The extensive experimental investigations for the aerodynamic characteristics of the incompressible two-dimensional turbulent separating and reattaching flow downstream of the rearward-facing step under positive, negative and zero streamwise pressure gradients are presented. The distributions of static pressure, boundary layer parameters, forward-flow fraction, turbulent stresses and energy balance in the regions of up- and downstream of the reattachment are measured and the reattachment position is determined.
For the accurate and reliable measurements, the newly developed split film sensor is employed. The split film sensor has many attractive advantages over a laser Doppler anemometry and a pulsed-wire anemometer. However, the prevailing calibration methods for the split film sensor are reliable for small pitch angle only. In the present study, the Stock's calibration method for the pitch angle response is improved to widen a reliable measurement range of the velocity magnitude and the pitch angle. Also the cheap and convenient forward-flow fraction measurement technique using a split film sensor and an electronic comparator is developed.
It is demonstrated that the streamwise distributions of static pressure coefficient and forward-flow fraction in the recirculation and reattachment region are given by similarity curves independent of pressure gradient. The reattachment length is effected by the streamwise pressure gradient and its magnitude increases with positive pressure gradient and decreases with negative pressure gradient. Measured data of turbulent kinetic energy balance and redeveloping boundary layer velocity profile as well as integral parameters indicate that the redevelopment zone downstream of the reattachment may be divided into two separate regions of upstream and downstream region. In the upstream recovery region the Clauser's shape factor is larger than that of the equilibrium boundary layer and the flow perturbation in the outer region of the redeveloping boundary layer is reduced rapidly. But in the downstream region the Clauser's shape factor is smaller and recovery takes place slowly. The pressure gradient has influence on the recovery process from the perturbation through the reattaching shear layer in the upstream recover region.
