CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

ADVANCED METHODS AND MULTIPHYSICS
Among them, the prediction of 1P-forces is essential for aircraft manufacturers because it impacts the
sizing of major parts of the aircraft (pylon, HTP, VTP). 1P-forces are unsteady transversal efforts on the
rotation axis of the propellers which are created when the inflow is inhomogeneous (incidence/sidestream
conditions, installation effect).
To evaluate 1P-forces, unsteady simulations of isolated Airbus generic CROR design using full 360 ˚ meshes
were computed. These large meshes are required to capture incidence and installation effects. Advanced
grid techniques (chimera or sliding mesh) are used in order to enable communication between the different
rotating parts (front and rear rotor) and the fixed parts (far field area) [CFD31]. The unsteady pressure field
over the whole CROR enables to calculate the 1P-forces (see figure 4.3).
FIG. 4.3: Pressure coefficient field with incidence effect
4.2.2 Air inlet (F. Sicot, G. Dufour, J.-F. Boussuge)
The air inlet of a jet engine plays a key role on engine operability : it channels the flow to the fan in such a
way that it should be as smooth and uniform as possible. Therefore the region between the nacelle tip and the
fan should be long enough to smooth out any disturbance and non-uniformity of the flow. The current trend
is to reduce this length to reduce the weight and drag of the nacelle and increase overall performances. One
of the most critical operating point is take-off in the presence of cross-winds which can generate detached
flow at the nacelle tip and lead to high distortions on the fan. These distortions must be minimized and CFD
can help engineers to estimate flow distortion on the fan and improve the nacelle design. First studies [3]
were performed at CERFACS for the nacelle alone. New studies including the fan started in 2011 (Fig. 4.4).
4.2.3 Jet in cross-flow (J-C. Jouhaud, Y. Hallez)
Aerothermal flows involving a jet in cross-flow are very common in aeronautics. A classical example is the
nacelle anti-ice system where a hot jet in cross-flow interacts with the wall of a turbo-fan engine nacelle.
An accurate description of the thermal boundary conditions is essential in this case : heat fluxes at the wall
have a strong influence on the flow/structure interaction. Thus, an accurate thermal boundary condition for
the fluid flow is obtained by coupling the fluid solver with a heat transfer solver in the walls [CFD96].
The compressible LES solver AVBP has been used to solve the fluid flow and the heat transfer problem
inside the scoop top wall has been addressed with the heat conduction solver AVTP (see Fig. 4.5a). The
organization of communications between these two codes is handled with the open source PALM library.
160 Jan. 2010 – Dec. 2011