The laser Doppler velocimeter (LDV) and hydrogen bubble ow visualization techniques have been used to measure the characteristics of turbulent boundary layer ow over riblets surface and to observe its coherent structure in the near wall region. The experimental results indicate that, in comparison with the turbulent boundary layer ow over a smooth surface, greater values are obtained for the thickness of viscous sublayer, the thickness of bu er region and the integral constant C in the log-law. Moreover, the maximum value of turbulent intensity u0=U is increased by 6.7%, but its position is decreased by 6.4%, the skewness factor and the atness factor are hardly a ected by the riblets surface. The non-dimensional value of low-speed streak spacing is reduced by 20%, this is also an indication of turbulent drag reduction.

Flow visualization was used to study the effects of a vectored trailing edge jet on the leading edge vortex breakdown of a 65 delta wing. The experimental results indicated that there is little effect of the jet on the leading edge vortex breakdown when the angle of the vectored jet is less than 10. With the increase of the vectored angle B, the effect of the jet on the flow becomes stronger, i.e., the jet delays the leading edge vortex breakdown in the direction of the vectored jet, and accelerates breakdown of the other leading edge vortex. Moreover, the effect of the jet control tends to be weaker with the angle of attack.

The effects on the wall pressure of the plate caused by the introduction of a gap near the ground and the flaps were investigated experi mentally. The mean pressure on the plate surface was found to decrease with the size changing of the gap near the ground when the gap size (g) is larger than the flap height (h), but the one in the recir culation region increase with the size of the gap when the gap size is about 0<g<2h. Three kinds of now strncture appear with increasing the gap sizes, and the transit point is at g/h-0.2, 0.8 respectively. For the zigzag tlap (d/h=0.19, d is the height of the zigzag), the vmation of wall pressure with g/h is similar to the flat flap in general. The zigzag affects the mean wall pressure in the region of 0<x/h<20 (the i'ecirculation zone) and can decrease the fluctu atthg pressure in the region ofx/h > 20 downstream.

The dye-injection flow visualisation technique was used to investigate the effect of the apex flap on the leading-edge vortex breakdown over a cropped 76/40 double delta wing. The angle of. attack of the experimental model varied from 20 to 40o, and tile length of the apex flap was 25%c and 50%c rcspcctivcly. By changing the angle of the apex flap, we found that the apex flap is an efficient method to control the leading edge vortex breakdown, and rbat there exists an angle of the apex flap at which the value of the leading edge vortex breakdown delay reaches maximum. Moreover, it is found that, for a< 28, the small apex flap is a better choice for delaying the vortex breakdown; for a> 28, the large apex flap is superior to the small one.