David D. Marshall

A New Inviscid Wall Boundary Condition Treatment for Embedded Boundary Cartesian Grid Schemes

David D. Marshall et al. — Mon, 25 Jul 2011 15:49:34 PDT

This work presents a new inviscid wall boundary condition technique for embedded Cartesian grid schemes. This scheme eliminates the time step restrictions associated with the arbitrarily small control volumes that can result when the surface cuts the Cartesian control volumes. The cells adjacent to the surface are removed from the control volume formulation and are instead solved via an interpolation technique which utilizes the wall boundary conditions to build the interpolating functions. Two different interpolation techniques are presented, one without considering wall curvature and one considering wall curvature. Results are compared to a two-dimensional airfoil case and a three-dimensional wing case.

An Embedded Boundary Cartesian Grid Scheme for Viscous Flows using a New Viscous Wall Boundary Condition Treatment

David D. Marshall et al. — Mon, 25 Jul 2011 15:49:32 PDT

This work presents a new viscous wall boundary condition technique for embedded Cartesian grid schemes in order to model laminar viscous flows. The development of viscous effects modeling using pure Cartesian grids with cut cells at the surface has been hampered by the widely varying control volume sizes associated with the mesh refinement and the cut cells associated with the solid surface. This scheme removes the cells adjacent to the surface from the control volume formulation. These cells are instead solved via an interpolation technique which utilizes the wall boundary conditions to build the interpolating functions. Two different interpolation techniques are presented, one without considering wall curvature and one considering wall curvature. Results are compared to subsonic and supersonic two-dimensional airfoil cases.

An Evaluation of Proposed Formula 1 Aerodynamic Regulations Changes Using Computational Fluid Dynamics

Robert L. Perry et al. — Tue, 19 Jul 2011 08:55:16 PDT

This report evaluates the proposed FIA Formula 1 World Championship aerodynamics rules changes intended to increase on track passing for the 2009 season. Two full Formula 1 cars were modeled under close drafting conditions, both under the current regulations and the proposed 2009 regulations to determine whether or not the FIA's goals of reducing down force by 50% and improving sensitivity to leading car wakes would be met. Under the current regulations, a car following another at 2.4 car lengths loses approximately 17% of it down force compared to isolation. The new regulations were counter productive and ineffective, failing both to reduce down force by 50% and lower that 17% performance detriment. Instead the cars became more sensitive - losing 26% of their down force in 2009 compared to 17% under current conditions. Though the new cars create an overall cleaner wake, the wake's effects are now concentrated near parts of the car which were previously insensitive.

Towards Efficient Viscous Modeling Based on Cartesian Methods for Automated Flow Simulation

Patrick Hu et al. — Tue, 19 Jul 2011 08:55:12 PDT

The advanced Computational Fluid Dynamics (CFD) techniques that address the current limitations of Cartesian-based Navier-Stokes CFD schemes are explored in current investigation. Three promising methods of implementing improved wall boundary conditions are applied: (1) the enhanced diamond path stencil approach, (2) the reformulated extended extrapolation boundary condition, and (3) the ghost cell method. Several initial testing cases have been conducted with all these three boundary conditions, including the flow past a circular cylinder, flow past a flat plate at different inclined angles and flow past an AGARD RAE2822 airfoil. All the results show the effectiveness of these boundary conditions in resolving both laminar and turbulent boundary layer. Among all these methods, the extended extrapolation boundary condition attains the better results than the other two methods.

Supersonic Channel Airfoils for Reduced Drag

Stephen M. Ruffin et al. — Tue, 19 Jul 2011 08:55:09 PDT

A proof-of-concept study is performed for a supersonic channel-airfoil concept,which can be applied to the leading edges of wings, tails, fins, struts, and other appendages of aircraft, atmospheric entry vehicles, and missiles in supersonic flight. It is designed to be beneficial at conditions in which the leading edge is significantly blunted and the Mach number normal to the leading edge is supersonic.The supersonic channel-airfoil concept is found to result in significantly reduced wave drag and total drag (including skin-friction drag) and significantly increased lift/drag although maximum heat-transfer rate was increased for the geometries tested.

