December 8, 2021
The core mission of the Italian Air Force, or Aeronautica Militare, is to guarantee the safety and security of Italy as a whole and to protect the country’s national air space. Within this context, the Italian Air Force Flight Test Centre at the Pratica di Mare Air Force base supports operational squadrons performing the testing, integration, and validation of new or modified weapons systems. The Italian Air Force Flight Test Centre routinely conducts air-to-air refueling tests, store integration and certification, fixed/rotary wing flight test programs, and flying/handling evaluations on fighter aircraft and helicopters supporting these high-risk activities with the use of computational fluid dynamics (CFD). Ansys Fluent fluid simulation software is the key driver for these testing scenarios and others behind Flight Test Centre’s efforts to optimize the performance of their aircraft and related systems.
The Flight Test Centre uses Ansys solutions to develop fluid dynamics and structural predictions in support of flight test campaigns, mainly in the areas of store integration and safe separation. These structures, or aircraft store, can be any number of devices for internal or external carriage mounted on aircraft suspension and release equipment. In the case of release, or store separation, testing is important, particularly before a new store, such as a weapon or a fuel tank, can be used in service. The purpose of safe separation testing is to ensure that a store can clear the aircraft on release safely, without posing risk to the aircraft or pilot.
The use of CFD in support of aircraft store and release testing aids in the development of numerical models that help the air force mitigate programmatic and safety risks. Using model validation, air force engineers can use predictions from numerical models to conduct flight testing campaigns safely and reduce the number of test points or flight hours. Data gathered from flight tests is then used to improve and validate the fluid dynamic model and determine an aircraft’s aerodynamic behavior with respect to air speed and altitude, without requiring extensive testing.
The aerodynamic behavior of the store can affect the store separation process in several ways. During flight, if the store does not separate from the jet properly, it can break or severely damage the aircraft, or create a structural phenomenon prone to structural divergence. New or modified structures mounted to the aircraft, for example, tend to vibrate and can generate divergent phenomena such as flutter. When prolonged, the up and down motion of the structure during flight can damage a wing or the fuselage of the plane. With Fluent, these scenarios are regularly predicted and tested with CFD.
Fluent greatly improves the Italian Air Force’s overall certification process. Before the use of the new predict-test-validate approach using simulation software, testing was based on the fly-fix-fly approach that involved a certain duration of flight time over several weeks, during which issues were only observed and uncovered in flight. After grounding the plane and addressing any issues, the aircraft was back in service until something happened again. With the use of CFD via Fluent, test results are predicted before the flight campaign, permitting engineers to simulate the most dangerous conditions and shape predictions based on multiple scenarios, while keeping both pilots and aircraft out of harm’s way.
One of the biggest benefits of using Fluent is its ability to provide access to geometry and meshing tools within one workbench, making it easier for the team to use a variety of solvers. Using Fluent, Air Force Flight Test Engineers can set up and solve a CFD problem, then visualize the results in both Fluent and in the CFD tool. This enabled the Flight Test Centre to perform separation prediction during their last flight campaign using Ansys mosaic meshing technology, ultimately leading to the development of a higher quality mesh compared to traditional overset meshing techniques. As a result, the Flight Test Centre was able to reduce mesh size by about 65%, with no reduction in calculation accuracy. Using this new technique, the Flight Test Centre will be able to develop more accurate numerical predictions in very short time frames by drawing on the computational power of a single workstation.
“With Ansys Fluent, we can predict through testing those conditions we want to focus on in flight to mitigate risks that are the most dangerous,” says Captain Alessandro d’Argenio, Ph.D. and Flight Test Engineer at the Italian Air Force Flight Test Centre. “CFD allows us to shorten the time requiring us to test and fly, while lowering the risk and cost of testing through validation, delivering more accurate results with greater efficiency.”
Fluent is the choice of the Italian Air Force for several reasons. It enables them to shift their focus from CFD prediction to other competing priorities, including the flight testing critical to their overall mission. With an easy-to-use, accurate interface, Fluent CFD software helps even the most basic user to achieve accurate results. In addition, Ansys software seamlessly integrates with other computational software, facilitating the data exchange necessary to perform other fluid analysis applications between programs.
Looking ahead, Ansys is delivering simulation tools that will shape the future of hypersonic speed in military aircraft. Using Ansys multiphysics simulations, users can capture the complex phenomena that occur as aircraft begin to travel at speeds above Mach 1, including strong shocks, plasma, ablation, structural deformation, and chemical nonequilibrium. Drawing on the power of Fluent, squadrons can shorten development time and reduce testing efforts to quickly address challenges specific to hypersonic design.