A transient numerical study for heat transfer and flow characteristics of dimpled piston cooling gallery of a diesel engine

Abstract

Piston cooling gallery is an effective cooling method to achieve an acceptable piston temperature field. This paper aims to analyze the effects of teardrop dimples size and dimple head-and-tail orientation on flow and heat transfer inside the cooling gallery. To do so, the computational fluid dynamics model for galleries with different teardrop dimples were established. The results indicate that the local oil flow patterns in the axial and circumferential directions are affected by the dimples. Compared with smooth gallery, the presence of dimple enlarges the fluid charge ratio (FCR). Specifically, when radius of teardrop shaped dimples are R2 and R3 respectively, their corresponding gallery FCRs achieve 55% and 58%. Further, the variation in FCR makes a difference in the distribution of heat transfer, an in-depth analysis finds the dimples increase the heat transfer area between the gallery surface and the oil and simultaneously reduce the space of oil suspending in the gallery. Therefore, the heat transfer coefficient of a dimpled gallery is always greater than that of the smooth gallery, with the maximum improvement of 2.42%. Moreover, the change of heat transfer distribution reconstructs the heat transfer uniformity of the cooling gallery, with the maximum improvement of 24.25%.

Keywords

• Cooling gallery
• Dimple
• Two-phase flow
• Heat transfer