Advances made in CFD technologies, coupled with the phenomenal growth in the speed and memory of computers in the last decade, have made it possible to routinely conduct aerodynamic simulations of complete aircraft configurations. The ability to model a complete aircraft at desired flight conditions provides valuable aerodynamic data to enable faster and cheaper design and evaluation cycles.

CFDRC provides the software and engineering services for a full range of aircraft configurations including military fixed wing, rotorcraft, civil transport, and business jets.

CFD solutions on complete military aircraft configurations have become a routine requirement. CFD solutions are used to augment test data or provide data that is difficult or impossible to obtain otherwise. Because CFD can model actual flight conditions, problems that arise with sub-scale ground testing are not a concern. Reynolds number effects, tunnel blockage effects, and support hardware effects do not exist with CFD. Obtaining flow field data near flight test vehicles is extremely difficult, while such data is inherent in the CFD solution.

The F/A-18 results shown here were obtained by CFDRC engineers from separate studies for buffet and control analysis and for store loaded aircraft aerodynamic predictions.

The helicopter rotor flow-field presents many challenges for flow prediction computational tools. Several flow phenomena including turbulence, blade stall, rolling vortices, and wildly disparate velocities on the retreating and advancing blades make rotorcraft flow fields some of the most difficult to predict.

The simulations shown here were performed by CFDRC engineers to predict the flow field of a generic ROtor Body INteraction (ROBIN) helicopter body with a four-bladed rotor in a hover configuration. The animation shows the time accurate predictions of the blade motion and its effects on fuselage surface pressure distribution.

CFDRC has developed several technologies for rotorcraft flow field predictions. Some of these technologies have been incorprated in the CFD-FASTRAN code, which provides a powerful tool for modeling rotorcraft aerodynamics. The chimera/overset grid methodology can be used to model the moving rotor-blade. The motion model dependencies capability can be used to model complex rotor motion such as lead, lag, and flapping. The code's high order schemes and several turbulence models can be used to model the highly viscous phenomena such as tip-vortex generation.

VSTOL aircraft in ground effect produce a very complex flow. High and low temperature gases impinge on the ground, spread, and mix in very intricate patterns. In the early stages of the design process, predictions of this type of flow are critical for analyses of ground crew safety, hot gas ingestion, twin-jet fountain effects, and VSTOL suckdown.

In a project for the U.S. Navy, CFDRC engineers conducted complete generic aircraft in VSTOL mode calculations in an effort to analyze ship airwake effects on aircraft take off and landing characteristics. In this simulation, the Chimera/overset grid technology was used to model all the open doors, inlets, landing gear and deflected surfaces of the aircraft in the complex flow field generated by the downward directed jets.

This analysis is an example of the use of CFD in preliminary design studies. This analysis conducted by CFDRC engineers coupled internal and external flows to determine the effectiveness of a splitter plate at the inlet face and the flow uniformity at the compressor face of an aircraft engine. Detailed information on the inlet flow was obtained without an expensive wind tunnel test. Using the data obtained from this analysis, the inlet geometry was altered and the flow uniformity through the inlet was improved.

Engine Inlet

Engine Face

This moving airfoil analysis was conducted to demonstrate some of the moving body capabilities of the technology that CFDRC developed and incorporated into the CFD-FASTRAN code. In this solution, the motion of the flap relative to the airfoil was prescribed using the Prescribed Motion Module. The aerodynamic loads on the system were calculated and used by the Rigid Body Motion 6-DOF Module to determine the motion of the entire airfoil-flap system. This type of solution process is easily applied to more complex geometries, enabling the simulation of maneuvering aircraft or moving control surfaces.