Towards real-time CFD simulation of in-flight icing

Despite the concerted efforts of manufacturers and certification agencies, incidents and accidents continue to happen to aircraft certificated to “Fly Into Known Icing”, falsely thought of as being “immune to in-flight icing”. The current successive process of CFD for ice shape prediction, then icing tunnel testing (experimental fluid dynamics- EFD), and finally flying in natural ice conditions (flight fluid dynamics-EFD), has many gaps that can only be filled by modern CFD. By developing compatible CFD tools able to simulate both the aerodynamics and icing in a concurrent engineering way, and by viewing the aircraft as a system and not as disjoint components, it will be shown how CFD, EFD and can be combined in a rigorous mathematical way to carry out a much faster, more complete and more thorough evaluation of the aircraft’s FIKI and result in a much safer aircraft. The Seminar will cover aspects of physical and mathematical modeling (impingement, accretion, de-icing, anti-icing, conjugate heat transfer, turbulence modeling), CFD (FEM, FVM, automatic mesh optimization) and the actual certification campaign of China’s first regional Jet, the ARJ21. The seminar will particularly focus on a reduced-order modeling (ROM) framework inching toward the calculation, via RANS, of the aerodynamics + water impingement + ice accretion + performance degradation, in real-time. The ROM methodology is based on Proper Orthogonal Decomposition, multi-dimensional interpolation and machine learning algorithms, along with an error driven iterative sampling method, to adaptively select an optimal set of snapshots. The methodology is applied for the first time to a “full aircraft” and to the “entire” icing certification envelope, providing invaluable additional data to the limited ones from icing tunnels or natural flight-testing. The level of accuracy achieved strongly supports the drive to incorporate more CFD information into in-flight icing certification and pilot training programs, leading to increased aviation safety

Real-time regional jet comprehensive aeroicing analysis via reduced order modeling

This paper presents a reduced-order modeling framework based on proper orthogonal decomposition, multidimensional interpolation, and machine learning algorithms, along with an error-driven iterative sampling method, to adaptively select an optimal set of snapshots in the context of in-flight icing certification. The methodology is applied, to the best of our knowledge for the first time, to a complete aircraft and to the entire icing certification envelope, providing invaluable additional data to those from icing tunnels or natural flight testing. This systematic methodology is applied to the shape/mass of ice and to the aerodynamics penalties in terms of lift, drag, and pitching moments. The level of accuracy achieved strongly supports the drive to incorporate more computational fluid dynamics information into in-flight icing certification and pilot training programs, leading to increased aviation safety

Finite element modeling of nonequilibrium fluid-wall interaction at high-Mach regime

The numerical modeling of the aerodynamic interactions at high-Altitudes and high-Mach numbers is considered in view of its importance when studying problems where the continuum hypothesis at the foundation of the Navier- Stokes equations becomes invalid. One of the difficulties associated with these flight conditions is that both the velocity and the temperature of the fluid do not abide by the no-slip conditions at the wall. A weak Galerkin finite element formulation of the Maxwell-Smoluchowki model is introduced to discretize the velocity slip and temperature jump conditions with better accuracy than the standard finite element approximation. The methodology is assessed on configurations such as cylinders and spheres for flow conditions ranging from quasi-equilibrium to nonequilibrium. Improvements are observed in the slip regime compared with available data. Nonetheless, the results in the transition regime highlight the need for more sophisticated physical modeling to address nonequilibrium at the wall

Ice accretion effects on helicopter rotor performance, via multibody and CFD approaches

A numerical approach for assessing the degraded aerodynamics and flight characteristics of ice-contaminated helicopter rotors is proposed. A hybrid two- and three-dimensional loose coupling strategy between multibody dynamics modeling and computational fluid dynamics icing is formulated that attempts to balance computational resources, model complexity, and accuracy for use during the early design phases. A quasi-3D formulation that considers the heat transfer and the motion of the water film due to centrifugal effects is introduced. The method is suited for the analysis of rime, glaze, and/or mixed ice conditions. Degraded aerodynamic and dynamic characteristics of the iced rotor and the changes in flight performance are assessed. The technique has been applied to the scenario of isolated helicopter rotors in hover and in forward flight. Deterioration of the figure of merit is also presented

Finite-element formulation of a Jacobian-free solver for supersonic viscous flows on hybrid grids

A parallel Jacobian-free solver for supersonic flows on unstructured hybrid meshes is proposed. An edge-based Finite Element formulation is used for spatial discretization with flow stabilized via either AUSM+-up or a Roe scheme. The Jacobian-free Newton-Krylov method is used as linear system solver and the lower-upper symmetric Gauss-Seidel method is used for matrix-free preconditioning. In the present formulation, second order approximations of spatial derivatives of the inviscid fluxes are introduced efficiently. Numerical results for Mach 1.93 flow past a sphere, Mach 4 flow past a waverider, and Mach 10.01 flow past a sphere, are presented