Experimental and theoretical analysis of heat transfer on a transonic blade.

Abstract

This dissertation involves the experimental and numerical analysis of heat transfer on a transonic high turning angle gas turbine blade, which has been performed on the supersonic cascade experimental facility at the University of KwaZulu-Natal (UKZN), as part of the continuous research and development project run under ARMSCOR. Efforts have been made to keep constant maintenance on the experimental rig. This now functional rig was used to generate experimental results, which were used to validate numerical models created using the commercially available computational fluid dynamics (CFD) package of FLUENT. The facility at UKZN is a continuously running cascade system, which consists of a plenum run under vacuum pressure and houses a four-blade cascade. One of these SMR-95 turbine blades is instrumented with thin-film gauges, which allow heat transfer measurement via a heat transfer analogy through electrical circuit boards. This blade is interchangeable with an instrumented blade with pressure tappings along its span for pressure distribution tests. This facility was used to validate flow measurements, and results compared to previous test data conducted on the rig, using two pressure transducers, a scanivalve and a data acquisition system with LabView software. The method of generating heat transfer measurement results involved pre-chilling the test blade in a cooling box, before rapidly plunging it directly into a hot-air stream. Re-instrumented and more sensitive thin-film gauges would react resistively according to the temperature change. The heat transfer coefficient distribution was calculated using LabView. The turbulence intensity at the inlet of the cascade was varied using a grid of rods of varying diameter. For 15% turbulence intensity, there was a 16% overall increase in heat transfer on the pressure side, and 25% increase on the suction side. For 25.5% turbulence intensity, there was an overall increase of 23% on the pressure side and 40% on the suction side. The results compared favourably to that of previous results generated by Stieger (1998). The experimental results were used to validate and compare to the CFD model developed in FLUENT. Improvements were made with the meshes developed previously, and results obtained showed that the general trend of distribution was similar, although certain models varied in the correct prediction of magnitude. This research includes a comprehensive study of various methods of numerical heat transfer measurement techniques, which would be used to replace the current ageing electrical heat transfer analogue method used at UKZN.