Argus Missile Fin Deployment

The Argus Missile is a ground penetrating sensor device that is dropped from an aircraft. The streamlined missile deploys 4 paddles to slow and stabilize on its descent. A computational analysis of this action is challenging due to the tight gaps between the folded paddles and missile body, the deployment action, and the motion of the sliding locking ring.Continue reading

Wing Aileron Flap

A test case of the F-15 wing, aileron and flap was used to demonstrate the application of the Cobalt v7.0 Overset Module to moving control surfaces. In this type of application, the motion is prescribed and the limits of the grid motion are known ahead of time. There is also a very tight space between the control surfaces and the wing where the code must create a good hole-cut throughout the motion cycle. This geometry also presents the overlap of three grids at the intersection of the wing, aileron, and flap. All these qualities combine to present a realistic application to be able to simulate.Continue reading

Prediction and Validation of Aerodynamic Characteristics for a Generic UCAV Configuration with Trailing-Edge Flaps


Illustrating the vortex dominated flow over the SACCON at an angle of attack of 16 degrees. DDES-SARC turbulence model used. Isosurface of vorticity magnitude shown colored by velocity magnitude.

UCAVs present significant nonlinear aerodynamic characteristics with respect to angle of attack, control surface deflections and frequency of motion even at low angles of attack, which makes the task of predicting the aerodynamic characteristics very complicated.  This application focuses on using Cobalt to predict and validate the aerodynamic static and dynamic forces on the Stability and Control Configuration (SACCON) uninhabitated combat air vehicle (UCAV) geometry with the addition of two trailing edge control surfaces on each wing. The work primarily looks at the effects of angle of attack for the control surfaces both undeflected and deflected, and the effects of sideslip and dynamic pitch and yaw motions for the control surfaces undeflected.Continue reading

Stability and Control Characteristics of High Performance Aircraft

A-10 aircraft with centerline fuel tank used in System Identification (SID) of CFD.

A-10 aircraft with centerline fuel tank used in System Identification (SID) of CFD. Isosurface of vorticity.

The motivation for this work is to initially use CFD so that flight test and wind tunnel resources can be applied where they are needed the most.  The combination of Cobalt with the resources of High Performance Computation program of the DoD allow for more in-depth simulations and quick turnaround.  This work is a good step toward the end goal of ‘flying’ an aircraft using Cobalt.

During this work, the A-10 with centerline fuel tank was simulated in order to compare CFD and SID of CFD versus wind tunnel.  Developing a SID model can be done in minutes and once validated, it can Continue reading

Abrupt Wing Stall

During envelope expansion flights of the F/A-18E/F in the Engineering and Manufacturing Development phase, the aircraft encountered uncommanded lateral activity, which was labeled “wing drop”. An extensive resolution process was undertaken by the Navy and its contractors to resolve this issue. A production solution was developed, which concluded revising the flight control laws and the incorporation of a porous wing fold fairing to eliminate the wing drop tendencies of the pre-production F/A-18E/F. The wing drop events were traced to an abrupt wing stall (AWS) on either the left or right wing panel, causing a sudden and severe roll-off in the direction of the stalled wing.

Continue reading

Ship/Airwake Analysis

Perhaps the most demanding of all aviation environments, the operation of aircraft from ship platforms involves turbulent airwake produced by a ship’s superstructure. This phenomenon is a major contribution to the workload required for such operations. Past airwake modeling efforts were, at best rudimentary, offering only representative levels of turbulence for a particular ship class. The current study involves the prediction of time variance for ship dynamics variables.

Continue reading

Optimizing Extraction Parachute Operational Parameters

C-130 with drogue chute.

C-130 with Drogue Chute.

A current area of interest in the US Army operational and test community is the application of aerial delivery at high speed and at relatively low altitudes. The High-Speed Container Delivery System (HSCDS) is such a program intended to address this type of operational need. In conjunction with this program, a series of simulations have been conducted that attempted to cover a parameter space of operational variables such as aircraft type, aircraft flight speed, extraction line length, and drogue parachute design and size. The objective here is that with validated and verified modeling and simulation results anchored to actual flight test data, future exploratory test and development work may be performed with increased reliance on information derived from modeling and simulation with potential savings in the use of airdrop assets.Continue reading

Cobalt v7.0 Released

Oscillating Aileron Geometry

Isosurface of Vorticity

Cobalt Solutions, LLC announces the release of Cobalt v7.0, the latest version of their unstructured flow solver.  The changes include a new Overset module along with speed-up in post-processing output and the addition of a few turbulence models.

Cobalt v7.0 introduces a new Overset module which provides improved hole-cuts and improved efficiency. The hole-cut interface is calculated to lie midway between non-cuttable boundaries of overset grids.  The result is a very smooth hole-cut - whether it is a full scale aircraft with tiny gaps in control surfaces or an aircraft with multiple weapons cluster in a weapons release simulation.  The implementation of the module follows the same guidelines as found in the flow solver Cobalt – robust and user-friendly.  The new Overset module is discussed here along with some examples: F-18 JDAM Weapon Separation, Argus Missile Paddle Deployment, Wing/Aileron/Flap.

The output of flow visualization data has been sped-up.  Depending on how many flow variables requested, a speed-up of 2x has been seen in average cases. 

Three turbulence models have been added: Hellsten’s EARSM (Explicit Algebraic Reynolds Stress Model) and EARSM-CC  (CC = curvature correction), and Menter’s SST-SAS model (SAS = Scale Adaptive Simulation).  This brings the total number of turbulence models in Cobalt to sixteen.   The complete list and references can be found in the User's Manual.