Analysis of fan-stage gap flow data generated using an LBM/VLES method

Quantitative analysis of the simulated flow field in the gap between the fan and fan exit guide vane (FEGV) computed with the Lattice Boltzmann based software PowerFLOWfor two different vane configurations and two solution methods is presented. One simulation used a coarser mesh near the rotor and a trip to trigger turbulent transition on the rotor. The other simulation did not rely on a trip but employed a much finer mesh near the rotor. The study compares the results of the simulations with experimental measurements to assess the mean flow, the turbulence intensity and the turbulence length scale. The research reported in this paper is a continuation of that discussed in a previous paper.1 The two computational methods led to slight differences in the turbulence intensity and turbulence length scale but not as large effect as was originally anticipated. As well, the simulation without the turbulence transition trip on the rotor significantly underpredicts the turbulence intensity. Both simulation methods predict much larger turbulence length scales than were measured. The lengthscale is calculated mutliple ways using the simulated data and all methods are in agreement. The turbulent velocity spectrum is analyzed and the ability for models such as Liepmann and Gauss to reconstruct it is assessed. Finally, the predicted acoustic power in the exhaust duct obtained from a low-order acoustic method with the simulated flow parameters used as input is provided. The results highlight the role the turbulent length scale plays in the acoustic prediction.