Basic Studies on Development of Ceramic Abradable Shroud

采用轴流式增压器，在设计前后两种情况下，对涡轮叶片排对面机匣壁上的局部换热系数和叶尖间隙流进行了详细的测量。结果总结如下：(1)局部换热系数沿出口截面方向单调减小，从与动叶排相对的壁面中部附近开始增大。h达到最大值后再次减小，在动叶末端下游约1个轴向弦长处，h再次增大。无论转速、叶尖间隙和负载状况如何，这些趋势通常都很明显。(2)另一方面，上述叶型随着转速的增加和叶顶间隙的减小而增加。(3)动叶对面区域的平均努塞尔数与叶尖间隙和雷诺数相关。Nu与Re的0.8次方成正比。(4)无论转速和载荷情况如何，Nu随着叶尖间隙的增大而逐渐变小。(5)加速度工况下Nu值最大，非设计点Nu值较小。(6)在与动叶相对的壁面中间后的下游方向，绝对速度矢量剖面呈现三维特征。在与动叶相对的壁面中部区域，叶片正下方区域的速度矢量变大，在叶片穿过后立即经过的区域壁面附近可以看到这种效应。这表明了叶尖间隙泄漏流动的行为。(7)加速度条件下的速度矢量完全大于设计点的速度矢量。(8)机匣壁面流场特征与局部换热特征相对应。

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.