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
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.
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
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
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
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 Effects 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
In this article, I will focus on the improved twisting utilizing the unfolding folded faces (UFF) algorithm discussed in the last BRC post. The new twisting limits for both the Onera M6 wing and the F-18C vertical tail will be shown. See “Bob’s Research Corner: Grid Def – Twist” for the previous twist limits.Continue reading
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
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
For the last month or so, I’ve been focusing on 3-D grids with deforming boundaries. I split this into two main categories: bending and twisting. This article will focus on bending only. I will make a post about twisting in the near future.
The goal of this project is to develop a grid deformation algorithm capable of handling larger than real world deformations. And by handling, I mean producing valid Cobalt grids. If I’m successful, then our customers can simulate real world cases such as aeroelastic deformations.
The first test case I’m going to show is an Onera M6 wing grid. The grid contains 2,276,261 cells (1,832,756 tets, 17,642 pyramids and 425,863 prisms) and is valid for Navier-Stokes simulations. The bending function used is a quadratic displacement based on an amplitude multiplying the square of the span location. The maximum deflection of the tip I could get was 9.25% of the span; anything larger resulted in the dreaded folded faces. For those not familiar with a folded face, first, define a face as the interface between two cells. When flow leaves one cell across a face, it enters the other cell. When a face becomes folded, then the centroids of both cells lie on the same side of the face. This means flow leaving one cell through the face, also leaves the other cells. This is VERY bad as conservation cannot be conserved! That being said, a 9.25% of the span deflection is not bad. This might be good enough for real world cases. Of course, I’d like to do better. The video below shows the bending of the wing compared to the original. And the images show the original grid versus the deformed grid.Continue reading