| Popis: |
Surface flow visualization techniques like the oil-and-dye technique provide information about the flow around a model that is to be investigated. Based on the assumption that the oil paint is being distributed along lines corresponding to the direction of the wall shear stress, the resulting streakline pattern allows identifying laminar-turbulent transition of the boundary layer and regions of separated flows. A complementary measurement technique, that is, a so-called surface fence probe embedded flush to the model's surface, allows determining the wall shear stress in magnitude and direction. Both techniques have been employed in the hub-side gap area of an annular compressor stator and the tip gap of a compressor rotor. For the stator, the streakline pattern computed from the surface fence probe data shows remarkable similarities with the digitized oil flow pattern. Using the fence's velocity vector field, a considerable gain of information about flow quantities like the divergence or the vorticity can be achieved. The rotor experiments provide evidence that if the fence is equipped with time-resolved pressure transducers, the flow vector's fluctuation values in magnitude and direction can be ascertained. This unique feature provides the ability to obtain the streakline pattern of the relative flow field on the casing wall as if the oil-and dye technique had been carried out in the rotor reference system. |