A Scientific Software Verification Library Based on the Method of Manufactured Solutions

David D. Marshall — Thu, 14 Jul 2011 14:04:34 PDT

A software library, avali, is being developed in the C++ programming language that applies the Method of Manufactured Solutions (MMS) to a variety of partial differential equation (PDE) problems. This library will allow researchers to utilize MMS as a software verification process without developing significant amounts of testing code. The library is split into 3 components: solution classes which can be used as manufactured solutions to PDE problems; PDE problem classes which represent specific types of PDEs to be solved (such as linear convection-diffusion equation or Poisson's equation); and post-processing classes that collect the convergence information and can perform various analysis techniques to the convergence data. In use, any solution class can be used with any PDE problem class and vice versa. This creates a significant amount of flexibility in this architecture and allows the end users to customize their MMS testing process. In addition, end users are able to develop their own solution classes in one of three ways: inheriting from the solution base class and implementing their own class; providing the functions (as source code to be compiled or as a software library with exported functions) required to evaluate the solution and its derivatives; or providing the solution equation as a string to be parsed by the library into a function. This paper will demonstrate a number of features of this library, as well as demonstrate its application in a typical use case.

Improved Meshing Technique for the Engine Exhaust of an Over-the-Wing Engine and Circulation Control Wing Configuration

John Pham et al. — Thu, 14 Jul 2011 14:04:31 PDT

This paper details the results of ongoing efforts to improve upon the meshing techniques required to produce accurate RANS CFD solutions for attached and separated flows for a Circulation Control aircraft. Work, thus far, under the current NASA Research Announcement (NRA) project has revolved around an unstructured near-body volume mesh due to its robustness for complicated geometries. However, it has been found that this technique does a poor job capturing detailed flow features such as the boundary layer, shear layer, and wake of large velocity-gradient regions. Its hindrance is primarily due to the limitations of current computational resources, thus new techniques are investigated to improve the quallty of CFD solutions while not impeding on resources. High quality hybrid near-body volume meshes that combine structured and unstructured meshing have been utilized to meet the goals of the project. The area around the engine and circulation control slots serves as the basis for improved meshing techniques. So far, a hybrid mesh has been successfully generated around the engine and the results of the CFD solutions have improved immensely.

The focus of this paper is to show a comparison of the quality of the CFD solution of old and new meshing techniques. In addition, preilminary results of a hybrid mesh around the circulation control slots are discussed and will be the focus of future work. It has been determined that the primary meshing software used, ICEM CFD does not allow enough user control to adequately refine particular regions in the flow field, thus, alternative meshing software will have to be explored. Current computing resources limit the total size of the mesh to about 35 million. However, given this constraint, the results clearly show that the hybrid mesh attains more refined and stable CFD solutions.

Investigation of the Unsteady Behavior of a Circulation Control Wing Using Computational Fluid Dynamics

Jonathon A. Lichtwardt et al. — Thu, 14 Jul 2011 14:04:28 PDT

This paper details the results of an investigation into the unsteady behavior of a circulation control wing using computational fluid dynamics. Oscillations in the lift coefficient of up to 10% are observed for steady state simulations. An investigation into the source of the unsteadiness is underway, and the results to date are presented. It is shown that the periodic oscillations are independent of the above the wing mounted engine effects on the cruise efficient short take-off and landing aircraft. The oscillations are also a viscous phenomenon that does not dampen as the solution marches through steady state. It is proposed that the cause of the oscillations is due to high streamline curvature at the trailing edge inboard wing section, due to flow turning caused by the slot flow normal condition at the circulation control slots. This paper presents the results into the origin of this unsteadiness.

