TECHNOLOGY AREA(S): Air Platform
OBJECTIVE: Develop coupling methodology for computational structural dynamics (CSD) and computational fluid dynamics (CFD) models of flexible rotorcraft fuselage and empennage structures to predict interactional buffet airloads, structural loads, and vibration.
DESCRIPTION: One of the most important, challenging, and chronic problems occurring during development of new or upgraded rotorcraft arises from the interactional aerodynamics of the complex, unsteady flowfield of the rotor, hub, and fuselage that generate significant adverse structural response of the flexible fuselage, horizontal and vertical tails, and the tail rotor of conventional helicopters. Similar problems arise for tilrotor and compound rotorcraft. Historically this problem has been nearly intractable with conventional aerodynamics and dynamics methodology, commonly leading to unexpected problems only revealed during prototype flight testing. As a consequence, expensive design changes, cut and try modifications, and program delays often occur. Current highfidelity CFD/CSD rotorcraft modeling that aeroelastically couple rotor system CFD aerodynamics to flexible blade CSD structural models is presently limited to 1-D elastic beam rotor blade and rigid fuselage models. Furthermore, existing rotorcraft CSD/CFD coupling interfaces do not encompass distributed CFD airloads coupling with flexible fuselage and empennage surfaces or structural dynamics models of fuselage and empennage structures. Therefore, a new general approach for a CFD/CSD aeroelastic analysis to couple an elastic fuselage/empennage with current CFD aerodynamics and flowfields is needed to improve overall fuselage/empennage loads and vibration predictions. Coupling should be applicable to full FEM fuselage models as well as reduced-order modeling. In most cases CFD and CSD geometries and meshes are incompatible, and this must be considered. Needed approaches must provide solutions that satisfy the following requirements: 1) Must be rigorous, consistent and energy conserving, 2) General and easily applied for arbitrary rotorcraft configurations, 3) Message passing between CFD and CSD parallel processing programs (file based I/O may be used in Phase I), 4) Must be demonstrated on a practical real-world problem.
PHASE I: Demonstrate the feasibility of the proposed fuselage CFD/CSD coupling approach by prototyping an elastic fuselage and developing initial coupling utilities. Prototype should demonstrate efficient and correct transfer of appropriate data between CFD and CSD programs.
PHASE II: Coupling utilities should be generalized for arbitrary fuselage configurations and user input should be automated to ensure ease of use. Interfaces will be developed for one or more CFD programs and the method shall be demonstrated on a real-world rotorcraft application.
PHASE III DUAL USE APPLICATIONS: Coupling utilities should be generalized for arbitrary fuselage configurations and user input should be automated to ensure ease of use. Interfaces will be developed for one or more CFD programs and the method shall be demonstrated on a real-world rotorcraft application.
KEYWORDS: CFD, CSD, elastic fuselage, rotorcraft, coupling