Prediction of high lift: review of present CFD capability

A survey is conducted of CFD methods applied to the computation of high-lift multi-element configurations over the last 10–15 years. Both 2-D and 3-D configurations are covered. The review is organized by configuration, in an effort to glean useful insights with respect to particular successes or failings of CFD methods as a whole. In general, for both 2-D and 3-D flows, if certain guidelines regarding grid, transition, and turbulence model are followed, then surface pressures, skin friction, lift, and drag can be predicted with reasonably good accuracy at angles of attack below stall. Velocity profiles can generally be predicted in 2-D flow fields, with the exception of the slat wake, which tends to be predicted too deep by most CFD codes for a range of different configurations. CFD codes can usually predict trends due to Reynolds number in 2-D, but they are inconsistent in the prediction of trends due to configuration changes. On the whole, 2-D CFD is unreliable for predicting stall (maximum lift and the angle of attack at which it occurs); in most cases, maximum lift is overpredicted, but for some configurations the opposite occurs. However, there is some evidence that stall misprediction of nominally 2-D experiments may be caused by 3-D effects, which are obviously not modeled by 2-D CFD. In general, 3-D computations are also inconsistent with respect to computing stall, but there have been fewer of these applications to date. The paper concludes with a list of challenges that confront CFD at the start of the next decade, which should witness a dramatic increase in the number of CFD applications for 3-D high-lift configurations.