Part 1: The Wind Tunnel Model Design and Fabrication of Cal Poly's AMELIA 10 Foot Span Hybrid Wing-Body Low Noise CESTOL Aircraft

Kristina K. Jameson et al. — Thu, 14 Jul 2011 14:04:26 PDT

Part 2: Preparation for Wind Tunnel Model Testing and Verification of Cal Poly’s AMELIA 10 Foot Span Hybrid Wing-Body Low Noise CESTOL Aircraft

Kristina Jameson et al. — Thu, 14 Jul 2011 14:04:23 PDT

A collaboration between California Polytechnic Corporation with Georgia Tech Research Institute (GTRI) and DHC Engineering worked on a NASA NRA to develop predictive capabilities for the design and performance of Cruise Efficient, Short Take-Off and Landing (CESTOL) subsonic aircraft. The focus of this work presented in this paper gives details of a large scale wind tunnel effort to validate predictive capabilities for this NRA for aerodynamic and acoustic performance during takeoff and landing. The model, Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA), was designed as a 100 passenger, N+2 generation, regional, cruise efficient short takeoff and land (CESTOL) airliner with hybrid blended wing-body with circulation control. AMELIA is a 1/11 scale with a corresponding 10 ft wing span. The National Full-Scale Aerodynamic Complex (NFAC) 40 ft by 80 ft wind tunnel was chosen to perform the large-scale wind tunnel test in the scheduled to start summer of 2011. The NFAC was chosen because both aerodynamic and acoustic measurements will be obtained simultaneously, the tunnel is large enough that the downwash created by the powered lift will not impinge on the tunnel walls, and the schedule and cost fit into Cal Poly’s time frame and budget. Several experimental measurement techniques will be used to obtain the necessary data to validate predictive codes being developed as apart of this effort: stationary microphones will be used to obtain far-field acoustic measurements including a 48 element phased array, the Fringe-Image Skin Friction (FISF) technique will be used to measure the global skin friction on the wing, and the a micro flow measurement device will measure the velocity profiles in the in the boundary and shear layers is still in development and presented in this paper. 1

A Surface Parameterization Method for Airfoil Optimization and High Lift 2D Geometries Utilizing the CST Methodology

Kevin A. Lane et al. — Thu, 30 Jun 2011 10:30:28 PDT

For aerodynamic modeling and optimization, it is desirable to limit the number of design variables to reduce model complexity and the requirements of the applied optimization scheme. The Class/Shape Transformation (CST) surface parameterization method presented by Kulfan has proven to be particularly useful for this while maintaining a wide range of applications. These include everything from smooth airfoils to 3D axi-symmetric bodies and wings. However, the CST method is confined to smooth geometries. This limits the CST method in applications incorporating discontinuous surfaces such as high lift aerodynamics with circulation control (CC) slots and flaps. The trailing edge slot on a circulation control wing (CCW) airfoil is not well modeled by the CST method. A parameterization of a CCW airfoil will result in the trailing edge slot being smoothed over. Therefore, a modified CST method must be utilized. For the case of parameterizing a known CCW airfoil, this is accomplished by detecting drastic changes in curvature and beginning a new parameterization in a "multi-surface parameterization" method. For creating a new CCW airfoil, this is achieved by modifying the 2D CST equations to incorporate a slot thickness term that also includes the horizontal location. These two methods can then be extended into 3D to model a circulation control wing (CCW) or even a blended wing body (BWB) aircraft incorporating CCW. The multi-surface parameterization modification can also be used to model other complex geometries to further enhance the robust nature of the CST method, thus creating a valuable design tool.

Inverse Airfoil Design Utilizing CST Parameterization

Kevin A. Lane et al. — Fri, 24 Jun 2011 15:24:16 PDT

An inverse airfoil design process is presented that makes use of the CST parameterization method. The CST method is very powerful in that it can easily represent any airfoil shape within the entire design space of smooth airfoils. This makes it an ideal modeling technique for an inverse design process because accurate airfoil geometry treatment is required. The downfall of some inverse design processes is that they do not accurately handle the leading edge region due to large flow gradients and high curvature distributions. One way to account for this is by representing airfoils with smooth analytic functions, such as the CST method. The inverse airfoil design process presented is based on the relation between pressure residuals and the required airfoil shape change. The pressure residuals give the sign of the normal vector with which to modify the airfoil shape. The CST method is then used as the smoothing algorithm. The inverse design method is simple, accurate, and efficient. It is shown to accurately determine the airfoil geometry in both subsonic and transonic flows. Since this method simply examines pressure distributions to modify the airfoil shape, the flow solver can be kept separate from the inverse design process, allowing any delity flow solver to be used.

