BRC: Malleatus, part 2

The next milestone reached in the continued development of Malleatus was the determination of user input.  As always, we want to provide enough control to the user while not overwhelming them with unnecessary knobs.  I was able to minimize the user input to three values.  The first two control the amount of influence the movement of boundaries have on grid points;  the values must lie between 0.0 and 1.0. The final input controls the unfolding of folded faces algorithm.  Additionally, initial parallelization work has begun.

For this post, I revisited the Onera M6 wing.  I wanted to show solutions obtaining under bending and twisting using the new user input.  The conditions used for the simulation were: M= 0.8395, angle of attack = 3.06 degrees, Pressure = 98,920.475 Pa and T was 300 degrees K.Continue reading

Bob’s Research Corner: Malleatus, part 1

Last year the focus of Bob’s Research Corner was to report on the evaluation and testing of various grid deformation techniques.  This year, I’m going to chronicle the transformation of last year’s research code into a production utility.  I’ve decided to name this utility Malleatus.  Malleatus means “beaten or shaped by a hammer” which invokes images of using a hammer to bend and shape a grid.  But grid deformation also requires a delicate hand, and the name references malleus which is the hammer-shaped bone in the middle ear that transmits vibrations of the eardrum.Continue reading

Computational Aerodynamic Modeling for Flight Dynamics Simulation of Ram-Air Parachutes

Aerodynamic models were generated to simulate the flight dynamics of a parafoil wing with and without trailing-edge deflection. The airfoil was provided by the Natick Soldier Research, Development, and Engineering Center (NSRDEC) and was based on a modified Clark-Y with a flat lower surface used as the cut pattern for drop tested systems. The wing is characterized with an aspect ratio of two and zero anhedral angle. Several derivatives of this wing geometry were tested in the Subsonic Wind Tunnel (SWT) of United States Air Force Academy (USAFA).

These wings have either an open or closed inlet, a round or flat leading edge (for closed wings) and are with and without the trailing edge deflection. The flat leading edge wings consist of a straight line connecting the wing’s lower surface to the upper surface. The TE deflection is approximately 45 as measured from the flat lower surface. For convenience, these wings were named S R, B R, S F , B F , in which S and B denote straight and bent trailing edges; R and F indicate round and flat leading edges.

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Journal Articles Added

The following journal articles have been added to our publications page:

Grid Quality and Resolution Effects for Aerodynamic Modeling of Ram-Air Parachutes
Ghoreyshi, Bergeron, Seidel, Lofthouse and Cummings, Journal of Aircraft, Vol 53, No 4, July-August 2016
Computational Aerodynamic Modeling for Flight Dynamics Simulation of Ram-Air Parachutes
Ghoreyshia, Bergeron, Jirásek, Seidel, Lofthouse and Cummings, Aerospace Science and Technology, Vol 54, Apr 2016
Vortical Flow Prediction of a Diamond Wing With Rounded Leading Edges
Ghoreyshi, Ryszka, Cummings and Lofthouse, Aerospace Science and Technology, Vol 57, Feb 2016

Canard-Wing Interference Effects on the Flight Characteristics of a Transonic Passenger Aircraft

Effects of canard wing interference on the flight characteristics of a civilian transonic cruiser are examined. The aircraft is an unconventional design concept with no historical data. The flight characteristics of the aircraft are predicted using aerodynamic models in the form of look-up tables, generated using high-fidelity computational fluid dynamics simulations and a potential ow solver. These tables contain longitudinal and lateral force and moment coefficients for different combinations of angle of attack, side-slip angle, and control surface deflections. Dynamic damping derivatives are calculated from time-accurate simulations of the aircraft models oscillating in pitch, roll, and yaw direction and using a linear regression estimation method. The static simulations are performed at a Mach number of 0.117, as reported in wind tunnel experiments, and for two different canard positions using an overset grid approach. The aerodynamic tables include canard deflections of [-30, -10, 0, 10] at angles of attack from -4 to 30 degrees. Lateral coefficients are simulated at sideslip angles of -6 and 6 degrees as well. The dynamic simulations are performed for aircraft oscillations about mean angles of attack between zero to ten degrees with a motion frequency of 1Hz and amplitude of 0.5 degrees. The predicted aerodynamic data are then compared with those measured in wind tunnel experiments and calculated from the potential ow solver. The results show that both static and dynamic predictions match reasonably well with experiments for the range of angles considered.Continue reading

Virtual Flight Testing of High Performance Fighter Aircraft Using High-Resolution CFD

This article discusses the current phase of a multi-year development effort to provide a computational method for determining static and dynamic stability and control characteristics of USAF high-performance fighter aircraft. The focus of this work is on the virtual flight test capability achieved by incorporating a pilot model, the F-16 flight control system (FLCS), and six degree-of-freedom (6-DoF) motion computation into the CFD maneuver simulation. Flight test maneuvers were performed in a virtual environment by using CFD to determine the forces and moments acting upon the aircraft and allowing the aircraft to respond as governed by the pilot model, FLCS, and 6-DoF. Virtual flight test simulations were accomplished with a full-scale F-16C aircraft using unstructured, viscous, overset grids and Cobalt with a MATLAB interface. Virtual flight test maneuver response is shown to compare well to validated, flight-test corrected data. This marriage of capabilities is rolled into a software suite known to the developers as COMSAC, which stands for COMputational Stability And Control.Continue reading

AIAA Aviation Conference Papers Added

The following papers from the summer AIAA Aviation Conference have been added to our publication page:

Virtual Flight Testing of High Performance Fighter Aircraft Using High-Resolution CFD
Ratcliff, Bodkin, Clifton and Willis, AIAA-2016-3854, Jun 2016
Canard-Wing Interference E ffects on the Flight Characteristics of a Transonic Passenger Aircraft 
Harrison, Darragh, Hamlington, Ghoreyshi and Lofthouse, AIAA-2016-4179, Jun 2016
Evaluation of Reduced-Order Models for Predictions of Separated and Vortical Flows 
Darragh, Hamlington, Ghoreyshi and Lofthouse, AIAA-2016-4325, Jun 2016

Bob’s Research Corner: Grid Def – More Bending

For the last several months, I’ve been working on an algorithm to increase the amount of bending my grid deformer can handle before the grid becomes invalid. I’m finally to the point where I believe I have a reliable algorithm that unfolds folded faces resulting from grid deformation. For this article, I will focus on bending only. I will show the increased bending limit for both the Onera M6 wing and the F-18C vertical tail shown previously in “Bob’s Research Corner: Grid Def – Bending”.Continue reading

Bob’s Research Corner: Grid Def – Twist

In this post, I’ll present the twisting results of my grid deformation code.  I’ve taken the same grids (Onera M6 wing and the F-18C vertical tail) and applied a twist along the mid-chord.  For information about the grids and the bending results, you can read “Bob’s Research Corner: Grid Def – Bending”.  Twisting along the mid-chord is based on the square of the span location times a maximum twist angle.

On the Onera M6 wing, the maximum twist angle achieved before encountering folded faces was 10.5 degrees. The maximum twist occurs at the wing tip.  This is an ok twist amount just like the bending result.  The results are shown below, first with a video of the wing twisting over 25 time-steps followed by still images comparing the original versus deformed grid.  The original grid is shown in red while the deformed grid is shown in blue.Continue reading