The effect of the outlet air duct design of a centrifugal compressor on the gas-dynamic and heat-exchange characteristics of the air flow

The specific, technical, and economic indicators of an engine can be significantly increased by using a turbocharger. The relevance of this study is that enhancing the design and physical processes in the elements of a centrifugal compressor can result in improved efficiency and productivity of the turbocharger and engine. The study’s objective was to create design strategies for upgrading the compressor outlet air duct to regulate the gas-dynamic and heat-exchange characteristics of the flow. The compressor outlet air duct of an automobile turbocharger served as the research object, and both the compressor and turbine wheels had a diameter of 61 mm. The scientific novelty of the article consists in the study of physical processes in the turbocharger outlet air duct (other authors’ studies were aimed at the inlet channels) and the development of original designs of outlet air ducts. Two approaches were employed: one to stabilize the flow by using a honeycomb in the air duct and another to increase flow turbulence by applying dimples on the channel surface. The study covered the range of rotor speeds from 20,000 to 60,000 min⁻¹ (1.9·10⁵ < Re < 3.3·10⁵). New experimental data on gas dynamics and heat transfer of flows for different air duct designs were obtained through tests on a laboratory bench and measuring equipment based on constant-temperature anemometers, a pressure sensor, thermocouples, tachometers, and an analog-to-digital converter. It has been shown that the use of a honeycomb in the air duct leads to a drop in air flow of up to 14 %, a decrease in turbulence number of up to 36 %, and an increase in the heat transfer coefficient of up to 21 % compared with the basic design. It was found that the application of dimples in the air duct causes a decrease in air flow of up to 8 %, an increase in the number of turbulences of up to 17 %, and an intensification of heat transfer of up to 25 %. Additionally, a simple examination was done to evaluate the impact of modernized air outlet ducts on the engine’s efficiency and power.