Lift Superposition and Aerodynamic Twist Optimization for Achieving Desired Lift Distributions

Kevin A. Lane et al. — Fri, 24 Jun 2011 15:24:15 PDT

A method for achieving an arbitrary lift distribution with an arbitrary planform is presented. This is accomplished through optimizing aerodynamic twist for a given number of either known airfoils or airfoils to be designed. The spanwise locations of these airfoils are optimized to get as close to the desired lift distribution as possible. Airfoils are linearly interpolated between these points. After aerodynamic twist, the planform is twisted geometrically using radial basis functions to model the twist distribution. The aerodynamic influence of each twist distribution is determined and all are superimposed to determine the function weights of each twist function, yielding the optimal twist to match the given lift. This method has been shown to match both an elliptical and a triangular lift distribution for an arbitrary planform. This method can also be used with any delity model, creating a powerful design tool.

Assessing the v²-f Turbulence Models for Circulation Control Applications

Travis M. Storm et al. — Fri, 24 Jun 2011 15:24:13 PDT

This paper explores the applicability of several variations of the v²-f turbulence model to circulation control flows. The effects of modifying the model to capture nonlinear eddy viscosity effects and streamline curvature effects are assessed. Results indicate that the v²-f turbulence model is capable producing more physically accurate results for circulation control flow fields than common modern turbulence modeling techniques.

Improved Computational and Experimental Validation Using Different Turbulence Models

Jay Marcos et al. — Wed, 01 Jun 2011 14:05:48 PDT

This paper will explore the methods and techniques necessary to perform a more accurate CFD validation of experimental results. The methods and techniques used will be validated against experimental wind tunnel data of a 2D high lift airfoil with a 3D engine performed by Georgia Tech Research Institute. Preliminary results showed that computational methods over predict the lift and drag coefficient, while still showing very similar trends in CL and CD. To further improve the preliminary results and the predictive capabilities, different turbulence models will be investigated. Results of this validation will assist in determining the appropriate turbulence models, boundary conditions, mesh characteristics and other CFD modeling techniques necessary to capture complicated flow physics associated with the coupling of circulation control wings and engine exhaust flows.

Circulation Control and Its Application to Extreme Short Take-Off and Landing Vehicles

Julianna B. de la Montanya et al. — Tue, 31 May 2011 10:10:33 PDT

Circulation Control is a high-lift method discovered in 1935 when Henry Coanda accidentally stumbled upon the technology. Research was conducted in the 1970‘s and 1980‘s to develop this technique, but the idea fell out of vogue until recently. Energy is introduced into the flow field by means of a jet ejected tangentially from a slot located near the trailing edge of the airfoil; thus changing the effective chamber of the airfoil and increasing lift. Extreme Short Take-Off and Landing (ESTOL) vehicles can use this technology to alleviate today‘s congested airports by reutilizing the small runways that are currently unexploited due to the recent trend of bigger aircraft. By examining the angle-of-attack, flap deflection angle, and jet blowing coefficient, a design space was analyzed for lift and drag revealing three-dimensional lift coefficients up to 3.5. After collecting the data, balanced field length and landing distances were calculated. These results revealed that the shortest balanced field length of 2,400 feet would be for a flap deflection angle of thirty degrees and a blowing coefficient equal to 0.35. Similarly, the shortest landing distance was calculated to be 2,000 feet for a flap deflection angle of ninety degrees and a blowing coefficient of 0.34. Both of these values fall within the NASA defined mission requirements46 for an ESTOL aircraft to have a balanced field length and landing distance between 2,000 to 3,000 feet, proving Circulation Control to be an extremely viable resource for ESTOL technology.

