WP2: FAN SURGE ANALYSIS

A mathematical and numerical methodology has been selected in order to perform the computations that have been carried out throughout the project. In order to decide the most suitable strategy, computations of two different fan geometries were performed. Experimental data of these fans was available and was used in order to calibrate the numerical model.

The final methodology is based on a compressible flow formulation discretized by means conservative numerical schemes which ensure numerical stability while numerical dissipation is avoided. As a LES model, the Variation Multi-scale closed with a Wall-Adapting Local Eddy-Viscosity model (VMS-WALE) has been used in order to obtain the sub-grid dissipation.

Since the geometry to be simulated includes rotating parts, the Arbitrary Lagrangian Eulerian (ALE) methodology has been used to deal with this issue. This strategy subtracts the non physical mass flows that are generated in the cell faces because of the mesh displacement when evaluating the convective flux.

Another issue that has been solved is the coexistence of rotating and static parts in the same domain. A sliding meshes methodology has been used in order to communicate flow variables through the common surfaces of the different mesh parts.

Regarding the boundary conditions, the mass flow is fixed at the inlet while non reflecting conditions are set at the outlet. Pressure and Temperature are prescribed initially at the whole domain in order to evaluate the fluid properties.

Finally, the methodology has been applied to the designs proposed by LMB and a final solution has been proposed. This proposal is studied in detail in deliverable 3.8.

(Flow recirculations(green/blue regions)on the blade surfaces of the design 1 fan)

(Comparison between the normal behavior in reference fan 1 and the unphysical vortex in reference fan 2)

(Evolution of the unphysical flow instability in the reference fan)