Experimental Investigations On Boundary Layers On Suction Surface Of Airfoils Under Steady Condition

Modern aircraft engines are characterized by high efficiency, low specific fuel consumption, large trust-weight ratio and could be run under different conditions. In order to catch the trend of developing high trust-weight ratio aircraft engines, the blades are being designed for increasingly higher values of aerodynamic loading. For the compressor airfoil, the boundary layers are easily separated from its suction surface under high adverse pressure gradient which results from high loading; for the turbine airfoil, when it works on the low Re number at high altitude, the suction surface boundary layers separate then reattach so that separation bubbles occur, which leads to large profile losses. In this thesis, relying on surface hot-film sensors, the aerodynamics of highly loaded compressor and turbine airfoils are investigated, especially on the influences of Reynolds numbers and inlet incidence angles on the separation point and transition process on the suction surface, which could give strong support to highly loaded airfoils' design.Measurements are made in a linear low speed cascade wind-tunnel in Institute of Engineering Thermophysics, CAS. The surface hot film sensors, which are boned directly to the suction surface of airfoils from the leading edge to the tail edge, are used to acquire the quasi-wall-shear stress signals, cooperating with hot wire anemometry. Regarding the relationship between raw hot-film data, statistical moments and intermittency, a careful examination is carried out on aerodynamics of suction surface's boundary layers. Meanwhile, the airfoil aerodynamic losses are obtained with the help of a three-hole probe at outlet of cascade under varying Reynolds numbers and incidence anglesThe experimental results show that:The boundary layers on the suction surface of compressor airfoil which influenced by strong adverse pressure gradient separate easily but fail to reattach. By increasing Reynolds numbers, the locations of separation and transition onset do not vary greatly; however, separation locations move forward to leading edge and transition distance reduce when incidence angle increase, which leads to the larger profile loss.For the boundary layer on suction surface of turbines airfoil, the locations of separation and transition onset would move backward to tailing edge with Reynolds numbers increasing; though increasing incidence angle has no influence on separation process. The transition distance would be shorter and cause less loss.