Exploiting of Virtual Blade Modelling on the performance study of a shrouded tail rotor

The present study describes the computational methodology adopted to evaluate the aerodynamic characteristics of a shrouded tail rotor. The dependence of the aerodynamic characteristics of a shrouded rotor on the shroud geometry and flight condition deeply affects the accuracy in estimating the thrust sharing of the antitorque system. Experimental testing and numerical investigations have been carried out in the past to characterize the shrouded tail rotor performance and the influence of the variation of the characteristic geometrical parameters. In this study, a modified Virtual Blade Model (VBM) approach has been exploited to model the structure of the flow field produced by the AW09 shrouded tail rotor operating in hover. The proposed modified VBM was tested on the isolated configuration along with the canonical model implementation. By correlation with experimental and numerical data, the introduced modification translated into modeling improvements both in terms of accuracy and stability. Finally, the modified model has been applied to the shrouded configuration by means of RANS and SBES simulations, and again the results are compared with experimental and numerical data. During the analysis different turbulence models were tested. The performance predictions achieved through Virtual Blade Modeling show a close correlation with the ones obtained by adopting a fully resolved blade approach with a significant saving in computational cost.