Schlieren visualization of micro gas turbine exhaust plume with different shapes of nozzle

Abstract

Schlieren visualization of the plume ejected from the microgas turbine nozzle was conducted to understand infrared signal characteristics of various shapes of the exhaust nozzle. At the same time, the precise temperature distribution and infrared signal measurement were performed and compared. The maximum thrust of the microgas turbine used in the experiment is 230 N, the maximum speed of revolution is 108,500 rpm, and the maximum exhaust gas temperature is 750 °C. Seven nozzles were used for this experiment which included a cone nozzle, five square nozzles with aspect ratios (AR) ranging from 1 to 5 and an S-shaped nozzle with aspect ratio 6. The infrared signal emitted from the exhaust plume decreased as the aspect ratio increased. Schlieren flow visualization images show that cone nozzle had a uniform flow pattern, while square nozzle had a bright triangle pattern in the dispersed plume. As the aspect ratio of square nozzles increased, a bright triangle pattern reduced in size. On comparing Schlieren visualization with the temperature distribution, it can be understood that the triangular shape of core plume plays a major role in the temperature diffusion with the surrounding air. Based on the temperature distribution and the results of the Schlieren visualization, three types of exhaust plume models are suggested. These three models are homogenous plume, intermediate plume and two-dimensional plume with hot core, which correspond to the cone nozzle, the AR2 square nozzle and AR5 square nozzle, respectively.