Three-dimensional simulation of two-phase flow in a complex gallery and telescopic pipe coupled system

Abstract Highly efficient cooling of heavy duty marine diesel engine pistons is one of the key parts of modern advanced engine piston design. Due to the high efficiency of the shaker cooling system, oil cooling galleries are extensively used. These galleries on low-speed marine engines are particularly complex, including a telescopic pipe and an air hole on the cross head. Few work has been done on coolant flow in such complex system under coupling of reciprocating, pressure and inertial force until now. The flow behaviour is relatively poorly understood. This study focuses on the influence of telescopic pipe on the two-phase flow details for a marine low-speed diesel engine. A 3D CFD model is established including both the piston gallery and a telescopic pipe. With this model, the change in the two-phase flow pattern with the progression of the crank angle was investigated, and the pressure and mass flow rate through typical sections of the oil cooling system were analysed. By changing the oil inlet pressure and crank shaft speed, key parameters characterising the flow pattern inside the galleries were compared. The numerical results demonstrate a strong correlation between the telescopic pipe and two-phase flow characteristics. Both decreasing the crank shaft speed and increasing the inlet pressure will reduce the backflow of outside air from the air hole boundary and increase the oil filling ratio. The proposed numerical model is able to predict the complex two-phase flow phenomenon in the gallery, which is important and provides a basis for further studies on the heat transfer mechanism and optimal design of the cooling system.