In this study we examine laminar velocity profiles of freely suspended flowing soap films. We introduce a new device which supports large uniform films for indefinite periods of time. The geometry of the flow is two-dimensional (2D), yet the measured velocity profiles depart from ideal 2D behavior. The main reason for this departure is that the soap film experiences an air drag force across its entire surface. Describing the air with Prandtl boundary layer theory, we predict the observed flow patterns with good accuracy. The downstream development of the profiles is self similar. Our models set an apparent upper limit on the film 2D viscosity of 5⋅10−6 surface poise for dilute soap concentrations. This measurement implies that the surfactant layers on the film may not contribute measurably to the 2D viscosity. For higher soap and glycerol concentrations the opposite appears to be true.

No abstract

No abstract

This paper presents experimental investigations of a straight high pressure turbine cascade with main focus on the transition location. The design of the turbine blade intends to stabilize the boundary layer in the acceleration region to achieve a laminar boundary layer at the shockwave boundary layer interaction. The indispensable usage of film cooling in a high pressure turbine upstream of the interaction zone can influence this flow regime. The experimental investigations were performed at the Wind Tunnel for Straight Cascades (EGG), Göttingen. The investigations were conducted at different Mach numbers and coolant mass flow ratios. Presented are results of infrared and hotfilm-sensor measurements to detect the boundary layer state. The flow field is shown by applying Schlieren technique, pressure taps and unsteady pressure sensitive paint. The results of this investigation will reveal the influence of the cooling on the transition location with respect to different Mach numbers.

No abstract