Experiments on a flat square plate at high angles of attack.

Abstract

The flow structure about flat plate of low-aspct ratio is still not well known although such plates have various practical applications, as lifting surfaces on missiles, tail surfaces on airplanes and flat plate like structure as heliostats, antennas and ships rudders. One of the most important phenomenon is that the normal force acting on such plates in an incompressible flow experiences an abrupt drop at some high angle of attack and this is accompanied by certain changes in the flow field. The objective of the present investigation is to study the effect of varying the Reynolds number on the flow behavior over a square flat sharp-edge plate as well as on the normal force acting on such plate. This experimental investigation includes surface flow visualization, mean pressure measurements and mean velocity measurements. It is carried out at Reynolds number ranging between 0.5 x 10 5 and 3.7 x 10 5 and at angles of attack between 20 degree and 50 degree. The results showed that the normal force coefficient is hardly affected by the change in Reynolds number for the same angle of attack, however, the influence of varying the Reynolds number on the percentage drop in the normal force is quite considerable as Reynolds number ranges between 1.5 x 10 5 and 3.7 x 10 5 the influence is reduced quite significantly. It is shown also that the change in Reynolds number does not have any significant influence on the shapes of the wake boundaries, however, the wake widen up when the angle of attack is changed from subcritical value to supercritical value for the same Reynolds number.