Critical Ice Accretion on Aircraft Wings
F. Saeed, S. Uppuluri, M.S. Selig, and M.B. Bragg
NASA Lewis Research Center

Aircraft wing ice accretion depends on several factors, but the most important is the airfoil leading-edge geometry where the ice first accretes. Owing to the myriad of scaling issues, full-scale tests are highly desirable, but the costs are often prohibitive. An approach has been devised that has the advantages of full-scale tests without the associated costs. The full-scale airfoil leading edge is tested along with a foreshortened aft section. The approach was validated through tests at NASA Lewis on a "hybrid" airfoil based on the Learjet Model 45 main-wing airfoil. An extension of the method to three-dimensional wings is now underway.

Low Reynolds Number Airfoil Design and Wind Tunnel Testing
C.A. Carroll, A.P. Broeren, P. Giguere, A. Gopalarathnam, C.A. Lyon and M.S. Selig
AeroVironment, Inc.; Private gifts

This research deals with enhancing the performance of airfoils for operation at low Reynolds numbers. For such airfoils, boundary-layer transition takes place through a laminar separation bubble that forms as the laminar boundary layer first separates, then becomes unstable, transitions to turbulent flow and reattaches to the airfoil to form the bubble. High drag produced by the bubble is the principal cause for the performance degradation at low Reynolds numbers. Wind-tunnel tests are being performed to validate newly developed low Reynolds number airfoil design philosophies aimed at mitigating the adverse bubble effects.

Hybrid Methods for Inverse Aerodynamic Design
A. Gopalarathnam and M.S. Selig
Boeing Corp.; Ford Motor Company

Inverse methods are widely in use for isolated airfoil design. Such methods, however, have not been developed for more complex two- and three-dimensional aerodynamic systems such as multi-element airfoils, cascades, wings, rotors and wing-fuselage junctures. The current work focuses on a unified approach towards developing inverse methods for designing complex aerodynamic systems. The approach is to use an isolated-airfoil inverse method to generate the airfoils that comprise the system and couple it using Newton iteration with inviscid and viscous analysis methods for the system. Key to the approach is a scheme to rapidly compute the sensitivities for the Newton iterations.

Design of High-Lift Multi-Element Airfoils for Race Car Wings
A. Gopalarathnam, W.J. Jasinski, A. Filippone, and M.S. Selig
Ford Motor Company

High aerodynamic down force, generated by the wings of race cars, is crucial to maximizing cornering performance. Currently, design tools are being developed for high-lift airfoils to be used on the wings of open-wheel race cars. These airfoils will maximize the down force while satisfying geometry constraints imposed by the race rules. An inverse design method for multi-element airfoils and a Matlab-based graphical user interface provides a rapid, interactive design environment. Wind-tunnel tests and computational analysis using VSAERO and PMARC were performed to develop a front wing/underbody aerodynamic model, which has been used to enhance the design tools.

CFD Modeling of Complex 3D Wing Systems
A. Filippone, and M.S. Selig
Ford Motor Company

Wing geometries used in car racing (Indy and Formula 1) have evolved toward a complicated degree of sophistication. These wings include vertical endplates, have 2 to 10 lifting elements, and are sometimes three-dimensional, with variable chord, vertical fences, Guerney flaps, etc. Some computational methods (for ex. VSAERO) are currently being validated against wind tunnel measurements taken at the UIUC low speed wind tunnel on both front- and rear wing configurations. The scope of this work is to assess the possibility of using rapid and accurate numerical approaches to the design of multi-element non-prismatic wings for Formula 1 racing cars.

Drag Reduction of Open Wheeled Race Cars
M.D. Soso and M.S. Selig
Ford Motor Company

The drag associated with different subsystems of open-wheeled race cars has an adverse effect on the aerodynamic efficiency of the vehicle, which ultimately manifests itself in lap times that are slower than the competition. Research is therefore being initiated on the endplates of the rear wing to determine whether different design configurations can engender significant drag reductions. In addition, the appropriate fairing of the junctions between different structural components is being investigated to further supplement the overall gains in drag reduction.

Some other drag reduction topics with Antonio Filippone are here.

Development and Verification of Design Methods for Racing Car Front Wings
C.A. Carroll, C.P. Crosby and M.S. Selig
Newman Haas Racing

The design of multi-element front wings for single-seat racing cars is a fairly challenging exercise in high-lift aerodynamics. In practice, extensive use is made of sophisticated moving-floor wind tunnels and empirical design methods. The focus of this research project is the development of a robust and reliable design method using existing computational fluid dynamics (CFD) codes. In this project a variety of computationally efficient two-dimensional and three-dimensional CFD methods are investigated, in order to develop an efficient design method. The ultimate objective is an efficient integrated design procedure for high-downforce (or high-lift) low-aspect-ratio wings operating in ground effect.

Blade Geometry Optimization for the Design of Wind Turbine Rotors
P. Giguere and M.S. Selig
National Renewable Energy Laboratory

A computer program is being developed to facilitate the aerodynamic blade design of horizontal axis wind turbines (HAWTs). Given a set of design requirements and constraints, the program provides optimum blade geometries according to the objective of the design. To allow for optimum aerodynamic designs while also considering structural and cost considerations, the program has a multi-objective optimization capability. The program relies on a genetic algorithm based optimization method and uses the PROPID code for rotor performance analysis. This new design method will significantly reduce the blade design cycle time and increase the performance of HAWTs.

