For real-time rotor inflow calculations, finite state inflow models are often used due to the fact that they are more computationally efficient compared to CFD models. Single rotor pressure and velocity potential inflow models have been shown to correctly predict induced velocities across a rotor disk. Both models are formulated from an incompressible potential flow solution and assume a rigid cylindrical wake structure. An extension of single rotor inflow models to a coaxial rotor system by superposition method is explored in this paper. In the velocity potential superposition method, rotor-to-rotor interactions are considered through individual rotor loads. For the pressure potential superposition approach, the coupling between upper and lower rotors are done through the apparent mass matrix (M-matrix) and the inflow influence coefficient matrix (L-matrix). The resulting two inflow models for a coaxial rotor system are compared using their response predictions both in time and frequency domains. Differences in transient responses between the two models are found when subjected to step perturbations on individual rotor loadings of a coaxial rotor system. In addition, significant phase differences between the models are observed in their frequency responses. The differences in transient responses between the two models can be attributed to the fact that it takes finite time for upper rotor inflow perturbations to propagate to the lower rotor, which is captured in the velocity potential superposition method as opposed to the pressure potential superposition method.
展开▼
