Problems in optimization design of HLFC sweep wing

An optimization platform is built for the Hybrid Laminar Flow Control (HLFC) sweep wing, based on the extended free-form deformation technique, radial basis function interpolation based mesh deformation, improved particle swarm optimization algorithm, and Reynolds-averaged Navier-Stokes solver coupled with the e^N method. Factors about the HLFC wing are researched including airfoil geometry, Reynolds number and suction distribution. The HLFC wing design methodology is discussed by comparing and analyzing how those factors affect the drag coefficient and length of the laminar area. The desired pressure characteristics for the HLFC wing with long laminar area and low drag coefficient are summarized. Results show that the pressure peak at the leading edge is relatively low and followed by a slight adverse pressure gradient, and then a long stable favorable pressure gradient is maintained until a shock wave. After the HLFC technology is applied, a sizable laminar area is obtained, and the friction drag and pressure drag are decreased obviously. Reduction of drag is far greater than the design result without the laminar control. The HLFC design should be based on comprehensive consideration of friction drag, pressure drag, strength of shock and trim drag (nose-down pitching moment). The case with the larger laminar area may not be equivalent to the case with the lowest drag. In general, the higher Reynolds number is, the harder laminar flow is to be maintained. Even though the Reynolds number is too high to maintain the natural laminar flow, the length of the laminar flow is still large if the HLFC technology is applied. Research on suction distribution illustrates that the suction system with variable suction distribution is more efficient for saving suction power compared with the suction system with constant suction distribution.