Already used extensively in engineering design for aero engines, computational fluid dynamics and other forms of simulation are being used in the aircraft maintenance market as part of the move toward a wider digitization of manufacturing.
According to Pennsylvania’s computer-aided engineering software developer Ansys, simulation—not just computational fluid dynamics (CFD), but computer simulation in general—already has made its presence felt in civil aerospace MRO. For example, CFD is used to simulate flow in duct work in the cabin to investigate sources of noise, or to assess the thermal comfort of passengers if seating arrangements are updated. If winglets are retrofitted to aircraft, or there are changes to nacelles, CFD also can be used to analyze aerodynamics.
Rob Harwood, global industry director at Ansys, explains: “The business case for CFD and simulation has always been clear—reduced cost and better operations. Airline operators run on very small margins. Anything that can reduce downtime of aircraft and maintenance costs is going to be very warmly welcomed in an era of ever-increasing fuel costs and tight competition.”
Such simulations can drive predictive analytics for maintenance. U.S. software firm Comsol, developer of multiphysics simulation software, says it has a number of users in the civil aerospace MRO market. For example, Comsol Multiphysics is being used for engine noise reduction when aircraft are in service. Chevrons on the nozzle exits of aero engines are being retrofitted with piezoelectric actuators that make them vibrate and cut down on noise-generating eddies from the nozzle exit. “This is a clever, low-cost way of reducing noise, simulated via virtual modeling,” says Bjorn Sjodin, vice president of product management at Comsol. “Engineers can see how the actuators will perform via simulation.”
The piezoelectric actuators used for the purpose of noise reduction are developing rapidly. Simulation means they can be cheaply and efficiently assessed prior to retrofitting. Ultimately, such work in the MRO market will feed into the design of new aero engines, Sjodin says.
Boeing is also using Comsol software simulations to investigate heat transfer within composite materials, such as those in its 787 aircraft, in the event of a lightning strike. The Boeing engineers are doing this to analyze the thermal expansion of composite materials, which can be unpredictable when a lightning strike occurs. Composites dissipate heat, but thermal expansion can mean delamination of composite layers. “This event [lightning strike] is well-understood for aluminium and other metals,” says Sjodin. “For composites, it is more complicated.”
Another area where Comsol thermal software simulations are being used is in nondestructive crack detection in wings. An electrical coil is panned over the aircraft fuselage, which heats up. A thermographic camera is used to detect anomalies in the heat response across the structure. Comsol customers are also experimenting with ultrasonic testing of cables within aircraft to detect wiring defects.
The Internet of Things (IoT), widely heralded as capable of transforming the efficiency and productivity of factories, potentially ushers in a new era for aircraft maintenance, offering the possibility of collecting operational data on the performance of aero engines and other parts of the airframe, and feeding it back into maintenance regimes. IoT means operational data can be captured and fed back into simulations to improve not just aircraft maintenance but also design.
Harwood says the IoT means “an ability to stream operational data into a platform, and have that drive simulations to really understand how a piece of equipment on board is performing—from the landing gear to the engine. This has clear MRO implications in terms of if, when and how things need to be adjusted and repaired,” he emphasizes.
The scope and sophistication of simulation for aircraft MRO is likely to increase. Comsol says its software is already being used to simulate corrosion, thanks to new technologies and algorithms that can predict it. “These are very sophisticated simulations that require a lot of expertise,” Sjodin suggests. Another area that may be investigated through simulation to a greater extent in the future is aircraft battery overheating, and subsequent fire risk. Aircraft manufacturers are interested in simulating the state of batteries that have been onboard aircraft for several years. “We try to predict the unpredictable,” says Sjodin.
Ansys, whose customers include Lufthansa Technik and Volvo Aero, now part of GKN, envisions a future in which the simulated “digital twin” of the entire aircraft is used to optimize parts replacement and support condition-based maintenance strategies. The eventual aim is to replace a part only when it needs replacing. Simulation of the digital twin would also help minimize aircraft downtime, generating as much revenue for the airline as possible. Harwood says: “Today, if an aircraft experiences a heavy landing, the pilot is intensely involved in triggering the subsequent investigations as to whether the aircraft is fit to continue or needs to be held.
“With the digital twin, things like this will be automated. Simulation will become a key part of the safety assessment process,” Harwood predicts.