Basic Studies on Development of Ceramic Abradable Shroud

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Detailed measurements of the local heat transfer coefficient and the tip clearance flow on the casing wall opposite the turbine blade row have been made under the conditions of both on- and off-design, using the axial-flow-type supercharger. The results are summarized as follows.(1) The local heat transfer coefficient decreases monotonically in the direction of outlet section and increases from near the middle of the wall opposite to the rotor blade row. Then h reaches a maximum value and decreases again and from near one axial chord length downstream of the end of the rotor blade, h increases again. These tendencies are generally evident regardless of rotational speed, tip clearance, and the condition of the load.(2) The above profile, on the other hand, increases similarly with an increase in the rotational speed and with a decrease in the tip clearance.(3) Mean Nusselt numbers in the region opposite to the rotor blade are correlated with the tip clearance and Reynolds number. Nu is proportional to the 0.8 power of Re.(4) Nu becomes smaller gradually with an increase in tip clearance regardless of rotational speed and the condition of the load.(5) Nu in the condition of acceleration is at its highest, and that in the on-design point is small.(6) In the downstream direction after the middle of the wall opposite to the rotor blade, the absolute velocity vector profiles show the three-dimensional behavior. At the middle region of the wall opposite to the rotor blade, the velocity vector becomes larger in the region directly under a blade and this effect can be seen near the wall in the region immediately after a blade passes through. This suggests the behavior of the tip clearance leakage flow.(7) The velocity vector in the condition of acceleration is wholly larger than that of the on-design point.(8) The characteristics of the flow field on the casing wall correspond to those of the local heat transfer.