The development of high-lift systems is a major step in the design of modern aircraft and has a strong influence on the overall aircraft performance and cost. Many trade-offs have to be considered by the developer: performance, maximum lift, weight, cost, noise, among others. The design and test of high-lift systems still requires many months of wind tunnel tests today. These are costly and generally do not fully represent real flight conditions accurately: installation effects can influence the results, small scale models cannot fully resolve all geometric details, and flight Reynolds and Mach numbers cannot be easily reproduced.
The aerospace industry looks to CFD for the answer. Simulation can be used during the preliminary and conceptual design stages – before wind tunnel or even flight tests are feasible. Design alternatives can be pursued with much more flexibility and at lower cost than in the wind tunnel. And CFD can – at least in theory – overcome the installation and scale effects of the wind tunnel.
But the accurate simulation of the highly unsteady and complex flow over a high-lift wing, in particular the prediction of maximum lift, is still out of reach for traditional CFD tools. Meshing of a full wing still takes weeks and requires significant simplifications – with unknown effects on solution accuracy. And simulations are generally steady-state, ignoring the important effects of the unsteady nature of the real world – particularly for high angles of attack when large regions of separated unsteady flow are dominating the lift performance.
The SIMULIA PowerFLOW software suite offers a promising alternative. High-lift wings can be represented in full geometric detail with slats, flaps, brackets, fairings and all other details included – no simplifications necessary. And PowerFLOW simulations are inherently transient, and can therefore predict the highly unsteady flow over high-lift systems more accurately – all the way to maximum lift and beyond. Numerous validations with our industrial partners have confirmed that PowerFLOW can predict high-lift aerodynamics more accurately than traditional CFD tools. And with modern computational hardware an overnight turnaround even for a complete and fully detailed wing is possible.
High-lift aerodynamics applications of PowerFLOW include:
- Prediction of cL,Max
- Optimization of slat and flap configurations
- Vortex generator design and placement
- Interaction of landing gears with high-lift systems
- Flap edge and slat noise reduction
- Flow control
Dynamic simulation of high-lift wing with increasing and decreasing angles of attack. A hysteresis effect (stall conditions persist for decreasing angles of attack) is correctly identified.
Above two videos: Simulation of flow control. A series of pulsed jets on the leading edge is used to delay stall on an experimental aircraft wing. The top animation shows the wing without flow control. The bottom animation the effect of the pulsed jets in reducing the size of the region of separated flow is clearly visible
SIMULIA SOFTWARE USED FOR THIS APPLICATION