Research on aerodynamic characteristics of transport aircraft with stall strips

In order to alleviate the violent roll motion during stall of a transport aircraft with landing flap configuration, the geometric parameters of stall strips are optimized and selected by numerical simulations and wind tunnel tests, and the aerodynamic force and flow field characteristics are studied. The height H and the install distance S from the leading edge are selected as design parameters for stall strips, and are evaluated by solving Reynolds Averaged Navior-Stokes (RANS) equations for the airfoil section of the landing flap configuration. The calculation indicates that smaller S value (installed closer to the upper surface) promotes earlier stall, while the larger H has similar but weaker effect. Separation bubble emerges after the stall strips when the angle of attack (AOA) of the airfoil becomes large, which grows larger and longer with increasing AOA. The bubble bursts eventually and causes the airfoil to stall earlier, leading to the rounded shape of the lift curve. The effect of the stall strips installed on the wing is studied by scaled model in wind tunnel tests, which shows that its spanwise length and arrangement have significant impact on the performance besides the cross section geometry. Four planform arrangements of stall strips are advanced and evaluated. Keeping the S parameter equal to 0, the stall trips installed at 40% half span with spanwise length of 2m change the abrupt stall of the lift curve to a flat roof type one, and eliminate the asymmetric roll moment after stall. The spanwise length of the stall strips is halved to form 2 new arrangements, which also ameliorate the stall of the lift curve and roll moment to some extent. The stall trips installed at 15% half span have no obvious effects on the stall characteristics. The suggested explanation is that the flow separation starts at about 40% half span of the wing at landing configuration, where the stall strips have the best performance.