An evaluation of methods and assumptions used in potential flow modelling of swirl recovery vanes

Abstract

Various potential flow methods with different assumptions are available to quantify the efficiency increase and thrust provided by a swirl recovery vane (SRV). In this paper, thrust coefficients and efficiency results obtained by different potential flow methods for the same SRV geometry at different advance ratios are presented. The methods include two VLM and four lifting line (LL) models with different assumptions. The models are compared in terms of accuracy with respect to RANS results and computational cost. This makes it possible to evaluate the benefits and drawbacks of neglecting or accounting for the presence of certain effects and modelling choices. The effects taken into account or deliberately neglected in different models include; finite propeller-SRV distance, nacelle presence, wake and free stream nonalignment, flow interaction between vane blades, the Kutta condition and SRV sweep. The wake angle behind the SRV is also varied and its effect on thrust coefficient is observed. In conclusion, accounting for the presence of a nacelle and finite slipstream distance respectively leads to 7.28% and 16.39% improvement in accuracy of the SRV thrust coefficient with negligible increase in CPU time. Not aligning the SRV wake with free stream direction has little impact on the computed thrust coefficient but causes the CPU time to increase steeply. Using a VLM based model rather a LL model and modelling vane interaction significantly increases CPU time whilst yielding the highest improvements in thrust coefficient accuracy (25.43% and 35.16%).