Visualisation of the Flow at the Tip of a High Speed Axial Flow Turbine Rotor

摘要

The previous work having relevance to the flow in the region of an unshrouded turbine rotor blade tip was examined and found that, although extensive information is available on the effect of leakage flow on the loss mechanisms on the suction side of the blade, an almost complete dearth of detailed information exists on the flow structure and mechanisms in the pressure side corner and tip gap regions which are considered important with respect to blade cooling. It would thus seem essential to lay a foundation of understanding from simple models and ending with the complex full speed situation. A logical qualitative prediction of the expected flows is presented. Apart from being complex with various zones of flow behaving almost independently from each other, the effect of upstream tangential unsymmetry (nozzle wakes) was shown to complicate the flow visualisation technique and render the normal type of continuous tracer injection of no use. Thus either an experimental rig is required which has tangentially uniform flow upstream of the rotor of a new type of pulse trace technique is needed. It is suggested that both of these requirements be adopted. Finally, since the flow in the pressure corner is the most important from a blade cooling point of view, it is suggested that this area should be studied first followed by the flow within the tip clearance tip.