Volume 79, Issue 6 -

The superhydrophobic and air retaining elytra of the backswimmer Notonecta glauca is a remarkable example in nature how to prevent the wetting of a surface immersed in water. To characterize this effect on the fluid flow μ particle image velocimetry measurements were performed on original elytra. A significant slip of the water phase on thin air layer on this type of surface the system was determined. Consequently this surface can be regarded as a source of drag reduction and can supply a model for artificial surfaces with similar properties. In addition the surface structure of the elytra of Notonecta glauca shows the capability of keeping the air layer fixed on the surface even for a relative velocity of the oncoming flow of up to 5 m / s.

Photoelastic Tomography is a novel optical measurement technique for shear measurements in flow. It utilizes the shear induced birefringence in fluids. The tomographic scan of the volume is carried out using parallel light sheets and measuring the intensity of scattered light with a camera. The three dimensional shear field is reconstructed from the image data with a new algorithm. The application and validation of this method are presented for a laminar, stationary pipe flow with a rectangular cross section.

Propeller-agitators are often used to improve mixing processes in technical installations. The dimensioning of these agitator-installations is based on experience so far. The dimensioning should be improved by our studies. An experimental setup is presented which allows synchronous measurements of the relevant coefficients K T and K Q by mechanical force and by velocity measurements using laser doppler anemomentry.

Reducing aircraft noise requires the analysis of the complex interaction between flow and sound phenomena in jet engine dampers. Therefore a Doppler global velocimeter with laser frequency modulation is used for the first time for the multi-point measurement of the acoustic particle velocity in a Kundt´s tube. As a result, particle velocity amplitudes within the hearing range have been resolved, the minimal measurement uncertainty amounts to 3 mm / s at a measurement period of 1 s. The measurement technique has high potential in respect of analyzing and optimizing jet engine dampers.

This paper investigates the time shift technique to classify bubbles. Previous experiments on water drops have been validated using phase doppler technique. We present an extension of this technique to measure bubbles in cavitation tunnels.