Aerodynamics & Aerodynamic Noise

Proper aerodynamics helps to ensure optimal range, efficiency, speed and maneuverability. Efforts to reduce noise, which is related mostly to landing gear and wing flaps, can greatly affect aerodynamics.

 

Image created for 1st AIAA High Lift Prediction Workshop, June, 2010 

Geometry and mesh provided by AIAA Applied Aerodynamics Technical Committee for benchmark. 

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Aerodynamics Aerodynamics

Aerodynamics is a key driver in the design of aircraft of all types.  For commercial aircraft, aerodynamics determines range and efficiency, which are airline performance benchmarks.  In the military sector, aerodynamics is critical to speed and maneuverability. For example, unmanned aircraft are being designed to perform ever-extreme maneuvers, since there’s no pilot on board to blackout from the resultant g-forces.

In developing cruise configuration aerodynamics for commercial craft, drag has historically been difficult to compute with CFD. ANSYS has long participated in industry benchmarks organized by the AIAA, beginning with the very first AIAA Drag Prediction Workshop. CFD software from ANSYS provides accurate results needed for correct guidance on trends including changes in configuration (engine installation, wing/body fairing) and operating conditions (Mach number, Reynolds number). The solvers are fast and robust: Pressure-based algorithms are unbeatable at low (subsonic) speeds, and density-based solvers provide shock-capturing capabilities for transonic flows and above. The technology features predictive models for transition of laminar to turbulent flows — especially important as manufacturers look to improve configurations and compute drag to within 1 count and in determining maximum lift for take-off and landing.  Separation will occur earlier — at lower angles of attack — if the boundary layer is laminar rather than turbulent. Simulations that assume fully turbulent flow typically provide nonconservative predictions for the amount of lift that will be produced at high angles of attack.

ANSYS software also enables engineers to predict aero-elastic effects with out-of-the-box coupling between CFD and FEA, a vital consideration to the design of high-lift systems with the wing highly loaded.

Simulating helicopters and propeller-driven aircraft is faster and easier with a virtual blade model (based on blade-element theory) to account for the time-averaged effects of the downwash produced  by the helicopter rotor. Time-accurate simulations also can be performed using the sliding mesh capabilities, in which one domain rotates inside another.

More-complicated body motions call for moving/deforming mesh capabilities, such as to simulate store separation or flapping of aero-elastic micro-air vehicle wings.  Recent advances move the boundary layer mesh in its entirety for high computational efficiency. 

Aerodynamic Noise Aerodynamic Noise

Noise is the byproduct of aircraft, and reducing it is a huge design/engineering goal. Exterior noise can create problems for those on the ground, while sound inside the aircraft can take a toll on passengers and those who must work around the constant noise.

Aircraft components that generate much of the noise — landing gear and wing flaps — are also the parts that affect general aerodynamics. To comply with government regulations for noise level, manufacturers are looking for ways to reduce the unsteadiness produced when these systems are engaged.

ANSYS CFD software is used to improve vehicle aerodynamics; it also can be applied to reduce unsteady loads when doors are open. Bounded central difference schemes maintain high accuracy without spurious oscillations by introducing enough upwinding to stabilize the numerical method. Out-of-the-box coupling between ANSYS CFD and ANSYS Mechanical software enables direct calculation of the store’s response to the unsteady loads. The Fowcs– Williams Hawkings method enables predicting far-field noise perceived by distant observers well beyond the extent of the computational domain.

Testing one part of the aircraft and then another is time-consuming and expensive. ANSYS software offers a robust set of tools that gives engineers the ability to seamlessly work through solutions, minimizing the amount of physical testing needed.