Research On Nacelle Cooling And Jet Noise Of An Auxiliary Power Unit

Nacelle cooling and jet noise suppression are the key engineering and technical problems in the design of Auxiliary Power Unit(APU).In this paper,a flow and heat transfer numerical simulation of a simplified three-dimensional model of an Auxiliary Power Unit was carried out.The effects of the operating conditions,cooling fan,mass flow of cooling air and the structure of the air intake were analyzed in APU nacelle cooling simulation.Large eddy simulation(LES)method and FW-H method were used in jet noise research.The influence of the muffler,exhaust temperature,mass flow of nacelle cooling air and chevron jet are analyzed on the flow field and sound field.The results are summarized as the following:For the reference APU model,the distribution of the flow field and temperature field in the nacelle are consistent under different operation conditions,and the cooling effect in the upstream of nacelle is obviously better than downstream of the nacelle.Due to the influence of the ambient temperature,Temperature at monitoring points exceeds the working limit under Condition 1.When the nacelle cooling air is sufficient,closing of the fan is beneficial to the heat transfer of the combustion chamber,at the expense of the dramatic increase of the electric motor temperature.The increase of nacelle cooling air can achieve the goal of taking out more heat in the cabin,while it has little effect on the optimization of the flow field,which cause the temperature in faint area even worse.Under the same condition,local high-temperature in nacelle can be eliminated through the reasonable layout of the cooling inlet to optimize the flow of cooling air.The exhaust muffler can reduce the jet noise 4-6dB without changing the exhaust structure.Increasing temperature of jet flow and increasing air flow of APU nacelle can both improve the speed of core area of the exhaust jet,which cause the noise increase accordingly.With the increasing number and penetration angle of chevron structure,the effect of noise suppression firstly increases and then decreased.Near-field noise directivity is affected by “Doppler effect”,while the far-field noise directivity is affected by only the quadrupole sound source.The strongest noise range are-18°to-54°and 18°to 54°.