Laminar-turbulent transition prediction for helicopter rotors in hover and forward flight – a RANS based investigation of transition mechanisms using empirical criteria

Abstract

The present paper deals with the laminar-turbulent transition prediction on helicopter rotors in hover and forward flight for RANS based rotor performance prediction. The investigation employs empirical criteria and covers transition mechanisms due to Tollmien-Schlichting and crossflow instabilities, laminar separation, bypass transition and attachment line contamination. An integral method and a family of chord- and spanwise velocity profiles are used for an approximate calculation of the laminar boundary layer quantities. The predicted transition positions are compared to the experimental data of a BO 105 in hover (DLR flight test) and of the 7AD rotor in forward flight (GOAHEAD wind tunnel test). The effect of the laminar flow on the predicted rotor performance is studied by comparison to fully turbulent results.