prospect of being a good alternative to resolve both the aforesaid issues. Circulation control airfoils are not only capable of producing very high values of lift (Cl values in excess of 8.0) at zero degree angle of attack, but also eliminate the noise generated by the conventional high lift devices and their associated weight penalty as well as their complex operation and storage. This will ensure not only satisfying the small takeoff and landing distances, but minimal acoustic signature in accordance with FAA requirements. The Circulation Control relies on the tendency of an emanating wall jet to independently control the circulation and lift on an airfoil. Unlike, conventional airfoil where rear stagnation point is located at the sharp trailing edge, circulation control airfoils possess a round trailing edge, therefore the rear stagnation point is free to move. The location of rear stagnation point is controlled by the blown jet momentum. This provides a secondary control in the form of jet momentum with which the lift generated can be controlled rather the only available control of incidence (angle of attack) in case of conventional airfoils. The use of Circulation control despite its promising potential has been limited only to research applications due to the lack of a simple prediction capability. This research effort was focused on the creation of a rapid prediction capability of Circulation Control Aerodynamic Characteristics which could help designers with rapid performance estimates for design space exploration. A morphological matrix was created with the available set of options which could be chosen to create this prediction capability starting with purely analytical physics based modeling to high fidelity CFD codes. Based on the available constraints, and desired accuracy metamodels has been created around the two dimensional circulation control performance results computed using Navier Stokes Equations (Computational Fluid Dynamics). DSS2, a two dimensional RANS code written by Professor Lakshmi Sankar was utilized for circulation control airfoil characteristics. The CFD code was first applied to the NCCR 1510-7607N airfoil to validate the model with available experimental results. It was then applied to compute the results of a fractional factorial design of experiments array. Metamodels were formulated using the neural networks to the results obtained from the Design of Experiments. Additional validation runs were performed to validate the model predictions. Metamodels are not only capable of rapid performance prediction, but also help generate the relation trends of response matrices with control variables and capture the complex interactions between control variables. Quantitative as well as qualitative assessments of results were performed by computation of aerodynamic forces and moments and flow field visualizations. Wing characteristics in three dimensions were obtained by integration over the whole wing using Prandtl's Wing Theory. The baseline Super STOL configuration was then analyzed with the application of circulation control technology. The desired values of lift and drag to achieve the target values of Takeoff and Landing performance were compared with the optimal configurations obtained by the model. The same optimal configurations were then subjected to Super STOL cruise conditions to perform a tradeoff analysis between Takeoff and Cruise Performance. Supercritical airfoils modified for circulation control were also thoroughly analyzed for Takeoff and Cruise performance and may constitute a viable option for Super STOL and STOL Designs. The prediction capability produced by this research effort can be integrated with the current conceptual aircraft modeling and simulation framework. The prediction tool is applicable within the selected ranges of each variable, but methodology and formulation scheme adopted can be applied to any other design space exploration.

Circulation control involves tangentially blowing air around a rounded trailing edge in order to augment the lift of a wing. The advantages of this technique over conventional mechanical controls are reduced maintenance and lower observability. Despite the technology first being proposed in the 1960s and well-studied since, circulation control is not in widespread use today. This is largely due to the high mass flow requirements. Increasing the jet velocity increases both the efficiency (in terms of mass flow) and effectiveness. However, as the jet velocity exceeds the speed of sound, shock structures form which cause the jet to separate. Recent developments in the field of fluidic thrust vectoring (FTV) have shown that an asymmetrical convergent-divergent nozzle capable of producing an irrotational vortex (IV) has the potential to prevent separation through eliminating stream-wise pressure gradients. In this study, the feasibility of preventing separation at arbitrarily high jet velocities through the use of asymmetrical nozzle geometries designed to maintain irrotational (and stream-wise pressure gradient free) flow is explored. Furthermore, the usefulness of an adaptive nozzle geometry for the purpose of extending circulation control device efficiency and effectiveness is defined. Through a series of experiments, the flow physics of supersonic curved wall jets is characterised across a range of nozzle geometries. IV and equivalent area ratio symmetrical convergent-divergent nozzles are compared across three slot height to radius ratios (H/R): H/R = 0.1, H/R = 0.15, H/R = 0.2. The conclusion of this study is that at low H/R (0.1 and 0.15), there is no significant difference in behaviour between IV and symmetrical nozzles, whilst at high H/R (0.2), the IV nozzles begin separating whilst correctly expanded due to the propagation of pressure upstream from the edge of the reaction surface via the boundary layer. Consequently, it is shown that symmetrical nozzles of equivalent mass flow at high H/R have a higher separation NPR compared to IV nozzles. Specifically, the elimination of favourable, in addition to adverse stream-wise pressure gradients contradicts the expected behaviour of IV nozzles. The separation NPR for nozzles tested in this study, in addition to past studies is subsequently plotted against the throat height to radius ratios (A*/R). This shows that in fact, no previous experiments have shown a higher separation NPR for IV nozzles compared to symmetrical nozzles of equivalent mass flow. The overall outcome is that neither fixed geometry IV, nor adaptive nozzles are justified to maintain attachment, or to improve efficiency. This is because fixed nozzle geometries designed for higher separation NPR do not show any performance deficit when operating at lower NPRs. However, the throat height could be varied to maximise effectiveness (at the expense of mass flow). The contributions to new knowledge made by this study are as follows: the development of a new method of combining shadowgraph and schlieren images to simplify and enhance visualisation of supersonic flows; the use of pressure sensitive paint (PSP) to study the structure of the supersonic curved wall jet before and after separation; the identification of a clear mechanism for the separation of supersonic curved wall jets, valid over a broad range of nozzle geometries (including a clarification of previously unexplained behaviour witnessed in prior studies); the explanation that reattachment hysteresis occurs due to the upstream movement of the point of local separation at full separation (specifically, this explains why certain geometries such as backward-facing steps prevent reattachment hysteresis).

