Endwall Heat Transfer Measurement Using Steady State Liquid Crystal Thermography with Stroboscopy in a Rotating Pin Fin Channel at High Rotation Number

• Main Authors: Huang, Szu-Chi, 黃思齊
• Other Authors: Liu, Yao-Hsien
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/by743w

博士 === 國立交通大學 === 機械工程系所 === 107 === Gas turbine is widely used for power generator and electricity production. Thermodynamically, higher thermodynamic efficiency is achieved by using higher turbine inlet temperatures. To protect turbine blades in long continuous operation, several cooling technologies are designed to increase the lifetime of gas turbine blade. In this study, a rectangular channel with an aspect ratio of 4:1 was selected to model internal cooling channel near the trailing edge of a turbine blade. The pin-fin arrays were designed in either inline or staggered patterns, and the Reynolds number ranged from 5,000 to 20,000. The pressurized air flow acted as the working fluid, and the highest rotation number was 0.39. Heat transfer was experimentally measured using a rotating pin-fin channel involving two channel orientations, namely 90° and 150°, with respect to a rotating axis. A newly developed method of liquid crystal thermography along with stroboscopic photography was used to obtain detailed heat transfer contours on the endwall surface. A detailed calibration was performed to quantify the uncertainties in the liquid crystal measurement from the stroboscope frequency, flash duration, and viewing angle. Results showed that, with the careful calibration process, the wide band liquid crystal thermography was valid for measuring heat transfer distribution of the rotating objects. The uncertainty in the temperature measurement was within 2.5%, and the primarily source of uncertainty was from the imperfect synchronization and marginal blur during rotation. This technique was useful to validate the rotating heat transfer distribution with high rotational speed in the future. For the heat transfer results, the influence of rotation was greater on the inline array than on the staggered array, engendering higher heat transfer enhancement on the leading and trailing surfaces. Compared with the other orientation, the inclined orientation (150°) engendered a larger spanwise heat transfer variation because of the shifted rotation-induced secondary flows. The inline array exhibited the highest rotation-induced heat transfer enhancement at the 90° orientation, and the highest enhancement levels were 90% and 40% on the trailing and leading surfaces in the analyzed region, respectively.