Propulsion & Power
Integrating an engine into an airframe is a task that presents several levels of engineering challenges. Engine placement must be done in a way that does not compromise aerodynamics, so that the craft operates at top efficiency, and that failure modes such as bird strike, blade-out and icing are taken into consideration.
If engine and pylon are not integrated properly with the rest of the vehicle, additional wave drag may result due to the formation of shocks. Aerospace engineers use ANSYS CFD software to minimize drag due to interference by parametrically adjusting geometry and installation. Shock-capturing algorithms accurately predict the strength and magnitude of shocks. Furthermore, engine installation must ensure that a uniform flow enters the engine. The engines must not ingest wakes from surfaces such as a wing, upstream, under a range of operating conditions.
Hot exhaust from the engines can impact vehicle surfaces, such as when deploying thrust reversers. Such cyclic heating can lead to thermal stresses and fatigue. ANSYS CFD software is used to predict hot flows and heat transfer. Fast, accurate results are obtained even at low landing speeds using pressure-based algorithms in ANSYS CFD software. ANSYS Mechanical is used to predict thermal stresses that arise in heated components.
To keep equipment from overheating, flows and temperatures inside the engine compartment must be properly managed, as its geometry is very complex. ANSYS was among the first companies to introduce flow solvers for unstructured meshes, which are normally required to model these geometric complexities.
The airplane's propulsion system must be closely integrated with all safety systems, especially fire suppression. To meet FAA requirements, fire suppressant must reach and maintain sufficient concentrations at various points in the engine compartment, displacing oxygen and extinguishing a fire. Transient simulations with ANSYS CFD software, which can predict concentrations as functions of time, entail the use of multiphase flow models on unstructured meshes.
Engines provide bleed air for other safety systems, such as anti-icing. ANYS CFD software is used to minimize the bleed air required to heat external surfaces; Efficiency here can help to maximize fuel efficiency as well.
Auxiliary power units (APUs), which provide power when the aircraft is on the ground, present different yet just as challenging, design problems. APUs are typically installed in small spaces, making it difficult to design efficient inlets that provide pressure recovery the compressor needs to operate. The task is made more challenging by the presence of fences and screens that prevent the ingestion of ice and other foreign substances into the engine.
Other safety features involve continued operation in the event of a failure or accident. Engines must be designed to ingest large birds, for example. The nacelle must be designed to contain blades so that centrifugal forces don't thrust them through the cabin of the aircraft. Explicit dynamics solutions from ANSYS enable engineers to simulate fragmentation of the blades and their impact on surrounding structures.
ANSYS software has the breadth of capabilities in meshing, aerodynamics, structural mechanics, impact dynamics, and electronics and control systems to help engineers to evaluate tradeoffs and optimize system integration. The depth of physical models in each discipline allows designers to accurately predict relevant phenomena and accurately work through complex solutions.