Aerodynamic analysis of rotor blades and ducted fan using improved panel and time-marching free wake coupling method

Abstract

Unsteady panel method is powerful tool to analyze the aerodynamics of rotor blades and ducted fan in the aspect that it considers real geometry. When using the free wake in the potential based panel method one of the problems is to obtain the value of the potential influenced by wake on the blade surface. The value is successfully obtained by modeling the free wake into equivalent doublet panel in the calculation of the potential value on the blade, whereas the velocity of the free wake is obtained by the conventional Biot-Savart law and parabolic interpolation is employed in order to include self-induced velocity. For the validation of the code, aerodynamic analyses of airplane wing and helicopter rotor blades are conducted. Not only aerodynamics but also the unsteady wake roll up phenomena are accurately predicted. In general, multi-blade rotor requires expensive computational time and storage. To resolve this problem, the periodic assumption is used and the full coefficient matrix is modified into the simplified matrix. Hence the computational time and storage is dramatically reduced without any change of solution. Although the effect of the detail azimuthal variation in the wake is not included in this fast calculation, it is useful to obtain the thrust on the blade, overall performance of fan and the near wake geometry. The panel and time-marching free wake coupling method is applied to the ducted fan, automobile cooling fan for application problem. The thrust coefficient over advance ratio is compared with experimental data. The flow velocity and pressure contour on body surface are depicted.