In this paper we extend previous work on fan-vane-pylon interaction to account for an additional row of struts between the vanes and the pylon(s). These struts have two effects: they generate their own potential field in addition to that generated by the pylon(s); and they also act to magnify the pylon generated field. The combined effect of the struts and pylon is to generate a nonuniform potential field which is much greater than that generated by the pylon(s) in isolation — and, indeed, much greater than that obtained by simple superposition of the pylon-alone and strut-alone fields — resulting in increased fan forcing and vane losses. We consider two engine configurations: one with struts positioned ahead of a pylon; and one with the struts integrated with two (unequal) pylons. Predictions are generated in two dimensions by using an inviscid CFD scheme for the struts and pylons, linked to a tandem actuator disc model to represent the fan and the outlet guide vanes (OGVs). The predictions are validated by comparison with some vane leading-edge static pressure measurements taken from a full scale engine. The OGV loss in the distorted flow is predicted by judicious use of OGV loss loops for uniform flow.
The predicted results for the first engine with separate struts and pylon show the magnification effect of the struts, and the increase in sectional losses due to the strut and pylon induced circumferential flow variations. It is shown that (at least) half of the increase in sectional losses can be recovered by cyclically staggering the struts with the strut stagger angles determined from a separate pylon-alone calculation. For the second engine with integrated struts and pylons the predictions show that there are even greater increases in the potential field transmitted through the vanes and in the sectional losses, which are two thirds higher than those for the OGVs in uniform flow. However, the predicted increase in OGV losses is reduced to only a fifth with a particular restaggered-strut design; moreover, the loss in the restaggered strut case is lower than that obtained for the isolated pylons with no integrated struts. The results also show that in determining the appropriate strut restagger angles it is important to take account of the back effect of the fan and OGVs.