Numerical Simulation on the Ventilation Cooling Performance of the Engine Nacelle under Hover and Forward Flight Conditions

The main objective of this work is to investigate, by means of numerical simulations, the performance of the engine nacelle ventilation cooling system of a helicopter under hover and forward flight conditions, and to propose a simplified method of evaluating the performance based on rotor downwash flow by taking the synthetical effect of engine nacelle, exhaust ejector and external flow of a helicopter into account. For the engine nacelle of a helicopter, an integrated model of the nacelle and exhaust ejector was set up including the domain of external flow. The unstructured grid and finite volume method were applied for domains and control equations discreteness, and the standard k-ε model was applied for solving turbulent control equations. Using the business CFD software, the flow field and the temperature field in the nacelle were calculated for single inlet scheme and double inlets scheme, total up to 9 schemes. The performance of the exhaust ejector was computed. And the influence on the ventilation cooling performance of the nacelle was analyzed for different inlet number, inlet size and inlet position. The comparisons were completed between flight trials and numerical simulation results, and they show good agreement. The results show that the method can predict the performance of the ventilation cooling system of the nacelle. Moreover, the study indicates that, for the same inlet scheme, the temperature of the nacelle in forward flight is lower than that under hovering condition, but the pumping coefficient of the exhaust ejector in forward flight is higher. The inlet position should avoid being located on the underside of the cowl. It is also indicated that the simulation results can be regarded as a reference for the design and optimization of the system.