An experimental study of heat transfer around turbine airfoils with closed-loop cooling.

摘要

Closed-Loop cooling has been identified as one of the promising cooling schemes for the next generation gas turbine systems. The closed-loop cooling design collects the spent coolants and directs them to be recovered to do useful work in engine cycle. Due to the requirement of the closed-loop cooling and adoption of innovative cooling methods, the geometric configuration of a closed-loop cooling design is usually complicated. The complexity induces the heat transfer and flow uncertainties and necessitates the detailed heat transfer study for the cooling design. The present research was designed to examine heat transfer of innovative closed-loop cooling designs of an advanced gas turbine system. A heat transfer measurement system employing the Thermochromic Liquid Crystal (TLC) has been developed in order to study detailed heat transfer of the complicated cooling designs. A hybrid technique has been proposed to combine two models: lumped heat capacity model and one-dimension model. The technique has been successfully demonstrated to be a reliable means by studying heat transfer phenomenon on pin fin arrays. Pin fin arrays, sometimes termed pedestals, are widely used in modern gas turbines to provide heat transfer enhancement. In addition, the study on pin fins array revealed effects of heat transfer by two increasingly important, yet not much being explored geometric parameters: shape of pin fin element and gap atop pin fin array. Heat transfer study using the measurement system has revealed detailed heat transfer distribution and eliminated heat transfer uncertainties for five scaled Perplex models of the most crucial designs in the closed-loop cooling system. This study has also demonstrated the improvement in design practice with assistance of the developed system. For a design that relies on the unverified data sets and correlation, the system provides a means to eliminate the uncertainties and provide prompt feedback to designers for modification of the design.