Performance of a New CFD Flow Solver Using a Hybrid Programming Paradigm

M. J. Berger et al. — Tue, 31 May 2011 10:10:32 PDT

This paper presents several algorithmic innovations and a hybrid programming style that lead to highly scalable performance using shared memory for a new computational fluid dynamics flow solver. This hybrid model is then converted to a strict message-passing implementation, and performance results for the two are compared. Results show that using this hybrid approach our OpenMP implementation is actually marginally faster than the MPI version, with parallel speedups of up to 599 out of 640 using OpenMP and 486 with MPI.

Introduction of Software Development Practices into Aerospace Engineering Curriculum

David D. Marshall et al. — Tue, 31 May 2011 10:10:30 PDT

This paper will discuss the attempts to incorporate software development practices into the aerospace engineering curriculum in order to improve the computer programming capabilities of the students. The main focus is on techniques to integrate functional decomposition, unit level testing, system integration and testing, and verification and validation processes without significantly increasing the workload on the students. The approach taken is an integrated approach where the required information needed for testing and validation are integrated into the course content via in-class examples and homework problems. This same approach was taken for the other software development skills. This has been integrated into sophomore, junior, senior and graduate level classes. The results of this effort have been an overall improvement int he quality of software that the average student submits and an increase in the complexity of the software that the students write.

Design and Performance of Circulation Control Flap Systems

Rory M. Golden et al. — Tue, 31 May 2011 10:10:28 PDT

The design of circulation control (CC) dual radius flap systems were investigated to characterize the parameters that make up the flap surface to offer further knowledge into the CC field of study. Multiple dual radius flap geometries, along with variants, were developed by varying specific flap parameters from a baseline configuration that had previously developed. The aerodynamics of the different flap geometries were analyzed using two-dimensional CFD. This research will explore the design of CC pneumatic flap systems to improve the performance of existing CC flap configurations, and provide insight into the characteristics of the CC flap geometry.

Propulsion System Modeling and Takeoff Distance Calculations for a Powered-Lift Aircraft with Circulation-Control Wing Aerodynamics

Mark Waters et al. — Tue, 31 May 2011 10:10:27 PDT

The computation of takeoff distance for powered-lift aircraft is complicated because of the coupling of aerodynamic performance (lift, drag and moment coefficients) with forward speed. Cal Poly has developed an analysis procedure to capture this coupling, and the development of this procedure is continuing. In the past year, Cal Poly has completed a Phase I NRA contract from the NASA for the configuration development and modeling of CESTOL aircraft. The primary objective of this contract was to identify an aircraft configuration in enough detail to proceed into a Phase II contract to design and construct a large scale wind tunnel model followed by a wind tunnel test to measure both aerodynamic performance and noise. Four aircraft configurations have been developed, and all but one of the configurations use circulation control wing aerodynamics (CCW) to produce powered-lift aerodynamic effect for the wing. The aircraft configuration selected for the Phase II contract makes extensive use of CCW to develop high lift aerodynamics for takeoff and initial climb and again for final descent and landing.

An additional goal for the Phase I project was the CFD modeling of the aerodynamics of a CESTOL aircraft, and to use the CFD results to develop a new aerodynamic meta-model. In addition, a meta-model for propulsion performance was to be developed and the two meta-models were to be integrated into an upgraded takeoff code written in MATLAB. These models all combined were to demonstrate an up-graded version of the Cal Poly takeoff performance procedure. However, at present, the aerodynamics meta-model is not yet complete and work will continue on into Phase II. Thus, no specific takeoff performance is demonstrated in this paper. However, in this paper details of the aircraft configurations are presented, the options available to proceed high pressure air to the wing slots to produce CCW aerodynamics are discussed, the propulsion metamodel is defined, the analysis procedure for the aerodynamics meta-model is discussed and the up-graded takeoff program is discussed.