Flow disturbances associated with Preston tubes in turbulent boundary layers

Disturbances from a surface cylinder aligned with the flow in turbulent boundary layers were investigated in order to study the flow around Preston tubes. Mean velocities and rms values of the fluctuations were obtained in the center plane of the cylinder when immersed in turbulent pipe flow. A rough estimate of the drag due to the surface cylinder was also obtained in this case. The pressure distribution near the cylinder was measured in a flat plate boundary layer, and flow visualizations were made with the oil flow technique. In addition, smoke pictures of the flow were obtained for cases when the boundary layer thickness on the plate was negligible compared to the tube diameter.