The Influence of the Spatial Discretization Methods on the Nozzle Impulse Flow Simulation Results

Vibration and noise caused by pressure pulsations in the volumetric compressor manifolds are one of the most important problems in the volumetric compressor's operation. For pressure pulsation attenuation, different types of mufflers are applied using a design based on the Helmholtz resonator approach. This design is not effective for variable revolution speed compressors and in this case other pressure pulsations attenuation methods are required. Nowadays, due to the increasing application of variable speed compressors new design methods are developed. One of the possibilities to attenuate pressure pulsations over a wide range of frequencies is the introduction of specially shaped nozzles in the gas duct flow directly after the compressor outlet chamber. It is well known that a nozzle can attenuate pressure pulsations, however, it increases the compressor power at the same time. The main criterion for the nozzle selection is the highest possible attenuation of pressure pulsations coupled with the lowest possible effect on the compressor pumping power. In some cases 25-30% of the pressure damping is good enough to reach the standard requirements. The method applying CFD impulse flow simulations has been developed for the estimation of the nozzle influence on pressure pulsations for all frequencies. The FLUENT/ANSYS software has been used for the simulation. The CFD simulation requires a lot of effort for proper selection of the boundary conditions, solution methods, turbulence models, discretization methods, mesh design etc. The results are in some cases surprisingly different between different methods. In this paper the flow simulations for the nozzle flow with the connecting pipe using impulse function as a mass inflow excitation is shown. In this investigation project various models and methods have been compared and results in 2D and recalculated into 0D time only dependent functions are presented.