多喷口高效能厚翼的研究

提出了以下高效能翼型的思想：用多喷口小速度切向吹气控制厚翼上的流动分离，使流动接近于理想流状况，以产生大升力，小阻力；因多喷口小速度吹气耗能小，故翼型的有效升阻比可以很大．基于雷诺平均N－S方程进行了数值模拟实验．主要结果表明：对于厚度为0.4的儒氏翼型，在升力系数高达3．5时，有效升阻比可达约50（单喷口吹气约为23）；对于厚度为0．4的"升力体"翼型，在升力系数达2．2时，有效升阻比可达40（喷口吹气约为10）．

EFFICIENT BOUNDARY LANER CONTROL ON THICK AIRFOILS USING MULTIPLE SLOTS BLOWING AT SMALL SPEEDS

Boundary layer control on thick airfoils or airfoils at large angle of attack, whichuses very small power input, is studied. The control method is to use multiple slots on the airfoilupper surface tangentially blowing at small speeds. Boundary layer loses its kinetic energy dueto wall friction and adverse pressure gradient gradually along airfoil surface. Therefore, supplyinga small amount of energy at each of the slots located along the airfoil upper surface energizesthe boundary layer and suppresses the separation. Since the kinetic energy of blowing jet isReceived 17 August 1998, revised 17 March 1999.1) The project supported by the National Natural Science FOundation of China (No. 19725210).2) Currently at R&C Center for Parallel Software ISCAS, Beijing 100080, China.proportional to the third power of the blowing speed, multiple slots blowing at small speeds willreduce the energy expenditure of blowing greatly. Moreover, under same blowing momentum rate(which is proportional to the square of the blowing speed), multiple slot blowing may control theboundary layer better than single slot blowing. The reason is as following. With single slot blowingat large speed, the very large difference between the speed of the jet and the incident flow causesstrong mixing and also there is high friction at the wall, hence high near-wall momentum can not bemaintained for large extent downstream, but with the multiple slot blowing at small speeds, thesedrawbacks will be much less significant. The method used for the study is numerically solving theNavier-Stokes equations with appropriate boundary layer and wall jet turbulence modeling. Theresults show that with very small control power expenditure, the boundary layer separation canbe suppressed and flow pattern close to that given by invicid flow theory can be obtained, leadingto large lift and very small drag. For example, for a Joukowsky airfoil of 40 percent thickness,at CL = 3.5, the ratio between lift to equivalent drag (drag with flow control energy taken intoaccount) is as large as 50.