The engineering problem of airfoil design has been of great theoretical interest for almost a century and has led to hundreds of papers written and dozens of methods developed over the years. This interest stems from the practical implications of airfoil design. Airfoil selection significantly influences the application's aerodynamic performance. Tailoring an airfoil profile to its specific application can have great performance advantages. This includes considerations of the lift and drag characteristics, pitching moment, volume for fuel and structure, maximum lift coefficient, stall characteristics, as well as off-design performance. A common way to think about airfoil design is optimization, the process of taking an airfoil and modifying it to improve its performance. The classic design goal is to minimize drag subject to required lift and thickness values to meet aerodynamic and structural constraints. This is typically an expensive operation depending on the selected optimization technique because several flow solutions are often required in order to obtain an updated airfoil profile. The optimizer requires gradients of the design space for a gradient-based optimizer, fitness values of the members of the population for a genetic algorithm, etc. An alternative approach is to specify some desired performance and find the airfoil profile that achieves this performance. This is known as inverse airfoil design. Inverse design is more computationally efficient than direct optimization because changes in the geometry can be related to the required change in performance, thus requiring fewer flow solutions to obtain an updated profile. The desired performance for an inverse design method is specified as a pressure or velocity distribution over the airfoil at given flight conditions. The improved efficiency of inverse design comes at a cost. Designing a target pressure distribution is no trivial matter and has severe implications on the end performance. There is also no guarantee a specified pressure or velocity distribution can be achieved. However, if an obtainable pressure or velocity distribution can be created that reflects design goals and meets design constraints, inverse design becomes an attractive option over direct optimization. Many of the available inverse design methods are only valid for incompressible flow. Of those that are valid for compressible flow, many require modifications to the method if shocks are present in the flow. The convergence of the methods are also greatly slowed by the presence of shocks. This paper discusses a series of novel inverse design methods that do not depend on the freestream Mach number. They can be applied to design cases with and without shocks while not requiring modifications to the methods. Shocks also do not have a significant impact on the convergence of the methods. Airfoils are represented with parametric equations from the CST method to control shape changes and relate them to the required changes in the pressure or velocity distribution. To display the power of the methods, design cases are presented in the subsonic and transonic regimes. A circulation control design case is also presented using one of the methods to further show the robustness of the method.

With the pursuit of more advanced and environmentally-friendly technologies of today’s society, the airline industry has been pushed further to investigate solutions that will reduce airport noise and congestion, cut down on emissions, and improve the overall performance of aircraft. These items directly influence airport size (runway length), flight patterns in the community surrounding the airport, cruise speed, and many other aircraft design considerations which are setting the requirements for next generation aircraft. Leading the research in this movement is NASA, which has set specific goals for the next generation regional airliners and has categorized the designs that meet the criteria as Cruise Efficient Short Takeoff and Land (CESTOL) aircraft. With circulation control (CC) technology addressing most of the next generation requirements listed above, it has recently been gaining more interest, thus the basis of this research. CC is an active flow control method that uses a thin sheet of high momentum jet flow ejected over a curved trailing edge surface and in turn utilizes Coanda effect to increase the airfoil’s circulation, augmenting lift, drag, and pitching moment. The technology has been around for more than 75 years, but is now gaining more momentum for further development due to its significant payoffs in both performance and system complexity. The goal of this research was to explore the design of the CC flap shape and how it influences the local flow field of the system, in attempt to improve the performance of existing CC flap configurations and provide insight into the aerodynamic characteristics of the geometric parameters that make up the CC flap. Multiple dual radius flaps and alternative flap geometry, prescribed radius, flaps were developed by varying specific flap parameters from a baseline dual radius flap configuration that had been previously developed and researched. The aerodynamics of the various flap geometries were analyzed at three different flight conditions using two-dimensional CFD. The flight conditions examined include two low airspeed cases with blown flaps at 60° and 90° of deflection, and a transonic cruise case with no blowing and 0° of flap deflection. Results showed that the shorter flaps of both flap configurations augmented greater lift for the low airspeed cases, with the dual radius flaps producing more lift than the corresponding length prescribed radius. The large lift generation of these flaps was accompanied by significant drag and negative pitching moments. The incremental lift per drag and moment produced was best achieved by the longer flap lengths, with the prescribed radius flaps out-performing each corresponding dual radius. Longer flap configurations also upheld the better cruise performance with the least amount of low airspeed flow, drag, and required angle of attack for a given cruise lift coefficient. The prescribed radius flaps also presented a favorable trait of keeping a more continuous skin friction distribution over the flap when the flaps were deflected, where all dual radius configurations experienced a distinct fluctuation at the location where the surface curvature changes between its two radii. The prescribed radius flaps displayed a similar behavior when the flaps were not deflected, during the cruise conditions analyzed. Performance trends for the different flap configurations, at all three flight conditions, are presented at the end of each respective section to provide guidance into the design of CC geometry. The results of the presented research show promise in modifying geometric surface parameters to yield improved aerodynamics and performance.