墙报-俘获湍动边界层流动的时间分辨层析PIV研究
A flat plate boundary layer flow was generated at the open test section of the circuit type 1m- wind tunnel ofthe DLR, Gottingen, at a free stream velocity of U亣 = 7 m/s with zero pressure gradients. A transparent andsmooth surface glass plate is utilized to provide optical access from its bottom and a good flow quality. Theplate has an elliptic leading edge to prevent flow separation. Four tripping wires, one with 1.5 mm diameterand three with 1 mm diameter were positioned with 1 mm x-distance close to the surface at (Rex). . 290along the whole span-wise elongation of the plate. This bypass transition of the flow results in thedevelopment of a turbulent boundary layer flow. In a box of about 34 x 18 x 35 mm3 in x-y and z-directionsaround (Rex). . 450 tracer particles has been illuminated by laser light pulses at 4 kHz with 21 mJ each inorder to achieve PIV recordings without using the frame straddling method. The light source was a Nd:YAGlaser from Lee Laser inc. Two highly reflective dielectric mirrors aligned in the x-y-direction are installednearly parallel and close to the surface of the flat plate on opposite sides of the measurement region. Thecollimated laser beam undergoes multiple reflections between the two mirrors passing through themeasurement volume approximately 15 times before exiting (see sketch left). This arrangement resulted ina light amplification with a factor ~5 with respect to a single pass system. The specific illuminationarrangement has the advantage that all viewing directions collect scattered light both in forward andbackward directions, which provided the level of light needed for imaging particles in the whole volume.