Compressible Flow: Slat and Flap Devices Effects on an Aircraft Wing

Slat and Flap Devices Effects on an Aircraft Wing, ANSYS Fluent Training

Description

This project simulates the airflow around a 3-D aircraft wing fitted with a slat on the leading edge and a flap on the trailing edge, using ANSYS Fluent.

This is a representative compressible-flow case. Near the wing the air moves fast enough that its density can no longer be treated as constant, so the flow must be solved with a density-based solver and the air modeled as an ideal gas whose density varies with pressure and temperature. Capturing these density changes — and the pressure field they produce over the wing — is exactly what the Compressible Flow model is built for.

A flap is a small aerodynamic surface on the trailing edge of the wing used to increase lift. Lift is what holds the aircraft up against its weight, and it grows with speed. When the aircraft slows down — as during takeoff and landing — lift drops, so it must be recovered: the flap rotates about its hinge at the trailing edge and increases the effective area of the wing exposed to the airflow. A slat is the equivalent device on the leading edge; it rotates about its hinge to increase the wing's contact area with the air, and it also raises drag, which helps the aircraft land more slowly.

The 3-D geometry was built in Design Modeler as a wing with a leading-edge slat and a trailing-edge flap. The model was meshed in ANSYS Meshing using an unstructured grid of 5,658,021 elements.

Simulation Methodology

Because the flow is compressible, the simulation uses a density-based solver with the ideal-gas law for density, and it is run as steady with gravity neglected. Turbulence is handled with the Spalart-Allmaras model, and the energy equation is enabled to resolve the temperature field.

For boundary conditions, the inlet is a velocity inlet with components of 271.958 m/s along x and 40.79 m/s along y (a combined freestream of about 275 m/s at a small angle of attack) and a temperature of 305.5 K. The outlet is a pressure outlet at 0 Pa gauge, the wing, flap, and slat are walls with zero heat flux, and a symmetry plane bounds the domain. The flow and the turbulence transport variable are both discretized with a second-order upwind scheme, and the solution is initialized from the inlet conditions.

Results & Conclusion

After solving, two-dimensional contours of pressure, temperature, velocity, Mach number, and density were obtained on a plane cutting through the flow adjacent to the wing, along with path lines and velocity vectors on the same plane and a pressure contour over the wing surface.

The contours clearly show the variation of velocity, density, and pressure around the wing. Comparing the pressure contour on the upper and lower surfaces reveals the pressure difference between them, which is the source of the lift force that counteracts the aircraft's weight.