Blade design Tradeoffs Using Low-Lift Airfoils for Stall Regulated Wind Turbines
P. Giguere and M.S. Selig
National Renewable Energy Laboratory

For stall-regulated wind turbines, the use of low-lift airfoils in the outboard blade region is desired to passively control peak power. This research effort aims at determining the practical lower limit for the maximum lift coefficient of airfoils tailored for stall-regulated turbines. The blade design tradeoffs between performance, structural and cost considerations are being systematically investigated for a 750-kW turbine. Directions for future airfoil designs and support to the ongoing trend of the industry to increase swept area for a given rated power should emerge from this work.

Horizontal Axis Wind Turbine Performance Prediction/Model Development
M.S. Selig
National Renewable Energy Laboratory

Noticeable discrepancies exist between wind turbine field test data and predicted power output from the blade element/momentum methods. Power is typically under-predicted at high wind speeds and over-predicted at low wind speeds. These discrepancies can be attributed to induced effects that are not properly accounted for by the classical Prandtl tip-loss model. A more accurate and computationally efficient tip loss model will be developed based on results from two state-of-the-art vortex-method rotor codes and recent field test data. The new model will then be integrated into existing performance prediction methods used in design.

Wind Turbine Post Stall Performance Prediction
Z. Du, N. Raj and M.S. Selig
National Renewable Energy Laboratory

Most design and analysis codes widely used for horizontal axis wind turbine performance prediction are based on 2D blade-element momentum methods, which underpredict rotor power output in the high-wind/peak-power condition. The main aim of this research is to describe and analyze the fundamental flow phenomena that characterize the boundary layer on rotating blades, and to develop a preliminary stall-delay model that modifies the 2D airfoil data so as to simulate the 3D stall-delay effects that give rise to higher lift and greater power. To date, three key parameters have been associated with stall delay, and a 3D stall-delay model has been developed for validation and further refinement.

An Improved Post Stall Model for HAWTs
N. Raj and M.S. Selig
National Renewable Energy Laboratory

A semi-empirical post-stall model was developed at UIUC to predict the post-stall behaviour of HAWTs. The model overpredicted power, leading to questions about the assumptions of the model. The model assumed that, inboard of the rotor, post-stall 3D effects on the blade delay the separation point, which thereby enhances lift and reduces drag from 2D values. Experimental evidence, however, indicates that the drag increases relative to 2D. This maybe due to higher induced drag caused by increased circulation because of enhanced lift. This has motivated the ongoing effort to modify the drag model to accurately predict power.

Discrete Vortex Simulation to Predict Separation on Airfoils
R. Raju and M.S. Selig
National Renewable Energy Laboratory

In order to predict the performance of a wind-turbine in the post-stall region, it is necessary to use airfoil stall characteristics at high angles of attack as input to a 3D model. A discrete vortex method is being made use of to determine the post-stall properties of airfoils. The method used here is a full vortex cloud method. Discrete vortices are released from every point on the airfoil and convected downstream in the flow field. At high angles of attack the vortices roll up on the surface of the airfoil, simulating separation that models the post-stall effects.

Correcting Inflow Measurements from Wind Turbines
J. Whale and M.S. Selig
National Renewable Energy Laboratory

In order to provide accurate performance data for wind turbine design codes, 3D field data must be tabulated in terms of sectional angles of attack. A 3D Lifting-Surface Inflow Correction Method (LSIM) is being developed at UIUC, using a vortex panel code, in order to correct the measured local flow angles to angles of attack. The method has been tested using hypothetical 3D data, based on field measurements from the National Renewable Energy Laboratories (NREL) and wind tunnel data from the Technical University of Delft. LSIM has been used to correct 3D data from the Combined Experiment Rotor at NREL.

Wind Turbines for Electric Power Generation: A Critical Anaysis
J. Whale, P. Giguere and M.S. Selig
Caterpillar, Inc.

An appraisal of wind energy was carried out at UIUC on behalf of Caterpillar, Inc. A literature search was performed to assess the current state of wind energy and wind turbine technology including market projections, machine design, control systems and blade manufacture. Design codes were used to provide quantitative information concerning blade design and turbine power output. Analysis tools on The Danish Wind Turbine Manufacturers Association website were used to provide information on wind turbine energy production and economics. The appraisal concluded that wind energy has become cost-competitive with conventional energy sources and has a rapidly growing worldwide market.

Pioneer UAV Flight Simulator
J.A. Scott and M.S. Selig
U.S. Naval Command Control and Ocean Surveillance Center

The US Navy currently operates the Pioneer unmanned aerial vehicle (UAV) from both land bases and aircraft carriers to gather battlefield reconnaissance. To better train pilots in operating and landing the UAV, the Navy has developed the External Pilot flight simulator. This simulator contains a comprehensive aerodynamics model which adequately models the aircraft's basic flight behavior. The purpose of this research is to increase the quality and realism of the simulator. Improvements being incorporated include a more realistic air turbulence model, a ground landing and handling model, and aircraft engine sounds.