Simulation of Tiltrotor Fountain Flow Field Effects Using a Finite Volume Technique - An Aero/Acoustic Study

This paper presents predicted aerodynamic and acoustic characteristics for a tiltrotor in hover. A model utilizing an efficient Navier-Stokes solver, ROTTILT, which is based on a 3D, steady, incompressible formulation is described. The results from coupling the ROTTILT solver with the comprehensive rotor code, CAMRADJA and the acoustic code, WOPWOP, are furnished for a V22 tiltrotor in hover. To simulate the correct flow field associated with a tiltrotor in hover which is dominated mainly by the presence of the fountain flow effect, a semi-span fuselage/wing/nacelle/proprotor is included in the model. The coupled CAMRADJA code provides the rotor trim information (i. e. , collective and cyclic pitch, Ci, etc. ) to the ROTTILT solver. Formulations and the flow discretizations employed in the ROTTILT are based on the finite volume procedure called "SIMPLER". The Navier-Stokes formulations are solved in Cartesian coordinates on a non-body fitted computational grid. The effect of these assumptions on the computed flow field and acoustics is discussed. The ROTTILT is iteratively coupled with CAMRADJA. The coupling method is similar to that of CAMRADJA with a rotor CFD flow solver. The converged blade airloads computed from ROTTILT are utilized by the noise prediction program WOPWOP. Currently, there is very limited measured performance and acoustic data available for the V22 aircraft where a full assessment of the flow computational accuracy can be made with confidence. However, the computed flow field results are examined qualitatively. The aerodynamic performance and the resultant acousdcs are also assessed against the data trends observed for the XV15 aircraft. This shows that major features of the tiiltrotor flow field in hover are captured using the ROTTILT solver.