Schlierenpictures of the flow through a cascade and analysis of the frequency of the turbulence at the backside of the cascade

Abstract

The new flashlamp is tested and its condensorlens designed. The set up with a condensoriens of 40 (mm) is satisfactory for black and white photos. For pictures in colour a condensoriens of 21.5 (mm) is needed. Four films with black and white photos are made to analyze the flow around the Brite 22N blade. Some photos are unsharp, because the lightbeam was not parallel to the blades. The von Karman frequency is obtained for machnumbers ranging from 0.4 till to 0.95 and with or without air coming out off the blades. Above Ma &#61 1 the flow is shocked and the von Karman frequency is not detectable. Without air coming out off the blades, the obtained Strouhalnumber is about 0.37. The expected number ranges from 0.1 till 0.25. If air is blown out off the blades, the thickness of the blade is split in two parts by the flow. Therefore the calculated Strouhalnumber is too large if the thickness isn't corrected. The R.M.S. value of the differences in the lightintensity is caused by the vortices in the wakeflow and is recorded at Ma &#61 0.7 and at 1, 2, 4 and 7 (mm) behind the blade. If the distance to the blade increases, the wakeflow becomes wider and the intensity decreases. The position of the largest R.M.S. value is dependent on the distancebehind the blade and whether air is blown out or not, because it is blown out at another angle as the surrounding flow.