HLFC后掠翼优化设计的若干问题

使用扩展自由变形参数化方法，基于径向基函数的动网格技术和改进的混合粒子群算法，考虑吸气的e^N转捩预测方法和雷诺平均Navier-Stokes求解器，搭建了针对混合层流流动控制（HLFC）后掠翼的优化设计平台，对HLFC后掠翼的气动外形设计、雷诺数影响、吸气分布设计等多个问题进行了研究，对比分析了在这些因素影响下HLFC后掠翼的阻力系数和层流区长度的差别，进而探索了相应的设计准则。研究表明，对于层流区较长和阻力系数较小的HLFC后掠翼来说，它们上表面的压力分布具有共同的特征：头部峰值较低，之后有一个小的逆压，接下来是一段较长的均匀稳定的顺压，这段顺压最后终结于一道激波。应用HLFC技术后，通过实现大面积的层流区，机翼的摩擦阻力和压差阻力均可显著地降低，降低的幅度远大于不考虑层流控制的设计结果。同时，HLFC机翼的设计应综合考虑摩擦阻力、压差阻力、激波强度和配平阻力（低头力矩），层流区最长不一定意味着阻力最小。一般来说，雷诺数越高，越难维持层流，但应用混合层流控制技术后，即使在难以实现自然层流的高雷诺数下，HLFC机翼依然有较长的层流区。通过对吸气分布的设计进行研究，说明了非均匀吸气比均匀吸气要更有效率一些，能够节省吸气量。

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.