Numerical Method for 3D Computation of Turbomachinery Tone Noise

D1 - Computational Aeroacoustics

The numerical method for 3D calculation of the turbomachinery tone noise generation, propagation and radiation in the near and far fields taking into account the interaction between rows is developed in CIAM. The method is implemented in 3DAS (3 Dimensional Acoustics Solver) CIAM domestic solver. It was used for calculations of acoustic characteristics of high bypass fans of turbofan engines (single rotating and counter-rotating), counter-rotating propellers and last stages of low pressure turbines.
The method under consideration is based on the solution of three-dimensional Euler equations for disturbances (linear or nonlinear) in the reference frame of blade rows. Calculation consists of two stages. The first stage – computation of the mean steady flow field in turbomachine by Reynolds-Averaged Navier-Stokes equations, semi-empirical model of turbulence, and "mixing-plane" interfaces between blade rows. The second stage is the unsteady inviscid calculation of disturbances over the mean flow field, taking into account interaction between rows. This interaction is provided by so called “sliding grids” interface, which transfer mean flow disturbances, and unsteady disturbances, from one row to another. The method allows us to consider potential, wake and vortex interactions. The main features of the solver are:
• The fourth order DRP scheme (Dispersion Relation Preserving Scheme) is used for spatial approximation.
• Second order, four stages LDDRK scheme (Low Dissipation and Dispersion Runge-Kutta Scheme) is used for time derivative approximation.
• Calculation can be performed either in time or in frequency domain.
Usage of CAA methods allows us to perform calculations with less grid points per wavelength, and therefore to use relatively coarse grids.
For the far-field radiation calculation the Ffowcs Williams method with a penetrable data surface is used.
Application of our method for the calculation of tone noise of a model ducted counter-rotating fan at approach flight conditions is presented. The results of the computation are compared with the results of experiment.