Research on Prediction of Cooling Air Flow in Small Air-Cooled Utility Engines

摘要

This report describes research on the prediction of the cooling air field for air-cooled engines using Computational Fluid Dynamics (CFD). The design of the cooling air field is very important for engine cooling, a factor which has a significant effect on engine performance, fuel consumption, noise, reliability, etc. However, the flow field is very complex because of the turbulence caused by a large number of components that are located in the flow passages and the cooling air generated by a centrifugal fan. In order to understand this flow field, calculations were performed using CFD and measurements were taken in an actual engine. Given practical considerations such as computing time, modeling time, correlation between calculation and test results, formulation of a database, etc., the fan P-Q (pressure versus volume flow rate) characteristics curve and the flow field were calculated separately when adopting CFD. In addition to visualization using Particle Image Velocimetry (PIV), pressure measurements and measurements of the P-Q characteristics of the cooling fan were done to measure the flow field in the actual engine. The correlation between the results of CFD calculations and measurements was studied. Almost suitable prediction results were achieved by setting the P-Q characteristics at the boundary surface of the rotational area, as obtained from the calculation of P-Q characteristics, as a fan boundary condition for CFD analysis of the cooling air field. This research has enabled the qualitative and quantitative prediction of the cooling air flow if air-cooled engines.